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Gary Hin-Fai Yam, Katarina Gaplovska-Kysela, Christian Zuber, Jürgen Roth; 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;48(4):1683-1690. doi: 10.1167/iovs.06-0943.
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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)-2α 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.
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