Probable substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex mediating the ubiquitination and subsequent proteasomal degradation of target proteins. Promotes the ubiquitination of HDAC1. Can function as antagonist of the Hedgehog pathway by affecting the nuclear transfer of transcription factor GLI1; the function probably occurs via HDAC1 down-regulation, keeping GLI1 acetylated and inactive. Inhibits cell growth and tumorigenicity of medulloblastoma (MDB) (PubMed:21472142). Protein modification; protein ubiquitination. Homopentamer (By similarity). Interacts with KCTD11; KCTD21 and KCTD11 may associate in pentameric assemblies. Interacts (via BTB domain) with CUL3; indicative for a participation in a BCR (BTB-CUL3-RBX1) E3 ubiquitin-protein ligase complex (PubMed:21472142). Highly expressed in cerebellum and brain. Expression is down-regulated in medulloblastoma.