Enhancement of sodium/iodide symporter expression in thyroid and breast cancer

The sodium/iodide symporter (NIS) mediates iodide uptake in the thyroid gland and lactating breast. NIS mRNA and protein expression are detected in most thyroid cancer specimens, although functional iodide uptake is usually reduced resulting in the characteristic finding of a 'cold' or non-functioning lesion on a radioiodine image. Iodide uptake after thyroid stimulating hormone (TSH) stimulation, however, is sufficient in most differentiated thyroid cancer to utilize beta-emitting radioactive iodide for the treatment of residual and metastatic disease. Elevated serum TSH, achieved by thyroid hormone withdrawal in athyreotic patients or after recombinant human thyrotropin administration, directly stimulates NIS gene expression and/or NIS trafficking to the plasma membrane, increasing radioiodide uptake. Approximately 10-20% differentiated thyroid cancers, however, do not express the NIS gene despite TSH stimulation. These tumors are generally associated with a poor prognosis. Reduced NIS gene expression in thyroid cancer is likely due in part, to impaired trans-activation at the proximal promoter and/or the upstream enhancer. Basal NIS gene expression is detected in about 80% breast cancer specimens, but the fraction with functional iodide transport is relatively low. Lactogenic hormones and various nuclear hormone receptor ligands increase iodide uptake in breast cancer cells in vitro, but TSH has no effect. A wide range of 'differentiation' agents have been utilized to stimulate NIS expression in thyroid and breast cancer using in vitro and in vivo models, and a few have been used in clinical studies. Retinoic acid has been used to stimulate NIS expression in both thyroid and breast cancer. There are similarities and differences in NIS gene regulation and expression in thyroid and breast cancer. The various agents used to enhance NIS expression in thyroid and breast cancer will be reviewed with a focus on the mechanism of action. Agents that promote tumor differentiation, or directly stimulate NIS gene expression, may result in iodine concentration in 'scan-negative' thyroid cancer and some breast cancer.     

Signaling through 3',5'-cyclic adenosine monophosphate and phosphoinositide-3 kinase induces sodium/iodide symporter expression in breast cancer

The sodium/iodide symporter (NIS) is a membrane transport glycoprotein normally expressed in the thyroid gland and lactating mammary gland. NIS is a target for radioiodide imaging and therapeutic ablation of thyroid carcinomas and has the potential for similar use in breast cancer treatment. To facilitate NIS-mediated radionuclide therapy, it is necessary to identify signaling pathways that lead to increased NIS expression and function in breast cancer. We examined NIS expression in mammary tumors of 14 genetically engineered mouse models to identify genetic manipulations associated with NIS induction. The cAMP and phosphoinositide-3 kinase (PI3K) signaling pathways are associated with NIS up-regulation. We showed that activation of PI3K alone is sufficient to increase NIS expression and radioiodide uptake in MCF-7 human breast cancer cells, whereas cAMP stimulation increases NIS promoter activity and NIS mRNA levels but is not sufficient to increase radioiodide uptake. This study is the first to demonstrate that NIS expression is induced by cAMP and/or PI3K in breast cancer both in vivo and in vitro.     

Modulation of sodium iodide symporter expression and function by LY294002, Akti-1/2 and Rapamycin in thyroid cells

The selective increase of Na(+)/I(-) symporter (NIS)-mediated active iodide uptake in thyroid cells allows the use of radioiodine I(131) for diagnosis and targeted treatment of thyroid cancers. However, NIS-mediated radioiodine accumulation is often reduced in thyroid cancers due to decreased NIS expression/function. As PI3K signaling is overactivated in many thyroid tumors, we investigated the effects of inhibitors for PI3K, Akt, or mTORC1 as well as their interplay on NIS modulation in thyroid cells under chronic TSH stimulation. PI3K inhibition by LY294002 increased NIS-mediated radioiodide uptake (RAIU) mainly through upregulation of NIS expression, however, mTORC1 inhibition by Rapamycin did not increase NIS-mediated RAIU despite increased NIS protein levels. In comparison, Akt inhibition by Akti-1/2 did not increase NIS protein levels, yet markedly increased NIS-mediated RAIU by decreasing iodide efflux rate and increasing iodide transport rate and iodide affinity of NIS. The effects of Akti-1/2 on NIS-mediated RAIU are not detected in nonthyroid cells, implying that Akti-1/2 or its derivatives may represent potential pharmacological reagents to selectively increase thyroidal radioiodine accumulation and therapeutic efficacy.     

