Figure 6. HFK-E2 cells at p26 inhibit the expression of p21. (A) Western blot of p21, p53, CDK1 and cyclin B1 in HFK at p3 and HFK-E2 at p26, using H2O2 as positive control of senescence. (B) A triplicate Western blot analysis confirms downregulation of p21 in HFK-E2 cells at p26 as compared to p3 HFK (**p<0.01). (C) The p53 protein, which is related to p21 expression, is also downregulated (**p<0.01), similar to CDK1 (D) (**p<0.01). (E) Cyclin B1 expression was not affected in HFK-E2 cells arrested at G2/M (ns). Of note, expression of both CDK1 and cyclin B1 is downregulated by treatment with H2O2. (**p<0.01).