MOLECULAR REGULATION OF THE GNRH RECEPTOR GENE BY GNRH

促性腺激素释放激素(GnRH)与垂体前叶促性腺激素细胞上的高亲和力受体结合后，刺激黄体生成素(LH)和卵泡刺激素(FSH)的合成，这是男性和女性正常性腺功能所必需的。因此，GnRH与其同源垂体受体的相互作用是调节生殖功能的中枢点。为了研究GnRH受体(GnRH)的转录调控，我们克隆了小鼠GnRHR的编码基因，发现GnRHR基因在促性腺激素来源的αT3-1细胞中的表达是由一个由类固醇生成因子-1(SF-1)结合位点、共识激活蛋白-1(AP-1)元件和我们称为GnRH受体激活序列(GRAS)的非规范元件组成的三部分增强子介导的。此外，1900bp的近端启动子足以在转基因小鼠中实现组织特异性表达和GnRH反应性。最近，我们已经确定GnRH对αT3-1细胞中GnRHR基因的调节部分是通过蛋白激酶C/细胞外信号调节的激酶依赖的典型AP-1位点的激活来实现的。我们还确定了转录因子FOS和Jun家族的成员都与GnRHR启动子中的AP-1结合。然而，需要进一步的研究来描绘导致促性腺激素释放激素激活AP-1的信号转导级联(S)和下游靶点。因此，我们提出了3个特异性目标：1)确定GnRH诱导GnRHR基因启动子是否需要双重MAPK信号级联；2)确定最终介导AP-1反式激活GnRHR的蛋白(S)；以及3)确定AP-1是否对转基因小鼠GnRH调节GnRHR基因启动子是必需的。

Upon binding to specific, high-affinity receptors on gonadotrope cells of the anterior pituitary gland, gonadotropin-releasing hormone (GnRH) stimulates the synthesis of luteinizing hormone (LH) and follicle stimulating hormone (FSH) which are essential for normal gonadal function in both males and females. Therefore, the interaction of GnRH with its cognate pituitary receptor serves as a central point for regulation of reproductive function. To examine transcriptional regulation of the GnRH receptor (GnRH), we have cloned the gene encoding the murine GnRHR and found that expression of the GnRHR gene in gonadotrope- derived alphaT3-1 cells is mediated by a tripartite enhancer comprised of a steroidogenic factor-1 (SF-1) binding site, a consensus activator protein-1 (AP-1) element and a non-canonical element we have termed the GnRH receptor activating sequence (GRAS). Further, 1900 bp of proximal promoter is sufficient to confer tissue-specific expression and GnRH responsiveness in transgenic mice. Recently, we have determined that GnRH regulation of the GnRHR gene in alphaT3-1 cells is partially mediated by protein kinase C/extracellular signal-regulated kinase dependent activation of the canonical AP-1 site. We have also determined that members of both the fos and jun family of transcription factors bind at AP-1 in the GnRHR promoter. Further studies are, however, necessary to delineate the signal transduction cascade(s) and downstream targets that lead to activation of AP-1 by GnRH. Accordingly, we propose 3 specific aims to: 1) determine if dual MAP kinase signaling cascades are necessary for GnRH induction of the GnRHR gene promoter; 2) identify the protein(s) that ultimately mediate GnRHR transactivation at AP-1; and 3) determine if AP-1 is necessary for GnRH regulation of the GnRHR gene promoter in transgenic mice.