The sodium-iodide symporter. Pathophysiologic,diagnostic and therapeutic significance

The sodium iodide symporter NIS) is an intrinsic plasma membrane protein that mediates the active transport of iodide in the thyroid gland and a number of extrathyrioidal tissues, in particular lactating mammary gland. Because of its crucial role in the ability of thyroid follicular cells to trap iodide of NIS opened an exciting and extensivenew field of thyroid-related research. Cloning and molecular characterization of NIS allowed investigation of its expression and regulation in thyroidal and nonthyroidal tissues, and its potential pathophysiological and therepeutic implications is benign and malignant thyroid diseases. In addition, NIS-mediated iodide accumulation allows diagnostic thyroid scintigraphy as well as effective therapeutic application of radio-iodide in benign and malignant thyroid disease. characterization and application of NIS as a novel therapeutic gene for cytoreductive gene therapy of extrathyroidal tumors, and the presence of high endogenous NIS expression in the majority of breast cancers further suggest a promising role of NIS in diagnosis and therapy of cancer outside the thyroid gland.     

Regulation of the sodium/iodide symporter by retinoids--a review.

Decrease or loss of iodide uptake, due to impaired expression and/or function of the sodium/iodide-symporter (NIS), is a major obstacle to the treatment of advanced thyroid carcinomas by radioiodide therapy. Several approaches are being evaluated to optimise or restore sufficient iodide transport in those cases, among them retinoid therapy. Retinoids with their growth-inhibiting and differentiation-inducing properties have been repeatedly used for treatment and chemoprevention of various cancers. In thyroid carcinoma cell lines they trigger changes in gene expression that may be interpreted as partial redifferentiation. Especially, they stimulate NIS mRNA expression and iodide uptake in human follicular thyroid carcinoma cells. Moreover, they also increase NIS expression and function in human mammary tumour cells. In a clinical pilot study to evaluate the feasibility of retinoid redifferentiation in the case of otherwise untreatable thyroid cancers, 21 of 50 patients showed an increase of radioiodide uptake after 5 weeks. This indicates that increasing NIS activity and radioiodide uptake by retinoic acid redifferentiation may be a therapeutic alternative for thyroid cancers refractory to other therapeutic modalities and probably also for mammary cancer.     

The sodium iodide symporter: its pathophysiological and therapeutic implications

The sodium iodide symporter (NIS) is an intrinsic plasma membrane protein that mediates the active transport of iodide in the thyroid gland and a number of extrathyroidal tissues, in particular lactating mammary gland. Because of its crucial role in the ability of thyroid follicular cells to trap iodide, cloning of NIS opened an exciting and extensive new field of thyroid-related research. Cloning and molecular characterization of NIS allowed investigation of its expression and regulation in thyroidal and nonthyroidal tissues, and its potential pathophysiological and therapeutic implications in benign and malignant thyroid disease. In addition to its key function in thyroid physiology, NIS-mediated iodide accumulation allows diagnostic thyroid scintigraphy as well as effective therapeutic application of radioiodine in benign and malignant thyroid disease. Characterization and application of NIS as a novel therapeutic gene and the presence of high native NIS expression in the majority of breast cancers further suggest a promising role of NIS in diagnosis and therapy of cancer outside the thyroid gland.     

MEK signaling modulates sodium iodide symporter at multiple levels and in a paradoxical manner

The Na(+)/I(-) symporter (NIS)-mediated iodide uptake is the basis for targeted radioiodine ablation of thyroid cancers. However, NIS-mediated radioiodide uptake (RAIU) activity is often reduced in thyroid cancers. As mitogen activated protein kinase (MAPK) signaling pathway is activated in about 70% of papillary thyroid carcinoma, we investigated whether MEK (MAPK kinase) inhibition will restore NIS protein levels and NIS-mediated RAIU activity in RET/PTC oncogene-transformed thyroid cells. We found that MEK inhibitor PD98059 increased NIS protein levels within 30 min of treatment. However, the increase of NIS protein level was not accompanied with an increase in NIS-mediated RAIU activity, particularly at early time points of PD98059 treatment. PD98059 also decreased RAIU activity mediated by exogenous NIS in non-thyroid cells. The transient decrease of RAIU activity by PD98059 in thyroid cells was not due to decreased NIS cell surface level, decreased NIS binding affinity for I(-) , or increased iodide efflux. While PD98059 moderately decreased Na(+)/K(+)-ATPase activity, ouabain titration indicates that the extent of decrease in Na(+)/K(+)-ATPase activity is much greater than the extent of decrease in RAIU activity. Additionally, a decrease of Na(+)/K(+)-ATPase activity was not accompanied with a decrease of biotin uptake activity mediated by Na(+)-dependent multivitamin transporter. Since PD98059 reduced V(max)- I(-) without decreasing NIS cell surface levels, it is most likely that PD98059 decreases the turnover rate of iodide transport with an yet to be identified mechanism.     

