Báo cáo khoa học: Mechanical regulation of the Cyr61/CCN1 and CTGF/CCN2 proteins Implications in mechanical stress-associated pathologies pptx

REVIEW ARTICLE Mechanical regulation of the Cyr61/CCN1 and CTGF/CCN2 proteins Implications in mechanical stress-associated pathologies Brahim Chaqour 1 and Margarete Goppelt-Struebe 2 1 Department of Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, NY, USA 2 Department of Nephrology and Hypertension, University Erlangen-Nuremberg, Germany Introduction Basic physiological processes ranging from blood cir- culation and the micturition reflex to the sense of touch and cell movement are primarily initiated by forces rather than molecules acting on cell surface receptors and initiating cascades of biochemical reac- tions. There is increasing evidence that mechanical strain plays an important role in maintaining normal tissue architecture by influencing cell function and behavior. Under extremely or even moderately strained conditions (i.e., hypertension, obstruction), the cellular Keywords actin cytoskeleton; bladder obstruction; fibrosis; hypertrophy; mechanical overload; mechanotransduction; RhoA signaling; shear stress; smooth muscle cells Correspondence B. Chaqour, Department of Anatomy and Cell Biology, State University of New York Medical Center, 450 Clarkson Avenue, Box 5, Brooklyn, NY 11203, USA Fax: +1 718 0270 3732 Tel: +1 718 270 8285 E-mail: bchaqour@downstate.edu M. Goppelt-Struebe, Department of Nephrology and Hypertension, University Erlangen-Nuremberg, Loschgestrasse 8, 91054 Erlangen, Germany Fax: +49 9131 8539202 Tel: +49 9131 8539201 E-mail: Goppelt-Struebe@rzmail. uni-erlangen.de (Received 10 April 2006, revised 1 June 2006, accepted 6 June 2006) doi:10.1111/j.1742-4658.2006.05360.x Cells in various anatomical locations are constantly exposed to mechanical forces from shear, tensile and compressional forces. These forces are signifi- cantly exaggerated in a number of pathological conditions arising from various etiologies e.g., hypertension, obstruction and hemodynamic over- load. Increasingly persuasive evidence suggests that altered mechanical signals induce local production of soluble factors that interfere with the physiologic properties of tissues and compromise normal functioning of organ systems. Two immediate early gene-encoded members of the family of the Cyr61/CTGF/Nov proteins referred to as cysteine-rich protein 61 (Cyr61 ⁄ CCN1) and connective tissue growth factor (CTGF ⁄ CCN2), are highly expressed in several mechanical stress-related pathologies, which result from either increased externally applied or internally generated forces by the actin cytoskeleton. Both Cyr61 and CTGF are structurally related but functionally distinct multimodular proteins that are expressed in many organs and tissues only during specific developmental or pathological events. In vitro assessment of their biological activities revealed that Cyr61 expression induces a genetic reprogramming of angiogenic, adhesive and structural proteins while CTGF promotes distinctively extracellular matrix accumulation (i.e., type I collagen) which is the principal hallmark of fibro- tic diseases. At the molecular level, expression of the Cyr61 and CTGF genes is regulated by alteration of cytoskeletal actin dynamics orchestrated by various components of the signaling machinery, i.e., small Rho GTPas- es, mitogen-activated protein kinases, and actin binding proteins. This review discusses the mechanical regulation of the Cyr61 and CTGF in var- ious tissues and cell culture models with a special attention to the cytoskel- etally based mechanisms involved in such regulation. Abbreviations CTGF, connective tissue growth factor; Cyr61, cysteine-rich protein 61; MAP, mitogen-activated protein; SRF, serum response factor; SSRE, shear stress-responsive elements; VEGF, vascular endothelial growth factor; CCN, Cyr61/CTGF/Nov. FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3639 components of organ systems, particularly fibroblasts, endothelial and smooth muscle cells, become subjected to mechanical inputs beyond a normally acceptable range. This may lead to an inappropriate response of the cells to altered types of mechanical signals. The transfer of such an excessive strain results in the production of various growth factors, cytokines, and hormones, ultimately leading to hypertrophic, hyper- proliferative and ⁄ or fibrotic responses. For instance, mechanical stress imposed on the vascular wall by the intraluminal blood pressure is critical for regulating its growth and phenotypic differentiation as shown by ex and in vivo studies [1]. Similarly, urethral obstruction induced experimentally results in altered pattern of stretch within the bladder wall, which triggers hyper- trophic and fibrotic responses [2]. Consistent with these in vivo observations, in vitro studies have shown that mechanical forces applied to and⁄ or generated by the cells results in profound alterations of the histo- morphometry, phenotype and function of the cells [3–7]. The onset of this process is characterized by the activation of a cascade of signaling events coupled to progressive and perhaps, interdependent changes of gene expression. The cysteine rich protein 61 (Cyr61) and connective tissue growth factor (CTGF) belong to the family of Cyr61/CTGF/Nov (CCN) proteins, structurally related secreted matricellular proteins with functions in adhe- sion, migration, proliferation and extracellular matrix synthesis [8,9]. While being minimally expressed in normally functioning quiescent adult tissues, the Cyr61 and CTGF genes are strongly up-regulated in mechan- ically challenged organ systems from various etiologies including hypertension, hemodynamic overload, meta- bolic injury and obstruction. These observations led to the hypothesis that mechanical factors typified by shear stress, tension, stretch and hydrostatic pressure might be primary inducers of the Cyr61 and CTGF genes in these pathological conditions [10]. Evidence in the literature indicates that the CTGF and Cyr61 genes are rapidly induced in cultured cells in response to physical and chemical stimuli, and that the early expression of these genes is the precursor to long-term modification in the cell’s phenotypical and synthetic features [8,11]. In most cases, Cyr61 and CTGF are coinduced upon exposure of the cells to various hormones, growth factors, inflammatory mole- cules and apoptotic agents. In particular, coinduction of Cyr61 and CTGF occurs upon stimulation of connective tissue type cells with transforming growth factor-b1 (TGF-b1), vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), angiotensin II, prostaglandins, bioactive lipids, thrombin, factor IX, estrogens and apoptotic agents [2,12–15]. The Cyr61 and CTGF genes are also