Post-transcriptional Regulation of the Sodium/Iodide Symporter by Thyrotropin

The Na+/I−symporter (NIS) is a key plasma membrane glycoprotein that mediates active I− transport in the thyroid gland (Dai, G., Levy, O., and Carrasco, N. (1996) Nature 379, 458–460), the first step in thyroid hormone biogenesis. Whereas relatively little is known about the mechanisms by which thyrotropin (TSH), the main hormonal regulator of thyroid function, regulates NIS activity, post-transcriptional events have been suggested to play a role (Kaminsky, S. M., Levy, O., Salvador, C., Dai, G., and Carrasco, N. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 3789–3793). Here we show that TSH induces de novo NIS biosynthesis and modulates the long NIS half-life (∼5 days). In addition, we demonstrate that TSH is required for NIS targeting to or retention in the plasma membrane. We further show that NIS is a phosphoprotein and that TSH modulates its phosphorylation pattern. These results provide strong evidence of the major role played by post-transcriptional events in the regulation of NIS by TSH. Beyond their inherent interest, it is also of medical significance that these TSH-dependent regulatory mechanisms may be altered in the large proportion of thyroid cancers in which NIS is predominantly expressed in intracellular compartments, instead of being properly targeted to the plasma membrane. The Na+/I−symporter (NIS) is a key plasma membrane glycoprotein that mediates active I− transport in the thyroid gland (Dai, G., Levy, O., and Carrasco, N. (1996) Nature 379, 458–460), the first step in thyroid hormone biogenesis. Whereas relatively little is known about the mechanisms by which thyrotropin (TSH), the main hormonal regulator of thyroid function, regulates NIS activity, post-transcriptional events have been suggested to play a role (Kaminsky, S. M., Levy, O., Salvador, C., Dai, G., and Carrasco, N. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 3789–3793). Here we show that TSH induces de novo NIS biosynthesis and modulates the long NIS half-life (∼5 days). In addition, we demonstrate that TSH is required for NIS targeting to or retention in the plasma membrane. We further show that NIS is a phosphoprotein and that TSH modulates its phosphorylation pattern. These results provide strong evidence of the major role played by post-transcriptional events in the regulation of NIS by TSH. Beyond their inherent interest, it is also of medical significance that these TSH-dependent regulatory mechanisms may be altered in the large proportion of thyroid cancers in which NIS is predominantly expressed in intracellular compartments, instead of being properly targeted to the plasma membrane. Na+/I− symporter thyroid-stimulating hormone membrane vesicles phenylmethanesulfonyl fluoride Hanks' balanced salt solution antibody phosphate-buffered saline room temperature sulfosuccinimidyl-2-(biotinamido)ethyl-1,3-dithiopropionate The Na+/I− symporter (NIS)1 is an intrinsic plasma membrane protein that mediates the active transport of I−in the thyroid and other tissues such as salivary glands, gastric mucosa, and lactating mammary gland (1Tazebay U.H. Wapnir I.L. Levy O. Dohan O. Zuckier L.S. Zhao Q.H. Deng H.F. Amenta P.S. Fineberg S. Pestell R.G. Carrasco N. Nat. Med. 2000; 6: 871-878Crossref PubMed Scopus (414) Google Scholar, 2De la Vieja A. Dohan O. Levy O. Carrasco N. Physiol. Rev. 2000; 80: 1083-1105Crossref PubMed Scopus (281) Google Scholar). NIS is of central significance in thyroid pathophysiology as the route by which I− reaches the gland for thyroid hormone biosynthesis and as a means for diagnostic scintigraphic imaging and for radioiodide therapy in thyroid cancer (3Mazaferri E.L. Braverman L.E. Utiger R.D. The Thyroid: A Fundamental and Clinical Text. 8th Ed. J. B. Lippincott, Philadelphia2000: 904-930Google Scholar). NIS couples the inward translocation of Na+ down its electrochemical gradient to the simultaneous inward translocation of I− against its electrochemical gradient (4Bagchi N. Fawcett D.M. Biochim. Biophys. Acta. 1973; 318: 235-251Crossref PubMed Scopus (49) Google Scholar, 5Weiss S.J. Philp N.J. Grollman E.F. Endocrinology. 