cAMP-dependent protein kinase activation inhibits proliferation and enhances apoptotic effect of tumor necrosis factor-α in NCI-H295R adrenocortical cells

Adrenocoiticotropin is the major regulator of adrenocortical development and function. It acts mainly through the cAMP-dependent protein kinase A (PKA) pathway. Our aim was to study the interaction of tumor necrosis factor-alpha (TNFalpha) and the PKA pathway in adrenocortical cell proliferation and apoptosis. The PKA activator Dibutyryl cAMP ((Bu)(2)cAMP) strongly induced differentiation and inhibited proliferation in the human adrenocortical cell line NCI-H295R (H295R). TNFa induced apoptosis of H295R cells. Interestingly, (BU)(2)cAMP treatment clearly enhanced TNIFalpha-induced apoptosis in H295R cells, but not in another human adrenocortical cell line SW-13, the mouse adrenocortical Y-1 cell line or the human HeLa cell line. his synergistic effect was not due to the (Bu)(2)cAMIP-induced glucocorticoid secretion since dexamethasone had no significant effect on the TNFalpha-induced apoptosis. (BU)(2)cAMP treatment rapidly increased the expression of the proto-oncogene c-myc in H295R cells, but not in SW-13, Y-1 or HeLa cells. In transient c-myc transfection assay, c-myc expression associated with decreased expression of the proliferation marker Ki-67 in H295R cells. In conclusion, cAMP-dependent protein kinase activation reduced proliferation and augmented TNFalpha-induced apoptosis in adrenocortical H295R cells, and these effects were associated with increased c-myc expression.