Distinct Role of Calmodulin and Calmodulin-dependent Protein Kinase-II in Lipopolysaccharide and Tumor Necrosis Factor-α-mediated Suppression of Apoptosis and Antiapoptotic c-IAP2 Gene Expression in Human Monocytic Cells

Exposure of phagocytic cells to bacterial endotoxin (lipopolysaccharide; LPS) or inflammatory cytokines confers antiapoptotic survival signals; however, in the absence of the appropriate stimulus, monocytes are programmed to undergo apoptosis. Macrophage survival may thus influence inflammatory and immune responses and susceptibility to microbial pathogens. Herein, we demonstrate that LPS and the proinflammatory cytokine, tumor necrosis factor-α (TNF-α), enhance monocytic cell survival through the induction of the antiapoptotic c-IAP2 gene in a human promonocytic THP-1 cell line. We also investigated the role of upstream signaling molecules including the mitogen-activated protein kinases, phosphatidylinositol 3-kinase, and the calcium signaling pathways in the regulation of c-IAP2 expression and eventual survival of monocytic cells. Our results suggest that LPS and TNF-α-induced c-IAP2 expression was regulated by calmodulin (CaM) through the activation of calmodulin-dependent protein kinase-II (CaMKII). In addition, CaM and CaMKII regulated c-IAP2 expression in LPSand TNF-α-stimulated cells through NF-κB activation. Moreover, the CaM/CaMKII pathway also regulated LPS- and TNF-α-mediated inhibition of apoptosis in these cells. Taken together, these results suggest that LPS- and TNF-α-induced c-IAP2 expression and its associated antiapoptotic survival signals in THP-1 cells are regulated selectively by CaM/CaMKII through NF-κB activation.