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Requirement of Inositol Pyrophosphates for Full Exocytotic Capacity in Pancreatic β Cells
Christopher Illies,1
Jesper Gromada,2
Roberta Fiume,1
Barbara Leibiger,1
Jia Yu,1
Kirstine Juhl,3
Shao-Nian Yang,1
Deb K. Barma,4
John R. Falck,4
Adolfo Saiardi,5
Christopher J. Barker,1*
Per-Olof Berggren1
Abstract:
Inositol pyrophosphates are recognized components of cellularprocesses that regulate vesicle trafficking, telomere length,and apoptosis. We observed that pancreatic β cells maintainhigh basal concentrations of the pyrophosphate diphosphoinositolpentakisphosphate (InsP7 or IP7). Inositol hexakisphosphatekinases (IP6Ks) that can generate IP7 were overexpressed. Thisoverexpression stimulated exocytosis of insulin-containing granulesfrom the readily releasable pool. Exogenously applied IP7 dose-dependentlyenhanced exocytosis at physiological concentrations. We determinedthat IP6K1 and IP6K2 were present in β cells. RNA silencingof IP6K1, but not IP6K2, inhibited exocytosis, which suggeststhat IP6K1 is the critical endogenous kinase. Maintenance ofhigh concentrations of IP7 in the pancreatic β cell mayenhance the immediate exocytotic capacity and consequently allowrapid adjustment of insulin secretion in response to increaseddemand.
1 The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, SE-171 76, Stockholm, Sweden. 2 Diabetes and Metabolism Disease Area, Novartis Institutes for BioMedical Research, Cambridge, MA 02139, USA. 3 Joslin Diabetes Center, Harvard Medical School, Boston, MA 02215, USA. 4 Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. 5 U.K. Medical Research Council (MRC) Cell Biology Unit and Laboratory for Molecular Cell Biology, Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK.
* To whom correspondence should be addressed. E-mail: chris.barker{at}ki.se
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