Tolbert L M, Lameh J
Department of Biopharmaceutical Sciences and Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA.
J Neurochem. 1998 Jan;70(1):113-9. doi: 10.1046/j.1471-4159.1998.70010113.x.
We have studied the effect of an antibody against the epitope EYMPME on the internalization of the human muscarinic cholinergic receptor hm1 tagged with the epitope at the amino terminus. The antibody to the tag induces internalization of the hm1 receptor within minutes after exposure of human embryonic kidney 293 cells transfected with the tagged receptor. This antibody-induced internalization is reversible following removal of the antibody. In contrast to hm1 internalization induced by the agonist carbachol, internalization induced by antibody is not blocked by the muscarinic antagonist atropine. The mechanism of antibody-mediated internalization does not appear to involve receptor dimerization by the antibody, as Fab fragments derived from the antibody also induce internalization. The pathway of antibody-induced internalization, similar to the agonist-induced process, is mediated by clathrin-coated vesicles. Furthermore, antibody treatment does not result in any second messenger production, as measured by phosphoinositide accumulation. Our data show that internalization of a G protein-coupled receptor can be triggered by interaction of the amino terminus of the receptor with an exogenous ligand and can occur independently of second messenger production. This result suggests that the receptor can exist in multiple conformations, each mediating distinct downstream events.
我们研究了一种针对表位EYMPME的抗体对在氨基末端标记有该表位的人毒蕈碱胆碱能受体hm1内化的影响。针对该标签的抗体在转染了标记受体的人胚肾293细胞暴露后几分钟内诱导hm1受体的内化。去除抗体后，这种抗体诱导的内化是可逆的。与激动剂卡巴胆碱诱导的hm1内化相反，抗体诱导的内化不受毒蕈碱拮抗剂阿托品的阻断。抗体介导的内化机制似乎不涉及抗体引起的受体二聚化，因为源自该抗体的Fab片段也能诱导内化。抗体诱导内化的途径与激动剂诱导的过程相似，是由网格蛋白包被的小泡介导的。此外，通过磷酸肌醇积累测量发现，抗体处理不会导致任何第二信使的产生。我们的数据表明，G蛋白偶联受体的内化可以由受体的氨基末端与外源配体的相互作用触发，并且可以独立于第二信使的产生而发生。这一结果表明，该受体可以以多种构象存在，每种构象介导不同的下游事件。
