Glucose-stimulated insulin secretion is coupled to the interaction of actin with the t-SNARE (target membrane soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein) complex.
The actin monomer sequestering agent latrunculin B depolymerized beta-cell cortical actin, which resulted in increased glucose-stimulated insulin secretion in both cultured MIN6 beta-cells and isolated rat islet cells. In perifused islets, latrunculin B treatment increased both first- and second-phase glucose-stimulated insulin secretion without any significant effect on total insulin content. This increase in secretion was independent of calcium regulation because latrunculin B also potentiated calcium-stimulated insulin secretion in permeabilized MIN6 cells. Confocal immunofluorescent microscopy revealed a redistribution of insulin granules to the cell periphery in response to glucose or latrunculin B, which correlated with a reduction in phalloidin staining of cortical actin. Moreover, the t-SNARE [target membrane soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor] proteins Syntaxin 1 and SNAP-25 coimmunoprecipitated polymerized actin from unstimulated MIN6 cells. Glucose stimulation transiently decreased the amount of actin coimmunoprecipitated with Syntaxin 1 and SNAP-25, and latrunculin B treatment fully ablated the coimmunoprecipitation. In contrast, the actin stabilizing agent jasplakinolide increased the amount of actin coimmunoprecipitated with the t-SNARE complex and prevented its dissociation upon glucose stimulation. These data suggest a mechanism whereby glucose modulates beta-cell cortical actin organization and disrupts the interaction of polymerized actin with the plasma membrane t-SNARE complex at a distal regulatory step in the exocytosis of insulin granules.
Thurmond
Debbie C
DC
Department of Biochemistry and Molecular Biology, Center for Diabetes Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA. dthurmon@iupui.edu.
Gonelle-Gispert
Carmen
C
Furukawa
Megumi
M
Halban
Philippe A
PA
Pessin
Jeffrey E
JE
D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000954:Antigens, Surface / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010477:Perfusion; D011233:Precipitin Tests; D050683:R-SNARE Proteins; D051381:Rats; D050600:SNARE Proteins; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D033921:Vesicular Transport Proteins
D000199:Actins; D000954:Antigens, Surface; D019086:Bridged Bicyclo Compounds, Heterocyclic; D015220:Calcium Channels; D007328:Insulin; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; C494210:Snap25 protein, rat; C494213:Stx1a protein, rat; D050825:Synaptosomal-Associated Protein 25; D050827:Syntaxin 1; D013844:Thiazoles; D053778:Thiazolidines; D033921:Vesicular Transport Proteins; D005947:Glucose; C037068:latrunculin B; D002118:Calcium