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CARRASCO
Expression of the Na+/I- symporter (NIS) is markedly decreased or absent in gastric cancer and intestinal metaplastic mucosa of Barrett esophagusAltorjay A, Dohán O, Szilágyi A, Paroder M, Irene L. Wapnir IL, Carrasco N BMC Cancer 2007, 7:5.
" Background: The sodium/iodide symporter (NIS) is a plasma membrane glycoprotein that mediates iodide (I-) transport in the thyroid, lactating breast, salivary glands, and stomach. Whereas NIS expression and regulation have been extensively investigated in healthy and neoplastic thyroid and breast tissues, little is known about NIS expression and function along the healthy and diseased gastrointestinal tract.
Methods: Thus, we investigated NIS expression by immunohistochemical analysis in 155 gastrointestinal tissue samples and by immunoblot analysis in 17 gastric tumors from 83 patients.
Results: Regarding the healthy GI tract, we observed NIS expression exclusively in the basolateral region of the gastric mucin-producing epithelial cells. In gastritis, positive NIS staining was observed in these cells both in the presence and absence of Helicobacter pylori. Significantly, NIS expression was absent in gastric cancer, independently of its histological type. Only focal faint NIS expression was detected in the direct vicinity of gastric tumors, i.e., in the histologically intact mucosa, the expression becoming gradually stronger and linear farther away from the tumor. Barrett mucosa with junctional and fundic-type columnar metaplasia displayed positive NIS staining, whereas Barrett mucosa with intestinal metaplasia was negative. NIS staining was also absent in intestinalized gastric polyps.
Conclusions: That NIS expression is markedly decreased or absent in case of intestinalization or malignant transformation of the gastric mucosa suggests that NIS may prove to be a significant tumor marker in the diagnosis and prognosis of gastric malignancies and also precancerous lesions such as Barrett mucosa, thus extending the medical significance of NIS beyond thyroid disease."
Hydrocortisone and purinergic signaling stimulate sodium/iodide symporter (NIS)-mediated iodide transport in breast cancer cells.Dohan O, De la Vieja A, Carrasco N. Mol Endocrinol. 2006 May;20(5):1121-37. Epub 2006 Jan 26.
"The sodium/iodide symporter (NIS) mediates a remarkably effective targeted radioiodide therapy in thyroid cancer; this approach is an emerging candidate for treating other cancers that express NIS, whether endogenously or by exogenous gene transfer. Thus far, the only extrathyroidal malignancy known to express functional NIS endogenously is breast cancer. Therapeutic efficacy in thyroid cancer requires that radioiodide uptake be maximized in tumor cells by manipulating well-known regulatory factors of NIS expression in thyroid cells, such as TSH, which stimulates NIS expression via cAMP. Similarly, therapeutic efficacy in breast cancer will likely depend on manipulating NIS regulation in mammary cells, which differs from that in the thyroid. Human breast adenocarcinoma MCF-7 cells modestly express endogenous NIS when treated with all-trans-retinoic acid (tRa). We report here that hydrocortisone and ATP each markedly stimulates tRa-induced NIS protein expression and plasma membrane targeting in MCF-7 cells, leading to at least a 100% increase in iodide uptake. Surprisingly, the adenyl cyclase activator forskolin, which promotes NIS expression in thyroid cells, markedly decreases tRa-induced NIS protein expression in MCF-7 cells. Isobutylmethylxanthine increases tRa-induced NIS expression in MCF-7 cells, probably through a purinergic signaling system independent of isobutylmethylxanthine's action as a phosphodiesterase inhibitor. We also observed that neither iodide, which at high concentrations down-regulates NIS in the thyroid, nor cAMP has a significant effect on NIS expression in MCF-7 cells. Our findings may open new strategies for breast-selective pharmacological modulation of functional NIS expression, thus improving the feasibility of using radioiodide to effectively treat breast cancer."
