Cell cycle arrest by prostaglandin A 1 at the G 1 /S phase interface with up‐regulation of oncogenes in S‐49 cyc − cells

Abstract Our previous studies have implied that prostaglandins inhibit cell growth independent of cAMP. Recent reports, however, have suggested that prostaglandin arrest of the cell cycle may be mediated through protein kinase A. In this report, in order to eliminate the role of c‐AMP in prostaglandin mediated cell cycle arrest, we use the‐49 lymphoma variant (cyc − ) cells that lack adenylate cyclase activity. We demonstrate that dimethyl prostaglandin A 1 (dmPGA 1 ) inhibits DNA synthesis and cell growth in cyc − cells. DNA synthesis is inhibited 42% by dmPGA 1 (50 μM) despite the fact that this cell line lacks cellular components needed for cAMP generation. The ability to decrease DNA synthesis depends upon the specific prostaglandin structure with the most effective form possessing the α,β unsaturated ketone ring. Dimethyl PGA 1 is most effective in inhibiting DNA synthesis in cyc − cells, with prostaglandins PGE 1 and PGB 1 being less potent inhibitors of DNA synthesis. DmPGE 2 caused a significant stimulation of DNA synthesis. S‐49 cyc ‐ variant cells exposed to (30–50 μm) dmPGA 1 , arrested in the G 1 phase of the cell cycle within 24 h. This growth arrest was reversed when the prostaglandin was removed from the cultured cells; growth resumed within hours showing that this treatment is not toxic. The S‐49 cyc − cells were chosen not only for their lack of adenylate cyclase activity, but also because their cell cycle has been extensively studied and time requirements for G 1 , S, G 2 , and M phases are known. Within hours after prostaglandin removal the cells resume active DNA synthesis, and cell number doubles within 15 h suggesting rapid entry into S‐phase DNA synthesis from the G 1 cell cycle block. The S‐49 cyc − cells are known to have a G 1 /S boundary through M phase transition time of 14.8 h, making the location of the prostaglandin cell cycle arrest at or very near the G 1 /S interface. The oncogenes, c ‐ fos and c ‐ myc which are normally expressed during G 1 in proliferating cells have a 2–3 fold enhanced expression in prostaglandin G 1 arrested cells. These data using the S‐49 variants demonstrate that dmPGA 1 inhibits DNA synthesis and arrests the cell cycle independent of cAMP‐mediated effects. The prostaglandin arrested cells maintain the gene expression of a G 1 synchronous cell which suggests a unique molecular mechanism for prostaglandin action in arresting cell growth. These properties indicate that this compound may be an effective tool to study molecular mechanisms of regulation of the cell cycle.