title: Spinocerebellar ataxia with axonal neuropathy: consequence of a Tdp1 recessive neomorphic mutation?
abstract: Tyrosyl-DNA phosphodiesterase 1 (Tdp1) cleaves the phosphodiester bond between a covalently stalled topoisomerase I (Topo I) and the 3' end of DNA. Stalling of Topo I at DNA strand breaks is induced by endogenous DNA damage and the Topo I-specific anticancer drug camptothecin (CPT). The H493R mutation of Tdp1 causes the neurodegenerative disorder spinocerebellar ataxia with axonal neuropathy (SCAN1). Contrary to the hypothesis that SCAN1 arises from catalytically inactive Tdp1, Tdp1-/- mice are indistinguishable from wild-type mice, physically, histologically, behaviorally, and electrophysiologically. However, compared to wild-type mice, Tdp1-/- mice are hypersensitive to CPT and bleomycin but not to etoposide. Consistent with earlier in vitro studies, we show that the H493R Tdp1 mutant protein retains residual activity and becomes covalently trapped on the DNA after CPT treatment of SCAN1 cells. This result provides a direct demonstration that Tdp1 repairs Topo I covalent lesions in vivo and suggests that SCAN1 arises from the recessive neomorphic mutation H493R. This is a novel mechanism for disease since neomorphic mutations are generally dominant.
authors.affiliation: Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Ryuki
authors.initials: R
authors.lastname: Hirano
authors.forename: Heidrun
authors.initials: H
authors.lastname: Interthal
authors.forename: Cheng
authors.initials: C
authors.lastname: Huang
authors.forename: Tomonori
authors.initials: T
authors.lastname: Nakamura
authors.forename: Kimiko
authors.initials: K
authors.lastname: Deguchi
authors.forename: Kunho
authors.initials: K
authors.lastname: Choi
authors.forename: Meenakshi B
authors.initials: MB
authors.lastname: Bhattacharjee
authors.forename: Kimiyoshi
authors.initials: K
authors.lastname: Arimura
authors.forename: Fujio
authors.initials: F
authors.lastname: Umehara
authors.forename: Shuji
authors.initials: S
authors.lastname: Izumo
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Northrop
authors.forename: Mustafa A M
authors.initials: MA
authors.lastname: Salih
authors.forename: Ken
authors.initials: K
authors.lastname: Inoue
authors.forename: Dawna L
authors.initials: DL
authors.lastname: Armstrong
authors.forename: James J
authors.initials: JJ
authors.lastname: Champoux
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takashima
authors.forename: Cornelius F
authors.initials: CF
authors.lastname: Boerkoel
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001369:Axons; D001761:Bleomycin / Q000494:pharmacology; D001921:Brain / Q000378:metabolism; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D002478:Cells, Cultured; D020552:Comet Assay; D004622:Embryo, Mammalian / Q000166:cytology; D005047:Etoposide / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D005808:Genes, Recessive; D006801:Humans; D000077146:Irinotecan; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D010727:Phosphoric Diester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011115:Polyneuropathies / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000378:metabolism; D019772:Topotecan / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D012333:RNA, Messenger; D001761:Bleomycin; D005047:Etoposide; D000077146:Irinotecan; D019772:Topotecan; D010727:Phosphoric Diester Hydrolases; C524959:Tdp1 protein, mouse; D002166:Camptothecin