Thyroidal iodide transport and thyroid cancer.Dohan O, Carrasco N. Cancer Treat Res. 2004;122:221-36. Review. [citation only]
The Na/I symporter (NIS): imaging and therapeutic applications.Dadachova E, Carrasco N. Semin Nucl Med. 2004 Jan;34(1):23-31. Review [abstract only]
"The Na(+)/I(-) symporter
(NIS) is the plasma membrane glycoprotein that mediates the active
uptake of I(-) in the thyroid, ie, the crucial first step in thyroid
hormone biosynthesis. NIS also mediates I(-) uptake in other tissues,
such as salivary glands, gastric mucosa, and lactating (but not
nonlactating) mammary gland. The ability of thyroid cancer cells to
actively transport I(-) via NIS provides a unique and effective
delivery system to detect and target these cells for destruction with
therapeutic doses of radioiodide. Breast cancer is the only malignancy
other than thyroid cancer to have been shown to functionally express
NIS endogenously. The considerable potential diagnostic and
therapeutic use of radioiodide in breast cancer is currently being
assessed. On the other hand, exogenous NIS gene transfer has
successfully been carried out into a variety of other cell lines and
tumors, including A375 human melanoma tumors, and SiHa cervix cancer,
human glioma, and hepatoma cell lines. Most notably, significant
radioiodine therapy results have been obtained in the NIS-transfected
human prostatic adenocarcinoma cell line LNCaP and in NIS-transfected
myeloma cells, both of which exhibited prolonged retention of radio
iodide even in the absence of I(-) organification. The therapeutic
potential of alternative NIS-transported radioisotopes with different
decay properties and a shorter, physical half-life than 131I(-), such
as beta-emitter 188Rhenium (188ReO(4)-) and alpha-emitter 211Astatine
(211At(-)), has been evaluated. In conclusion, it is clear that the
remarkable progress made in the last few years in the molecular
characterization of NIS has created new opportunities for the
development of diagnostic and therapeutic applications for NIS in
nuclear medicine."
The Na+/I- symporter mediates iodide uptake in breast cancer metastases and can be selectively down-regulated in the thyroid.Wapnir IL, Goris M, Yudd A, Dohan O, Adelman D, Nowels K, Carrasco N. Clin Cancer Res. 2004 Jul 1;10(13):4294-302.
"PURPOSE: The Na(+)/I(-) symporter (NIS) is a key plasma membrane protein that mediates active iodide (I(-)) transport in the thyroid, lactating breast, and other tissues. Functional NIS expression in thyroid cancer accounts for the longstanding success of radioactive iodide ((131)I) ablation of metastases after thyroidectomy. Breast cancer is the only other cancer demonstrating endogenous functional NIS expression. Until now, NIS activity in breast cancer metastases (BCM) was unproven.
EXPERIMENTAL DESIGN: Twenty-seven women were scanned with (99m)TcO(4)(-) or (123)I(-) to assess NIS activity in their metastases. An (131)I dosimetry study was offered to patients with I(-)-accumulating tumors. Selective down-regulation of thyroid NIS was tested in 13 patients with T(3) and in one case with T(3) + methimazole (MMI; blocks I(-) organification). NIS expression was evaluated in index and/or metastatic tumor samples by immunohistochemistry.
RESULTS: I(-) uptake was noted in 25% of NIS-expressing tumors (two of eight). The remaining cases did not show NIS expression or activity. Thyroid I(-) uptakes were decreased to </=2.8% at 24 h in T(3)-treated patients and 1/100 normal with T(3)/MMI. Uptake (2.9%) was calculated in a peribronchial metastasis on (131)I dosimetry scans at 4 h with disappearance of the signal by 24 h. We estimated a therapeutic dose of 3000 cGy could be achieved in this metastasis with 100 mCi of (131)I if the tumor exhibited the same dynamics as the T(3)/MMI-suppressed thyroid.
CONCLUSIONS: This is the first article of in vivo, scintigraphically detected, NIS-mediated I(-) accumulation in human BCM. T(3)/MMI down-regulation of thyroid NIS makes (131)I-radioablation of BCM possible with negligible thyroid uptake and radiation damage."
Kinetics of perrhenate uptake and comparative biodistribution of perrhenate, pertechnetate, and iodide by NaI symporter-expressing tissues in vivo.Zuckier LS, Dohan O, Li Y, Chang CJ, Carrasco N, Dadachova E. J Nucl Med. 2004 Mar;45(3):500-7.
