SYNERGISM BETWEEN PROTEIN-KINASE-C AND CAMP-DEPENDENT PATHWAYS IN THE EXPRESSION OF THE INTERLEUKIN-1-BETA GENE IS MEDIATED VIA THE ACTIVATOR-PROTEIN-1 (AP-1) ENHANCER ACTIVITY

In many different cell types treatment with phorbol esters (e.g. 4beta-phorbol 12-myristate 13-acetate, PMA) leads to the activation of protein-kinase C (PKC) and subsequently to the activation of the activator-protein-1(AP-1)-responsive gene expression. We have previously reported that a structural analog of cAMP (dibutyryl cAMP, Bt2cAMP) or agents elevating the endogenous cAMP levels strongly enhanced the PMA-induced interleukin-1beta(IL-1beta)-gene expression in human myeloid leukemia cells (THP-1, HL-60). We have now examined the role of AP-1 in the regulation of the IL-1beta gene expression by PKC and cAMP in THP-1 cells. AP-1 is a complex composed of products of the jun and fos gene families. Our studies show that Bt2cAMP enhances the PMA-induced c-fos and jun-B expression, but inhibits c-jun expression. Electrophoretic mobility-shift assay revealed that Bt2cAMP also increased the PMA-induced AP-1 DNA-binding activity. The functional role of the increased AP-1 DNA-binding activity was studied by transfecting THP-1 cells with reporter constructs containing AP-1 sites [Col-TREx5/TK-CAT and IL-1beta-X-CAT, which contains the putative 12-O-tetradecanoyl-phorbol-13-acetate(TPA)-responsive element of the IL-1beta gene]. Transient transfection assay demonstrated that Bt2cAMP similarily increased the PMA-induced transcription from both of these reporter constructs. Taken together, these results suggest that cAMP increases the PMA-induced AP-1 activity which then leads to increased IL-1beta expression.