title: The Translational Repressor 4E-BP1 Contributes to Diabetes-Induced Visual Dysfunction.
abstract: OBJECTIVE
  The translational repressor 4E-BP1 interacts with the mRNA cap-binding protein eIF4E and thereby promotes cap-independent translation of mRNAs encoding proteins that contribute to diabetic retinopathy. Interaction of 4E-BP1 with eIF4E is enhanced in the retina of diabetic rodents, at least in part, as a result of elevated 4E-BP1 protein expression. In the present study, we examined the role of 4E-BP1 in diabetes-induced visual dysfunction, as well as the mechanism whereby hyperglycemia promotes 4E-BP1 expression.
  
  
  METHODS
  Nondiabetic and diabetic wild-type and 4E-BP1/2 knockout mice were evaluated for visual function using a virtual optomotor test (Optomotry). Retinas were harvested from nondiabetic and type 1 diabetic mice and analyzed for protein abundance and posttranslational modifications. Similar analyses were performed on cells in culture exposed to hyperglycemic conditions or an O-GlcNAcase inhibitor (Thiamet G [TMG]).
  
  
  RESULTS
  Diabetes-induced visual dysfunction was delayed in mice deficient of 4E-BP1/2 as compared to controls. 4E-BP1 protein expression was enhanced by hyperglycemia in the retina of diabetic rodents and by hyperglycemic conditions in retinal cells in culture. A similar elevation in 4E-BP1 expression was observed with TMG. The rate of 4E-BP1 degradation was significantly prolonged by either hyperglycemic conditions or TMG. A PEST motif in the C-terminus of 4E-BP1 regulated polyubiquitination, turnover, and binding of an E3 ubiquitin ligase complex containing CUL3.
  
  
  CONCLUSIONS
  The findings support a model whereby elevated 4E-BP1 expression observed in the retina of diabetic rodents is the result of O-GlcNAcylation of 4E-BP1 within its PEST motif.
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: William P
authors.initials: WP
authors.lastname: Miller
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Mihailescu
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Chen
authors.initials: C
authors.lastname: Yang
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States 2Department of Ophthalmology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United.
authors.forename: Alistair J
authors.initials: AJ
authors.lastname: Barber
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Jefferson
authors.affiliation: Department of Cellular and Molecular Physiology The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Dennis
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental; D003930:Diabetic Retinopathy / Q000209:etiology / Q000235:genetics / Q000503:physiopathology*; D039642:Eukaryotic Initiation Factors; D005786:Gene Expression Regulation; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010448:Peptide Initiation Factors / Q000378:metabolism; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics*; D010766:Phosphorylation; D012313:RNA / Q000235:genetics*; D012097:Repressor Proteins; D012160:Retina / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014792:Visual Acuity
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D010448:Peptide Initiation Factors; D010750:Phosphoproteins; D012097:Repressor Proteins; D012313:RNA