coinduced by mechanical stretch, but a higher strain level is required for induc- tion of CTGF than Cyr61 suggesting that under mechanically strained conditions their genes may not be coordinately regulated [16,17]. This notion is sup- ported by the observation that CTGF gene induction is delayed compared to that of Cyr61 in the bladder wall experiencing mechanical overload through urethral obstruction [2]. Differential pattern of expression of these genes underlies their distinctively nonredundant functions despite their relatively high structural homol- ogy (40% at the amino acid level). Correspondingly, Cyr61- and CTGF-deficient mice show different phenotypes: loss of Cyr61 expression leads to early embryonic lethality due to placental insufficiency and compromised vessel integrity, while lack of the CTGF expression affects primarily the skeletal development as a result of impaired chondrocyte proliferation and extracellular matrix production and turnover [18,19]. In this review we describe in vivo and in vitro evi- dence relating CTGF and Cyr61 to mechanical stress and discuss the molecular mechanisms of mechano- transduction leading to the induction of these multi- functional proteins. The readers are referred to other reviews describing in detail the structural and biologi- cal activities of these proteins [8,9,11]. Mechanical modulation of CTGF and Cyr61 gene expression in vitro and in vivo Mechanical regulation in bone and cartilage Cartilage and bone provide ideal tissues for the study of the mechanical regulation and function of Cyr61 and CTGF, because these tissues experience a wide range of strains during normal use, due to both their own cytoskeletally generated tension and external load- ing. Additionally, endochondral ossification is regula- ted by many factors, including mechanical stimuli, which can suppress or accelerate chondrocyte matur- ation. The role of CTGF in bone was investigated by the group of Takigawa who provided evidence that CTGF is a prohypertrophic chondrocyte-specific gene product, implicated in proliferation and differentiation of chondrocytes, and in skeletal growth and mode- ling ⁄ remodeling [20]. Mechanical strain is also implica- ted in cartilage biology as either cyclic tensile strains or shear promote cartilage growth and ossification [21]. In an in vitro study, Wong et al. compared the effects of tensile strain and cyclic hydrostatic pressure on CTGF expression in primary chondrocytes [22]. Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B. Chaqour and M. Goppelt-Struebe 3640 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS Their data indicated that tensile strain induced CTGF, whereas hydrostatic pressure was without effect, which is in contrast to the up-regulation of CTGF in mesangial cells exposed to hydostatic pressure [23]. Meanwhile, continuous application of mechanical sti- mulation was also performed in vivo in experimental tooth movement, a model for mechanical-dependent bone growth [24]. CTGF mRNA expression was increased in osteocytes at both the compressed and the stretched side of the teeth, indicative of complex signa- ling pathways in both types of stress, i.e., tension and compression. With regard to Cyr61 expression, there is evidence showing that Cyr61 is down-regulated during differen- tiation of mesenchymal stem cells into chondrocytes or osteoblasts, but it is up-regulated during fracture heal- ing, suggesting a role for Cyr61 in chondrogenesis and bone formation [25–27]. In this case, it has been postu- lated that Cyr61 contributes to bone healing through its angiogenic potential. However, in-depth analyses of the mechanical regulation and functional significance of Cyr61 expression in cartilage and bone remain to be performed given the important role of Cyr61 in skel- etal development [28]. Tensile forces in skin disorders: role of myofibroblasts During wound healing, skin fibroblasts at the edge of the wound differentiate into myofibroblasts known for their contractile capability and their capacity to prolif- erate and migrate generating strong contractile forces that permit wound tissue edge closing. Interestingly, increased levels of CTGF and Cyr61 were found in fibroblasts in closing wounds [29,30]. In addition, the specialized cases of keloids, which apparently develop in regions of the body that are subjected to relatively higher mechanical strain than others, are lesions highly enriched in CTGF [31,32]. The scar that persists is itself a tissue under increased mechanical strain and contains abnormally high levels of CTGF. Thus, keloids repre- sent another example of situation in which the mechan- ical regulation of Cyr61 and CTGF is of relevance. TGF-b which is a major profibrotic and fibrogenic molecule, is one of the potent inducers of CTGF gene expression in wound healing and in various pathophys- iological situations. In scleroderma, the initial transac- tivation of CTGF is mediated through TGF-b specific smad signaling pathway, whereas the maintenance of CTGF expression is independent of TGF- b signaling [33,34]. However, up-regulation of the CTGF gene is neither always preceded nor systematically accompan- ied by a concomitant increase of TGF-b expression. In particular, CTGF expression is increased in patients with radiation enteritis with established fibrosis with- out a concomitant up-regulation of TGF-b [35]. These observations indicate that even though TGF-b is the major regulator of CTGF, additional factors must be considered to understand the physiological and patho- physiological relevance of this protein in the skin. Three-dimentional collagen-1 matrices are a com- mon model system to investigate the influence of mechanical stress on the cell biology of fibroblasts [36]. In this model system, increased mechanical stress was shown to up-regulate the CTGF gene while the release of mechanical stress led to a rapid down-regulation of CTGF expression [37,38]. Similarly, CTGF was down- regulated when renal fibroblasts were cultured on top of soft collagen matrices allowing a relaxed phenotype compared to cells cultured on rigid surfaces [39]. The flexible adaptation of CTGF synthesis to differences in mechanical stress argues in favor of an important role of CTGF in the cell’s response to both externally imposed and internally generated mechanical stress. Moreover, TGF-b-mediated fibroblast differentiation was enhanced when mechanical tension was applied to cells [40]. TGF-b-mediated differentiation and subse- quent matrix contraction were dependent on CTGF expression, but it was not promoted by CTGF alone [41]. Fibroblast differentiation may thus be an example of an effective cooperation between soluble mediators and environmental cues. Modulation of CTGF and Cyr61 expression by hemodynamic forces Altered