Báo cáo khoa học: Passage through the Golgi is necessary for Shiga toxin B subunit to reach the endoplasmic reticulum pptx

Passage through the Golgi is necessary for Shiga toxin B subunit to reach the endoplasmic reticulum Jenna McKenzie1, Ludger Johannes2,3, Tomohiko Taguchi4 and David Sheff1 Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA, USA Institut Curie, Centre de Recherche, Laboratoire Trafic, Signalisation et Ciblage Intracellulaires, Paris, France CNRS UMR144, Paris, France Department of Biochemistry, Osaka University Graduate School of Medicine, Japan Keywords endosomes; Golgi; membrane traffic; retrograde traffic; Shiga toxin Correspondence D Sheff, Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242-2600, USA Fax: +1 319 335 8930 Tel: +1 319 335 7705 E-mail: david-sheff@uiowa.edu (Received 11 November 2008, revised January 2009, accepted January 2009) doi:10.1111/j.1742-4658.2009.06890.x Both Shiga holotoxin and the isolated B subunit, navigate a retrograde pathway from the plasma membrane to the endoplasmic reticulum (ER) of mammalian cells to deliver catalytic A subunits into the cytosol This route passes through early ⁄ recycling endosomes and then through the Golgi Although passage through the endosomes takes only 30 min, passage through the Golgi is much slower, taking hours This suggests that Golgi passage is a key step in retrograde traffic However, there is no empirical data demonstrating that Golgi passage is required for the toxins to enter the ER In fact, an alternate pathway bypassing the Golgi is utilized by SV40 virus Here we find that blocking Shiga toxin B access to the entire Golgi with AlF4) treatment, temperature block or subcellular surgery prevented Shiga toxin B from reaching the ER This suggests that there is no direct endosome to ER route available for retrograde traffic Curiously, when Shiga toxin B was trapped in endosomes, it entered the cytosol directly from the endosomal compartment Our results suggest that trafficking through the Golgi apparatus is required for Shiga toxin B to reach the ER and that diversion into the Golgi may prevent toxin escape from endosomes into the cytosol Shiga toxin (Stx) is a bacterial exotoxin responsible for an estimated 165 million annual cases of severe dysentery worldwide [1] The toxin attacks cytosolic targets in mammalian cells To reach these targets, the toxin navigates a retrograde pathway that passes sequentially through the plasma membrane, endosomes, Golgi and endoplasmic reticulum (ER) [2–5] Passage through the Golgi appears to be rate limiting on this pathway, resulting in prominent labeling of this organelle However, such prominent labeling may be misleading Recycled transferrin was assumed to pass sequentially through the early endosomes (EEs) and recycling endosomes (REs) based on prominent labeling of the RE at later time points [5,6] It later became evident that the majority of transferrin actually bypasses the RE The same may be true for Golgi passage of Stx Empirical data supporting a requirement for passage through the Golgi is lacking Indeed, treatment with brefeldin A provides protection against the holotoxin, suggesting involvement of the Golgi However, that protection is incomplete, suggesting that Golgi passage may be favored but not required [7,8] Furthermore, other toxins, such as diphtheria toxin, bypass the Golgi and ER by escaping the endosomal compartment directly into the cytosol [9] SV40 virus is internalized into a specialized compartment which can communicate directly Abbreviations BFA, brefeldin A; EE, early endosome; ER, endoplasmic reticulum; MEM, minimal Eagle’s medium; PDI, protein disulfide isomerase; RE, recycling endosome; Stx, Shiga toxin; StxB, Shiga toxin B; Tfn, transferrin; TfnR, transferrin receptor; TGN, trans-Golgi network; WGA, wheatgerm agglutinin FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1581 Shiga toxin in the Golgi J McKenzie et al with the ER, bypassing endosomes and Golgi [10] There may even be alternative retrograde pathways between the endosomes and ER that either include or bypass the Golgi, where the majority of traffic normally passes through the Golgi To investigate these possibilities, we examined the fate of Stx where access to the Golgi was blocked Stx is secreted by Shigella dysenteriae It is highly homologous to the Shiga-like toxins (also termed verotoxins) secreted by enterohemorrhagic strains of Escherichia coli Stx is a member of the A-B5 family of toxins, which are composed of one enzymatic A subunit, noncovalently bound to a B subunit composed of a homopentamer of B fragments [11] The Stx A subunit is an rRNA N-glycosidase, which stops protein synthesis and causes cell death [12] The A subunit must be delivered to the host-cell cytosol to encounter its ribosomal substrate To reach this destination, it is carried by a homopentameric B subunit (StxB) along a retrograde pathway from the plasma membrane through the EE ⁄ RE to the Golgi and the ER Stx takes advantage of trafficking through the Golgi to facilitate cleavage and activation of the catalytic A subunit by trans-Golgi network (TGN) resident furin protease [13] The catalytic domain remains attached to the anchor domain by a disulfide bridge that is cleaved when the complex enters the cytosol Entry of the catalytic A subunit into the cytosol is via retrotranslocation [14–16] The B subunit initially gains entry to cells by binding the neutral glycosphingolipid, globotriaosyl ceramide (Gb3 or CD77) at the cell surface [17] Bound toxin is endocytosed via both clathrin-dependent and -independent mechanisms and is delivered to EEs [18–20] There is no known protein receptor for Stx B subunit (StxB), and the mechanism by which it is recruited into clathrin-coated pits remains unknown StxB binding to Gb3 at the cell surface induces changes in plasma membrane topology resulting in the formation of tubular invaginations that facilitate internalization [21] It remains to be determined whether this toxin-induced pathway or clathrinmediated endocytosis is predominant in normal cells In both cases, newly internalized StxB appears to be delivered to EEs StxB binding is not a passive process Binding and endocytosis of the toxin is accompanied by activation of Syk kinase and activation of microtubule networks, which facilitate transport into the cell [22,23] Passage of Stx through the EEs ⁄ REs is well documented and involves many proteins that are now being identified [3,9,24] Two Rab GTPases, Rab11a and Rab6A¢, regulate retrograde traffic of Stx from the EEs ⁄ REs to the Golgi, suggesting that this is a 1582 regulated vesicular trafficking process [25,26] In addition, components of the retromer complex, specifically sorting nexins and and Vps26 are required for traffic of Stx through the endosomes, but it is still unclear if this mediates an intra-endosomal step or if they are required for delivery to the TGN [27–29] Delivery to the TGN does appear to involve the GARP complex, first identified in yeast as mediator of retrograde traffic into the Golgi [30] It is clear that Stx does not pass through the late endosomes [24] Instead, direct transport to the TGN is mediated by syntaxin 5, syntaxin 6, and syntaxin 16, a pathway that is shared by the endogenous protein TGN38, which cycles between Golgi and plasma membrane via REs [31,32] Unlike TGN38, traffic of StxB from endosomes to Golgi is dependent upon the Golgin, GCC185 [31,33–35] Here we examine the traffic of StxB which follows the same route as the holotoxin through the retrograde trafficking pathway [15,36] We perturbed access to the Golgi by an AlF4) treatment, temperature block and subcellular surgery to examine whether there exit routes for StxB to bypass the