Tay-Sachs disease mutations in HEXA target the α chain of hexosaminidase A to endoplasmic reticulum-associated degradation.
Loss of function of the enzyme β-hexosaminidase A (HexA) causes the lysosomal storage disorder Tay-Sachs disease (TSD). It has been proposed that mutations in the α chain of HexA can impair folding, enzyme assembly, and/or trafficking, yet there is surprisingly little known about the mechanisms of these potential routes of pathogenesis. We therefore investigated the biosynthesis and trafficking of TSD-associated HexA α mutants, seeking to identify relevant cellular quality control mechanisms. The α mutants E482K and G269S are defective in enzymatic activity, unprocessed by lysosomal proteases, and exhibit altered folding pathways compared with wild-type α. E482K is more severely misfolded than G269S, as observed by its aggregation and inability to associate with the HexA β chain. Importantly, both mutants are retrotranslocated from the endoplasmic reticulum (ER) to the cytosol and are degraded by the proteasome, indicating that they are cleared via ER-associated degradation (ERAD). Leveraging these discoveries, we observed that manipulating the cellular folding environment or ERAD pathways can alter the kinetics of mutant α degradation. Additionally, growth of patient fibroblasts at a permissive temperature or with chemical chaperones increases cellular Hex activity by improving mutant α folding. Therefore modulation of the ER quality control systems may be a potential therapeutic route for improving some forms of TSD.
Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, PA 19104.
Devin
D
Dersh
Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, PA 19104.
Yuichiro
Y
Iwamoto
Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, PA 19104 yargon@mail.med.upenn.edu.
Yair
Y
Argon
D004721:Endoplasmic Reticulum / Q000378:metabolism; D060746:Endoplasmic Reticulum-Associated Degradation / Q000502:physiology; D057809:HEK293 Cells; D054818:Hexosaminidase A / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D061251:Primary Cell Culture; D021381:Protein Transport / Q000502:physiology; D059748:Proteolysis; D013661:Tay-Sachs Disease / Q000235:genetics / Q000378:metabolism; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
D018832:Molecular Chaperones; D054818:Hexosaminidase A; D001619:beta-N-Acetylhexosaminidases
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