PDF(Pubmed)
Abstract：
BACKGROUND: Desensitization of G protein-coupled receptors (GPCRs) refers to the attenuation of receptor responsiveness by prolonged or intermittent exposure to agonists. The binding of β-arrestin to the cytoplasmic cavity of the phosphorylated receptor, which competes with the G protein, has been widely accepted as an extensive model for explaining GPCRs desensitization. However, studies on various GPCRs, including dopamine D2-like receptors (D2R, D3R, D4R), have suggested the existence of other desensitization mechanisms. The present study employed D2R/D3R variants with different desensitization properties and utilized loss-of-function approaches to uncover the mechanisms underlying GPCRs homologous desensitization, focusing on the signaling cascade that regulates the ubiquitination of AKT.
RESULTS: AKT undergoes K8/14 ubiquitination by TRAF6, which occurs in the nucleus and promotes its membrane recruitment, phosphorylation and activation under receptor desensitization conditions. The nuclear entry of TRAF6 relies on the presence of the importin complex. Src regulates the nuclear entry of TRAF6 by mediating the interaction between TRAF6 and importin β1. Ubiquitinated AKT translocates to the plasma membrane where it associates with Mdm2 to phosphorylate it at the S166 and S186 residues. Thereafter, phosphorylated Mdm2 is recruited to the nucleus, resulting in the deubiquitination of β-Arr2. The deubiquitinated β-Arr2 then forms a complex with Gβγ, which serves as a biomarker for GPCRs desensitization. Like in D3R, ubiquitination of AKT is also involved in the desensitization of β2 adrenoceptors.
CONCLUSIONS: Our study proposed that the property of a receptor that causes a change in the subcellular localization of TRAF6 from the cytoplasm to the nucleus to mediate AKT ubiquitination could initiate the desensitization of GPCRs.
RESULTS: AKT undergoes K8/14 ubiquitination by TRAF6, which occurs in the nucleus and promotes its membrane recruitment, phosphorylation and activation under receptor desensitization conditions. The nuclear entry of TRAF6 relies on the presence of the importin complex. Src regulates the nuclear entry of TRAF6 by mediating the interaction between TRAF6 and importin β1. Ubiquitinated AKT translocates to the plasma membrane where it associates with Mdm2 to phosphorylate it at the S166 and S186 residues. Thereafter, phosphorylated Mdm2 is recruited to the nucleus, resulting in the deubiquitination of β-Arr2. The deubiquitinated β-Arr2 then forms a complex with Gβγ, which serves as a biomarker for GPCRs desensitization. Like in D3R, ubiquitination of AKT is also involved in the desensitization of β2 adrenoceptors.
CONCLUSIONS: Our study proposed that the property of a receptor that causes a change in the subcellular localization of TRAF6 from the cytoplasm to the nucleus to mediate AKT ubiquitination could initiate the desensitization of GPCRs.
摘要：
背景：G蛋白偶联受体（GPCRs）的脱敏是指通过长时间或间歇性暴露于激动剂来减弱受体反应性。β-抑制蛋白与磷酸化受体的细胞质腔的结合，与G蛋白竞争，已被广泛接受为解释GPCRs脱敏的广泛模型。然而,对各种GPCR的研究，包括多巴胺D2样受体（D2R，D3R,D4R),提出了其他脱敏机制的存在。本研究采用了具有不同脱敏特性的D2R/D3R变体，并利用功能丧失方法来揭示GPCRs同源脱敏的潜在机制。关注调节AKT泛素化的信号级联。
结果：AKT通过TRAF6进行K8/14泛素化，这发生在细胞核中并促进其膜募集，受体脱敏条件下的磷酸化和激活。TRAF6的核进入依赖于输入蛋白复合物的存在。Src通过介导TRAF6与输入蛋白β1之间的相互作用来调节TRAF6的核进入。泛素化的AKT易位到质膜,在那里它与Mdm2结合以在S166和S186残基处磷酸化它。此后,磷酸化的Mdm2被募集到细胞核，导致β-Arr2的去泛素化。然后去泛素化的β-Arr2与Gβγ形成复合物，作为GPCRs脱敏的生物标志物。像在D3R，AKT的泛素化也参与β2肾上腺素受体的脱敏。
结论：我们的研究表明，导致TRAF6从细胞质到细胞核的亚细胞定位变化以介导AKT泛素化的受体的特性可以启动GPCRs的脱敏。
结果：AKT通过TRAF6进行K8/14泛素化，这发生在细胞核中并促进其膜募集，受体脱敏条件下的磷酸化和激活。TRAF6的核进入依赖于输入蛋白复合物的存在。Src通过介导TRAF6与输入蛋白β1之间的相互作用来调节TRAF6的核进入。泛素化的AKT易位到质膜,在那里它与Mdm2结合以在S166和S186残基处磷酸化它。此后,磷酸化的Mdm2被募集到细胞核，导致β-Arr2的去泛素化。然后去泛素化的β-Arr2与Gβγ形成复合物，作为GPCRs脱敏的生物标志物。像在D3R，AKT的泛素化也参与β2肾上腺素受体的脱敏。
结论：我们的研究表明，导致TRAF6从细胞质到细胞核的亚细胞定位变化以介导AKT泛素化的受体的特性可以启动GPCRs的脱敏。