Golgi while trafficking from endosomes to ER Using these systems, we determined that Golgi transit is required for trafficking to the ER Results StxB co-localizes with transferrin-positive endosomes We first sought to establish a time-line for retrograde traffic of StxB in green monkey kidney BSC-1 cells These cells were selected due to their distinct endosomal and Golgi morphologies that allow ready visual identification Like HeLa cells, different strains of BSC-1 cells show different affinities for StxB Our laboratory strain (a gift from I Mellman) binds StxB readily Another strain reported by Spooner et al [37] does not For co-localization studies, cells were infected with adenovirus containing human transferrin receptor (TfnR), a well-studied marker of the endocytic recycling pathway [5,38] This infection did not alter the morphology of internalized StxB observed in uninfected cells (not shown) Cells were labeled on ice with both Cy3–StxB and Alexa 488–transferrin (Tfn) for 30 Internalization of both labels was performed at 37 °C in label-free medium for the indicated times (Fig 1A) After min, Tfn was in peripheral puncta representing EEs (Fig 1A; min) [5] StxB co-localized with Tfn throughout the EEs This suggested that although internalization of StxB may be through clathrin-dependent or -independent mechanisms, FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al Shiga toxin in the Golgi A B C Fig Trafficking of StxB in BSC-1 cells Cy-3 StxB was bound to BSC-1 cells on ice and internalized at 37 °C for the times shown (A) StxB passes through Tfn-positive endosomes Alexa 488 Tfn and StxB bound to BSC-1 cells expressing human Tfn receptor on ice and then warmed for times shown Both co-localized up to 20 By 45 Tfn (green) and StxB (red) had separated Arrow indicates perinuclear endosome StxB remained in a Golgi-like ribbon for the remainder of the Tfn ⁄ StxB time-course 60–180 (B) Internalized StxB (red) with cells fixed and immunolabeled for Golgi marker GM130 (green) Note co-localization (yellow) (C) Internalized StxB (red) with cells fixed and immunolabeled for ER marker PDI (green) Note co-localization at 240 Inset is indicated area magnified Bars = 10 lM they converge on the EEs [39,40] After 10 min, StxB and Tfn co-localized in both the peripheral EEs and a perinuclear organelle, identified by Tfn pulses as the RE (Fig 1A; 10 min) [41] After 30 min, Tfn primarily labeled the endosomes, although the signal was weaker due to recycling of Tfn into the media, whereas StxB had entered a separate perinuclear structure (Fig 1A; 30 min) This structure had the appearance of a Golgi ribbon in these cells The difference in localization was more obvious after 45 (Fig 1A; 45 arrow indicates transferrin-containing endosomes) At the later times, Tfn had recycled out of the endosomes and was no longer clearly visible although StxB remained in Golgi morphology (Fig 1A; 60, 120 min) [38,42] At 180 min, the internalized StxB took on a lacy appearance typical of the ER (Fig 1A), suggesting that a substantial amount of the toxin had been delivered to the ER [43] Thus, endocytosed StxB was delivered into the endocytic recycling pathway within min, was transferred to perinuclear endosomes within 10–20 min, and then was delivered to the Golgi within 30–45 of internalization FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1583 Shiga toxin in the Golgi J McKenzie et al StxB is delayed in the Golgi before entering the ER We next characterized the passage of StxB through the Golgi of BSC-1 cells under normal cell culture conditions (Fig 1B,C) The distribution of StxB at various time points was compared with that of the cis ⁄ medial Golgi marker GM130, or the ER marker protein disulfide isomerase (PDI) [44,45] Cells were labeled with StxB as before and fixed for immunofluorescence StxB initially partly co-localized with the cis ⁄ medial Golgi marker GM130 after 20 (Fig 1B), and co-localization increased up to 120 (Fig 1B) This confirmed that StxB passes from the transferrin-positive endosomes to the Golgi rather than to another compartment such as late endosomes [24] Passage through the Golgi was slow, as observed elsewhere [2] To determine how long it took for StxB to enter the ER, we internalized StxB for up to h and labeled the cells for the ER marker, PDI (Fig 1C) StxB remained in a perinuclear ribbon (Golgi, as shown by co-localization in Fig 1B) up to 120 StxB began to co-localize with PDI at 150 (not shown) and 180 (not shown) By 240 (Fig 1C), StxB was localized to the ER as shown by co-localization with the ER resident, PDI These data support the observation that passage through the Golgi is the slowest step in the retrograde pathway, requiring up to 120 [46] Taken together, Fig 1A–C established a normal timecourse of StxB traffic in BSC-1 cells We used this time-course as a basis for our further experiments Passage through the Golgi is required for StxB to reach the ER in cytoplasts We wished to test directly if passage through the Golgi ⁄ TGN was required for StxB entry into the ER To accomplish this, we made use of subcellular surgery to create cytoplasts lacking a Golgi apparatus [47] Peripheral extensions of adherent BSC-1 cells were cleaved using a glass micro-pipette to create cytoplasts (peripheral areas lacking a nucleus) and karyoplasts, containing the nucleus, the Golgi apparatus and the REs [48] Cytoplasts generated in this manner lack a Golgi apparatus, and importantly, cannot regenerate one [47] By contrast, cytoplasts can regenerate functional REs from peripheral EEs, as we have previously demonstrated Recycling of Tfn in cytoplasts is complete and follows the same kinetics in cytoplasts as in whole cells [6] Cytoplasts and karyoplasts were labeled with StxB and Tfn for at 37 °C (rather than on ice to avoid releasing the cytoplast from the coverslip) and both ligands were chased into the cytoplasts for various times (Fig 2A) After 10 min, StxB co-local1584 ized with Tfn in endosomal structures (Fig 2A; 10 yellow arrow) After 30 min, Tfn and StxB continued to co-localize with Tfn in endosomes (compare Fig 2A; 30 to Fig 1A) Because Tfn recycles out of cytoplasts at longer StxB internalization times (120 min), it was necessary to add Tfn to the media for and chase in unlabeled media for the final 25 of the assay before fixation to illuminate the endocytic pathway Surprisingly, after 120 min, although the majority StxB (red arrows) remained inside the cytoplasts, it did not co-localize with endosomal structures (labeled with Tfn, green arrow) Rather, it appeared in a diffuse cytosolic-like pattern (red arrows, Fig 2A; 120 min) To ensure that Golgi was not inadvertently included in the cytoplasts, we immunolabeled cytoplasts for GM130 and found it to be absent from the cytoplast, but readily visible in the karyoplast (Fig 2B) To identify which compartment the StxB had entered, we chased StxB into cytoplasts for 120 and labeled the plasma membrane (wheatgerm agglutinin, WGA; Fig 2C), ER (PDI; Fig 2D), and cytosol (Rho GDI; Fig 2E) StxB (red arrows) did not co-localize with WGA (green arrows; Fig 2C) and thus had not recycled to the plasma membrane Nor did it co-localize with the ER marker, even when allowing 240 for co-localization with PDI (green arrows; Fig 2D) However, StxB did co-localize with cytosolic GDI (yellow arrow; Fig 2E), suggesting that StxB was in the cytosol The GDI immunolabel required methanol fixation, which causes a grainy cast to cytosolic proteins Cytosolic depletion using SLO or saponin proved unfeasible as treated cytoplasts detached from the coverslip Together, these results suggest that when the Golgi was absent, StxB did not enter the ER Furthermore, under these conditions the toxin was