SYNERGISTIC STIMULATION OF INTERLEUKIN-6 RELEASE AND GENE-EXPRESSION BY PHORBOL ESTERS AND INTERLEUKIN-1-BETA IN RAT CORTICAL ASTROCYTES - ROLE OF PROTEIN-KINASE-C ACTIVATION AND BLOCKADE

The involvement of protein kinase C and its interaction with interleuk in 1 beta in the control of interleukin 6 release by cortical astrocyt es was studied. The blockade of protein kinase C catalytic domain, by staurosporine, as well as the desensitization of protein kinase C by s hort-term phorbol 12-myristate 13-acetate pretreatment, increased the basal release of interleukin 6 by rat cortical astrocytes, whereas cal phostin C, an antagonist of phorbol ester binding on protein kinase C regulatory domain, did not affect the basal release of the cytokine. T he activation of protein kinase C by phorbol le-myristate 13-acetate e nhanced concentration- and time-dependently interleukin 6 release. Thi s stimulatory action of phorbol 12-myristate 13-acetate was significan tly reduced by staurosporine, by calphostin C, and by the desensitizat ion of protein kinase C, Interleukin 1 beta increased interleukin 6 re lease in a concentration-related manner. Protein kinase C inhibition, by staurosporine or desensitization, potentiated severalfold, whereas calphostin C reduced interleukin 1 beta stimulation of interleukin 6 r elease. The treatment of cortical astrocytes with both interleukin 1 b eta (3 ng/ml) and phorbol 12-myristate 13-acetate (10 nM) caused a syn ergistic stimulation of interleukin 6 release and its gene expression, an effect that was not relieved by either 20 nM staurosporine or by c alphostin C but was slightly affected by protein kinase C desensitizat ion. In conclusion, our data show that in rat cortical astrocytes the basal release of interleukin 6 is under a tonic inhibition exerted by a protein kinase C isoform or isoforms sensitive to blockade by stauro sporine and desensitization but insensitive to calphostin C. Interleuk in 1 beta stimulated interleukin 6 secretion via a mechanism that is a lso negatively modulated by a protein kinase C isoform or isoforms sen sitive to staurosporine and desensitization. Finally, we showed that i nterleukin Ip and phorbol 12-myristate 13-acetate synergistically stim ulated interleukin 6 release and its gene expression, operating in a m anner insensitive to protein kinase C blockers and slightly reduced by protein kinase C desensitization.