1984; 114: 1108-1113Crossref PubMed Scopus (116) Google Scholar, 6Eskandari S. Loo D.D. Dai G. Levy O. Wright E.M. Carrasco N. J. Biol. Chem. 1997; 272: 27230-27238Abstract Full Text Full Text PDF PubMed Scopus (379) Google Scholar) with a 2:1 Na+/I−stoichiometry (6Eskandari S. Loo D.D. Dai G. Levy O. Wright E.M. Carrasco N. J. Biol. Chem. 1997; 272: 27230-27238Abstract Full Text Full Text PDF PubMed Scopus (379) Google Scholar). Cloning and sequencing of the rat NIS cDNA revealed a protein of 618 amino acids (7Dai G. Levy O. Carrasco N. Nature. 1996; 379: 458-460Crossref PubMed Scopus (964) Google Scholar), which is highly homologous (87% identity) to the subsequently cloned human NIS (8Smanik P.A. Liu Q. Furminger T.L. Ryu K. Xing S. Mazzaferri E.L. Jhiang S.M. Biochem. Biophys. Res. Commun. 1996; 226: 339-345Crossref PubMed Scopus (467) Google Scholar). The current secondary structure model depicts NIS as a protein with 13 transmembrane segments, the amino terminus facing the extracellular side and the carboxyl terminus facing the cytosol, both of which we have demonstrated experimentally (9Levy O. De la Vieja A. Ginter C.S. Riedel C. Dai G. Carrasco N. J. Biol. Chem. 1998; 273: 22657-22663Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar). The iodine-containing thyroid hormones triiodothyronine and thyroxine play essential roles in promoting the development and maturation of the nervous system, skeletal muscle, and lungs and in regulating intermediary metabolism in virtually all tissues. Thyroid-stimulating hormone (TSH) is the primary hormonal regulator of thyroid function overall and has long been known to stimulate I− uptake activity in the thyroid (10Vassart G. Dumont J.E. Endocr. Rev. 1992; 13: 596-611PubMed Google Scholar). No thyroidal I− uptake is detected in humans whose serum TSH levels are suppressed (11Martino E. Bartalena L. Pinchera A. Braverman L.E. Utiger R.D. The Thyroid: A Fundamental and Clinical Text. 8th Ed. J. B. Lippincott, Philadelphia2000: 762-773Google Scholar). In addition, up-regulation of NIS thyroid expression and I−uptake activity by TSH has been demonstrated in rats in vivo(12Levy O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar), in the rat thyroid-derived FRTL-5 cell line (13Weiss S.J. Philp N.J. Ambesi-Impiombato F.S. Grollman E.F. Endocrinology. 1984; 114: 1099-1107Crossref PubMed Scopus (184) Google Scholar), and in human thyroid primary cultures (14Kogai T. Curcio F. Hyman S. Cornford E.M. Brent G.A. Hershman J.M. J. Endocrinol. 2000; 167: 125-135Crossref PubMed Scopus (72) Google Scholar, 15Saito T. Endo T. Kawaguchi A. Ikeda M. Nakazato M. Kogai T. Onaya T. J. Clin. Endocrinol. 82: 3331-3336PubMed Google Scholar). TSH up-regulates I− uptake activity by a cAMP-mediated increase in NIS transcription (13Weiss S.J. Philp N.J. Ambesi-Impiombato F.S. Grollman E.F. Endocrinology. 1984; 114: 1099-1107Crossref PubMed Scopus (184) Google Scholar, 16Marcocci C. Cohen J.L. Grollman E.F. Endocrinology. 1984; 115: 2123-2132Crossref PubMed Scopus (30) Google Scholar, 17Kogai T. Endo T. Saito T. Miyazaki A. Kawaguchi A. Onaya T. Endocrinology. 1997; 138: 2227-2232Crossref PubMed Scopus (227) Google Scholar, 18Ohno M. Zannini M. Levy O. Carrasco N. Di Lauro R. Mol. Cell. Biol. 1999; 19: 2051-2060Crossref PubMed Scopus (214) Google Scholar). After TSH withdrawal a reduction of both intracellular cAMP levels and I− uptake activity is observed in FRTL-5 cells. This is a reversible process, as I− uptake activity can be restored either by TSH or agents that increase cAMP (13Weiss S.J. Philp N.J. Ambesi-Impiombato F.S. Grollman E.F. Endocrinology. 