able to escape the endosomes directly into the cytosol At no time was an ER morphology or co-localization with PDI of StxB observed While it is possible that some remnant Golgi, below the threshold of visualization, was present in the cytoplast, it was clearly insufficient to mediate StxB traffic to the ER This phenomenon may occur to some extent during normal transit of the endosomes, although the amount of toxin available for escape may be minimal as the toxin passes rapidly through the endosomes to the Golgi It may, however, correspond to the brefeldin A-resistant toxicity reported elsewhere [8] Aluminum fluoride traps StxB and Tfn in perinuclear endosomes We wished to confirm the requirement for Golgi passage and to quantify escape of StxB from endosomes FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al Shiga toxin in the Golgi A C B D E Fig StxB cannot access the ER in BSC-1 cytoplasts BSC-1 cells were manually cut with a glass needle to create karyoplasts (k) containing both the nucleus and Golgi and cytoplasts (c) All cytoplasts and karyoplasts were labeled with Cy-3 StxB (red) that was internalized for times shown (A) Shiga and Tfn (green) internalized together for 10 then chased for 10 or 30 For 120 min, Tfn was internalized for the final 25 (B) Cytoplast with StxB (red) immunolabeled for Golgi marker GM130 (green) (C) Cytoplast stained for plasma membrane with wheat germ agglutinin (green) Note that the cytoplast has moved next to the karyoplast but the two remain separate (D) Cytoplast labeled for ER marker PDI (green), at various times of StxB (red) internalization Note exclusion of StxB from ER (E) Cytoplast labeled for cytosolic marker GDI (green) note co-localization (yellow) with StxB (red) Insets are cytoplasts presented in single channels with larger inset showing a magnified view of the combined channels Red arrows indicate StxB, green arrows indicate other compartment markers as indicated Bars = 10 lM into the cytosol However, cytoplasts are extremely small, and must be made individually, making fractionation impossible Therefore, we used a pharmacological approach Aluminum fluoride (AlF4)) is an activator of small GTPases and is well-documented to block recycling of Tfn from the RE [5,49] Although the precise target of AlF4) at the RE is not known, the effect of this drug on Tfn recycling is immediate and remarkably specific to recycling out of the RE in nonpolar cells and to basolateral recycling from the RE in polarized cells [5] Treatment for > h results in dispersal of the Golgi although both the TGN and the ER remain functional [50,51] Because StxB co-localized extensively with Tfn in perinuclear REs, we suspected that AlF4) might also block retrograde StxB from the endosomes to the TGN just as it did for recycling traffic to the plasma membrane Fortuitously, both StxB and Tfn were trapped together in the REs following AlF4) treatment (Fig 3) This was especially apparent after 60 min, when Tfn would normally have recycled out of the cell, and StxB would normally have moved to the Golgi Both remained in the endosomes of treated cells after 60 and even 120 (Fig 3; 60 min, 120 min, yellow arrows) Although this result is based on the fortunate effects of AlF4) treatment on these two pathways, it does not necessarily imply that the same drug target is involved in both retrograde and recycling pathways It does, however, present a unique opportunity As in the cytoplast, StxB is prevented from reaching the Golgi, and it is trapped inside of the endosomes This allowed us to quantify the consequences of trapping StxB in endosomes StxB leaks into the cytosol when trapped at endosomes StxB trapped in the endosomes of AlF4)-treated cells took on a diffuse cytosolic appearance at later time points following internalization (Fig 3; 120 min, red FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1585 Shiga toxin in the Golgi J McKenzie et al Fig Aluminum fluoride traps Stx in endosomes Both StxB (red) and Tfn (green) were bound to BSC-1 cells on ice Both were internalized at 37 °C for times shown in the presence of AlF4) Yellow arrows indicate where both Tfn and StxB have been trapped in a perinuclear endosome Red arrows indicate StxB in diffuse distribution Inset is magnification of indicated area Bar = 10 lM arrows) RE-associated versus peripheral fluorescence was measured using NIH image in 20 cells; 20 ± 7% was found in the periphery The diffuse material did not have an ER morphology, however, AlF4) is known to disperse the medial Golgi in some cells after extended treatment (> 120 min) [50] To determine which cellular compartment StxB had entered, we performed a series of co-localizations (Fig 4) The distribution of StxB was compared to the cis ⁄ medial Golgi marker GM130 in BSC-1 cells in the presence of AlF4) Although dispersed, the Golgi remained clearly visible as structures surrounding StxB-labeled endosomes at times up to 240 (Fig 4A) GM130 did not co-localize with the StxB in punctate (endosomal) structures nor did it co-localize with the diffuse StxB (Fig 4A) This confirmed both that AlF4) treatment prevented access to the Golgi and that StxB was not in the fragmented Golgi It was possible that AlF4) treatment may have allowed StxB to bypass the Golgi and enter the ER However, despite changes in ER morphology (Fig 4B), StxB did not co-localize with the ER marker PDI, even at 240 (Fig 4B) As with the cytoplasts, StxB prevented from reaching the Golgi by AlF4) did not access the ER A fraction of the internalized StxB appeared to escape the endosomes as had occurred in 1586 the cytoplasts This suggested that StxB alone could escape endosomes if it was not sequestered into the Golgi It was not completely clear if the extra-endosomal StxB was in a membrane or cytosolic fraction It was also unclear if endosomal escape was specific for StxB or resulted from AlF4) treatment altering the endosomal membranes to allow escape of all cargo To differentiate between these possibilities, we used a cell fractionation approach to separate cytosol from membrane-bound organelles Iodinated StxB was bound to BSC-1 cells on ice, washed, then warmed in the presence or absence of AlF4) to initiate internalization Cells were harvested after 120 of chase, then homogenized in a ball-bearing cell homogenizer so as to recover intact organelles Membrane and cytosolic fractions were separated via Opti-prep step-gradients In these experiments, (Fig 5A) cytosol was collected from the top of the gradient, and all membranes were collected from an Optiprep cushion at the bottom of the gradient As a control for rupture of endosomes, 125 I-labeled Tfn was bound to the cell surface and then chased into the endosomal compartments of control cells Because Tfn normally recycles rapidly out of the cell, it was chased for 20 in control cells or for 120 in AlF4)-treated cells This ensured that Tfn would be in the REs [5,6] Because Tfn is released FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al Shiga toxin in the Golgi A B Fig Aluminum fluoride traps StxB in endosomes (A) StxB (red) bound to BSC-1 cells and internalized for times shown in the presence of AlF4) Cells were stained for Golgi marker GM130 (green) Note diffuse StxB Red arrows indicate StxB in endosomal structure, Green arrows indicate the Golgi (B) Cells labeled as in A but stained for ER marker PDI (green) Green arrows indicate ER structures ER morphology is altered (compare with Fig 1) Bar = 10 lM A B Fig StxB trapped in the endosomes leaks into the cytosol (A) Quantification of StxB in cytosol 125I-labeled StxB or 125I-labeled Tfn internalized into BSC-1 cells expressing transferrin receptor for 120 Cells were harvested and homogenized Total cytosol was separated