TY - JOUR
T1 - The Werner syndrome protein promotes CAG/CTG repeat stability by resolving large (CAG)n/(CTG)n hairpins
AU - Chan, Nelson L.S.
AU - Hou, Caixia
AU - Zhang, Tianyi
AU - Yuan, Fenghua
AU - Machwe, Amrita
AU - Huang, Jian
AU - Orren, David K.
AU - Gu, Liya
AU - Li, Guo Min
PY - 2012/8/31
Y1 - 2012/8/31
N2 - Expansion of CAG/CTG repeats causes certain neurological and neurodegenerative disorders, and the formation and subsequent persistence of stable DNA hairpins within these repeats are believed to contribute to CAG/CTG repeat instability. Human cells possess a DNA hairpin repair (HPR) pathway, which removes various (CAG)n and (CTG)n hairpins in a nick-directed and strand-specific manner. Interestingly, this HPR system processes a (CTG)n hairpin on the template DNA strand much less efficiently than a (CAG)n hairpin on the same strand (Hou, C., Chan, N. L., Gu, L., and Li, G. M. (2009) Incision-dependent and error-free repair of (CAG)n/(CTG)n hairpins in human cell extracts. Nat. Struct. Mol. Biol. 16, 869-875), suggesting the involvement of an additional component for (CTG)nHPR. To identify this activity, a functional in vitro HPR assay was used to screen partially purified HeLa nuclear fractions for their ability to stimulate (CTG)n HPR. We demonstrate here that the stimulating activity is the Werner syndrome protein (WRN). Although WRN contains both a 3′→5′ helicase activity and a 3′→5′ exonuclease activity, the stimulating activity was found to be the helicase activity, as a WRN helicase mutant failed to enhance (CTG)n HPR. Consistently, WRN efficiently unwound large (CTG)n hairpins and promoted DNA polymerase δ-catalyzed DNA synthesis using a (CTG) n hairpin as a template. We, therefore, conclude that WRN stimulates (CTG)n HPR on the template DNA strand by resolving the hairpin so that it can be efficiently used as a template for repair or replicative synthesis.
AB - Expansion of CAG/CTG repeats causes certain neurological and neurodegenerative disorders, and the formation and subsequent persistence of stable DNA hairpins within these repeats are believed to contribute to CAG/CTG repeat instability. Human cells possess a DNA hairpin repair (HPR) pathway, which removes various (CAG)n and (CTG)n hairpins in a nick-directed and strand-specific manner. Interestingly, this HPR system processes a (CTG)n hairpin on the template DNA strand much less efficiently than a (CAG)n hairpin on the same strand (Hou, C., Chan, N. L., Gu, L., and Li, G. M. (2009) Incision-dependent and error-free repair of (CAG)n/(CTG)n hairpins in human cell extracts. Nat. Struct. Mol. Biol. 16, 869-875), suggesting the involvement of an additional component for (CTG)nHPR. To identify this activity, a functional in vitro HPR assay was used to screen partially purified HeLa nuclear fractions for their ability to stimulate (CTG)n HPR. We demonstrate here that the stimulating activity is the Werner syndrome protein (WRN). Although WRN contains both a 3′→5′ helicase activity and a 3′→5′ exonuclease activity, the stimulating activity was found to be the helicase activity, as a WRN helicase mutant failed to enhance (CTG)n HPR. Consistently, WRN efficiently unwound large (CTG)n hairpins and promoted DNA polymerase δ-catalyzed DNA synthesis using a (CTG) n hairpin as a template. We, therefore, conclude that WRN stimulates (CTG)n HPR on the template DNA strand by resolving the hairpin so that it can be efficiently used as a template for repair or replicative synthesis.
UR - http://www.scopus.com/inward/record.url?scp=84865746126&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84865746126&partnerID=8YFLogxK
U2 - 10.1074/jbc.M112.389791
DO - 10.1074/jbc.M112.389791
M3 - Article
C2 - 22787159
AN - SCOPUS:84865746126
SN - 0021-9258
VL - 287
SP - 30151
EP - 30156
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 36
ER -