Role of the cyclic adenosine 3',5'-monophosphate response element in efficient expression of the rat thyrotropin receptor promoter.
The "minimal" promoter region of the TSH receptor gene, -195 to -39 basepairs (bp), exhibits basal promoter activity, thyroid specificity, and negative regulation by TSH via its cAMP signal. In FRT thyroid cells and by comparison to pTRCAT5'-199, 5'-deletion mutants of chloramphenicol acetyltransferase (CAT) constructs from -199 to -150 bp of the minimal promoter decrease basal CAT activity by 50%, whereas continued deletion to -146 bp increases activity more than 4-fold. Continued deletion to -131 bp results in basal activity less than that of the -199 bp construct. An octameric cAMP response element (CRE)-like sequence, TGAGGTCA, is within -146 to -131 bp and starts at -139 bp. Its mutation to a consensus CRE (TGACGTCA) or AP1 (TGAGTCA) site or mutation of several residues flanking its 3'-terminus can improve promoter activity as much as 8-fold compared to pTRCAT5'-199. A nonpalindromic mutation to CGAGGACA decreases basal promoter activity to the level of the 199-bp minimal promoter. The CRE-like sequence between -139 and -132 bp is a constitutive enhancer of promoter activity in FRT thyroid cells, since, ligated to a simian virus-40-promoter-driven CAT gene, it increases CAT activity in the absence of forskolin in proportion to copy number and independent of direction or position. It can, however, function as a cAMP-responsive CRE, as evidenced by the fact that forskolin increases the activity of the same simian virus-40-promoter-driven CAT gene constructs in Buffalo rat liver (BRL) cells. DNAase-I footprinting shows that the CRE region is protected by a purified binding region peptide of the CRE-binding protein, activating transcription factor-2, and recombinant AP1 (human c-jun) as well as by BRL, FRT, and FRTL-5 rat thyroid cell nuclear extracts. Gel mobility shift analyses show that multiple CRE-binding proteins in the BRL, FRT, and FRTL-5 cell nuclear extracts form complexes with the CRE-like site, that one of these is CRE-binding protein, and that all form complexes with mutant sequences of the CRE-like site in a manner that exactly parallels their effects on constitutive enhancer function in FRT thyroid cells. We show, therefore, that the CRE-like site in the minimal TSH receptor promoter functions as a constitutive enhancer of promoter activity in FRT thyroid cells yet is a cAMP-responsive CRE.(ABSTRACT TRUNCATED AT 400 WORDS)
Ikuyama
S
S
Laboratory of Biochemistry and Metabolism, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Shimura
H
H
Hoeffler
J P
JP
Kohn
L D
LD
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000502:physiology*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D051381:Rats; D011989:Receptors, Thyrotropin / Q000235:genetics*; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D013961:Thyroid Gland; D013972:Thyrotropin / Q000494:pharmacology*; D014162:Transfection
D009838:Oligodeoxyribonucleotides; D011989:Receptors, Thyrotropin; D011994:Recombinant Proteins; D013972:Thyrotropin; D000242:Cyclic AMP; D015500:Chloramphenicol O-Acetyltransferase