ADENOSINE INHIBITS DNA-SYNTHESIS STIMULATED WITH TSH, INSULIN, AND PHORBOL 12-MYRISTATE 13-ACETATE IN RAT-THYROID FRTL-5 CELLS

Adenosine has been shown to modulate cell proliferation in FRTL-5 thyr oid cells, although the mechanisms by which this interaction occurs is still unclear. In the present study we investigated the effects of ad enosine on the H-3-thymidine incorporation, cell cycle kinetics, and e xpression of the transcription factor c-Fos in cells stimulated via th ree different mitogenic pathways, i.e., by thyroid stimulating hormone (TSH) [adenosine 3',5'-cyclic monophosphate(cAMP)], insulin (tyrosine kinase), or phorbol 12-myristate 13-acetate (protein kinase C). Addit ion of adenosine to cells grown in medium containing hormones and seru m did not inhibit the incorporation of H-3-thymidine. If adenosine was added to hormone-deprived cells together with any of the tested mitog ens, the stimulation of the H-3-thymidine incorporation was inhibited in a dose-dependent manner. The inhibition was significantly lower whe n the cells were preincubated with TSH or insulin for 48 h. Flow cytom etric studies showed that adenosine evoked an inhibition of the cells in the G(0)/G(1) phase. Submaximal doses of adenosine (10 nM-10 mu M) were able to induce c-Fos expression in FRTL-5 cells. However, the mit ogen-induced expression of c-Fos was not reduced by maximal dose of ad enosine (100 mu M). The effect of adenosine on DNA synthesis was not d ependent on pertussis toxin-sensitive C-proteins. In addition, adenosi ne A(1)- or A(2)-receptor antagonists did not block the effect of aden osine. The effect of adenosine was abolished by treatment of the cells with adenosine deaminase, suggesting that the observed effect was not mediated by a metabolite of adenosine. The results suggest that adeno sine is an effective blocker of mitogen-evoked DNA synthesis of FRTL-5 cells, provided that adenosine is administered simultaneously with th e mitogen. (C) 1997 Wiley-Liss, Inc.