In vitro complementation of Tdp1 deficiency indicates a stabilized enzyme-DNA adduct from tyrosyl but not glycolate lesions as a consequence of the SCAN1 mutation.
A homozygous H493R mutation in the active site of tyrosyl-DNA phosphodiesterase (TDP1) has been implicated in hereditary spinocerebellar ataxia with axonal neuropathy (SCAN1), an autosomal recessive neurodegenerative disease. However, it is uncertain how the H493R mutation elicits the specific pathologies of SCAN1. To address this question, and to further elucidate the role of TDP1 in repair of DNA end modifications and general physiology, we generated a Tdp1 knockout mouse and carried out detailed behavioral analyses as well as characterization of repair deficiencies in extracts of embryo fibroblasts from these animals. While Tdp1(-/-) mice appear phenotypically normal, extracts from Tdp1(-/-) fibroblasts exhibited deficiencies in processing 3'-phosphotyrosyl single-strand breaks and 3'-phosphoglycolate double-strand breaks (DSBs), but not 3'-phosphoglycolate single-strand breaks. Supplementing Tdp1(-/-) extracts with H493R TDP1 partially restored processing of 3'-phosphotyrosyl single-strand breaks, but with evidence of persistent covalent adducts between TDP1 and DNA, consistent with a proposed intermediate-stabilization effect of the SCAN1 mutation. However, H493R TDP1 supplementation had no effect on phosphoglycolate (PG) termini on 3' overhangs of double-strand breaks; these remained completely unprocessed. Altogether, these results suggest that for 3'-phosphoglycolate overhang lesions, the SCAN1 mutation confers loss of function, while for 3'-phosphotyrosyl lesions, the mutation uniquely stabilizes a reaction intermediate.
Hawkins
Amy J
AJ
Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA 23298, USA.
Subler
Mark A
MA
Akopiants
Konstantin
K
Wiley
Jenny L
JL
Taylor
Shirley M
SM
Rice
Ann C
AC
Windle
Jolene J
JJ
Valerie
Kristoffer
K
Povirk
Lawrence F
LF
D000818:Animals; D015139:Blotting, Southern; D015153:Blotting, Western; D002384:Catalysis; D018736:DNA Adducts / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D053904:DNA Breaks, Single-Stranded; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005816:Genetic Complementation Test; D006016:Glycolates / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics*; D010727:Phosphoric Diester Hydrolases / Q000502:physiology*; D019000:Phosphotyrosine / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000378:metabolism
D018736:DNA Adducts; D006016:Glycolates; D019000:Phosphotyrosine; D010727:Phosphoric Diester Hydrolases; C524959:Tdp1 protein, mouse; C013193:phosphoglycolate