Zip5: a candidate protein for zinc transport from maternal circulation into the mammary gland

Abstract

An extraordinary amount of zinc (Zn) moves through the mammary gland (MG) and into milk during lactation, but the mechanism by which the MG accumulates Zn from maternal circulation is not yet understood. We postulate that a Zip protein is responsible for importing Zn into the MG. Zn accumulation in the MG in vivo was visualized using X‐ray fluorescence microscopy. Candidate Zip proteins (Zip1, 3, 5, 6, 8, 10) were identified by real‐time PCR in secreting mouse mammary epithelial cells (HC11). This screen identified Zip5 by a 10‐fold increase in mRNA expression relative to non‐secreting cells. To confirm Zip5 protein expression during lactation, we assessed expression by immunblotting. Zip5 protein expression was ~3 fold higher in lactating compared with non‐lactating MG, further supporting the hypothesis that Zip5 is important for Zn accumulation in the MG during lactation. To confirm that Zip5 was appropriately localized to transport Zn from maternal circulation, we successfully localized Zip5 to the serosal membrane of epithelial cells in mouse MG using immunohistochemistry, and by cell surface biotinylation and confocal microscopy in HC11 cells. In conclusion, our data supports the postulate that Zip5 is a candidate for Zn accumulation from maternal circulation as it is localized appropriately and protein expression increases during lactation in the MG.Supported by intramural funds to SLKGrant Funding Source: intramural funds to SLK