Hsp27 suppresses the formation of inclusion bodies induced by expression of R120G alpha B-crystallin, a cause of desmin-related myopathy.

The R120G mutation in the small heat shock protein (sHSP) alpha B-crystallin has been identified in a family suffering from desmin-related myopathy. In this study, we characterized the features of transiently expressed R120G alpha B-crystallin in mammalian cells. In addition, we examined interactions of this mutant alpha B-crystallin with Hsp27, another representative sHSP. In HeLa cells, transiently expressed R120G alpha B-crystallin was mainly fractionated in the insoluble fraction, although wild-type alpha B-crystallin was predominantly found in the soluble fraction. In immunofluorescence studies, we found 15-25% of R120G alpha B-crystallin-expressing cells to contain multiple cytosolic inclusion bodies, in which Hsp27 was also localized. When R120G alpha B-crystallin and Hsp27 were transiently co-expressed in HeLa cells, the amount of R120G alpha B-crystallin in the soluble fraction was greater than with expression of R120G alpha B-crystallin alone. Moreover, co-expression resulted in reduced formation of inclusion bodies, suggesting that Hsp27 acts as a molecular chaperone for R120G alpha B-crystallin.