The atypical KRASQ22K mutation directs TGF-β response towards partial epithelial-to-mesenchymal transition in patient-derived colorectal cancer tumoroids

Transforming growth factor beta (TGF-β) exhibits complex and context-dependent cellular responses. While it mostly induces tumor-suppressive effects in early stages of tumorigenesis, its tumor promoting properties are evident in advanced disease. This TGF-β duality is still not fully understood, and whether TGF-β supports invasion and metastasis by influencing cancer cells directly, or rather through the stromal tumor compartment remains a matter of debate. Here, we utilized a library of colorectal cancer (CRC) patient-derived tumoroids (PDTs), representing a spectrum of tumor stages, to study cancer cell-specific responses to TGF-β. Using medium conditions allowing for the differentiation of PDTs, we observed TGF-β induced tumor-suppressive effects in early-stage tumoroids. PDTs with TGF-β pathway mutations or PDTs derived from metastatic tumors were insensitive to the treatment. Notably, one tumoroid line harboring an atypical KRASQ22K mutation underwent partial epithelial-to-mesenchymal transition (EMT), associated with morphological changes and increased invasiveness. On a molecular level, this was accompanied by elevated expression of mesenchymal genes, as well as deregulation of pathways associated with matrix remodeling and cell adhesion. Our results suggest that tumor cell intrinsic responses to TGF-β are critical in determining its tumor-suppressive or -promoting effects.