hemodynamic forces are primarily responsible for the initiation of early atherosclerotic lesions, which are located preferentially in specific regions of the arterial wall subjected to nonuniform blood flow [42,43]. CTGF and Cyr61 are strongly expressed in endothelial cells of atherosclerotic lesions although a definite role for CTGF in the pathogenesis of athero- sclerotic lesions has not yet been established [44–47]. In vitro studies showed that CTGF and Cyr61 belong to the group of genes which are strongly up-regulated in endothelial cells exposed to nonuniform shear stress [48]. Conversely, constant shear stress reduced CTGF and Cyr61 mRNA expression in primary human umbi- lical vein endothelial cells (HUVEC) [49,50]. These observations are consistent with the notion that physiological shear stress protects the lining endothe- lium against fibrotic and atherosclerotic diseases which are predominantly initiated in areas of turbulent flow. However, other studies reported conflicting data. In particular, Eskin et al. have shown CTGF mRNA B. Chaqour and M. Goppelt-Struebe Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3641 expression remained unaltered when laminar flow was applied for 24 h in cultured HUVEC or bovine endothelial cells, while our own data showed a down- regulation of CTGF protein in HUVEC (Cicha and Goppelt-Struebe, unpublished results and [51]). A microarray analysis showed that CTGF mRNA was up-regulated by turbulent as well as laminar flow, which is in contrast to the in vivo situation, where CTGF is not expressed in normal vessels exposed to uniform laminar shear stress [52]. Utilization of differ- ent types of cells and apparatus, and various shear stress regimens may account for the discrepancies among data from various laboratories. Investigations of the biological effects of mechanical forces have focused originally on endothelial cells, as the layer of endothelial cells lining blood vessels pro- tects the smooth muscle from the direct shearing effects of the flowing blood. However, the pulsing blood clearly stretches the entire vascular wall including the underlying smooth muscle layers. Using an animal model of pulmonary hypertension, Lee et al. have shown that CTGF gene expression was up-regulated in vascular smooth muscle cells of arteries and arterioles [53]. Studies with cultured smooth muscle cells from various tissue beds showed that Cyr61 is also strongly but transiently up-regulated upon the application of up to 7.5% cyclic biaxial strain to cultured monolayer smooth muscle cells while the expression of CTGF was unaffected at this strain level [16]. The minimal strain required to trigger CTGF up-regulation was 10% [17]. Strain-mediated up-regulation of Cyr61 in bladder smooth muscles cells regulates the expression of several mechano-sensitive genes including VEGF, a-actin and a v integrin subunit genes [54]. Cyr61 is also one of the earliest genes whose expression is turned on in smooth muscle-rich tissues (e.g., aorta and bladder) with the onset of, and throughout the time period of, hyperten- sion or bladder outlet obstruction [2,55]. Mechanical regulation of the CTGF gene in kidney disorders Altered hemodynamics have an impact on end organs such as the kidney, and result in significant alterations of its filtering units, the glomeruli. CTGF expression has been extensively studied in renal diseases [56–58]. Hypertension which often precipitates the development of diabetic nephropathy in hyperglycemic individuals was associated with increased cardiac and renal levels of CTGF [59]. High glucose and TGF-b were identi- fied as major inducers of CTGF under these condi- tions. However, it is noteworthy that the synthesis of renal glomerular proteins is also modulated by mesan- gial cell stretch. In particular, systemic arterial hyper- tension and conditions of impaired glomerular pressure autoregulation lead to excessive expansion and repetitive cycles of distension-contraction of the elastic glomeruli [60]. An enhanced glomerular capil- lary pressure in experimental animal models was asso- ciated with an increased synthesis of extracellular matrix proteins and inflammatory mediators [61]. Increased capillary plasma flow rates may add to the up-regulation of CTGF in glomeruli of diabetic rats or patients, although the increased glucose levels are con- sidered to be the major pathophysiological cause of diabetic alterations of gene expression [62,63]. Increased glomerular capillary pressure and wall ten- sion are transmitted to resident glomerular cells. This process was investigated by exposing mesangial cells to cyclic stress in vitro, which transiently up-regulated CTGF [58]. In another study, sustained up-regulation of CTGF was attributed to increased hydrostatic pres- sure and was associated with the induction of program cell death of mesangial cells [23]. Thus, both in vivo and in vitro studies stress an important role of mechan- ical strain in the kidney and associated pathologies. However, the molecular details of mechano-transduc- tion in glomerular cells have not been investigated yet. Of particular interest is that the podocytes, forming an epithelial layer enveloping the glomerular capillaries, produce increased amounts of Cyr61 and CTGF in animal models of glomerulonephritis and diabetic nephropathy [64,65]. Whether mechanical factors are the primary inducers of Cyr61 and CTGF under these conditions is unknown. How is mechanical stress translated into Cyr61 and CTGF gene expression? Mechanistically, the transfer of excessive strain results in the activation of multiple signaling cascades, cul- minating in the reprogramming of gene expression and the production of growth factors such as Cyr61 and CTGF. Understanding the mechanisms whereby mechanical forces induce Cyr61 and CTGF gene expression is important so that mechano-transduction- based therapies and ⁄ or pharmacological intervention can be formulated to prevent ⁄ reverse the deleterious effects of excessive strain and mechanical overload. However, the notion of separate and linear pathways linking mechanical stimuli to the expression of a mec- hano-sensitive gene is an oversimplification. Instead, complex and interdependent signaling networks are probably involved. The most important sensors of mechanical stress are integrins linking extracellular matrix proteins to Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B. Chaqour and M. Goppelt-Struebe 3642 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS intracellular signaling. Organization of integrins into focal complexes is dependent on the type of matrix molecule and it is modulated by the physical state of the matrix [66]. Integrins are coupled via adaptor mole- cules, such as integrin linked kinase, to the actin cyto- skeleton and to various