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 (By similarity). Interacts with proteins of the S100 family S100A1, S100A6, S100B, S100P and S100A12 in a calcium-dependent manner (By similarity). Cytoplasmic in unstimulated cultured neurons. Upon increase of calcium, it localizes to a ring around the nucleus. In neuroblastoma cells, after a Retinoic acid (RA) induction and calcium increase, it localizes in both the nucleus and cytoplasm. The nuclear and perinuclear fractions may be phosphorylated. Highly expressed in brain and EAT cells. Expressed at low level in heart, muscle, and at very low level in the liver, spleen, lung, kidney and stomach. Phosphorylated on serine residues. Phosphorylated upon induction by RA or at high calcium concentrations.