Effects of the tumor promoter TPA on the induction of DNA synthesis in normal and RSV‐transformed rat fibroblasts

Publisher Website
Google Scholar
Abstract
Induction of DNA synthesis by the tumor promoter tetradecanoyl phorbol acetate (TPA) was studied in a line of cultured rat fibroblasts (Rat‐1) and their ffRous sarcoma virus‐transformed derivative (Rat‐1(RSV)). Following serum deprivation for 54 h to achieve quiescene, semiconservative DNA replication was measured by incubation of cells in BrdUrd and FdUrd after serum stimulation in the presence or absence of TPA. Optimal concentrations of TPA (0.1–0.5 μg/ ml) in serum‐free medium induced a small increase (10–15%) in the amount of DNA made over a 30‐h period in both Rat‐1 and Rat‐1 (RSV) cells. When Rat‐1 cells were stimulated by a 4‐h serum pulse, 30% of the DNA was replicated by 30 h. If the serum pulse was follwed by TPA addition, 702% DNA replication wass observed. If the serum pulse was preceded by TPA addition, the onset of DNA synthesis waas delayed by several hous, but stimulation of DNA synthesis occurred. In contrast, the Rat‐1 (RSV) cells did not show an increase in DNA synthesis induced by TPA in similar protocols, but the serum‐induced onset on DNA synthesis was delayed by several hours in the presence of TPA. Therefore, TPA acts as a co‐inducer of DNA synthesis in the Rat‐1 but not in the Rat‐(RSV) cells. The parent alcohol, phorbol, was inactive in Rat‐1 cells, but delayed the onset of DNA synthesis in the Rat(RSV) cells. We conclude that the co‐inducing and delaying activities of TPA on DNA synthesis appear to be distinct and to act at different points in the G1 phase of the cell cycle.