TNF-a and IL-1a induce heme oxygenase-1 via protein kinase C, Ca21, and phospholipase A2 in endothelial cells

Terry, Christi M., Jennifer A. Clikeman, John R. Hoidal, and Karleen S. Callahan. TNF-a and IL-1a induce heme oxygenase-1 via protein kinase C, Ca21, and phospholipase A2 in endothelial cells. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H1493–H1501, 1999.—Heme oxygenase-1 (HO-1), an enzyme important in protection against oxidant stress, is induced in human vascular endothelial cells by the cytokines tumor necrosis factor-a (TNF-a) and interleukin-1a (IL-1a). However, the signaling mediators that regulate the induction are not known. This study examined the involvement of protein kinase C (PKC), phospholipase A2 (PLA2), calcium, and oxidants in cytokine induction of HO-1. Acute exposure to the PKC activator phorbol 12-myristate 13acetate (PMA) stimulated HO-1 mRNA. However, prolonged exposure, which downregulates most PKC isoforms, blocked induction of HO-1 mRNA by IL-1a and TNF-a. Additionally, the phosphatase inhibitors okadaic acid and calyculin enhanced cytokine induction of HO-1. Mepacrine, a PLA2 inhibitor, prevented HO-1 induction by cytokine, suggesting a role for arachidonate, the product of PLA2 hydrolysis of phospholipids, in HO-1 expression. The intracellular calcium chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N8,N8-tetraacetic acid acetoxymethyl ester (BAPTA-AM) blocked cytokine induction of HO-1. Paradoxically, the calcium ionophore A-23187 prevented HO-1 induction by cytokine but not by PMA. Finally, the oxidant scavenger N-acetylcysteine inhibited HO-1 induction by cytokines. These results demonstrate that TNF-a and IL-1a induction of HO-1 requires PKC-mediated phosphorylation and PLA2 activation as well as oxidant generation.