signaling molecules including mitogen-activated protein (MAP) kinases and small GTPases [67,68]. The small GTPases of the Rho family are central in mechano-transduction, mediating the formation of focal complexes [69], and also as trans- ducers of signals leading to changes in gene expression and cellular shape and morphology [70]. The impact of altered cell morphology, rearrangement of focal adhe- sion complexes and changes in F-actin structures on CTGF expression was demonstrated when fibroblasts were cultured in 3D collagen gels [38]. There is a clear evidence that the Cyr61 gene is regu- lated through mechano-transduction pathways that appear to converge at the level of cytoskeletal actin dynamics [16]. Transduction mechanisms involving protein kinase C and phosphatidyl inositol 3-kinase activation partly blocked stretch-induced Cyr61 gene expression in smooth muscle cells [71]. Selective inhibi- tion of Rho ⁄ actin signaling pathways altered this stretch effect as well, and a superinduction of the Cyr61 gene was observed upon treatment of the cells with actin polymerization-inducing drugs alone. The Cyr61 gene appears to be particularly sensitive to the physiological state of G-actin because the sole treat- ment of the cells with swinholide, which induces actin dimerization, was sufficient to induce up-regulation in the expression of the Cyr61 gene [71]. In line with these results it was shown in NIH 3T3 fibroblasts that the Cyr61 gene belongs to a group of target genes of serum response factor (SRF), which are dependent on RhoA- actin signaling [72]. Additionally, the promoter region of the Cyr61 gene contains so-called shear stress-respon- sive elements (SSRE) representing the core sequence of NF-jB binding sites found previously in shear stress- responsive genes in endothelial cells [73]. A study by Grote et al . [74] has shown that mechanical stretch of vascular smooth muscle cells leads to enhanced expres- sion of the Cyr61 gene via the mechano-sensitive tran- scription factor early growth response factor-1 (Egr-1), a transcription factor which is up-regulated independ- ently of cytoskeletal actin remodeling [72]. Therefore, additional studies are needed to determine the contri- bution of both stretch-responsive and actin dynamic- sensitive elements within the Cyr61 promoter and their cognate transcription factors, and the relevance of these findings in pathological conditions. While data related to the mechanical regulation of Cyr61 are still limited, more detailed studies focused on the regulation of CTGF. In the network of interact- ing signaling mediators, RhoA GTPase seems to play a major role in maintaining the basal turnover of CTGF mRNA and also in the stimulated expression of CTGF. Interference with RhoA signaling by toxin B or more specifically C3 exoenzyme prevented up-regu- lation of CTGF by lysophosphatidic acid, a known activator of RhoA [75]. Similarly, disruption of micro- tubuli by colchicine, which activates RhoA in a recep- tor-independent way, also activated CTGF in a toxinB-sensitive manner [76]. Involvement of RhoA in CTGF expression was confirmed by overexpression of constitutively active RhoA or dominant negative RhoA ([39] and S. Muehlich & M. Goppelt-Struebe, unpublished results). RhoA signaling interacts with other signaling pathways involved in CTGF expres- sion. Inhibition of RhoA-associated kinase inhibited TGF-b-mediated up-regulation of CTGF, which is primarily mediated via the Smad 3⁄ 4 signaling path- way [77,78]. Similarly, angiotensin-mediated induction of CTGF requires signaling through MAP kinases and RhoA GTPase. Angiotensin II-induced activation of MAP kinase and adhesion-dependent activation of RhoA signaling converged at the level of CTGF mRNA expression renal fibroblasts [78]. Furthermore, RhoA can be an important target for pharmacologi- cal interference with CTGF expression. By inhibition of the post-translational modification of RhoA, statins (hydroxymethyl glutaryl CoA reductase inhibi- tors) inhibit CTGF induction in vitro and in vivo [79– 82]. The Rho-kinase inhibitors, Y27632 or fasudil, which inhibit CTGF expression in vitro, may be another way to interfere with overexpression of CTGF in vivo. Activation of RhoA increases the formation of F-actin stress fibers via downstream mediators, among them RhoA-associated kinase (ROCK) [83]. Given the inhibition of CTGF expression by inhibitors of ROCK, it was obvious to investigate the direct effect of changes in actin organization on CTGF expression as a potential molecular mechanism of mechano-sens- ing. Changes in the ratio of G- and F-actin were not only observed in experimental in vitro settings, but also detectable in vivo. In diabetic glomeruli, which are exposed to increased mechanical strain, actin was found to be disorganized and the structure of the fibrillar F-actin was disrupted [84]. Recruitment of G-actin into F-actin stress fibers by jasplakinolide increased CTGF expression, whereas disruption of F-actin by latrunculin B reduced CTGF expression [76]. Unexpectedly, cytochalasin D, which also rapidly disintegrated actin stress fibers, transi- ently increased CTGF [85]. Both cytochalasin D and B. Chaqour and M. Goppelt-Struebe Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3643 latrunculin B enhance the cellular content of G-actin [86], however, the availability of G-actin as modula- tor of gene expression seems to be different upon treatment with both agents: cytochalasin D was shown to sequester and thus reduce the effective level of G-actin [74,87]. These data indicate that rather than being regulated by F-actin stress fibers, the expression of CTGF seems to be sensitive to changes in the level of G-actin. In line with this hypothesis, overexpression of mutant G-actin that is no longer able to polymerize into F-actin [88] significantly reduced the expression of CTGF in endothelial cells (unpublished result). There is increasing evidence that G-actin plays a role as regulator of cellular traffic and also gene transcription [89]. Coactivator proteins such as myocardin-related transcription factors bind to G-actin as well as the transcription factor SRF. These coactivators thus connect proteins that until recently were considered to belong to functionally unrelated families such as transcription factors and structural cytoskeletal proteins. SRF, by interacting with a response element located about 4 kb upstream of the transcription start site in the CTGF promoter seems to be involved as a link between cytoskeletal rearrangement and CTGF transcription in endothelial cells (Goppelt-Struebe, unpublished result). We have recently studied the molecular mechanisms whereby externally applied mechanical strain or stretch regulates the expression of the CTGF gene. We found that an altered pattern