title: Glucagon-like peptide-1 enhances glucokinase activity in pancreatic β-cells through the association of Epac2 with Rim2 and Rab3A.
abstract: Glucokinase (GK), which phosphorylates D-glucose, is a major glucose sensor in β-cells for glucose-stimulated insulin secretion (GSIS) and is a promising new drug target for type 2 diabetes (T2D). In T2D, pancreatic β-cells exhibit defective glucose sensitivity, which leads to impaired GSIS. Although glucagon-like peptide-1-(7-36)-amide (GLP-1) is known to enhance β-cell glucose sensitivity, the effect of GLP-1 on GK activity is still unknown. The present study demonstrated that GLP-1 pretreatment for 30 min significantly enhanced GK activity in a glucose-dependent manner, with a lower Michaelis-Menten constant (K(m)) but unchanged maximal velocity (V(max)). Thus, GLP-1 acutely enhanced cellular glucose uptake, mitochondrial membrane potential, and cellular ATP levels in response to glucose in rat INS-1 and native β-cells. This effect of GLP-1 occurred via its G protein-coupled receptor pathway in a cAMP-dependent but protein kinase A-independent manner with evidence of exchange protein activated by cAMP (Epac) involvement. Silencing Epac2, interacting molecule of the small G protein Rab3 (Rim2), or Ras-associated protein Rab3A (Rab3A) significantly blocked the effect of GLP-1. These results suggested that GLP-1 can further potentiate GSIS by enhancing GK activity through the signaling of Epac2 to Rim2 and Rab3A, which is the similar pathway for GLP-1 to potentiate Ca(2+)-dependent insulin granule exocytosis. The present finding may also be an important mechanism of GLP-1 for recovery of GSIS in T2D.
authors.affiliation: Department of Physiology, Keimyung University School of Medicine, Daegu 704-701, Korea.
authors.forename: Jae-Hyung
authors.initials: JH
authors.lastname: Park
authors.forename: Sun-Joo
authors.initials: SJ
authors.lastname: Kim
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Park
authors.forename: Dae-Gu
authors.initials: DG
authors.lastname: Son
authors.forename: Jae-Hoon
authors.initials: JH
authors.lastname: Bae
authors.forename: Hyoung Kyu
authors.initials: HK
authors.lastname: Kim
authors.forename: Jin
authors.initials: J
authors.lastname: Han
authors.forename: Dae-Kyu
authors.initials: DK
authors.lastname: Song
mesh_terms: D000255:Adenosine Triphosphate; D000818:Animals; D045744:Cell Line, Tumor; D003847:Deoxyglucose / Q000737:chemistry / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D005941:Glucokinase / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D018613:Microscopy, Confocal; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014316:Tritium; D020826:rab3A GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; C531571:Rapgef4 protein, rat; C484282:Rims2 protein, rat; D014316:Tritium; D052216:Glucagon-Like Peptide 1; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D005941:Glucokinase; D020826:rab3A GTP-Binding Protein; D005947:Glucose