C3 production of cultured human epidermal keratinocytes is enhanced by IFN gamma and TNF alpha through different pathways

We investigated the regulation of C3 production by human cultured epidermal keratinocytes by enzyme-linked immunosorbent assay, The results showed that IFN gamma and TNF alpha enhanced the synthesis of C3 by epidermal keratinocytes in a concentration-dependent manner. Moreover, a protein kinase C (PKC) inhibitor blocked C3 production, whereas PMA enhanced it. There was a synergistic effect between IFN gamma and TNF alpha. In experiments to investigate the role of protein tyrosine kinase (PTK) in C3 production, we found that treatment with herbimycin A, a specific inhibitor for the c-Src-related PTK, caused significant enhancement of the C3 production induced by IFN gamma or TNF alpha, suggesting that c-Src-type PTK(s) provides a negative signal to C3 production. Each competitive inhibitor of PTK, genistein or tyrphostin, substantially increased the C3 production by IFN gamma at lower concentrations, although each agent had little effect on TNF alpha-associated production of C3 at the same concentrations. The data show that proinflammatory cytokines IFN gamma and TNF alpha synergistically augment C3 production by epidermal keratinocytes by different pathways.