Dominant negative farnesyltransferase alpha-subunit inhibits insulin mitogenic effects

Farnesylation of p21Ras is required for translocation to the plasma membran e and subsequent activation by growth factors. Previously we demonstrated t hat insulin stimulates the phosphorylation of farnesyltransferase (FTase) a nd its activity, whereby the amount of farnesylated p21Ras anchored at the plasma membrane is increased. Herein we report that substitution of alanine for two serine residues (S60A)(S62A) of the alpha -subunit of FTase create s a dominant negative (DN) mutant. VSMC expressing the FTase alpha -subunit (S60A)(S62A) clone showed a 30% decreased basal FTase activity concurrent with a 15% decrease in the amount of farnesylated p21Ras compared ;to contr ols, Expression of alpha -subunit (S60A,S62A) blunted FTase phosphorylation and activity in the presence of hyperinsulinemia, and inhibited insulin-st imulated increases in farnesylated p21Ras. Insulin-stimulated VSMC expressi ng the FTase alpha -subunit (S60A,S62A) showed decreased (i) phosphorylatio n of FTase, (ii) FTase activity, (iii) amounts of farnesylated p21Ras, (iv) DNA synthesis, and (v) migration, Thus, down-regulation of FTase activity appears to mitigate the potentially detrimental mitogenic effects of hyperi nsulinemia on VSMC. (C) 2001 Academic Press.