Extracellular Vesicle–Packaged miR-99a Reprograms Fibroblasts to Create an Inflammatory Niche That Drives Colorectal Cancer Metastasis

Inflammation and epithelial-to-mesenchymal transition are hallmarks of cancer progression. A better understanding of the mechanisms driving these processes could help uncover strategies to treat and prevent metastasis. In this study, we found that extracellular vesicle (EV)-mediated cross-talk between colorectal cancer cells and fibroblasts facilitates inflammation and promotes metastasis. Fibroblasts were highly activated in primary tumors from patients with colorectal cancer with metastatic disease, and EVs secreted from highly metastatic colorectal cancer cells promoted fibroblast activation. Mechanistically, EV-packaged miR-99a-5p (EV-miR-99a) specifically targeted NLRP2 mRNA in fibroblasts and activated the proinflammatory NFκB signaling pathway, thereby converting normal fibroblasts into cancer-associated fibroblasts (CAF). EV-miR-99a-activated CAFs enhanced the migratory capacity of colorectal cancer cells by secreting CCL7, which potently induced epithelial-to-mesenchymal transition by increasing the expression of multiple E-cadherin repressors via the CCR5-mTOR-p70S6K pathway. Expression of miR-99a in colorectal cancer cells was upregulated by TGFβ1 secreted from CAFs in an NFκB-dependent manner, forming an miR-99a/TGFβ1 regulatory circuit. The communication between colorectal cancer cells and fibroblasts engendered a proinflammatory niche that facilitated metastasis, which could be abolished by treatment with the p70S6K inhibitor LY2584702. Clinically, EV-miR-99a levels in the plasma correlated with the metastatic status of patients with colorectal cancer. Together, these findings highlight the metastasis-promoting function of an inflammatory fibroblast niche induced by cancer cell-derived EVs and provide potential targets for the prediction and management of colorectal cancer metastasis. SIGNIFICANCE: Extracellular vesicle-mediated cross-talk between colorectal cancer cells and fibroblasts orchestrates a proinflammatory niche that induces and facilitates metastasis and provides potential targets for disease prediction and therapeutic intervention.