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      Effect of Inhibition of Farnesylation and Geranylgeranylation on Renal Fibrogenesis in vitro

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          Background: The Ras and Rho family of GTPases serve as essential molecular switches in the downstream signalling of many cytokines involved in the regulation of renal fibroblast activity. Prenylation is a post-translational process critical to the membrane localization and function of these GTPases. We studied the effects of a farnesyltransferase inhibitor BMS-191563 and geranylgeranyltransferase inhibitor GGTI-298 on renal fibrogenesis in vitro. Methods: Functional studies examined the effects of BMS-191563 and GGTI-298 on rat renal fibroblast kinetics, collagen synthesis and collagen gel contraction. Pro-collagen α1(I) mRNA expression was measured by Northern analysis and CTGF expression by Western blotting. Results: Fibroblast proliferation was significantly reduced by both agents. Exposure of fibroblasts to BMS-191563 resulted in a significant reduction in total collagen production and pro-collagen α1(I) mRNA expression, an effect also observed but to a lesser degree with GGTI-298. Both agents significantly reduced CTGF protein expression. Fibroblast-mediated collagen I lattice contraction was decreased at 48 h by GGTI-298, an effect not observed with BMS-191563. Consistent with this finding, marked actin filament disassembly was evident by phalloidin staining of fibroblasts exposed to GGTI-298. Conclusion: BMS-191563 and GGTI-298 exhibit different effects on renal fibroblast function reflecting their predominant roles in inhibiting prenylation of Ras or Rho proteins respectively. Further studies are warranted to establish their potential therapeutic application in the treatment of progressive renal disease.

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          Most cited references 27

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          Signaling from Rho to the actin cytoskeleton through protein kinases ROCK and LIM-kinase.

          The actin cytoskeleton undergoes extensive remodeling during cell morphogenesis and motility. The small guanosine triphosphatase Rho regulates such remodeling, but the underlying mechanisms of this regulation remain unclear. Cofilin exhibits actin-depolymerizing activity that is inhibited as a result of its phosphorylation by LIM-kinase. Cofilin was phosphorylated in N1E-115 neuroblastoma cells during lysophosphatidic acid-induced, Rho-mediated neurite retraction. This phosphorylation was sensitive to Y-27632, a specific inhibitor of the Rho-associated kinase ROCK. ROCK, which is a downstream effector of Rho, did not phosphorylate cofilin directly but phosphorylated LIM-kinase, which in turn was activated to phosphorylate cofilin. Overexpression of LIM-kinase in HeLa cells induced the formation of actin stress fibers in a Y-27632-sensitive manner. These results indicate that phosphorylation of LIM-kinase by ROCK and consequently increased phosphorylation of cofilin by LIM-kinase contribute to Rho-induced reorganization of the actin cytoskeleton.
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            Proteins regulating Ras and its relatives.

            GTPases of the Ras superfamily regulate many aspects of cell growth, differentiation and action. Their functions depend on their ability to alternate between inactive and active forms, and on their cellular localization. Numerous proteins affecting the GTPase activity, nucleotide exchange rates and membrane localization of Ras superfamily members have now been identified. Many of these proteins are much larger and more complex than their targets, containing multiple domains capable of interacting with an intricate network of cellular enzymes and structures.
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              All ras proteins are polyisoprenylated but only some are palmitoylated.

              The C-terminal CAAX motif of the yeast mating factors is modified by proteolysis to remove the three terminal amino acids (-AAX) leaving a C-terminal cysteine residue that is polyisoprenylated and carboxyl-methylated. Here we show that all ras proteins are polyisoprenylated on their C-terminal cysteine (Cys186). Mutational analysis shows palmitoylation does not take place on Cys186 as previously thought but on cysteine residues contained in the hypervariable domain of some ras proteins. The major expressed form of c-K-ras (exon 4B) does not have a cysteine residue immediately upstream of Cys186 and is not palmitoylated. Polyisoprenylated but nonpalmitoylated H-ras proteins are biologically active and associate weakly with cell membranes. Palmitoylation increases the avidity of this binding and enhances their transforming activity. Polyisoprenylation is essential for biological activity as inhibiting the biosynthesis of polyisoprenoids abolishes membrane association of p21ras.

                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                January 2006
                22 September 2005
                : 102
                : 1
                : e19-e29
                aDepartment of Nephrology, Royal Melbourne Hospital, bDepartment of Medicine, Melbourne University, Melbourne, Australia
                88403 Nephron Exp Nephrol 2006;102:e19–e29
                © 2006 S. Karger AG, Basel

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                Page count
                Figures: 7, References: 37, Pages: 1
                Self URI (application/pdf): https://www.karger.com/Article/Pdf/88403
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