PO-067 Autophagy modulates response to cisplatin in thyroid cancer cells

Abstract

Introduction Large scale sequencing studies have identified that 93% of the colorectal cancer (CRC) patients carry at least one mutation in genes implicated in Wnt signalling pathway. Notably, majority of the CRC patients (88%) carry either APC or b-catenin mutations that can activate the Wnt signalling pathway. Recent evidences suggest that Wnt/b-catenin signalling activity is regulated by CDH17 in hepatocellular carcinoma. As CDH17 is exclusively expressed in the intestine and overexpressed in CRC, we hypothesised that CDH17 could be utilised as a therapeutic target to treat CRC patients. Material and methods RNA interference-based stable knockdowns were established in a panel of CRC cells with varying mutations in APC and b-catenin. Wnt signalling activity of the cells were measured by TOPflash assay. Apoptosis studies were performed using fluorescence activated cell sorting. Cells were further subjected to immunoprecipitations with anti-CDH17 and anti-b-catenin antibodies followed by label-free quantitative proteomics analysis. A monoclonal antibody was developed to block CDH17 and sensitise CRC cells to chemotherapeutic drugs. Results and discussions Knockdown of CDH17 in CRC cells downregulated b-catenin and attenuated Wnt signalling activity irrespective of APC and/or b-catenin mutations. Furthermore, CDH17 silencing induced apoptosis and sensitised CRC cells to the chemotherapeutic drugs 5-Fluorouracil. Immunoprecipitations using anti-CDH17 and anti-b-catenin antibodies followed by label-free quantitative proteomics analysis highlighted no direct interaction between CDH17 and b-catenin hence implying an indirect regulation of b-catenin expression and Wnt signalling pathway by CDH17. The analysis revealed Ecadherin and FAT1 as common interactors of CDH17 and bcatenin. Quantitative proteomic analysis of cell lysates revealed the upregulation of FAT1, a negative regulator of Wnt signalling pathway, upon knockdown of CDH17. Monoclonal antibodies developed against CDH17 were able to increase apoptosis and sensitivity of CRC cells to 5-Fluorouracil. Conclusion Overall, these findings suggest that CDH17 can attenuate Wnt signalling pathway and induce apoptosis irrespective of the APC and b-catenin mutational status. As Wnt signalling pathway is aberrated in 93% of CRC patients, the membrane protein CDH17 can be exploited as therapeutic target to treat CRC.