Prostaglandins A and J arrest the cell cycle of cultured vascular smooth muscle cells without suppression of c-myc expression

The effects of prostaglandins (PGs) A and J, which are antitumor eicosanoids, on the proliferation of cultured vascular smooth muscle cells were investigated. Serum-stimulated DNA synthesis was potently inhibited by PGA1, PGA2, PGJ2, and δ12-PGJ2 in similar dose-dependent fashions. The effects of PGA1 and PGA2 were reversible when they were removed from the culture media, whereas recoveries were only partial in the cells treated with PGJ2 and δ12-PGJ2. PGs were effective even if they were added immediately before entry into S phase. Inhibition of DNA synthesis was sustained when hydroxyurea, which blocks cell cycle at the G1S border, was added after the removal of PGA2, and vice versa; PGs blocked DNA synthesis when they were added after the removal of hydroxyurea. Levels of c-myc mRNA formed two peaks during the G1 phase, at 1–2 h and at 8–12 h. The PGs did not affect the first elevation, but enhanced the second and sustained it up to 18–24 h, whereas in controls, c-myc mRNA decreased quickly after entry into S phase. The rate of degradation of c-myc mRNA was much smaller in PG-treated cells than in nontreated cells. We conclude, therefore, that PGA and PGJ inhibit a crucial event(s) in the cell cycle occurring at the G1S border, but that this inhibition is not accompanied by the reduction in c-myc gene expression in contrast with some types of tumor cells treated With PGs.