INHIBITION OF TYPE-I AND TYPE-II GERANYLGERANYL-PROTEIN TRANSFERASES BY THE MONOTERPENE PERILLYL ALCOHOL IN NIH3T3 CELLS

The monoterpene perillyl alcohol has anticancer activities that includ e both prevention and treatment of a wide variety of cancers in animal models. In purified enzyme studies, perillyl alcohol inhibited farnes yl-protein transferase and type I geranylgeranyl-protein transferase. However, whether and which of the polyprenyl-protein transferases is i nhibited by perillyl alcohol in vivo is not known. The previously repo rted monoterpene induced inhibition of the incorporation of [C-14]meva lonolactone into proteins in cultured cells could be due to an inhibit ion of one or several enzymes in the mevalonate pathway or to changes in the levels of protein substrates for isoprenylation. In the current study, we first analyzed the levels of individual phosphorylated isop renoid intermediates between mevalonate and geranylgeranyl pyrophospha te in NIH3T3 cells labeled for 4 hr with [C-14]mevalonolactone and fou nd that perillyl alcohol did not inhibit the synthesis of these interm ediates. Next, proteins including Ras, RhoA, and Rab6 were immunopreci pitated from NIH3T3 cells. Perillyl alcohol was found to inhibit the i ncorporation of [C-14]mevalonolactone into RhoA and Rab6 but not Ras p rotein. The cellular levers of these three proteins were constant over the 4-hr treatment period. Finally, the distribution of Ras, Rap1, an d Rab6 proteins between the aqueous and the detergent-enriched phases was measured. Rap1 and Rab6 but not Ras from perillyl alcohol-treated NIH3T3 cells accumulated in the aqueous phase. Thus, we conclude that perillyl alcohol can inhibit the in vivo prenylation of specific prote ins by type I and type II geranylgeranyl-protein transferases but not farnesyl-protein transferase in NIH3T3 cells. (C) 1997 Elsevier Scienc e Inc.