Exosomes Derived from the Human Primary Colorectal Cancer Cell Line SW480 Orchestrate Fibroblast-Led Cancer Invasion.

In localized tumours, basement membrane (BM) prevents invasive outgrowth of tumour cells into surrounding tissues. When carcinomas become invasive, cancer cells either degrade the BM or reprogram the stromal fibroblasts to breach the BM barrier and lead invasion of cancer cells into surrounding tissues in a process called fibroblast-led invasion. However, tumour-derived factors orchestrating fibroblast-led invasion remains poorly understood. Here we show that although early-stage primary colorectal adenocarcinoma (SW480) cells are themselves unable to invade MatrigelTM matrix, they secrete exosomes that reprogram normal fibroblasts to acquire de novo capacity to invade matrix and lead invasion of SW480 cells. Strikingly, cancer cells follow the leading fibroblasts as collective epithelial-clusters, thereby circumventing the need for epithelial to mesenchymal transition, a key event associated with invasion. Moreover, acquisition of pro-invasive phenotype by fibroblasts treated with SW480-derived exosomes relied on exosome-mediated MAPK pathway activation. Mass spectrometry-based protein profiling revealed that cancer exosomes upregulated CRL1541 proteins implicated in focal adhesion (ITGA2/A6/AV, ITGB1/B4/B5, EGFR, CRK), regulators of actin cytoskeleton (RAC1,ARF1, ARPC3, CYFIP1,NCKAP1, ICAM1, ERM complex) and signalling pathways (MAPK, Rap1, RAC1, Ras) important in pro-invasive remodelling of the extracellular matrix. Blocking tumour exosome-mediated signalling to stromal fibroblasts could therefore represent an attractive therapeutic strategy in restraining tumours by perturbing stroma-driven invasive outgrowth. This article is protected by copyright. All rights reserved.