USP37 deubiquitinates Lys-11-linked polyubiquitin chains from cyclin-A (CCNA1 and CCNA2), which opposes the Lys-11-linked polyubiquitination mediated by the anaphase-promoting complex (APC/C) during G1/S transition, thereby promoting S phase entry. Phosphorylation by CDK2 at Ser-628 during G1/S phase maximizes USP37 deubiquitinase activity (Huang et al. 2011).