Structure of the Phosphorylation Motif of the oncogenic Protein beta-Catenin Recognized By a Selective Monoclonal Antibody
[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.
[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.   
Publication Abstract from PubMed
The interaction of the P-beta-Cat(19-44) peptide, a 26 amino acid peptide (K(19)AAVSHWQQQSYLDpSGIHpSGATTTAP(44)) that mimics the phosphorylated beta-Catenin antigen, has been studied with its monoclonal antibody BC-22, by transferred nuclear Overhauser effect NMR spectroscopy (TRNOESY) and saturation transfer difference NMR (STD NMR) spectroscopy. This antibody is specific to diphosphorylated beta-Catenin and does not react with the non-phosphorylated protein. Phosphorylation of beta-Catenin at sites Ser33 and Ser37 on the DSGXXS motif is required for the interaction of beta-Catenin with the ubiquitin ligase SCF(beta-TrCP). beta-TrCP is involved in the ubiquitination and proteasome targeting of the oncogenic protein beta-Catenin, the accumulation of which has been implicated in various human cancers. The three-dimensional structure of the P-beta-Cat(19-44) in the bound conformation was determined by TRNOESY NMR experiments; the peptide adopts a compact structure in the presence of mAb with formation of turns around Trp25 and Gln26, with a tight bend created by the DpS(33)GIHpS(37) motif; the peptide residues (D32-pS37) forming this bend are recognized by the antibody as demonstrated by STD NMR experiments. STD NMR studies provide evidence for the existence of a conformational epitope containing tandem repeats of phosphoserine motifs. The peptide's epitope is predominantly located in the large bend and in the N-terminal segment, implicating bidentate association. These findings are in excellent agreement with a recently published NMR structure required for the interaction of beta-Catenin with the SCF(beta-TrCP) protein.
STD and TRNOESY NMR studies for the epitope mapping of the phosphorylation motif of the oncogenic protein beta-catenin recognized by a selective monoclonal antibody.,Megy S, Bertho G, Gharbi-Benarous J, Baleux F, Benarous R, Girault JP FEBS Lett. 2006 Oct 2;580(22):5411-22. Epub 2006 Sep 14. PMID:16996060
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