title: The F-actin modifier villin regulates insulin granule dynamics and exocytosis downstream of islet cell autoantigen 512.
abstract: OBJECTIVE
  Insulin release from pancreatic islet β cells should be tightly controlled to avoid hypoglycemia and insulin resistance. The cortical actin cytoskeleton is a gate for regulated exocytosis of insulin secretory granules (SGs) by restricting their mobility and access to the plasma membrane. Prior studies suggest that SGs interact with F-actin through their transmembrane cargo islet cell autoantigen 512 (Ica512) (also known as islet antigen 2/Ptprn). Here we investigated how Ica512 modulates SG trafficking and exocytosis.
  
  
  METHODS
  Transcriptomic changes in Ica512 (-/-) mouse islets were analyzed. Imaging as well as biophysical and biochemical methods were used to validate if and how the Ica512-regulated gene villin modulates insulin secretion in mouse islets and insulinoma cells.
  
  
  RESULTS
  The F-actin modifier villin was consistently downregulated in Ica512 (-/-) mouse islets and in Ica512-depleted insulinoma cells. Villin was enriched at the cell cortex of β cells and dispersed villin (-/-) islet cells were less round and less deformable. Basal mobility of SGs in villin-depleted cells was enhanced. Moreover, in cells depleted either of villin or Ica512 F-actin cages restraining cortical SGs were enlarged, basal secretion was increased while glucose-stimulated insulin release was blunted. The latter changes were reverted by overexpressing villin in Ica512-depleted cells, but not vice versa.
  
  
  CONCLUSIONS
  Our findings show that villin controls the size of the F-actin cages restricting SGs and, thus, regulates their dynamics and availability for exocytosis. Evidence that villin acts downstream of Ica512 also indicates that SGs directly influence the remodeling properties of the cortical actin cytoskeleton for tight control of insulin secretion.
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Hassan
authors.initials: H
authors.lastname: Mziaut
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Bernard
authors.initials: B
authors.lastname: Mulligan
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hoboth
authors.affiliation: Biotechnology Center Dresden, 01307 Dresden, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Otto
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Ivanova
authors.affiliation: Biotechnology Center Dresden, 01307 Dresden, Germany.
authors.forename: Maik
authors.initials: M
authors.lastname: Herbig
authors.affiliation: Boehringer Ingelheim Pharma GmbH & Co. KG. Cardiometabolic Research, 88397 Biberach, Germany.
authors.forename: Desiree
authors.initials: D
authors.lastname: Schumann
authors.affiliation: Boehringer Ingelheim Pharma GmbH & Co. KG. Cardiometabolic Research, 88397 Biberach, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Hildebrandt
authors.affiliation: Helmholtz Centre for Infection Research (HZI), Braunschweig Integrated Centre for Systems Biology (BRICS), 38124 Braunschweig, Germany.
authors.forename: Jaber
authors.initials: J
authors.lastname: Dehghany
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Sönmez
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany.
authors.forename: Carla
authors.initials: C
authors.lastname: Münster
authors.affiliation: Helmholtz Centre for Infection Research (HZI), Braunschweig Integrated Centre for Systems Biology (BRICS), 38124 Braunschweig, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Meyer-Hermann
authors.affiliation: Biotechnology Center Dresden, 01307 Dresden, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Guck
authors.affiliation: Max Planck Institute for Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
authors.forename: Yannis
authors.initials: Y
authors.lastname: Kalaidzidis
authors.affiliation: Paul Langerhans Institute Dresden of the Helmholtz Center Munich at the Univ. Hospital, Faculty of Medicine Carl Gustav Carus, Technische Univ. Dresden, 01307 Dresden, Germany; German Center for Diabetes Research (DZD e.V.), 85674 Neuherberg, Germany; Max Planck Institute for Molecular Cell Biology and Genetics, 01307 Dresden, Germany. Electronic address: Michele.Solimena@tu-dresden.de.
authors.forename: Michele
authors.initials: M
authors.lastname: Solimena
keywords: D, diffusion coefficient; EGFP, enhanced green fluorescent protein; F-actin; Granules; IPGTT, intraperitoneal glucose tolerance test; IVGTT, intravenous glucose tolerance test; Ica512; Ica512, islet cell autoantigen; Insulin; OGTT, oral glucose tolerance test; RT-DC, real-time deformability cytometry; SE, standard error; SG, secretory granules; Secretion; TIRFM, total internal reflection fluorescence microscopy; Villin