Endocrine Abstracts

Background

Thyroid hormone transporting proteins Mct8 and Mct10 have been detected at the plasma membrane of thyroid epithelial cells, whereas Lat2 was found predominantly at vesicular membranes. In this study we look into the effects of inhibiting thyroid hormone transporters on their subcellular localisation to better understand their fate and trafficking pathways in thyrocytes. Thus, a pharmacological intervention study with specific inhibitors of thyroid hormone transporters was conducted using a human thyroid epithelial cell line as a model.

Method: The localization of the thyroid hormone transporters Mct8, Mct10, and Lat2 was analyzed in human Nthy-ori 3-1 thyroid epithelial cells by indirect immunofluorescence, and the protein levels were determined by immunoblotting.

Results: Although Mct8 and Mct10 have been shown to be located at the basolateral plasma membrane domain of thyroid follicle cells in situ, our results of this in vitro study reveal their localization in vesicles. Lat2 was predominantly vesicular, both in situ and in vitro. In order to identify whether these vesicles belong to the secretory or the endocytic pathway, co-localization studies with Lamp2 as an endo-lysosomal marker were performed. The results suggest that Lat2 is present in vesicles other than late endosomes or lysosomes.

Conclusion: Nthy-ori 3-1 cells represent an in vitro-model suited to study the expression, localization, and trafficking of thyroid hormone transporters like Lat2, Mct8, and Mct10. Future studies will have to include other compartment-specific markers to identify the subcellular location of endogenous and over-expressed thyroid hormone transporters in thyrocytes.