Induction of Connective Tissue Growth Factor by Activation of Heptahelical Receptors

Abstract

Expression of connective tissue growth factor (CTGF) was induced in renal mesangial cells by activation of heptahelical receptors by serotonin (5-HT) and lysophosphatidic acid (LPA). Induction of CTGF mRNA was transient with maximal expression after 1 to 2 h, whereas induction ofCTGF by transforming growth factor beta (TGF-β) increased over time. In contrast to the induction of other early response genes (Egr-1 and cyclooxygenase-2), LPA-mediated induction of CTGF was pertussis toxin-insensitive and independent of p42/44 MAP kinase activation. 5-HT-mediatedCTGF induction was due to activation of 5-HT2Areceptors and likewise independent of p42/44 MAP kinase activation. Upon stimulation, enhanced levels of CTGF protein were detected in cellular homogenates, whereas no protein was detectable in cell culture supernatants. Inhibition of proteins of the Rho family by toxin B abrogated basal as well as CTGF expression stimulated by LPA, 5-HT, and TGF-β. Inhibition of the downstream mediator of RhoA, the Rho kinase by Y-27632 partially reduced induction ofCTGF by LPA and TGF-β. Toxin B not only affected gene expression, but disrupted the actin cytoskeleton similarly as observed after treatment with cytochalasin D. Disassembly of actin stress fibers by cytochalasin D partially reduced basal and stimulatedCTGF expression. These data indicate that an intact actin cytoskeleton is critical for the expression of CTGF. Elimination of the input of Rho proteins by toxin B, however, was significantly more effective and their effect on CTGFexpression thus goes beyond disruption of the cytoskeleton. These findings thus establish activation of heptahelical receptors coupled to pertussis toxin-insensitive G proteins as a novel signaling pathway to induce CTGF. Proteins of the Rho family and an intact cytoskeleton were identified as critical determinants ofCTGF expression induced by LPA and 5-HT, and also by TGF-β. Expression of connective tissue growth factor (CTGF) was induced in renal mesangial cells by activation of heptahelical receptors by serotonin (5-HT) and lysophosphatidic acid (LPA). Induction of CTGF mRNA was transient with maximal expression after 1 to 2 h, whereas induction ofCTGF by transforming growth factor beta (TGF-β) increased over time. In contrast to the induction of other early response genes (Egr-1 and cyclooxygenase-2), LPA-mediated induction of CTGF was pertussis toxin-insensitive and independent of p42/44 MAP kinase activation. 5-HT-mediatedCTGF induction was due to activation of 5-HT2Areceptors and likewise independent of p42/44 MAP kinase activation. Upon stimulation, enhanced levels of CTGF protein were detected in cellular homogenates, whereas no protein was detectable in cell culture supernatants. Inhibition of proteins of the Rho family by toxin B abrogated basal as well as CTGF expression stimulated by LPA, 5-HT, and TGF-β. Inhibition of the downstream mediator of RhoA, the Rho kinase by Y-27632 partially reduced induction ofCTGF by LPA and TGF-β. Toxin B not only affected gene expression, but disrupted the actin cytoskeleton similarly as observed after treatment with cytochalasin D. Disassembly of actin stress fibers by cytochalasin D partially reduced basal and stimulatedCTGF expression. These data indicate that an intact actin cytoskeleton is critical for the expression of CTGF. Elimination of the input of Rho proteins by toxin B, however, was significantly more effective and their effect on CTGFexpression thus goes beyond disruption of the cytoskeleton. These findings thus establish activation of heptahelical receptors coupled to pertussis toxin-insensitive G proteins as a novel signaling pathway to induce CTGF. Proteins of the Rho family and an intact cytoskeleton were identified as critical determinants ofCTGF expression induced by LPA and 5-HT, and also by TGF-β. connective tissue growth factor cyclooxygenase lysophosphatidic acid mitogen-activated protein kinase serotonin transforming growth factor β pertussis toxin fetal calf serum 4-morpholinepropanesulfonic acid glyceraldehyde-3-phosphate dehydrogenase Connective tissue growth factor (CTGF)1 belongs to the family of low affinity insulin-like growth factor binding proteins, which consists of Mac25, the nov oncogenes, and cyr61 (1Kim H.S. Nagalla S.R. Oh Y. Wilson E. Roberts Jr., C.T. Rosenfeld R.G. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 12981-12986Crossref PubMed Scopus (284) Google Scholar), and is also classified as a member of the CCN (CYR61, CTGF, and NOV) family (2Bork P. FEBS Lett. 1993; 327: 125-130Crossref PubMed Scopus (552) Google Scholar, 3Lau L.F. Lam S.C. Exp. Cell Res. 1999; 248: 44-57Crossref PubMed Scopus (580) Google Scholar). These proteins share structural homologies and function as growth modulators. CTGF was first purified from conditioned medium of human umbilical vein endothelial cells and shown to account for much of the bioactivity previously attributed to platelet-derived growth factor (4Bradham D.M. Igarashi A. Potter R.L. Grotendorst G.R. J. Cell Biol. 1991; 114: 1285-1294Crossref PubMed Scopus (811) Google Scholar). Recent data obtained with aortic smooth muscle cells and breast cancer cells demonstrated that CTGF may act as a mediator of growth arrest and apoptosis (5Murphy M. Godson C. Cannon S. Kato S. Mackenzie H.S. Martin F. Brady H.R. J. Biol. Chem. 1999; 274: 5830-5834Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar, 6Hishikawa K. Oemar B.S. Tanner F.C. Nakaki T. Fujii T. Luscher T.F. Circulation. 1999; 100: 2108-2112Crossref PubMed Scopus (93) Google Scholar, 7Hishikawa K. Oemar B.S. Tanner A.M. Nakaki T. Luscher T.F. Fujii T. J. Biol. Chem. 1999; 274: 37461-37466Abstract Full Text Full Text PDF PubMed Scopus (148) Google Scholar). In fibroblasts, it is most potently induced by transforming growth factor beta (TGF-β) (8Grotendorst G.R. Okochi H. Hayashi N. Cell Growth Differ. 1996; 7: 469-480PubMed Google Scholar). It stimulates fibroblast cell proliferation and mediates TGF-β-induced anchorage-independent growth (9Kothapalli D. Frazier K.S. Welply A. Segarini P.R. Grotendorst G.R. Cell Growth Differ. 1997; 8: 61-68PubMed Google Scholar). Furthermore, CTGF is a potent stimulator of extracellular matrix synthesis (10Frazier K. Williams S. Kothapalli D. Klapper H. Grotendorst G.R. J. Investig. Dermatol. 1996; 107: 404-411Abstract Full Text PDF PubMed Scopus (673) Google Scholar, 11Duncan M.R. Frazier K.S. Abramson S. Williams S. Klapper H. Huang X. Grotendorst G.R. FASEB J. 1999; 13: 1774-1786Crossref PubMed Scopus (579) Google Scholar). Elevated levels of CTGF are found in fibrotic lesions (e.g.Refs. 12Igarashi A. Nashiro K. Kikuchi K. Sato S. Ihn H. Fujimoto M. Grotendorst G.R. Takehara K. J. Investig. Dermatol. 1996; 106: 729-733Abstract Full Text PDF PubMed Scopus (394) Google Scholar, 13Oemar B.S. Werner A. Garnier J.M. Do D.D. Godoy N. Nauck M. Marz W. Rupp J. Pech M. Luscher T.F. Circulation. 1997; 95: 831-839Crossref PubMed Scopus (290) Google Scholar, 14Dammeier J. Brauchle M. Falk W. Grotendorst G.R. Werner S. Int. J. Biochem. Cell Biol. 1998; 30: 909-922Crossref PubMed Scopus (146) Google Scholar) and suggested to be functionally involved in the development and progression of fibrotic diseases. In the kidney,CTGF mRNA levels were elevated in the majority of biopsies obtained from patients with various types of renal diseases characterized by glomerulosclerosis and tubulointerstitial fibrosis (15Ito Y. Aten J. Bende R.J. Oemar B.S. Rabelink T.J. Weening J.J. Goldschmeding R. Kidney Int. 1998; 53: 853-861Abstract Full Text Full Text PDF PubMed Scopus (515) Google Scholar). In the glomerulus, basal expression of CTGF was detected in epithelial podocytes. In the inflamed glomerulus, CTGF was up-regulated in proliferating epithelial cells and also observed in mesangial cells. Mesangial cells cultured in vitro express basal levels ofCTGF mRNA, which are further increased by TGF-β (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar). In accordance with elevated CTGF expression in diabetic glomerulosclerosis (15Ito Y. Aten J. Bende R.J. Oemar B.S. Rabelink T.J. Weening J.J. Goldschmeding R. Kidney Int. 1998; 53: 853-861Abstract Full Text Full Text PDF PubMed Scopus (515) Google Scholar, 