Zinc transporter ZIP8 (SLC39A8) and zinc influence IFN-γ expression in activated human T cells

The zinc transporter ZIP8 is highly expressed in T cells derived from human subjects. T cell ZIP8 expression was markedly up-regulated upon in vitro activation. T cells collected from human subjects who had received oral zinc supplementation (15 mg/day) had higher ex-pression of the activation marker IFN- upon in vitro ac-tivation, indicating a potentiating effect of zinc on T cell activation. Similarly, in vitro zinc treatment of T cells along with activation resulted in increased IFN- ex-pression with a maximum effect at 3.1 M. Knockdown of ZIP8 in T cells by siRNA decreased ZIP8 levels in nonactivated and activated cells and concomitantly re-duced secretion of IFN- and perforin, both signatures of activation. Overexpression of ZIP8 by transient transfection caused T cells to exhibit enhanced activa-tion. Confocal microscopy established that ZIP8 is lo-calized to the lysosome where ZIP8 abundance is in-creased upon activation. Loss of lysosomal labile zinc in response to activation was measured by flow cytom-etry using a zinc fluorophore. Zinc between 0.8 and 3.1 M reduced CN phosphatase activity in a linear man-ner. CN was also inhibited by the CN inhibitor FK506 and ZIP8 overexpression. The results suggest that zinc at low concentrations, through inhibition of CN, sustains phosphorylation of the transcription factor CREB, yield-ing greater IFN- expression in T cells. ZIP8, through control of zinc transport from the lysosome, may pro-vide a secondary level of IFN- regulation in T cells. J. Leukoc. Biol. 86: 000–000; 2009