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J Mol Endocrinol. 2018 Nov 1. pii: JME-18-0048.R2. doi: 10.1530/JME-18-0048. [Epub ahead of print]

Kalirin/Trio Rho GDP/GTP exchange factors regulate proinsulin and insulin secretion.

Author information

1
Q Dufurrena, Medicine, Stony Brook University Health Sciences Center School of Medicine, Stony Brook, United States.
2
N Bäck, Anatomy, Helsingin Yliopisto Laaketieteellinen tiedekunta, Helsinki, Finland.
3
R Mains, Neuroscience, University of Connecticut Health Center, Farmington, 06030-3401, United States.
4
L Hodgson, Anatomy and Structural Biology, Yeshiva University Albert Einstein College of Medicine, Bronx, United States.
5
H Tanowitz, Pathology, Yeshiva University Albert Einstein College of Medicine, Bronx, United States.
6
P Mandela, School of Pharmacy, University of Saint Joseph, Hartford, United States.
7
E Eipper, Neuroscience, University of Connecticut Health Center, Farmington, 06030-3401, United States.
8
R Kuliawat, Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, 10461, United States.

Abstract

Key features for progression to pancreatic β-cell failure and disease are loss of glucose responsiveness and an increased ratio of secreted proinsulin to insulin. Proinsulin and insulin are stored in secretory granules (SGs) and the fine-tuning of hormone output requires signal mediated recruitment of select SG populations according to intracellular location and age. The GTPase Rac1 coordinates multiple signaling pathways that specify SG release and Rac1 activity is controlled in part by GDP/GTP exchange factors (GEFs). To explore the function of two large multidomain GEFs, Kalirin and Trio in β-cells, we manipulated their Rac1-specific GEF1 domain activity by using small molecule inhibitors and by genetically ablating Kalirin. We examined age related secretory granule behavior employing radiolabeling protocols. Loss of Kalirin/Trio function attenuated radioactive proinsulin release by reducing constitutive-like secretion and exocytosis of 2-hour old granules. At later chase times or at steady state, Kalirin/Trio manipulations decreased glucose stimulated insulin output. Finally, use of a Rac1 FRET biosensor with cultured β-cell lines, demonstrated that Kalirin/Trio GEF1 activity was required for normal rearrangement of Rac1 to the plasma membrane in response to glucose. Rac1 activation can be evoked by both glucose metabolism and signaling through the incretin glucagon-like peptide 1 (GLP-1) receptor. GLP-1 addition restored Rac1 localization/activity and insulin secretion in the absence of Kalirin, thereby assigning Kalirin's participation to stimulatory glucose signaling.

PMID:
30407917
PMCID:
PMC6494717
[Available on 2020-05-01]
DOI:
10.1530/JME-18-0048

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