Evidence That Ca2+ within the Microdomain of the L-Type Voltage Gated Ca2+ Channel Activates ERK in MIN6 Cells in Response to Glucagon-Like Peptide-1

Joanne Selway,Nina Storey,Terence P Herbert,Roberto Rigatti,Jing Lu,Gary B Willars,Stuart E Dryer

doi:10.1371/journal.pone.0033004

Joanne Selway, Nina Storey + Show 5 more

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https://doi.org/10.1371/journal.pone.0033004

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Journal: PloS one	Publication Date: Mar 7, 2012
Citations: 20	License type: CC BY 4.0

Affiliation: University of Leicester

Abstract

Glucagon like peptide-1 (GLP-1) is released from intestinal L-cells in response to nutrient ingestion and acts upon pancreatic β-cells potentiating glucose-stimulated insulin secretion and stimulating β-cell proliferation, differentiation, survival and gene transcription. These effects are mediated through the activation of multiple signal transduction pathways including the extracellular regulated kinase (ERK) pathway. We have previously reported that GLP-1 activates ERK through a mechanism dependent upon the influx of extracellular Ca2+ through L-type voltage gated Ca2+ channels (VGCC). However, the mechanism by which L-type VGCCs couple to the ERK signalling pathway in pancreatic β-cells is poorly understood. In this report, we characterise the relationship between L-type VGCC mediated changes in intracellular Ca2+ concentration ([Ca2+]i) and the activation of ERK, and demonstrate that the sustained activation of ERK (up to 30 min) in response to GLP-1 requires the continual activation of the L-type VGCC yet does not require a sustained increase in global [Ca2+]i or Ca2+ efflux from the endoplasmic reticulum. Moreover, sustained elevation of [Ca2+]i induced by ionomycin is insufficient to stimulate the prolonged activation of ERK. Using the cell permeant Ca2+ chelators, EGTA-AM and BAPTA-AM, to determine the spatial dynamics of L-type VGCC-dependent Ca2+ signalling to ERK, we provide evidence that a sustained increase in Ca2+ within the microdomain of the L-type VGCC is sufficient for signalling to ERK and that this plays an important role in GLP-1- stimulated ERK activation.

Highlights

Glucagon like peptide-1 (GLP-1) is a hormone secreted from intestinal L-cells in response to nutrients
In order to investigate the temporal correlation of GLP-1 plus glucose-stimulated L-type voltage gated Ca2+ channels (VGCC)-dependent extracellular regulated kinase (ERK) activation with increases in [Ca2+]i, changes in [Ca2+]i were assessed by single-cell epifluorescence microscopy in response to glucose, GLP-1 plus glucose or GLP-1 plus glucose in the presence of nifedipine
The present study shows that GLP-1 plus glucose-stimulated ERK activation in pancreatic b-cells is dependent upon the influx of Ca2+ through L-type VGCC (Figure 1) and that the sustained activation of the L-type VGCC is critical for the sustained activation of ERK (Figure 2), demonstrating that the two processes are tightly coupled

Summary

Introduction

GLP-1 is a hormone secreted from intestinal L-cells in response to nutrients (for reviews see [1,2]). The primary site of GLP-1 action is the pancreatic b-cell where it stimulates proliferation, differentiation, insulin gene transcription, and the potentiation of glucose-dependent insulin secretion. These effects are mediated through the activation of the GLP-1 receptor (GLP-1R), a Gas-protein coupled receptor of the secretin/ glucagon type B family. GLP-1 potentiates glucose-stimulated ERK activation [3,4,5,6,7], and importantly the activation of ERK has been shown to play a positive role in the stimulation of pancreatic b-cell proliferation, differentiation, survival and insulin gene transcription [7,8,9]. In the pancreatic b-cell line MIN6 (mouse insulinoma 6), glucoseinduced ERK1/2 activation enhances insulin secretion via the phosphorylation of synapsin I [10]

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