title: Chaperone suppression of cellular toxicity of huntingtin is independent of polyglutamine aggregation.
abstract: Polyglutamine protein aggregation is associated with eight inherited neurodegenerative disorders. In Huntington's disease, N-terminal fragments of mutant huntingtin form intracellular aggregates and mediate cellular toxicity. Recent studies have shown that chaperones inhibit polyglutamine-mediated aggregation and cellular toxicity. Because chaperones also inhibit caspase activation to protect cells from death, it remains unclear whether the protective effect of chaperones on polyglutamine-mediated cellular toxicity is dependent on their inhibition of protein aggregation. In this study, we show that several chaperones including HSP 40, HSP 70, and N-ethylmaleimide-sensitive factor can inhibit cellular toxicity caused by N-terminal mutant huntingtin fragments. However, only HSP 40 is able to inhibit huntingtin aggregation. Furthermore, time-course study suggests that the protection of chaperones against huntingtin toxicity is not the result of their suppression of huntingtin aggregation. Chaperones inhibit caspase-3 and caspase-9 activation mediated by mutant huntingtin, and this inhibition is independent of huntingtin aggregation. We propose that the inhibition of caspase activity by chaperones is involved in their suppression of polyglutamine toxicity.
authors.affiliation: Department of Genetics, Emory University, School of Medicine, Atlanta, Georgia 30322, USA.
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.forename: S H
authors.initials: SH
authors.lastname: Li
authors.forename: X J
authors.initials: XJ
authors.lastname: Li
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D017931:DNA Primers; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D018832:Molecular Chaperones / Q000378:metabolism*; D052066:N-Ethylmaleimide-Sensitive Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000633:toxicity*; D009474:Neurons / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000633:toxicity*; D010455:Peptides / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D017931:DNA Primers; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C086055:HTT protein, human; D006360:Heat-Shock Proteins; D000071058:Huntingtin Protein; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D033921:Vesicular Transport Proteins; C097188:polyglutamine; D052066:N-Ethylmaleimide-Sensitive Proteins