title: Nucleo-cytosolic shuttling of FoxO1 directly regulates mouse Ins2 but not Ins1 gene expression in pancreatic beta cells (MIN6).
abstract: The Forkhead box transcription factor FoxO1 regulates metabolic gene expression in mammals. FoxO1 activity is tightly controlled by phosphatidylinositol 3-kinase (PI3K) signaling, resulting in its phosphorylation and nuclear exclusion. We sought here to determine the mechanisms involved in glucose and insulin-stimulated nuclear shuttling of FoxO1 in pancreatic β cells and its consequences for preproinsulin (Ins1, Ins2) gene expression. Nuclear-localized endogenous FoxO1 translocated to the cytosol in response to elevated glucose (3 versus 16.7 mM) in human islet β cells. Real-time confocal imaging of nucleo-cytosolic shuttling of a FoxO1-EGFP chimera in primary mouse and clonal MIN6 β cells revealed a time-dependent glucose-responsive nuclear export, also mimicked by exogenous insulin, and blocked by suppressing insulin secretion. Constitutively active PI3K or protein kinase B/Akt exerted similar effects, while inhibitors of PI3K, but not of glycogen synthase kinase-3 or p70 S6 kinase, blocked nuclear export. FoxO1 overexpression reversed the activation by glucose of pancreatic duodenum homeobox-1 (Pdx1) transcription. Silencing of FoxO1 significantly elevated the expression of mouse Ins2, but not Ins1, mRNA at 3 mM glucose. Putative FoxO1 binding sites were identified in the distal promoter of rodent Ins2 genes and direct binding of FoxO1 to the Ins2 promoter was demonstrated by chromatin immunoprecipitation. A 915-bp glucose-responsive Ins2 promoter was inhibited by constitutively active FoxO1, an effect unaltered by simultaneous overexpression of PDX1. We conclude that nuclear import of FoxO1 contributes to the suppression of Pdx1 and Ins2 gene expression at low glucose, the latter via a previously unsuspected and direct physical interaction with the Ins2 promoter.
authors.affiliation: Section of Cell Biology, Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Faculty of Medicine, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Gargi
authors.initials: G
authors.lastname: Meur
authors.forename: Qingwen
authors.initials: Q
authors.lastname: Qian
authors.forename: Gabriela
authors.initials: G
authors.lastname: da Silva Xavier
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Pullen
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuboi
authors.forename: Caroline
authors.initials: C
authors.lastname: McKinnon
authors.forename: Laura
authors.initials: L
authors.lastname: Fletcher
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Tavaré
authors.forename: Stephen
authors.initials: S
authors.lastname: Hughes
authors.forename: Paul
authors.initials: P
authors.lastname: Johnson
authors.forename: Guy A
authors.initials: GA
authors.lastname: Rutter
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000096:biosynthesis* / Q000235:genetics; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000502:physiology*; D013549:Sweetening Agents / Q000378:metabolism / Q000494:pharmacology; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; D018398:Homeodomain Proteins; C514817:Ins1 protein, mouse; D007328:Insulin; D011993:Recombinant Fusion Proteins; D013549:Sweetening Agents; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D005947:Glucose