LIPOPOLYSACCHARIDE-INDUCED CYTOKINE PRODUCTION IN HUMAN MONOCYTES - ROLE OF TYROSINE PHOSPHORYLATION IN TRANSMEMBRANE SIGNAL-TRANSDUCTION

The signal transduction events that follow the binding of lipopolysacc haride (LPS) to the macrophage cell surface are not well defined. Is t he current studies LPS was found to induce alterations in phosphorylat ion of monocyte proteins on tyrosine. Herbimycin A and genistein, inhi bitors of tyrosine kinases, markedly attenuated LPS-induced tumor necr osis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) protein and mRN A production. Reciprocally, the tyrosine phosphatase inhibitor sodium orthovanadate enhanced LPS-induced production of TNF-alpha. LPS induce d a concentration-dependent increase in tyrosine phosphorylation of se veral proteins, which paralleled and preceded the onset of LPS-induced TNF-alpha production. LPS stimulation had different but reproducible effects on three members of the src family of tyrosine kinases. Both H ck and Lyn kinase activity increased before the onset of TNF-alpha pro duction. consistent with their participation in the observed LPS-induc ed tyrosine phosphoprotein accumulation. In contrast, Yes kinase activ ity was not affected. These observations were made at concentrations o f LPS that required serum rich in LPS-binding protein and the monocyte surface antigen CD14 for TNF-alpha production. These data indicate th at tyrosine kinases and phosphatases are involved in the signal transd uction cascade by which LPS induces production of TNF-alpha and IL-6 b y human monocytes, and suggest that Lyn and Hck are candidate particip ants in this process.