Limonene and related monoterpenes have been shown to impair the incorporation of mevalonic acid-derived isoprene compounds, that is farnesyl pyrophosphate, into HAS and RAS-related proteins. As farnesylation is critical for RAS's membrane localization and function, the isoprenylation pathways have received attention as potential targets of anti-RAS pharmacologic maneuvers. We have expanded on these prior studies and demonstrate that one of limonene's metabolic derivatives, perillyl alcohol, decreases the levels of antigenic RAS in the human-derived myeloid THP-1 and lymphoid RPMI-8402 cell lines. Both limonene and perillyl alcohol decrease levels of [35S]methionine-labeled RAS proteins in cells that have been pulsed with radiolabeled methionine for 4 h. In contrast, lovastatin, which inhibits hydroxymethylglutaryl coenzyme A reductase and thus depletes cells of farnesyl pyrophosphate, does not diminish levels of total antigenic RAS but rather results in a shift in the RAS protein; levels of farnesylated RAS decrease whereas levels of unmodified/unfarnesylated RAS increase. As limonene and perillyl alcohol do not induce such a shift, we conclude that these monoterpenes decrease farnesylated RAS protein levels by a mechanism that is clearly distinct from that of either depleting cells of farnesyl pyrophosphate or inhibiting the enzyme farnesyl protein transferase that catalyzes the post-translational farnesylation of RAS. Perillyl alcohol decreases antigenic RAS levels but does not decrease levels of another membrane-tethered protein, the α subunit of the heterotrimeric G protein. Furthermore, perillyl alcohol decreases the levels of radiolabeled methionine incorporated into immunoprecipitable RAS to a greater extent than it decreases radiolabeled methionine incorporated into total cellular protein. Thus there is some degree of specificity for the activity of perillyl alcohol to depress RAS levels.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology