Iodide transport is a specialized function of thyroid cells that is critical for thyroid hormone formation. Previous studies in this laboratory focused on iodide transport and iodine metabolism in thyroid. These studies have been extended to other ion-transport processes in thyroid including those involved in pH regulation and those required for epithelial cell metabolism. Transport proteins identified and characterized include an anion-exchange protein AE2 and the proton-dependent monocarboxylate transporters, MCT1 and MCT4. Unlike AE2, the expression of MCT transcript and protein is several fold higher in thyroid cells cultured with TSH when compared to cells cultured in its absence. In rat thyroid slices, AE2 was localized in the apical membrane of follicular cells, while MCT4 was found in the basal membrane. Proton-lactate egress across the basal membrane and mediated by MCT, can limit cytosolic acidoses from TSH-enhanced aerobic glycolysis. In collaborative studies with Dr. Brian Sauer, a model system for the heterologous expression of MCT in Saccharomyces cerevisiae was developed. Studies with MCT tagged with green fluorescent protein showed that transfected MCT was expressed in the plasma membrane of yeast and useful for functional studies of MCT, a transporter protein that is important for regulating cellular pH, volume, and metabolism.