1984; 114: 1099-1107Crossref PubMed Scopus (184) Google Scholar, 18Ohno M. Zannini M. Levy O. Carrasco N. Di Lauro R. Mol. Cell. Biol. 1999; 19: 2051-2060Crossref PubMed Scopus (214) Google Scholar). I− uptake activity surprisingly persists in membrane vesicles (MV) prepared from FRTL-5 cells that, when intact, have completely lost I− uptake activity due to prolonged TSH deprivation (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar). This suggests that mechanisms other than transcriptional might also operate to regulate NIS activity in response to TSH. Here we provide evidence for post-transcriptional regulation of NIS function by TSH. Our results show for the first time that NIS is a phosphoprotein and that the NIS phosphorylation pattern is regulated by TSH. Furthermore, our data indicate that in the absence of TSH, NIS is redistributed from the plasma membrane to intracellular compartments. This suggests that under TSH deprivation, the loss of I−transport activity in FRTL-5 cells is due to NIS intracellular distribution. Interestingly and contrary to expectations, NIS is overexpressed in some thyroid cancers, notwithstanding their decreased I− uptake activity (20Arturi F. Russo D. Giuffrida D. Schlumberger M. Eur. J. Endocrinol. 2000; 143: 623-627Crossref PubMed Scopus (61) Google Scholar,21Saito T. Endo T. Kawaguchi A. Ikeda M. Katoh R. Kawaio A. Muramatsu A. Onaya T. J. Clin. Invest. 1997; 101: 1296-1300Crossref Google Scholar). 2Dohán, O., Baloch, Z., Banrevi, Z., Livolsi, V., and Carrasco, N. (2001) JCEM 86, in press. 2Dohán, O., Baloch, Z., Banrevi, Z., Livolsi, V., and Carrasco, N. (2001) JCEM 86, in press. Moreover, overexpressed NIS in these cells is predominantly retained intracellularly.2 The intracellular NIS redistribution pattern that we observed in FRTL-5 cells maintained in the absence of TSH resembles that reported in thyroid tumors, underscoring the importance of elucidating the mechanisms that govern the subcellular localization of NIS. FRTL-5 rat thyroid cells, kindly provided by Dr. L. D. Kohn (National Institutes of Health, Bethesda, MD), were grown in Ham's F-12 media (Life Technologies, Inc.) supplemented with 5% calf serum, 1 mm non-essential amino acids (Life Technologies, Inc.), 10 mm glutamine, 100 units/ml penicillin, 100 μg/ml streptomycin, and a six-hormone mixture (6H) containing insulin (1.3 μm), hydrocortisone (1 μm), transferrin (60 pm),l-glycyl-histidyl-lysine (2.5 μm), somatostatin (6.1 nm), and TSH (1 milliunits/ml) as reported previously (23Weiss S.J. Philp N.J. Grollman E.F. Endocrinology. 1984; 114: 1090-1098Crossref PubMed Scopus (333) Google Scholar). Cells were grown in a humidified atmosphere with 5% CO2 the of TSH deprivation, FRTL-5 cells were in the TSH FRTL-5 cells are in for (23Weiss S.J. Philp N.J. Grollman E.F. Endocrinology. 1984; 114: 1090-1098Crossref PubMed Scopus (333) Google Scholar). TSH from the and all other were from for I− transport were prepared as previously (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar). FRTL-5 cells in or were and in mm 1 mm 10 mm containing and phenylmethanesulfonyl fluoride Cells were with a The for and the for 1 The in mm 1 mm 10 mm and in for were prepared as that the in mm 1 mm 10 mm I− transport in cells were with FRTL-5 cells in that were either in or (23Weiss S.J. Philp N.J. Grollman E.F. Endocrinology. 1984; 114: 1090-1098Crossref PubMed Scopus (333) Google Scholar). the cells were with of Hanks' balanced salt solution Cells were with containing activity for in a humidified atmosphere with 5% were by the solution and with by the cells with of and in a in by the (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar). I− uptake expressed as of I− of in FRTL-5 were as (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar). were and containing of protein were for uptake by room temperature with an of a solution containing activity 1 mm 10 mm were the time by the of of mm 1 mm and 1 mm by retained by by in were of and to were as