Effect of adenosine 3':5'-cyclic monophosphate and inhibition of protein kinase A on heat sensitivity in H35 hepatoma cells.

Abstract

To investigate the role of the cyclic adenosine 3':5'-monophosphate (AMP) signal transductions pathway in heat-induced cell death and the development of thermotolerance. Reuber H35 rat hepatoma cells were heated after preincubation with various compounds known to modulate the cyclic AMP signal transduction pathway. Cell survival was determined by colony-forming ability. Preincubation of H35 cells with forskolin, a stimulator of adenylate cyclase, in combination with IBMX (3-isobutyl-1-methylxanthine), an inhibitor of cyclic AMP phosphodiesterase, results in thermosensitization. Similar results are obtained with various cyclic AMP analogs. Maximum thermosensitization occurs with 0.5 mM dibutyryl cyclic AMP (DBcAMP) after a preincubation period of 5 h and heating in the presence of the drug. The same relative degree of thermosensitization is found with 8-Cl-cAMP, but at a 10-fold lower concentration. Thermosensitization by DBcAMP is prevented by H89, a specific inhibitor of cyclic AMP-dependent protein kinase (PKA). Without additional cyclic AMP-inducing factors, H89 induces thermoprotection. None of the drug treatments are cytotoxic at 37 degrees C. DBcAMP does not affect the development of heat-induced thermotolerance but it reduces its expression to an extent similarly found in the observed thermosensitization in nonthermotolerant cells. The results strongly indicate that the cyclic AMP signal transduction pathway is involved in the process of heat-induced cell death. DBcAMP reduces the expression of thermotolerance, but does not affect its induction.