PO-288 Stroma cells increase expression of tumor-promoting RAC1B in colorectal cancer cells

• Published in: ESMO open 2018-07, Vol.3 (Suppl 2), p.A340-A340
• Main Authors: De Sousa Pereira, J, Jordan, P, Matos, P
• Format: Article
• Language: English
• ISSN: 2059-7029; 2059-7029
• DOI: 10.1136/esmoopen-2018-EACR25.802

IntroductionAn inflammatory microenvironment is a tumor-promoting condition that provides survival signals to which cancer cells respond with changes in their gene expression. One key gene regulatory mechanism that responds to extracellular signals is alternative splicing. For example RAC1B, a RAC1 alternative splicing variant that we previously identified in a subset of BRAF-mutated colorectal tumours, was found increased in samples from inflammatory bowel disease patients or following experimentally-induced acute colitis in a mouse model. The main goal of this work is to determine the pro-inflammatory signals that lead to increased RAC1B expression in colorectal cells.Material and methodsCaco-2 colorectal cells were either grown as polarised cell monolayer on porous filter membranes and then co-cultured with different stromal cell lines (fibroblasts, monocytes and macrophages) or grown as cysts in 3D matrices. RAC1B expression was analysed by RT-PCR, Western blot and confocal fluorescence microscopy.Results and discussionsCulture conditions for polarised 2D and 3D models were established as physiologically more relevant colon cell models. Co-culture experiments with polarised cells revealed that the presence of fibroblasts and/or M1 macrophages induced a transient increase in RAC1B protein levels in the colorectal cells, accompanied by a progressive loss of epithelial organisation. The cytokines secreted by fibroblasts and macrophages are currently being identified.ConclusionOur data indicate that extracellular signals from stromal cells can affect gene expression in colorectal cancer cells. The observed increase in alternatively spliced RAC1B will help to understand the tumor-promoting effect of inflammation and identify novel therapeutic strategies.