of mechanical stretch in either cultured bladder smooth muscle cells or the bladder wall in vivo as a result of urethral obstruction induces translocation and binding of NF-jB to a highly con- served NF-jB binding site in the proximal promoter region of the CTGF gene [17]. Our data also indicated that nuclear translocation of NF-jB and transactiva- tion of the CTGF promoter can be blocked upon disruption of actin stress fibers by a cell-penetrating peptide containing the N-terminal sequence Ac-EEED of smooth muscle a-actin. The mechanical activation of NF-jB appears as a consistent theme linking mechanical stimuli to activation of various stretch- or shear stress-sensitive genes and is associated with destabilization of IjB, an NF-jB inhibitor. The stabil- ity of IjB in resting cells depends on its anchorage to the actin cytoskeleton, possibly via its ankyrin repeat domain. Interestingly, stretch-dependent activation of the CTGF promoter was also inhibited by the RhoA- associated kinase inhibitor, Y-27632, which has been shown both to alter the actin network and to inhibit NF-jB binding activity by inducing cytosolic stabiliza- tion of IjBa [90]. Therefore, stretch-mediated activa- tion of the CTGF gene promoter is coupled to dynamic rearrangement of the actin cytoskeleton asso- ciated with IjB destabilization in bladder smooth mus- cle cells. Which biological activities do Cyr61 and CTGF manifest in mechanical stress conditions? Mechanical stress experiments in vitro help to under- stand how internally generated and ⁄ or externally imposed forces on the cells lead to changes in gene expression. In these types of experiments, comparisons are made between cells cultured under static conditions and cyclically stretched or shear deformed cells. How- ever, as reported for Cyr61 and CTGF, their expres- sion declined rapidly and even disappeared after a short period of mechanical deformation, when the stretching environment became the cell’s new nor- malcy. The rapid reestablishment of basal expression might be indicative of an adaptive mechanism in which compensatory signaling pathways are activated to allow gene transcription to return to normal levels in the stimulated cells. At these later time points, cells may more accurately represent those in vivo, which normally exist in a mechanically active environment. In pathological conditions, however, such compensa- tory mechanisms do not seem to take place because the up-regulation of Cyr61 and CTGF appeared to be both rapid and long lasting in the affected tissues [2,57]. Identification of all factors that either prevent or allow down-regulation of Cyr61 and CTGF in vivo should provide new clues on how to interfere with their uncontrolled overexpression in pathological con- ditions. However, the expression, even transient, of Cyr61 or CTGF may have long-term implications. Previous studies suggested that Cyr61 can regulate the expres- sion of genes involved in angiogenesis and matrix remodeling [18,29]. In agreement with this, interference with Cyr61 in mechanically stimulated cells markedly reduced mechanical strain-induced VEGF, av integrin and smooth muscle a-actin gene expression but had no effect on type I collagen, fibronectin and myosin heavy chain isoform expression [54]. An intact cytoskeleton is required for Cyr61-dependent regulation of gene expression, indicating that cytoskeleton integrity is required for both Cyr61 expression and activity. There- fore, Cyr61 may well be an integral part of the mechano-transduction process by promoting the expression of mechano-sensors such as integrins and ⁄ or by propagating the mechanical signal to neigh- boring cells via the expression of autocrine and para- crine factors such as VEGF. Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B. Chaqour and M. Goppelt-Struebe 3644 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS CTGF is a protein which exerts its effects character- istically by interaction with other proteins in a syner- gistic or inhibitory manner [91,92]. Furthermore, CTGF itself is able to modulate cytoskeletal structures [93]. Regulation of CTGF by mechanical forces may thus add to the complexity and variability of the regu- lation of cellular communication. Collectively, both the expression and function of the immediate early genes Cyr61 and CTGF cannot be separated from the mechanically dynamic structures inside and outside the cells and tissues. Conclusion Further analysis of Cyr61 and CTGF gene activation by mechanical forces will require obtaining more infor- mation on the mechanical receptors involved in sensing and converting the mechanical signals into chemical ones (Fig. 1). In particular, it is not clear whether there are any specific regulators at the receptor level of signal transmission, or whether targeting of Cyr61 and CTGF is achieved by specific cofactors at the level of cellular signaling molecules or transcription factors. The complex interactions among signaling molecules and the actin cytoskeleton in mechanically challenged cells probably implicate general as well as specific or selective interactions among coactivators and corepres- sors. This needs to be addressed in future studies. Much more detailed studies are also necessary to decipher the various levels of complexity in the regula- tion of the Cyr61 and CTGF genes by mechanical signals in different cell types and in various mechanical stress conditions. In particular, it is critically important to determine (i) whether or not the mechanisms involved in the mechanical regulation of the Cyr61 and CTGF genes are cell type-specific and ⁄ or vary as a function of the type of mechanical stimuli, e.g., ten- sion, compression, shear deformation, etc.; (ii) whether such mechanisms operate in native cells and in the whole tissue in response to an altered pattern of mechanical signals; (iii) the extent to which mechanical signals override or cooperate with chemical signals ori- ginating from growth factors and cytokines; (iiii) the potential feed back or feed forward mechanisms, which either perpetuate the mechanical signals in pathological conditions or allow their quick resolution as demon- strated in the transient expression of both the Cyr61 and CTGF genes. These types of investigations will provide the necessary information to more adequately reverse ⁄ prevent the deleterious effects of Cyr61 and CTGF expression in various mechanical stress-associ- ated pathologies. Acknowledgements This work was supported by grants from the National Institutes of Health and National Institute of Diabetes, digestive and kidney diseases R01-DK060572 and R21- DK068483 (to B.C.) and the Deutsche Forschungsg- emeinschaft SFB423-B3 (to M. G S.). References 1 Hill MA, Davis MJ, Meininger GA, Potocnik SJ & Murphy TV (2006) Arteriolar myogenic signalling mechanisms: Implications for local vascular function. Clin Hemorheol Microcirc 34, 67–79. 