previously O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar). were with and for to were also as O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar) with of antibody and of a were by an and were as previously O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar). FRTL-5 cells in in the or absence of TSH were and for with and supplemented with 5% calf Cells were with for the by and with media supplemented with for the Cells were with in containing and by a with mm mm serum and protein were and for for were with of for by the of a of protein for were for and with mm 1 mm 10 mm with mm 1 mm 10 mm and with 10 mm were for in to were and in were and for in FRTL-5 cells in or as a of a previously S. G. 1997; PubMed Scopus Google Scholar). Cells were grown in to Cells were with with mm and 1 and for with sulfosuccinimidyl-2-(biotinamido)ethyl-1,3-dithiopropionate in mm mm and mm Cells were for with 100 and with in mm mm of mm containing and to as A. were with A were to the and The the for to from the were with A and with mm mm and mm The with mm were in and for FRTL-5 cells in the of TSH were cells were to or for the Cells were with with in for and with Cells were with in for 10 Cells were with mm in for 10 and with Cells were with in for 1 and with of After cells the were an from were with and to in the for and NIS with a with a in as previously G.A. E. J. Biol. Chem. Full Text PDF PubMed Google Scholar). Cells were grown to in and for in of supplemented with 5% calf 100 to the and for Cells were with in containing 10 mm mm mm and 100 and μg/ml μg/ml and mm After NIS to and to NIS by The NIS from the and with as PubMed Scopus Google Scholar). were with in 100 for with and in 100 1 for these of the from the The as previously G.A. E. J. Biol. Chem. Full Text PDF PubMed Google Scholar). were in by for by and were from and cells, were by We I− uptake activity in FRTL-5 cells the of 10 TSH from the and in prepared from these cells are a of vesicles from all subcellular the membrane. reported previously (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar), I− transport activity decreased by in cells of TSH I− transport activity decreased by in 1 TSH I− uptake completely in cells, in it as as of the the reduction of I−uptake in cells due to a in NIS we from these cells to with 1 and we the to NIS O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar). NIS expression decreased to of its of TSH deprivation, NIS expression in 1 I− uptake in cells completely 1 I− transport activity in from cells persists the time is with NIS expression in these cells. NIS is in the absence of TSH, cells that been of TSH for were for 10 with and for NIS and that de novo biosynthesis of NIS when cells were maintained in the of TSH NIS for to 10 TSH deprivation 1 in the absence of de novo NIS biosynthesis that I− uptake observed in from cells is by NIS to TSH The that NIS prolonged TSH deprivation in the absence novo NIS biosynthesis suggests that NIS has a long the half-life of NIS and it is by TSH, cells maintained in the of TSH were with for and for in the or absence of TSH NIS as an The to a that, also by serum The half-life of NIS to be in the and in the absence of TSH This that TSH modulates the long half-life of it by the of TSH NIS the plasma we cell in the of TSH and the of 10 TSH from the that facing the extracellular be we the and plasma The with and with of the the A of the that NIS the plasma membrane decreased time TSH withdrawal in a that with the in NIS activity in cells 1 of TSH deprivation a in both intracellular and cell by TSH withdrawal a in NIS detected the plasma membrane than in intracellular This that TSH regulates the subcellular of NIS. The regulatory role played by TSH in the subcellular of NIS further by of NIS subcellular localization in response to TSH withdrawal a a of NIS the carboxyl cells were and to with the that NIS expression TSH deprivation, were with In the of TSH, FRTL-5 cells predominantly a the of the cells, of plasma membrane localization for NIS days). intracellular also The cell pattern decreased of TSH, completely by which an intracellular pattern The intracellular NIS pattern observed and the In by the NIS decreased and further from the by of the with or when the the first that the observed is for NIS O. Dai G. Riedel C. Ginter C.S. Paul E.M. Lebowitz A.N. