NOVEL LOCATION AND FUNCTION OF A THYROID-HORMONE RESPONSE ELEMENT

We describe a novel thyroid hormone response element (TRE)-containing sequence, clone 144, isolated by immunoprecipitation of nuclear thyroid hormone receptor (TR)-DNA complexes from the rat pituitary tumor cell line GH4. These cells express several mRNAs of similar to 10 kb that hybridize to the TRE-containing genomic clone 144. These mRNAs are up-regulated at the transcriptional level in the absence of thyroid hormone (T3) and repressed in its presence, The sequence protected from DNase I digestion by TR in clone 144 contains two consensus TRE half-sites arranged as inverted palindromes. The clone 144 TRE is located in the 3' untranslated region (UTR) of several related mRNAs, A reporter construct transfected into 293 cells was responsive to TR regulation when the clone 144 TRE was inserted in the 3' UTR but not when inserted upstream of the promoter. As found for the endogenous 144 mRNAs, the 144 TRE reporter construct is activated by TR in the absence of T3, but not in its presence, Deletion analysis showed that clone 144 sequences flanking the TRE were necessary for TR-mediated regulation, suggesting that the mechanism by which TR regulates transcription through a TRE in the 3' UTR is different from that through the TREs located in the promoter region.