DNA damage-inducing drugs cause premature senescence.

<p>(A) HepG2 cells were cultured in RPMI medium with 0.1% DMSO or 10 µM etoposide for 0, 12, 24, 36 and 48 hours. (B) U2OS cells were cultured in RPMI medium with 0.1% DMSO, 2 µM etoposide, or 2 µM bleomycin for 0, 3, 5 and 7 days. For the assay of SA-β-Gal activity, cells stained with blue color were counted as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080411#s2" target="_blank">Materials and Methods</a>. The data (mean ± S.D.) were obtained from at least three independent experiments. Significant test results (<i>P</i> values) are shown.