Effect of an inflammatory microenvironment on alternative splicing-mediated gene expression plasticity in colorectal cells

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Pro-Inflammatory Cytokines Trigger the Overexpression of Tumour-Related Splice Variant RAC1B in Polarized Colorectal Cells

Publication . Pereira, Joana F. S.; Bessa, Cláudia; Matos, Paulo; Jordan, Peter

Simple Summary: Tumours are now known to develop more quickly when the tumour cell mass is located in a tissue that shows signs of chronic inflammation. Under such conditions, inflammatory cells from the surrounding tumour microenvironment provide survival signals to which cancer cells respond. We have previously found that some colorectal tumours overexpress the protein RAC1B that sustains tumour cell survival. Here we used a colon mucosa-like in vitro cell model and found that the presence of cancer-associated fibroblasts and pro-inflammatory macrophages stimulated colorectal cells to increase their RAC1B levels. Under these conditions, the secreted survival signals were analysed, and interleukin-6 identified as the main trigger for the increase in RAC1B levels. The results contribute to understand the tumour-promoting effect of inflammation at the molecular level.

2022-03-09Journal article

Open access

A Signaling View into the Inflammatory Tumor Microenvironment

Publication . Pereira, Joana F. S.; Jordan, Peter; Matos, Paulo

The development of tumors requires an initiator event, usually exposure to DNA damaging agents that cause genetic alterations such as gene mutations or chromosomal abnormalities, leading to deregulated cell proliferation. Although the mere stochastic accumulation of further mutations may cause tumor progression, it is now clear that an inflammatory microenvironment has a major tumor-promoting influence on initiated cells, in particular when a chronic inflammatory reaction already existed before the initiated tumor cell was formed. Moreover, inflammatory cells become mobilized in response to signals emanating from tumor cells. In both cases, the microenvironment provides signals that initiated tumor cells perceive by membrane receptors and transduce via downstream kinase cascades to modulate multiple cellular processes and respond with changes in cell gene expression, metabolism, and morphology. Cytokines, chemokines, and growth factors are examples of major signals secreted by immune cells, fibroblast, and endothelial cells and mediate an intricate cell-cell crosstalk in an inflammatory microenvironment, which contributes to increased cancer cell survival, phenotypic plasticity and adaptation to surrounding tissue conditions. Eventually, consequent changes in extracellular matrix stiffness and architecture, coupled with additional genetic alterations, further fortify the malignant progression of tumor cells, priming them for invasion and metastasis. Here, we provide an overview of the current knowledge on the composition of the inflammatory tumor microenvironment, with an emphasis on the major signals and signal-transducing events mediating different aspects of stromal cell-tumor cell communication that ultimately lead to malignant progression.

2021-06-15Journal article

Open access

Microenvironment-induced changes in expression of tumor-promoting RAC1B in colorectal cells

Publication . Pereira, Joana; Gonçalves, Vânia; Matos, Paulo; Jordan, Peter

Introduction: An 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 tumors, 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 from stromal cells that lead to increased RAC1B expression in colorectal cells. Material and Methods: Caco-2 colorectal cells were either grown as polarized 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 analyzed by RT-PCR, Western blot and confocal fluorescence microscopy. Results and Discussions: Culture conditions for polarized 2D and 3D models were established as physiologically more relevant colon cell models. Co-culture experiments with polarized 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 organization. The cytokines secreted by stromal cells are currently being identified. Conclusion: Our 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.

2020-03-03Conference object

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