A placenta-specific enhancer of the human syncytin gene.
The cis- and trans-acting factors that are critical for placenta-specific expression of the human syncytin gene are unknown. We identified a 146-base pair (bp) region of the 5'-flanking region of the human syncytin gene from nt-294 to -148 that is essential for basal gene expression in human BeWo and JEG3 choriocarcinoma cell lines but not in hepatoblastoma and kidney cell lines. Ligation of the 146-bp fragment to a SV40 promoter or a human beta-globin minimal promoter markedly enhanced promoter activity in the placenta cells but not in the liver and kidney cells. DNase I footprint assays indicated that nuclear extracts from BeWo cells but not HepG2 cells protected four regions (FP1-FP4) of the 146-bp fragment. Site-directed mutagenesis of an SP1-binding site in FP3 and a GATA-binding site in FP4 significantly repressed promoter activity in the placenta cells. Overexpression of SP1 (Sp1 transcription factor) and GATA2 (GATA binding protein 2) and GATA3 induced syncytin promoter activity but had little or no effect on the activities of syncytin promoter fragments containing mutations in the SP1- and GATA-binding sites. GATA2 and -3 mRNA levels increased markedly during spontaneous in vitro differentiation of human cytotrophoblast cells when the cytotrophoblast cells fused to form a syncytium. These findings strongly suggest that the 146-bp region of the 5'-flanking region (nt-294/-148) of the human syncytin gene acts as a placenta-specific enhancer. Binding of SP1 and GATA family members to this enhancer is critical for cell-specific expression of the syncytin gene.
Cheng
You-Hong
YH
Department of Pediatrics, University of Cincinnati College of Medicine and Division of Endocrinology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
Handwerger
Stuart
S
D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology; D004742:Enhancer Elements, Genetic / Q000502:physiology*; D005260:Female; D050989:GATA2 Transcription Factor; D050990:GATA3 Transcription Factor; D005786:Gene Expression Regulation / Q000502:physiology*; D015686:Gene Products, env / Q000096:biosynthesis*; D006801:Humans; D010920:Placenta / Q000378:metabolism*; D011257:Pregnancy Proteins / Q000096:biosynthesis*; D011268:Pregnancy-Specific beta 1-Glycoproteins / Q000502:physiology; D011401:Promoter Regions, Genetic; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic / Q000502:physiology*; D014327:Trophoblasts / Q000378:metabolism
D004268:DNA-Binding Proteins; D050989:GATA2 Transcription Factor; C494711:GATA2 protein, human; D050990:GATA3 Transcription Factor; C494749:GATA3 protein, human; D015686:Gene Products, env; D011257:Pregnancy Proteins; D011268:Pregnancy-Specific beta 1-Glycoproteins; D015534:Trans-Activators; D014157:Transcription Factors; C405335:syncytin