The Carboxyl Terminus of Human Cytomegalovirus-encoded 7 Transmembrane Receptor US28 Camouflages Agonism by Mediating Constitutive Endocytosis*
The Carboxyl Terminus of Human Cytomegalovirus-encoded 7 Transmembrane Receptor US28 Camouflages Agonism by Mediating Constitutive Endocytosis*
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DOI：
10.1074/jbc.m213179200
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发表时间：
2003-05
影响因子：
4.8
通讯作者：
M. Waldhoer;P. Casarosa;M. Rosenkilde;M. Smit;R. Leurs;Jennifer L. Whistler;T. Schwartz
中科院分区：
文献类型：
--
作者：
M. Waldhoer;P. Casarosa;M. Rosenkilde;M. Smit;R. Leurs;Jennifer L. Whistler;T. Schwartz
US 28是由人巨细胞病毒编码的四种7跨膜（7 TM）趋化因子受体之一，并已显示以配体非依赖性、组成型活性方式进行信号传导和内吞。在这里，我们表明，US 28的组成性活动和组成性内吞作用的性质是可分离的实体，在这种病毒趋化因子受体。我们产生了嵌合和突变的US 28蛋白，其组成性内吞（US 28 Δ300、US 28 Δ317、US 28-NK 1-ctail和US 28-ORF 74-ctail）或信号传导特性（US 28 R129 A）发生了改变。通过使用这一系列的突变体，我们表明，US 28的胞质尾域本身调节受体的内吞作用，独立的信号传导能力的核心域的US 28。US 28 c-tail的组成性内吞性质可转座至其他7 TM受体、疱疹病毒8编码的ORF 74和速激肽NK 1受体（ORF 74-US 28-ctail和NK 1-US 28-ctail）。缺失US 28 C末端导致组成性内吞作用减少，因此通过磷酸肌醇周转、NF-κB和cAMP反应元件结合蛋白转录测定评估的所有受试受体的信号传导能力增强。我们进一步表明，US 28的组成性内吞特性影响其趋化因子配体fractalkine/CX 3CL 1的作用，并表明在没有US 28 C末端的情况下，fractalkine/CX 3CL 1作为US 28的激动剂。这首次证明了7 TM受体的内吞性质可以掩盖配体的激动剂性质。
US28 is one of four 7 transmembrane (7TM) chemokine receptors encoded by human cytomegalovirus and has been shown to both signal and endocytose in a ligand-independent, constitutively active manner. Here we show that the constitutive activity and constitutive endocytosis properties of US28 are separable entities in this viral chemokine receptor. We generated chimeric and mutant US28 proteins that were altered in either their constitutive endocytic (US28Δ300, US28Δ317, US28-NK1-ctail, and US28-ORF74-ctail) or signaling properties (US28R129A). By using this series of mutants, we show that the cytoplasmic tail domain of US28 per se regulates receptor endocytosis, independent of the signaling ability of the core domain of US28. The constitutive endocytic property of the US28 c-tail was transposable to other 7TM receptors, the herpes virus 8-encoded ORF74 and the tachykinin NK1 receptor (ORF74-US28-ctail and NK1-US28-ctail). Deletion of the US28 C terminus resulted in reduced constitutive endocytosis and consequently enhanced signaling capacity of all receptors tested as assessed by inositol phosphate turnover, NF-κB, and cAMP-responsive element-binding protein transcription assays. We further show that the constitutive endocytic property of US28 affects the action of its chemokine ligand fractalkine/CX3CL1 and show that in the absence of the US28 C terminus, fractalkine/CX3CL1 acts as an agonist on US28. This demonstrates for the first time that the endocytic properties of a 7TM receptor can camouflage the agonist properties of a ligand.