Differential Prenylation of Proteins as a Function of Mevalonate Concentration in CHO Cells

The incorporation of [5-3H]mevalonate into prenylated proteins and polyisoprenoid lipids has been determined as a function of mevalonate concentration in Chinese hamster ovary (CHO) cells that are inhibited in mevalonate synthesis. The relative incorporation of mevalonate into the different end products of isoprenoid metabolism was markedly dependent upon the concentration of mevalonate in the medium. The synthesis of cholesterol was dominant at higher concentrations of mevalonate while higher molecular weight isoprenoids were favored at the lower concentrations. The relative incorporation of mevalonate into the different prenylcysteines of prenylated proteins was dependent upon mevalonate concentration with geranylgeranylcysteine being the principal product at higher concentrations. At low levels of mevalonate farnesylcysteine synthesis predominated and geranylcysteine was detected. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from CHO cells that had been radiolabeled at different concentrations of [3H]mevalonate had different patterns on fluorography with relatively few proteins labeled at low concentrations. A study of this effect on the prenylcysteines of a specific protein, Ras, showed considerably less sensitivity to mevalonate concentration than bulk protein. These results indicate that the specific proteins that are prenylated depend upon the availability of the isoprenyl diphosphate substrates.