16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar), elevation of glucose levels enhancedCTGF mRNA levels in cultured mesangial cells (5Murphy M. Godson C. Cannon S. Kato S. Mackenzie H.S. Martin F. Brady H.R. J. Biol. Chem. 1999; 274: 5830-5834Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar). Up-regulation of CTGF by glucose was blocked by anti-TGF-β antibodies, confirming CTGF as a downstream target of TGF-β in mesangial cells (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar). Besides TGF-β, CTGF itself was able to induce its own mRNA expression (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar). Mesangial cells are thus target cells of CTGF, as also shown by the induction of extracellular matrix proteins (fibronectin and collagen I and IV) (5Murphy M. Godson C. Cannon S. Kato S. Mackenzie H.S. Martin F. Brady H.R. J. Biol. Chem. 1999; 274: 5830-5834Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar). CTGF belongs to the group of proteins coded for by immediate early response genes, which in general are induced by a variety of different mediators. As an example, cyclooxygenase-2 (Cox-2) is induced by growth factors, cytokines, and low molecular mediators acting via serpentine receptors (17Goppelt-Struebe M. Prostaglandins Leukot. Essent. Fatty Acids. 1995; 52: 213-222Abstract Full Text PDF PubMed Scopus (139) Google Scholar). This prompted us to further investigate the regulation of CTGFmRNA and protein expression in renal mesangial cells. Lysophosphatidic acid (LPA) is generated by cleavage of glycerophospholipids in membranes of stimulated cells. Increased release of LPA is observed in tissue injury, inflammation, and neoplasia (18Goetzl E.J. An S. FASEB J. 1998; 12: 1589-1598Crossref PubMed Scopus (490) Google Scholar). Activated platelets are an abundant source of LPA, and high levels of the lysophospholipid (2–20 μm) are detectable in serum (19Eichholtz T. Jalink K. Fahrenfort I. Moolenaar W.H. Biochem. J. 1993; 291: 677-680Crossref PubMed Scopus (577) Google Scholar). Via binding to seven transmembrane receptors (edg receptors), LPA modulates cell proliferation and differentiation and mediates cellular effects such as chemotaxis, adhesion, contraction, or aggregation, which are related to cytoskeletal rearrangements (18Goetzl E.J. An S. FASEB J. 1998; 12: 1589-1598Crossref PubMed Scopus (490) Google Scholar). Treatment of mesangial cells with LPA led to contraction of the cells (20Inoue C.N. Forster H.G. Epstein M. Circ. Res. 1995; 77: 888-896Crossref PubMed Scopus (46) Google Scholar) and stimulated proliferation (21Gaits F. Salles J.-P. Chap H. Kidney Int. 1997; 51: 1022-1027Abstract Full Text PDF PubMed Scopus (34) Google Scholar,22Inoue C.N. Ko Y.H. Guggino W.B. Forster H.G. Epstein M. Proc. Soc. Exp. Biol. Med. 1997; 216: 370-379Crossref PubMed Scopus (34) Google Scholar). Proliferation was shown to be mediated by the induction of the expression of the immediate early gene Egr-1 (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar). of an early response was induced by LPA in mesangial cells (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar). LPA-mediated induction of the early response genes was pertussis mediated by G proteins of the Furthermore, activation of heptahelical receptors to pertussis toxin-insensitive G proteins also led to the induction of early response genes as by serotonin (5-HT) M. M. J. Biol. Chem. Full Text PDF PubMed Google Scholar, M. M. J. 1998; PubMed Scopus (34) Google Scholar). of p42/44 MAP kinase was a signaling in the kinase was by LPA or 5-HT, and of p42/44 MAP kinase induction of (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar, M. A. M. Biochem. J. 1999; PubMed Scopus Google Scholar). It was thus to that the early response gene CTGF be target of LPA in mesangial cells. on the on the induction of Egr-1 and mesangial cells were to investigate the induction of CTGF by activation of heptahelical receptors and to the signaling for CTGF which not in in cell human TGF-β was obtained from was from LPA, serotonin and cytochalasin D were from toxin was from Cell culture were from was from Toxin B from was by F. and K. Y-27632 was by mesangial cells were as J. Google Scholar) and were in medium with 2 and Mesangial cells were in in medium with cells were in medium for was as previously M. M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). for the was to the of and P. N. Biochem. PubMed Scopus Google Scholar) with was of was by of with 1 as was to membranes by and by for 2 was with with the from was a from the of Biochem. 