Elevation of cyclic AMP levels in HL-60 cells accumulated in G1 or G2 by transmethylation inhibitors

Abstract

Effects of the transmethylation inhibitors 3-deazaadenosine (c3Ado) and 3-deaza-(+/-)-aristeromycin (c3Ari) on cell cycle and cyclic AMP (cAMP) concentrations in human promyelocytic leukemia cells (HL-60) were studied by flow cytometry and radioimmunoassay techniques. Previously described cell cycle accumulations, after incubation with drugs (25 microM) for two cell doublings (36 hr), were localized to G1 and G2 after incubation with c3Ado and c3Ari, respectively. cAMP levels were elevated in cells treated with c3Ado (35%) and c3Ari (92%) for 36 hr. Addition of the phosphodiesterase (PDE) inhibitor theophylline, increased cAMP levels further, while cAMP responsiveness to the beta-adrenergic stimulator isoproterenol was attenuated after c3Ado and c3Ari incubation. Homocysteine thiolactone (Hcy) alone reduced cell growth slightly (5%) and increased cAMP levels (17%). Hcy increased the growth inhibitory effects of c3Ado, while no modulating effect was seen in combination with c3Ari, nor did Hcy counteract the effects on the cell cycle perturbations. The results suggest that c3Ado- and c3Ari-induced cell cycle accumulation is, at least in part, mediated through cAMP elevation, possibly due to PDE inhibition secondary to S-adenosyl-homocysteine hydrolase inhibition and S-adenosyl-homocysteine build-up.