Protein kinase Cδ and protein tyrosine kinase regulate peptidoglycan-induced nuclear factor-κB activation and inducible nitric oxide synthase expression in mouse peritoneal macrophages in vitro

Bacteria and their ubiquitous cell wall component peptidoglycan (PGN) activate the innate immune system of the host and induce the release of inflammatory molecules. Nitric oxide (NO) is a potent molecule involved in the cytotoxic effects mediated by macrophages (MΦ) against microorganisms. This study investigates the signaling pathway involved in inducible nitric oxide synthase (iNOS) expression and nitric oxide release caused by peptidoglycan from Staphylococcus aureus in mouse peritoneal macrophages. Protein tyrosine kinase inhibitor, genestein and PKCδ inhibitor, rottlerin attenuated the PGN-induced expression of iNOS and NO. H-7, a PKC inhibitor did not significantly affected the PGN-induced iNOS expression and NO release. NF-κB inhibitor, curcumin also inhibited PGN-induced NO release. Treatment of MΦ with PGN caused an increase in protein tyrosine kinase activity, expression and activation of PKCδ, IκB phosphorylation and p65 (NF-κB) nuclear translocation. The PGN-induced IκB phosphorylation and p65 nuclear translocation was inhibited in macrophages pretreated with rottlerin and genestein. No paracrine or autocrine effect of TNF-α on PGN-induced iNOS expression and NO release was observed. These observations suggest that PGN induces enhanced expression of iNOS and NO production through activation of protein tyrosine kinases and PKCδ, which in turn initiates NF-κB activation and translocation to nucleus.