Cloning and characterization of the thyroid iodide transporter.
Iodide (I-) is an essential constituent of the thyroid hormones T3 and T4, and is accumulated by the thyroid. The transport of iodide, the first step in thyroid hormogenesis, is catalysed by the Na+/I- symporter, an intrinsic membrane protein that is crucial for the evaluation, diagnosis and treatment of thyroid disorders. Although several other important thyroid proteins involved in hormogenesis have been characterized, the Na+/I- symporter has not. Here we report the isolation of a complementary DNA clone that encodes this symporter, as a result of functional screening of a cDNA library from a rat thyroid-derived cell line (FRTL-5) in Xenopus laevis oocytes. Oocyte microinjection of an RNA transcript made in vitro from this cDNA clone elicited a more than 700-fold increase in perchlorate-sensitive Na+/I- symport activity over background. To our knowledge, this is the first iodide-transporting molecule to have its cDNA cloned, providing a missing link in the thyroid hormone biosynthetic pathway.
Dai
G
G
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Levy
O
O
Carrasco
N
N
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D027981:Symporters; D013961:Thyroid Gland / Q000378:metabolism*; D014982:Xenopus laevis; D000099209:Sodium-Iodide Symporters
D002352:Carrier Proteins; D018076:DNA, Complementary; D008565:Membrane Proteins; D027981:Symporters; D000099209:Sodium-Iodide Symporters