from total membranes using an Optiprep ⁄ ⁄ 25% step gradient Average values for the percent of each ligand in the cytosol with and without AlF4) are shown Error bars are SD *Significant change n = 15 for StxB conditions, n = for Tfn conditions (B) Cell fractionation of BSC-1 organelles to identify those containing internalized ligands on preformed linear 8–25% Optiprep gradients Top of gradient is to the left (I) 125I-labeled StxB internalized in the absence (dark red, closed circles) or presence (orange, open circles) of AlF4) for h Bar indicates cytosolic fractions Bars and indicate endosome or Golgi associated peaks in treated cells Bar indicates a peak of membrane bound StxB found only in treated cells (II) Positions in the gradient of cytosol (red), plasma membrane (orange), lysosomes (yellow), REs (green), Golgi (light blue), ER (dark blue) and cell debris (purple) Supporting data are given in Fig S1 (III) 125I-labeled Tfn internalized for 25 in control cells to locate RE (at h it is recycled out of the cell), Bar (dark blue closed squares) and h in AlF4) treated cells (treatment prevents recycling) (light blue, open squares) Note that some Tfn remains at the plasma membrane Bar (n = 1, results typical) FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1587 Shiga toxin in the Golgi J McKenzie et al from its receptor at the neutral pH of the gradient, it acts as a sensitive indicator of endosomal rupture during handling It also serves as a specific indicator of changes in endosomal fragility due to AlF4) treatment Figure 5A shows that there was no difference in cytosolic transferrin between control and AlF4)-treated cells (Fig 5A; Tfn and Tfn + AlF4)) Thus, endosomes were not made more fragile by the drug treatment By contrast, the amount of StxB found in the cytosol was significantly larger in the presence of AlF4) (Fig 5A; StxB vs StxB + AlF4)) The difference was statistically significant with P < 0.0001 (Student’s t-test) This cytosolic escape was not observed when StxB was internalized for only 20 (data not shown), a time at which StxB remained in endosomes and was not visualized in the cytosol in intact cells Cytosolic StxB accounted for 12% of the radiolabeled StxB, but analysis of cell fluorescence had found that 25% of internalized StxB was not in the endosomes To resolve this difference, we utilized a different density gradient protocol to fractionate organelles within the cell 125I-labeled StxB cell homogenates from control and AlF4)-treated cells were applied to preformed linear 8–25% Optiprep gradients We have previously described the use of these gradients for the fractionation of cellular organelles [5] Gradients were characterized by locating fractions containing alkaline phosphodiesterase activity (plasma membrane), B-hexosaminidase activity (lysosomes) radiolabeled Tfn internalized for 25 (REs), added phenol red (cytosol), GM130 (Golgi) and PDI (ER) The position of the peak activity for each organelle is shown in the color-coded bar in Fig 5B (II), and in Fig S1 StxB internalized for 60 in control cells co-localized with Golgi and REs (which could not be readily distinguished in this gradient) However, AlF4) treatment shifted the distribution of both StxB and Tfn into a doublet of peaks at, and just below, the density of REs (Fig 5B) In this representative experiment, 9% of StxB was observed in the cytosol in AlF-treated cells compared with 3% in control cells Also, 24% of StxB was observed in a dense fraction (compared with 8% in control cells) that did not co-segregate with any of the characterized organelles Although this could not be identified, we speculate that it may represent transport vesicles derived from the endosomes, unable to reach the Golgi This fraction would account for the difference between non-endosomal StxB observed microscopically and that observed in the cytosolic fraction of step gradients above These results suggest that AlF4) can block retrograde traffic at the endosomes and that StxB is able to escape the endosomes to the cytosol Taken together 1588 with the cytoplast results, this suggests that when StxB is trapped within the endosomes, it can ‘escape’ into the cytosol, as previously suggested for dendritic cells and macrophages [52,53] A similar escape has also been observed for the Stx A subunit [8] A temperature block separates StxB and Tfn It remained possible that StxB was equally capable of entering the cytosol from any organelle along the retrograde pathway We tested this possibility by using a temperature block to trap StxB within the TGN for a time In HeLa cells, it has been reported that maintaining the cells at 20 °C traps StxB along with Tfn in the endosomes [24] We too observed this effect in HeLa cells (Fig S2) However, reducing the temperature to 20 °C in BSC-1 cells had a surprising and useful effect Both Tfn and StxB were bound to BSC-1 cells and internalized at 20 °C for various lengths of time (Fig 6A) As expected, Tfn did not recycle out of the endosomes, but remained in the perinuclear region After 30 min, StxB appeared to co-localize with Tfn in the majority of cells However, after 60 min, StxB separated into another perinuclear structure that did not co-localize with Tfn This distribution was maintained up to 180 We suspected that this other structure might be part of the Golgi due to the ribbon-like appearance Fortunately, in BSC-1 cells, the TGN and cis ⁄ medial Golgi can be discriminated visually (although there is slight overlap) using the TGN marker TGN46 and the cis ⁄ medial marker GM130 (Fig 6B) We therefore compared the localization of StxB with that of TGN46 and GM130 after 120 and 180 of internalization at 20 °C There was striking co-localization of StxB with the TGN marker at both time points (Fig 6C) suggesting that at 20 °C in BSC-1 cells, StxB was trapped in the TGN This was very different from the situation at 37 °C (Fig 6D) where StxB co-localized with both TGN and cis ⁄ medial Golgi in as little as 90 We wished to confirm that we were seeing co-localization in the TGN and not at ER exit sites StxB internalized at 20 °C co-localized with TGN46 but clearly did not co-localize with the ER exit site marker Sec31, again suggesting that StxB was trapped specifically at the TGN at this temperature (Fig 6E) These results suggested that BSC-1 cells, unlike HeLa cells, hold StxB in the TGN at 20 °C This difference between HeLa and BSC-1 cells provided a natural experiment in BSC-1 cells to test if StxB could escape into the cytosol when it was held in the TGN instead of the endosomes Notably, no escape of StxB into the cytosol was seen in the cells held at 20 °C FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al Shiga toxin in the Golgi A B C D E Fig A 20 °C temperature block traps Stx in the TGN in BSC-1 cells (A) StxB (red) and Tfn (green) were internalized for times shown at 20 °C Yellow arrows indicate co-localization at earlier times, red arrows indicate StxB differently distributed than Tfn (B) anti-GM130 for cis ⁄ medial Golgi (green) and anti-TGN46 for TGN (red) are visually resolved, two BSC-1 cells are shown (C) StxB (red) co-localizes with TGN46 (blue) but not with GM130 (green) when internalized at 20 °C Purple arrows indicate co-localization of StxB and TGN46 Red bordered inset shows magnification of cytosol in a cell adjacent to the labeled Golgi Note lack of cytosolic StxB (D) Same as (C) but internalized at 37 °C Yellow arrow indicates partial co-localization of GM130 and StxB (E) StxB (red) co-localizes with TGN46 (blue) but not with ER exit point marker Sec31 (green) when internalized at 20 °C Upper insets are enlarged versions of regions indicated Lower insets are Sec31 (green), StxB (red) and a merge of only Sec31 