E3 ubiquitin-protein ligase that promotes the ubiquitination and proteasomal degradation of SIN3B (PubMed:20170641). Independently of its E3 ligase activity, acts as a CTNNB1 stabilizer through USP7-mediated deubiquitination of CTNNB1 and promotes Wnt signaling (By similarity). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with SIN3B (PubMed:20170641). Interacts with CTNNB1 (via Armadillo repeats 2-8) (By similarity). Interacts with USP7 (via MATH domain) (By similarity). Auto-ubiquitinated; leads to proteasomal degradation.