Figure 1.

Inhibition of USP7 activity selectively downregulates MDM2 expression and partially restores p53 expression in senescent cells (SnCs). (a) Western blotting analysis of p53, MDM2 p21, and USP7 protein levels in nonradiated (non‐IR) and radiated WI‐38 fibroblasts at indicated time points. Representative images of Western blots are shown. (b) Western blotting analysis of p53, MDM2, and USP7 protein levels in nonsenescent (non‐SnC) and senescent (SnC) WI‐38 fibroblasts induced to senescence by replicative exhaustion (REP‐SnC) or ionizing radiation (IR‐SnC). Representative images of Western blots are shown in the left panel, and fold changes in p53 expression are presented in the right panel as mean ± SEM of 3 independent experiments with non‐SnC values set at 1. **p < .01 and ***p < .001. (c) Effect of USP7 inhibition by P5091 or P22077 on p53, MDM2 and USP7 protein levels in non‐SnC and IR‐SnC WI‐38 cells after the cells were treated with P5091 or P22077 (15 µM) for 72 hr. Representative images of Western blots are shown in the left panel, and fold changes in p53 and MDM2 levels relative to vehicle‐treated non‐SnC are presented in the right panel as mean ± SEM of 4 independent experiments. *p < .05 and **p < .01. (d) Proteasome inhibition by MG132 abrogated the effects of P5091 on MDM2 and p53 protein levels in IR‐SnCs. IR‐SnCs were pretreated with MG132 for 1 hr and then with P5091 for 72 hr. Representative images of Western blots are shown