Zhang P, Mellon S H
Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco 94143-0556, USA.
Mol Endocrinol. 1997 Jun;11(7):891-904. doi: 10.1210/mend.11.7.9940.
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.
孤儿核受体类固醇生成因子1（SF-1）在调节大鼠睾丸间质细胞和肾上腺皮质细胞中P450c17基因的表达方面发挥着关键作用。其他未被SF-1结合的DNA序列也参与了这两种细胞类型中大鼠P450c17基因的转录调控。-447/-399区域或-447/-419区域可增强基础转录和cAMP诱导的转录，而-418/-399区域比完整的-447/-399 DNA更能增强基础转录。-447/-399 DNA序列包含孤儿核受体结合基序AGGTCA的三个不完全拷贝，至少三种已知的孤儿核受体，即鸡卵清蛋白上游启动子转录因子（COUP-TF）、SF-1和神经生长因子诱导的早期反应基因（NGFI-B），可与-447/-399 DNA结合。当这三个元件呈线性排列时，AGGTCA三联体被一组核蛋白结合，而当这些元件分开时，则被另一组蛋白结合。当元件分开时，COUP-TF不再结合，-418/-399区域被一种能极大刺激基础转录的蛋白结合。-447/-419区域被两种不同的蛋白结合，这两种蛋白介导基础转录和cAMP刺激的转录。我们将结合-418/-399的蛋白称为转录类固醇生成因子诱导物-1（StF-IT-1），结合-447/-419的蛋白之一称为StF-IT-2。StF-IT-1和StF-IT-2在睾丸间质细胞和肾上腺细胞中均有发现，且两种细胞类型中的转录调控相似。SF-1和NGF-IB可能通过取代COUP-TF（一种转录抑制因子）来增加转录，因为这些蛋白共享DNA结合结构域。然而，单独作为单体结合的SF-1和NGF-IB均不能增加转录。相反，这些蛋白必须与另一种DNA结合蛋白，如StF-IT-2相互作用，才能增加转录。StF-IT-2也需要与结合在DNA上的SF-1（或NGF-IB）相互作用，自身不能增加转录。这种作用机制不同于SF-1调节大鼠P450c17基因-84/-55区域转录的机制。因此，我们定义了一种孤儿核受体作为单体与DNA结合的新作用机制。
