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Glucose and insulin synergistically activate phosphatidylinositol 3-kinase to trigger oscillations of phosphatidylinositol 3,4,5-trisphosphate in beta-cells
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
2006 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 281, no 51, 39121-39127 p.Article in journal (Refereed) Published
Abstract [en]

In insulin-secreting β-cells, activation of phosphatidylinositol 3′-OH-kinase with resulting formation of phosphatidylinositol 3,4,5-trisphosphate (PIP3) has been implicated in the regulation of ion channels, insulin secretion, and gene transcription as well as in cell growth and survival, but the kinetics of PIP3 signals following physiological stimulation of insulin secretion is unknown. Using evanescent wave microscopy and a green fluorescent protein-tagged PIP3-binding protein domain for real-time monitoring of plasma membrane PIP3 concentration in single MIN6 β-cells, we now demonstrate that glucose stimulation of insulin secretion results in pronounced PIP3 oscillations via autocrine stimulation of insulin receptors. Glucose lacked effect when insulin secretion was prevented with the hyperpolarizing agent diazoxide, but the sugar dose dependently enhanced the PIP3 response to maximal insulin stimulation without affecting the rate of PIP3 degradation. We conclude that glucose is an important co-activator of phosphatidylinositol-3′-OH-kinase and that the plasma membrane PIP 3 concentration in β-cells undergoes oscillations due to pulsatile release of insulin.

Place, publisher, year, edition, pages
2006. Vol. 281, no 51, 39121-39127 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:uu:diva-22912DOI: 10.1074/jbc.M607445200ISI: 000242898700019PubMedID: 17074763OAI: oai:DiVA.org:uu-22912DiVA: diva2:50685
Available from: 2007-01-23 Created: 2007-01-23 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Oscillatory Signaling and Insulin Secretion from Single ß-cells
Open this publication in new window or tab >>Oscillatory Signaling and Insulin Secretion from Single ß-cells
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

cAMP and Ca2+ are key regulators of exocytosis in many cells, including insulin-secreting pancreatic β-cells. Glucose-stimulated insulin secretion from β-cells is pulsatile and driven by oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i), but little is known about the kinetics of cAMP signaling and the mechanisms of cAMP action. Evanescent wave microscopy and fluorescent translocation biosensors were used to monitor plasma membrane-related signaling events in single MIN6-cells and primary mouse β-cells. Glucose stimulation of insulin secretion resulted in pronounced oscillations of the membrane phospholipid PIP3 caused by autocrine activation of insulin receptors. Glucose also triggered oscillations of the sub-plasma membrane cAMP concentration ([cAMP]pm). These oscillations were preceded and enhanced by elevations of [Ca2+]i, but conditions raising cytoplasmic ATP triggered [cAMP]pm elevations without accompanying changes in [Ca2+]i. The [cAMP]pm oscillations were also synchronized with PIP3 oscillations and both signals were suppressed after inhibition of adenylyl cyclases. Protein kinase A (PKA) was important for promoting concomitant initial elevations of [cAMP]pm and [Ca2+]i, and PKA inhibitors diminished the PIP3 response when applied before glucose stimulation, but did not affect already manifested PIP3 oscillations. The glucose-induced PIP3 oscillations were markedly suppressed in cells treated with siRNA against the cAMP-dependent guanine nucleotide exchange factor Epac2. Pharmacological activation of Epac restored PIP3 responses after adenylyl cyclase or PKA inhibition. Glucose and other cAMP-elevating stimuli induced redistribution of fluorescence-tagged Epac2 from the cytoplasm to the plasma membrane. This translocation was modulated by [Ca2+]i and depended on intact cyclic nucleotide-binding and Ras-association domains. In conclusion, glucose generates cAMP oscillations in β-cells via a concerted action of Ca2+ and metabolically generated ATP. The oscillations are important for the magnitude and kinetics of insulin secretion. While both protein kinase A and Epac is required for initiation of insulin secretion the cAMP-dependence of established pulsatility is mediated by Epac2.

Place, publisher, year, edition, pages
Uppsala: A U U, 2010. 71 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 520
Keyword
cAMP, Ca2+, oscillations, beta-cell, insulin secretion, evanescent wave microscopy, PIP3, PKA, Epac
National Category
Cell and Molecular Biology
Research subject
Medical Cell Biology
Identifiers
urn:nbn:se:uu:diva-113686 (URN)978-91-554-7718-9 (ISBN)
Public defence
2010-03-19, B21, BMC, Husargatan 3, Uppsala, 09:15 (English)
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Supervisors
Available from: 2010-02-25 Created: 2010-02-02 Last updated: 2018-01-12Bibliographically approved

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