Human chorionic somatomammotropin gene enhancer activity is dependent on the blockade of a repressor mechanism.
The human chorionic somatomammotropin genes (hCS-A and -B) are expressed at high levels in the syncytiotrophoblast during pregnancy. A 22-base-pair (bp) transcriptional enhancer factor-1 (TEF-1) element in a 1022-bp fragment of the hCS-B 3'-flanking DNA (nucleotides 1-1022) was shown to be important for efficient promoter activity in placental cells. However, the TEF-1 site used alone does not contain all of the information required for the complete enhancer activity seen with the 1022-bp fragment. A 241-bp region of the 1022-bp fragment (nucleotides 1-241) maintains full enhancer activity in placental cells. Interactions between placental nuclear factors and sequences distinct from the TEF-1 element (nucleotides 117-139) were identified by gel mobility shift assay using the up-stream region corresponding to nucleotides 1-80. Interaction between these factors and the TEF-1 element was indicated by competition of the 1-80 bp region for complex formation by a TEF-1 site. We mutated sequences within the 1-80 bp region of the 241-bp enhancer fragment and assessed the enhancer function of wild-type and modified 241-bp fragments. We identified a sequence (DF-1 site) upstream of the TEF-1 site which is required for hCS-B enhancer function. DF-1 derepresses a repressor mechanism present in the 241-bp fragment that inhibits TEF-1 activity. A component of this repressor mechanism (RF-1 site) is present in the 1-80 bp region adjacent to the DF-1 site. Gel mobility shift competition analysis shows that the RF-1 and DF-1 sites participate in the formation of a common complex or compete for common protein factors in a tissue-specific manner.
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Department of Physiology, University of Manitoba, Winnipeg, Canada.
Cattini
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D001483:Base Sequence; D001665:Binding Sites; D002822:Choriocarcinoma / Q000473:pathology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D005260:Female; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D005813:Genes, Synthetic; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D009841:Oligonucleotides / Q000138:chemical synthesis / Q000378:metabolism; D009928:Organ Specificity; D010920:Placenta / Q000378:metabolism*; D010928:Placental Lactogen / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D012689:Sequence Homology, Nucleic Acid; D013539:Simian virus 40 / Q000235:genetics; D000091262:TEA Domain Transcription Factors; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014594:Uterine Neoplasms / Q000473:pathology
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009841:Oligonucleotides; D000091262:TEA Domain Transcription Factors; C057182:TEAD1 protein, human; D014157:Transcription Factors; D010928:Placental Lactogen