Crystal Structure of a beta-catenin/BCL9/Tcf4 complex
[CTNB1_HUMAN] Defects in CTNNB1 are associated with colorectal cancer (CRC) [MIM:114500]. Note=Activating mutations in CTNNB1 have oncogenic activity resulting in tumor development. Somatic mutations are found in various tumor types, including colon cancers, ovarian and prostate carcinomas, hepatoblastoma (HB), hepatocellular carcinoma (HCC). HBs are malignant embryonal tumors mainly affecting young children in the first three years of life. Defects in CTNNB1 are a cause of pilomatrixoma (PTR) [MIM:132600]; a common benign skin tumor.   Defects in CTNNB1 are a cause of medulloblastoma (MDB) [MIM:155255]. MDB is a malignant, invasive embryonal tumor of the cerebellum with a preferential manifestation in children.  Defects in CTNNB1 are a cause of susceptibility to ovarian cancer (OC) [MIM:167000]. Ovarian cancer common malignancy originating from ovarian tissue. Although many histologic types of ovarian neoplasms have been described, epithelial ovarian carcinoma is the most common form. Ovarian cancers are often asymptomatic and the recognized signs and symptoms, even of late-stage disease, are vague. Consequently, most patients are diagnosed with advanced disease. Note=A chromosomal aberration involving CTNNB1 is found in salivary gland pleiomorphic adenomas, the most common benign epithelial tumors of the salivary gland. Translocation t(3;8)(p21;q12) with PLAG1. Defects in CTNNB1 may be a cause of mesothelioma malignant (MESOM) [MIM:156240]. An aggressive neoplasm of the serosal lining of the chest. It appears as broad sheets of cells, with some regions containing spindle-shaped, sarcoma-like cells and other regions showing adenomatous patterns. Pleural mesotheliomas have been linked to exposure to asbestos. [BCL9_HUMAN] Note=A chromosomal aberration involving BCL9 is found in a patient with precusor B-cell acute lymphoblastic leukemia (ALL). Translocation t(1;14)(q21;q32). This translocation leaves the coding region intact, but may have pathogenic effects due to alterations in the expression level of BCL9. Several cases of translocations within the 3'-UTR of BCL9 have been found in B-cell malignancies. [TF7L2_HUMAN] Note=Constitutive activation and subsequent transactivation of target genes may lead to the maintenance of stem-cell characteristics (cycling and longevity) in cells that should normally undergo terminal differentiation and constitute the primary transforming event in colorectal cancer (CRC). Genetic variations in TCF7L2 are associated with susceptibility to non-insulin-dependent diabetes mellitus (NIDDM) [MIM:125853]. NIDDM is characterized by an autosomal dominant mode of inheritance, onset during adulthood and insulin resistance.
[CTNB1_HUMAN] Key downstream component of the canonical Wnt signaling pathway. In the absence of Wnt, forms a complex with AXIN1, AXIN2, APC, CSNK1A1 and GSK3B that promotes phosphorylation on N-terminal Ser and Thr residues and ubiquitination of CTNNB1 via BTRC and its subsequent degradation by the proteasome. In the presence of Wnt ligand, CTNNB1 is not ubiquitinated and accumulates in the nucleus, where it acts as a coactivator for transcription factors of the TCF/LEF family, leading to activate Wnt responsive genes. Involved in the regulation of cell adhesion. Acts as a negative regulator of centrosome cohesion. Involved in the CDK2/PTPN6/CTNNB1/CEACAM1 pathway of insulin internalization. Blocks anoikis of malignant kidney and intestinal epithelial cells and promotes their anchorage-independent growth by down-regulating DAPK2.    [BCL9_HUMAN] Involved in signal transduction through the Wnt pathway. Promotes beta-catenin's transcriptional activity (By similarity). [TF7L2_HUMAN] Participates in the Wnt signaling pathway and modulates MYC expression by binding to its promoter in a sequence-specific manner. Acts as repressor in the absence of CTNNB1, and as activator in its presence. Activates transcription from promoters with several copies of the Tcf motif 5'-CCTTTGATC-3' in the presence of CTNNB1. TLE1, TLE2, TLE3 and TLE4 repress transactivation mediated by TCF7L2/TCF4 and CTNNB1. Expression of dominant-negative mutants results in cell-cycle arrest in G1. Necessary for the maintenance of the epithelial stem-cell compartment of the small intestine.   
Publication Abstract from PubMed
The canonical Wnt pathway plays critical roles in embryonic development, stem cell growth, and tumorigenesis. Stimulation of the Wnt pathway leads to the association of beta-catenin with Tcf and BCL9 in the nucleus, resulting in the transactivation of Wnt target genes. We have determined the crystal structure of a beta-catenin/BCL9/Tcf-4 triple complex at 2.6 A resolution. Our studies reveal that the beta-catenin binding site of BCL9 is distinct from that of most other beta-catenin partners and forms a good target for developing drugs that block canonical Wnt/beta-catenin signaling. The BCL9 beta-catenin binding domain (CBD) forms an alpha helix that binds to the first armadillo repeat of beta-catenin, which can be mutated to prevent beta-catenin binding to BCL9 without affecting cadherin or alpha-catenin binding. We also demonstrate that beta-catenin Y142 phosphorylation, which has been proposed to regulate BCL9-2 binding, does not directly affect the interaction of beta-catenin with either BCL9 or BCL9-2.
Crystal structure of a beta-catenin/BCL9/Tcf4 complex.,Sampietro J, Dahlberg CL, Cho US, Hinds TR, Kimelman D, Xu W Mol Cell. 2006 Oct 20;24(2):293-300. PMID:17052462
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.