title: Cellular processing of myocilin.
abstract: BACKGROUND
  Myocilin (MYOC) is a gene linked directly to juvenile- and adult-onset open angle glaucoma. Mutations including Pro370Leu (P370L) and Gln368stop (Q368X) have been identified in patients. In the present study, we investigated the processing of myocilin in human trabecular meshwork (TM) cells as well as in inducible, stable RGC5 cell lines.
  
  
  RESULTS
  The turnover and photoactivation experiments revealed that the endogenous myocilin in human trabecular meshwork (TM) cells was a short-lived protein. It was found that the endogenous myocilin level in TM cells was increased by treatment of lysosomal and proteasomal inhibitors, but not by autophagic inhibitor. Multiple bands immunoreactive to anti-ubiquitin were seen in the myocilin pull down, indicating that myocilin was ubiquitinated. In inducible cell lines, the turnover rate of overexpressed wild-type and mutant P370L and Q368X myocilin-GFP fusion proteins was much prolonged. The proteasome function was compromised and autophagy was induced. A decreased PSMB5 level and an increased level of autophagic marker, LC3, were demonstrated.
  
  
  CONCLUSIONS
  The current study provided evidence that in normal homeostatic situation, the turnover of endogenous myocilin involves ubiquitin-proteasome and lysosomal pathways. When myocilin was upregulated or mutated, the ubiquitin-proteasome function is compromised and autophagy is induced. Knowledge of the degradation pathways acting on myocilin can help in design of novel therapeutic strategies for myocilin-related glaucoma.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Ye
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Xiang
authors.initials: X
authors.lastname: Shen
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Rajalekshmy
authors.initials: R
authors.lastname: Shyam
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Beatrice Y J T
authors.initials: BY
authors.lastname: Yue
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois, United States of America.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Ying
mesh_terms: D000328:Adult; D001343:Autophagy / Q000528:radiation effects; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005136:Eye Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008027:Light; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000528:radiation effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014129:Trabecular Meshwork / Q000166:cytology* / Q000378:metabolism* / Q000528:radiation effects; D054875:Ubiquitination / Q000528:radiation effects; D055815:Young Adult; D051176:beta Catenin / Q000378:metabolism; D000099179:Myocilin
chemical_list: D003598:Cytoskeletal Proteins; D005136:Eye Proteins; D006023:Glycoproteins; D049452:Green Fluorescent Proteins; D008869:Microtubule-Associated Proteins; D046988:Proteasome Endopeptidase Complex; D011993:Recombinant Fusion Proteins; D051176:beta Catenin; D000099179:Myocilin; C477012:MAP1LC3A protein, human; C088874:PSMB5 protein, human
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