1993; PubMed Scopus Google Scholar). for CTGF of human was by N. R. J. Am. Soc. Nephrol. 1997; 8: Scholar). was obtained with a were detected by As a for of the the gene or the were or the was with in and by of the was by were for in by the of the or expression. for was to proteins were 1 1 of protein was by a and with an CTGF. was by S. J. Brauchle M. Werner S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). were cultured and on in a stimulation, the cells were with in for and with in for the actin cytoskeleton was with for TGF-β characterized as a potent of CTGF in different cell human mesangial cells (5Murphy M. Godson C. Cannon S. Kato S. Mackenzie H.S. Martin F. Brady H.R. J. Biol. Chem. 1999; 274: 5830-5834Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar). This was mesangial cells were with TGF-β with of CTGFmRNA expression 1 was observed after 2 CTGF mRNA levels were further increased h, of heptahelical serotonin (5-HT) and lysophosphatidic acid (LPA) a but more transient of CTGF by LPA was observed after 1 1 was with was observed with 2 Induction of CTGF by LPA was were and to induce CTGF mRNA induction 1 Increased proliferation of mesangial cells and the induction of the early response genes Egr-1 were observed in the of LPA (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar). LPA were the to in serum (2–20 (19Eichholtz T. Jalink K. Fahrenfort I. Moolenaar W.H. Biochem. J. 1993; 291: 677-680Crossref PubMed Scopus (577) Google were not to effects of the mesangial cells were with LPA TGF-β, the mRNA expression was 1 of LPA, which by not expression, not significantly induction of CTGF. was also observed with TGF-β and not Treatment of mesangial cells with the of protein synthesis the of basal CTGF mRNA mRNA levels were increased with most due to the of the synthesis of In with the of CTGF as an immediate early response gene G.R. Okochi H. Hayashi N. Cell Growth Differ. 1996; 7: 469-480PubMed Google Scholar), LPA-mediated induction of CTGF was not in the of but increased CTGF is a and it was thus to CTGF protein in cell culture supernatants. CTGF protein was detectable the cells were stimulated with LPA or TGF-β for to and the cell culture were more of cellular by with a CTGF J. Brauchle M. Werner S. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar) the induction of a protein of the cells were with LPA or with TGF-β This suggested that CTGF was the or more to the cells as shown for human mesangial cells (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar). was detected which was not This was as for the of the 2 of protein expression to the of mRNA of mesangial cells with LPA and TGF-β in an increased expression of CTGF protein that was 2 of a protein of was detected on most but with also As (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar) expression of mRNA was reduced by of the cells with pertussis toxin whereas induction of early response gene was not affected by to different types of G proteins with for not significantly CTGF induction by LPA or 5-HT, activation of G proteins of the or family in signaling and In with induction of CTGF was by with a of which to proteins of mesangial cells with and LPA not further CTGF expression, expression was increased and T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar). LPA and 5-HT, p42/44 mitogen-activated protein in mesangial cells M. A. M. Biochem. J. 1999; PubMed Scopus Google Scholar, M. S. Biochem. J. 2000; Google Scholar). These were shown to be of and induction of the early response genes Egr-1 and in mesangial cells and T. F. M. Biochem. J. 1998; PubMed Scopus Google and M. M. J. 1998; PubMed Scopus (34) Google Scholar). Treatment of mesangial cells with the led to a of MAP kinase over a of M. S. Biochem. J. 2000; Google Scholar). basal expression of CTGF was reduced by the cells were with or and Induction of LPA or 5-HT, however, was not by was independent of p42/44 MAP kinase activation. Rho proteins characterized as downstream mediators of LPA signaling in cellular A. