USP1 and osteosarcoma: Furthermore, hUSP1 has been shown to help to maintain stem cell characteristics in both osteosarcoma cells and mesenchymal stem cells by deubiquitinating and thus stabilizing inhibitors of DNA binding, which in turn antagonize the basic helix-loop-helix transcription factors responsible for differentiation [21].Both full-length and C-terminally truncated USP1 isoforms are able to deubiquitinate PCNA-Ub and FANCD2-Ub, and to regulate the DNA damage repair response and hence genomic stability [13, 22].