and StxB Purple arrows indicate co-localization of StxB and TGN46 Green and red arrows indicate locations of ER exit sites and StxB respectively Bar = 10 lM even after 180 (Fig 6C; red box and E) Taken together these results suggest that StxB cannot escape the TGN into the cytosol, and that escape may be dependent upon some property of the endosomes such as low pH found in EEs or membrane composition [54,55] FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1589 Shiga toxin in the Golgi J McKenzie et al Discussion Stx is an A–B5 toxin that binds to the plasma membrane lipid Gb3 In this respect it is like cholera toxin and SV40 virus, both of which bind to the ganglioside GM1 [56,57] Both toxins, and the virus are transported to the ER after internalization [58] However, whereas cholera toxin appears to pass through endosomes and the Golgi, SV40 bypasses both the normal endocytic organelles and the Golgi, trafficking directly from a specialized endocytic population to the ER [10] These examples demonstrate that binding to a glycolipid receptor, and even trafficking to the ER not guarantee passage through the Golgi Furthermore, even if passage through the Golgi is a normal component of the retrograde pathway, it does not automatically follow that this pathway is exclusive of other routes We sought to determine whether retrograde traffic of StxB required passage through the Golgi to reach the ER A morphological examination of retrograde traffic, as performed here, suggests that StxB appears to progress sequentially from the plasma membrane to the endosomes to the Golgi and then to the ER However, just as the majority of Tfn actually bypasses the RE, a fraction of StxB may actually bypass the Golgi [5] Alternatively, the Golgi transit route could be preferred and mask a lower flux endosome to ER route We used cytoplasts to physically separate endosomes and ER from the Golgi in an isolated piece of living cells We had previously determined that these cytoplasts are able to regenerate a fully functional endocytic system with both EEs and REs [6] They also contain ER, as demonstrated here However, they are unable to regenerate a Golgi, which allowed us to test directly whether Golgi transit was required for StxB to progress from endosomes to the ER [47] In the absence of a Golgi, StxB was unable to access the ER in cytoplasts Had a slower or lower flux pathway connected the endosomes directly to the ER, we would have seen StxB in the ER of the cytoplasts Although it remains possible that such a pathway exists for some endogenous proteins, it is clearly not accessed by StxB Our findings raise the question of why StxB should take such a circuitous path from plasma membrane to cytosol Other toxins such as diphtheria toxin and anthrax toxin take advantage of low endosomal pH to penetrate the endosomal membrane and enter the cytosol directly [59] Our results may shed some light on the host–pathogen interaction that has developed around the retrograde traffic of StxB In cytoplasts, StxB was trapped at the endosomes There are several possible alternative routes that would be available out of the 1590 EE compartments The most obvious would be to recycle out of the endosomes and return to the plasma membrane along with Tfn However, StxB did not reappear at the plasma membrane in any visible amount A second possibility would be for StxB to be shunted into late endosomes (also found in cytoplasts) [6] However, we did not see co-localization with lysosomal proteins (J McKenzie & D Sheff, unpublished observations) To our surprise, StxB appeared to enter the cytosol directly from the endosomes in cytoplasts Because cytoplasts are extremely small and must be formed manually, we were unable to perform biochemical analysis or cell fractionation on these preparations However, we were fortunate in finding that AlF4) treatment blocked exit of StxB from the endosomes Despite being a generalized inhibitor of GTPase function in the endocytic recycling pathway, AlF4) is specific for egress from REs [5] Using AlF4), we were able to confirm that 12% of internalized StxB accessed the cytosol directly from the endosomes This result is inconsistent with prior findings that a small percentage of Stx A subunit (5%) can effectively reach its target even when traffic along the postendosomal retrograde pathway is impaired by disruption of the Golgi with brefeldin A [8] It is also consistent with the prior finding that 10% of cell-associated StxB reaches the cytosol in human monocyte derived macrophages [53] This is particularly relevant because monocytes-derived macrophages internalize StxB, but not support retrograde traffic of StxB from endosomes to the Golgi [52] Furthermore, our finding that StxB trapped in the TGN could not enter the cytosol, suggests that endocytic membranes are particularly susceptible to penetration by StxB Thus toxicity in the monocyte-derived macrophages may paradoxically result from the inability of the cell to transport toxin out of the endosomes and into the Golgi (provided that the toxin would then not be able to exit the Golgi) Penetration of the endosomal membrane by StxB was surprising in light of the normal retrograde pathway taken by StxB However, endosomal escape is known not only for bacterial toxins such as diphtheria toxin, but also for fibroblast growth factor following endocytosis [54, 60–62] Such translocation may represent another physiological pathway that is subverted by StxB when the Golgi pathway is unavailable Clearly StxB cannot be present in the cytosol while membrane bound This suggested that the toxin was able to dissociate from Gb3 while inside the endosome Such dissociation is unlikely to be a result of low pH because acid wash of bound StxB does not remove it from the plasma membrane However, StxB can bind up to 15 Gb3 molecules, mediated through three FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al different sites on each B subunit of the pentamer [63] The overall Kd of the StxB ⁄ Gb3 complex is 10)9 m This results from the combined associations of all sites with Gb3 molecules in the membrane However, binding to site II formed by the cleft between monomers is much weaker that that of site I [63] Thus if Gb3 is present at lower concentrations in the endosomes than at the plasma membrane, one would expect dissociation of the cleft-bound Gb3 from the complex, and dissociation of the entire molecule when Gb3 concentrations become sufficiently low Recently, it has been demonstrated that decreasing the concentration of Gb3 available at the plasma membrane in Vero cells results in a precipitous decline in StxB binding [64] We would suggest that the concentration of Gb3 may be significantly lower within endosomes than at the plasma membrane, providing the possibility for some StxB to no longer be bound to the receptor [53] Further examination of this effect is beyond the scope of this study The ability of StxB to penetrate the endosomal membrane raised the important question of whether the endosomal membrane was uniquely permeable to StxB If StxB can cross any membrane, then it would be expected that it could directly penetrate the plasma membrane, and this is not the case, as demonstrated by cell lines lacking Gb3 which are resistant to the toxin [65] Our use of BSC-1 cells allowed use to take advantage of a unique feature of the 20 °C temperature block in these cells Rather that trapping StxB at the endosomes as in HeLa cells, StxB was able to traffic to the TGN in these cells Although all trafficking is slowed (or stopped in some cases) at this temperature, this would still allow for escape of the StxB into the cytosol at long incubation times We did not observe StxB entering the cytosol under these