Regulation of zinc homeostasis by inducible NO synthase-derived NO: nuclear metallothionein translocation and intranuclear [Zn.sup.2+] release

[Zn.sup.2+] is critical for the functional and structural integrity of cells and contributes to a number of important processes including gene expression. It has been shown that NO exogenously applied via NO donors resulting in nitrosative stress leads to cytoplasmic [Zn.sup.2+] release from the zinc storing protein metallothionein (MT) and probably other proteins that complex [Zn.sup.2+] via cysteine thiols. We show here that, in cytokine-activated murine aortic endothelial cells, NO derived from the inducible NO synthase (iNOS) induces a transient nuclear release of [Zn.sup.2+]. This nuclear [Zn.sup.2+] release depends on the presence of MT as shown by the lack of this effect in activated endothelial cells from MT-deficient mice and temporally correlates with nuclear MT translocation. Data also show that NO is an essential but not sufficient signal for MT-mediated [Zn.sup.2+] trafficking from the cytoplasm into the nucleus. In addition, we found that, endogenously via iNOS, synthesized NO increases the constitutive mRNA expression of both MT-1 and MT-2 genes and that nitrosative stress exogenously applied via an NO donor increases constitutive MT mRNA expression via intracellular [Zn.sup.2+] release. In conclusion, we here provide evidence for a signaling mechanism based on iNOS-derived NO through the regulation of intracellular [Zn.sup.2+] trafficking and homeostasis.