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Excess iodide induces an acute inhibition of the sodium/iodide symporter in thyroid male rat cells by increasing reactive oxygen species.

ABSTRACT: Na+/I- symporter (NIS) mediates iodide (I-) uptake in the thyroid gland, the first and rate-limiting step in the biosynthesis of the thyroid hormones. The expression and function of NIS in thyroid cells is mainly regulated by TSH and by the intracellular concentration of I-. High doses of I- for 1 or 2 days inhibit the synthesis of thyroid hormones, a process known as the Wolff-Chaikoff effect. The cellular mechanisms responsible for this physiological response are mediated in part by the inhibition of I- uptake through a reduction of NIS expression. Here we show that inhibition of I- uptake occurs as early as 2 hours or 5 hours after exposure to excess I- in FRTL-5 cells and the rat thyroid gland, respectively. Inhibition of I- uptake was not due to reduced NIS expression or altered localization in thyroid cells. We observed that incubation of FRTL-5 cells with excess I- for 2 hours increased H2O2 generation. Furthermore, the inhibitory effect of excess I- on NIS-mediated I- transport could be recapitulated by H2O2 and reverted by reactive derived oxygen species scavengers. The data shown here support the notion that excess I- inhibits NIS at the cell surface at early times by means of a posttranslational mechanism that involves reactive derived oxygen species.

SUBMITTER: Arriagada AA

PROVIDER: S-EPMC5393323 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Excess iodide induces an acute inhibition of the sodium/iodide symporter in thyroid male rat cells by increasing reactive oxygen species.

Arriagada Alejandro A AA Albornoz Eduardo E Opazo Ma Cecilia MC Becerra Alvaro A Vidal Gonzalo G Fardella Carlos C Michea Luis L Carrasco Nancy N Simon Felipe F Elorza Alvaro A AA Bueno Susan M SM Kalergis Alexis M AM Riedel Claudia A CA

Endocrinology 20150116 4

Na+/I- symporter (NIS) mediates iodide (I-) uptake in the thyroid gland, the first and rate-limiting step in the biosynthesis of the thyroid hormones. The expression and function of NIS in thyroid cells is mainly regulated by TSH and by the intracellular concentration of I-. High doses of I- for 1 or 2 days inhibit the synthesis of thyroid hormones, a process known as the Wolff-Chaikoff effect. The cellular mechanisms responsible for this physiological response are mediated in part by the inhibi ...[more]

PMID: 25594695

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Project description:BackgroundSodium/iodide symporter (NIS)-mediated iodide uptake plays an important physiological role in regulating thyroid gland function, as well as in diagnosing and treating Graves' disease and thyroid cancer. High-mobility group box 1 (HMGB1), a highly conserved nuclear protein, is a positive regulator of autophagy conferring resistance to chemotherapy, radiotherapy and immunotherapy in cancer cells. Here the authors intended to identify the role of HMGB1 in Hank's balanced salt solution (HBSS)-induced autophagy, explore NIS protein degradation through a autophagy-lysosome pathway in thyroid cancer cells and elucidate the possible molecular mechanisms.MethodsImmunohistochemical staining and reverse transcription-polymerase chain reaction (RT-PCR) were performed for detecting the expression of HMGB1 in different tissues. HMGB1 was knocked down by lentiviral transfection in FTC-133/TPC-1 cells. Autophagic markers LC3-II, p62, Beclin1 and autophagosomal formation were employed for evaluating HMGB1-mediated autophagy in HBSS-treated cells by Western blot, immunofluorescence and electron microscopy. Western blot, quantitative RT-PCR and gamma counter analysis were performed for detecting NIS expression and iodide uptake in HMGB1-knockdown cells after different treatments. The reactive oxygen species (ROS) level, ROS-mediated LC3-II expression and HMGB1 cytosolic translocation were detected by fluorospectrophotometer, flow cytometry, Western blot and immunofluorescence. HMGB1-mediated AMPK, mTOR and p70S6K phosphorylation (p-AMPK, p-mTOR & p-p70S6K) were detected by Western blot. Furthermore, a nude murine model with transplanted tumor was employed for examining the effect of HMGB1-mediated autophagy on imaging and biodistribution of 99mTcO4-. NIS, Beclin1, p-AMPK and p-mTOR were detected by immunohistochemical staining and Western blot in transplanted tumor samples.ResultsHMGB1 was a critical regulator of autophagy-mediated NIS degradation in HBSS-treated FTC-133/TPC-1 cells. And HMGB1 up-regulation was rather prevalent in thyroid cancer tissues and closely correlated with worse overall lymph node metastasis and clinical stage. HMGB1-knockdown dramatically suppressed autophagy, NIS degradation and boosted iodide uptake in HBSS-treated cells. Moreover, HBSS enhanced ROS-sustained autophagy and promoted the cytosolic translocation of HMGB1. A knockdown of HMGB1 suppressed LC3-II conversion and NIS degradation via an AMPK/mTOR-dependent signal pathway through a regulation of ROS generation, rather than ATP. Furthermore, these data were further supported by our in vivo experiment of xenografts formed by HMGB1 knockdown cells reverting the uptake of 99mTcO4- as compared with control shRNA-transfected cells in hunger group.ConclusionsActing as a critical regulator of autophagy-mediated NIS degradation via ROS/AMPK/mTOR pathway, HMGB1is a potential intervention target of radioiodine therapy in thyroid cancer.

