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Reporting period: 2016-09-01 to 2018-08-31

The major problems of cancer disease are 1) the relapse and resistance to current therapies that have been associated with the presence of cancer stem cells (CSCs) and 2) the spread of invasive metastatic cells to distant organs that is responsible for most cancer-associated deaths. CSCs represent a tumour cell subpopulation with the ability to self-renew and differentiate into non-CSCs. In carcinoma cells, the acquisition of stemness properties has been closely related to epithelial-mesenchymal transition (EMT), a key process in cancer invasion and metastasis. However, although EMT can be considered a process that generates CSCs, the connection between CSCs and metastasis is not yet well understood. Interestingly, in melanoma, a non-epithelial tumour, transition from elongated-mesenchymal to amoeboid mode of movement (MAT) driven by Rho-ROCK signalling has been associated with increased stemness. Nevertheless, how very contractile cells regulate genes involved in EMT, tumour initiation and metastatic spread remains unexplored. Moreover, it is not known if the same genes regulate all these processes. As increasing cellular plasticity via EMT in carcinoma cells or via MAT in melanoma cells correlates with increasing stemness, we hypothesized a molecular link between the pathways regulating both migration and stemness abilities. Therefore, the main goal of this proposal has been to understand how tumour cells can acquire stem cell traits to successfully metastasize and how this can be regulated by the actomyosin cytoskeletal by using an interdisciplinary approach that combines state-of-the-art techniques in molecular and cellular biology, biochemistry, in vivo imaging and animal models. This has allow us to identify key important genes regulating both stemness traits and metastatic spread and identified prognostic markers of distant relapse and patient survival.
Bioinformatics analysis comparing different transcriptomes for EMT and CSC programmes have been performed to identify important signalling pathways involved in migration and stemness properties, and key genes have been selected to further investigation in the project. We assessed the effect of knocking down the selected key genes using siRNAs in the in vitro and in vivo stemness traits of cancer cells (Work Package 1). We used the same siRNA approach to test the impact of the selected genes in the regulation of invasive traits on cancer cells (Work Package 2). Moreover, a shRNA stably transfected cell line against our most promising candidate involved in the regulation of stemness and migration was generated to assess its role in tumour initiation abilities and metastasis formation in vivo (Work Package 1 and 4). During the project we also identified an important metabolic marker able to regulate both stemness and invasive features (Work Package 3). Finally, to extend our observations to the clinical setting, all the markers identified in the project were assessed by immunohistochemistry in human tumour samples and we identified prognostic markers of disease-free survival and overall survival (Work Package 4). The results obtained in this project will be submitted shortly to an open access peer-review journal.
The major causes of cancer deaths are relapse and resistance to current therapies associated with the presence of cancer stem cells and metastatic growth in distant organs. The present project has identified an important signalling pathway regulating both invasive tumour behaviour and stemness traits to promote tumour initiation and metastasis. In addition, we have identified a marker of recurrence and patient survival, one of the major challenges in cancer research. Together this results significantly contribute to increase our knowledge in cancer metastasis and can open new lines of research in order to develop novel therapeutic targets to prevent tumour relapse and metastasis formation.