Division of Hematology & Oncology Rhode Island Hospital and Brown University School of Medicine Providence, RI 02903, USA.
Steroids. 2011 Aug;76(9):892-6. doi: 10.1016/j.steroids.2011.02.018. Epub 2011 Feb 25.
G-protein-coupled receptor 30 (GPR30/GPER) belongs to the seven transmembrane receptor (7TMR) superfamily, the most common class of surface receptor with approximately 800 known members. GPER promotes estrogen binding and rapid signaling via membrane-associated enzymes resulting in increased cAMP and release of heparan bound epidermal growth factor (proHB-EGF) from breast cancer cells. However, GPER is predominately localized intracellularly in breast cancer cells with minor amounts of receptor on the cell surface, an observation that has caused some controversy regarding its potential role as a plasma membrane estrogen receptor. Using the widely employed approach of tracking recombinant 7TMRs by surface labeling live cells, we have begun to characterize and compare the endocytic fate of GPER to other similarly labeled 7TMRs. Upon ectopic expression in human embryonic kidney HEK-293 cells, functional GPER is generated as these cells acquire the capacity to stimulate cAMP and activate cyclic AMP responsive binding protein in response to estradiol-17 beta stimulation. GPER is detectable on the cell surface by immunofluorescent analysis using HA-specific antibodies, albeit the bulk of the receptor is located intracellularly. Like β1AR (beta 1 adrenergic receptor) and CXCR4 (C-X-C chemokine receptor 4), GPER exits the plasma membrane via clathrin-coated pits and enters early endosomes. Interestingly, GPER has a destination that is uncommon among 7TMRs, as it accumulates in a perinuclear compartment. Like many 7TMRs (approximately one-third), GPER trafficking from the plasma membrane is constitutive (occurs in the absence of agonist). However, its route of intracellular trafficking is highly unusual, as 7TMRs typically recycle to the plasma membrane (e.g. β1AR) or are degraded in lysosomes (e.g. CXCR4). The accumulation of GPER in the perinuclear space and its possible significance for attenuating estrogen action via this newly recognized membrane estrogen receptor is discussed herein.
G 蛋白偶联受体 30（GPR30/GPER）属于七次跨膜受体（7TMR）超家族，是最常见的表面受体之一，大约有 800 个已知成员。GPER 通过膜相关酶促进雌激素结合和快速信号转导，导致 cAMP 增加和乳腺癌细胞中肝素结合的表皮生长因子（proHB-EGF）的释放。然而，GPER 在乳腺癌细胞中主要定位于细胞内，细胞表面只有少量受体，这一观察结果引起了一些关于其作为质膜雌激素受体的潜在作用的争议。通过跟踪活细胞表面标记的重组 7TMRs 的广泛应用方法，我们已经开始表征和比较 GPER 的内吞作用与其它类似标记的 7TMRs。在人胚肾 HEK-293 细胞中外源表达时，这些细胞获得了刺激 cAMP 和激活环磷酸腺苷反应结合蛋白的能力，以响应雌二醇-17β的刺激，从而产生功能性的 GPER。通过使用 HA 特异性抗体的免疫荧光分析，可在细胞表面检测到 GPER，尽管受体的大部分位于细胞内。与β1AR（β1 肾上腺素能受体）和 CXCR4（C-X-C 趋化因子受体 4）一样，GPER 通过网格蛋白包被陷窝从质膜中输出，并进入早期内体。有趣的是，GPER 具有在 7TMR 中不常见的归宿，因为它在核周区积累。与许多 7TMR 一样（约三分之一），GPER 从质膜的运输是组成型的（在没有激动剂的情况下发生）。然而，其细胞内运输途径非常不寻常，因为 7TMR 通常会再循环到质膜（例如β1AR）或在溶酶体中降解（例如 CXCR4）。GPER 在核周空间的积累及其可能通过这种新发现的膜雌激素受体来减弱雌激素作用的意义，本文进行了讨论。
