Study of regulatory mechanism of inflammatory response by purinergic signaling

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We investigated whether the purinergic signaling system could be altered with inflammatory condition. Treatment of human umbilical vein endothelial cells(HUVEC) with IFN-γ enhanced ATP-induced increase in intracellular Ca^<2+> concentration. This effect of IFN-γ was resulted from up-regulation of P2X_4 receptor expression and down-regulation of nucleoside triphosphate diphosphohydrolase 1 (NTPDase1). Effects of IFN-γ on the purinergic signaling system in HUVEC were mediated by Jak-STAT pathway and further enhanced synergistically by other inflammatory cytokines, such as IL-1β and TNF-α. Stimulation of quiescent HUVEC by ATP caused a rapid induction of cyclooxyganase(COX) 2 mRNA, protein and enzyme activity. The effect of ATP was mediated by ionotropic receptors, probably P2X_4 receptors through a mechanism involving p38MAP kinase-mediated COX2 mRNA stabilization. The ATP-induced COX2 induction was augmented in IFN-γ-treated HUVEC. Unlike the effects on HUVEC, IFN-γ increased ATP hydrolysis in murine macrophage J774 cells in a time- and concentration-dependent manner, accompanied by marked increase in NTPDase1 mRNA. Up-regulation of NTPDase1 by IFN-γ was inhibited by cycloheximide, Jak inhibitor and orthovanadate, a protein tyrosine phosphatase inhibitor, but enhanced by tyrosine kinase inhibitors (herbimycin A, PP2 and genistein) and p42/44 MAP kinase inhibitors. These results suggest that IFN-γ causes the up-regulation of NTPDase1 in a tyrosine phosphatase-dependent manner. The differential regulation of NTPDase1 expression in macrophages and EC by IFN-γ may contribute to the macrophage-endothelium interaction under the vascular inflammation.