USP4 and colorectal cancer: Recent studies have found that ACE2 can be ubiquitinated by MDM2 [24], and USP4 is a deubiquitinating enzyme that excises protein substrates and links them to ubiquitin, reversing the ubiquitination degradation process, and maintains cells stability growth [37], and overexpression of USP4 can promote colorectal cancer growth by deubiquitinating the oncogene PRL-3 [38].