L-Arginine prevents cereblon-mediated ubiquitination of glucokinase and stimulates glucose-6-phosphate production in pancreatic \u03b2-cells

Jaeyong Cho,Yukio Horikawa,Yoichi Imai,Jun Takeda,Takeshi Imai,Yumi Imai,Mayumi Enya,Hiroshi Handa

doi:10.1038/s42003-020-01226-3

Abstract

We sought to determine a mechanism by which L-arginine increases glucose-stimulated insulin secretion (GSIS) in β-cells by finding a protein with affinity to L-arginine using arginine-immobilized magnetic nanobeads technology. Glucokinase (GCK), the key regulator of GSIS and a disease-causing gene of maturity-onset diabetes of the young type 2 (MODY2), was found to bind L-arginine. L-Arginine stimulated production of glucose-6-phosphate (G6P) and induced insulin secretion. We analyzed glucokinase mutants and identified three glutamate residues that mediate binding to L-arginine. One MODY2 patient with GCKE442* demonstrated lower C-peptide-to-glucose ratio after arginine administration. In β-cell line, GCKE442* reduced L-arginine-induced insulin secretion compared with GCKWT. In addition, we elucidated that the binding of arginine protects glucokinase from degradation by E3 ubiquitin ligase cereblon mediated ubiquitination. We conclude that L-arginine induces insulin secretion by increasing G6P production by glucokinase through direct stimulation and by prevention of degradation.

Highlights

We sought to determine a mechanism by which L-arginine increases glucose-stimulated insulin secretion (GSIS) in β-cells by finding a protein with affinity to L-arginine using arginine-immobilized magnetic nanobeads technology
Arginine is necessary for insulin secretion in response to glucose but not to G6P indicating that arginine may play a role for G6P production by GCK in β-cells
In fed state, L-arginine binds to GCK via three glutamate residues of E256, E442, and E443, stimulates G6P production, and promotes insulin secretion

Summary

Introduction

We sought to determine a mechanism by which L-arginine increases glucose-stimulated insulin secretion (GSIS) in β-cells by finding a protein with affinity to L-arginine using arginine-immobilized magnetic nanobeads technology. Glucokinase (GCK), the key regulator of GSIS and a disease-causing gene of maturity-onset diabetes of the young type 2 (MODY2), was found to bind L-arginine. L-Arginine stimulated production of glucose-6phosphate (G6P) and induced insulin secretion. We conclude that L-arginine induces insulin secretion by increasing G6P production by glucokinase through direct stimulation and by prevention of degradation. GCK is highly expressed in pancreatic β-cells and hepatocytes It phosphorylates glucose in the presence of adenosine triphosphate (ATP) and magnesium[1,2,3]. Some GCK mutants that reduce kinase activity cause the impairment in glucose-induced insulin secretion (GSIS). L-Arginine prevents ubiquitination-dependent proteolysis of GCK in β-cells by the chemically inducible E3 ubiquitin ligase cereblon that is identified as a protein responsible for teratogenicity of thalidomide through ubiquitination-dependent degradation of cognate proteins[19,20,21]

Methods

Results

Conclusion