Cooperation of DNA-pkcs and WRN helicase in the maintenance of telomeric D-loops

Abstract

Werner syndrome is an inherited human progeriod syndrome caused by mutations in the gene encoding theWerner Syndrome protein, WRN. It has both 3'-5' DNA helicase and exonuclease activities, and is suggested to have rolesin many aspects of DNA metabolism, including DNA repair and telomere maintenance. The DNA-PK complex also functionsin both DNA double strand break repair and telomere maintenance. Interaction between WRN and the DNA-PK complexhas been reported in DNA double strand break repair, but their possible cooperation at telomeres has not been reported. This study analyzes the in vitro and in vivo interaction at the telomere between WRN and DNA-PKcs, the catalytic subunitof DNA-PK. The results show that DNA-PKcs selectively stimulates WRN helicase but not WRN exonuclease in vitro, affecting that WRN helicase unwinds and promotes the release of the full-length invading strand of a telomere D-loopmodel substrate. In addition, the length of telomeric G-tails decreases in DNA-PKcs knockdown cells, and this phenotype isreversed by overexpression of WRN helicase. These results suggest that WRN and DNA-PKcs may cooperatively prevent G-tail shortening in vivo. © Kusumoto-Matsuo et al.