Nuclear factor-kappa B and caspases co-operatively regulate the activationand apoptosis of human macrophages

Accumulating evidence suggests that macrophages function as major effector cells in the pathological process of various human diseases. We examined he re the role of nuclear factor-kappa B (NF-kappa B) and caspases in the regu lation of activation and apoptosis of macrophages. Activation of the human monoblastic leukaemia cell line, U937, by phorbol 12-myristate 13-acetate ( PMA) increased the expression of CD14/CD86, and cytokine production. PMA st imulation also increased the expression of both pro-caspase-8 and pro-caspa se-3 in U937, but not apoptosis or intracellular caspase-3 activity. PMA al so increased the expression of X-chromosome-linked inhibitor of apoptosis p rotein (XIAP) in U937, suggesting an inhibitory action for XIAP on the casp ase cascade in PMA-stimulated U937. Electrophoretic mobility shift assay (E MSA) showed a significant increase of nuclear NF-kappa B activity in PMA-st imulated U937. When a potent NF-kappa B inhibitor, pyrrolidine dithiocarbam ate (PDTC), was added to U937 cell culture in the presence of PMA, apoptosi s was triggered by activation of caspase-3, which was induced by caspase-8 activation. XIAP expression was markedly suppressed in PMA-treated U937 in the presence of PDTC. The inhibitors of caspase-8 and caspase-3 mostly inhi bited apoptosis of U937 treated with PMA in the presence of PDTC. Furthermo re, a phenotype of U937 treated with PMA and PDTC in the presence of caspas e inhibitor was almost identical to that of unstimulated U937. Our results suggest that the signalling pathways involved in the activation and apoptos is of human macrophages could be co-operatively regulated by the use of NF- kappa B and caspase inhibitors, thus enabling the control of macrophage fun ction and number.