Regulation by thyroid-stimulating hormone of sodium/iodide symporter gene expression and protein levels in FRTL-5 cells.
To investigate the mechanism of I- transport stimulation by TSH, we studied the effects of TSH on Na+/I- symporter (NIS) messenger RNA (mRNA) and protein levels in FRTL-5 cells and correlated these with I- transport activity. When 1 mU/ml TSH was added to quiescent FRTL-5 cells, a 12-h latency was observed before the onset of increased I- transport activity, which reached a maximum [approximately 27 times basal (5H medium) levels] at 72 h. In contrast, Northern blot analysis, using rat NIS complementary DNA as a probe, revealed that addition of TSH to these cells significantly increased NIS mRNA at 3-6 h, reaching a maximum after 24 h (approximately 5.9 times basal levels). Forskolin and (Bu)2cAMP mimicked this stimulatory effect on both the I- transport activity and mRNA levels. D-ribofranosylbenzimidazole, a transcription inhibitor, almost completely blocked TSH-induced stimulation of I- transport and NIS mRNA levels. Western blot analysis demonstrated that TSH increased NIS protein levels at 36 h, reaching a maximum at 72 h, in parallel with the kinetics of TSH-induced I- transport activity. However, it also showed that the amount of NIS protein already present in FRTL-5 cell membranes before the addition of TSH was about one third of the maximum level induced by TSH. These results indicate that stimulation of I- transport activity by TSH in thyrocytes is partly due to a rapid increase in NIS gene expression, followed by a relatively slow NIS protein synthesis. However, the existence of an abundant amount of protein in quiescent FRTL-5 cells with very low I- transport activity also suggests that this activity is controlled by another TSH-regulated factor(s).
Kogai
T
T
Third Department of Internal Medicine, Yamanashi Medical University, Tamaho, Japan.
Endo
T
T
Saito
T
T
Miyazaki
A
A
Kawaguchi
A
A
Onaya
T
T
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D016466:CHO Cells; D002352:Carrier Proteins / Q000096:biosynthesis*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000187:drug effects*; D007454:Iodides / Q000378:metabolism; D007700:Kinetics; D008565:Membrane Proteins / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D027981:Symporters; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013961:Thyroid Gland / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D000099209:Sodium-Iodide Symporters
D003994:Bucladesine; D002352:Carrier Proteins; D005576:Colforsin; D007454:Iodides; D008565:Membrane Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D027981:Symporters; D013755:Tetradecanoylphorbol Acetate; D013972:Thyrotropin; D000099209:Sodium-Iodide Symporters