Alteration of DNA Synthesis and p53 Level by Modulators of Adenylate Cyclase System and Other Second Messenger Systems in Human Oral Keratinocytes

Abstract

To study the role of adenylate cyclase system and other mediators of signal transduction pathway in the cell cycle arrest which provides enough time for the cells to repair damaged DNA, we examined the cellular response of primarily cultured human oral keratinocytes (HOKs) to UV irradiation, UV irradiation reduced replicative DNA synthesis of HOKs in a dose-drpendent manner without significant changes in viability. Dibutyryl cAMP(5 uM) and forskotin (5 uM) partly inhibited the reduction in replicative DNA failed to inhibit the reduction in replicative DNA synthesis at 12th hour after irradiation. At 24th hour after irradiation, none of the agents inhibited the suppression of DNA synthesis. The reduction in DNA synthesis was accompanied by marked p53 induction, which was completely blocked by dibutyryl cAMP (5 uM) forskolin (5 uM), IBMX (5 uM) and dibutyryl cGMP (5 uM). Treatment of TPA (5 uM), staurosporin (10 uM) and dexamethasone (1 uM) reduced DNA synthesis in HOKs ana prompted death of the cells. Those drugs, however. did not induce p53 indicating that different mechanism from that for UV irradiation may be involved in the reduction of replicative DNA synthesis. Increased reparative DNA synthesis induced by UV irradiation was suppressed by forskolin. Our results suggest that cAMP may be involved in DNA damage-induced cell cycle arrest and DNA repair, and cAMP and cGMP may be associated with blockade of p53 induction.