UCHL1 and inflammatory bowel disease: Patients with inflammatory bowel disease (IBD) have higher levels of angiotensin-converting enzyme 2 (ACE2) expression in the gut (217).ACE2 deubiquitination mediated by deubiquitination enzyme UCHL1 and ACE2 SUMO mediated by E3 SUMO protein ligase PIAS4 can increase ACE2 protein levels, while AP2-mediated lysosomal degradation can decrease ACE2 protein levels (218, 219).