Figure 3.

Zn and Zn transporters involved in mammary gland function. Mammary gland is comprised of a network of branched ductal structures terminating at acinar units, also known as lobules. These structures are lined with MEC responsible for the production and secretion of milk into the collecting ducts for the developing neonate. (A) Although only localization of Zip3 and ZnT2 has been clearly established in normal/nonlactating tissue, ZnT4 is also known to be expressed. Zip6 and Zip7 are expressed in breast cells; however, their role in normal mammary gland is unknown. (B) During lactation, ZnT2 plays a major role in the secretion of Zn into milk, while Zip3 plays a role in the reuptake of Zn from the lumen. The localization and contribution of other Zn transporters during MEC differentiation and lactation remains to be determined and is an important question. (C) Hyper-accumulation of Zn has been associated with breast cancer. A limited number of Zn transporters (Zip5, Zip6, Zip7, Zip8, and Zip10) and MT have been shown to be overexpressed in this disease. However, their specific contribution to this phenotype and in MEC is remains to be delineated.