{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nSLC30A2 encodes the zinc transporter ZnT2, a protein primarily expressed in highly specialized secretory cells—including mammary epithelial cells, pancreatic acinar cells, prostate, and even select immune and β‐cells—where it plays a central role in importing zinc into secretory vesicles. Two main isoforms of ZnT2 have been described: one predominantly residing in intracellular secretory compartments to mediate vesicular zinc accumulation and secretion (thereby ensuring adequate milk zinc content), and a smaller isoform associated with the plasma membrane that also contributes to zinc export. These coordinated functions are critical for maintaining zinc homeostasis in tissues with unique zinc requirements, particularly in the lactating breast where proper zinc secretion is essential for neonatal development."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nMutations and non‐synonymous variants in SLC30A2 have been repeatedly associated with transient neonatal zinc deficiency (TNZD) in exclusively breastfed infants. Missense mutations such as H54R, G87R, and T288S, among others, alter ZnT2’s trafficking, stability, and zinc transport capability. These mutations often result in aberrant protein localization—ranging from perinuclear aggresomal accumulation or endoplasmic reticulum–Golgi retention to misdirected plasma membrane targeting—and may exert dominant-negative effects or lead to haploinsufficiency, thereby reducing zinc secretion into breast milk. As a result, infants may experience severe zinc deficiency with clinical manifestations that underscore the critical role of ZnT2 in lactational zinc transport."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}, {"type": "fg_fs", "start_ref": "4", "end_ref": "8"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its fundamental role in zinc secretion during lactation, the function and expression of ZnT2 are finely tuned by both zinc status and specific transcriptional regulators. ZnT2 gene expression is up-regulated in response to zinc, a process modulated by metal-responsive transcription factor-1 (MTF-1), while elements such as the zinc finger E-box binding homeobox (ZEB) act as suppressors. Moreover, post-translational modifications, including phosphorylation (as seen with the T288S variant), further impact ZnT2’s intracellular distribution—promoting its accumulation in lysosomes and mitochondria, thereby affecting cellular oxidative status and overall cell function. Similar regulatory dynamics have been observed in breast cancer cells and even in pancreatic β-cells, suggesting that ZnT2’s influence extends across diverse cellular contexts."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "9", "end_ref": "14"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nPopulation-based studies further reveal that SLC30A2 variants are relatively common and not only dictate the zinc content of breast milk but may also influence broader aspects of mammary gland function, including milk volume and epithelial cell integrity. Genetic screening of lactating women has identified numerous novel missense mutations that disrupt zinc transport and are associated with markers of breast dysfunction, altered immune response, and even changes in gut microbial composition in neonates. These findings emphasize that SLC30A2/ZnT2 is not solely a mediator of zinc secretion but is also a key modulator of tissue homeostasis and cellular signaling in both normal physiology and disease states."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "15", "end_ref": "19"}]}, {"type": "t", "text": ""}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Winyoo Chowanadisai, Bo Lönnerdal, Shannon L Kelleher "}, {"type": "b", "children": [{"type": "t", "text": "Identification of a mutation in SLC30A2 (ZnT-2) in women with low milk zinc concentration that results in transient neonatal zinc deficiency."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2006)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M605821200"}], "href": "https://doi.org/10.1074/jbc.M605821200"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "17065149"}], "href": "https://pubmed.ncbi.nlm.nih.gov/17065149"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Veronica Lopez, Shannon L Kelleher "}, {"type": "b", "children": [{"type": "t", "text": "Zinc transporter-2 (ZnT2) variants are localized to distinct subcellular compartments and functionally transport zinc."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochem J (2009)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1042/BJ20081189"}], "href": "https://doi.org/10.1042/BJ20081189"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "19496757"}], "href": "https://pubmed.ncbi.nlm.nih.gov/19496757"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Samina Alam, Stephen R Hennigar, Carla Gallagher, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Exome Sequencing of SLC30A2 Identifies Novel Loss- and Gain-of-Function Variants Associated with Breast Cell Dysfunction."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Mammary Gland Biol Neoplasia (2015)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/s10911-015-9338-z"}], "href": "https://doi.org/10.1007/s10911-015-9338-z"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "26293594"}], "href": "https://pubmed.ncbi.nlm.nih.gov/26293594"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "Inbal Lasry, Young Ah Seo, Hadas Ityel, et al. "}, {"type": "b", "children": [{"type": "t", "text": "A dominant negative heterozygous G87R mutation in the zinc transporter, ZnT-2 (SLC30A2), results in transient neonatal zinc deficiency."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2012)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M112.368159"}], "href": "https://doi.org/10.1074/jbc.M112.368159"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "22733820"}], "href": "https://pubmed.ncbi.nlm.nih.gov/22733820"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Naoya Itsumura, Yoshie Kibihara, Kazuhisa Fukue, et al. 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"}, {"type": "b", "children": [{"type": "t", "text": "Loss-of-function "}, {"type": "a", "children": [{"type": "t", "text": "i"}], "href": "i"}, {"type": "t", "text": "SLC30A2"}, {"type": "a", "children": [{"type": "t", "text": "/i"}], "href": "/i"}, {"type": "t", "text": " mutants are associated with gut dysbiosis and alterations in intestinal gene expression in preterm infants."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Gut Microbes (2022)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1080/19490976.2021.2014739"}], "href": "https://doi.org/10.1080/19490976.2021.2014739"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "34965180"}], "href": "https://pubmed.ncbi.nlm.nih.gov/34965180"}]}]}]}