REGULATION OF FOLLITROPIN ACTIONS

目前对G蛋白偶联受体(GPCRs)调节的研究表明，靶细胞中的反馈调节环以协调的方式影响这些受体的功能特性和密度。这一调控的两个重要方面是GPCRs被被称为G蛋白偶联受体激酶(GRKs)的蛋白激酶家族所磷酸化，以及GPCRs与一家族被称为arrestins的蛋白质的关联。由磷酸化的GPCRs和阻滞素形成的复合体被认为是GPCRs与G蛋白解偶联、GPCRs内部化以及随后内部化受体循环和/或下调的共同分子中间产物。卵泡刺激素受体(FSHR)是GPCR家族中的一个独特的成员。其中，磷酸化位点的独特性(即细胞内的第一个和第三个环)以及磷酸化对内化的非必要作用预示着与其他GPCR相比，一种不寻常的调控模式。本文提出的研究将进一步探索arrestin-2或-3如何影响FSHR的解偶联和运输，并将确定参与内化、解偶联和arrestin结合的FSHR的结构基序。具体目的如下：(1)验证GRK2催化的FSHR的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。我们还认为arrestin-2和arrestin-3在解偶联和内化过程中可能发挥不同的作用。)确定负责结合arrestin-2或-3的FSHR的结构特征。(3)确定FSHR的结构特征，这些结构特征参与了FSH的内化和rFSHR与其效应系统的解偶联。(4)确定内化的FSH-FSHR复合体的命运和内化的功能后果。这些研究应能为调节FSHR的功能和细胞贩运提供有价值的见解，特别是对一般的GPCRs。

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.