title: Activation of unfolded protein response in transgenic mouse lenses.
abstract: OBJECTIVE
  Overloading of unfolded or misfolded proteins in the endoplasmic reticulum (ER) can cause ER stress and activate the unfolded protein response (UPR) in the cell. The authors tested whether transgene overexpression in the mouse lens would activate the UPR.
  
  
  METHODS
  Transgenic mice expressing proteins that either enter the ER secretory pathway or are synthesized in cytosol were selected. Activation of the UPR was assessed by determining the expression levels of the ER chaperone protein BiP, the spliced form of X-box binding protein-1 (Xbp-1) mRNA, and the transcription factor CHOP. Changes in the ubiquitin-proteasome system in the mouse lens were detected by ubiquitin immunofluorescence.
  
  
  RESULTS
  BiP expression was upregulated in the fiber cells of transgenic mouse lenses expressing platelet-derived growth factor-A (PDGF-A), dominant-negative fibroblast growth factor receptor (DN-FGFR), or DN-Sprouty2 (DN-Spy2). BiP upregulation occurred around embryonic day 16.5, primarily in the fiber cells adjacent to the organelle free zone. Fiber cell differentiation was disrupted in the PDGF-A and DN-Spry2 lenses, whereas the fiber cells were degenerating in the DN-FGFR lens. High levels of UPR activation and ubiquitin-labeled protein aggregates were found in the DN-FGFR lens, indicating inefficient disposal of unfolded/misfolded proteins in the fiber cells.
  
  
  CONCLUSIONS
  This study implies that overexpression of some transgenes in the lens can induce ER or overall cell stress in fiber cells, resulting in the activation of UPR signaling pathways. Therefore, investigators should assess the levels of UPR activation when they analyze the downstream effects of transgene expression in the lens.
authors.affiliation: Department of Ophthalmology, School of Medicine, University of Missouri, Columbia, Missouri, USA. renekerl@health.missouri.edu
authors.forename: Lixing W
authors.initials: LW
authors.lastname: Reneker
authors.forename: Huiyi
authors.initials: H
authors.lastname: Chen
authors.forename: Paul A
authors.initials: PA
authors.lastname: Overbeek
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000235:genetics*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D019084:Fluorescent Antibody Technique, Indirect; D005786:Gene Expression Regulation / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000235:genetics*; D020287:In Situ Nick-End Labeling; D047908:Intracellular Signaling Peptides and Proteins; D007908:Lens, Crystalline / Q000378:metabolism*; D008565:Membrane Proteins; D051379:Mice; D008822:Mice, Transgenic; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051742:Transcription Factor CHOP / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D044767:Ubiquitin-Protein Ligases; D056811:Unfolded Protein Response / Q000502:physiology*; D015854:Up-Regulation; D000071717:X-Box Binding Protein 1
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C497250:Ddit3 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse; D051742:Transcription Factor CHOP; D044767:Ubiquitin-Protein Ligases; D017346:Protein Serine-Threonine Kinases; C118389:Spry2 protein, mouse