2 Chaqour B, Whitbeck C, Han JS, Macarak E, Horan P, Chichester P & Levin R (2002) Cyr61 and CTGF are molecular markers of bladder wall remodeling after out- let obstruction. Am J Physiol Endocrinol Metab 283, E765–E774. 3 Gunst SJ, Tang DD & Opazo SA (2003) Cytoskeletal remodeling of the airway smooth muscle cell: a mechan- ism for adaptation to mechanical forces in the lung. Respir Physiol Neurobiol 137, 151–168. 4 Janmey PA & Weitz DA (2004) Dealing with mechanics: mechanisms of force transduction in cells. Trends Biochem Sci 29, 364–370. 5 Knoll R, Hoshijima M & Chien K (2003) Cardiac mechanotransduction and implications for heart disease. J Mol Med 81, 750–756. 6 Silver FH, DeVore D & Siperko LM (2003) Role of mechanophysiology in aging of ECM: effects of changes Fig. 1. Schematic model of the mechanical regulation of Cyr61 and CTGF indicating different regulatory levels and open questions (see Conclusions). Mediators, which have been related to mechanical stimulation of Cyr61 or CTGF gene induction, are shown in the mid- dle panel; details are outlined in the text. B. Chaqour and M. Goppelt-Struebe Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3645 in mechanochemical transduction. J Appl Physiol 95, 2134–2141. 7 Ingber DE (2002) Mechanical signaling and the cellu- lar response to extracellular matrix in angiogenesis and cardiovascular physiology. Circ Res 91 , 877– 887. 8 Brigstock DR (2003) The CCN family: a new stimulus package. J Endocrinol 178, 169–175. 9 Takigawa M (2003) CTGF ⁄ Hcs24 as a multifunctional growth factor for fibroblasts, chondrocytes and vascular endothelial cells. Drug News Perspect 16, 11–21. 10 Chaqour B & Goppelt-Struebe M (2005) Regulation of CCN proteins by alterations of the cytoskeleton. In CCN Proteins: a New Family of Cell Growth and Differ- entiation Regulators (Perbal B & Takigawa M, eds), pp. 177–196. Imperial College Press, London. 11 Perbal B (2004) CCN proteins: multifunctional signal- ling regulators. Lancet 363, 62–64. 12 Brigstock DR (2002) Regulation of angiogenesis and endothelial cell function by connective tissue growth factor (CTGF) and cysteine-rich 61 (CYR61). Angiogen- esis 5, 153–165. 13 Kireeva ML, Latinkic BV, Kolesnikova TV, Chen CC, Yang GP, Abler AS & Lau LF (1997) Cyr61 and Fisp12 are both ECM-associated signaling molecules: activities, metabolism, and localization during develop- ment. Exp Cell Res 233, 63–77. 14 Liang Y, Li C, Guzman VM, Evinger AJ III, Protzman CE, Krauss AH & Woodward DF (2003) Comparison of prostaglandin F2alpha, bimatoprost (prostamide), and butaprost (EP2 agonist) on Cyr61 and connective tissue growth factor gene expression. J Biol Chem 278, 27267–27277. 15 Pendurthi UR, Allen KE, Ezban M & Rao VM (2000) Factor VIIa and thrombin induce the expression Cyr61 and connective tissue growth factor, extracellular matrix signaling proteins that could act as possible downstream mediators in factor VIIa tissue factor-induced signal transduction. J Biol Chem 275, 14632–14641. 16 Tamura I, Rosenbloom J, Macarak E & Chaqour B (2001) Regulation of Cyr61 gene expression by mechani- cal stretch through multiple signaling pathways. Am J Physiol Cell Physiol 281, C1524–C1532. 17 Chaqour B, Yang R & Sha Q (2006) Mechanical Stretch Modulates the Promoter Activity of the Profibrotic Fac- tor CCN2 Through Increased Actin Polymerization and NF-Kappa B Activation. J Biol Chem, doi:10.1074/ jbc.M600214200. 18 Mo FE, Muntean AG, Chen CC, Stolz DB, Watkins SC & Lau LF (2002) CYR61 (CCN1) is essential for placental development and vascular integrity. Mol Cell Biol 22, 8709–8720. 19 Ivkovic S, Yoon BS, Popoff SN, Safadi FF, Libuda DE, Stephenson RC, Daluiski A & Lyons KM (2003) Connective tissue growth factor coordinates chondro- genesis and angiogenesis during skeletal development. Development 130, 2779–2791. 20 Takigawa M, Nakanishi T, Kubota S & Nishida T (2003) Role of CTGF ⁄ HCS24 ⁄ ecogenin in skeletal growth control. J Cell Physiol 194, 256–266. 21 Wong M & Carter DR (2003) Articular cartilage func- tional histomorphology and mechanobiology: a research perspective. Bone 33, 1–13. 22 Wong M, Siegrist M & Goodwin K (2003) Cyclic tensile strain and cyclic hydrostatic pressure differentially regu- late expression of hypertrophic markers in primary chondrocytes. Bone 33, 685–693. 23 Hishikawa K, Oemar BS & Nakaki T (2001) Static pres- sure regulates connective tissue growth factor expression in human mesangial cells. J Biol Chem 276, 16797– 16803. 24 Yamashiro T, Fukunaga T, Kobashi N, Kamioka H, Nakanishi T, Takigawa M & Takano-Yamamoto T (2001) Mechanical stimulation induces CTGF expres- sion in rat osteocytes. J Dent Res 80, 461–465. 25 Hadjiargyrou M, Ahrens W & Rubin CT (2000) Tem- poral expression of the chondrogenic and angiogenic growth factor CYR61 during fracture repair. J Bone Miner Res 15, 1014–1023. 26 Lienau J, Schell H, Epari DR, Schutze N, Jakob F, Duda GN & Bail HJ (2005) CYR61 (CCN1) Protein Expression during Fracture Healing in an Ovine Tibial Model and Its Relation to the Mechanical Fixation Sta- bility. J Orthop Res 24, 254–262. 27 Schutze N, Noth U, Schneidereit J, Hendrich C & Jakob F (2005) Differential expression of CCN-family members in primary human bone marrow-derived mesenchymal stem cells during osteogenic, chondrogenic and adipogenic differentiation. Cell Commun Signal 3, doi:10.1186/1478-811X-3-5. 28 O’Brien TP & Lau LF (1992) Expression of the growth factor-inducible immediate early gene cyr61 correlates with chondrogenesis during mouse embryonic develop- ment. Cell Growth Differ 3, 645–654. 29 Chen CC, Mo FE & Lau LF (2001) The angiogenic fac- tor Cyr61 activates a genetic program for wound heal- ing in human skin fibroblasts. J Biol Chem 276, 47329– 47337. 30 Leask A, Denton CP & Abraham DJ (2004) Insights into the molecular mechanism of chronic fibrosis: the role of connective tissue growth factor in scleroderma. J Invest Dermatol 122, 1–6. 31 Igarashi A, Nashiro K, Kikuchi K, Sato S, Ihn H, Fujimoto M, Grotendorst GR & Takehara K (1996) Connective tissue growth factor gene expression in tis- sue sections from localized scleroderma, keloid, and other fibrotic skin disorders. J Invest Dermatol 106, 729–733. 32 Ito Y, Aten J, Bende RJ, Oemar BS, Rabelink TJ, Weening JJ & Goldschmeding R (1998) Expression of Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B. Chaqour and M. Goppelt-Struebe 3646 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS connective tissue growth factor in human renal fibrosis. Kidney Int 53, 853–861. 33 Leask A, Holmes A, Black CM & Abraham DJ (2003) Connective tissue growth factor gene regulation. Requirements for its induction by transforming growth factor-beta 2 in fibroblasts. J Biol Chem 278 , 13008– 13015. 