CDKN2A and neoplasm: ARF-binding protein 1 (ARF-BP1, HUWE1) is a HECT domain-containing E3 ligase that regulates p53 levels to induce tumor suppression via the stabilization of p53 and the activation of apoptosis.289–291 ARF-BP1 contains a ubiquitin-associated domain (UBA, 1318-54), a WWE domain (1612-92), and a HECT domain in the C-terminal sequences (4036-4734).289 The UBA domain is a small motif shown in various proteins to be related to the ubiquitination pathway.292 ARF-BP1 is a primary binding partner of ARF in cells without p53.