USP1 and osteosarcoma: Similarly, USP1 deubiquitinated the proliferating cell nuclear antigen (PCNA) to govern the error‐prone translesion synthesis repair pathway.[116] In addition, USP1 activities are involved in regulating a feedback loop to inhibit DDR checkpoint kinase 1(CHK1) activity,[117] thereby regulating cellular differentiation in osteosarcoma cells via deubiquitination, and impairing the stability of DNA‐binding protein inhibitors.[118] USP4 can directly regulate DNA end resection.