May be involved in calcium-dependent ubiquitination and subsequent proteasomal degradation of target proteins. Probably serves as a molecular bridge in ubiquitin E3 complexes. Participates in the ubiquitin-mediated degradation of beta-catenin (CTNNB1) (By similarity). Monomer or homodimer. Component of some large E3 complex at least composed of UBE2D1, SIAH1, CACYBP/SIP, SKP1, APC and TBL1X. Interacts directly with SIAH1, SIAH2 and SKP1. Interacts with proteins of the S100 family S100A1, S100A6, S100B, S100P and S100A12 in a calcium-dependent manner (By similarity). Phosphorylated on serine residues. Phosphorylated upon induction by RA or at high calcium concentrations (By similarity).