ABSTRACT
Zinc is an essential micronutrient and cytoprotectant involved in the host response to inflammatory stress. We tested whether zinc transporters, the critical regulators that maintain intracellular zinc concentrations, play a role in cell survival, particularly in lung epithelia, during inflammation. Initially, mRNA transcripts were quantitatively measured by RT-PCR for all known human zinc transporters, including 14 importers (SLC39A(1-14)) and 10 exporters (SLC30A(1-10)), in primary human lung epithelia obtained from multiple human donors and BEAS-2B cell cultures under baseline and TNF-alpha-stimulated conditions. While many zinc transporters were constitutively expressed, only SLC39A8 (Zip8) mRNA was strongly induced by TNF-alpha. Endogenous Zip8 protein was not routinely detected under baseline conditions. In sharp contrast, TNF-alpha induced the expression of a glycosylated protein that translocated to the plasma membrane and mitochondria. Increased Zip8 expression resulted in an increase in intracellular zinc content and coincided with cell survival in the presence of TNF-alpha. Inhibition of Zip8 expression using a short interfering RNA probe reduced cellular zinc content and impaired mitochondrial function in response to TNF-alpha, resulting in loss of cell viability. These data are the first to characterize human Zip8 and remarkably demonstrate that upregulation of Zip8 is sufficient to protect lung epithelia against TNF-alpha-induced cytotoxicity. We conclude that Zip8 is unique, relative to other Zip proteins, by functioning as an essential zinc importer at the onset of inflammation, thereby facilitating cytoprotection within the lung.
