Grad J M, Lyons L S, Robins D M, Burnstein K L
Department of Molecular & Cellular Pharmacology, University of Miami School of Medicine, Miami, Florida 33101, USA.
Endocrinology. 2001 Mar;142(3):1107-16. doi: 10.1210/endo.142.3.8049.
Androgen and glucocorticoid receptor (AR, GR), two closely related members of the nuclear receptor superfamily, can recognize a similar cis-acting DNA sequence, or hormone response element (HRE). Despite this apparent commonality, these receptors regulate distinct target genes in vivo. The AR gene itself is regulated by AR but not GR in a variety of cell types, including osteoblast-like cells, as shown here. To understand this specificity, we first identified the DNA sequences responsible for androgen-mediated up-regulation of AR messenger RNA. A 6.5-kb region encompassing exon D, intron 4, and exon E of the AR gene contains four exonic HREs and exhibits cell type-specific, AR-mediated transcriptional enhancement when placed upstream of a heterologous promoter and reporter gene. A 350-bp fragment consisting of just exons D and E exhibits the same cell- and androgen-specificity as the 6.5-kb region, as well as the native AR gene. Consistent with a role for the exonic HREs, androgen regulation via this intragenic enhancer requires the HREs as well as a functional receptor DNA binding domain. A panel of AR/GR chimeric receptors was used to test which AR domains (amino-terminal, DNA binding or ligand binding) confer androgen-specific regulation of the 350-bp enhancer. Only chimeric receptors containing the amino-terminus of AR induced reporter gene activity from the AR gene enhancer. Further, a constitutively active AR consisting of only the AR amino-terminus and DNA binding domain (AA phi) retained the capacity to activate the internal responsive region, unlike a constitutively active chimera harboring the GR amino-terminus and AR DNA binding domain (GA phi). Thus, the AR amino terminus is the sole determinant for androgen-specific regulation of the AR gene internal enhancer. These findings support a model in which the amino termini of ARs bound to HREs within the AR gene interact with an exclusive auxiliary factor(s) to elicit androgen-specific regulation of AR messenger RNA. This is the first example of androgen-specific response in which the necessary and sufficient distinguishing capacity resides within the AR amino terminus.
雄激素和糖皮质激素受体（AR、GR）是核受体超家族中两个密切相关的成员，它们能够识别相似的顺式作用DNA序列，即激素反应元件（HRE）。尽管存在这种明显的共性，但这些受体在体内调节不同的靶基因。如本文所示，在包括成骨样细胞在内的多种细胞类型中，AR基因本身受AR而非GR的调控。为了理解这种特异性，我们首先确定了负责雄激素介导的AR信使RNA上调的DNA序列。一个包含AR基因外显子D、内含子4和外显子E的6.5 kb区域含有四个外显子HRE，当置于异源启动子和报告基因上游时，表现出细胞类型特异性的、AR介导的转录增强。一个仅由外显子D和E组成的350 bp片段与6.5 kb区域以及天然AR基因表现出相同的细胞和雄激素特异性。与外显子HRE的作用一致，通过这种基因内增强子的雄激素调节需要HRE以及功能性受体DNA结合结构域。一组AR/GR嵌合受体被用于测试哪些AR结构域（氨基末端、DNA结合或配体结合）赋予350 bp增强子雄激素特异性调节。只有包含AR氨基末端的嵌合受体诱导了来自AR基因增强子的报告基因活性。此外，仅由AR氨基末端和DNA结合结构域组成的组成型活性AR（AA phi）保留了激活内部反应区域的能力，这与包含GR氨基末端和AR DNA结合结构域的组成型活性嵌合体（GA phi）不同。因此，AR氨基末端是AR基因内部增强子雄激素特异性调节的唯一决定因素。这些发现支持了一个模型，即与AR基因内HRE结合的AR氨基末端与一种排他性辅助因子相互作用，以引发AR信使RNA的雄激素特异性调节。这是雄激素特异性反应的第一个例子，其中必要且充分的区分能力存在于AR氨基末端。
