Rapid association of protein kinase C-epsilon with insulin granules is essential for insulin exocytosis.
Glucose-dependent exocytosis of insulin requires activation of protein kinase C (PKC). However, because of the great variety of isoforms and their ubiquitous distribution within the beta-cell, it is difficult to predict the importance of a particular isoform and its mode of action. Previous data revealed that two PKC isoforms (alpha and epsilon) translocate to membranes in response to glucose (Zaitzev, S. V., Efendic, S., Arkhammar, P., Bertorello, A. M., and Berggren, P. O. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 9712-9716). Using confocal microscopy, we have now established that in response to glucose, PKC-epsilon but not PKC-alpha associates with insulin granules and that green fluorescent protein-tagged PKC-epsilon changes its distribution within the cell periphery upon stimulation of beta-cells with glucose. Definite evidence of PKC-epsilon requirement during insulin granule exocytosis was obtained by using a dominant negative mutant of this isoform. The presence of this mutant abolished glucose-induced insulin secretion, whereas transient expression of the wild-type PKC-epsilon led to a significant increase in insulin exocytosis. These results suggest that association of PKC-epsilon with insulin granule membranes represents an important component of the secretory network because it is essential for insulin exocytosis in response to glucose.
Mendez
Carlos F
CF
Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, SE-171 76 Stockholm, Sweden.
Leibiger
Ingo B
IB
Leibiger
Barbara
B
Høy
Marianne
M
Gromada
Jesper
J
Berggren
Per-Olof
PO
Bertorello
Alejandro M
AM
D000818:Animals; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000648:ultrastructure*; D025802:Electric Capacitance; D005089:Exocytosis / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D007340:Insulinoma; D007425:Intracellular Membranes / Q000201:enzymology* / Q000502:physiology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D007700:Kinetics; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008820:Mice, Obese; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D016297:Mutagenesis, Site-Directed; D010190:Pancreatic Neoplasms; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D051381:Rats; D011993:Recombinant Fusion Proteins; D014162:Transfection; D014407:Tumor Cells, Cultured
D007004:Hypoglycemic Agents; D007328:Insulin; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; C497256:Prkce protein, mouse; C497257:Prkce protein, rat; C496630:Prkca protein, mouse; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D051744:Protein Kinase C-epsilon; D005947:Glucose; D005905:Glyburide