Dexamethasone stimulation of retinoic Acid-induced sodium iodide symporter expression and cytotoxicity of 131-I in breast cancer cells

CONTEXT: The sodium iodide symporter (NIS) mediates the active iodide uptake in the thyroid gland as well as lactating breast tissue. Recently induction of functional NIS expression was reported in the estrogen receptor-positive human breast cancer cell line MCF-7 by all-trans retinoic acid (atRA) treatment in vitro and in vivo, which might offer the potential to treat breast cancer with radioiodine. OBJECTIVE: In the current study, we examined the effect of dexamethasone (Dex) on atRA-induced NIS expression and therapeutic efficacy of 131-I in MCF-7 cells. DESIGN: For this purpose, NIS mRNA and protein expression levels in MCF-7 cells were examined by Northern and Western blot analysis after incubation with Dex (10(-9) to 10(-7) m) in the presence of atRA (10(-6) m) as well as immunostaining using a mouse monoclonal human NIS-specific antibody. In addition, NIS functional activity was measured by iodide uptake and efflux assay, and in vitro cytotoxicity of 131-I was examined by in vitro clonogenic assay. RESULTS: After incubation with Dex in the presence of atRA, NIS mRNA levels in MCF-7 cells were stimulated up to 11-fold in a concentration-dependent manner, whereas NIS protein levels increased up to 16-fold and iodide accumulation was stimulated up to 3- to 4-fold. Furthermore, iodide efflux was modestly decreased after stimulation with Dex in the presence of atRA. Furthermore, in the in vitro clonogenic assay, selective cytotoxicity of 131-I was significantly increased from approximately 17% in MCF-7 cells treated with atRA alone to 80% in MCF-7 cells treated with Dex in the presence of atRA. CONCLUSION: Treatment with Dex in the presence of atRA significantly increases functional NIS expression levels in addition to inhibiting iodide efflux, resulting in an enhanced selective killing effect of 131-I in MCF-7 breast cancer cells.     

Valproic acid induces the expression of the Na+/I- symporter and iodine uptake in poorly differentiated thyroid cancer cells

In poorly differentiated thyroid cancer, molecular characteristics are reported to be lost such as to cause insensitivity of the tumor to radiometabolic therapy. Considerable work is in progress to identify compounds that redifferentiate thyroid cancer cells. The present study evaluates the action of valproic acid, a potent anticonvulsant recently reported to inhibit histone deaceytlase, on cultured thyroid cancer cells. N-PA (poorly differentiated) and ARO (anaplastic) cells were treated with increasing valproic acid concentrations.; expression of mRNA and cell localization pattern for the Na+/I- symporter (NIS), as well as 125I uptake, were evaluated before and after treatment. Valproic acid induced NIS gene expression, NIS membrane localization and iodide accumulation in N-PA cells; it was effective at clinically-safe doses in the therapeutic range. In ARO cells, only induction of NIS mRNA was observed, and was not followed by any change in iodide uptake. Valproic acid is thus effective at restoring the ability of N-PA cells to accumulate iodide and its use in clinical trials may be recommended.     

A perspective view of sodium iodide symporter research and its clinical implications

The sodium iodide symporter (NIS) is an intrinsic plasma membrane protein that mediates active iodide transport into the thyroid gland and into several extrathyroidal tissues, in particular the lactating mammary gland. Cloning and molecular characterization of the NIS have allowed the investigation of its key role in thyroid physiology as well as its potential pathophysiological and therapeutic implications in benign and malignant thyroid diseases. Similarly, elucidating the mechanisms underlying the regulation of NIS in lactating mammary gland and breast cancer, in which more than 80% of cases express endogenous NIS, may lead to findings that have novel implications for pathophysiology and therapy. Two approaches may, in the future, pave the way to extend the use of radioiodide treatment to nonthyroidal cancer. One is based on the reinduction of endogenous NIS expression in thyroid and breast cancer by targeting the main mechanisms involving tumoral transformation and dedifferentiation. The other is based on the application of NIS as a novel cytoreductive gene therapy strategy. NIS offers the unique advantage that it can be used both as a reporter and as a therapeutic gene, so that it is possible to image, monitor, and treat the tumor with radioiodide, just as in differentiated thyroid cancer. This review summarizes the main recent findings in NIS research that have a direct impact on diagnosis and therapeutic management.     

Expression of the human sodium/iodide symporter (hNIS) in xenotransplanted human thyroid carcinoma.

