V-K-RAS LEADS TO PREFERENTIAL FARNESYLATION OF P21(RAS) IN FRTL-5 CELLS - MULTIPLE INTERFERENCE WITH THE ISOPRENOID PATHWAY

The isoprenoid pathway in FRTL-5 thyroid cells was found to be deeply altered on transformation with v-K-Pas. A dramatic overall reduction o f protein prenylation was found in v-K-ras-transformed cells in compar ison with the parent FRTL-5 cells, as shown by labeling cells with [H- 3]mevalonic acid. This phenomenon was accompanied bg a relative increa se of p21(ras) farnesylation and by a decrease of the ratio between th e amounts of geranylgeraniol and farnesol bound to prenylated proteins . Analysis of protein prenylation in FRTL-5 cells transformed by a tem perature-sensitive mutant of the v-K-ras oncogene indicated that these variations represent an early and specific marker of active K-ras, Co nversely; FRTL-5 cells transformed with Harvey-ras showed a pattern of [H-3]-mevalonate (MVA)-labeled proteins similar to that of nontransfo rmed cells. The K-ras oncogene activation also resulted in an overall decrease of [H-3]-MVA incorporation into isopentenyl-tRNA together wit h an increase of unprocessed [H-3]-MVA and no alteration in [H-3]-MVA uptake. The effects of v-K-ras on protein prenylation could be mimicke d in FRTL-5 cells by lowering the concentration of exogenous [H-3]-MVA whereas increasing the [H-3]-MVA concentration did not revert the alt erations observed in transformed cells. Accordingly, v-K-rns expressio n was found to: (i) down-regulate mevalonate kinase; (ii) induce farne syl-pyrophosphate synthase expression; and (iii) augment protein farne syltransferase but not protein geranylgeranyl-transferase-I activity. Among these events, mevalonate kinase downregulation appeared to be re lated strictly to differential protein prenylation. This study represe nts an example of how expression of the v-K-ras oncogene, through mult iple interferences with the isoprenoid metabolic pathway, may result i n the preferential farnesylation of the ras oncogene product p21(ras).