A Novel Interacting Protein SERP1 Regulates the N‐Linked Glycosylation and Function of GLP‐1 Receptor in the Liver

Abstract

Glucagon-like peptide 1 (GLP-1) exerts multiple effects on metabolism through its receptor, GLP-1R, in the liver. Activation and transduction of GLP-1R require complex interactions of largely unknown accessory proteins, and these processes are crucial to the response to endoplasmic reticulum (ER) stress. Using the membrane-based split ubiquitin yeast two-hybrid system (MYTH) and a human liver cDNA library, we obtained the human GLP-1R interactome and identified SERP1 as a potential interacting protein based on its ability to stabilize membrane proteins and facilitate N-linked glycosylation. GLP-1R and SERP1 were co-expressed in HEK-293 cells, and their interaction was confirmed by co-immunoprecipitation. We then found that overexpression of SERP1 could rescue GLP-1R glycosylation after application of tunicamycin to block N-linked glycosylation. SERP1 overexpression also attenuated exendin-4-stimulated cAMP accumulation and AMPK activation. However, the glycosylation and function of mutant GLP-1R, in which all three sites for N-linked glycosylation were mutated, were not increased with overexpression of SERP1. Moreover, as a GLP-1R interactor, SERP1 could also partly reverse the accumulation of tunicamycin-induced ER stress. Taken together, our findings identify a group of proteins that interact with GLP-1R and show that one specific interacting protein, SERP1, has an important role in facilitating the glycosylation of GLP-1R and rescuing its activities after ER stress induced by tunicamycin. J. Cell. Biochem. 118: 3616-3626, 2017. © 2017 Wiley Periodicals, Inc.

Sepsis plasma-derived exosomal miR-1-3p induces endothelial cell dysfunction by targeting SERP1

“…To investigate the potential target genes that induced miR-1-3p biofunction, the TargetScan and miRDB databases were used to analyze related potential genes, and SERP1 was identified as a perspective target. SERP1 was reported to regulate cell proliferation and apoptosis as well as cell membrane stability by increasing glycosylation levels of GLP1R [15]. The protein levels of SERP1 and GLP1R were reduced in the CLP rats' lung tissue compared with the sham group (Figure 4A,B).…”

Identification of TSPAN4 as Novel Histamine H4 Receptor Interactor

“…GPCRs have been found to also interact with other membrane and/or intracellular proteins in addition to heterotrimeric G proteins, GRKs, and β-arrestins. These so-called GPCR interacting proteins (GIPs) can mediate and/or modulate GPCR signaling and/or trafficking [16][17][18], and have been identified by various biochemical (e.g., pull-downs from cell lysates using Glutathione S-transferase (GST) or His6-tagged GPCR C-tails [19,20], or HDL-reconstituted GPCR [21]), cell biological (e.g., ascorbate peroxidase (APEX)-catalyzed proximity labeling in living cells followed by affinity chromatography, enzyme digestion, and mass spectrometric analysis [22][23][24]), and genetic approaches (e.g., membrane yeast two-hybrid (MYTH) [25][26][27][28][29][30][31]).…”

Exendin-4 improves glucose metabolism in insulin-resistant cells by upregulating the phosphorylative AMPK

“…10,11 GLP-1 analogue, Exendin-4 (Ex-4), has been used in clinical treatment of type 2 diabetes mellitus (T2DM). 12,13 Recent studies have found that GLP-1 promotes the phosphorylation of AMPK in hepatocytes and reduces the glucose content of hepatocytes in diabetic mice. 13 Other studies showed that exenatide had direct protective effects on endothelial cells through the AMPK/Akt pathway in a GLP-1 receptor-dependent manner.…”

“…12,13 Recent studies have found that GLP-1 promotes the phosphorylation of AMPK in hepatocytes and reduces the glucose content of hepatocytes in diabetic mice. 13 Other studies showed that exenatide had direct protective effects on endothelial cells through the AMPK/Akt pathway in a GLP-1 receptor-dependent manner. 14,15 However, the interaction of GLP-1 and AMPK in the treatment of diabetes is not clear.…”