34 Holmes A, Abraham DJ, Chen Y, Denton C, Shi-wen X, Black CM & Leask A (2003) Constitutive connective tissue growth factor expression in scleroderma fibro- blasts is dependent on Sp1. J Biol Chem 278, 41728– 41733. 35 Vozenin-Brotons MC, Milliat F, Sabourin JC, de Gou- ville AC, Francois A, Lasser P, Morice P, Haie-Meder C, Lusinchi A, Antoun S, Bourhis J, Mathe D, Girinsky T & Aigueperse J (2003) Fibrogenic signals in patients with radiation enteritis are associated with increased connective tissue growth factor expression. Int J Radiat Oncol Biol Phys 56, 561–572. 36 Grinnell F (2003) Fibroblast biology in three-dimen- sional collagen matrices. Trends Cell Biol 13, 264–269. 37 Schild C & Trueb B (2004) Three members of the con- nective tissue growth factor family CCN are differen- tially regulated by mechanical stress. Biochim Biophys Acta 1691, 33–40. 38 Schild C & Trueb B (2002) Mechanical stress is required for high-level expression of connective tissue growth factor. Exp Cell Res 274, 83–91. 39 Graness A, Cicha I & Goppelt-Struebe M (2006) Con- tribution of Src-FAK signaling to the induction of con- nective tissue growth factor in renal fibroblasts. Kidney Int 68, 1341–1349. 40 Arora PD, Narani N & McCulloch CA (1999) The compliance of collagen gels regulates transforming growth factor-beta induction of alpha-smooth muscle actin in fibroblasts. Am J Pathol 154, 871–882. 41 Garrett Q, Khaw PT, Blalock TD, Schultz GS, Groten- dorst GR & Daniels JT (2004) Involvement of CTGF in TGF-beta1-stimulation of myofibroblast differentiation and collagen matrix contraction in the presence of mechanical stress. Invest Ophthalmol Vis Sci 45, 1109– 1116. 42 Nerem RM (1992) Vascular fluid mechanics, the arterial wall, and atherosclerosis. J Biomech Eng 114, 274–282. 43 Cunningham KS & Gotlieb AI (2005) The role of shear stress in the pathogenesis of atherosclerosis. Lab Invest 85, 9–23. 44 Oemar BS, Werner A, Garnier JM, Do DD, Godoy N, Nauck M, Marz W, Rupp J, Pech M & Luscher TF (1997) Human connective tissue growth factor is expressed in advanced atherosclerotic lesions. Circula- tion 95, 831–839. 45 Schober JM, Chen N, Grzeszkiewicz TM, Jovanovic I, Emeson EE, Ugarova TP, Ye RD, Lau LF & Lam SC (2002) Identification of integrin alpha(M) beta(2) as an adhesion receptor on peripheral blood monocytes for Cyr61 (CCN1) and connective tissue growth factor (CCN2): immediate-early gene products expressed in atherosclerotic lesions. J Lipid Mediat Cell Signal 99, 4457–4465. 46 Cicha I, Yilmaz A, Klein M, Raithel D, Brigstock DR, Daniel WG, Goppelt-Struebe M & Garlichs CD (2005) Connective tissue growth factor is overexpressed in complicated atherosclerotic plaques and induces mono- nuclear cell chemotaxis in vitro. Arterioscler Thromb Vasc Biol 25, 1008–1013. 47 Panutsopulos D, Arvanitis DL, Tsatsanis C, Papalam- bros E, Sigala F & Spandidos DA (2005) Expression of heregulin in human coronary atherosclerotic lesions. J Vasc Res 42, 463–474. 48 Yoshisue H, Suzuki K, Kawabata A, Ohya T, Zhao H, Sakurada K, Taba Y, Sasaguri T, Sakai N, Yamashita S, Matsuzawa Y & Nojima H (2002) Large scale isola- tion of non-uniform shear stress-responsive genes from cultured human endothelial cells through the prepara- tion of a subtracted cDNA library. Atherosclerosis 162, 323–334. 49 McCormick SM, Eskin SG, McIntire LV, Teng CL, Lu CM, Russell CG & Chittur KK (2001) DNA microar- ray reveals changes in gene expression of shear stressed human umbilical vein endothelial cells. Proc Natl Acad Sci USA 98, 8955–8960. 50 McCormick SM, Frye SR, Eskin SG, Teng CL, Lu CM, Russell CG, Chittur KK & McIntire LV (2003) Microarray analysis of shear stressed endothelial cells. Biorheology 40, 5–11. 51 Eskin SG, Turner NA & McIntire LV (2004) Endothe- lial cell cytochrome P450 1A1 and 1B1: up-regulation by shear stress. Endothelium 11, 1–10. 52 Garcia-Cardena G, Comander J, Anderson KR, Black- man BR & Gimbrone MA Jr (2001) Biomechanical acti- vation of vascular endothelium as a determinant of its functional phenotype. Proc Natl Acad Sci USA 98, 4478–4485. 53 Lee YS, Byun J, Kim JA, Lee JS, Kim KL, Suh YL, Kim JM, Jang HS, Lee JY, Shin IS, Suh W, Jeon ES & Kim DK (2005) Monocrotaline-induced pulmonary hypertension correlates with upregulation of connective tissue growth factor expression in the lung. Exp Mol Med 37, 27–35. 54 Zhou D, Herrick DJ, Rosenbloom J & Chaqour B (2005) Cyr61 mediates the expression of VEGF, alphav- integrin, and alpha-actin genes through cytoskeletally based mechanotransduction mechanisms in bladder smooth muscle cells. J Appl Physiol 98, 2344–2354. 55 Unoki H, Furukawa K, Yonekura H, Ueda Y, Katsuda S, Mori M, Nakagawara K, Mabuchi H & Yamamoto H (2003) Up-regulation of cyr61 in vascular smooth muscle cells of spontaneously hypertensive rats. Lab Invest 83, 973–982. B. Chaqour and M. Goppelt-Struebe Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3647 56 Goldschmeding R, Aten J, Ito Y, Blom I, Rabelink T & Weening JJ (2000) Connective tissue growth factor: just another factor in renal fibrosis? Nephrol Dial Transplant 15, 296–299. 57 Abdel WN & Mason RM (2004) Connective tissue growth factor and renal diseases: some answers, more questions. Curr Opin Nephrol Hypertens 13, 53–58. 58 Riser BL & Cortes P (2001) Connective tissue growth factor and its regulation: a new element in diabetic glo- merulosclerosis. Ren Fail 23, 459–470. 59 Peng H, Carretero OA, Brigstock DR, Oja-Tebbe N & Rhaleb NE (2003) Ac-SDKP reverses cardiac fibrosis in rats with renovascular hypertension. Hypertension 42 , 1164–1170. 60 Cortes P, Riser BL, Yee J & Narins RG (1999) Mechanical strain of glomerular mesangial cells in the pathogenesis of glomerulosclerosis: clinical implications. Nephrol Dial Transplant 14, 1351–1354. 61 Ingram AJ & Scholey JW (2000) Stress-responsive signal transduction mechanisms in glomerular cells. Curr Opin Nephrol Hypertens 9, 49–55. 62 Wahab NA, Yevdokimova N, Weston BS, Roberts T, Li XJ, Brinkman H & Mason RM (2001) Role of con- nective tissue growth factor in the pathogenesis of dia- betic nephropathy. Biochem J 359, 77–87. 63 Zatz R, Meyer TW, Rennke HG & Brenner BM (1985) Predominance of hemodynamic rather than metabolic factors in the pathogenesis of diabetic glomerulopathy. Proc Natl Acad Sci USA 82, 5963–5967. 64 Sawai K, Mori K, Mukoyama M, Sugawara A, Suga- nami T, Koshikawa M, Yahata K, Makino H, Nagae T, Fujinaga Y, Yokoi H, Yoshioka T, Yoshimoto A, Tanaka I & Nakao K (2003) Angiogenic protein Cyr61 is expressed by podocytes in anti-Thy-1 glomerulone- phritis. J Am Soc Nephrol 14, 1154–1163. 65 Roestenberg P, van Nieuwenhoven FA, Joles JA, Tris- chberger C, Martens PP, Oliver N, Aten J, Hoppener JW & Goldschmeding R (2006) Temporal expression profile and distribution pattern indicate a role of con- nective tissue growth factor (CTGF ⁄ CCN-2) in diabetic nephropathy in mice. Am J Physiol Renal Physiol 290, F1344–F1354. 