Figure 3.

Downregulation of CatB activity by CST1 knockdown induces cellular senescence. (a) CatB activity was measured in the culture supernatant (left) or cell lysate (right) of CST1 knockdown cells. CatB activity of the culture supernatant (left) or cell lysate (right) from rCys-SN treated cells (b), or culture supernatant of CatB knockdown cells (c) was analyzed using a CatB activity fluorometric assay kit. (d) Effect of CatB knockdown on cellular senescence. After CST1 or CatB knockdown, cellular senescence was quantified by calculating the percentage of SA-β-gal-positive cells. To confirm the function of CatB associated with cellular senescence, MDA-MB-231 cells were treated with CatB inhibitors. The efficacy of the inhibitors was confirmed by the analysis of extracellular or intracellular CatB activity (e), and cellular senescence induced by the inhibitors was quantified by SA-β-gal staining (f). Scale bars, 50 μm. Data were obtained from three independent experiments, and values are presented as the means±S.E.M. *P<0.05; **P<0.01; ***P<0.001 by Student's t-test