α-subunit of farnesyltransferase is phosphorylated in vivo: Effect of protein phosphatase-1 on enzymatic activity

Farnesyltransferase is a heterodimer consisting of a 49 kDa α-subunit and a 46 kDa β-subunit. In this report, we demonstrate that the endogenous heterodimeric farnesyltransferase protein is phosphorylated at the α-subunit in vivo and phosphorylation plays a role in the regulation of farnesyltransferase activity. In vivo ³²P-labeling of PC-12 cells followed by immunoprecipitation with specific anti rat α-subunit IgG showed a labeled α-subunit protein band at an expected molecular mass of 49 kDa. Treatment of PC-12 cells with protein phosphatase inhibitor, Calyculin A, resulted in a decrease in FTase activity, and phophoserine/phosphothreonine-specific protein phosphatase-1 treatment of PC-12 and GM37 cell extracts resulted in 100% and 375% increase in farnesyltransferase activity, respectively, compared to untreated extracts.