"Pertechnetate (as (99m)TcO(4)(-)), (123)I(-), and (131)I(-) have a long and successful history of use in the diagnosis and therapy of thyroid cancer, with uptake into thyroid tissue mediated by the sodium-iodide symporter (NIS). NIS has also emerged as a potential target for radiotherapy of nonthyroid malignancies that express the endogenous or transfected symporter. Perrhenates (as (188)ReO(4)(-) and (186)ReO(4)(-)) are promising therapeutic substrates of NIS, although less is known about their behavior in vivo. In this study, we endeavored to characterize the biologic behavior of perrhenate, especially in relation to iodide and pertechnetate, to better explore its possible therapeutic role. METHODS: We describe the simultaneous biodistribution and uptake in vivo of iodide, pertechnetate, and perrhenate in groups of healthy CD1 mice, either with or without coadministration of perchlorate (ClO(4)(-)), a potent NIS inhibitor. Animals administered single radiopharmaceuticals were imaged as a means of illustrating these findings. Kinetic properties of perrhenate were compared with those of iodide in a stably transfected NIS-bearing Madin-Darby canine kidney (MDCK) cell line. RESULTS: Biodistributions of iodide, pertechnetate, and perrhenate in live mice were remarkably similar. Activity in salivary gland and stomach was severalfold greater than in blood, remained elevated over the initial 2 h, and subsequently washed out. A similar pattern characterized pertechnetate and perrhenate uptake by the thyroid, in which the 2-h concentration was slightly more elevated than at the 20-min time point. However, uptake subsequently decreased by 19 h. In contrast, iodide continued to increase through the 19-h time point, presumably as a result of organification. The addition of perchlorate sharply decreased uptake of all 3 radiopharmaceuticals by the stomach, salivary glands, and thyroid and resulted in their rapid clearance, paralleling blood-pool clearance. In tissues that do not express NIS (liver, muscle, spleen), uptake of all 3 radiopharmaceuticals was low and rapidly decreased over time, paralleling blood-pool clearance. Similar findings were seen in kidney, where only minimal amounts of NIS are expressed in tubular cells. In stably transfected MDCK cells, steady-state accumulation of iodide was approximately 4-fold higher than that of perrhenate at 30 min. No active transport was demonstrated in nontransfected MDCK cell lines or after perchlorate administration. Uptake values measured at different concentrations of substrate demonstrated saturation kinetics. Apparent maximal velocity values for perrhenate and iodide were 25.6 +/- 1.4 and 106 +/- 3.2 pmol/ micro g, respectively, and corresponding affinity constant values were 4.06 +/- 0.87 and 24.6 +/- 1.81 micro mol/L. CONCLUSION: Perrhenate is avidly taken up by NIS in a manner similar to iodide and pertechnetate in vivo, with the exception of organification of iodide by the thyroid. By more fully appreciating the behavior of perrhenate, especially in relation to iodide and pertechnetate, we can better realize its potential role in the diagnosis and therapy of NIS-bearing tissues."
The Q267E mutation in the sodium/iodide symporter (NIS) causes congenital iodide transport defect (ITD) by decreasing the NIS turnover number.De La Vieja A, Ginter CS, Carrasco N. J Cell Sci. 2004 Feb 15;117(Pt 5):677-87. Epub 2004 Jan 20.
"The Na(+)/I(-) symporter (NIS) is a key plasma membrane glycoprotein that mediates active iodide (I(-)) transport in the thyroid and other tissues. Since isolation of the cDNA encoding NIS (G. Dai, O. Levy, and N. Carrasco (1996) Nature 379, 458-460), ten mutations in NIS have been identified as causes of congenital iodide transport defect (ITD). Two of these mutations (T354P and G395R) have been thoroughly characterized at the molecular level. Both mutant NIS proteins are inactive but normally expressed and correctly targeted to the plasma membrane. The hydroxyl group at the beta-carbon of residue 354 is essential for NIS function, whereas the presence of a charged or large side-chain at position 395 interferes with NIS function. We report the extensive molecular analysis of the Q267E mutation in COS-7 cells transfected with rat or human Q267E NIS cDNA constructs. We used site-directed mutagenesis to engineer various residue substitutions into position 267. In contrast to previous suggestions that Q267E NIS was inactive, possibly because of a trafficking defect, we conclusively show that Q267E NIS is modestly active and properly targeted to the plasma membrane. Q267E NIS exhibited lower V(max) values for I(-) than wild-type NIS, suggesting that the decreased level of activity of Q267E NIS is due to a lower catalytic rate. That Q267E NIS retains even partial activity sets this ITD-causing mutant apart from T354P and G395R NIS. The presence of charged residues (of any polarity) other than Glu at position 267 rendered NIS inactive without affecting its expression or targeting, but substitution with neutral residues at this position was compatible with partial activity."
