The Xenopus laevis isoform of G protein-coupled receptor 3 (GPR3) is a constitutively active cell surface receptor that participates in maintaining meiotic arrest in X-laevis oocytes
The Xenopus laevis isoform of G protein-coupled receptor 3 (GPR3) is a constitutively active cell surface receptor that participates in maintaining meiotic arrest in X-laevis oocytes
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DOI：
10.1210/me.2008-0124
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发表时间：
2008-08-01
影响因子：
--
通讯作者：
Hammes, Stephen R.
中科院分区：
文献类型：
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作者：
Deng, James;Lang, Stephanie;Hammes, Stephen R.
卵母细胞在减数分裂前期I停滞，直至排卵，此时促性腺激素触发一部分卵母细胞在一个被称为“成熟”的过程中恢复减数分裂。减数分裂停滞是通过一种机制维持的，即持续性环磷酸腺苷（cAMP）的产生超过磷酸二酯酶介导的降解，导致细胞内cAMP升高。研究表明，一种组成性激活的Gα(s)偶联受体——G蛋白偶联受体3（GPR3）是负责维持小鼠卵母细胞减数分裂停滞的分子之一。在此，我们利用更易于操作的非洲爪蟾卵母细胞模型系统来描述GPR3的信号传导和功能特性。我们从卵母细胞中克隆了非洲爪蟾的GPR3异构体（XGPR3），并表明过表达的XGPR3会大幅通过Gβγ信号传导提高卵母细胞内的cAMP。过表达的XGPR3抑制了类固醇触发的激酶激活以及分离卵母细胞的成熟，还抑制了促性腺激素诱导的有卵泡包裹的卵母细胞的成熟。相反，使用反义寡脱氧核苷酸消耗XGPR3会降低细胞内cAMP水平，并增强类固醇和促性腺激素介导的卵母细胞成熟。有趣的是，对非洲爪蟾卵母细胞进行胶原酶处理会切割并使细胞表面的XGPR3失活，这增强了类固醇触发的卵母细胞成熟以及丝裂原活化蛋白激酶（MAPK）的激活。此外，人绒毛膜促性腺激素对有卵泡包裹的卵母细胞的处理会触发金属蛋白酶介导的卵母细胞表面XGPR3的切割。总之，这些结果表明GPR3调节卵母细胞对促进成熟信号的反应，并且促性腺激素介导的金属蛋白酶激活可能通过使组成性GPR3信号失活在使卵母细胞对成熟敏感方面起到部分作用。
Oocytes are held in meiotic arrest in prophase I until ovulation, when gonadotropins trigger a subpopulation of oocytes to resume meiosis in a process termed " maturation." Meiotic arrest is maintained through a mechanism whereby constitutive cAMP production exceeds phosphodiesterasemediated degradation, leading to elevated intracellular cAMP. Studies have implicated a constitutively activated G alpha(s)-coupled receptor, G proteincoupled receptor 3 (GPR3), as one of the molecules responsible for maintaining meiotic arrest in mouse oocytes. Here we characterized the signaling and functional properties of GPR3 using the more amenable model system of Xenopus laevis oocytes. We cloned the X. laevis isoform of GPR3 (XGPR3) from oocytes and showed that overexpressed XGPR3 elevated intraoocyte cAMP, in large part via G beta gamma signaling. Overexpressed XGPR3 suppressed steroid-triggered kinase activation and maturation of isolated oocytes, as well as gonadotropin-induced maturation of follicle-enclosed oocytes. In contrast, depletion of XGPR3 using antisense oligodeoxynucleotides reduced intracellular cAMP levels and enhanced steroid- and gonadotropin-mediated oocyte maturation. Interestingly, collagenase treatment of Xenopus oocytes cleaved and inactivated cell surface XGPR3, which enhanced steroid- triggered oocyte maturation and activation of MAPK. In addition, human chorionic gonadotropin-treatment of follicle-enclosed oocytes triggered metalloproteinase-mediated cleavage of XGPR3 at the oocyte cell surface. Together, these results suggest that GPR3 moderates the oocyte response to maturation-promoting signals, and that gonadotropin-mediated activation of metalloproteinases may play a partial role in sensitizing oocytes for maturation by inactivating constitutive GPR3 signaling.