Stalk-dependent and Stalk-independent Signaling by the Adhesion G Protein-coupled Receptors GPR56 (ADGRG1) and BAI1 (ADGRB1)
Stalk-dependent and Stalk-independent Signaling by the Adhesion G Protein-coupled Receptors GPR56 (ADGRG1) and BAI1 (ADGRB1)
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DOI：
10.1074/jbc.m115.689349
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发表时间：
2016-02-12
影响因子：
4.8
通讯作者：
Hall, Randy A.
中科院分区：
文献类型：
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作者：
Kishore, Ayush;Purcell, Ryan H.;Hall, Randy A.
粘附 G 蛋白偶联受体 (aGPCR) 是一个庞大但人们知之甚少的七次跨膜蛋白家族。 aGPCR 家族的一个决定性特征是保守的 GAIN 结构域，它具有自蛋白水解活性，可以裂解第一个跨膜结构域附近的受体。一些 aGPCR，包括 ADGRB1（BAI1 或 B1）和 ADGRG1（GPR56 或 G1），被发现在被截短以模拟 GAIN 结构域切割 (NT) 时表现出显着增加的组成型活性。最近的报告表明，通过 GAIN 结构域切割揭示的新 N 端茎可以作为束缚激动剂直接激活 aGPCR。我们在两种不同的 aGPCR B1 和 G1 的研究中测试了这一假设，方法是设计缺乏整个 NT（包括茎）的突变受体（B1-和 G1-SL，其中 SL 表示无茎）。通过一系列信号分析对这些受体进行了评估，并与两种受体的全长野生型和模拟切割（NT）形式进行了比较。我们发现 B1-SL 在多项测定中表现出强大的信号传导活性，表明近膜茎区域对其激活不是必需的。然而，对于 G1，结果好坏参半，SL 突变体在多种信号转导测定（包括 TGF 脱落、NFAT 荧光素酶激活和 -arrestin 招募）中表现出强大的活性，但在不同的测定（SRF 荧光素酶激活）中相对于 NT 活性降低。这些数据支持一个模型，其中 aGPCR 下游某些途径的激活是茎依赖性的，而向其他途径发出的信号是茎无关的。
The adhesion G protein-coupled receptors (aGPCRs) are a large yet poorly understood family of seven-transmembrane proteins. A defining characteristic of the aGPCR family is the conserved GAIN domain, which has autoproteolytic activity and can cleave the receptors near the first transmembrane domain. Several aGPCRs, including ADGRB1 (BAI1 or B1) and ADGRG1 (GPR56 or G1), have been found to exhibit significantly increased constitutive activity when truncated to mimic GAIN domain cleavage (NT). Recent reports have suggested that the new N-terminal stalk, which is revealed by GAIN domain cleavage, can directly activate aGPCRs as a tethered agonist. We tested this hypothesis in studies on two distinct aGPCRs, B1 and G1, by engineering mutant receptors lacking the entire NT including the stalk (B1- and G1-SL, with SL indicating stalkless). These receptors were evaluated in a battery of signaling assays and compared with full-length wild-type and cleavage-mimicking (NT) forms of the two receptors. We found that B1-SL, in multiple assays, exhibited robust signaling activity, suggesting that the membrane-proximal stalk region is not necessary for its activation. For G1, however, the results were mixed, with the SL mutant exhibiting robust activity in several signaling assays (including TGF shedding, activation of NFAT luciferase, and -arrestin recruitment) but reduced activity relative to NT in a distinct assay (activation of SRF luciferase). These data support a model in which the activation of certain pathways downstream of aGPCRs is stalk-dependent, whereas signaling to other pathways is stalk-independent.