The sodium/iodide Symporter (NIS): characterization, regulation, and medical significance.Dohan O, De la Vieja A, Paroder V, Riedel C, Artani M, Reed M, Ginter CS, Carrasco N. Endocr Rev. 2003 Feb;24(1):48-77. Review.
"The Na(+)/I(-) symporter (NIS) is an integral plasma membrane glycoprotein that mediates active I(-) transport into the thyroid follicular cells, the first step in thyroid hormone biosynthesis. NIS-mediated thyroidal I(-) transport from the bloodstream to the colloid is a vectorial process made possible by the selective targeting of NIS to the basolateral membrane. NIS also mediates active I(-) transport in other tissues, including salivary glands, gastric mucosa, and lactating mammary gland, in which it translocates I(-) into the milk for thyroid hormone biosynthesis by the nursing newborn. NIS provides the basis for the effective diagnostic and therapeutic management of thyroid cancer and its metastases with radioiodide. NIS research has proceeded at an astounding pace after the 1996 isolation of the rat NIS cDNA, comprising the elucidation of NIS secondary structure and topology, biogenesis and posttranslational modifications, transcriptional and posttranscriptional regulation, electrophysiological analysis, isolation of the human NIS cDNA, and determination of the human NIS genomic organization. Clinically related topics include the analysis of congenital I(-) transport defect-causing NIS mutations and the role of NIS in thyroid cancer. NIS has been transduced into various kinds of cancer cells to render them susceptible to destruction with radioiodide. Most dramatically, the discovery of endogenous NIS expression in more than 80% of human breast cancer samples has raised the possibility that radioiodide may be a valuable novel tool in breast cancer diagnosis and treatment."
Advances in Na(+)/I(-) symporter (NIS) research in the thyroid and beyond.Dohan O, Carrasco N. Mol Cell Endocrinol. 2003 Dec 31;213(1):59-70. Review. [abstract only]
"The Na(+)/I(-) symporter (NIS) is a plasma membrane glycoprotein that mediates active iodide uptake in the thyroid-the essential first step in thyroid hormone biosynthesis-and in other tissues, such as salivary and lactating mammary glands. Thyroidal radioiodide uptake has been used for over 60 years in the diagnosis and effective treatment of thyroid cancer and other diseases. However, the NIS cDNA was only isolated in 1996 by expression cloning in Xenopus laevis oocytes, marking the beginning of the molecular characterization of NIS and the study of its regulation, both in the thyroid and other tissues. One of the most exciting current areas of NIS research-radioiodide treatment of extrathyroidal cancers-was launched by the discovery of functional expression of endogenous NIS in breast cancer and by the ectopic transfer of the NIS gene into otherwise non NIS-expressing cancers. This review summarizes the main findings in NIS research, emphasizing the most recent developments."
Immunohistochemical profile of the sodium/iodide symporter in thyroid, breast, and other carcinomas using high density tissue microarrays and conventional sections.Wapnir IL, van de Rijn M, Nowels K, Amenta PS, Walton K, Montgomery K, Greco RS, Dohan O, Carrasco N. J Clin Endocrinol Metab. 2003 Apr;88(4):1880-8.
"Extrathyroidal cancers could potentially be targeted with (131)I, if the Na(+)/I(-) symporter (NIS) were functional. Using immunohistochemical methods we probed 1278 human samples with anti-NIS antibody, including 253 thyroid and 169 breast conventional whole tissue sections (CWTS). Four high density tissue microarrays containing a wide variety of breast lesions, normal tissues, and carcinoma cores were tested. The results of the normal microarray were corroborated in 50 CWTS. Nineteen of 34 normal tissues, including bladder, colon, endometrium, kidney, prostate, and pancreas, expressed NIS. Nineteen of 25 carcinomas demonstrated NIS immunopositivity; 55.7% of 479 carcinoma microarray cores expressed NIS, including prostate (74%), ovary (73%), lung (65%), colon (62.6%), and endometrium (56%). NIS protein was present in 75% benign thyroid lesions, 73% thyroid cancers, 30% normal-appearing, peritumoral breasts, 88% ductal carcinomas in situ, and 76% invasive breast carcinoma CWTS. Comparatively, breast microarray cores had lower immunoreactivity. Plasma membrane immunopositivity was confirmed in thyrocytes, salivary ductal, gastric mucosa, and lactating mammary cells. In other tissues, immunoreactivity was predominantly intracellular, particularly in malignant lesions. Thus, NIS is present in many normal epithelial tissues and is predominantly expressed intracellularly in many carcinomas. Elucidating the regulatory mechanisms that render NIS functional in extrathyroidal carcinomas may make (131)I therapy feasible."
