PO-203 A novel member in the β-catenin destruction complex: may MAPK14/P38α foster new therapeutic approaches in colorectal cancer?

Abstract

IntroductionOne of the most commonly deregulated signalling pathways in colorectal cancer (CRC) is the Wnt cascade, which is controlled by APC. APC regulates β-catenin levels, thereby modulating the transcriptional activity of the TCF/LEF transcription factors. High levels of nuclear β-catenin lead to constitutive activation of the Wnt pathway, loss of normal cellular architecture and neoplastic transformation. Previous reports indicate that Wnts are capable of activating p38 MAPKs. A few older studies carried out in other tissues provided evidence that Wnt3a could activate p38 suggesting that the p38 pathway may feed into the canonical Wnt/β-catenin pathway at least at the level of GSK3β. We recently showed that p38α is required to maintain CRC metabolism and survival, as its inhibition leads to activation of FoxO3A, autophagy, cell death and tumour growth reduction both in vitro and in vivo.Material and methodsWe performed extensive characterisation of the functional interaction between p38 and the APC/β-catenin/GSK3β complex (co-localization analysis by confocal microscopy and co-immunoprecipitation studies) in several cell lines in vitro and in the APCMin/+ mouse preclinical model in vivo.Results and discussionsOur data showed that CRC cells have higher levels of activated p38 than their normal counterparts, and experiments using kinase-specific inhibitors revealed that these cells are ‘addicted’ to p38 activity. Interestingly, p38α blockade reduced the size and number of adenomas in the small bowel of APCMin/+ mice. Significant results were obtained in vivo by co-immunoprecipitation analysis of tissues from normal mice and APCMin/+ mice treated or not with AOM. Our findings confirmed the presence of p38α in APC/β-catenin/GSK3β complexes in CRC cells. Importantly, p38α co-localised with β-catenin in both normal and cancer cells; however, these proteins were confined to the cytoplasm in colonocytes, while they occupied discrete nuclear regions in CRC cells. These data were further corroborated by the inhibitory effect of p38α blockade on β-catenin-responsive genes (i.e. c-Myc, cyclin D1/2). Characterisation of this novel functional interaction was also extended with chromatin immunoprecipitation experiments.ConclusionIdentification of p38α as a novel member of the APC/β-catenin/GSK3β complex could help elucidate mechanisms contributing to human colon tumour pathogenesis and allow for the development of new strategies for CRC treatment.