A phosphatidylcholine-specific phospholipase C regulates activation of p42/44 mitogen-activated protein kinases in lipopolysaccharide-stimulated human alveolar macrophages

This study uses human alveolar macrophages to determine whether activation of a phosphatidylcholine (PC)-specific phospholipase C (PC-PLC) is linked t o activation of the p42/44 (ERK) kinases by LPS. LPS-induced ERK kinase act ivation was inhibited by tricyclodecan-9-yl xanthogenate (D609), a relative ly specific inhibitor of PC-PLC. LPS also increased amounts of diacylglycer ol (DAG), and this increase in DAG was inhibited by D609. LPS induction of DAG was, at least in part, derived from PC hydrolysis, Ceramide was also in creased in LPS-treated alveolar macrophages, and this increase in ceramide was inhibited by D609, Addition of exogenous C, ceramide or bacterial-deriv ed sphingomyelinase to alveolar macrophages increased ERK kinase activity. LPS also activated PKC zeta, and this activation was inhibited by D609. LPS -activated PKC zeta phosphorylated MAP kinase kinase, the kinase directly u pstream of the ERK kinases, LPS-induced cytokine production (RNA and protei n) was also inhibited by D609, As an aggregate, these studies support the h ypothesis that one way by which LPS activates the ERK kinases is via activa tion of PC-PLC and that activation of a PC-PLC is an important component of macrophage activation by LPS.