SEMINARIO: Ana Rosa Márquez / Rabeah Amre Almhassneh

12:00 – 12:30: Ana Rosa Márquez

Title

Abstract:

12:30 – 13:00: Rabeah Amre Almhassneh

Understanding the molecular mechanisms of APC C-terminal missense mutations in young colorectal cancer patients.

Abstract: Colorectal cancer (CRC) is a leading cause of cancer-related mortality worldwide, with increasing incidence in early-onset patients. The tumour suppressor Adenomatous Polyposis Coli (APC) is essential for epithelial homeostasis and is one of the earliest driver genes altered in CRC. Historically, APC mutations resulting in truncated fragments have been studied in the context of Wnt pathway. However, APC mutations span across the gene, with a relatively increased contribution of missense variants in the C-terminal. This study investigates the molecular basis of C-terminal APC mutations that promote tumour progression, independently of canonical Wnt/β-catenin signaling. We identified and characterized two pathogenic APC missense mutations found in young patients. In culture, those two mutations impaired cell migration and invasion. Getting deeper in the phenotype, we found the mutant cells presented a reduction in actin filaments levels, as well as in actin organization/alignment at focal adhesions. In addition, in vitro assays using purified proteins showed that both mutations impair actin bundling and nucleation, which could explain the cellular actin phenotypes. Both mutant cellular models displayed reduced β1 integrin activation, which was restored by MnCl₂, consistent with impaired inside-out signaling rather than structural integrin defects. Importantly, in one of the mutant cell lines, MnCl2 treatment restored also motility defects, suggesting that the cytoskeleton-integrin axis might be the responsible for the observed phenotype. Neither mutation affected β-catenin localization and/or cell proliferation, suggesting that the phenotypes observed might be Wnt-independent. Overall, this study identifies a previously underappreciated role for C-terminal APC missense mutations in regulating the cytoskeleton-integrin axis, leading to impaired migration and invasion. These findings provide mechanistic insight into early onset of colorectal cancer and highlight cytoskeletal regulation as a potential therapeutic vulnerability in that disease.