Figure 7.

Persistent exposure to a low dose of H₂O₂ results in ROS accumulation leading to long-term p53 phosphorylation, p21 transcription and an increase in senescence in partially functional TP53 HNSCC cells. Western blot showing differences in protein expression of p21 and phosphorylation of p53 at early and late time points in HNSCC cells after treatment with either (a) 50 μM H₂O₂ for 1 h daily or (b) 2 Gy daily, with indicated cells lines also treated with NAC daily. C) DCFDA staining and flow cytometry performed 96 h after cells were treated with the conditions shown in a and b or, for comparison, with one treatment of either 2 Gy or 50 μM H₂O₂. Error bars represent S.D. of each sample performed in triplicate. (d) Indicated cell lines were treated with conditions described in c, with DHE staining and flow cytometry performed at 96 h. Error bars represent S.D. of each sample performed in triplicate. (e) Quantitation of SA-β-gal-positive senescent cells (those staining blue) from four randomly selected fields