G PROTEIN PATHWAYS AND REGULATION IN RPE CELLS

调节视网膜色素上皮(RPE)的功能可能 涉及在RPE中优先表达的受体和G蛋白 细胞。我们过去在RPE细胞中鉴定新的G蛋白的努力已经 很成功。我们还研究了G蛋白的信号转导机制 在RPE细胞中通过分子克隆可能编码的RPE特异性cDNA 信号转导通路的组成。我们最近的发现指出 存在一种独特的受体介导的G蛋白偶联过程 RPE细胞。 我们已经在牛RPE细胞中发现了一种新的G蛋白偶联受体， 暂定为RPE-视网膜G蛋白偶联受体或RGR。 这种新的七螺旋受体与亚家族有显著的同源性 视觉色素，原位杂交表明它是 选择性地表达在RPE细胞、内核层细胞和 神经节细胞层的特定细胞。它不是在 光感受器，或在视网膜以外的组织中，可能除了 大脑。这种受体在RPE中的定位，高水平的 它的mRNA表达，以及它与视觉色素的同源性表明 这种受体的功能在视觉过程中很重要 牵涉到RPE。 RGR基因可能编码一种新的视蛋白同系物，与视黄醛结合。 其功能可能是催化视黄醛异构化或作为 捕获11顺式视网膜的蛋白质。RGR的替代功能可以是 结合活化蛋白介导一种新的G蛋白反应途径 并与异源三聚体G蛋白偶联。我们预测RGR 基因在脊椎动物中高度保守。RPE中RGR的丰度 细胞会强烈地表明它参与了一个重大的和 RPE的专业角色。 我们将通过生物化学表征来检验这些假设和其他假设 RGR基因产物。这项提议的目标是进一步 鉴定RGR基因，确定其可能的受体功能 RGR，并阐明RPE中特殊的G蛋白途径及其调控 细胞。这种选择性表达的视蛋白的分子克隆 视黄素同系物为进一步研究提供了切入点 RPE的功能、分化和疾病。

Regulation of the functions of the retinal pigment epithelium (RPE) may involve receptors and G proteins that are expressed preferentially in RPE cells. Our past efforts to identify novel G proteins in RPE cells have been successful. We have also investigated G protein signaling mechanisms in RPE cells by molecular cloning of RPE-specific cDNAs that may encode the components of signal transduction pathways. Our recent findings point to the presence of a unique receptor-mediated G protein-coupled process in the RPE cell. We have identified in bovine RPE cells a novel G protein-coupled receptor, tentatively referred to as RPE-retinal G protein-coupled receptor or RGR. This novel heptahelical receptor is notably homologous, to the subfamily of visual pigments, and it has been shown by in situ hybridization to be selectively expressed in RPE cells, cells in the inner nuclear layer, and specific cells of the ganglion cell layer. It is not expressed in the photoreceptors, or in tissues other than the retina, except possibly the brain. The localization of this receptor in the RPE, the high level of expression of its mRNA, and its homology to the visual pigments suggest that the function of this receptor is important in the visual process involving the RPE. The RGR gene may encode a novel opsin homologue that binds retinaldehyde. Its function may be to catalyze retinaldehyde isomerization or act as a trapping protein for 11-cis-retinal. An alternative function of RGR may be to mediate a novel G protein response pathway by binding to an activating ligand and coupling to a heterotrimeric G protein. We predict that the RGR gene is highly conserved in vertebrates. The abundance of RGR in the RPE cell would strongly suggest that it participates in a major and specialized role of the RPE. We will test these and other hypotheses by biochemical characterization of the RGR gene product. The objectives of this proposal are to further characterize the RGR gene, determine the putative receptor function of RGR, and elucidate specialized G protein pathways and regulation in RPE cells. The molecular cloning of this selectively expressed opsin or retinochrome homologue provides an entry point for further investigation of RPE function, differentiation, and disease.