Werner helicase relocates into nuclear foci in response to DNA damaging agents and co-localizes with RPA and Rad51.
BACKGROUND
Werner syndrome (WS) is an autosomal recessive disorder with many features of premature ageing. Cells derived from WS patients show genomic instability, aberrations in the S-phase and sensitivity to genotoxic agents. The gene responsible for WS (WRN) encodes a DNA helicase belonging to the RecQ helicase family. Although biochemical studies showed that the gene product of WRN (WRNp) interacts with proteins that participate in DNA metabolism, its precise biological function remains unclear.


RESULTS
Using immunocytochemistry, we found that WRNp forms distinct nuclear foci in response to DNA damaging agents, including camptothecin (CPT), etoposide, 4-nitroquinolin-N-oxide and bleomycin. The presence of aphidicolin inhibited CPT-induced WRNp foci strongly but not bleomycin-induced foci. These WRNp foci overlapped with the foci of replication protein A (RPA) almost entirely and with the foci of Rad51 partially, implicating cooperative functions of these proteins in response to DNA damage. We also found that WRNp foci partially co-localize with sites of 5-bromo-2'-deoxy-uridine incorporation.


CONCLUSIONS
These findings suggest that WRNp form nuclear foci in response to aberrant DNA structures, including DNA double-strand breaks and stalled replication forks. We propose that WRNp takes part in the homologous recombinational repair and in the processing of stalled replication forks.
Sakamoto
S
S
AGENE Research Institute, 200 Kajiwara, Kamakura, Kanagawa 247-0063, Japan.
Nishikawa
K
K
Heo
S J
SJ
Goto
M
M
Furuichi
Y
Y
Shimamoto
A
A
D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology; D016590:Aphidicolin / Q000378:metabolism; D001761:Bleomycin / Q000494:pharmacology; D002166:Camptothecin / Q000494:pharmacology; D002460:Cell Line; D002467:Cell Nucleus / Q000648:ultrastructure; D004249:DNA Damage / Q000502:physiology; D004265:DNA Helicases / Q000187:drug effects* / Q000648:ultrastructure*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*; D004305:Dose-Response Relationship, Drug; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D009153:Mutagens / Q000494:pharmacology*; D011506:Proteins / Q000648:ultrastructure*; D051135:Rad51 Recombinase; D015534:Trans-Activators; D014898:Werner Syndrome / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
D004268:DNA-Binding Proteins; D009153:Mutagens; D011506:Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D001761:Bleomycin; D016590:Aphidicolin; D015112:4-Nitroquinoline-1-oxide; D005047:Etoposide; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D004265:DNA Helicases; D002166:Camptothecin