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google and M. 1999; PubMed Scopus Google Scholar). Treatment of mesangial cells for with various of toxin B, an of RhoA, and led to a of basal and CTGF expression ofCTGF levels by toxin B was and no expression was detectable of the membranes induction ofCTGF was to treatment with toxin B Induction of the early response gene also reduced but to a of in LPA-mediated signaling was shown by the which with Rho a downstream target of M. T. N. M. Moolenaar W.H. F. M. H. S. J. Cell Biol. 1998; PubMed Scopus Google Scholar). reduced LPA-mediated induction of CTGF by It also with TGF-β as toxin B Inhibition of CTGF expression by toxin B was also observed the protein Inhibition of Rho family proteins affected the actin cytoskeleton. Mesangial cells in culture a high of actin in stress fibers Treatment of mesangial cells with toxin B led to in due to a of the actin cytoskeleton. more of the stress fibers was observed the cells were with cytochalasin D. as a for the effect of toxin B on CTGF mRNA expression was by of toxin B and cytochalasin D. of mesangial cells for 1 with toxin B basal and or LPA-mediated induction whereas treatment with cytochalasin partially reduced basal and stimulated CTGF induction effect of cytochalasin D was effective 1 with no further of CTGFexpression the of cytochalasin D was increased from 1 to 2 not of cytochalasin D with CTGF mRNA expression. mesangial cells were with toxin B or cytochalasin D for 1 and further with LPA μm) for 1 or TGF-β for B, to the CTGFexpression in different expression of with LPA after 1 or TGF-β after was to are of (LPA) and (TGF-β) Inhibition was for was low molecular mediators LPA and mesangial cell contraction, and gene induction and thus a in the of and the progression of M. J. N. J. Am. Soc. Nephrol. 1996; 7: Google Scholar, C.N. Epstein M. Forster H.G. Y. K. Sci. 1999; PubMed Google Scholar). Furthermore, related to increased matrix in mesangial cells by induction of TGF-β and enhanced synthesis of collagen M. M. T. Y. T. T. H. S. M. Kidney Int. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). Induction ofCTGF by LPA and in mesangial cells further mediators to the development and progression of renal In mesangial CTGF characterized as a downstream mediator of TGF-β, but was also induced in an by CTGF (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar). data activation of pertussis toxin-insensitive heptahelical receptors by LPA and as novel signaling pathway to Induction was transient with maximal mRNA levels after 1 to 2 were observed were stimulated by factor and M. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), whereas CTGF mRNA levels more due to J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). of heptahelical receptors may thus on the cell or the to different downstream signaling CTGF induction by LPA or was to pertussis of G proteins of the or pertussis toxin-insensitive G proteins, LPA receptors to to proteins J. H. W. D. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google or M. D. A. Moolenaar W.H. Biol. 1999; PubMed Scopus Google and that of G protein also be involved in LPA-mediated induction of CTGF. receptors characterized on mesangial cells to the effects of as well as induction of immediate early response genes M. M. J. 1998; PubMed Scopus (34) Google Scholar, Am. J. 1995; Google Scholar, M. M. 1997; PubMed Scopus Google Scholar). effects were pertussis toxin-insensitive in with of receptors to In contrast to the induction of CTGF, LPA-mediated induction of the transient expression of early response genes Egr-1 was pertussis in mesangial cells (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar) as was induction in N. M. Biol. 1999; PubMed Scopus Google Scholar), of G proteins of the LPA receptors not characterized in mesangial and it is thus not pertussis and effects are mediated by different receptors or by of G shown activation of p42/44 MAP in mesangial cells 2 by LPA, which was to pertussis whereas activation by was pertussis toxin-insensitive M. S. Biochem. J. 2000; Google Scholar). with p42/44 MAP kinase activation led to an of and Egr-1 expression (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar, M. M. J. 1998; PubMed Scopus (34) Google Scholar). of p42/44 MAP not significantly to or CTGF expression, with signaling different from to expression. Induction of a protein related to CTGF, to be to on the M. