Ge Yunjun, Yang Dehua, Dai Antao, Zhou Caihong, Zhu Yue, Wang Ming-Wei
*The National Center for Drug Screening and the CAS Key Laboratory of Receptor Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
Biosci Rep. 2014 Nov 21;34(6):e00152. doi: 10.1042/BSR20140120.
GLP-1R (glucagon-like peptide-1 receptor) mediates the 'incretin effect' and many other anti-diabetic actions of its cognate ligand, GLP-1 (glucagon-like peptide-1). It belongs to the class B family of GPCRs (G protein-coupled receptors) and possesses an N-terminal putative SP (signal peptide). It has been reported that this sequence is required for the synthesis of GLP-1R and is cleaved after receptor synthesis. In the present study, we conducted an in-depth exploration towards the role of the putative SP in GLP-1R synthesis. A mutant GLP-1R without this sequence was expressed in HEK293 cells (human embryonic kidney 293 cells) and displayed normal functionality with respect to ligand binding and activation of adenylate cyclase. Thus the putative SP does not seem to be required for receptor synthesis. Immunoblotting analysis shows that the amount of GLP-1R synthesized in HEK293 cells is low when the putative SP is absent. This indicates that the role of the sequence is to promote the expression of GLP-1R. Furthermore, epitopes tagged at the N-terminal of GLP-1R are detectable by immunofluorescence and immunoblotting in our experiments. In conclusion, the present study points to different roles of SP in GLP-1R expression which broadens our understanding of the functionality of this putative SP of GLP-1R and possibly other Class B GPCRs.
胰高血糖素样肽-1受体（GLP-1R）介导其同源配体胰高血糖素样肽-1（GLP-1）的“肠促胰岛素效应”及许多其他抗糖尿病作用。它属于G蛋白偶联受体（GPCRs）的B类家族，具有一个N端假定信号肽（SP）。据报道，该序列是GLP-1R合成所必需的，且在受体合成后被切割。在本研究中，我们对假定的信号肽在GLP-1R合成中的作用进行了深入探究。一种没有该序列的突变型GLP-1R在人胚肾293细胞（HEK293细胞）中表达，并且在配体结合和腺苷酸环化酶激活方面表现出正常功能。因此，假定的信号肽似乎并非受体合成所必需。免疫印迹分析表明，当不存在假定的信号肽时，HEK293细胞中合成的GLP-1R量较低。这表明该序列的作用是促进GLP-1R的表达。此外，在我们的实验中，通过免疫荧光和免疫印迹可检测到在GLP-1R N端标记的表位。总之，本研究指出了信号肽在GLP-1R表达中的不同作用，这拓宽了我们对GLP-1R以及可能其他B类GPCRs这一假定信号肽功能的理解。