conditions, suggesting that the TGN membrane is less permeable to StxB than that of the endosomes One tempting possibility is that the difference in membrane permeability has driven host–pathogen interactions over the course of evolution Some toxins, such as anthrax toxin have evolved mechanisms to avoid recycling out of the endosomes by rapidly entering the cytosol Our data suggest that while StxB can accomplish this penetration, the process is slow and inefficient Host cells may have acquired the ability to sequester the toxin in the Golgi, thereby preserving the cell so that over time the toxin may be degraded Such a possibility is supported by the rapid and near quantitative diversion of StxB from the endocytic pathway into the Golgi The slow passage of the toxin through the Golgi also argues in favor of this possibility The response of the pathogen to this sequestration appears to have been to develop a mechanism to exploit retro- Shiga toxin in the Golgi grade transport out of the Golgi into the ER While this process is also slow, it is quantitative, and results in delivery of the bulk of the toxin to the ER where the A subunit can retrotranslocate into the cytosol by exploiting the translocon [16,66] In this case, the current retrograde transport of StxB and of holotoxin may have developed as a series of host–pathogen interactions and adaptive responses Although our data cannot be conclusive in this respect it is at the least supportive of the possibility Materials and methods Cells and reagents BSC-1 cells clone CCL-26 from ATCC (Manassas, VA, USA) were cultured in minimal Eagle’s medium (MEM) supplemented with 10% fetal bovine serum, 1% nonessential amino acids, 1% sodium pyruvate, 100 unitsỈmL)1 penicillin and 100 lgỈmL)1 streptomycin in 5% CO2, 95% air NaF and AlCl3 were obtained from Fisher (Fair Lawn, NJ, USA) Recombinant wild-type StxB derived from S dysenteriae was produced from clone in pSU108 The protein was induced and purified as previously described [24,67] Purified StxB was labeled using Alexa-dye protein labeling kits from Invitrogen (Carlsbad, CA, USA) according to manufacturers directions Polyclonal rabbit anti-Sec31 serum (kind gift from the Warren Lab, Max F Perutz Laboratories, Vienna, Austria); mouse anti-GM130 mAb from BD Biosciences (San Jose, CA, USA); mouse anti-PDI mAb from Nventa (San Diego, CA, USA); polyclonal sheep anti-TGN46 from Serotec (Raleigh, NC, USA); polyclonal rabbit anti-(Rho GDI clone K-21) from Santa Cruz (Santa Cruz, CA, USA); Alexa 488-labeled WGA, Alexa488 human holotransferrin, Alexa 488 goat anti-mouse IgG, Alexa 488 goat anti-rabbit IgG and Alexa 633 donkey anti-sheep IgG were obtained from Invitrogen (Carlsbad, CA, USA) 125I-conjugated Tfn and StxB were made using Iodo-Gen (Pierce ⁄ Thermo Scientific, Rockford, IL, USA) as previously described for Tfn [5] StxB and Tfn labeling BSC-1 cells were grown on glass coverslips For cytoplasts, square gridded coverslips (Belco) were used and cells for live images were grown on glass-bottom 35 mm dishes For Tfn uptake experiments, cells were preincubated in serumfree media for 30 at 37 °C to clear Tfn from the cell Cells were chilled on ice and labeled with a : 200 dilution of 0.22 mgỈmL)1 Cy3 StxB and a : 100 dilution of mgỈmL)1 Alexa 488–Tfn in NaCl ⁄ Pi Internalization was performed by placing the cells in 37 °C MEM for indicated times Tfn was omitted as indicated When noted, 50 lm aluminum chloride ⁄ 30 mm sodium fluoride was included during internalization For 20 °C block studies, cells were FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1591 Shiga toxin in the Golgi J McKenzie et al labeled in MEM (without fetal bovine serum) at 20 °C instead of on ice, for min, media was then replaced with MEM Cytoplasts are sensitive to cold and so were labeled for at 37 °C in MEM followed by unlabeled MEM at 37 °C Cytoplast creation BSC-1 cells were grown on gridded coverslips for days to allow cells to spread out Glass needles were prepared using 1.0 mm o.d., 0.50 mm i.d., 10 cm length capillaries from Sutter Instruments (Novato, CA, USA) on a Sutter Instruments P-97 micropipette puller For microsurgery, cells were transferred to bicarbonate-free MEM buffered with 10 mm Hepes pH 7.4 Cellular microsurgery was performed using the glass needle mounted in a Sutter Instruments MP-285 micromanipulator with a joystick controller under manual control Cuts took an average of Cytoplasts were allowed to recover for at least h after microsurgery prior to labeling Cytoplasts were fixed as for whole cells described previously [5] ER was detected by western blot for PDI Endosomes were identified by the presence of 125 I-labeled Tfn internalized for 25 Immunofluorescence Cells were washed with NaCl ⁄ Pi, fixed in 3% PFA at room temperature for 15 Cells were permeabilized with 0.05% (w ⁄ v) saponin in NaCl ⁄ Pi with 3% BSA for h then washed three times in blocking buffer (0.05% saponin, 3% BSA, NaCl ⁄ Pi) for For PDI labeling, permeabilization was performed by 0.04% Triton X-100 in NaCl ⁄ Pi for then washed three times in blocking buffer (3% BSA, NaCl ⁄ Pi) for 5min For GDI labeling, cells were rinsed with cold NaCl ⁄ Pi then fixed for in 100% methanol at )20 °C For immunolabeling, cells were incubated with a : 200 dilution of antibodies (except PDI, : 500) at room temperature for 45 Cells were visualized with appropriate Alexa-conjugated secondary antibodies at : 200 dilution for 30 at room temperature, washed and mounted Membrane and cytosol fractionation BSC-1 cells were grown to near confluency in 35 mm dishes For Tfn labeling, BSC-1 cells were infected with human Tfn receptor expressing adenovirus at an MOI of > 50, 24 h prior to use Cells were serum starved for 30 then labeled on ice with 125I-labeled Tfn or StxB for 30 Cells were then rinsed with chilled NaCl ⁄ Pi and warmed in MEM to 37 °C in presence or absence of AlF4) For control cells (Tfn, no AlF), the radiolabeled Tfn was taken up warm for then chased for 20 min, because it would otherwise recycle back out to the cell surface Cells were then harvested and homogenized via a ball-bearing cell homogenizer Post nuclear supernatants were then generated by centrifugation at 1000 g for Two different fractionations were performed To separate cytosol from membranes, the supernatant was overlaid onto a layer of 8% Optiprep which was in turn overlaid onto a layer of 25% OPTI-Prep (diluted with ICT buffer: 78 mm KCl, mm MgCl2, 8.37 mm CaCl2 10 mm EGTA, 50 mm Hepes ⁄ KOH pH 7.0) [6,68] Cytosol remained in the top fraction, while membranes and organelles were recovered from the ⁄ 25% interface after centrifugation at 100 000 g for 120 at °C CPM in each fraction was counted in a gamma counter for and the data compiled Data were normalized to the total counts in each tube Each condition was repeated at least four times For density gradient organelle fractionation, the supernatant was overlaid onto an 8–25% preformed linear gradient of Optiprep created using a Gradient master from Biocomp (Toronto, Canada) and centrifuged at 100 000 g for 20 h to allow density equilibration of organelles in the gradient Cytosol was identified visually using phenol red Plasma membrane, lysosomes and Golgi were identified by enzyme assay as 1592 Image analysis All images were acquired on a Zeiss 200M inverted microscope equipped with a Hamamatsu ER camera operated by Openlab from Improvision (Coventry, UK) on a Macintosh G4 computer from Apple (Cupertino, CA, USA) Low exposure and high exposure images of all cells were obtained For cytoplasts, low exposures are shown for karyoplast and cytoplast, and the inset is of the higher exposure due to the low levels of signal in cytoplasts Contrast in images was optimized