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). p42/44 MAP kinase may also be involved in to be protein is a downstream signaling of LPA in cell types A. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google and M. 1999; PubMed Scopus Google Scholar). Inhibition of Rho proteins by toxin B in a ofCTGF mRNA expression. This effect was not to LPA-mediated CTGF expression but was also observed the cells were stimulated with or TGF-β. or Egr-1 mRNA expression, induction of CTGF was to toxin B related to the different signaling expression which was on as shown by the effect of was reduced to a with the of CTGF mRNA expression, toxin B disrupted the actin cytoskeleton. stress which are in mesangial cells were first and in a the shown that treatment with toxin B in the not to cell by apoptosis or (23Reiser T. F. M. Biochem. J. 1998; PubMed Scopus Google Scholar). Inhibition of Rho a downstream kinase of RhoA, in actin P. Cell Biol. 1999; 11: PubMed Scopus Google Scholar), also LPA-mediated to a for and stress disruption of the cytoskeleton by cytochalasin D also affected the induction of LPA and more by TGF-β, an of an intact cytoskeleton to from the the of TGF-β signaling is mediated by proteins which are in the and the in E. P. FASEB J. 1999; 13: PubMed Scopus Google Scholar). or activation is by disruption of the actin cytoskeleton not Furthermore, ofCTGF by TGF-β is on a novel response with (8Grotendorst G.R. Okochi H. Hayashi N. Cell Growth Differ. 1996; 7: 469-480PubMed Google Scholar). of the TGF-β signaling which are on an intact actin thus to be disruption of the actin as observed after treatment of the cells with cytochalasin not in a in CTGF mRNA expression to the by toxin B, effects of with Rho protein activation. target proteins of and the other of the the of which mRNA expression is not in different cell but mediators to gene expression not identified M. 1999; PubMed Scopus Google Scholar). CTGF is a but due to its binding to and other matrix it is detectable in the or as protein on the cell N. S. Growth 1998; PubMed Scopus Google M. B.L. Oh Y. Rosenfeld R. 1999; PubMed Google Scholar). In a (16Riser B.L. Denichilo M. Cortes P. Baker C. Grondin J.M. Yee J. Narins R.G. J. Am. Soc. Nephrol. 2000; 11: 25-38Crossref PubMed Scopus (21) Google Scholar) observed increased levels of CTGF protein in mesangial cell after treatment of the cells with in accordance with a high of CTGF. These data are in accordance with CTGF protein was only detectable in cellular In accordance with the in levels of of mesangial cells with TGF-β or LPA also increased CTGF with an molecular of was detected by the the of CTGF protein and after with different types of more be with antibodies, which are more with to the of and CTGF J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). induction of CTGF mRNA and protein in mesangial cells is not to TGF-β as a but is stimulated by activation of heptahelical receptors coupled to pertussis toxin-insensitive G In the activation by serotonin and LPA, but other of heptahelical receptors also to be of CTGF expression thus the of CTGF activation. of the cytoskeletal on CTGF further mesangial cells are cells that their of in the regulation of CTGF and signaling is by and H. C. A. J. P. P. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, P. F. M. R. M. J. J. 1996; PubMed Scopus Google Scholar, J.M. T. E. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar), thus regulation of CTGF expression to of such as or of with the of Rho proteins is by M. D. Circ. Res. 1998; PubMed Scopus Google Scholar), and and are potent of J. and M. RhoA, with cytoskeletal thus to be an of signaling the expression of M. is CTGF was by S. the by N. and toxin B by F. and K.