ZnT4 is localized to the trans‐Golgi apparatus and contributes to zinc secretion from mammary epithelial cells

The mammary gland transfers approximately 1–3 mg zinc (Zn)/d into milk to support the growth and development of the offspring. A point mutation in ZnT4 results in the lethal milk syndrome in mice which reduces Zn secretion into milk by ~35%. Without further Zn supplementation, pups born to dams homozygous for this mutation die within days. We utilized mouse mammary epithelial cells (HC11) to determine the precise role of ZnT4 in Zn secretion from the mammary gland. Expression of a ZnT4/HA fusion protein was localized to the trans ‐Golgi apparatus and decreased cytosolic Zn concentration by ~70%, implicating ZnT4 in Zn sequestration into the trans ‐Golgi apparatus. We utilized the labile Zn fluorophore Fluozin‐3AM to verify that Zn pools in the Golgi apparatus were expanded and determined that expression of ZnT4/HA increased vesicularized Zn pools by ~24%. Importantly, expansion of Zn pools in the Golgi apparatus increased Zn secretion by ~13%. Taken together, these data indicate that ZnT4 transports Zn into the trans ‐Golgi apparatus and thereby contributes to Zn secretion from the mammary gland. Determining the precise role of ZnT4 in the mammary gland helps to elucidate the mechanism by which optimal nutrition is delivered to the developing offspring. Grant Funding Source : NIH R01 HD058614