Anoctamin 1 is Apically Expressed on Thyroid Follicular Cells and Contributes to ATP- and Calcium-Activated Iodide Efflux

Abstract

Background/Aims: Iodide efflux from thyroid cells into the follicular lumen is essential for the synthesis of thyroid hormones, however, the pathways mediating this transport have only been partially identified. A calcium-activated pathway of iodide efflux has long been recognized, but its molecular identity unknown. Anoctamin 1 (ANO1) is a calcium-activated chloride channel (CaCC), and this study aims to investigate its contribution to iodide fluxes in thyroid cells. Methods: RT-PCR, immunohistochemistry, and live cell imaging with the fluorescent halide biosensor YFP-H148Q/I152L were used to study the expression, localization and function of ANO1 in thyroid cells. Results: ANO1 mRNA was detected in human thyroid tissue and FRTL-5 thyrocytes, and ANO1 protein was localized to the apical membrane of follicular cells. ATP induced a transient loss of iodide from FRTL-5 cells that was dependent on the mobilization of intracellular calcium, and was inhibited by CaCC/ANO1 inhibitors and siRNA against ANO1. Calcium-activated iodide efflux was also observed in CHO cells over-expressing the Sodium Iodide Symporter (NIS) and ANO1. Conclusion: ANO1 in thyrocytes functions as a calcium-activated channel mediating iodide efflux, and may contribute to the rapid delivery of iodide into the follicular lumen for the synthesis of thyroid hormones following activation by calcium-mobilizing stimuli.