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). Homodimer. Interacts with proteins of the S100 family S100A1, S100A6, S100B, S100P and S100A12 in a calcium-dependent manner (By similarity). 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. Cytoplasmic at low calcium concentrations. In neuroblastoma cells, after a retinoic acid (RA) induction and calcium increase, it localizes in both the nucleus and cytoplasm. The nuclear fraction may be phosphorylated. Phosphorylated on serine residues. Phosphorylated upon induction by RA or at high calcium concentrations.