Bifunctional Anti-/Prooxidant Potential of Metallothionein: Redox Signaling of Copper Binding and Release

被引:28
作者
Fabisiak, James P. [1 ]
Pearce, Linda L. [2 ]
Borisenko, Grigory G. [1 ]
Tyurina, Yulia Y. [1 ]
Tyurin, Vladimir A. [1 ]
Razzack, Jamal [3 ]
Lazo, John S. [2 ]
Pitt, Bruce R. [2 ]
Kagan, Valerian E. [1 ,2 ]
机构
[1] Univ Pittsburgh, Dept Environm & Occupat Hlth, Sch Publ Hlth, Pittsburgh, PA 15238 USA
[2] Univ Pittsburgh, Dept Pharmacol, Pittsburgh, PA 15238 USA
[3] Univ Pittsburgh, Dept Med, Sch Med, Pittsburgh, PA 15238 USA
关键词
D O I
10.1089/ars.1999.1.3-349
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Metallothioneins (MTs) are cysteine-rich metal-binding proteins that exert cytoprotection during metal exposure and oxidative stress. The roles of MT in copper (Cu) binding and release and modulation of redox cycling are unresolved. W e hypothesized that Cu-binding to MT renders Cu redox inactive, but that oxidation of free thiols critical for metal binding can reduce MT/Cu interactions and potentiate Cu redox cycling. Overexpression of MT in cells by cadmium pretreatment or ectopic overexpression by gene transfer confers protection from Cu-dependent lipid oxidation and cytotoxicity. Using a chemically defined model system (Cu/ascorbate/H2O2) to study Cu/MT interactions, we observed that MT inhibited Cu-dependent oxidation of luminol. In the absence of H2O2, MT blocked Cu-dependent ascorbyl radical production with a stoichiometry corresponding to Cu/MT ratios <= 12. In the presence of H2O2/Cu-dependent hydroxyl radical formation was inhibited only up to Cu/MT ratios <= 6. Using low-temperature EPR of free Cu2+ to assess Cu/MT physical interactions, we observed that the maximal amount of Cu1+ bound to MT corresponded to 12 molar equivalents of Cu/MT with Cu and ascorbate alone and was reduced in the presence of H2O2. 2,2'-Dithiodipyridine titration of MT SH-groups revealed a 50% decrease after H2O2, which could be regenerated by dihydrohpoic acid (DHLA). DHLA regeneration of thiols in MT was accompanied by restoration of MT's ability to inhibit Cu-dependent oxidation of ascorbate. Thus, optimum ability of MT to inhibit Cu-redox cycling directly correlates with its ability to bind Cu. Some of this Cu, however, appears releasable following oxidation of the thiolate metal-binding clusters. W e speculate that redox-dependent release of Cu from MT serves both as a mechanism for physiological delivery of Cu to specific target proteins, as well as potentiation of cellular damage during oxidative stress. Antiox. Redox Signal. 1, 349-364.
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页码:349 / U60
页数:17
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