PI3K is involved in the IGF-I inhibition of TSH-induced sodium/iodide symporter gene expression.
Here we studied the role of IGF-I on the regulation of the sodium/iodide symporter (NIS) gene expression in FRTL-5 thyroid cells. IGF-I did not modify NIS mRNA levels but inhibited TSH- and forskolin-induced NIS mRNA expression in a dose-dependent manner. We explored the signaling pathways by which IGF-I mediates the repression of NIS expression. Inhibition of either the MAPK kinase or PKC activities had no effect. Interestingly, inhibition of PI3K blocked IGF-I repression of TSHinduced NIS mRNA and protein levels. This effect takes place at the transcriptional level, as IGF-I inhibited TSH-induced transcription of a luciferase reporter construct containing a 2.8-kb DNA fragment of the rat NIS promoter. The inhibitory effect of IGF-I on the NIS promoter was blocked by the PI3K inhibitor LY294002 and was mimicked by overexpression of a vector harboring the constitutively activated catalytic subunit of PI3K. Using internal deletions of the NIS promoter, we defined a region from -1,947 to -1,152 responsible for the observed IGF-I/PI3K inhibitory effect. When fused to a heterologous promoter, this region inhibits transcription in response to IGF-I. These results demonstrate a central role for PI3K in the repression of NIS gene transcription by IGF-I and suggest the existence, within the above defined promoter region, of putative PI3K-responsive elements.
García
Bibian
B
Instituto de Investigaciones Biomédicas "Alberto Sols," Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Madrid, Spain E-28029.
Santisteban
Pilar
P
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D005576:Colforsin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D027981:Symporters / Q000096:biosynthesis / Q000235:genetics*; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D013972:Thyrotropin / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection; D000099209:Sodium-Iodide Symporters
D002867:Chromones; D005576:Colforsin; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D012333:RNA, Messenger; D027981:Symporters; D013972:Thyrotropin; D000099209:Sodium-Iodide Symporters; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one