Fessart Delphine, Simaan May, Laporte Stéphane A
Hormones and Cancer Research Unit, Department of Medicine, McGill University, Royal Victoria Hospital, 687 Pine Avenue West, Montréal, Québec, Canada H3A 1A1.
Mol Endocrinol. 2005 Feb;19(2):491-503. doi: 10.1210/me.2004-0246. Epub 2004 Oct 21.
Beta-arrestins are multifunctional adapters involved in the internalization and signaling of G protein-coupled receptors (GPCRs). They target receptors to clathrin-coated pits (CCPs) through binding with clathrin and clathrin adapter 2 (AP-2) complex. They also act as transducers of signaling by recruiting c-Src kinase to certain GPCRs. Here we sought to determine whether c-Src regulates the recruitment of AP-2 to beta-arrestin and the angiotensin II (Ang II) type 1 receptor (AT1R) during internalization. We show that the agonist stimulation of native AT1R in vascular smooth muscle cells (VSMCs) induces the formation of an endogenous complex containing c-Src, beta-arrestins and AP-2. In vitro studies using coimmunoprecipitation experiments and a yeast three-hybrid assay reveal that c-Src stabilizes the agonist-independent association between beta-arrestin2 and the beta-subunit of AP-2 independently of the kinase activity of c-Src. However, although c-Src expression promoted the rapid dissociation of AP-2 from both beta-arrestin and AT1R after receptor stimulation, a kinase-inactive mutant of c-Src failed to induce the dissociation of AP-2 from the agonist-occupied receptor. Thus, the consequence of c-Src in regulating the dissociation of AP-2 from the receptor was also examined on the internalization of AT1R by depleting c-Src in human embryonic kidney (HEK) 293 cells using a small interfering RNA strategy. Experiments in c-Src depleted cells reveal that AT1R remained mostly colocalized with AP-2 at the plasma membrane after Ang II stimulation, consistent with the observed delay in receptor internalization. Moreover, coimmunoprecipitation experiments in c-Src depleted HEK 293 cells and VSMCs showed an increased association of AP-2 to the agonist-occupied AT1R and beta-arrestin, respectively. Together, our results support a role for c-Src in regulating the dissociation of AP-2 from agonist-occupied AT1R and beta-arrestin during the clathrin-mediated internalization of receptors and suggest a novel function for c-Src kinase in the internalization of AT1R.
β - 抑制蛋白是多功能衔接蛋白,参与G蛋白偶联受体(GPCRs)的内化和信号传导。它们通过与网格蛋白和网格蛋白衔接蛋白2(AP - 2)复合物结合,将受体靶向至网格蛋白包被小窝(CCPs)。它们还通过将c - Src激酶招募至某些GPCRs来充当信号转导分子。在此,我们试图确定c - Src在受体内化过程中是否调节AP - 2与β - 抑制蛋白及血管紧张素II(Ang II)1型受体(AT1R)的结合。我们发现,血管平滑肌细胞(VSMCs)中天然AT1R的激动剂刺激可诱导形成一种包含c - Src、β - 抑制蛋白和AP - 2的内源性复合物。使用免疫共沉淀实验和酵母三杂交试验进行的体外研究表明,c - Src可稳定β - 抑制蛋白2与AP - 2的β亚基之间不依赖激动剂的结合,且不依赖于c - Src的激酶活性。然而,尽管c - Src的表达促进了受体刺激后AP - 2从β - 抑制蛋白和AT1R的快速解离,但c - Src的激酶失活突变体未能诱导AP - 2从被激动剂占据的受体上解离。因此,我们还使用小干扰RNA策略在人胚肾(HEK)293细胞中耗尽c - Src,研究了c - Src对AT1R内化过程中AP - 2从受体解离的影响。在c - Src耗尽的细胞中进行的实验表明,Ang II刺激后,AT1R在质膜上大多仍与AP - 2共定位,这与观察到的受体内化延迟一致。此外,在c - Src耗尽的HEK 293细胞和VSMCs中进行的免疫共沉淀实验表明,AP - 2分别与被激动剂占据的AT1R和β - 抑制蛋白的结合增加。总之,我们的结果支持c - Src在网格蛋白介导的受体内化过程中调节AP - 2从被激动剂占据的AT1R和β - 抑制蛋白上解离的作用,并提示c - Src激酶在AT1R内化过程中具有新功能。
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