MDM2 and neoplasm: Third, since USP7 has key roles in the p53 tumor suppressor pathway through stabilization of p53 via increasing MDM2 [6, 52], while USP22 is reported to antagonize p53 transcriptional activation by deubiquitinating Sirt1 to suppress [34], we further investigated p53p53 the effect of USP22 and USP7 inhibition on the p53 pathway.