CTNNB1 encodes the protein b-catenin, a transcriptional activator involved in the WNT signaling pathway. Somatic gain-of-function mutations in CTNNB1 result in aberrant accumulation of the b-catenin protein and are prevalent in a wide range of solid tumors, including endometrial carcinoma, ovarian carcinoma, hepatocellular carcinoma, and colorectal carcinoma, among others. Genetic alterations in CTNNB1 have been identified in 4% of non-small cell lung cancers. The CTNNB1 S45P mutation is likely oncogenic, but no real progress has been made in targeting oncogenic mutant forms of CTNNB1 in lung cancer. However, CTNNB1 mutation-positive cancers are presumed to be resistant to pharmacologic inhibition of upstream components of the WNT pathway, instead requiring direct inhibition of b-catenin function. In one study pharmacological inhibition of b-catenin suppressed EGFR-L858R/T790M mutated lung tumor and genetic deletion of the b-catenin gene dramatically reduced lung tumor formation in transgenic mice, suggesting that b-catenin plays an essential role in lung tumorigenesis and that targeting the b-catenin pathway may provide novel strategies to prevent lung cancer development or overcome resistance to EGFR TKIs. These results should be interpreted in the clinical context.

Beta catenin is a transcriptional co-regulator and an adapter protein for cellular adhesion; it comprises part of the Wnt signaling pathway and intracellular levels of beta-catenin are regulated by its phosphorylation, ubiquitination and proteosomal degradation. Accumulation of nuclear beta catenin can lead to a tumoral phenotype and oncogenic transformation in a variety of solid tumors. Various oncogenic mutants of beta catenin have been found in different tumor types which alter its degradation, leading to its accumulation and promoting tumor growth. Some of these mutations are located at the N-terminus of the protein at the sites of phosphorylation which normally regulate its degradation. Interestingly, in a recent study, 38% of patients with myelodysplastic syndromes or acute myeloid leukaemia, showed increased β-catenin signalling and nuclear accumulation of beta catenin in osteoblasts was associated with increased Notch signalling in haematopoietic cells consistent with a model where abnormalities of osteolineage cells are associated with myeloid malignancies. In addition, aberrant Wnt siganling has been reported to play a role in chronic myeloid leukemia, acute lymphoblastic leukemia and non-hodgkin lymphomas. Inhibition of beta catenin using small molecule inhibitors is currently being investigated in various tumor types. Recent studies suggest that targeting of the Wnt pathway and beta catenin may be promising targets in the therapy of acute myeloid leukemia.