Sodium 4-phenylbutyrate acts as a chemical chaperone on misfolded myocilin to rescue cells from endoplasmic reticulum stress and apoptosis

Invest Ophthalmol Vis Sci. 2007 Apr;48(4):1683-90. doi: 10.1167/iovs.06-0943.


Purpose: To evaluate the effect of chemical chaperones on the trafficking of secretion-incompetent primary open-angle glaucoma-associated mutant myocilin and the possibility to rescue cells coexpressing mutant and wild-type myocilin from endoplasmic reticulum (ER) stress and apoptosis.

Methods: CHO-K1, HEK293 and human trabecular meshwork cells were transfected to express wild-type or mutant (C245Y, G364V, P370L, Y437H) myocilin-green fluorescent protein fusion protein and were treated or not with various chemical chaperones (glycerol, dimethylsulfoxide, or sodium 4-phenylbutyrate) for different time periods. The secretion, Triton X-100 solubility, and intracellular distribution of wild-type and mutant myocilin were analyzed by immunoprecipitation, Western blotting, and confocal double immunofluorescence. The effect of sodium 4-phenylbutyrate on ER stress proteins and apoptosis was examined in cells coexpressing mutant and wild-type myocilin.

Results: Treatment with sodium 4-phenylbutyrate, but not with glycerol or dimethylsulfoxide, reduced the amount of detergent-insoluble myocilin aggregates, diminished myocilin interaction with calreticulin, and restored the secretion of mutant myocilin. Heteromeric complexes formed by mutant and wild-type myocilin induced the ER stress-associated phosphorylated form of ER-localized eukaryotic initiation factor (eIF)-2alpha kinase and the active form of caspase 3, which resulted in an increased rate of apoptosis. Sodium 4-phenylbutyrate treatment of cells coexpressing mutant and wild-type myocilin relieved ER stress and significantly reduced the rate of apoptosis.

Conclusions: These findings indicate that sodium 4-phenylbutyrate protects cells from the deleterious effects of ER-retained aggregated mutant myocilin. These data point to the possibility of a chemical chaperone treatment for myocilin-caused primary open-angle glaucoma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Blotting, Western
  • CHO Cells / drug effects
  • Caspase 3 / metabolism
  • Cricetinae
  • Cricetulus
  • Cytoskeletal Proteins / genetics
  • Cytoskeletal Proteins / metabolism*
  • Endoplasmic Reticulum / drug effects*
  • Eye Proteins / genetics
  • Eye Proteins / metabolism*
  • Fluorescent Antibody Technique, Indirect
  • Glycoproteins / genetics
  • Glycoproteins / metabolism*
  • Humans
  • Kidney / embryology
  • Microscopy, Confocal
  • Molecular Chaperones / pharmacology*
  • Phenylbutyrates / pharmacology*
  • Plasmids
  • Protein Folding
  • Reverse Transcriptase Polymerase Chain Reaction
  • Trabecular Meshwork / drug effects*
  • Trabecular Meshwork / metabolism
  • Transfection
  • eIF-2 Kinase / metabolism


  • Cytoskeletal Proteins
  • Eye Proteins
  • Glycoproteins
  • Molecular Chaperones
  • Phenylbutyrates
  • trabecular meshwork-induced glucocorticoid response protein
  • 4-phenylbutyric acid
  • eIF-2 Kinase
  • Caspase 3