Importance of geranylgeranyl pyrophosphate for mesangial cell DNA synthesis

Background. Farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) are isoprenoid products of the intracellular mevalonate pathway used for prenylation of several low molecular weight G proteins, including Ras. It is likely that platelet-derived growth factor (PDGF) stimulation of mesangial cell proliferation requires prenylated, low molecular weight G proteins. The purpose of this study was to investigate the dependence of platelet-derived growth factor-stimulated mesangial cell DNA synthesis and cell membrane Ras incorporation on FPP and GGPP. Methods. Quiescent human mesangial cells were exposed to PDGF (25 ng/ml) to stimulate DNA synthesis. Some cells were also treated with the HMG-CoA reductase inhibitor lovastatin (2.5 to 10.0 μM), which inhibits isoprenoid synthesis, in the presence or absence of exogenous FPP or GGPP. DNA synthesis was assessed by thymidine incorporation, and Western blot analysis was used to measure total cell membrane Ras. Results. Stimulation of mesangial cells with PDGF did not increase total cell membrane Ras. Lovastatin reduced cell membrane Ras, and this was prevented by simultaneous exposure of mesangial cells to exogenous FPP (2.5 to 10.0 μM) or GGPP (1 to 5 μM). Lovastatin also reduced PDGF-stimulated mesangial cell DNA synthesis by 90%, and this was completely prevented by simultaneous exposure of cells to exogenous GGPP (1 μM), but not to FPP. Conclusions. The results of this study suggest that both FPP and GGPP can provide for mesangial cell membrane Ras localization and that PDGF-stimulated mesangial cell DNA synthesis requires the isoprenoid GGPP.