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: Jae-Hyung Park, Sun-Joo Kim, Sung-Hee Park, Dae-Gu Son, Jae-Hoon Bae, Hyoung Kyu Kim, Jin Han, Dae-Kyu Song
• Journal: Endocrinology (Endocrinology) Vol. 153 Issue 2 Pg. 574-82 (Feb 2012) ISSN: 1945-7170 [Electronic] United States
• PMID: 22147008 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Guanine Nucleotide Exchange Factors
• Nerve Tissue Proteins
• RNA, Small Interfering
• Rapgef4 protein, rat
• Rims2 protein, rat
• Tritium
• Glucagon-Like Peptide 1
• Adenosine Triphosphate
• Deoxyglucose
• Glucokinase
• rab3A GTP-Binding Protein
• Glucose

Topics

• Adenosine Triphosphate
• Animals
• Cell Line, Tumor
• Deoxyglucose (chemistry, metabolism)
• Gene Expression Regulation (physiology)
• Glucagon-Like Peptide 1 (pharmacology)
• Glucokinase (metabolism)
• Glucose (pharmacology)
• Guanine Nucleotide Exchange Factors (genetics, metabolism)
• Insulin-Secreting Cells (drug effects, enzymology, metabolism)
• Male
• Membrane Potential, Mitochondrial (drug effects, physiology)
• Microscopy, Confocal
• Nerve Tissue Proteins (genetics, metabolism)
• Oxygen Consumption
• RNA, Small Interfering (genetics)
• Rats
• Rats, Sprague-Dawley
• Tritium
• rab3A GTP-Binding Protein (genetics, metabolism)