Rapid communication: predominant intracellular overexpression of the Na(+)/I(-) symporter (NIS) in a large sampling of thyroid cancer cases.Dohan O, Baloch Z, Banrevi Z, Livolsi V, Carrasco N. J Clin Endocrinol Metab. 2001 Jun;86(6):2697-700.
"Here we report the
analysis of the Na(+)/I(-) symporter (NIS) protein expression in 57
thyroid cancer samples by immunohistochemistry with high-affinity
anti-NIS Abs. As many as 70% of these samples exhibited increased NIS
expression with respect to the normal surrounding thyroid tissue. Most
significantly, NIS was located in these samples either in both the
plasma membrane and intracellular compartments simultaneously, or
exclusively in intracellular compartments. This suggests that NIS is
clearly expressed or even overexpressed in most thyroid cancer cells,
but malignant transformation in some of these cells interferes either
with the proper targeting of NIS to the plasma membrane, or with the
mechanisms that retain NIS in the plasma membrane after it has been
targeted. The results further indicate that, in addition to indicating
NIS expression in cases where it is absent (approximately 30%),
improvements in (131)I radioablation therapy might result from
promoting targeting of NIS to the plasma membrane in the majority
(approximately 70%) of thyroid cancers."
Post-transcriptional regulation of the sodium/iodide symporter by thyrotropin.Riedel C, Levy O, Carrasco N. J Biol Chem. 2001 Jun 15;276(24):21458-63. Epub 2001 Apr 4.
"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 ( approximately 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 mammary gland iodide transporter is expressed during lactation and in breast cancer.Tazebay UH, Wapnir IL, Levy O, Dohan O, Zuckier LS, Zhao QH, Deng HF, Amenta PS, Fineberg S, Pestell RG, Carrasco N. Nat Med. 2000 Aug;6(8):871-8.
"The sodium/iodide symporter mediates active iodide transport in both healthy and cancerous thyroid tissue. By exploiting this activity, radioiodide has been used for decades with considerable success in the detection and treatment of thyroid cancer. Here we show that a specialized form of the sodium/iodide symporter in the mammary gland mediates active iodide transport in healthy lactating (but not in nonlactating) mammary gland and in mammary tumors. In addition to characterizing the hormonal regulation of the mammary gland sodium/iodide symporter, we demonstrate by scintigraphy that mammary adenocarcinomas in transgenic mice bearing Ras or Neu oncogenes actively accumulate iodide by this symporter in vivo. Moreover, more than 80% of the human breast cancer samples we analyzed by immunohistochemistry expressed the symporter, compared with none of the normal (nonlactating) samples from reductive mammoplasties. These results indicate that the mammary gland sodium/iodide symporter may be an essential breast cancer marker and that radioiodide should be studied as a possible option in the diagnosis and treatment of breast cancer."
Thyroid Iodide Transport: The Na+/I- Symporter (NIS)Carrasco N in Braverman LE, Utiger RD, The Thyroid, 8th ed. 2000, pp 52-61.
"The ability of thyroid follicular cells to concentrate I- was first reported as early as 1915. The thyroid gland was found to be capable of concentrating I- by a factor of 20- to 40-fold with respect to its concentration in the plasma under physiologic conditions. Hence the existence of a thyroid I- transporter was inferred, and some of its properties were elucidated over the years. I- accumulation in the thyroid has long been shown to be an active transport process that occurs against the I- electrochemical gradient, stimulated by thyrotropin (thyroid-stimulating hormone; TSH), and blocked by the well-known classic competitive inhibitors, the anions thiocyanate and perchlorate. Eventually, it was determined that the thyroid I- transporter is a Na+/I- symporter (NIS), i.e., an intrinsic plasma membrane transport protein that couples the inward "downhill" translocation of Na+ to the inward "uphill" translocation of I-. The driving force for the process is the inwardly directed Na+ gradient generated by the Na+/K+ adenosine triphosphatase (ATPase).... No molecular information on NIS was available until 1996, when after a decades-long search by numerous investigators, a complementary DNA (cDNA) encoding rat NIS was finally isolated."
Molecular analysis of the sodium/iodide symporter: impact on thyroid and extrathyroid pathophysiology.De La Vieja A, Dohan O, Levy O, Carrasco N. Physiol Rev. 2000 Jul;80(3):1083-105. Review.
"The Na(+)/I(-) symporter (NIS) is an intrinsic membrane protein that mediates the active transport of iodide into the thyroid and other tissues, such as salivary glands, gastric mucosa, and lactating mammary gland. NIS plays key roles in thyroid pathophysiology as the route by which iodide reaches the gland for thyroid hormone biosynthesis and as a means for diagnostic scintigraphic imaging and for radioiodide therapy in hyperthyroidism and thyroid cancer. The molecular characterization of NIS started with the 1996 isolation of a cDNA encoding rat NIS and has since continued at a rapid pace. Anti-NIS antibodies have been prepared and used to study NIS topology and its secondary structure. The biogenesis and posttranslational modifications of NIS have been examined, a thorough electrophysiological analysis of NIS has been conducted, the cDNA encoding human NIS (hNIS) has been isolated, the genomic organization of hNIS has been elucidated, the regulation of NIS by thyrotropin and I(-) has been analyzed, the regulation of NIS transcription has been studied, spontaneous NIS mutations have been identified as causes of congenital iodide transport defect resulting in hypothyroidism, the roles of NIS in thyroid cancer and thyroid autoimmune disease have been examined, and the expression and regulation of NIS in extrathyroidal tissues have been investigated. In gene therapy experiments, the rat NIS gene has been transduced into various types of human cells, which then exhibited active iodide transport and became susceptible to destruction with radioiodide. The continued molecular analysis of NIS clearly holds the potential of an even greater impact on a wide spectrum of fields, ranging from structure/function of transport proteins to the diagnosis and treatment of cancer, both in the thyroid and beyond."
Escape from the acute Wolff-Chaikoff effect is associated with a decrease in thyroid sodium/iodide symporter messenger ribonucleic acid and protein.Eng PH, Cardona GR, Fang SL, Previti M, Alex S, Carrasco N, Chin WW, Braverman LE. Endocrinology. 1999 Aug;140(8):3404-10.
"In 1948, Wolff and Chaikoff reported that organic binding of iodide in the thyroid was decreased when plasma iodide levels were elevated (acute Wolff-Chaikoff effect), and that adaptation or escape from the acute effect occurred in approximately 2 days, in the presence of continued high plasma iodide concentrations. We later demonstrated that the escape is attributable to a decrease in iodide transport into the thyroid, lowering the intrathyroidal iodine content below a critical inhibitory threshold and allowing organification of iodide to resume. We have now measured the rat thyroid sodium/iodide symporter (NIS) messenger RNA (mRNA) and protein levels, in response to both chronic and acute iodide excess, in an attempt to determine the mechanism responsible for the decreased iodide transport. Rats were given 0.05% NaI in their drinking water for 1 and 6 days in the chronic experiments, and a single 2000-microg dose of NaI i.p. in the acute experiments. Serum was collected for iodine and hormone measurements, and thyroids were frozen for subsequent measurement of NIS, TSH receptor, thyroid peroxidase (TPO), thyroglobulin, and cyclophilin mRNAs (by Northern blotting) as well as NIS protein (by Western blotting). Serum T4 and T3 concentrations were significantly decreased at 1 day in the chronic experiments and returned to normal at 6 days, and were unchanged in the acute experiments. Serum TSH levels were unchanged in both paradigms. Both NIS mRNA and protein were decreased at 1 and 6 days after chronic iodide ingestion. NIS mRNA was decreased at 6 and 24 h after acute iodide administration, whereas NIS protein was decreased only at 24 h. TPO mRNA was decreased at 6 days of chronic iodide ingestion and 24 h after acute iodide administration. There were no iodide-induced changes in TSH receptor and thyroglobulin mRNAs. These data suggest that iodide administration decreases both NIS mRNA and protein expression, by a mechanism that is likely to be, at least in part, transcriptional. Our findings support the hypothesis that the escape from the acute Wolff-Chaikoff effect is caused by a decrease in NIS, with a resultant decreased iodide transport into the thyroid. The observed decrease in TPO mRNA may contribute to the iodine-induced hypothyroidism that is common in patients with Hashimoto's thyroiditis."
The Na+/I- symporter (NIS): recent advances.Levy O, De la Vieja A, Carrasco N. J Bioenerg Biomembr. 1998 Apr;30(2):195-206. Review.
"The Na+/I- symporter (NIS) catalyzes the accumulation of iodide into thyroid cells, an essential step in the biosynthesis of thyroid hormones. As a result of the isolation of the rat NIS cDNA, steadfast advances in the study of NIS at the molecular level have resulted in the following accomplishments: generation of high-affinity anti-NIS antibodies, elucidation of NIS stoichiometry and specificity by electrophysiological analysis, biochemical and immunological experimental testing of the proposed NIS secondary structure model, monitoring the regulation of NIS protein expression by thyroid stimulating hormone and iodide, characterization of the rat NIS gene promoter, isolation of the cDNA clone encoding human NIS and subsequent determination of human NIS genomic organization, description of NIS mutations in patients with congenital lack of iodide transport, and the molecular identification of NIS in extrathyroidal tissues."
N-linked glycosylation of the thyroid Na+/I- symporter (NIS). Implications for its secondary structure model.Levy O, De la Vieja A, Ginter CS, Riedel C, Dai G, Carrasco N. J Biol Chem.
1998 Aug 28;273(35):22657-63. "The Na+/I- symporter (NIS), a 618-amino acid membrane glycoprotein that catalyzes the active accumulation of I- into thyroid cells, was identified and characterized at the molecular level in our laboratory (Dai, G., Levy, O., and Carrasco, N. (1996) Nature 379, 458-460). Because mature NIS is highly glycosylated, it migrates in SDS-polyacrylamide gel electrophoresis as a broad polypeptide of higher molecular mass (approximately 90-110 kDa) than nonglycosylated NIS (approximately 50 kDa). Using site-directed mutagenesis, we substituted both separately and simultaneously the asparagine residues in all three putative N-linked glycosylation consensus sequences of NIS with glutamine and assessed the effects of the mutations on function and stability of NIS in COS cells. All mutants were active and displayed 50-90% of wild-type NIS activity, including the completely nonglycosylated triple mutant. This demonstrates that to a considerable extent, function and stability of NIS are preserved in the partial or even total absence of N-linked glycosylation. We also found that Asn225 is glycosylated, thus proving that the hydrophilic loop that contains this amino acid residue faces the extracellular milieu rather than the cytosol as previously suggested. We demonstrated that the NH2 terminus faces extracellularly as well. A new secondary structure model consistent with these findings is proposed."
Identification of a structural requirement for thyroid Na+/I- symporter (NIS) function from analysis of a mutation that causes human congenital hypothyroidism.Levy O, Ginter CS, De la Vieja A, Levy D, Carrasco N. FEBS Lett. 1998 Jun 5;429(1):36-40. [abstract only]
"Patients with congenital lack of I transport do not accumulate I in their thyroids, often resulting in severe hypothyroidism. A single amino acid substitution in the thyroid Na+/I- symporter (NIS), proline replacing threonine at position 354 (T354P), was recently identified as the cause of this condition in two independent patients. Here we report that the lack of I- transport activity in T354P NIS generated by site-directed mutagenesis, is not due to a structural change induced by proline, but rather to the absence of a hydroxyl group at the beta-carbon of the amino acid residue at position 354. Hence, this hydroxyl group is essential for NIS function."
Thyroid Na+/I- symporter. Mechanism, stoichiometry, and specificity.Eskandari S, Loo DD, Dai G, Levy O, Wright EM, Carrasco N. J Biol Chem. 1997 Oct 24;272(43):27230-8.
"The rat thyroid Na+/I- symporter (NIS) was expressed in Xenopus laevis oocytes and characterized using electrophysiological, tracer uptake, and electron microscopic methods. NIS activity was found to be electrogenic and Na+-dependent (Na+ >> Li+ >> H+). The apparent affinity constants for Na+ and I- were 28 +/- 3 mM and 33 +/- 9 microM, respectively. Stoichiometry of Na+/anion cotransport was 2:1. NIS was capable of transporting a wide variety of anions (I-, ClO3-, SCN-, SeCN-, NO3-, Br-, BF4-, IO4-, BrO3-, but perchlorate (ClO4-) was not transported. In the absence of anion substrate, NIS exhibited a Na+-dependent leak current (approximately 35% of maximum substrate-induced current) with an apparent Na+ affinity of 74 +/- 14 mM and a Hill coefficient (n) of 1. In response to step voltage changes, NIS exhibited current transients that relaxed with a time constant of 8-14 ms. Presteady-state charge movements (integral of the current transients) versus voltage relations obey a Boltzmann relation. The voltage for half-maximal charge translocation (V0.5) was -15 +/- 3 mV, and the apparent valence of the movable charge was 1. Total charge was insensitive to [Na+]o, but V0.5 shifted to more negative potentials as [Na+]o was reduced. NIS charge movements are attributed to the conformational changes of the empty transporter within the membrane electric field. The turnover rate of NIS was >/=22 s-1 in the Na+ uniport mode and >/=36 s-1 in the Na+/I- cotransport mode. Transporter density in the plasma membrane was determined using freeze-fracture electron microscopy. Expression of NIS in oocytes led to a approximately 2. 5-fold increase in the density of plasma membrane protoplasmic face intramembrane particles. On the basis of the kinetic results, we propose an ordered simultaneous transport mechanism in which the binding of Na+ to NIS occurs first."