Project description:Background: The ability of thyroid follicular epithelial cells to accumulate iodide via the sodium/iodide symporter (NIS) is exploited to successfully treat most thyroid cancers, although a subset of patients lose functional NIS activity and become unresponsive to radioiodide therapy, with poor clinical outcome. Our knowledge of NIS regulation remains limited, however. While numerous membrane proteins are functionally regulated via dimerization, there is little definitive evidence of NIS dimerization, and whether this might impact upon radioiodide uptake and treatment success is entirely unknown. We hypothesized that NIS dimerizes and that dimerization is a prerequisite for iodide uptake. Methods: Coimmunoprecipitation, proximity ligation, and Förster resonance energy transfer (FRET) assays were used to assess NIS:NIS interaction. To identify residues involved in dimerization, a homology model of NIS structure was built based on the crystal structure of the dimeric bacterial protein vSGLT. Results: Abundant cellular NIS dimerization was confirmed in vitro via three discrete methodologies. FRET and proximity ligation assays demonstrated that while NIS can exist as a dimer at the plasma membrane (PM), it is also apparent in other cellular compartments. Homology modeling revealed one key potential site of dimeric interaction, with six residues <3Å apart. In particular, NIS residues Y242, T243, and Q471 were identified as critical to dimerization. Individual mutation of residues Y242 and T243 rendered NIS nonfunctional, while abrogation of Q471 did not impact radioiodide uptake. FRET data show that the putative dimerization interface can tolerate the loss of one, but not two, of these three clustered residues. Conclusions: We show for the first time that NIS dimerizes in vitro, and we identify the key residues via which this happens. We hypothesize that dimerization of NIS is critical to its trafficking to the PM and may therefore represent a new mechanism that would need to be considered in overcoming therapeutic failure in patients with thyroid cancer.

Project description:The sodium-iodide symporter (NIS) mediates transport of iodide across the basolateral membrane of thyroid cells. NIS expression in thyroid cancer (TC) cells allows the use of radioactive iodine (RAI) as a diagnostic and therapeutic tool, being RAI therapy the systemic treatment of choice for metastatic disease. Still, a significant proportion of patients with advanced TC lose the ability to respond to RAI therapy and no effective alternative therapies are available. Defective NIS expression is the main reason for impaired iodide uptake in TC and NIS downregulation has been associated with several pathways linked to malignant transformation. NF-κB signaling is one of the pathways associated with TC. Interestingly, NIS expression can be negatively regulated by TNF-α, a bona fide activator of NF-κB with a central role in thyroid autoimmunity. This prompted us to clarify NF-kB's role in this process. We confirmed that TNF-α leads to downregulation of TSH-induced NIS expression in non-neoplastic thyroid follicular cell-derived models. Notably, a similar effect was observed when NF-κB activation was triggered independently of ligand-receptor specificity, using phorbol-myristate-acetate (PMA). TNF-α and PMA downregulation of NIS expression was reverted when NF-κB-dependent transcription was blocked, demonstrating the requirement for NF-kB activity. Additionally, TNF-α and PMA were shown to have a negative impact on TSH-induced iodide uptake, consistent with the observed transcriptional downregulation of NIS. Our data support the involvement of NF-κB-directed transcription in the modulation of NIS expression, where up- or down-regulation of NIS depends on the combined output to NF-κB of several converging pathways. A better understanding of the mechanisms underlying NIS expression in the context of normal thyroid physiology may guide the development of pharmacological strategies to increase the efficiency of iodide uptake. Such strategies would be extremely useful in improving the response to RAI therapy in refractory-TC.

Dataset Information

Excess iodide induces an acute inhibition of the sodium/iodide symporter in thyroid male rat cells by increasing reactive oxygen species.

Publications

Excess iodide induces an acute inhibition of the sodium/iodide symporter in thyroid male rat cells by increasing reactive oxygen species.

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