PRENYLATED PROTEINS AND LYMPHOCYTE-PROLIFERATION - INHIBITION BY D-LIMONENE AND RELATED MONOTERPENES

The aim of the present study was to explore the role of post-translati onal isoprenoid modification of cellular proteins in the proliferation of human lymphocytes. We here report that treatment of phytohemagglut inin-stimulated peripheral blood mononuclear cells with monoterpenes i ncluding d-limonene, perillic acid and perillyl alcohol (0.5-5 mM) whi ch selectively inhibit the isoprenylation of 21-26-kDa proteins result ed in a dose-dependent inhibition of DNA synthesis. Cell cycle analysi s revealed that perillic acid arrested cells in G(1) and prevented cel ls from entering S phase in a manner similar to that induced by the sp ecific 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor, compactin. However, unlike compactin, the perillic acid-induced effects on lympho cyte proliferation were not prevented by addition of mevalonate. We al so examined the incorporation of [H-3]mevalonate into proteins in rest ing and phytohemagglutinin-stimulated lymphocytes during the first 30h of culture. While in unstimulated lymphocytes radioactivity was predo minantly incorporated into a cluster of 21-26-kDa proteins, mitogenic stimulation was associated with a striking increase in [H-3]mevalonate incorporation into a protein (approximate to 68 kDa) with migration c haracteristics similar to that of nuclear lamin B. Treatment of phytoh emagglutinin-stimulated lymphocytes with 5 mM d-limonene, 2.5 mM peril lic acid or 1.25 mM perillyl alcohol strongly suppressed [H-3]mevalona te-labeling of proteins to a degree that correlated with the level of DNA synthesis inhibition. These findings suggest that those mevalonate -derived products required for lymphocyte proliferation may include on e or more isoprenylated proteins and that the isoprenylation of these proteins is required for cell cycle progression.