Moderate doses of iodide in vivo inhibit cell proliferation and the expression of thyroperoxidase and Na+/I- symporter mRNAs in dog thyroid.Uyttersprot N, Pelgrims N, Carrasco N, Gervy C, Maenhaut C, Dumont JE, Miot F. Mol Cell Endocrinol. 1997 Aug 8;131(2):195-203. [abstract only]
"The function and the growth of adult thyroid gland is controlled by the opposite actions of thyrotropin (TSH) and iodide, the main substrate of the gland. Iodide deprivation leads to stimulation of the thyroid, improving the efficiency of iodide transport for hormone biosynthesis. We have investigated cell proliferation and thyroid specific gene expression 24 and 48 h after administering KI to dogs previously treated with goitrogens and perchlorate. In the hypothyroid dogs T3 and T4 serum levels decreased from 53 +/- 4 to < 30 ng/dl and from 1.6 +/- 0.6 to < 1 microg/dl respectively; TSH concentration increased from 0.16 +/- 0.02 to 2.7 +/- 0.4 ng/ml. After a 24 h moderate KI treatment (300 microg KI/dog of +/- 10 kg) serum T3 concentrations rose higher than the initial normal values, while T4 concentrations increased to reach values equivalent to the normal level. The high TSH concentration did not change significantly. The hyperplasia of the chronically stimulated thyroid resulting from goitrogens/NaClO4 treatment was not modified by this short term treatment with KI. In contrast, KI decreased the weight of the total gland and the level of cell proliferation, as determined by the fraction of cells incorporating BrdU. The effect of acute administration of KI on the expression of four major thyroid genes, the TSH receptor (TSHr), thyroglobulin (Tg), thyroperoxidase (TPO), and Na+/I- symporter (NIS) was analyzed by Northern blot. Tg, TPO and NIS mRNA expressions were up-regulated by chronic stimulation. The expression of the mRNAs of TSHr and Tg did not significantly differ between hyperstimulated and KI-treated dogs while TPO and NIS mRNA expression decreased after a 48 h KI treatment. TPO and NIS are therefore the only of these four genes whose expression is acutely modulated by iodide in vivo. Under TSH stimulation low doses of iodide resulted in: (1) decreased cell proliferation, (2) reestablished synthesis and secretion of thyroid hormones, (3) diminished TPO and NIS mRNA expression. Notably low doses of iodide under the same conditions had no effect on Tg and TSHr mRNA expression."
The Mediator of Thyroidal Iodide Accumulation: The Sodium/Iodide SymporterDai G, Levy O, Amzel LM, Carrasco N Handbook of Biological Physics, Volume 2, edited by W.N. Konings, H.R. Kaback and J.S. Lolkema. 1996 Elsevier Science B.V.
"The Na+/I– symporter (NIS) is a key plasma membrane protein that catalyzes the active accumulation of iodide (I–) in the thyroid gland, i.e. the first and critical rate-limiting step in the biosynthesis of the thyroid hormones [1,2]. NIS is located in the basolateral membrane of the hormone-producing thyroid follicular cells or thyrocytes [3,4]. In 1995 a cDNA clone that encodes NIS was isolated in our laboratory by functional screening of a cDNA library from a rat thyroid-derived cell line (FRTL-5 cells) in Xenopus laevis oocytes [5]. The sequence of NIS comprises 618 amino acids (relative molecular mass 65,196). The hydropathic profile and secondary structure predictions of the protein suggest that the cloned cDNA encodes for an intrinsic membrane protein with 12 putative transmembrane domains. NIS is the first I– transporting molecule whose cDNA has been cloned. NIS plays a crucial role in the evaluation, diagnosis, and treatment of various thyroid pathological conditions."
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