Multiple orphan nuclear receptors converge to regulate rat P450c17 gene transcription: novel mechanisms for orphan nuclear receptor action.
The orphan nuclear receptor steroidogenic factor-1 (SF-1) plays a key role in regulating the expression of the rat P450c17 gene in testicular Leydig and in adrenocortical cells. Other DNA sequences, not bound by SF-1, are also involved in transcriptional regulation of the rat P450c17 gene in both cell types. The region from -447/-399 or from -447/-419 increased both basal and cAMP-induced transcription, and the region from -418/-399 increased basal transcription to a greater extent than the intact -447/-399 DNA. The -447/-399 DNA sequence contains three imperfect copies of the orphan nuclear receptor-binding motif, AGGTCA, and at least three known orphan nuclear receptors, chicken ovalbumin upstream promoter transcription factor (COUP-TF), SF-1, and an early response gene induced by nerve growth factor (NGFI-B), bind to -447/-399 DNA. The AGGTCA triad is bound by one set of nuclear proteins when these three elements are colinear and is bound by a different set of proteins when these elements are separated. When the elements are separated, COUP-TF no longer binds, and the region -418/-399 is bound by a protein that greatly stimulates basal transcription. The region -447/-419 is bound by two different proteins that mediate both basal and cAMP-stimulated transcription. We call the protein binding to -418/-399 steroidogenic factor inducer of transcription-1 (StF-IT-1), and one of the proteins binding to -447/-419, StF-IT-2. SF-1 binds to a second AGGTCA element in the -447/-419 region. StF-IT-1 and StF-IT-2 are both found in Leydig and adrenal cells, and transcriptional regulation is similar in both cell types. SF-1 and NGF-IB may increase transcription by displacing COUP-TF (a transcriptional repressor) because these proteins share DNA-binding domains. However, neither SF-1 nor NGF-IB alone, binding as monomers, increases transcription. Rather, these proteins must interact with another DNA-binding protein, e.g. StF-IT-2, to increase transcription. StF-IT-2 also requires interaction with SF-1 (or NGF-IB) bound to DNA and cannot increase transcription by itself. This mechanism of action is different from the mechanism by which SF-1 regulates transcription from the -84/-55 region of the rat P450c17 gene. Thus, we have defined a novel mechanism of action for orphan nuclear receptors that bind to DNA as monomers.
Zhang
P
P
Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco 94143-0556, USA.
Mellon
S H
SH
D000818:Animals; D001345:Autoradiography; D001483:Base Sequence; D051838:COUP Transcription Factor I; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D018983:DNA Footprinting; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D051717:Fushi Tarazu Transcription Factors; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D018398:Homeodomain Proteins; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000235:genetics; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear; D013254:Steroid 17-alpha-Hydroxylase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics*; D016335:Zinc Fingers / Q000235:genetics*
D051838:COUP Transcription Factor I; D017931:DNA Primers; D004268:DNA-Binding Proteins; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; C497591:Nr2f1 protein, rat; D018160:Receptors, Cytoplasmic and Nuclear; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; C515060:steroidogenic factor 1, rat; D004247:DNA; D013254:Steroid 17-alpha-Hydroxylase