Protein kinase C regulation of neuronal zinc signaling mediates survival during preconditioning


Address correspondence and reprint requests to Elias Aizenman, Department of Neurobiology, University of Pittsburgh School of Medicine, E1405 Biomedical Science Tower, 3500 Terrace Street, Pittsburgh, PA 15261, USA. E-mail:


Sub-lethal activation of cell death processes initiate pro-survival signaling cascades. As intracellular Zn2+ liberation mediates neuronal death pathways, we tested whether a sub-lethal increase in free Zn2+ could also trigger neuroprotection. Neuronal free Zn2+ transiently increased following preconditioning, and was both necessary and sufficient for conferring excitotoxic tolerance. Lethal exposure to NMDA led to a delayed increase in Zn2+ that contributed significantly to excitotoxicity in non-preconditioned neurons, but not in tolerant neurons, unless preconditioning-induced free Zn2+ was chelated. Thus, preconditioning may trigger the expression of Zn2+-regulating processes, which, in turn, prevent subsequent Zn2+-mediated toxicity. Indeed, preconditioning increased Zn2+-regulated gene expression in neurons. Examination of the molecular signaling mechanism leading to this early Zn2+ signal revealed a critical role for protein kinase C (PKC) activity, suggesting that PKC may act directly on the intracellular source of Zn2+. We identified a conserved PKC phosphorylation site at serine-32 (S32) of metallothionein (MT) that was important in modulating Zn2+-regulated gene expression and conferring excitotoxic tolerance. Importantly, we observed increased PKC-induced serine phosphorylation in immunopurified MT1, but not in mutant MT1(S32A). These results indicate that neuronal Zn2+ serves as an important, highly regulated signaling component responsible for the initiation of a neuroprotective pathway.