Core component of the CTLH E3 ubiquitin-protein ligase complex that selectively accepts ubiquitin from UBE2H and mediates ubiquitination and subsequent proteasomal degradation of the transcription factor HBP1 (PubMed:29911972). Acts as a positive regulator of Wnt signaling pathway by promoting beta-catenin (CTNNB1) nuclear accumulation (PubMed:28829046). Homodimer; may also form higher oligomers (By similarity). Identified in the CTLH complex that contains GID4, RANBP9 and/or RANBP10, MKLN1, MAEA, RMND5A (or alternatively its paralog RMND5B), GID8, ARMC8, WDR26 and YPEL5 (PubMed:17467196, PubMed:29911972). Within this complex, MAEA, RMND5A (or alternatively its paralog RMND5B), GID8, WDR26, and RANBP9 and/or RANBP10 form the catalytic core, while GID4, MKLN1, ARMC8 and YPEL5 have ancillary roles (PubMed:29911972). Interacts with RANBP9. Part of a complex consisting of RANBP9, MKLN1 and GID8 (PubMed:12559565). Interacts with CTNNB1, AXIN1 and GSK3B (PubMed:28829046). Localizes in the cytoplasm in the absence of Wnt stimulation and in the nucleus in the presence of Wnt stimulation. Up-regulated in colorectal cancer tissues (at protein level). Polyubiquitinated through 'Lys-48'-polyubiquitin chains, leading to proteasomal degradation in the absence of Wnt stimulation. Belongs to the GID8 family.