Substrate-specific adapter of a BCR (BTB-CUL3-RBX1) E3 ubiquitin ligase complex that acts as a negative regulator of Wnt signaling pathway and ER-Golgi transport. The BCR(KLHL12) complex is involved in ER-Golgi transport by regulating the size of COPII coats, thereby playing a key role in collagen export, which is required for embryonic stem (ES) cells division: BCR(KLHL12) acts by mediating monoubiquitination of SEC31 (SEC31A or SEC31B). As part of the BCR(KLHL12) complex, also acts as a negative regulator of the Wnt signaling pathway by mediating ubiquitination and subsequent proteolysis of DVL3. The BCR(KLHL12) complex also mediates polyubiquitination of DRD4, without leading to degradation of DRD4. Component of the BCR(KLHL12) E3 ubiquitin ligase complex, at least composed of CUL3 and KLHL12 and RBX1. This complex interacts with DVL3 upon activation of the Wnt signaling pathway by WNT3A. Interacts with DRD4, KLHL12 and SEC31A. Ubiquitously expressed. Highly expressed in testis and at lower levels in the submandibular salivary gland. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.