Regulation of solute carrier family 26 member 7 (Slc26a7) by thyroid stimulating hormone in thyrocytes

Abstract

Iodine transportation is an important step in thyroid hormone biosynthesis. Uptake of iodine into the thyroid follicle is mediated mainly by the basolateral sodium-iodide symporter (NIS or solute carrier family 5 member 5: SLC5A5), and iodine efflux across the apical membrane into the follicular lumen is mediated by pendrin (SLC26A4). In addition to these transporters, SLC26A7, which has recently been identified as a causative gene for congenital hypothyroidism, was found to encode a novel apical iodine transporter in the thyroid. Although SLC5A5 and SLC26A4 have been well-characterized, little is known about SLC26A7, including its regulation by TSH, the central hormone regulator of thyroid function. Using rat thyroid FRTL-5 cells, we showed that the mRNA levels of Slc26a7 and Slc26a4, two apical iodine transporters responsible for iodine efflux, were suppressed by TSH, whereas the mRNA level of Slc5a5 was induced. Forskolin and dibutyryl cAMP (dbcAMP) had the same effect as that of TSH on the mRNA levels of these transporters. TSH, forskolin and dbcAMP also had suppressive effects on SLC26A7 promoter activity, as assessed by luciferase reporter gene assays, and protein levels, as determined by Western blot analysis. TSH, forskolin and dbcAMP also induced strong localization of Slc26a7 to the cell membrane according to immunofluorescence staining and confocal laser scanning microscopy. Together, these results suggest that TSH suppresses the expression level of Slc26a7 but induces its accumulation at the cell membrane, where it functions as an iodine transporter.

Thyroglobulin regulates the expression and localization of the novel iodide transporter solute carrier family 26 member 7 (SLC26A7) in thyrocytes

“…Recently, we evaluated the role of TSH on SLC26A7 expression using rat thyroid FRTL-5 cells and showed that TSH significantly suppressed SLC26A7 mRNA and protein expression. Although suppression of SLC26A7 is thought to result in decreased iodide transport activity, we additionally demonstrated that TSH induces localization of SLC26A7 to the plasma membrane, where it functions as a transporter [12].…”

“…Total RNA was purified using the RNeasy Plus Mini Kit (Qiagen, Hilden, Germany). cDNA was synthesized using the High-Capacity cDNA Reverse Transcription Kit (Applied Biosystems, Waltham, MA, USA) as described previously [12,22]; briefly, 1 μg total RNA was incubated with a mixture of 2 μL 10× RT buffer, 2 μL 10× RT Random Primers, 1 μL MultiScribe TM Reverse Transcriptase (50 U/μL), and 0.8 μL 25× dNTPs for 10 min at 25°C, 120 min at 37°C, and 5 min at 85°C. Real-time PCR was performed using Fast SYBR Green Master Mix (Applied Biosystems) and run on the Thermal Cycler Dice Real Time System III (Takara Bio, Tokyo, Japan) for 30 sec at 95°C, followed by 40 cycles of 5 sec at 95°C and 60 sec at 60°C, and then 1 cycle of 15 sec at 95°C, 30 sec at 60°C, and 15 sec at 95°C for dissociation.…”

“…pGL3-Basic reporter plasmids harboring the 5'flanking regions of the human SLC26A7 gene were prepared previously [12]. FRTL-5 cells maintained in basal medium in 6-well plates (Greiner Bio-One) were transfected with 1 μg of the luciferase reporter plasmids using FuGENE HD transfection reagent (Promega, Madison, WI, USA).…”

“…Cells were then treated with 1 mU/mL TSH and/or 5 mg/mL Tg. Immunofluorescence staining was performed as described previously [12]. Briefly, cells were fixed using 10% neutral buffered formalin for 10 min at room temperature and then permeabilized with PBS containing 0.1% Triton X-100.…”

Genome-wide identification of altered RNA m6A profiles in vascular tissue of septic rats

“…The phylogenetically ancient SLC26 gene family encodes multifunctional anion exchangers and anion channels transporting a broad range of substrates, including Cl - , HCO 3- , sulfate, oxalate, I − , and formate. It has been reported that SLC 26 member 7 (SLC26A7) was identified as a chloride–bicarbonate anion exchanger and/or as a Cl - channel in the kidney and stomach [ 34 , 35 ], whose gene mutations cause congenital deafness and dyshormonogenic goiter [ 36 ]. Alterations in Cl - channels can affect intracellular water content, vascular tone and arterial blood pressure.…”