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 5568-5573Crossref PubMed Scopus (199) Google Scholar). These are with the that TSH is required for NIS localization the cell the absence of TSH time NIS to to in intracellular compartments. These data the that in to regulating NIS TSH also regulates the subcellular of NIS. In the absence of TSH, novo NIS biosynthesis NIS is from the plasma membrane to intracellular time the The by which TSH regulates the subcellular of NIS is has been to be in and subcellular of S. R.D. 1999; PubMed Scopus Google Scholar, A. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, D. Liu J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus (61) Google Scholar, C. Liu J. J. Biol. 2000; PubMed Scopus Google Scholar, T. S. M. E. J. 2000; PubMed Google Scholar, S.M. G.A. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). NIS has for for protein protein and Furthermore, TSH in the thyroid are by the that phosphorylation might be in the regulation of NIS distribution. FRTL-5 cells were for and NIS with and the to The revealed that NIS of the of TSH in the the decreased expression of NIS in cells, the in these cells than in grown in the of the NIS phosphorylation is by TSH, we in the or absence of TSH, and NIS to with as under The when TSH from that when TSH were in the and in the absence of TSH. these to be to both for and for as by the These results indicate that NIS is a phosphoprotein and that the NIS phosphorylation pattern is by TSH. The regulation of membrane transport is a highly that levels Physiol. Rev. 1999; PubMed Scopus Google Scholar, Physiol. Rev. 1999; PubMed Scopus Google Scholar, J.E. S. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). Here we show that is the for NIS being the that mediates the first step active I− in thyroid hormone a regulatory for TSH, which is the primary hormonal regulatory of thyroid function has long been that TSH thyroidal I− uptake by NIS transcription cAMP (13Weiss S.J. Philp N.J. Ambesi-Impiombato F.S. Grollman E.F. Endocrinology. 1984; 114: 1099-1107Crossref PubMed Scopus (184) Google T. Endo T. Saito T. Miyazaki A. Kawaguchi A. Onaya T. Endocrinology. 1997; 138: 2227-2232Crossref PubMed Scopus (227) Google Scholar, 18Ohno M. Zannini M. Levy O. Carrasco N. Di Lauro R. Mol. Cell. Biol. 1999; 19: 2051-2060Crossref PubMed Scopus (214) Google Scholar). Our provide evidence that TSH also regulates NIS by post-transcriptional our we demonstrated by that NIS is in FRTL-5 cells as as 10 TSH withdrawal 1 and that de novo NIS biosynthesis TSH it is that NIS detected in FRTL-5 cells to be to TSH This is with NIS being a protein with an long as suggested previously T. Endo T. Saito T. Miyazaki A. Kawaguchi A. Onaya T. Endocrinology. 1997; 138: 2227-2232Crossref PubMed Scopus (227) Google Scholar, A. F. S. B. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). by we that NIS half-life is in the and in the absence of TSH the NIS half-life in the absence of TSH is than in the of the it is long to for the of I− uptake activity in from cells of TSH the of activity that first to the that NIS might be regulated (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar), a further by T. Endo T. Saito T. Miyazaki A. Kawaguchi A. Onaya T. Endocrinology. 1997; 138: 2227-2232Crossref PubMed Scopus (227) Google Scholar, A. F. S. B. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). In addition, it has been (14Kogai T. Curcio F. Hyman S. Cornford E.M. Brent G.A. Hershman J.M. J. Endocrinol. 