calyculin-a and geranylgeranyl-pyrophosphate

We have recently reported that the activation of mitogen-activated protein kinase (MAPK) through specific protein kinase C (PKC) isoforms is required for basic fibroblast growth factor (bFGF)-induced proliferation of coronary smooth muscle cells (cSMC). In this study, we investigated the effects of the 3hydroxy-3-methyl glutaryl coenzyme A (HMG CoA) reductase inhibitor lovastatin on bFGF-induced signal transduction in cSMC. The present study shows that lovastatin inhibits bFGF-stimulated DNA synthesis in cSMC, and that this inhibition is reversed by mevalonate (50 micromol/l) and by geranylgeranyl-pyrophosphate (1-5 micromol/l). Although lovastatin prevented Ras farnesylation the amount of bFGF-stimulated MAPK phosphorylation decreased only partially after lovastatin treatment. In addition, lovastatin pretreatment resulted in a sustained phosphorylation of MAPK. We observed a dose-dependent lovastatin-dependent increase in PKC activity, which could be prevented by mevalonate. This increase was comparable to the one induced by calyculin A (2 nmol/l), an inhibitor of protein phosphatase PP-1 and PP-2A. Lovastatin inhibited the expression of the PP-1 protein, which is involved in bFGF-induced DNA synthesis in cSMC. Thus, our data suggest that, lovastatin possibly affects the dephosphorylation processes of PKC and MAPK by inhibition of PP-1/PP-2A protein phosphatases which are involved in the bFGF-induced mitogenesis in cSMC.

Topics: Animals; Blotting, Western; Cattle; Cells, Cultured; DNA; Dose-Response Relationship, Drug; Enzyme Inhibitors; Fibroblast Growth Factor 2; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Lovastatin; MAP Kinase Signaling System; Marine Toxins; Mevalonic Acid; Muscle, Smooth; Myocardium; Oxazoles; Phosphoprotein Phosphatases; Phosphoric Monoester Hydrolases; Phosphorylation; Polyisoprenyl Phosphates; Protein Isoforms; Protein Kinase C; Protein Prenylation; ras Proteins; Time Factors