Geranylgeraniol Promotes Entry of UT-2 Cells into the Cell Cycle in the Absence of Mevalonate

Abstract

Although UT-2 cells, a mutant clone of Chinese hamster ovary cells, have been shown to require mevalonate for growth due to a deficiency in 3-hydroxy-3-methylglutaryl-CoA reductase, the precise mevalonate-derived product(s) essential for proliferation has not been identified. These studies show that UT-2 cells proliferate in the presence of free geranylgeraniol (GG-OH), as well as mevalonate. Cell growth was optimal when the culture medium was supplemented with 5–10 μMGG-OH. Under these growth conditions [3H]GG-OH is actively incorporated into UT-2 proteins. Prominent [3H]geranylgeranylated polypeptides in the size range (19–27 kDa) of the small GTP-binding proteins are observed by SDS–PAGE. Analysis of the butanol-soluble products released from the metabolically labeled proteins by digestion with Pronase E reveals that the proteins contain [3H]geranylgeranylated cysteine residues. Even though [3H]farnesol is also incorporated into cysteinyl residues of a different set of UT-2 proteins, farnesol added at 10 μMdid not satisfy the mevalonate requirement for cell growth. These results show that UT-2 cells divide in the presence of exogenously supplied GG-OH, providing evidence that one or more geranylgeranylated proteins are essential for entry of UT-2 cells, and probably other mammalian cells, into the cell cycle.