HDAC inhibition induces markers of senescence. (A) Butyrate and TSA induce the expression of the senescence-associated cell cycle inhibitor protein p21WAF1. Proliferating WI-38 cells were treated with butyrate (BA) or TSA for 24 hours. Cytosolic extracts were prepared and equivalent protein levels were analyzed by immunoblot using an anti-p21WAF1 antibody. Untreated samples (0 hours) consisted of cytosolic extracts prepared from naïve cells. Results are shown in triplicate. (B) Butyrate and TSA rapidly induce senescent-like morphologies in young WI-38 cells. Proliferating WI-38 cells were treated with butyrate or TSA for 0, 24, 48, and 72 hours, as indicated. Phase contrast images of cell morphology were taken at 100 × magnification. An image of WI-38 cells propagated to replicative senescence is also shown.