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Relationship between mevalonate and mitogenesis in human fibroblasts stimulated with platelet-derived growth factor
Abstract:
Relationships between mevalonate and DNA synthesis were explored in quiescent human fibroblasts stimulated with human platelet-derived growth factor (PDGF). Studies of others have indicated that mevalonate, or a product of mevalonate other than cholesterol, is essential for DNA replication. The present studies were designed to determine whether there was a critical time in the cell cycle when mevalonate was necessary for later DNA synthesis to occur. Compactin and mevinolin, inhibitors of hydroxymethylglutaryl CoA reductase, were employed to block both the synthesis of mevalonate and of DNA. Compactin inhibited the sharp peak of DNA synthesis which occurs in cells 24 h after PDGF addition in a concentration-dependent manner. This suppression of DNA synthesis was not prevented by low density lipoprotein but was fully reversed by mevalonate. Compactin inhibited DNA synthesis when the inhibitor was present during the time interval 10-20 h after PDGF addition. Its presence only in the interval before 10 h or after 20 h had no effect. Conversely, mevalonate could fully overcome the compactin block in DNA synthesis when present during the period of from 10-20 h after PDGF addition. Mevalonate present only before 10 h or after 20 h had no effect. When mevalonate was added to mevinolin-blocked cells for the interval 10-15 h after PDGF, the mevinolin block of DNA synthesis was 68% overcome; in contrast, only 20% of the reversal of the mevinolin block was seen when mevalonate was added from 15-20 h. Addition of mevalonate for only the 2-h interval of from 10-12 h after PDGF overcame the mevinolin block of DNA synthesis (assayed at 24 h) by 50%. The results show that there is a critical time period, several h before S phase, when PDGF-stimulated cells require mevalonate in order for DNA synthesis to proceed at 24 h. This critical period comprised the interval of approximately 10-20 h after PDGF addition and especially the early part of this interval.