Lookup NU author(s): Dr Rita Barresi,
Professor Katherine Bushby
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Mutations of HSP B 5 (also known as CRYAB or all-crystallin), a bona fide heat shock protein and molecular chaperone encoded by the HSPB5 (crystallin, alpha B) gene, are linked to multisystem disorders featuring variable combinations of cataracts, cardiomyopathy, and skeletal myopathy. This study aimed to investigate the pathological mechanisms involved in an early onset myofibrillar myopathy manifesting in a child harboring a homozygous recessive mutation in HSPB5, 343delT. To study HSPB5 343delT protein dynamics, we utilize model cell culture systems including induced pluripotent stein cells derived from the 343delT patient (343delT/343delT) along with isogenic, heterozygous, gene -corrected control cells (WT Kit 343delT) and BHK21 cells, a cell line lacking endogenous HSPB5 expression. 343delT/343delT and WT KI/343delT-induced pluripotent stem cell-derived skeletal myotubes and cardiomyocytes did not express detectable levels of 343delT protein, contributable to the extreme insolubility of the mutant protein. Overexpression of HSPB5 343delT resulted in insoluble mutant protein aggregates and induction of a cellular stress response. Co-expression of 343delT with WT prevented visible aggregation of 343delT and improved its solubility. Additionally, in vitro refolding of 343delT in the presence of WT rescued its solubility. We demonstrate an interaction between WT and 343delT both in vitro and within cells. These data support a loss-of-function model for the myopathy observed in the patient because the insoluble mutant would be unavailable to perform normal functions of HSPB5, although additional gain-of-function effects of the mutant protein cannot be excluded. Additionally, our data highlight the solubilization of 343delT by WT, concordant with the recessive inheritance of the disease and absence of symptoms in carrier individuals.
Author(s): Mitzelfelt KA, Limphong P, Choi MJ, Kondrat FDL, Lai SP, Kolander KD, Kwok WM, Dai Q, Grzybowski MN, Zhang HL, Taylor GM, Lui Q, Thao MT, Hudson JA, Barresi R, Bushby K, Jungbluth H, Wraige E, Geurts AM, Benesch JLP, Riedel M, Christians ES, Minella AC, Benjamina IJ
Publication type: Article
Publication status: Published
Journal: Journal of Biological Chemistry
Print publication date: 15/07/2016
Online publication date: 19/05/2016
Acceptance date: 02/04/2016
ISSN (print): 0021-9258
ISSN (electronic): 1083-351X
Publisher: American Society for Biochemistry and Molecular Biology, Inc.
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