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

Abstract Inflammation and epithelial-to-mesenchymal transition (EMT) are hallmarks of cancer progression. A better understanding of the mechanisms driving these processes could help uncover strategies to treat and prevent metastasis. Here, we found that extracellular vesicle (EV)-mediated crosstalk between colorectal cancer (CRC) cells and fibroblasts facilitates inflammation and promotes metastasis. Fibroblasts were highly activated in primary tumors from CRC patients with metastatic disease, and EVs secreted from highly metastatic CRC cells promoted fibroblast activation. Mechanistically, EV-packaged miR-99a-5p (EV-miR-99a) specifically targeted NLRP2 mRNA in fibroblasts and activated the pro-inflammatory NF-κB signaling pathway, thereby converting normal fibroblasts into cancer-associated fibroblasts (CAFs). EV-miR-99a-activated CAFs enhanced the migratory capacity of CRC cells by secreting CCL7, which potently induced EMT by increasing the expression of multiple E-cadherin repressors via the CCR5-mTOR-p70S6K pathway. Expression of miR-99a in CRC cells was upregulated by TGF-β1 secreted from CAFs in an NF-κB-dependent manner, forming an miR-99a/TGF-β1 regulatory circuit. The communication between CRC 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 CRC patients. 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 CRC metastasis.