using photoshop from Adobe (San Jose, CA, USA) on an Apple G5 computer Acknowledgements This work supported by a grant to JM from the American Heart Association #081365G as well as to DS from American Heart Association #035078N Support for TT was provided by 21st Century Center of Excellence Program from the Ministry of Education, Culture, Sports, Science and Technology of Japan, The Core Research for Evolutional Science and Technology (CREST), JSPS (Japan Society for the Promotion of Science) Core-to-Core Program Grants-in-aid for Scientific Research (18050019), and Senri Life Science Foundation Grants Many thanks to Graham Warren for discussions about the Golgi and to Lawrence Pelletier for discussions about cytoplasts and Stx We would also like to thank Mark Stamnes, Heidi Hehnly, Naava Naslavsky and Steve Caplan for their thoughtful discussions and suggestions FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al References World Health Organization (2006) Global Burden of Disease and Risk Factors Oxford University Press ⁄ World Bank, New York Sandvig K, Spilsberg B, Lauvrak SU, Torgersen ML, Iversen TG & van Deurs B (2004) Pathways followed by protein toxins into cells Int J Med Microbiol 293, 483–490 Johannes L & Decaudin D (2005) Protein toxins: intracellular trafficking for targeted therapy Gene Ther 12, 1360–1368 Mallard F & Johannes L (2003) Shiga toxin B-subunit as a tool to study retrograde transport Method Mol Med 73, 209–220 Sheff DR, Daro EA, Hull M & Mellman I (1999) The receptor recycling pathway contains two distinct populations of early endosomes with different sorting functions J Cell Biol 145, 123–139 Sheff DR, Kroschewski R & Mellman I (2002) Actin dependence of polarized receptor recycling in Madin– Darby canine kidney cell endosomes Mol Biol Cell 13, 262–275 Khine AA, Tam P, Nutikka A & Lingwood CA (2004) Brefeldin A and filipin distinguish two globotriaosyl ceramide ⁄ verotoxin-1 intracellular trafficking pathways involved in Vero cell cytotoxicity Glycobiology 14, 701–712 Tam PJ & Lingwood CA (2007) Membrane cytosolic translocation of verotoxin A1 subunit in target cells Microbiology 153, 2700–2710 Sandvig K & van Deurs B (2005) Delivery into cells: lessons learned from plant and bacterial toxins Gene Ther 12, 865–872 10 Pelkmans L, Kartenbeck J & Helenius A (2001) Caveolar endocytosis of simian virus 40 reveals a new twostep vesicular-transport pathway to the ER Nat Cell Biol 3, 473–483 11 O’Brien AD, Tesh VL, Donohue-Rolfe A, Jackson MP, Olsnes S, Sandvig K, Lindberg AA & Keusch GT (1992) Shiga toxin: biochemistry, genetics, mode of action, and role in pathogenesis Curr Top Microbiol Immunol 180, 65–94 12 Endo Y, Tsurugi K, Yutsudo T, Takeda Y, Ogasawara T & Igarashi K (1988) Site of action of a Vero toxin (VT2) from Escherichia coli O157:H7 and of Shiga toxin on eukaryotic ribosomes RNA N-glycosidase activity of the toxins Eur J Biochem 171, 45–50 13 Kurmanova A, Llorente A, Polesskaya A, Garred O, Olsnes S, Kozlov J & Sandvig K (2007) Structural requirements for furin-induced cleavage and activation of Shiga toxin Biochem Biophys Res Commun 357, 144–149 14 Johannes L & Goud B (2000) Facing inward from compartment shores: how many pathways were we looking for? Traffic 1, 119–123 Shiga toxin in the Golgi 15 Sandvig K, Ryd M, Garred O, Schweda E, Holm PK & van Deurs B (1994) Retrograde transport from the Golgi complex to the ER of both Shiga toxin and the nontoxic Shiga B-fragment is regulated by butyric acid and cAMP J Cell Biol 126, 53–64 16 Yu M & Haslam DB (2005) Shiga toxin is transported from the endoplasmic reticulum following interaction with the luminal chaperone HEDJ ⁄ ERdj3 Infect Immun 73, 2524–2532 17 Jacewicz M, Clausen H, Nudelman E, Donohue-Rolfe A & Keusch GT (1986) Pathogenesis of Shigella diarrhea XI Isolation of a Shigella toxin-binding glycolipid from rabbit jejunum and HeLa cells and its identification as globotriaosylceramide J Exp Med 163, 1391–1404 18 Lauvrak SU, Torgersen ML & Sandvig K (2004) Efficient endosome-to-Golgi transport of Shiga toxin is dependent on dynamin and clathrin J Cell Sci 117, 2321–2331 19 Nichols BJ (2002) A distinct class of endosome mediates clathrin-independent endocytosis to the Golgi complex Nat Cell Biol 4, 374–378 20 Sandvig K, Olsnes S, Brown JE, Petersen OW & van Deurs B (1989) Endocytosis from coated pits of Shiga toxin: a glycolipid-binding protein from Shigella dysenteriae J Cell Biol 108, 1331–1343 21 Romer W, Berland L, Chambon V, Gaus K, Windschiegl B, Tenza D, Aly MR, Fraisier V, Florent JC, Perrais D et al (2007) Shiga toxin induces tubular membrane invaginations for its uptake into cells Nature 450, 670–675 22 Lauvrak SU, Walchli S, Iversen TG, Slagsvold HH, Torgersen ML, Spilsberg B & Sandvig K (2006) Shiga toxin regulates its entry in a Syk-dependent manner Mol Biol Cell 17, 1096–1109 23 Hehnly H, Sheff D & Stamnes M (2006) Shiga toxin facilitates its retrograde transport by modifying microtubule dynamics Mol Biol Cell 17, 4379–4389 24 Mallard F, Antony C, Tenza D, Salamero J, Goud B & Johannes L (1998) Direct pathway from early ⁄ recycling endosomes to the Golgi apparatus revealed through the study of Shiga toxin B-fragment transport J Cell Biol 143, 973–990 25 Wilcke M, Johannes L, Galli T, Mayau V, Goud B & Salamero J (2000) Rab11 regulates the compartmentalization of early endosomes required for efficient transport from early endosomes to the trans-Golgi network J Cell Biol 151, 1207–1220 26 Del Nery E, Miserey-Lenkei S, Falguieres T, Nizak C, Johannes L, Perez F & Goud B (2006) Rab6A and Rab6A’ GTPases play non-overlapping roles in membrane trafficking Traffic 7, 394–407 27 Popoff V, Mardones GA, Tenza D, Rojas R, Lamaze C, Bonifacino JS, Raposo G & Johannes L (2007) The retromer complex and clathrin define an early endosomal retrograde exit site J Cell Sci 120, 2022–2031 FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1593 Shiga toxin in the Golgi J McKenzie et al 28 Bujny MV, Popoff V, Johannes L & Cullen PJ (2007) The retromer component sorting nexin-1 is required for efficient retrograde transport of Shiga toxin from early endosome to the trans Golgi network J Cell Sci 120, 2010–2021 29 Utskarpen A, Slagsvold HH, Dyve AB, Skanland SS & Sandvig K (2007) SNX1 and SNX2 mediate retrograde transport of Shiga toxin Biochem Biophys Res Commun 358, 566–570 30 Perez-Victoria FJ, Mardones GA & Bonifacino JS (2008) Requirement of the Human GARP complex for mannose 6-phosphate-receptor-dependent sorting of cathepsin D to lysosomes Mol Biol Cell 19, 2350–2362 31 Mallard F, Tang BL, Galli T, Tenza D, Saint-Pol A, Yue X, Antony C, Hong W, Goud B & Johannes L (2002) Early ⁄ recycling endosomes-to-TGN transport involves two SNARE complexes and a Rab6 isoform J Cell Biol 156, 653–664 32 Ghosh RN, Mallet WG, Soe TT, McGraw TE & Maxfield FR (1998) An endocytosed TGN38 chimeric protein is delivered to the TGN after trafficking through the endocytic recycling compartment in CHO cells J Cell Biol 142, 923–936 33 Derby MC, Lieu ZZ, Brown D, Stow JL, Goud B & Gleeson PA (2007) The trans-Golgi network golgin, GCC185, is required for endosome-to-Golgi transport and maintenance of Golgi structure Traffic 8, 758–773 34 Amessou M, Fradagrada A, Falguieres T, Lord JM, Smith DC, Roberts LM, Lamaze C & Johannes L (2007) Syntaxin 16 and syntaxin are required for efficient retrograde transport of several exogenous and endogenous cargo proteins J Cell Sci 120, 1457–1468 35 Wang Y, Tai G, Lu L, Johannes L, Hong W & Luen Tang B (2005) Trans-Golgi network syntaxin 10 functions distinctly from syntaxins and 16 Mol Membr Biol 22, 313–325 36 Torgersen ML, Lauvrak SU & Sandvig K (2005) The A-subunit of surface-bound Shiga toxin stimulates clathrin-dependent