cAMP induces stromal interaction molecule 1 (STIM1) puncta but neither Orai1 protein clustering nor store-operated Ca2+ entry (SOCE) in islet cells.
The events leading to the activation of store-operated Ca(2+) entry (SOCE) involve Ca(2+) depletion of the endoplasmic reticulum (ER) resulting in translocation of the transmembrane Ca(2+) sensor protein, stromal interaction molecule 1 (STIM1), to the junctions between ER and the plasma membrane where it binds to the Ca(2+) channel protein Orai1 to activate Ca(2+) 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 β-cells and glucagon-secreting α-cells within intact mouse and human pancreatic islets. ER Ca(2+) 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 Ca(2+) store filling and inhibits SOCE, stimulated retranslocation of STIM1 to the bulk ER. This effect was evident at much lower glucose concentrations in α- than in β-cells consistent with involvement of SOCE in the regulation of glucagon secretion. Epinephrine stimulated subplasmalemmal translocation of STIM1 in α-cells and retranslocation in β-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.
Department of Medical Cell Biology, Uppsala University, BMC Box 571, SE-751 23 Uppsala, Sweden and.
Geng
G
Tian
Physiological Laboratory, Department of Cellular and Molecular Physiology, University of Liverpool, Liverpool L69 3BX, United Kingdom.
Alexei V
AV
Tepikin
Department of Medical Cell Biology, Uppsala University, BMC Box 571, SE-751 23 Uppsala, Sweden and.
Anders
A
Tengholm
Department of Medical Cell Biology, Uppsala University, BMC Box 571, SE-751 23 Uppsala, Sweden and. Electronic address: erik.gylfe@mcb.uu.se.
Erik
E
Gylfe
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000328:Adult; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D050416:Glucagon-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000378:metabolism*; D000071740:ORAI1 Protein; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D000071737:Stromal Interaction Molecule 1
D000316:Adrenergic alpha-Agonists; D015220:Calcium Channels; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; C520430:Orai1 protein, mouse; C103530:STIM1 protein, human; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium; D004837:Epinephrine