PI3K is involved in the IGF-I inhibition of TSH-induced sodium/iodide symporter gene expression

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2002-02, Vol.16 (2), p.342-352
• Main Authors: García, Bibian, Santisteban, Pilar
• Format: Article
• Language: English
• Subjects: Animals; Blotting, Western; Cell Line; Chromones - pharmacology; Colforsin - antagonists & inhibitors; Colforsin - pharmacology; Gene Expression Regulation - drug effects; Insulin - pharmacology; Insulin-Like Growth Factor I - pharmacology; Morpholines - pharmacology; Mutation - genetics; Phosphatidylinositol 3-Kinases - antagonists & inhibitors; Phosphatidylinositol 3-Kinases - metabolism; Promoter Regions, Genetic - genetics; Rats; RNA, Messenger - genetics; RNA, Messenger - metabolism; Signal Transduction - drug effects; Symporters - biosynthesis; Symporters - genetics; Thyroid Gland - cytology; Thyroid Gland - drug effects; Thyroid Gland - enzymology; Thyroid Gland - metabolism; Thyrotropin - antagonists & inhibitors; Thyrotropin - pharmacology; Transcriptional Activation - drug effects; Transfection
• ISSN: 0888-8809
• DOI: 10.1210/me.16.2.342

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.