Characterization of the rat thyroid iodide transporter using anti-peptide antibodies. Relationship between its expression and activity.

Anti-peptide antibodies directed against the C-terminal portion (amino acids 603-618) of the rat thyroid iodide transporter (rTIT) have been produced to characterize the molecular forms of rTIT in the rat thyroid and in the functional rat thyroid cell line, FRTL-5. rTIT is located on the basolateral membrane of rat thyroid follicular cells and randomly distributed on the plasma membrane of FRTL-5 cells that do not exhibit cell polarity. The major rTIT component corresponds to an 80-90-kDa glycosylated protein. After treatment of cell membrane fractions with N-glycosidase F or incubation of FRTL-5 cells with tunicamycin, rTIT has an apparent molecular mass of about 55 kDa. FRTL-5 cells cultured in the presence of TSH exhibit a high rTIT content and a high iodide uptake activity (IUA). Upon either removal of TSH or addition of cycloheximide, IUA declines more rapidly than rTIT. The half-life of rTIT was about 4 days. Re-exposure of 7-day TSH-deprived FRTL-5 cells to TSH causes a rapid synthesis of the glycosylated rTIT but a delayed re-induction of IUA. Tunicamycin totally prevents the TSH-dependent re-expression and activity of rTIT. Our data bring basic information on the location, structure, and turnover of rTIT and suggest that its activity is subjected to diverse control mechanisms including regulatory proteins.