@article{26c2b8840c9d4a9bbff08eeada79db8c,
title = "Kalirin/Trio Rho GDP/GTP exchange factors regulate proinsulin and insulin secretion",
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 SG behavior employing radiolabeling protocols. Loss of Kalirin/Trio function attenuated radioactive proinsulin release by reducing constitutive-like secretion and exocytosis of 2-h-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{\textquoteright}s participation to stimulatory glucose signaling.",
keywords = "CDC42, Glucose signaling, Guanine nucleotide exchange factor (GEF), Kalirin, Pancreatic β-cells, Proinsulin/insulin secretion, Protein sorting, Ras-related C3 botulinum toxin substrate 1 (Rac1), Secretory granules, Serine/threonine-protein kinase PAK 1 (PAK1), Trio",
author = "Quinn Dufurrena and Nils B{\"a}ck and Richard Mains and Louis Hodgson and Tanowitz, {Herbert B.} and Prashant Mandela and Betty Eipper and Regina Kuliawat",
note = "Funding Information: The work was supported by National 阀nstitutes of Health grants DK068843 (R K), CA205262 and GM129098 (L H), DK032948 (B A E, R E M), Einstein Research Fellowship, Office of Medical Student Research, Office of Medical Education, Albert Einstein College of Medicine and the Medical Scholars Program (Q D), Finska L{\"a}kares{\"a}llskapet and the Perkl{\'e}n Foundation (N B). Human pancreatic islets were provided by the N 阀DDK-funded 阀ntegrated 阀slet Distribution Program at City of Hope, N 阀H Grant # 2UC4DK098085. The authors thank J Nachbar for expert assistance with using 阀mageJ for analysis of images and the Analytical 阀maging Facility of the Albert Einstein College of Medicine as well as the NC 阀 cancer center that provides them with support (grant P30CA013330) for the use of microscopes. Peng Guo, Einstein{\textquoteright}s local expert on Light Microscopy & 阀mage Analysis was instrumental in getting us started with the quantitative evaluation of images. R Muzumdar and L Klein provided much help in setting up the EL 阀SA assays and the general advice of Weiss laboratory members is also gratefully acknowledged. The authors thank the Electron Microscopy Unit of the 阀nstitute of Biotechnology, University of Helsinki, for providing laboratory facilities. Funding Information: The work was supported by National Institutes of Health grants DK068843 (R K), CA205262 and GM129098 (L H), DK032948 (B A E, R E M), Einstein Research Fellowship, Office of Medical Student Research, Office of Medical Education, Albert Einstein College of Medicine and the Medical Scholars Program (Q D), Finska L?kares?llskapet and the Perkl?n Foundation (N B). Human pancreatic islets were provided by the NIDDK-funded Integrated Islet Distribution Program at City of Hope, NIH Grant # 2UC4DK098085. The authors thank J Nachbar for expert assistance with using ImageJ for analysis of images and the Analytical Imaging Facility of the Albert Einstein College of Medicine as well as the NCI cancer center that provides them with support (grant P30CA013330) for the use of microscopes. Peng Guo, Einstein?s local expert on Light Microscopy & Image Analysis was instrumental in getting us started with the quantitative evaluation of images. R Muzumdar and L Klein provided much help in setting up the ELISA assays and the general advice of Weiss laboratory members is also gratefully acknowledged. The authors thank the Electron Microscopy Unit of the Institute of Biotechnology, University of Helsinki, for providing laboratory facilities. Publisher Copyright: {\textcopyright} 2019 Society for Endocrinology.",
year = "2019",
month = jan,
doi = "10.1530/JME-18-0048",
language = "English (US)",
volume = "62",
pages = "47--65",
journal = "Journal of Molecular Endocrinology",
issn = "0952-5041",
publisher = "Society for Endocrinology",
number = "1",
}