The uptake of iodide in thyroid epithelial cells is mediated by the sodium/iodide symporter (NIS). The uptake of iodide is of vital importance for thyroid physiology and is a prerequisite for radioiodine therapy in thyroid cancer. Loss of iodide uptake due to diminished expression of the human NIS (hNIS) is frequently observed in metastasized thyroid cancer. So far, no animal model for the study of radioiodine therapy in thyroid cancer has been available. Strategies to restore iodide uptake in thyroid cancer include the exploration of hNIS gene transfer into hNIS defective thyroid cancer. We have performed a stable transfection of hNIS into the hNIS defective follicular thyroid carcinoma cell line FTC133. Stably transfected colonies exhibited high uptake of Na125I, which could be blocked completely with sodium perchlorate. hNIS transfected FTC133 and non-transfected cell lines injected subcutaneously in nude mice formed tumors after 6 weeks. Iodide uptake in the hNIS transfected tumor was much higher than in non-transfected tumor, but a rapid release of radioactivity from the hNIS transfected tumor was observed. Further studies are necessary to investigate the role of hNIS in relation to other thyroid specific proteins in iodide metabolism in thyroid cancer.     

Retinoic acid stimulation of the sodium/iodide symporter in MCF-7 breast cancer cells is mediated by the insulin growth factor-I/phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase signaling pathways

CONTEXT: All-trans retinoic acid (tRA) induces differentiation in MCF-7 breast cancer cells, stimulates sodium/iodide symporter (NIS) gene expression, and inhibits cell proliferation. Radioiodine administration after systemic tRA treatment has been proposed as an approach to image and treat some differentiated breast cancer. OBJECTIVE: The objective of this work was to study the relative role of genomic and nongenomic pathways in tRA stimulation of NIS expression in MCF-7 cells. DESIGN: We inspected the human NIS gene locus for retinoic acid-responsive elements and tested them for function. The effects of signal transduction pathway inhibitors were also tested in tRA-treated MCF-7 cells and TSH-stimulated FRTL-5 rat thyroid cells, followed by iodide uptake assay, quantitative RT-PCR of NIS, and cell cycle phase analysis. RESULTS: Multiple retinoic acid response elements around the NIS locus were identified by sequence inspection, but none of them was a functional tRA-induced element in MCF-7 cells. Inhibitors of the IGF-I receptor, Janus kinase, and phosphatidylinositol 3-kinase (PI3K), significantly reduced NIS mRNA expression and iodide uptake in tRA-stimulated MCF-7 cells but not FRTL-5 cells. An inhibitor of p38 MAPK significantly reduced iodide uptake in both tRA-stimulated MCF-7 cells and TSH-stimulated FRTL-5 cells. IGF-I and PI3K inhibitors did not significantly reduce the basal NIS mRNA expression in MCF-7 cells. Despite the chronic inhibitory effects on cell proliferation, tRA did not reduce the S-phase distribution of MCF-7 cells during the period of NIS induction. CONCLUSION: The IGF-I receptor/PI3K pathway mediates tRA-stimulated NIS expression in MCF-7 but not FRTL-5 thyroid cells.     

Effect of Iodide on Human Choriogonadotropin, Sodium-Iodide Symporter Expression, and Iodide Uptake in BeWo Choriocarcinoma Cells

CONTEXT: Active placental transport of maternal iodide by the thyroidal sodium iodide symporter (NIS) provides an essential substrate for fetal thyroid hormone synthesis. NIS is expressed in trophoblast and is regulated by human choriogonadotropin (hCG). In thyroid, iodide down-regulates expression of several genes including NIS. Placentas of iodine-deficient rats demonstrate up-regulation of NIS mRNA, suggesting a role for iodide in regulating placental NIS. OBJECTIVES AND METHODS: The objectives were to examine effects of iodide on expression of NIS and hCG in BeWo choriocarcinoma cells. Gene expression was studied by quantitative real-time PCR. Effects on NIS protein expression were assessed by Western blotting. Functional activity of NIS was measured by (125)I uptake. Expression of hCG protein was assessed by immunoassay of secreted hormone. RESULTS: Iodide inhibited NIS mRNA and membrane protein expression as well as (125)I uptake, which were paralleled by decreased betahCG mRNA expression and protein secretion. Iodide had no effects on pendrin expression. Addition of hCG increased NIS mRNA expression. This effect was partially inhibited by addition of iodide. The inhibitory effects of iodide on NIS mRNA expression were abolished by propylthiouracil and dithiothreitol. CONCLUSIONS: We conclude that expression of placental NIS is modulated by maternal iodide. This may occur through modulation of hCG effects on NIS and hCG gene expression.