title: Congenital cataract causing mutants of αA-crystallin/sHSP form aggregates and aggresomes degraded through ubiquitin-proteasome pathway.
abstract: BACKGROUND
  Mutations of human αA-crystallin cause congenital cataract by protein aggregation. How mutations of αA-crystallin cause disease pathogenesis through protein aggregation is not well understood. To better understand the cellular events leading to protein aggregation, we transfected cataract causing mutants, R12C, R21L, R21W, R49C, R54C, R116C and R116H, of human αA-crystallin in HeLa cells and examined the formation of intracellular protein aggregates and aggresomes by confocal microscopy.
  
  
  RESULTS
  YFP-tagged human αA-wild-type (αA-wt) was sub-cloned and the mutants were generated by site-directed mutagenesis. The αA-wt and the mutants were individually transfected or co-transfected with CFP-tagged αA-wt or αB-wild-type (αB-wt) in HeLa cells. Overexpression of these mutants forms multiple small dispersed cytoplasmic aggregates as well as aggresomes. Co-expression of αB-wt with these mutants significantly inhibited protein aggregates where as co-expression with αA-wt enhanced protein aggregates which seems to be due to co-aggregation of the mutants with αA-wt. Aggresomes were validated by double immunofluorescence by co-localization of γ-tubulin, a centrosome marker protein with αA-crystallin. Furthermore, increased ubiquitination was detected in R21W, R116C and R116H as assessed by western blot analyses. Immunostaining with an ubiquitin antibody revealed that ubiquitin inclusions in the perinuclear regions were evident only in R116C transfected cells. Pulse chase assay, after cycloheximide treatment, suggested that R116C degraded faster than the wild-type control.
  
  
  CONCLUSIONS
  Mutants of αA-crystallin form aggregates and aggresomes. Co-expression of αA-wt with the mutants increased aggregates and co-expression of αB-wt with the mutants significantly decreased the aggregates. The mutant, R116C protein degraded faster than wild-type control and increased ubiquitination was evident in R116C expressing cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America.
authors.forename: Ilangovan
authors.initials: I
authors.lastname: Raju
authors.forename: Edathara C
authors.initials: EC
authors.lastname: Abraham
mesh_terms: D015153:Blotting, Western; D002386:Cataract / Q000151:congenital* / Q000235:genetics*; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D025821:Polyubiquitin / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D059748:Proteolysis; D011993:Recombinant Fusion Proteins; D015203:Reproducibility of Results; D015398:Signal Transduction; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination; D038202:alpha-Crystallin A Chain / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D006360:Heat-Shock Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; D038202:alpha-Crystallin A Chain; D025821:Polyubiquitin; D046988:Proteasome Endopeptidase Complex