Anborgh P H, Seachrist J L, Dale L B, Ferguson S S
The John P. Robarts Research Institute and Department of Physiology, University of Western Ontario, London, Canada.
Mol Endocrinol. 2000 Dec;14(12):2040-53. doi: 10.1210/mend.14.12.0565.
Beta-arrestins target G protein-coupled receptors (GPCRs) for endocytosis via clathrin-coated vesicles. Beta-arrestins also become detectable on endocytic vesicles in response to angiotensin II type 1A receptor (AT1AR), but not beta2-adrenergic receptor (beta2AR), activation. The carboxyl-terminal tails of these receptors contribute directly to this phenotype, since a beta2AR bearing the AT1AR tail acquired the capacity to stimulate beta-arrestin redistribution to endosomes, whereas this property was lost for an AT1AR bearing the beta2AR tail. Using beta2AR/AT1AR chimeras, we tested whether the beta2AR and AT1AR carboxyl-terminal tails, in part via their association with beta-arrestins, might regulate differences in the intracellular trafficking and resensitization patterns of these receptors. In the present study, we find that beta-arrestin formed a stable complex with the AT1AR tail in endocytic vesicles and that the internalization of this complex was dynamin dependent. Internalization of the beta2AR chimera bearing the AT1AR tail was observed in the absence of agonist and was inhibited by a dominant-negative beta-arrestin1 mutant. Agonist-independent AT1AR internalization was also observed after beta-arrestin2 overexpression. After internalization, the beta2AR, but not the AT1AR, was dephosphorylated and recycled back to the cell surface. However, the AT1AR tail prevented beta2AR dephosphorylation and recycling. In contrast, although the beta2AR-tail promoted AT1AR recycling, the chimeric receptor remained both phosphorylated and desensitized, suggesting that receptor dephosphorylation is not a property common to all receptors. In summary, we show that the carboxyl-terminal tails of GPCRs not only contribute to regulating the patterns of receptor desensitization, but also modulate receptor intracellular trafficking and resensitization patterns.
β-抑制蛋白通过网格蛋白包被的小泡将G蛋白偶联受体（GPCRs）靶向进行内吞作用。响应1A型血管紧张素II受体（AT1AR）激活时，β-抑制蛋白也可在内吞小泡上被检测到，但β2肾上腺素能受体（β2AR）激活时则不然。这些受体的羧基末端尾巴直接导致了这种表型，因为带有AT1AR尾巴的β2AR获得了刺激β-抑制蛋白重新分布到内体的能力，而带有β2AR尾巴的AT1AR则失去了这一特性。利用β2AR/AT1AR嵌合体，我们测试了β2AR和AT1AR的羧基末端尾巴是否部分通过与β-抑制蛋白的结合，可能调节这些受体在细胞内运输和再敏化模式上的差异。在本研究中，我们发现β-抑制蛋白在内吞小泡中与AT1AR尾巴形成了稳定的复合物，并且该复合物的内化依赖发动蛋白。在没有激动剂的情况下观察到带有AT1AR尾巴的β2AR嵌合体的内化，并且被显性负性β-抑制蛋白1突变体所抑制。在过表达β-抑制蛋白2后也观察到了不依赖激动剂的AT1AR内化。内化后，β2AR而非AT1AR被去磷酸化并循环回到细胞表面。然而，AT1AR尾巴阻止了β2AR的去磷酸化和循环。相反，尽管β2AR尾巴促进了AT1AR的循环，但嵌合受体仍然磷酸化且脱敏，这表明受体去磷酸化并非所有受体的共同特性。总之，我们表明GPCRs的羧基末端尾巴不仅有助于调节受体脱敏模式，还能调节受体在细胞内的运输和再敏化模式。