66 Katz BZ, Zamir E, Bershadsky A, Kam Z, Yamada KM & Geiger B (2000) Physical state of the extracellu- lar matrix regulates the structure and molecular compo- sition of cell-matrix adhesions. Mol Biol Cell 11, 1047– 1060. 67 Li C & Xu Q (2000) Mechanical stress-initiated signal transductions in vascular smooth muscle cells. Cell Sig- nal 12, 435–445. 68 Attwell S, Mills J, Troussard A, Wu C & Dedhar S (2003) Integration of cell attachment, cytoskeletal locali- zation, and signaling by integrin-linked kinase (ILK), CH-ILKBP, and the tumor suppressor PTEN. Mol Biol Cell 14, 4813–4825. 69 Balaban NQ, Schwarz US, Riveline D, Goichberg P, Tzur G, Sabanay I, Mahalu D, Safran S, Bershadsky A, Addadi L & Geiger B (2001) Force and focal adhesion assembly: a close relationship studied using elastic micropatterned substrates. Nat Cell Biol 3, 466–472. 70 Ridley AJ (2001) Rho family proteins: coordinating cell responses. Trends Cell Biol 11, 471–477. 71 Han JS, Macarak E, Rosenbloom J, Chung KC & Cha- qour B (2003) Regulation of Cyr61 ⁄ CCN1 gene expres- sion through RhoA GTPase and p38MAPK signaling pathways. Eur J Biochem 270, 3408–3421. 72 Miralles F, Posern G, Zaromytidou A & Treisman R (2003) Actin dynamics control SRF activity by regula- tion of its coactivator MAL. Cell 113, 329–342. 73 Resnick N, Collins T, Atkinson W, Bonthron DT, Dewey CF Jr & Gimbron MA Jr (1993) Platelet-derived growth factor B chain promoter contains a cis-acting fluid shear-stress-responsive element. Proc Natl Acad Sci USA 90, 4591–4595. 74 Grote K, Bavendiek U, Grothusen C, Flach I, Hilfiker- Kleiner D, Drexler H & Schieffer B (2004) Stretch-indu- cible expression of the angiogenic factor CCN1 in vas- cular smooth muscle cells is mediated by Egr-1. J Biol Chem 279, 55675–55681. 75 Hahn A, Heusinger-Ribeiro J, Lanz T, Zenkel S & Goppelt-Struebe M (2000) Induction of connective tis- sue growth factor by activation of heptahelical recep- tors. Modulation by rho proteins and the actin cytoskeleton. J Biol Chem 275, 37429–37435. 76 Ott C, Iwanciw D, Graness A, Giehl K & Goppelt- Struebe M (2003) Modulation of the expression of con- nective tissue growth factor by alterations of the cytos- keleton. J Biol Chem 278, 44305–44311. 77 Goppelt-Struebe M, Hahn A, Iwanciw D, Rehm M & Banas B (2001) Regulation of connective tissue growth factor (ccn2; ctgf) gene expression in human mesangial cells: modulation by HMG CoA reductase inhibitors (statins). Mol Pathol 54, 176–179. 78 Iwanciw D, Rehm M, Porst M & Goppelt-Struebe M (2003) Induction of connective tissue growth factor by angiotensin II: integration of signaling pathways. Arter- ioscler Thromb Vasc Biol 23, 1782–1787. 79 Eberlein M, Heusinger-Ribeiro J & Goppelt-Struebe M (2001) Rho-dependent inhibition of the induction of connective tissue growth factor (CTGF) by HMG CoA reductase inhibitors (statins). Br J Pharmacol 133, 1172– 1180. 80 Muehlich S, Schneider N, Hinkmann F, Garlichs CD & Goppelt-Struebe M (2004) Induction of connective tissue growth factor (CTGF) in human endothelial cells by lysophosphatidic acid, sphingosine- 1-phosphate, and platelets. Atherosclerosis 175, 261– 268. 81 Watts KL & Spiteri MA (2004) Connective Tissue Growth Factor expression and induction by Transform- Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B. Chaqour and M. Goppelt-Struebe 3648 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS [...]... Rocks: multifunctional kinases in cell behaviour Nat Rev Mol Cell Biol 4, 446– 456 Cortes P, Mendez M, Riser BL, Guerin CJ, RodriguezBarbero A, Hassett C & Yee J (2000) F-actin fiber distribution in glomerular cells: structural and functional implications Kidney Int 58, 2452–2461 Goppelt-Struebe M, Heusinger-Ribeiro J & Fischer B (2002) Dual role of cytochalasin D in the regulation of connective tissue... actin in 89 90 91 92 93 control of transcription by serum response factor Mol Biol Cell 13, 4167–4178 Gettemans J, Van Impe K, Delanote V, Hubert T, De Vandekerckhove J & V (2005) Nuclear actin-binding proteins as modulators of gene transcription Traffic 6, 847–857 Bourgier C, Haydont V, Milliat F, Francois A, Holler V, Lasser P, Bourhis J, Mathe D & Vozenin-Brotons MC (2005) Inhibition of Rho kinase... Cipolla MJ, Gokina NI & Osol G (2002) Pressureinduced actin polymerization in vascular smooth muscle as a mechanism underlying myogenic behavior FASEB J 16, 72–76 Sotiropoulos A, Gineitis D, Copeland J & Treisman R (1999) Signal-regulated activation of serum response factor is mediated by changes in actin dynamics Cell 98, 159–169 Posern G, Sotiropoulos A & Treisman R (2002) Mutant actins demonstrate... radiation induced fibrogenic phenotype in intestinal smooth muscle cells through alteration of the cytoskeleton and connective tissue growth factor expression Gut 54, 336–343 Abreu JG, Ketpura NI, Reversade B & De Robertis EM (2002) Connective-tissue growth factor (CTGF) modulates cell signalling by BMP and TGF-beta Nat Cell Biol 4, 599–604 Inoki I, Shiomi T, Hashimoto G, Enomoto H, Nakamura H, Makino K,... Connective tissue growth factor binds vascular endothelial growth factor (VEGF) and inhibits VEGF-induced angiogenesis FASEB J 16, 219–221 Crean JK, Furlong F, Finlay D, Mitchell D, Conway B, Brady HR, Godson C & Martin F (2004) Connective tissue growth factor [CTGF] ⁄ CCN2 stimulates mesangial cell migration through integrated dissolution of focal adhesion complexes and activation of cell polarization FASEB.. .Mechanical regulation of Cyr61 ⁄ CCN1 and CTGF ⁄ CCN2 B Chaqour and M Goppelt-Struebe 82 83 84 85 86 87 88 ing Growth Factor {beta}, is abrogated by Simvastatin via a Rho signalling mechanism Am J Physiol Lung Cell Mol Physiol 287, L1323–L1332 Song Y, Li C & Cai L (2004) Fluvastatin prevents nephropathy likely through suppression of connective tissue growth factor-mediated... ⁄ CCN2 stimulates mesangial cell migration through integrated dissolution of focal adhesion complexes and activation of cell polarization FASEB J 18, 1541–1543 FEBS Journal 273 (2006) 3639–3649 ª 2006 The Authors Journal compilation ª 2006 FEBS 3649 . focused on the regulation of CTGF. In the network of interact- ing signaling mediators, RhoA GTPase seems to play a major role in maintaining the basal turnover of CTGF mRNA and also in the stimulated. results in the activation of multiple signaling cascades, cul- minating in the reprogramming of gene expression and the production of growth factors such as Cyr61 and CTGF. Understanding the mechanisms. protein kinases, and actin binding proteins. This review discusses the mechanical regulation of the Cyr61 and CTGF in var- ious tissues and cell culture models with a special attention to the