Zinc inhibits doxorubicin-activated calcineurin signal transduction pathway in H9c2 embryonic rat cardiac cells

Elevation of the zinc-binding protein metallothionein (MT) in the heart inhibits doxorubicin (DOX)-induced myocardial apoptosis and heart hypertrophy. Zinc release from MT in response to oxidative stress has been suggested as a mechanism of action of MT protection from DOX toxicity, and calcineurin is involved in the signaling pathways leading to myocardial apoptosis and heart hypertrophy. The present study was undertaken to determine if zinc can modulate the DOX-activated calcineurin signaling pathway. H9c2 cells were treated with 1 muM DOX, and zinc release was monitored by a zinc ion-specific fluorophore, zinquin ethyl ester. Additionally, DOX-activated calcineurin signaling was detected by a calcineurin-dependent nuclear factor of activated T-cell reporter. DOX treatment induced an increase in intracellular labile zinc and activated calcineurin signaling. Pretreatment of H9c2 cells with a zinc-specific, membrane-permeable chelating agent, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), inhibited the increase in intracellular labile zinc and increased the DOX-activated calcineurin signaling. Pretreatment of H9c2 cells with exogenously added zinc attenuated the DOX-activated calcineurin signaling in a dose-dependent manner. However, neither TPEN nor addition of exogenous zinc affected DOX-induced cellular hypertrophy or DOX-induced decrease in cell viability. Additionally, inhibition of DOX-induced calcineurin signaling with the calcineurin inhibitors cyclosporine A or tacrolimus (FK506) failed to restrict the DOX-induced decrease in cell viability. These results indicate that zinc suppresses DOX-induced calcineurin signaling in H9c2 cells; however, calcineurin signaling is not involved in the DOX-induced decrease in cell viability in H9c2 cells. (It had been shown previously that calcineurin is also not necessary for DOX-induced H9c2 cell hypertrophy.).