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cAMP Induces Stromal Interaction Molecule 1 (STIM1) Puncta but neither Orai1 Protein Clustering nor Store-operated Ca2+ Entry (SOCE) in Islet 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.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Cell Biology.
2012 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 287, no 13, 9862-9872 p.Article in journal (Refereed) Published
Abstract [en]

The events leading to the activation of store-operated Ca2+ entry (SOCE) involve Ca2+ depletion of the endoplasmic reticulum (ER) resulting in translocation of the transmembrane Ca2+ sensor protein, stromal interaction molecule 1 (STIM1), to the junctions between ER and the plasma membrane where it binds to the Ca2+ channel protein Orai1 to activate Ca2+ influx. Using confocal and total internal reflection fluorescence microscopy, we studied redistribution kinetics of fluorescence-tagged STIM1 and Orai1 as well as SOCE in insulin-releasing beta-cells and glucagon-secreting alpha-cells within intact mouse and human pancreatic islets. ER Ca2+ depletion triggered accumulation of STIM1 puncta in the subplasmalemmal ER where they co-clustered with Orai1 in the plasma membrane and activated SOCE. Glucose, which promotes Ca2+ store filling and inhibits SOCE, stimulated retranslocation of STIM1 to the bulk ER. This effect was evident at much lower glucose concentrations in alpha-than in beta-cells consistent with involvement of SOCE in the regulation of glucagon secretion. Epinephrine stimulated subplasmalemmal translocation of STIM1 in beta-cells and retranslocation in beta-cells involving raising and lowering of cAMP, respectively. The cAMP effect was mediated both by protein kinase A and exchange protein directly activated by cAMP. However, the cAMP-induced STIM1 puncta did not co-cluster with Orai1, and there was no activation of SOCE. STIM1 translocation can consequently occur independently of Orai1 clustering and SOCE.

Place, publisher, year, edition, pages
2012. Vol. 287, no 13, 9862-9872 p.
National Category
Cell and Molecular Biology
Identifiers
URN: urn:nbn:se:uu:diva-173662DOI: 10.1074/jbc.M111.292854ISI: 000302167200019OAI: oai:DiVA.org:uu-173662DiVA: diva2:524454
Available from: 2012-05-02 Created: 2012-05-02 Last updated: 2017-12-07Bibliographically approved
In thesis
1. On the Generation of cAMP Oscillations and Regulation of the Ca2+ Store-operated Pathway in Pancreatic Islet α- and β-cells
Open this publication in new window or tab >>On the Generation of cAMP Oscillations and Regulation of the Ca2+ Store-operated Pathway in Pancreatic Islet α- and β-cells
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Insulin and glucagon are released in pulses from pancreatic β- and α-cells, respectively. Both cell types are electrically excitable, and elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) due to depolarization with voltage-dependent entry of the cation is the main trigger of hormone secretion. Store-operated Ca2+ entry  (SOCE) also contributes to the [Ca2+]i elevation and this process has been suggested to be particularly important for glucagon secretion. cAMP is another important messenger that amplifies Ca2+-triggered secretion of both hormones, but little is known about cAMP dynamics in islet cells. In type-2 diabetes, there is deteriorated β-cell function associated with elevated concentrations of fatty acids, but the underlying mechanisms are largely unknown. To clarify the processes that regulate insulin and glucagon secretion, cAMP signalling and the store-operated pathway were investigated in β- and α-cells, primarily within their natural environment in intact mouse and human islets of Langerhans. Fluorescent biosensors and total internal reflection microscopy were used to investigate signalling specifically at the plasma membrane (PM). Adrenaline increased and decreased the sub-PM cAMP concentration ([cAMP]pm) in immuno-identified α-cells and β-cells, respectively, which facilitated cell identification. Glucagon elicited [cAMP]pm oscillations in α- and β-cells, demonstrating both auto- and paracrine effects of the hormone. Whereas glucagon-like peptide 1 (GLP-1) consistently elevated [cAMP]pm in β-cells, only few α-cells responded, indicating that GLP-1 regulates glucagon secretion without changes of α-cell [cAMP]pm. Both α- and β-cells responded to glucose with pronounced oscillations of [cAMP]pm that were partially Ca2+-dependent and synchronized among islet β-cells. The glucose-induced cAMP formation was mediated by plasma membrane-bound adenylyl cyclases. Several phosphodiesterases (PDEs), including the PDE1, -3, -4, and -8 families, were required for shaping the [cAMP]pm signals and pulsatile insulin secretion. Prolonged exposure of islets to the fatty acid palmitate deteriorated glucose-stimulated insulin secretion with loss of pulsatility. This defect was associated with impaired cAMP generation, while [Ca2+]i signalling was essentially unaffected. Stromal interacting molecule 1 (STIM1) is critical for activation of SOCE by sensing the Ca2+ concentration in the endoplasmic reticulum (ER). ER Ca2+ depletion caused STIM1 aggregation, co-clustering with the PM Ca2+ channel protein Orai1 and SOCE activation. Glucose, which inhibits SOCE by filling the ER with Ca2+, reversed the PM association of STIM1. Consistent with a role of the store-operated pathway in glucagon secretion, this effect was maximal at the low glucose concentrations that inhibit glucagon release, whereas considerably higher concentrations were required in β-cells. Adrenaline induced STIM1 translocation to the PM in α-cells and the reverse process in β-cells, partially reflecting the opposite effects of adrenaline on cAMP in the two cell types. However, cAMP-induced STIM1 aggregates did not co-cluster with Orai1 or activate SOCE, indicating that STIM1 translocation can occur independently of Orai1 clustering and SOCE.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 860
Keyword
cAMP, oscillations, adrenaline, GLP-1, phosphodiesterase, palmitate, STIM1, Orai1, store-operated calcium entry, insulin secretion, glucagon secretion, β-cell, α-cell
National Category
Cell and Molecular Biology
Research subject
Medical Cell Biology
Identifiers
urn:nbn:se:uu:diva-191852 (URN)978-91-554-8584-9 (ISBN)
Public defence
2013-03-07, B22, BMC, Uppsala University, Husargatan 3, 751 23, Uppsala, 09:15 (English)
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Supervisors
Available from: 2013-02-13 Created: 2013-01-14 Last updated: 2013-04-02Bibliographically approved

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Tian et al JBC 2012(1744 kB)236 downloads
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Tian, GengTengholm, AndersGylfe, Erik

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