To test this idea, we transduced cervical cancer (Hela) and breast cancer (MCF7) cells with conditional shRNAs targeting WRN or GFP and we observed a rapid suppression of proliferation and an increase in the frequency of cells stained for senescence-associated β-galactosidase (SA-β-gal) after the induction with doxycycline (Fig. S4, Supporting Information), which is consistent with a previous study (Opresko et al., 2007). Here, WRN is linked to breast cancer.