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Title

Suppression of Pdx-1 perturbs proinsulin processing, insulin secretion and GLP-1 signalling in INS-1 cells

Authors
Iezzi, M.
Antinozzi, P. A.
Gauthier, B. R.
Published in Diabetologia. 2005, vol. 48, no. 4, p. 720-731
Abstract AIMS/HYPOTHESIS: Mutations in genes encoding HNF-4alpha, HNF-1alpha and IPF-1/Pdx-1 are associated with, respectively, MODY subtypes-1, -3 and -4. Impaired glucose-stimulated insulin secretion is the common primary defect of these monogenic forms of diabetes. A regulatory circuit between these three transcription factors has also been suggested. We aimed to explore how Pdx-1 regulates beta cell function and gene expression patterns. METHODS: We studied two previously established INS-1 stable cell lines permitting inducible expression of, respectively, Pdx-1 and its dominant-negative mutant. We used HPLC for insulin processing, adenovirally encoded aequorin for cytosolic [Ca2+], and transient transfection of human growth hormone or patch-clamp capacitance recordings to monitor exocytosis. RESULTS: Induction of DN-Pdx-1 resulted in defective glucose-stimulated and K+-depolarisation-induced insulin secretion in INS-1 cells, while overexpression of Pdx-1 had no effect. We found that DN-Pdx-1 caused down-regulation of fibroblast growth factor receptor 1 (FGFR1), and consequently prohormone convertases (PC-1/3 and -2). As a result, DN-Pdx-1 severely impaired proinsulin processing. In addition, induction of Pdx-1 suppressed the expression of glucagon-like peptide 1 receptor (GLP-1R), which resulted in marked reduction of both basal and GLP-1 agonist exendin-4-stimulated cellular cAMP levels. Induction of DN-Pdx-1 did not affect glucokinase activity, glycolysis, mitochondrial metabolism or ATP generation. The K+-induced cytosolic [Ca2+] rise and Ca2+-evoked exocytosis (membrane capacitance) were not abrogated. CONCLUSIONS/INTERPRETATION: The severely impaired proinsulin processing combined with decreased GLP-1R expression and cellular cAMP content, rather than metabolic defects or altered exocytosis, may contribute to the beta cell dysfunction induced by Pdx-1 deficiency.
Keywords Adenosine Triphosphate/metabolismAnimalsCalcium Signaling/physiologyCell Line, TumorCyclic AMP/metabolismDose-Response Relationship, DrugDoxycycline/pharmacologyExocytosis/physiologyGene Expression/drug effects/geneticsGene Expression Regulation, Neoplastic/drug effectsGlucokinase/geneticsGlucose/metabolism/pharmacologyGlycolysisHomeodomain Proteins/genetics/metabolism/ physiologyHuman Growth Hormone/genetics/secretionInsulin/ secretionIslets of Langerhans/drug effects/metabolismMitochondria/metabolismMutationProinsulin/ metabolismProprotein Convertases/geneticsRNA, Messenger/genetics/metabolismRatsReceptor Protein-Tyrosine Kinases/geneticsReceptor, Fibroblast Growth Factor, Type 1Receptors, Fibroblast Growth Factor/geneticsReceptors, Glucagon/genetics/ physiologySignal Transduction/ physiologyTime FactorsTrans-Activators/genetics/metabolism/ physiologyTransfection
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PMID: 15756539
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WANG, Haiyan et al. Suppression of Pdx-1 perturbs proinsulin processing, insulin secretion and GLP-1 signalling in INS-1 cells. In: Diabetologia, 2005, vol. 48, n° 4, p. 720-731. https://archive-ouverte.unige.ch/unige:9086

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Deposited on : 2010-07-12

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