SIGNAL-TRANSDUCTION MECHANISMS OF HLA-DR-MEDIATED INTERLEUKIN-1-BETA PRODUCTION IN HUMAN MONOCYTES - ROLE OF PROTEIN-KINASE-C AND TYROSINE KINASE ACTIVATION

The signal transduction pathways leading to the expression of IL-1beta in human monocytes via HLA-DR stimulation were investigated. SEB, a s taphylococcal enterotoxin that binds to HLA-DR molecules, induced IL-1 beta expression in human monocytes. Protein synthesis inhibition by cy cloheximide did not inhibit SEB-mediated IL-1beta signal, indicating t hat protein synthesis is not required for the MHC class-II-mediated IL -1beta expression. The effect of PKC, PKA, and tyrosine kinase inhibit ors on HLA-DR-mediated IL-1beta mRNA expression was then determined. H 7, a preferential PKC inhibitor, completely inhibited IL-1beta signal induced by SEB. The role of PKC on HLA-DR-mediated IL-1beta induction was further confirmed by the ability of SEB to activate PKC on monocyt es directly when measured with labeled phorbol ester ([H-3]Pbt2)-bindi ng capacity of whole cells. HA 1004, a preferential PKA inhibitor, and isobutyl-methyl-xanthine (IBMX), which inhibits the degradation of cA MP, had no effect on SEB-induced IL-1beta signal, excluding the role o f cAMP on HLA-DR-mediated IL-1beta expression. Two tyrosine kinase inh ibitors, genistein and dihydroxycinnamate, both inhibited SEB-induced IL-1beta mRNA in monocytes. SEB also induced enhanced tyrosine phospho rylation of several proteins in human monocytes when determined with a ntiphosphotyrosine immunoblotting. Our results demonstrate that both P KC and protein tyrosine kinases are involved in HLA-DR-induced IL-1bet a expression in human monocytes.