Differential Activation Mechanisms of Erk-1/2 and p70S6K by Glucose in Pancreatic β-Cells

Briaud, Isabelle; Lingohr, Melissa K.; Dickson, Lorna M.; Wrede, Christian; Rhodes, Christopher J.

doi:10.2337/diabetes.52.4.974

Cited by 157 publications

(155 citation statements)

References 49 publications

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Section: Discussionsupporting

confidence: 89%

“…Similarly to our findings, treatment of isolated rat islets with high glucose had no effect on Akt phosphorylation, but 100 nmol/l insulin did [38,39]. In addition, no effect of glucose on Akt was observed in INS-1 cells treated for under 1 h [15,39,42]. However, high glucose has been shown to activate Akt after 1 h in INS-1 cells [42,43], and after 2 h in MIN6 cells and mouse islets [17], which does not coincide with the kinetics of glucose-stimulated insulin release.…”

Section: Discussionsupporting

confidence: 89%

“…Therefore, in our hands, glucose was unable to induce Akt phosphorylation in human islets immediately following isolation. Similarly to these findings, treatment of isolated rat islets with high glucose had no effect on Akt phosphorylation, although 100 nmol/l insulin did [38,39].…”

Section: Regular Medium Replacement Decreases Akt Phosphorylationsupporting

confidence: 58%

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Autocrine insulin action activates Akt and increases survival of isolated human islets

et al. 2006

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Aims/hypothesis The phosphatidylinositol 3-kinase (PI3K)/ Akt pathway plays a critical role in promoting the survival of pancreatic beta cells. Akt becomes activated in isolated human islets following overnight culture despite significant levels of cell death. The aim of the current study was to identify the cause of the observed increase in Akt phosphorylation in isolated islets. We hypothesised that a factor secreted by the islets in culture was acting in an autocrine manner to activate Akt. Methods In order to identify the stimulus of the PI3K/Akt pathway in culture, we examined the effects of different culture conditions on Akt phosphorylation and islet survival during the immediate post-isolation period. Results We demonstrated that islet-conditioned medium induced Akt phosphorylation in freshly isolated human islets, whereas frequent medium replacement decreased Akt phosphorylation. Following overnight culture, islet-conditioned medium contained significantly elevated levels of insulin, indicating that insulin may be responsible for the observed increase in Akt phosphorylation. Indeed, treatment with an anti-insulin antibody or with inhibitors of insulin receptor/IGF receptor 1 kinase activity suppressed Akt phosphorylation, leading to decreased islet survival. In addition, dispersion of islets into single cells also suppressed Akt phosphorylation and induced islet cell death, indicating that islet integrity is also required for maximal Akt phosphorylation. Conclusions/interpretation Our findings demonstrate that insulin acts in an autocrine manner to activate Akt and mediate the survival of isolated human islets. These findings provide new information on how culturing islets prior to transplantation may be beneficial to their survival by allowing for autocrine activation of the pro-survival Akt pathway.

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Section: Discussionsupporting

confidence: 89%

Section: Discussionsupporting

confidence: 89%

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Autocrine insulin action activates Akt and increases survival of isolated human islets

et al. 2006

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“…How-ever, the published results are inconsistent with respect to whether this activation is dependent on [3] or independent of [4,5] Ras and Raf kinases. These discrepancies may be attributed to the different beta cell lines used in the different studies.…”

Section: Introductionmentioning

confidence: 95%

“…Glucose and GLP-1 have been shown to activate ERK in numerous beta cell lines and in murine islets [3][4][5]. How-ever, the published results are inconsistent with respect to whether this activation is dependent on [3] or independent of [4,5] Ras and Raf kinases.…”

