Mechanisms of Adhesion GPCR Action

总结/摘要：GPR 56/ADGRG 1是一种去孤儿化的脑粘附G蛋白偶联受体（AGPCR） 与生理配体胶原蛋白结合我们提出了新的证据，证明GPR 56存在于人体表面， 和小鼠血小板。这是非常有趣的，考虑到自主血小板激活，导致凝血 形成是由血小板与暴露在血管损伤部位的胶原蛋白相互作用介导的。我们 发现血小板GPR 56的药理学活化足以引起生理性血小板活化 伤口愈合（止血）和血液凝固（血栓形成）所需的程序。此外，Gpr 56敲除 在小鼠血管壁损伤模型中，小鼠具有严重的出血障碍和血凝块形成的显著缺陷。 我们假设GPR 56是介导初始G蛋白12/13依赖的血小板胶原受体。 当血小板沿着暴露的胶原蛋白滚动/移位到它们的稳定粘附部位时， 血管伤口的后缘我们将研究血小板GPR 56介导的G蛋白信号传导， 血小板形状变化，体外血小板活化，以及GPR 56在小鼠止血和 血栓形成我们发现令人信服的初步证据表明，来自Gpr 56基因敲除小鼠的血小板显著增加， 当小鼠血液以高流速流过表面时， 剪切力我们认为GPR 56并不直接参与稳定的血小板粘附，而是在血小板翻滚时， 在胶原蛋白表面，GPR 56被刺激以引起形状变化，从而允许血小板稳定地 通过不同的非GPCR胶原受体粘附。在发现血小板上的GPR 56之前，我们提出了一种新的方法。 AGPCR激活的一般模型需要受体N-末端的锚定，以及剪切力介导的 受体解离，导致AGPCR栓系激动剂暴露以诱导G蛋白信号传导。的 血小板携带的GPR 56经历的条件与该理论模型非常一致。我们的工作 还包括使用新开发的光交联激动剂探针进行生物化学研究， 相关AGPCR、GPR 56和GPR 114的激动剂结合位点。

Summary/Abstract: GPR56/ADGRG1 is a deorphanized brain Adhesion G protein Coupled Receptor (AGPCR) with a physiological ligand, collagen. We present new evidence that GPR56 is present on the surface of human and mouse platelets. This is very intriguing considering that autonomous platelet activation that leads to clot formation is mediated by platelet interactions with collagen that becomes exposed at sites of vessel injury. We found that pharmacological activation of platelet GPR56 is sufficient to elicit the physiological platelet activation program required for wound healing (hemostasis) and blood clotting (thrombosis). Moreover, Gpr56 knockout mice have a severe bleeding disorder and dramatic defects in clot formation in mouse vessel wall injury models. We hypothesize that GPR56 is the platelet collagen receptor that mediates the initial G protein 12/13-dependent platelet shape changes while platelets roll/translocate along exposed collagen to their site of stable adhesion at the lagging edges of blood vessel wounds. We will investigate platelet GPR56-mediated G protein signaling, platelet shape changes, in vitro platelet activation, and the role of GPR56 in mouse models of hemostasis and thrombosis. We found compelling preliminary evidence that platelets from Gpr56 knockout mice are dramatically defective in adhering to an immobilized collagen surface when mouse blood is flowed over the surface at high shear force. We propose that GPR56 is not directly involved in stable platelet adhesion, but as platelets tumble across the collagen surface, GPR56 is stimulated to cause the shape changes that allow platelets to then stably adhere via distinct non-GPCR collagen receptors. Before discovering GPR56 on platelets we proposed a general model of AGPCR activation that required anchoring of the receptor N-termini, and shear force-mediated receptor dissociation that leads to exposure of the AGPCR tethered agonists to induce G protein signaling. The conditions experienced by platelet-borne GPR56 align remarkably well with this theoretical model. Our work also includes conducting biochemical studies using newly developed photo-crosslinking agonist probes to define the agonist binding sites of the related AGPCRs, GPR56 and GPR114.