Abstract
Werner syndrome (WS) is an autosomal recessive disorder whose phenotype mimics premature aging. This syndrome is caused by mutations in WRN, a member of the RecQ DNA helicase family, of which biological function remains unclear. In the present study, we investigated the relationship between WRN protein deficiency and telomere dysfunction in WS cells. WS cells showed 10-fold more dicentrics than normal cells when they are examined in culture at similar senescence level monitored by senescence-associated β-galactosidase positive ratio, suggesting the constitutive telomeric instability in WS cells. Therefore, we examined telomere stability in Ws cells by telomere FISH, and found that there were two abnormal signals, extra telomere signals (ETS) and loss of telomere signals (LTS), emerged spontaneously in normal and WS cell metaphases. The results indicated that the frequencies of ETS and LTS were 2-fold higher in WS cells than in normal cells and that the frequency of ETS was elevated by the treatment with hydrogen peroxide, indicating that ETS is produced in response to the oxidative stress and that telomeres in WS cells are sensitive to the oxidative stress. However, the numbers of DNA double strand breaks detected by phosphorylated ATM foci at telomeres were much lower than those of ETS in both normal cells and WS cells, suggesting that double strand breaks are not involved in the production of ETS. The present study suggests that WRN protein functions to protect telomeres from damage by intracellular oxidative stress.
