THE TYROSINE PHOSPHORYLATION OF A P72(SYK)-LIKE PROTEIN IN ACTIVATED MURINE RESIDENT PERITONEAL-MACROPHAGES

As a marker of macrophage activation, IL-1 alpha was measured after st imulation of murine resident peritoneal macrophages (RPM) with endotox in-associated protein (EP). Significant IL-1 alpha was produced by EP- stimulated RPM from both C3H/OuJ and C3H/HeJ mouse strains. This EP-me diated IL-1 alpha production was blocked by tyrosine kinase inhibitors including genistein and tyrphostin, suggesting the involvement of a p rotein tyrosine kinase in the activation of RPM by EP. Immunoblot anal ysis using antiphosphotyrosine antibody showed that EP induces the tyr osine phosphorylation of a 71 kD protein (p71). The p71 and the spleen tyrosine kinase p72(syk) found in other cell types share common featu res including: similar molecular weight, PKC independent tyrosine phos phorylation, and inhibition of phosphorylation by piceatannol. Further more, immunoblot analysis using anti-p72(syk) antibody detected the p7 2(syk) kinase in EP-activated RPM. These results suggest that the acti vation of RPM involves an early tyrosine phosphorylation of p72(syk) o r a p72(syk)-1ike protein.