Abstract 2982: Metastatic and non-metastatic colorectal cancer cells differentially regulate fibroblast cell cycle via extracellular vesicles
Authors: Bhome Rahul , House Louise M. , Sanchez-Elsner Tilman , Thirdborough Stephen M. , Sayan Emre , Mirnezami Alex H. 
Published: July 2017

Cancer-associated fibroblasts are critical to tumor progression. There exists a dynamic crosstalk between cancer and stromal compartments, which maintains a permissive tumor microenvironment. Extracellular vesicles (EVs) play a significant role in this intercellular communication. Colorectal cancer (CRC) cells can be categorized according to epithelial-mesenchymal transition (EMT) status, and therefore metastatic capacity. We aimed to investigate the effect of EMT on EV-mediated cancer-fibroblast signaling.

CRC cell lines (DLD-1, HCT116, SW620 and SW480) were characterized by western blotting to determine EMT status. EVs were isolated from conditioned media by serial centrifugation and validated by transmission electron microscopy, western blotting and nanoparticle tracking analysis. Fluorescently labeled EVs and cells were detected and evaluated by flow cytometry and fluorescence microscopy. Increasing concentrations of EVs from CRC cells were co-cultured with fibroblasts for 24h. Activation/inhibition of signaling pathways was examined by western blotting. EV microRNA (miRNA) profiles were obtained, validated by qPCR and submitted for target and pathway analysis.

DLD-1, HCT116 and SW620 cells express E-cadherin and are considered epithelial, whereas SW480 lacks E-cadherin, expresses ZEB-1, and is considered mesenchymal. EVs were spherical, enriched in ALIX, TSG101, CD63 and had a mean diameter of 90nm. EVs from CRC cells were shown to transfer directly to primary ex vivo patient-derived fibroblasts and fibroblast cell lines. Transfer of EVs from epithelial CRC cells abrogated ERK activity in fibroblasts, even at the lowest concentration, and was associated with reduced fibroblast proliferation, whereas EVs from mesenchymal cells had no effect. MiRNA profiling of EVs from epithelial and mesenchymal CRC cells showed a 10-fold upregulation of miR-143-3p in epithelial compared to mesenchymal EVs. MiRNA target analysis and experimental validation show that miR-143-3p directly targets KRAS and HRAS, providing a potential miRNA-orchestrated mechanism of action for the downregulation of fibroblast ERK activity in the tumor microenvironment.

Importantly, CRC cellular ERK activity is not reflected in fibroblasts treated with CRC EVs, suggesting that EVs do not directly transmit ERK protein or mRNA. However, miRNAs are the most stable EV cargo, and we show that epithelial but not mesenchymal CRC EVs contain upregulated miRNAs, which target critical components of the ERK pathway. Downregulation of ERK activity has been shown to induce fibroblast senescence, a phenotype linked to cancer progression. We hypothesize that differential regulation occurs because epithelial CRC cells are juxtaposed with fibroblasts in the tumor core, where senescent cancer associated fibroblasts are frequently observed, whereas mesenchymal CRC cells are at the invasive front or in the circulation.

Citation Format: Rahul Bhome, Louise M. House, Tilman Sanchez-Elsner, Stephen M. Thirdborough, Emre Sayan, Alex H. Mirnezami. Metastatic and non-metastatic colorectal cancer cells differentially regulate fibroblast cell cycle via extracellular vesicles [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2982. doi:10.1158/1538-7445.AM2017-2982