Cancer-Associated Fibroblasts are the Main Source of Epithelial-to-Mesenchymal Signaling in the Tumor Microenvironment

Epithelial-to-mesenchymal transition (EMT) is associated with tumor initiation, metastasis, and drug resistance. However, the mechanisms underlying these associations are largely unknown. We studied several tumor types to identify the source of EMT gene expression signals and a potential mechanism of resistance to immuno-oncology treatment. Across tumor types, EMT-related gene expression was strongly associated with expression of stroma-related genes. Based on RNA sequencing of multiple patient-derived xenograft models, EMT-related gene expression was enriched in the stroma versus parenchyma. EMT-related markers were predominantly expressed by cancer-associated fibroblasts (CAFs), cells of mesenchymal origin which produce a variety of matrix proteins and growth factors. Scores derived from a 3-gene CAF transcriptional signature (COL1A1, COL1A2, COL3A1) were sufficient to reproduce association between EMT-related markers and disease prognosis. Our results suggest that CAFs are the primary source of EMT signaling and have potential roles as biomarkers and targets for immuno-oncology therapies. Resected tumors and adjacent normal tissues were procured from BioIVT (BioIVT, Westbury, NY) from 14 treatment-naive patients with colorectal or renal cell carcinoma. Tissue samples were enzymatically dissociated and single cells were sorted for live, nucleated CD45+ and CD45− cells to enrich for immune and non-immune cells, followed by generating single-cell sequencing libraries.