Regulates cell proliferation through the inhibition of cell cycle arrest at the G1 phase (PubMed:22842486). Also negatively regulates p53-mediated apoptosis (PubMed:22842486). Expressed in many tumors of several types, such as melanoma, head and neck squamous cell carcinoma, lung carcinoma and breast carcinoma, but not in normal tissues except for testes and placenta.