TNF-alpha and IL-1 alpha induce heme oxygenase-1 via protein kinase C, Ca2+, and phospholipase A(2) in endothelial cells

Heme oxygenase-1 (HO-1), an enzyme important in protection against oxidant stress, is induced in human vascular endothelial cells by the cytokines tum or necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha). However, the signaling mediators that regulate the induction are not known. This study examined the involvement of protein kinase C (PKC), phospholipa se A(2) (PLA(2)), calcium, and oxidants in cytokine induction of HO-1. Acut e exposure to the PKC activator phorbol 12-myristate 13-acetate (PMA) stimu lated HO-1 mRNA. However, prolonged exposure, which downregulates most PKC isoforms, blocked induction of HO-1 mRNA by IL-1 alpha and TNF-alpha. Addit ionally, the phosphatase inhibitors okadaic acid and calyculin enhanced cyt okine induction of HO-1. Mepacrine, a PLA(2) inhibitor, prevented HO-1 indu ction by cytokine, suggesting a role for arachidonate, the product of PLA(2 ) hydrolysis of phospholipids, in HO-1 expression. The intracellular calciu m chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxy methyl 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 indu ction by cytokines. These results demonstrate that TNF-alpha and IL-1 alpha induction of HO-1 requires PKC-mediated phosphorylation and PLA(2) activat ion as well as oxidant generation.