title: Molecular chaperone function for myocilin.
abstract: OBJECTIVE
  Myocilin is thought to be a stress response protein, but its exact molecular functions have not been established. Studies were conducted to see whether myocilin can act as a general molecular chaperone.
  
  
  METHODS
  Myocilin was isolated and purified from porcine trabecular meshwork (TM) cell culture media. Its ability to protect citrate synthase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the restriction endonuclease DrdI from thermal inactivation was evaluated. Light scattering was used to evaluate thermally induced aggregation of citrate synthase. Myocilin induction was assessed after exposure of TM cells to several types of stress treatments.
  
  
  RESULTS
  Levels of extracellular myocilin expressed by TM cells were increased in response to mechanical stretch, heat shock, TNFα, or IL-1α. Myocilin protected citrate synthase activity against thermal inactivation for 5 minutes at 55°C in a concentration-dependent manner, with nearly full protection of 1.5 μM citrate synthase in the presence of 650 nM myocilin. Myocilin significantly reduced thermal aggregation of citrate synthase to levels 36% to 44% of control levels. Myocilin also protected GAPDH from thermal inactivation for 10 minutes at 45°C. Myocilin at 18 nM was more effective than 1 μM bovine serum albumin at protecting DrdI from thermal inactivation.
  
  
  CONCLUSIONS
  Myocilin is induced in response to several cellular stresses and displays general molecular chaperone activity by protecting DrdI, citrate synthase, and GAPDH from thermal inactivation. Myocilin also suppresses the thermal aggregation of citrate synthase. One function of myocilin may be to serve as a molecular chaperone.
authors.affiliation: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA.
authors.forename: Ann Marie
authors.initials: AM
authors.lastname: Anderssohn
authors.forename: Kalani
authors.initials: K
authors.lastname: Cox
authors.forename: Kevin
authors.initials: K
authors.lastname: O'Malley
authors.forename: Scott
authors.initials: S
authors.lastname: Dees
authors.forename: Mojgan
authors.initials: M
authors.lastname: Hosseini
authors.forename: Lacey
authors.initials: L
authors.lastname: Boren
authors.forename: Anthony
authors.initials: A
authors.lastname: Wagner
authors.forename: John M
authors.initials: JM
authors.lastname: Bradley
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Kelley
authors.forename: Ted S
authors.initials: TS
authors.lastname: Acott
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000502:physiology*; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors; D005136:Eye Proteins / Q000502:physiology*; D024602:Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating) / Q000378:metabolism; D006023:Glycoproteins / Q000502:physiology*; D006358:Hot Temperature; D018832:Molecular Chaperones / Q000502:physiology*; D013314:Stress, Mechanical; D013312:Stress, Physiological; D013552:Swine; D014129:Trabecular Meshwork / Q000378:metabolism*; D000099179:Myocilin
chemical_list: D002950:Citrate (si)-Synthase; D003598:Cytoskeletal Proteins; D015252:Deoxyribonucleases, Type II Site-Specific; D004791:Enzyme Inhibitors; D005136:Eye Proteins; D024602:Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating); D006023:Glycoproteins; D018832:Molecular Chaperones; D000099179:Myocilin; C059773:endodeoxyribonuclease DrdI