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Description

Sodium/iodide cotransporter (UniProt: Q92911, also known as Na(+)/I(-) cotransporter, Sodium-iodide symporter, Na(+)/I(-) symporter, Solute carrier family 5 member 5) is encoded by the SLC5A5 (also known as NIS) gene (Gene ID: 6528) in human. Sodium/iodide cotransporter is a multi-pass membrane protein that mediates iodide uptake in thyroid gland. It is expressed primarily in thyroid tissue, but is present in lower levels in mammary gland and ovary. It is found in the basolateral membrane of thyroid follicular cells where it mediates efficient iodide uptake from the bloodstream into the thyroid using the sodium gradient generated by Na+/K+-ATPase. It transports one iodide ion along with two sodium ions following the inwardly directed sodium gradient. Sodium/iodide cotransporter expression is significantly reduced in tumors. The presence of symporter in mammary glands leads to secretion of iodine in milk that is required for thyroid function in neonatal animals. NIS gene and protein expression is stimulated by thyroid-stimulating hormone. Both human and rat NIS contain N-glycosylation sites, however, glycosylation is not required for its full activity. Mutations in SLC5A5 gene are known to cause thyroid dyshormonogenesis (TDH1) that is characterized by the inability of the thyroid to maintain a concentration difference of readily exchangeable iodine between the plasma and the thyroid gland, leading to congenital hypothyroidism. Autoantibodies to NIS adversely affect iodide transport.