DOLICHOL-LIKE LIPIDS WITH STIMULATORY EFFECT ON DNA-SYNTHESIS - SUBSTRATES FOR PROTEIN DOLICHYLATION

Substantial evidence has suggested that a nonsterol product of mevalon ic acid (MVA) is essential for the initiation of DNA synthesis in mamm alian cells. Several possible isoprenoid candidates have been suggeste d, but the identity of this compound still remains unknown. In this st udy we have isolated and purified MVA products from SV40-transformed h uman fibroblasts and identified fractions with a growth-stimulatory ef fect. The cells were labelled With [C-14]MVA in the presence of inhibi tors of 3-hydroxy-3-methylglutaryl coenzyme A (HMC-CoA) reductase. Aft er lipid extraction, the [C-14]MVA-labelled lipids were subjected to h igh performance liquid chromatography and size-exclusion chromatograph y, and the effect of the fractionated eluate on the DNA synthesis of a rrested MVA-depleted target cells was tested. Thereby we found a fract ion of [C-14]MVA-labelled lipids with a substantial stimulatory effect on DNA synthesis. The chromatographic behavior suggested that the gro wth-stimulating tractions contained dolichol-20. This was confirmed by mass spectrometric analysis. Similar results were obtained when lipid s from hepatocellular carcinoma cells and a sample from breast tumor w ere isolated and analyzed by the same procedure. The mechanisms by whi ch these compounds induce DNA synthesis are unknown. Recent data obtai ned in our laboratory have provided evidence that dolichyl groups are covalently linked to tumor cell proteins, which implicates a new biolo gical function for long-chain polyisoprenoid alcohols (Hjertman et al. [1997] FEES Lett 416:235-238). In this study Lye demonstrate that tum or cells containing dolichol-like growth-stimulatory lipids also conta ined dolichylated proteins. This raises the question whether the growt h-stimulatory dolichol-like lipids serve as substrates for the dolichy lation reaction. (C) 1998 Wiley-Liss, Inc.