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Proc Natl Acad Sci U S A. 2020 Mar 23. pii: 201917280. doi: 10.1073/pnas.1917280117. [Epub ahead of print]

Deficiency in classical nonhomologous end-joining-mediated repair of transcribed genes is linked to SCA3 pathogenesis.

Author information

1
Department of Internal Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, University of Texas Medical Branch, Galveston, TX 77555.
2
Department of Neurosurgery, Center for Neuroregeneration, The Houston Methodist Research Institute, Houston, TX 77030.
3
Department of Cancer and DNA Damage Responses, Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
4
School of Medicine, Life and Health Sciences Research Institute, University of Minho, 4710-057 Braga, Portugal.
5
ICVS (Life and Health Sciences Research Institute)/3B's-PT Government Associate Laboratory, 4710-057 Braga/GuimarĂ£es, Portugal.
6
Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093.
7
Department of Neurology, The Houston Methodist Research Institute, Houston, TX 77030.
8
Department of Neurology and Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, TX 77555.
9
Department of Neurosciences, University of California San Diego, La Jolla, CA 92093.
10
Department of Internal Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, University of Texas Medical Branch, Galveston, TX 77555; tkhazra@utmb.edu.

Abstract

Spinocerebellar ataxia type 3 (SCA3) is a dominantly inherited neurodegenerative disease caused by CAG (encoding glutamine) repeat expansion in the Ataxin-3 (ATXN3) gene. We have shown previously that ATXN3-depleted or pathogenic ATXN3-expressing cells abrogate polynucleotide kinase 3'-phosphatase (PNKP) activity. Here, we report that ATXN3 associates with RNA polymerase II (RNAP II) and the classical nonhomologous end-joining (C-NHEJ) proteins, including PNKP, along with nascent RNAs under physiological conditions. Notably, ATXN3 depletion significantly decreased global transcription, repair of transcribed genes, and error-free double-strand break repair of a 3'-phosphate-containing terminally gapped, linearized reporter plasmid. The missing sequence at the terminal break site was restored in the recircularized plasmid in control cells by using the endogenous homologous transcript as a template, indicating ATXN3's role in PNKP-mediated error-free C-NHEJ. Furthermore, brain extracts from SCA3 patients and mice show significantly lower PNKP activity, elevated p53BP1 level, more abundant strand-breaks in the transcribed genes, and degradation of RNAP II relative to controls. A similar RNAP II degradation is also evident in mutant ATXN3-expressing Drosophila larval brains and eyes. Importantly, SCA3 phenotype in Drosophila was completely amenable to PNKP complementation. Hence, salvaging PNKP's activity can be a promising therapeutic strategy for SCA3.

KEYWORDS:

ATXN3; DNA double-strand break repair; PNKP; RNA-templated TC-NHEJ; spinocerebellar ataxia type-3

PMID:
32205441
DOI:
10.1073/pnas.1917280117

Conflict of interest statement

The authors declare no competing interest.

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