The inhibition of human mesangial cell proliferation by S-trans, trans-farnesylthiosalicylic acid

Background. Many of the proliferative cytokines implicated in human mesangial cell (HMC) proliferation signal through the superfamily of Ras GTPases. The Ras antagonist, S-trans, trans- farnesylthiosalicylic acid (FTS), was used to investigate the effects of the inhibition of Ras signaling on HMC proliferation. Methods. Ras expression and membrane localization, MAPK, and Akt activation were analyzed by Western blotting. Ras activation was determined with a pull-down assay using the Ras-binding domain of Raf. HMC growth curves were assessed using the MTS assay of viable cell number, while DNA synthesis was measured with BrdU incorporation. Hoechst 33342 staining was used to determine apoptosis. Results. FTS reduced the membrane localization of Ras in both serum and platelet-derived growth factor (PDGF). FTS (7.5-20 μmol/L) potently inhibited PDGF-induced HMC proliferation but had no effect on serum-induced proliferation. FTS (10-20 μmol/L) inhibited both Ras and phospho-MAPK activation by serum and PDGF. Furthermore, FTS (10-20 μmol/L) increased HMC apoptosis in the presence of PDGF but not in serum. Moreover, PDGF-stimulated activation of the survival protein Akt was inhibited by FTS. In contrast, serum-stimulated activation of Akt was unaffected by FTS. Conclusion. FTS (5-20 μmol/L) inhibits PDGF-induced but not serum-induced HMC proliferation. FTS (10-20 μmol/L) also promotes HMC apoptosis in the presence of PDGF but not serum. These effects appear to be mediated by inhibitory effects on Ras-dependent signaling that occur as a result of the dislodgment of Ras from its membrane-anchorage sites by FTS. The selectivity of FTS toward PDGF-driven HMC proliferation suggests that FTS may be a valuable therapeutic in mesangioproliferative renal disease.