uptake of the toxin FEBS J 272, 4103–4113 37 Spooner RA, Watson P, Smith DC, Boal F, Amessou M, Johannes L, Clarkson GJ, Lord JM, Stephens DJ & Roberts LM (2008) The secretion inhibitor Exo2 perturbs trafficking of Shiga toxin between endosomes and the trans-Golgi network Biochem J 414, 471–484 38 Hopkins CR & Trowbridge IS (1983) Internalization and processing of transferrin and the transferrin receptor in human carcinoma A431 cells J Cell Biol 97, 508–521 39 Vago R, Marsden CJ, Lord JM, Ippoliti R, Flavell DJ, Flavell SU, Ceriotti A & Fabbrini MS (2005) Saporin and ricin A chain follow different intracellular routes to enter the cytosol of intoxicated cells FEBS J 272, 4983–4995 1594 40 Saint-Pol A, Yelamos B, Amessou M, Mills IG, Dugast M, Tenza D, Schu P, Antony C, McMahon HT, Lamaze C et al (2004) Clathrin adaptor epsinR is required for retrograde sorting on early endosomal membranes Dev Cell 6, 525–538 41 Daro E, Van der Sluijs P, Galli T & Mellman I (1996) Rab4 and cellubrevin define different early endosome populations on the pathway of transferrin receptor recycling Proc Natl Acad Sci USA 93, 9559– 9564 42 Sheff D, Pelletier L, O’Connell CB, Warren G & Mellman I (2002) Transferrin receptor recycling in the absence of perinuclear recycling endosomes J Cell Biol 156, 797–804 43 Johannes L, Tenza D, Antony C & Goud B (1997) Retrograde transport of KDEL-bearing B-fragment of Shiga toxin J Biol Chem 272, 19554–19561 44 Nakamura N, Rabouille C, Watson R, Nilsson T, Hui N, Slusarewicz P, Kreis TE & Warren G (1995) Characterization of a cis-Golgi matrix protein, GM130 J Cell Biol 131, 1715–1726 45 Parkkonen T, Kivirikko KI & Pihlajaniemi T (1988) Molecular cloning of a multifunctional chicken protein acting as the prolyl 4-hydroxylase beta-subunit, protein disulphide-isomerase and a cellular thyroid-hormonebinding protein Comparison of cDNA-deduced amino acid sequences with those in other species Biochem J 256, 1005–1011 46 Kim JH, Johannes L, Goud B, Antony C, Lingwood CA, Daneman R & Grinstein S (1998) Noninvasive measurement of the pH of the endoplasmic reticulum at rest and during calcium release Proc Natl Acad Sci USA 95, 2997–3002 47 Pelletier L, Jokitalo E & Warren G (2000) The effect of Golgi depletion on exocytic transport Nat Cell Biol 2, 840–846 48 Maniotis A & Schliwa M (1991) Microsurgical removal of centrosomes blocks cell reproduction and centriole generation in BSC-1 cells Cell 67, 495–504 49 Colombo MI, Lenhard J, Mayorga L, Beron W, Hall H & Stahl PD (1994) Inhibition of endocytic transport by aluminum fluoride implicates GTPases as regulators of endocytosis Mol Membr Biol 11, 93–100 50 Back N, Litonius E, Mains RE & Eipper BA (2004) Fluoride causes reversible dispersal of Golgi cisternae and matrix in neuroendocrine cells Eur J Cell Biol 83, 389–402 51 Hammond C & Helenius A (1994) Quality control in the secretory pathway: retention of a misfolded viral membrane glycoprotein involves cycling between the ER, intermediate compartment, and Golgi apparatus J Cell Biol 126, 41–52 52 Falguieres T, Mallard F, Baron C, Hanau D, Lingwood C, Goud B, Salamero J & Johannes L (2001) Targeting of Shiga toxin B-subunit to retrograde transport route FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works J McKenzie et al 53 54 55 56 57 58 59 60 61 62 63 in association with detergent-resistant membranes Mol Biol Cell 12, 2453–2468 Falguieres T & Johannes L (2006) Shiga toxin B-subunit binds to the chaperone BiP and the nucleolar protein B23 Biol Cell 98, 125–134 Yamashiro DJ & Maxfield FR (1984) Acidification of endocytic compartments and the intracellular pathways of ligands and receptors J Cell Biochem 26, 231–246 Yamashiro DJ, Tycko B, Fluss SR & Maxfield FR (1984) Segregation of transferrin to a mildly acidic (pH 6.5) para-Golgi compartment in the recycling pathway Cell 37, 789–800 Chinnapen DJ, Chinnapen H, Saslowsky D & Lencer WI (2006) Rafting with cholera toxin: endocytosis and trafficking from plasma membrane to ER FEMS Microbiol Lett 266, 129–137 Campanero-Rhodes MA, Smith A, Chai W, Sonnino S, Mauri L, Childs RA, Zhang Y, Ewers H, Helenius A, Imberty A et al (2007) N-glycolyl GM1 ganglioside as a receptor for simian virus 40 J virol 81, 12846–12858 Schelhaas M, Malmstrom J, Pelkmans L, Haugstetter J, Ellgaard L, Grunewald K & Helenius A (2007) Simian virus 40 depends on ER protein folding and quality control factors for entry into host cells Cell 131, 516– 529 Sandvig K & van Deurs B (2002) Transport of protein toxins into cells: pathways used by ricin, cholera toxin and Shiga toxin FEBS Lett 529, 49–53 Haugsten EM, Malecki J, Bjorklund SM, Olsnes S & Wesche J (2008) Ubiquitination of fibroblast growth factor receptor is required for its intracellular sorting but not for its endocytosis Mol Biol Cell 19, 3390– 3403 Sorensen V, Wiedlocha A, Haugsten EM, Khnykin D, Wesche J & Olsnes S (2006) Different abilities of the four FGFRs to mediate FGF-1 translocation are linked to differences in the receptor C-terminal tail J Cell Sci 119, 4332–4341 Haugsten EM, Sorensen V, Brech A, Olsnes S & Wesche J (2005) Different intracellular trafficking of FGF1 endocytosed by the four homologous FGF receptors J Cell Sci 118, 3869–3881 Ling H, Boodhoo A, Hazes B, Cummings MD, Armstrong GD, Brunton JL & Read RJ (1998) Structure of Shiga toxin in the Golgi 64 65 66 67 68 the Shiga-like toxin I B-pentamer complexed with an analogue of its receptor Gb3 Biochemistry 37, 1777– 1788 Hanashima T, Miyake M, Yahiro K, Iwamaru Y, Ando A, Morinaga N & Noda M (2008) Effect of Gb3 in lipid rafts in resistance to Shiga-like toxin of mutant Vero cells Microb Pathog 45, 124–133 Keusch JJ, Manzella SM, Nyame KA, Cummings RD & Baenziger JU (2000) Cloning of Gb3 synthase, the key enzyme in globo-series glycosphingolipid synthesis, predicts a family of alpha 1,4-glycosyltransferases conserved in plants, insects, and mammals J Biol Chem 275, 25315–25321 LaPointe P, Wei X & Gariepy J (2005) A role for the protease-sensitive loop region of Shiga-like toxin in the retrotranslocation of its A1 domain from the endoplasmic reticulum lumen J Biol Chem 280, 23310– 23318 Amessou M, Popoff V, Yelamos B, Saint-Pol A & Johannes L (2006) Measuring retrograde transport to the trans-Golgi network Curr Protoc Cell Biol Chapter 15, Unit 15, 10 Kuge O, Dascher C, Orci L, Rowe T, Amherdt M, Plutner H, Ravazzola M, Tanigawa G, Rothman JE & Balch WE (1994) Sar1 promotes vesicle budding from the endoplasmic reticulum but not Golgi compartments J Cell Biol 125, 51–65 Supporting information The following supplementary material is available: Fig S1 Fractionation of BSC-1 organelles on an 8–25% Optiprep gradient Fig S2 A 20 °C temperature block in HeLa cells This supplementary material can be found in the online version of this article Please note: Wiley-Blackwell is not responsible for the content or functionality of any supplementary materials supplied by the authors Any queries (other than missing material) should be directed to the corresponding author for the article FEBS Journal 276 (2009) 1581–1595 Journal compilation ª 2009 FEBS No claim to original US government works 1595 ... the inability of the cell to transport toxin out of the endosomes and into the Golgi (provided that the toxin would then not be able to exit the Golgi) Penetration of the endosomal membrane by... traffic in BSC-1 cells We used this time-course as a basis for our further experiments Passage through the Golgi is required for StxB to reach the ER in cytoplasts We wished to test directly if passage. .. pathway into the Golgi The slow passage of the toxin through the Golgi also argues in favor of this possibility The response of the pathogen to this sequestration appears to have been to develop