Abstract：
Arrestins are key negative regulators of G Protein-Coupled Receptors (GPCRs) through mediation of G protein desensitisation and receptor internalisation. Arrestins can also contribute to signal transduction by scaffolding downstream signalling effectors for activation. GPCR kinase (GRK) enzymes phosphorylate the intracellular C-terminal domain, or intracellular loop regions of GPCRs to promote arrestin interaction. There are seven different GRK subtypes, which may uniquely phosphorylate the C-terminal tail in a type of \'phosphorylation barcode,\' potentially differentially contributing to arrestin translocation and arrestin-dependent signalling. Such contributions may be exploited to develop arrestin-biased ligands. Here, we examine the effect of different GRK subtypes on the ability to promote translocation of arrestin-2 and arrestin-3 to the cannabinoid CB1 receptor (CB1) with a range of ligands. We find that most GRK subtypes (including visual GRK1) can enhance arrestin-2 and -3 translocation to CB1, and that GRK-dependent changes in arrestin-2 and arrestin-3 translocation were broadly shared for most agonists tested. GRK2/3 generally enhanced arrestin translocation more than the other GRK subtypes, with some small differences between ligands. We also explore the interplay between G protein activity and GRK2/3-dependent arrestin translocation, highlighting that high-efficacy G protein agonists will cause GRK2/3 dependent arrestin translocation. This study supports the hypothesis that arrestin-biased ligands for CB1 must engage GRK5/6 rather than GRK2/3, and G protein-biased ligands must have inherently low efficacy.
摘要：
抑制素通过介导G蛋白脱敏和受体内化是G蛋白偶联受体（GPCR）的关键负调节因子。抑制素还可以通过支架下游信号传导效应子进行激活来促进信号转导。GPCR激酶（GRK）酶磷酸化细胞内C末端结构域，或GPCRs的胞内环区域以促进抑制蛋白相互作用。有七种不同的GRK亚型,它可以在一种磷酸化条形码中独特地磷酸化C末端尾部，\'可能不同地促进抑制素易位和抑制素依赖性信号传导。可以利用这种贡献来开发arrestin偏置的配体。这里,我们研究了不同GRK亚型对一系列配体促进arrestin-2和arrestin-3向1型大麻素受体(CB1)易位的能力的影响.我们发现，大多数GRK亚型（包括视觉GRK1）可以增强arrestin-2和-3向CB1的易位，并且GRK依赖性的arrestin-2和arrestin-3易位变化在大多数测试的激动剂中（广泛）共享。GRK2/3通常比其他GRK亚型更增强抑制蛋白易位，配体之间有一些小的差异。我们还探索了G蛋白活性与GRK2/3依赖性抑制蛋白易位之间的相互作用，强调高效G蛋白激动剂会引起GRK2/3依赖性抑制蛋白易位。这项研究支持以下假设：CB1的arrestin偏向配体必须接合GRK5/6而不是GRK2/3，并且G蛋白偏向配体必须具有固有的低功效。
