EIF4G1 and carboxypeptidase e axis dysregulation in O-GlcNAc transferase-deficient pancreatic β-cells contributes to hyperproinsulinemia in mice

Seokwon Jo, Amber Lockridge, Emilyn U Alejandro

Research output: Contribution to journalArticle

Abstract

An early hallmark of type 2 diabetes is a failure of proinsulin- to-insulin processing in pancreatic β-cells, resulting in hyperproinsulinemia. Proinsulin processing is quite sensitive to nutrient flux, and β-cell-specific deletion of the nutrientsensing protein modifier OGlcNAc transferase (βOGTKO) causes β-cell failure and diabetes, including early development of hyperproinsulinemia. The mechanisms underlying this latter defect are unknown. Here, using several approaches, including site-directed mutagenesis, Click O-GlcNAc labeling, immunoblotting, and immunofluorescence and EM imaging, we provide the first evidence for a relationship between the O-GlcNAcylation of eukaryotic translation initiation factor 4γ1 (eIF4G1) and carboxypeptidase E (CPE)-dependent proinsulin processing in βOGTKO mice. We first established that βOGTKO hyperproinsulinemia is independent of age, sex, glucose levels, and endoplasmic reticulum-CCAAT enhancerbinding protein homologous protein (CHOP)-mediated stress status. Of note, OGT loss was associated with a reduction in β-cell-resident CPE, and genetic reconstitution of CPE in βOGTKO islets rescued the dysfunctional proinsulin-to-insulin ratio. We show that although CPE is not directly OGlcNAc modified in islets, over expression of the suspected OGT target eIF4G1, previously shown to regulate CPE translation in-cells, increases islet CPE levels, and fully reverses βOGTKO islet-induced hyperproinsulinemia. Furthermore, our results reveal that OGT O-GlcNAc-modifies eIF4G1 at Ser-61 and that this modification is critical for eIF4G1 protein stability. Together, these results indicate a direct link between nutrient-sensitive OGT and insulin processing, underscoring the importance of post-translational O-GlcNAc modification in general cell physiology.

Original languageEnglish (US)
Pages (from-to)13040-13050
Number of pages11
JournalJournal of Biological Chemistry
Volume294
Issue number35
DOIs
StatePublished - Jan 1 2019

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Carboxypeptidase H
Carboxypeptidases
Proinsulin
Insulin
Medical problems
Processing
Nutrients
Proteins
Eukaryotic Initiation Factors
Food
Cell Physiological Phenomena
Mutagenesis
Protein Stability
Physiology
Transferases
Site-Directed Mutagenesis
Islets of Langerhans
Immunoblotting
Endoplasmic Reticulum
Labeling

PubMed: MeSH publication types

  • Journal Article

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EIF4G1 and carboxypeptidase e axis dysregulation in O-GlcNAc transferase-deficient pancreatic β-cells contributes to hyperproinsulinemia in mice. / Jo, Seokwon; Lockridge, Amber; Alejandro, Emilyn U.

In: Journal of Biological Chemistry, Vol. 294, No. 35, 01.01.2019, p. 13040-13050.

Research output: Contribution to journalArticle

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abstract = "An early hallmark of type 2 diabetes is a failure of proinsulin- to-insulin processing in pancreatic β-cells, resulting in hyperproinsulinemia. Proinsulin processing is quite sensitive to nutrient flux, and β-cell-specific deletion of the nutrientsensing protein modifier OGlcNAc transferase (βOGTKO) causes β-cell failure and diabetes, including early development of hyperproinsulinemia. The mechanisms underlying this latter defect are unknown. Here, using several approaches, including site-directed mutagenesis, Click O-GlcNAc labeling, immunoblotting, and immunofluorescence and EM imaging, we provide the first evidence for a relationship between the O-GlcNAcylation of eukaryotic translation initiation factor 4γ1 (eIF4G1) and carboxypeptidase E (CPE)-dependent proinsulin processing in βOGTKO mice. We first established that βOGTKO hyperproinsulinemia is independent of age, sex, glucose levels, and endoplasmic reticulum-CCAAT enhancerbinding protein homologous protein (CHOP)-mediated stress status. Of note, OGT loss was associated with a reduction in β-cell-resident CPE, and genetic reconstitution of CPE in βOGTKO islets rescued the dysfunctional proinsulin-to-insulin ratio. We show that although CPE is not directly OGlcNAc modified in islets, over expression of the suspected OGT target eIF4G1, previously shown to regulate CPE translation in-cells, increases islet CPE levels, and fully reverses βOGTKO islet-induced hyperproinsulinemia. Furthermore, our results reveal that OGT O-GlcNAc-modifies eIF4G1 at Ser-61 and that this modification is critical for eIF4G1 protein stability. Together, these results indicate a direct link between nutrient-sensitive OGT and insulin processing, underscoring the importance of post-translational O-GlcNAc modification in general cell physiology.",
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AB - An early hallmark of type 2 diabetes is a failure of proinsulin- to-insulin processing in pancreatic β-cells, resulting in hyperproinsulinemia. Proinsulin processing is quite sensitive to nutrient flux, and β-cell-specific deletion of the nutrientsensing protein modifier OGlcNAc transferase (βOGTKO) causes β-cell failure and diabetes, including early development of hyperproinsulinemia. The mechanisms underlying this latter defect are unknown. Here, using several approaches, including site-directed mutagenesis, Click O-GlcNAc labeling, immunoblotting, and immunofluorescence and EM imaging, we provide the first evidence for a relationship between the O-GlcNAcylation of eukaryotic translation initiation factor 4γ1 (eIF4G1) and carboxypeptidase E (CPE)-dependent proinsulin processing in βOGTKO mice. We first established that βOGTKO hyperproinsulinemia is independent of age, sex, glucose levels, and endoplasmic reticulum-CCAAT enhancerbinding protein homologous protein (CHOP)-mediated stress status. Of note, OGT loss was associated with a reduction in β-cell-resident CPE, and genetic reconstitution of CPE in βOGTKO islets rescued the dysfunctional proinsulin-to-insulin ratio. We show that although CPE is not directly OGlcNAc modified in islets, over expression of the suspected OGT target eIF4G1, previously shown to regulate CPE translation in-cells, increases islet CPE levels, and fully reverses βOGTKO islet-induced hyperproinsulinemia. Furthermore, our results reveal that OGT O-GlcNAc-modifies eIF4G1 at Ser-61 and that this modification is critical for eIF4G1 protein stability. Together, these results indicate a direct link between nutrient-sensitive OGT and insulin processing, underscoring the importance of post-translational O-GlcNAc modification in general cell physiology.

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