Evidence for post-translational incorporation of a product of mevalonic acid into Swiss 3T3 cell proteins.

Previous studies have identified several cellular requirements for mevalonic acid that appear unrelated to cholesterol, dolichol, or ubiquinone. To search for other products of mevalonic acid that might account for these requirements we cultured Swiss 3T3 cells in the presence of mevinolin, an inhibitor of mevalonic acid biosynthesis, then labeled the cells with exogenous radioactive mevalonic acid. Upon analyzing the radioactive material formed, we found that 40-50% of it was not extractable into lipid solvents, and that most of the lipid-insoluble material behaved like protein when treated with sodium dodecyl sulfate:chloroform:phenol, RNase, or proteinase K. Further analysis by electrophoresis revealed that radioactivity was associated with a few specific proteins that had apparent molecular weights of 13,000-58,000. Control experiments indicated that authentic radioactive (R)-mevalonic acid was the active precursor. Other lines of evidence suggested that mevalonate was first converted to an isoprenoid compound, then covalently incorporated into proteins by way of a cycloheximide-insensitive mechanism. These results suggest that Swiss 3T3 cells possess novel metabolic products of mevalonic acid metabolism that are formed by post-translational incorporation of isoprenoids into specific cell proteins.