CAAX Peptidomimetic FTI-244 Decreases Platelet-Derived Growth Factor Receptor Tyrosine Phosphorylation Levels and Inhibits Stimulation of Phosphatidylinositol 3-Kinase but Not Mitogen-Activated Protein Kinase

Cysteine farnesylation of the Ras carboxyl terminal tetrapeptide CAAX motif (where C=cysteine, A=leucine, isoleucine, or valine, and X=methionine or serine) is required for Ras biological activity. In this report, we describe the effects of inhibitors of farnesyltransferase (FTase), the enzyme responsible for this lipid modification, on platelet-derived growth factor (PDGF) signaling in NIH-3T3 cells. In vitro, the CAAX peptidomimetic FTI-232 exhibits potent inhibition of FTase activity (IC₅₀=150 nM) and its carboxyl-methylated counterpart, FTI-244, inhibits Ras processing in vivo. Treatment of NIH-3T3 cells with FTI-244 inhibits PDGF-induced DNA synthesis but not stimulation of mitogen-activated protein kinase (MAPK). However, FTI-244 significantly reduces PDGF-induced tyrosine phosphorylation levels of PDGF receptor (PDGFR) as well as its association with, and activation of, phosphatidylinositol-3-kinase (PI-3-K), a key enzyme in PDGF-induced mitogenesis.