2000; 167: 125-135Crossref PubMed Scopus (72) Google Scholar) that TSH NIS and protein levels in both and human primary of I− uptake is observed in that NIS may be regulated by such post-transcriptional events as subcellular distribution. are by post-transcriptional regulation of their to the plasma membrane by from the plasma membrane to intracellular D. J. Physiol. 2000; Google Scholar, R.D. 2000; PubMed Scopus Google Scholar). the J.E. S. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar) is targeted to the plasma membrane in response to the is in the of its S. R.D. 1999; PubMed Scopus Google Scholar). it that regulation of the subcellular of NIS might also be a in I− We have a NIS plasma membrane and NIS activity that the loss of NIS activity TSH withdrawal is due to a in the of NIS the cell Furthermore, we observed that TSH deprivation, intracellular NIS a than plasma membrane NIS A These data the that active NIS in the plasma membrane TSH is are redistributed to intracellular in response to TSH withdrawal the of de novo NIS and the reduction of the NIS This model the of NIS activity in from cells of TSH that, when intact, NIS TSH regulates I− uptake by the subcellular of the intrinsic of the NIS as previously (19Kaminsky S.M. Levy O. Salvador C. Dai G. Carrasco N. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3789-3793Crossref PubMed Scopus (95) Google Scholar). In TSH NIS transcription and it is also required for targeting NIS to it the plasma membrane. might these The by which TSH regulates NIS to be NIS for the protein protein and We have observed that NIS is and that the NIS phosphorylation pattern when cells are in the as to the absence of TSH This that TSH modulates NIS that phosphorylation has been reported to play a role in regulating targeting of other such as the S. R.D. 1999; PubMed Scopus Google Scholar), D. Liu J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus (61) Google Scholar), C. Liu J. J. Biol. 2000; PubMed Scopus Google Scholar), A. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), T. S. M. E. J. 2000; PubMed Google Scholar), and S.M. G.A. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), it be of to NIS phosphorylation a role in NIS targeting as The regulatory a key in the TSH and the thyroid the TSH NIS by mechanisms transcriptional and to of I− uptake in thyroid hormone and a in thyroid hormone levels TSH in the and I−uptake in the The results are highly to thyroid is of major diagnostic importance that thyroid cancers decreased I− uptake to the (11Martino E. Bartalena L. Pinchera A. Braverman L.E. Utiger R.D. The Thyroid: A Fundamental and Clinical Text. 8th Ed. J. B. Lippincott, Philadelphia2000: 762-773Google Scholar). the of thyroid cancer cells to transport I− is the for radioiodide therapy to be against thyroid cells or of the in I− uptake observed in thyroid it long been that NIS expression be decreased in thyroid cancer cells. NIS has surprisingly been in thyroid cancers to be overexpressed retained intracellularly.2 This suggests that of thyroid cells with the of NIS to the plasma membrane. we have also observed both plasma membrane and intracellular NIS expression in cancer (1Tazebay U.H. Wapnir I.L. Levy O. Dohan O. Zuckier L.S. Zhao Q.H. Deng H.F. Amenta P.S. Fineberg S. Pestell R.G. Carrasco N. Nat. Med. 2000; 6: 871-878Crossref PubMed Scopus (414) Google Scholar). The the post-transcriptional mechanisms in the regulation of NIS by TSH. These are some of the mechanisms that may be in thyroid Whereas have to NIS transcription in thyroid cancer C. J. 2000; PubMed Scopus Google Scholar, M. R. J. Clin. Endocrinol. PubMed Scopus Google Scholar), our indicate that an of the regulatory of NIS and is for the development of to the I−transport of thyroid cancers and increase the of radioiodide therapy in these We are A. De la O. M. and A. for their and of the We J. and G. for and with phosphorylation We also M. E. B. C. and A. for of the