| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 100 === Mutations in the small heat shock protein (sHSP) αB-crystallins cause a range of human diseases including dilated cardiomyopathy (DCM), desmin-related myopathy (DRM) and congenital cataracts. DRM was the first discovered associated with desmin mutations which can affect themselves and closely interacted proteins that typically tending to incomplete assembly of desmin and formation of electro-dense granulofilamentous materials. These diseases involve the disruption of the intermediate filament (IF) cytoskeleton and thus identified intermediate filaments as important physiological targets of sHSPs. Recently, a missense mutation Gly154Ser (G154S) in αB-crystallin was reported to be associated with a late-onset distal vacuolar myopathy without cardiac or respiratory dysfunction and cataracts. This mutation affects a highly conserved amino acid residue among the αB-crystallin in mammals and has been identified earlier in patients with isolated cardiomyopathy. In this study, the effects of G154S mutation on αB-crystallin’s ability to interact with desmin IFs was investigated in details using a combination of biochemical, molecular and cell biological approaches. Cosedimentation assay showed that the G154S mutation increased the binding of αB-crystallin to assembled desmin IFs. Transmission electron microscopy confirmed that the G154S αB-crystallin particles decorated the assembled desmin filaments. Transient transfection studies revealed that the expression of G154S αB-crystallin did not affect its distribution but accomplishment of slightly decreased of solubility in C2C12 cell fraction study compared to the wild type αB-crystallin. This is in contrast to the R120G mutation reported in desmin-related myopathy, where this mutation affected the solubility of αB-crystallin and promoted its interaction with desmin filament leading to intracellular aggregates formation in transiently transfected cells. When transfected into a range of cell lines, both R120G and G154S αB-crystallin mutants, but not the wild type protein, increased the phosphorylation of αB-crystallin at Ser59 site. Taken together, these data suggest that the G154S mutation may be involved in the pathogenesis of myopathy through a mechanism that is different from the R120G mutation found in DRM.
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