Regulation of Cellular Zn Redistribution: A Role of ZnT2

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DESCRIPTION (provided by applicant): The long-term goal of this application aims to determine how tissues with extraordinary zinc (Zn) requirements, such as mammary gland and prostate, redistribute cellular Zn pools during secretion. Impaired Zn secretion from the mammary gland during lactation results in severe neonatal Zn deficiency. This compromises neuronal and behavioral development, impairs immune function, and increases infant morbidity and/or mortality. Aberrant Zn transport is also implicated in breast cancer. Dysfunctional prostate Zn transport impairs sperm viability and is associated with prostate cancer. These observations underscore the need to understand Zn transport mechanisms in these highly specialized tissues. Zinc transporter-2 (ZnT2) expression is restricted to tissues such as mammary gland and prostate. A mutation in ZnT2 reduces Zn secretion into milk in humans and ZnT2-suppression in mammary epithelial cells reduces Zn secretion in vitro. Discrete ZnT2 isoforms have been identified which are associated with mitochondria (mZnT2) and intracellular vesicles (sZnT2) in mammary epithelial cells. Mitochondrial Zn uptake and Zn concentration parallels mZnT2 abundance, while Zn secretion parallels sZnT2 abundance. Similar to observations in prostate cells, the hormone prolactin shifts Zn distribution in mammary epithelial cells. Prolactin contracts mitochondrial Zn pools while concurrently increasing Zn transport. This redistribution is associated with decreased mZnT2 and increased sZnT2 abundance. We hypothesize that prolactin regulates discrete ZnT2 isoforms to redistribute cellular Zn pools from mitochondria to secretory vesicles to facilitate extraordinary Zn secretion in highly specialized secretory tissues. We propose to use the mammary gland as a representative system to explore potential mechanisms responsible for cellular Zn redistribution using animal and cell models. The four specific aims of this application are to, (1) determine if mitochondrial ZnT2 facilitates expansion of a mitochondrial Zn pool using genomic and proteomic approaches; (2) determine mechanisms by which prolactin redistributes cellular Zn pools through changes in sZnT2 during secretion; (3) develop a transgenic mammary gland mouse model to determine if cellular Zn pools are redistributed by mZnT2 and sZnT2 in vivo; (4) develop a ZnT2-null mouse model to document the biological significance ZnT2 and determine if other Zn transporters participate in Zn pool redistribution in mammary gland and prostate in vivo. Taken together, these studies will identify specific mechanisms which regulate cellular Zn redistribution in highly specialized tissues and are crucial to our understanding of cellular function, Zn metabolism and human health and disease. The mammary and prostate glands are highly specialized secretory tissues that are responsible for extraordinary Zn secretion. Impaired Zn secretion from the mammary gland during lactation results in severe neonatal Zn deficiency which compromises neuronal and behavioral development, impairs immune function, and increases infant morbidity and/or mortality. Aberrant Zn transport is also implicated in breast cancer. Dysfunctional Zn transport in prostate has been implicated in prostate cancer, sperm viability and impaired reproductive function. These observations underscore the need to understand Zn transport mechanisms in these unique tissues. Thus, this application has significance for improving public health outcomes and advancing our understanding of basic cellular mechanisms. PUBLIC HEALTH RELEVANCE: The mammary and prostate glands are highly specialized secretory tissues that are responsible for extraordinary Zn secretion. Impaired Zn secretion from the mammary gland during lactation results in severe neonatal Zn deficiency which compromises neuronal and behavioral development, impairs immune function, and increases infant morbidity and/or mortality. Aberrant Zn transport is also implicated in breast cancer. Dysfunctional Zn transport in prostate has been implicated in prostate cancer, sperm viability and impaired reproductive function. These observations underscore the need to understand Zn transport mechanisms in these unique tissues. Thus, this application has significance for improving public health outcomes and advancing our understanding of basic cellular mechanisms.