Glycosylation of Sodium/Iodide Symporter (NIS) Regulates Its Membrane Translocation and Radioiodine Uptake

Abstract

PurposeHuman sodium/iodide symporter (hNIS) protein is a membrane glycoprotein that transports iodide ions into thyroid cells. The function of this membrane protein is closely regulated by post-translational glycosylation. In this study, we measured glycosylation-mediated changes in subcellular location of hNIS and its function of iodine uptake.MethodsHeLa cells were stably transfected with hNIS/tdTomato fusion gene in order to monitor the expression of hNIS. Cellular localization of hNIS was visualized by confocal microscopy of the red fluorescence of tdTomato. The expression of hNIS was evaluated by RT-PCR and immunoblot analysis. Functional activity of hNIS was estimated by radioiodine uptake. Cyclic AMP (cAMP) and tunicamycin were used to stimulate and inhibit glycosylation, respectively. In vivo images were obtained using a Maestro fluorescence imaging system.ResultscAMP-mediated Glycosylation of NIS resulted in increased expression of hNIS, stimulating membrane translocation, and enhanced radioiodine uptake. In contrast, inhibition of glycosylation by treatment with tunicamycin dramatically reduced membrane translocation of intracellular hNIS, resulting in reduced radioiodine uptake. In addition, our hNIS/tdTomato fusion reporter successfully visualized cAMP-induced hNIS expression in xenografted tumors from mouse model.ConclusionsThese findings clearly reveal that the membrane localization of hNIS and its function of iodine uptake are glycosylation-dependent, as our results highlight enhancement of NIS expression and glycosylation with subsequent membrane localization after cAMP treatment. Therefore, enhancing functional NIS by the increasing level of glycosylation may be suggested as a promising therapeutic strategy for cancer patients who show refractory response to conventional radioiodine treatment.

Selumetinib Activity in Thyroid Cancer Cells: Modulation of Sodium Iodide Symporter and Associated miRNAs

“…In addition to the restoration of NIS transcript observed in all cell lines, a modulation of NIS protein level was found in all cell lines treated with selumetinib. The 68 kDa fragment representing non-/partial-glycosylated NIS [ 39 ] was up-regulated in TPC1 and BCPAP cells and down-regulated in C643 and 8505C cells.…”

Glycosylation in the Thyroid Gland: Vital Aspects of Glycoprotein Function in Thyrocyte Physiology and Thyroid Disorders

“…Activation of the cAMP cascade leads to an increase of iodine uptake and translocation to the plasma membrane in thyroid cells. Decreased translocation to the membrane and reduced iodine uptake were found in tunicamycin-treated follicular cells with impaired NIS N -glycosylation at the early step of N -glycan synthesis [ 82 ].…”

Differentiated Thyroid Carcinoma with Elevated Thyroglobulin and Negative Radioiodine Whole-Body Scan Metastases

“…Other proteins, including thyroperoxidase (TPO) and pendrin, also play an important role in the thyroid metabolism of iodine [83]. Strategies of gene transfection focused on NIS; TPO has been studied to enhance tumor uptake iodine [84,85]. Co-transfection of the hNIS and hTPO genes can lead to longer retention of radio iodine [85].…”