To investigate whether WRN is involved in telomere deprotection during prolonged mitotic arrest, we used lentiviral transduction of short hairpin RNA (shRNA) to deplete WRN in telomerase-immortalized IMR-90 fibroblasts expressing HPV oncogenes E6 and E7, which target p53 and Rb tumor suppressors, respectively27 (Fig. 1a). Here, RB1 is linked to neoplasm.