Intracellular safeguarding functions of metallothioneins (MTs) include sequestering transition and heavy metals, scavenging free radicals and protecting against electrophiles. We report that MT protection against Cu-induced cytotoxicity can be reversed and pro-oxidant and pro-apoptotic effects can be induced in HL-60 cells exposed to NO. We demonstrate that in ZnCl2-pretreated HL-60 cells loaded with copper nitrilotriacetate (Cu-NTA), exposure to an NO donor, S-nitroso-N-acetyl penicillamine, resulted in S-nitrosylation and oxidation of MT cysteines. This disruption of MT Cu-binding thiolate clusters caused loosening and release of redox-active Cu, enhanced redox-cycling activity of Cu and increased peroxidation of major classes of membrane phospholipids. We also found that Cu-induced oxidative stress in ZnCl2-pretreated/Cu-NTA-loaded HL-60 cells was accompanied by apoptosis documented by characteristic changes of nuclear morphology, internucleosomal DNA cleavage, externalization of phosphatidylserine, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. We conclude that in Cu-challenged cells, NO can reverse the protective role of MTs and convert them into pro-oxidant, pro-apoptotic implements.
Nitric oxide-dependent pro-oxidant and pro-apoptotic effect of metallothioneins in HL-60 cells challenged with cupric nitrilotriacetate
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Shang-Xi LIU, Kazuaki KAWAI, Vladimir A. TYURIN, Yulia Y. TYURINA, Grigory G. BORISENKO, James P. FABISIAK, Peter J. QUINN, Bruce R. PITT, Valerian E. KAGAN; Nitric oxide-dependent pro-oxidant and pro-apoptotic effect of metallothioneins in HL-60 cells challenged with cupric nitrilotriacetate. Biochem J 1 March 2001; 354 (2): 397–406. doi: https://doi.org/10.1042/bj3540397
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