Sodium–iodide symporter (NIS)

The **Sodium–iodide symporter (NIS)** is an integral plasma membrane glycoprotein responsible for the active transport of iodide ions into cells, most notably the thyroid follicular cells[1][2][5][6]. NIS is encoded by the *SLC5A5* gene and consists of 13 transmembrane domains[1][2][4][6]. Its primary physiological function is to mediate iodide uptake, the essential first step in the biosynthesis of thyroid hormones (triiodothyronine/T3 and thyroxine/T4)[1][2][5][6]. The transporter operates by co-transporting two sodium ions with one iodide ion, utilizing the sodium gradient to concentrate iodide inside thyroid follicular cells up to 50-fold above plasma levels[2][3][5]. Beyond the thyroid, NIS is expressed in tissues such as the salivary glands, stomach, and lactating mammary gland, where its functional roles are less well understood[1][2][5]. Clinically, the transporter's ability to concentrate iodide is exploited in diagnostic imaging and in the radioiodide treatment of thyroid cancer and hyperthyroidism, as well as in gene therapy strategies for targeted delivery of radioactive agents to non-thyroidal tumors[1][3][5]. Expression or function loss—such as through SLC5A5 mutations—results in congenital hypothyroidism, a disease requiring early intervention to prevent intellectual disability[4][5]. NIS also presents challenges in therapy due to off-target uptake and environmental inhibition by perchlorate and related compounds[5].

Other names

Sodium/iodide cotransporterSLC5A5Na+/I− symporter

Active transport of iodide into cells via symport with sodium ions; radioiodide uptake for thyroid ablation/cancer therapy; competitive inhibition by various anions; gene therapy vector for targeted radioisotope delivery