STIMULATION OF NA+-K+-ATPASE BY THYROTROPIN IN CULTURED THYROID FOLLICULAR CELLS

Thyroid-stimulating hormone (TSH; thyrotropin) produces a pleiotropic response in the thyroid gland, accelerating nearly every aspect of metabolic turnover within the follicular epithelia. We examined the effects of TSH on expression of Na+-K+-ATPase in FRTL-5 cells, a cell line derived from rat thyroid. TSH (10 mU/ml) produced a nearly twofold increase in abundance of the mRNA encoding the catalytic alpha(1)-subunit within 6 h of treatment. With the four mRNAs encoding the beta(1)-subunit, TSH produced a striking increase in abundance, but this regulation was discoordinate, and some species increased more than others. Similar increases in mRNA abundance were elicited by activators of the adenosine 3',5'-cyclic monophosphate second messenger system. In contrast to the alpha(1)- and beta(1)-mRNAs, the abundance of the mRNA encoding the beta(2)-subunit was unchanged with TSH after 6 h, indicating that the effects of thyrotropin were not universal or indiscriminate. Thyrotropin also caused a 76% increase in Na+-K+-ATPase activity and a 46% increase in pump-mediated transport after 48 h. These studies suggest that the changes in metabolic turnover initiated by TSH during hormone synthesis include upregulation of the Na+-K+ pump.