Section: Introductionmentioning

confidence: 98%

The Rap–B-Raf signalling pathway is activated by glucose and glucagon-like peptide-1 in human islet cells

et al. 2005

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Aims/hypothesis: Glucose and glucagon-like peptide-1 have been shown to activate extracellular signalregulated kinase (ERK) and phosphoinositide 3-kinase in beta cells. We examined the contributions of the small GTPases Rap and Ras and the serine-threonine kinases BRaf and Raf-1 to the activation of these kinases in human islet cells. Methods: The expression of Rap, Ras, B-Raf and Raf-1 in human islets was examined by immunohistochemistry and immunoblotting. Human islets were incubated in glucose at concentrations of 2.5 and 15 mmol/l and were stimulated with 10 nmol/l glucagon-like peptide-1. The activation of ERK and Raf kinases was examined by phosphorylation-specific antibodies and immuno-complexed kinase assays. The activation of Rap and Ras was determined by pull-down assays. Stimulation of phosphoinositide 3-kinase was detected by immuno-complexed lipid kinase assays. Results: Extracellular-regulated kinase and protein kinase B (a downstream target of phosphoinositide 3-kinase) were activated in islets stimulated with glucose and glucagon-like peptide-1. In these islets, the Rap-B-Raf signalling pathway was activated preferentially compared with Ras and Raf-1, and activated Rap and B-Raf mediated ERK stimulation in kinase assays in vitro. In addition, Rap rather than Ras mediated activation of phosphoinositide 3-kinase in islets stimulated with glucose and glucagon-like peptide-1. Conclusions/interpretation: In human islet cells, glucose and glucagon-like peptide-1 activate the Rap and BRaf signalling module, which mediates ERK activation in assays in vitro. Rap also activates phosphoinositide 3-kinase, delineating central roles for Rap and B-Raf as therapeutic targets for beta cell growth in diabetes mellitus.

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Magnetic labeling of pancreatic β‐cells modulates the glucose‐ and insulin‐induced phosphorylation of ERK1/2 and AKT

Kim

Tian

Lin

et al. 2012

Contrast Media & Molecular

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This study was undertaken to investigate the effect of a magnetic resonance imaging (MRI) contrast agent, superparamagnetic iron oxide nanoparticle (SPIO), on signal transduction by glucose and insulin in pancreatic β-cells. INS-1 cells were labeled in culture medium containing clinically approved SPIO for 24 h. Labeled and unlabeled cells were stimulated with glucose (25 mM) or insulin (0.1-1 µM) for 12 h. The phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2) and protein kinase B (AKT) and intracellular insulin protein levels were assessed by Western blotting. After labeling with increasing amounts of SPIO, cytotoxicity was not observed, yet the intracellular iron concentration increased in a dose-dependent manner. SPIO labeling (200 µg Fe ml(-1)) induced a significant increase in ERK1/2 and AKT phosphorylation (labeled vs unlabeled, p < 0.05), but significantly reduced the glucose-stimulated phosphorylation of ERK1/2 and AKT and insulin-stimulated phosphorylation of AKT (labeled vs unlabeled, p < 0.05). The level of intracellular insulin protein was found to be lower in labeled cells than unlabeled cells (labeled vs unlabeled, p < 0.05). This study demonstrates that SPIO labeling alters some fundamental functional variables, at least in INS-1 cells, through modulation of the glucose- or insulin-induced activation of ERK1/2 and AKT, which leads to insulin biosynthesis.

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Differential Activation Mechanisms of Erk-1/2 and p70S6K by Glucose in Pancreatic β-Cells

Abstract: Glucose can activate the mitogen-activated kinases, Erk-1/2, and the ribosomal-S6 kinase, p70 S6K , in ␤-cells, contributing to an increase in mitogenesis. However, the signaling mechanism by which glucose induces Erk-1/2 and p70 S6K phosphorylation activation is undefined.

Cited by 157 publications

References 49 publications

Autocrine insulin action activates Akt and increases survival of isolated human islets

Autocrine insulin action activates Akt and increases survival of isolated human islets

The Rap–B-Raf signalling pathway is activated by glucose and glucagon-like peptide-1 in human islet cells

Magnetic labeling of pancreatic β‐cells modulates the glucose‐ and insulin‐induced phosphorylation of ERK1/2 and AKT

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