SUMOylation regulates insulin exocytosis downstream of secretory granule docking in rodents and humans.
OBJECTIVE
The reversible attachment of small ubiquitin-like modifier (SUMO) proteins controls target localization and function. We examined an acute role for the SUMOylation pathway in downstream events mediating insulin secretion.


METHODS
We studied islets and β-cells from mice and human donors, as well as INS-1 832/13 cells. Insulin secretion, intracellular Ca(2+), and β-cell exocytosis were monitored after manipulation of the SUMOylation machinery. Granule localization was imaged by total internal reflection fluorescence and electron microscopy; immunoprecipitation and Western blotting were used to examine the soluble NSF attachment receptor (SNARE) complex formation and SUMO1 interaction with synaptotagmin VII.


RESULTS
SUMO1 impairs glucose-stimulated insulin secretion by blunting the β-cell exocytotic response to Ca(2+). The effect of SUMO1 to impair insulin secretion and β-cell exocytosis is rapid and does not require altered gene expression or insulin content, is downstream of granule docking at the plasma membrane, and is dependent on SUMO-conjugation because the deSUMOylating enzyme, sentrin/SUMO-specific protease (SENP)-1, rescues exocytosis. SUMO1 coimmunoprecipitates with the Ca(2+) sensor synaptotagmin VII, and this is transiently lost upon glucose stimulation. SENP1 overexpression also disrupts the association of SUMO1 with synaptotagmin VII and mimics the effect of glucose to enhance exocytosis. Conversely, SENP1 knockdown impairs exocytosis at stimulatory glucose levels and blunts glucose-dependent insulin secretion from mouse and human islets.


CONCLUSIONS
SUMOylation acutely regulates insulin secretion by the direct and reversible inhibition of β-cell exocytosis in response to intracellular Ca(2+) elevation. The SUMO protease, SENP1, is required for glucose-dependent insulin secretion.
Department of Pharmacology and Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.
Xiao-Qing
XQ
Dai
Greg
G
Plummer
Marina
M
Casimir
Youhou
Y
Kang
Catherine
C
Hajmrle
Herbert Y
HY
Gaisano
Jocelyn E
JE
Manning Fox
Patrick E
PE
MacDonald
D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D010450:Endopeptidases / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008854:Microscopy, Electron; D025842:SUMO-1 Protein / Q000378:metabolism*; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*; D058207:Sumoylation / Q000502:physiology*; D050857:Synaptotagmins / Q000378:metabolism
D007328:Insulin; D025842:SUMO-1 Protein; D050857:Synaptotagmins; D010450:Endopeptidases; C404512:SENP1 protein, human; D003546:Cysteine Endopeptidases; D005947:Glucose; D002118:Calcium
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