USP28 and neoplasm: Furthermore, p53 is a tumor suppressor, and a previous study showed that ΔNp63 can inhibit the transactivation of p53 by binding to the tumor protein p53 (TP53) gene at proapoptotic gene promotors and then inactivating it [15, 60, 62], suggesting that the function of USP28 in squamous cancer cells may be mediated by p53.