REGULATION OF FOLLITROPIN ACTIONS

目前对G蛋白偶联受体（gpcr）调控的研究表明，靶细胞中的反馈调控回路以坐标方式影响这些受体的功能特性和密度。这种调节的两个重要方面是gpcr被称为G蛋白偶联受体激酶（GRKs）的蛋白激酶家族磷酸化，以及gpcr与称为阻滞蛋白的蛋白家族的关联。磷酸化的GPCR和抑制因子形成的复合物被认为是GPCR与G蛋白解偶联、GPCR内化以及随后的再循环和/或内化受体下调的常见分子中间体。卵泡激素受体（FSHR）在几个方面都是GPCR家族中独特的成员。其中，磷酸化位点（即第一和第三胞内环）的独特性以及磷酸化在内化中的非必要作用，与其他gpcr相比，预示着一种不同寻常的调节模式。本文提出的研究将进一步探讨逮捕-2或-3如何影响FSHR的解耦和贩运，并将定义涉及内化、解耦和逮捕结合的FSHR的结构基序。具体目的如下：(1)验证grk2催化的FSHR磷酸化是内化所必需的，而grk6催化的磷酸化是解偶联所必需的假设。我们还提出，在解耦和内化过程中，arrestin-2和arrestin-3可能发挥不同的作用。)定义FSHR负责结合抑制-2或-3的结构特征。(3)明确参与卵泡激素（FSH）内化和FSHR与其效应系统解耦的FSHR的结构特征。(4)定义内化FSH-FSHR复合体的命运和内化的功能后果。这些研究应该为FSHR的功能调控和细胞运输提供有价值的见解，特别是gpcr。

Current research on the regulation of G protein-coupled receptors (GPCRs) shows that feedback regulatory loops in the target cell affect the functional properties and density of these receptors in a coordinate fashion. Two important aspects of this regulation are the phosphorylation of the GPCRs by a family of protein kinases known as G protein-coupled receptor kinases (GRKs) and the association of GPCRs with a family of proteins known as arrestins. The complex formed by the phosphorylated GPCR and the arrestins is believed to be a common molecular intermediate in the uncoupling of the GPCRs from G proteins, the internalization of GPCRs and the subsequent recycling and/or down-regulation of the internalized receptors. The follitropin receptor (FSHR) is a unique member of the GPCR family in several aspects. Among these, the uniqueness of loci of phosphorylation (i.e., the first and third intracellular loops) and the non-essential role for phosphorylation on internalization predict an unusual mode of regulation when compared with other GPCRs. The studies proposed herein will further explore how arrestin-2 or -3 affect the uncoupling and the trafficking of the FSHR and will define the structural motifs of the FSHR that are involved in internalization, uncoupling, and arrestin binding. The specific aims are as follows: (1) Test the hypothesis that the GRK2-catalyzed phosphorylation of the FSHR is necessary for internalization while the GRK6-catalyzed phosphorylation is necessary for uncoupling. We also propose that arrestin-2 and arrestin-3 may play different roles in uncoupling and internalization. ) Define the structural features of the FSHR that are responsible for binding arrestin-2 or -3. (3) Define the structural features of the FSHR that are involved in the internalization of follitropin (FSH) and the uncoupling of the rFSHR from its effector system. (4) Define the fate of the internalized FSH-FSHR complex and the functional consequences of internalization. These studies should provide valuable insights about the regulation of the function and the cellular trafficking of the FSHR in particular and GPCRs in general.