Cell-cycle-related changes of 3':5'-cyclic GMP levels in Novikoff hepatoma cells.

Abstract

Intracellular and extracellular levels of cyclic[c]GMP and cAMP were studied in synchronized Novikoff rat hepatoma cells. Intracellular levels of cGMP increased spontaneously from 2-fold (without Colcemid) to 10-fold (with Colcemid), in proportion to the number of cells in mitosis. As cells entered mitosis, cellular cAMP declined simultaneously with the rise in cGMP. These reciprocal changes in cyclic nucleotide levels were reversed as cells passed out of metaphase and through anaphase. Maximum cAMP and minimum cGMP concentrations occurred during G-1. Less marked reciprocal fluctuations in both cyclic nucleotides were also found in S phase and early G-2, where the ratio of cAMP to cGMP concentrations fell and then increased. These changes in cyclic nucleotide ratios were closely correlated with major cell cycle transitions at the boundaries between G-1/S phase, S-phase/G2, G-2/prophase and metaphase/anaphase. Most, but not all, of the extracellular cyclic nucleotides were extruded when cells traversed mitosis. Colcemid or vinblastine completely prevented the appearance of extracellular cAMP but augmented the appearance of extracellular cGMP in parallel with the accumulation of mitotic cells. These results reflected changes in intracellular cyclic nucleotides and indicated that increased intracellular turnover of cGMP and cAMP occurred before and after metaphase, respectively. Elevated cGMP levels during mitosis and S phase are consistent with potential modulatory roles for this cyclic nucleotide in proliferation.