The Chemokine Receptor CCR1 Is Constitutively Active, Which Leads to G Protein-independent, β-Arrestin-mediated Internalization
The Chemokine Receptor CCR1 Is Constitutively Active, Which Leads to G Protein-independent, β-Arrestin-mediated Internalization
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DOI：
10.1074/jbc.m113.503797
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发表时间：
2013-11-08
影响因子：
4.8
通讯作者：
Handel, Tracy M.
中科院分区：
文献类型：
--
作者：
Gilliland, C. Taylor;Salanga, Catherina L.;Handel, Tracy M.
G蛋白偶联受体被其相关配体激活已被广泛研究，随着最近GPCR晶体结构的扩大，越来越多的关于配体依赖受体激活的分子机制的结构信息开始出现。然而，一些GPCRs也能够在没有激动剂结合的情况下采用活性构象，从而启动信号转导和受体下调。在这份报告中，我们发现CC型趋化因子受体1(CCR1)显示出显著的结构性活性，导致多种细胞反应。CCR1的表达足以抑制cAMP的形成，增加F-肌动蛋白的含量，并导致人和小鼠白细胞的基础迁移。这种结构性活性导致受体的基础磷酸化，β-arrestin-2的募集，以及随后的受体内化。CCR1同时与Gα(I)和β-arrestin-2形成多蛋白复合体，可通过同源齐聚或受体聚集来调节。这些数据表明，CCR1存在两种功能状态；尽管CCR1具有高构成活性，但与Gα(I)偶联的受体具有典型的GPCR功能，CCR1β-arrestin-2复合体是G蛋白非依赖性构成受体内化所必需的。百日咳毒素不敏感的受体对趋化因子的摄取提示CCR1β-arrestin-2复合体可能与受体的潜在清除功能有关，这可能在炎症过程中维持趋化因子的梯度和受体在复杂领域的趋化因子反应中起重要作用。
Activation of G protein-coupled receptors by their associated ligands has been extensively studied, and increasing structural information about the molecular mechanisms underlying ligand-dependent receptor activation is beginning to emerge with the recent expansion in GPCR crystal structures. However, some GPCRs are also able to adopt active conformations in the absence of agonist binding that result in the initiation of signal transduction and receptor down-modulation. In this report, we show that the CC-type chemokine receptor 1 (CCR1) exhibits significant constitutive activity leading to a variety of cellular responses. CCR1 expression is sufficient to induce inhibition of cAMP formation, increased F-actin content, and basal migration of human and murine leukocytes. The constitutive activity leads to basal phosphorylation of the receptor, recruitment of beta-arrestin-2, and subsequent receptor internalization. CCR1 concurrently engages G alpha(i) and beta-arrestin-2 in a multiprotein complex, which may be accommodated by homo-oligomerization or receptor clustering. The data suggest the presence of two functional states for CCR1; whereas receptor coupled to G alpha(i) functions as a canonical GPCR, albeit with high constitutive activity, the CCR1.beta-arrestin-2 complex is required for G protein-independent constitutive receptor internalization. The pertussis toxin-insensitive uptake of chemokine by the receptor suggests that the CCR1.beta-arrestin-2 complex may be related to a potential scavenging function of the receptor, which may be important for maintenance of chemokine gradients and receptor responsiveness in complex fields of chemokines during inflammation.