CHARACTERIZATION OF THE RAT-THYROID IODIDE TRANSPORTER USING ANTIPEPTIDE 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 thyro id and in the functional rat thyroid cell line, FRTL-5. rTIT is locate d on the basolateral membrane of rat thyroid follicular cells and rand omly distributed on the plasma membrane of FRTL-5 cells that do not ex hibit cell polarity, The major rTIT component corresponds to an 80-90k Da glycosylated protein, After treatment of cell membrane fractions wi th N-glycosidase F or incubation of FRTL-5 cells with tunicamycin, rTI T has an apparent molecular mass of about 55 kDa, FRTL-5 cells culture d 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 cycl oheximide, 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 TS H causes a rapid synthesis of the glycosylated rTIT but a delayed re-i nduction of IUA, Tunicamycin totally prevents the TSH-dependent re-exp ression and activity of rTIT, Our data bring basic information on the location, structure, and turnover of rTIT and suggest that its activit y is subjected to diverse control mechanisms including regulatory prot eins.