Induction of CHOP and apoptosis by nitric oxide in p53-deficient microglial cells

Excessive nitric oxide (NO) has been implicated in neurotoxicity after stre sses such as ischemia. NO toxicity is generally thought to be mediated by t he DNA damage-p53 pathway or mitochondrial dysfunction. We investigated the mechanism of NO toxicity by using murine microglial MG5 cells established from p53-deficient mice. When MG5 cells were exposed to bacterial lipopolys accharide plus interferon-gamma, mRNA and protein for inducible NO synthase (iNOS) were markedly induced, and apoptosis occurred. Under these conditio ns, we found that mRNA and protein for CHOP/GADD153, a C/EBP family transcr iption factor which is involved in endoplasmic reticulum (ER) stress-induce d apoptosis, are induced. iNOS mRNA was induced 2 h after treatment, wherea s CHOP mRNA began to increase at 6 h with a time lag. CHOP mRNA was also in duced by NO donors S-nitroso-N-acetyl-DL-penicillamine (SNAP) or NOC18, or a peroxynitrite generator 3-(4-morpholinyl)-sydnonimine hydrochloride (SIN- 1). Bip/GRP78, an ER chaperone which is known to be induced by ER stress, w as also induced by SNAP or SIN-1, indicating that NO causes ER stress. Thes e results suggest that NO-induced apoptosis in MG5 cells occurs through the ER stress pathway involving CHOP, but is independent of p53. (C) 2001 Fede ration of European Biochemical Societies. Published by Elsevier Science B.V . All rights reserved.