GONADAL RECEPTORS/MECHANISMS OF ACTION OF PEPTIDE HORMONES IN STEROIDOGENIC CELLS

1)LH受体：促黄体激素受体（LHR）是控制性腺功能的重要组成部分。已在5176 bp区域（来自ATG）内鉴定了人LHR基因的启动子结构域。在性腺和非性腺组织中，主要转录位点（TSS）位于该TATA基因的176 bp启动子内。在人睾丸（~ 1087 bp）和绒毛膜癌细胞（~ 245至463 bp）中鉴定了上游TSS。在大鼠中，LHR基因似乎在几种体外系统（稳定和原代细胞培养物）中被上游序列（~ 176至2056 bp）组成型抑制。然而，在人类中存在细胞类型特异性上游抑制。啮齿类动物和人类之间的差异可能与细胞特异性转录因子的存在有关，和/或由于LHR基因的5个侧翼的差异（60%相似性）。不能排除上游启动子参与人类细胞，这也可以解释LHR mRNA在胎盘肿瘤细胞（绒毛膜癌）中相对于正常胎盘细胞的过度表达。176 bp的启动子包含两个Sp1结构域的核心重要性，与内源性Sp1和Sp3因子相互作用。一个不完美的雌激素受体半位点反应元件直接重复，位于启动子5的Sp1位点，被确定为Sp1/Sp3驱动的基础转录的抑制位点。该位点的突变导致基础启动子活性增加100%。该调控位点可能对该基因在性腺和非性腺组织中的表达具有差异性调控作用。2)催乳素受体：人类催乳素受体（hPRLR）基因的结构已经解析。5-非翻译区包含6个替代的第一外显子：hE 1 -3，大鼠/小鼠的人类同源物，和hE 1-N1-5，人类特异性。它还含有一个共同的非编码外显子2。编码区包含外显子3-10。不同组织中hPRLR基因启动子的差异利用可能通过激活不同的启动子来赋予个体催乳素应答。3)类固醇生成的激素控制：17-B类固醇脱氢酶3型（17 b-HSD）是一种Leydig细胞酶，从雄烯二酮产生睾酮。我们的研究表明，该酶的活性是依赖于细胞葡萄糖通过ATP的产生。克隆了大鼠酶同工型3。这种酶在转录水平上被促性腺激素下调.在无葡萄糖存在下，转染细胞中的酶活性显著降低。这些研究为阐明17 b-HSD活性的调节机制提供了基础。

1) The LH receptor: The luteinizing hormone receptor (LHR) is an essential component in the control of gonadal function. The promoter domain of the human LHR gene has been identified within the 5 176bp region (from ATG). The major transcriptional sites (TSS) are located within the 176 bp promoter of this TATAless gene in gonadal and non-gonadal tissues. Upstream TSS were identified in the human testis (- 1087 bp) and choriocarcinoma cells (-245 to 463 bp). In the rat, the LHR gene appears to be constitutively inhibited by upstream sequences (-176 to 2056 bp) in several in vitro systems (stable and primary cell cultures). However, in the human there is cell- type specific upstream inhibition. The differences between rodent and human may be related to the presence of cell-specific transcriptional factor(s) and or due to differences in the 5 flanking of the LHR gene (60% similarity). The participation of an upstream promoter in human cells cannot be excluded, which also may explain the over-expression of LHR mRNA in JAR tumor cells (choriocarcinoma) vs. normal placental cells. The 176 bp promoter contains two Sp1 domains of central importance which interact with endogenous Sp1 and Sp3 factors. An imperfect estrogen receptor half-site response element direct-repeat, located within the promoter 5 to the Sp1 sites, was identified as the inhibitory site for Sp1/Sp3-driven basal transcription. Mutation of this site causes a 100% increase in basal promoter activity. This regulatory site may contribute to the differential regulation of expression of the gene in gonadal and non-gonadal tissues. 2) Prolactin receptor: The structure of the human prolactin receptor (hPRLR) gene has been resolved. The 5-untranslated region contains 6 alternative first exons: hE1-3, the human homolog of the rat/mouse, and hE1-N1-5, human-specific. It also contains one common non- coding exon 2. The coding region comprises exons 3-10. The differential promoter utilization of the hPRLR gene in diverse tissues may confer individual prolactin responses through activation of different promoters. 3) Hormonal Control of Steroidogenesis: 17-b steroid dehydrogenase type 3 (17b-HSD) is a Leydig cell enzyme that generates testosterone from androstenedione. Our studies have demonstrated that the enzyme activity is dependent on cell glucose through ATP generation. The rat enzyme isoform 3 was cloned. This enzyme is down- regulated by gonadotropin at the transcriptional level. The enzyme activity in transfected cells was markedly reduced in the absence of glucose. These studies provide a basis for elucidation of the regulatory mechanism(s) of 17b-HSD activity.