Expression of connective tissue growth factor in human renal fibroblasts: regulatory roles of RhoA and cAMP.
The induction of connective tissue growth factor (CTGF) was investigated in a human renal fibroblast cell line that exhibited many characteristics of primary human renal fibroblasts. Induction of CTGF mRNA was observed after treatment of the cells with transforming growth factor-beta (TGF-beta) or, even more prominently, lysophosphatidic acid (LPA). LPA induced a rapid transient increase in CTGF mRNA expression, with maximal levels being observed after 1 to 2 h. This increase was accompanied by CTGF protein synthesis. Induction of CTGF was insensitive to pertussis toxin and was not dependent on the activation of p42/44 mitogen-activated protein kinases. Inhibition of the proteins of the Rho family with toxin B from Clostridium difficile abrogated basal and LPA-mediated induction of CTGF. Specific targeting of RhoA with C3 exotoxin or of the Rho kinases with the inhibitor Y-27632 similarly prevented induction of CTGF, implicating RhoA as a signaling module downstream of LPA. Inhibition of RhoA depolymerized the actin cytoskeleton, as did treatment with cytochalasin D. Preincubation of the human renal fibroblasts with cytochalasin D prevented induction of CTGF by LPA, indicating a strong contribution of an intact cytoskeleton. Interference with RhoA signaling similarly inhibited the induction of CTGF by TGF-beta. Elevation of intracellular levels of cAMP and thus activation of protein kinase A prevented induction of CTGF expression. The cytoskeletal effects of cAMP, however, were reversed by LPA. These data indicate complex interactions involving LPA-mediated activation of RhoA- and protein kinase A-dependent signaling pathways. The data thus demonstrate the regulatory functions of the small GTPase RhoA and of an intact cytoskeleton in the expression of CTGF after stimulation with LPA or TGF-beta. Analogous signal transduction pathways were previously demonstrated in rat mesangial cells, suggesting a more general role for RhoA in the regulation of CTGF expression.
Heusinger-Ribeiro
Juliane
J
Medical Clinic IV, University of Erlangen-Nuremberg, Erlangen, Germany.
Eberlein
Michael
M
Medical Clinic IV, University of Erlangen-Nuremberg, Erlangen, Germany.
Wahab
Nadia Abdel
NA
Imperial College School of Medicine, Molecular Pathology Section, London, United Kingdom.
Goppelt-Struebe
Margarete
M
Medical Clinic IV, University of Erlangen-Nuremberg, Erlangen, Germany.
D000199:Actins / Q000502:physiology; D055513:Connective Tissue Growth Factor; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003599:Cytoskeleton / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology; D020742:rhoA GTP-Binding Protein / Q000502:physiology*
D000199:Actins; C526317:CCN2 protein, human; C526316:CCN2 protein, rat; D006133:Growth Substances; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020742:rhoA GTP-Binding Protein