Transcription of cholesterol side-chain cleavage cytochrome P450 in the placenta: activating protein-2 assumes the role of steroidogenic factor-1 by binding to an overlapping promoter element.
Progesterone is essential to the sustenance of pregnancy in humans and other mammals. From the second trimester on, the human placenta is the sole origin of de novo synthesized steroid hormones. In mice, placentation at midgestation is accompanied by a temporal rise of steroid hormone synthesis commencing in the giant cells of the mouse trophoblast. In doing so, the giant trophoblasts, as any other steroidogenic cell, express high levels of the key steroidogenic enzyme, cholesterol side-chain cleavage cytochrome P450 (P450scc). Because steroidogenic factor 1 (SF-1), the transcription factor required for expression of P450scc in the adrenals and the gonads, is not expressed in the placenta, we hypothesized that placenta-specific nuclear factor(s) (PNF) assumes the role of SF-1 by binding to the same promoter region that harbors the SF-1 recognition site in the P450scc gene. To address this possibility, we used SCC1, a well conserved proximal region in the P450scc genes (-60/-32 in the rat gene) to purify PNF from human term placenta. Sequencing of the purified PNF revealed that it is the alpha isoform of the human activating protein-2 (AP-2alpha). Specific antibodies tested in EMSA confirmed that AP-2alpha is the predominant isoform that binds SCC1 in the human placenta, whereas AP-2gamma is the only mouse placental protein that binds this oligonucleotide. Functional studies showed that coexpression of the rat P450scc promoter (-378/+8 CAT) and AP-2 isoforms (alpha or gamma) in human embryonic kidney 293 cells results in a marked activation of chloramphenicol acetyltransferase (CAT) transcription that is dependent on an intact AP-2 motif, GCCTTGAGC. This motif conforms with consensus sequences previously determined for binding of the AP-2 alpha and gamma isoforms. Mutations of the AP-2 element ablated binding of AP-2 to SCC1, as well as severely diminished the promoter activity in primary mouse giant trophoblasts and human choriocarcinoma JAR cells. Collectively, these studies suggest that expression of placental P450scc is governed by AP-2 factors that bind to a cis-element that largely overlaps the sequence required for recognition of SF-1 in other steroidogenic tissues.
Ben-Zimra
Micha
M
Department of Biological Chemistry, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel 91904.
Koler
Moriah
M
Orly
Joseph
J
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005260:Female; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; C515057:NR5A1 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; C493673:TFAP2A protein, human; C493679:TFAP2C protein, human; C493668:Tfap2a protein, mouse; C583890:Tfap2c protein, mouse; D050656:Transcription Factor AP-2; D014157:Transcription Factors; C515058:steroidogenic factor 1, mouse; C515060:steroidogenic factor 1, rat; D004247:DNA; D002786:Cholesterol Side-Chain Cleavage Enzyme