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Chakraborty A , Tapryal N , Venkova T , Mitra J , Vasquez V , Sarker AH , Duarte-Silva S , Huai W , Ashizawa T , Ghosh G , Maciel P , Sarkar PS , Hegde ML , Chen X , Hazra TK
Deficiency in classical nonhomologous end-joining-mediated repair of transcribed genes is linked to SCA3 pathogenesis
Proc Natl Acad Sci U S A. 2020 Apr 7;117(14) :8154-8165
PMID: 32205441    PMCID: PMC7148577    URL: https://www.ncbi.nlm.nih.gov/pubmed/32205441
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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.
Chakraborty, Anirban Tapryal, Nisha Venkova, Tatiana Mitra, Joy Vasquez, Velmarini Sarker, Altaf H Duarte-Silva, Sara Huai, Weihan Ashizawa, Tetsuo Ghosh, Gourisankar Maciel, Patricia Sarkar, Partha S Hegde, Muralidhar L Chen, Xu Hazra, Tapas K eng P30 AG053760/AG/NIA NIH HHS/ R01 NS088645/NS/NINDS NIH HHS/ P30 ES006676/ES/NIEHS NIH HHS/ R01 NS096305/NS/NINDS NIH HHS/ R01 NS073976/NS/NINDS NIH HHS/ Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't Proc Natl Acad Sci U S A. 2020 Apr 7;117(14):8154-8165. doi: 10.1073/pnas.1917280117. Epub 2020 Mar 23.