A Wnt-Induced Phenotypic Switch in Cancer-Associated Fibroblasts Inhibits EMT in Colorectal Cancer

Abstract

Tumor progression is recognized as a result of an evolving cross-talk between tumor cells and their surrounding nontransformed stroma. Although Wnt signaling has been intensively studied in colorectal cancer, it remains unclear whether activity in the tumor-associated stroma contributes to malignancy. To specifically interfere with stromal signals, we generated Wnt-independent tumor organoids that secrete the Wnt antagonist Sfrp1. Subcutaneous transplantation into immunocompetent as well as immunodeficient mice resulted in a strong reduction of tumor growth. Histologic and transcriptomic analyses revealed that Sfrp1 induced an epithelialmesenchymal transition (EMT) phenotype in tumor cells without affecting tumor-intrinsic Wnt signaling, suggesting involvement of nonimmune stromal cells. Blockage of canonical signaling using Sfrp1, Dkk1, or fibroblast-specific genetic ablation of b-catenin strongly decreased the number of cancerassociated myofibroblasts (myCAF). Wnt activity in CAFs was linked with distinct subtypes, where low and high levels induced an inflammatory-like CAF (iCAF) subtype or contractile myCAFs, respectively. Coculture of tumor organoids with iCAFs resulted in significant upregulation of EMT markers, while myCAFs reverted this phenotype. In summary, we show that tumor growth and malignancy are differentially regulated via distinct fibroblast subtypes under the influence of juxtacrine Wnt signals.

Signaling pathways in cancer-associated fibroblasts and targeted therapy for cancer

“…Interestingly, by generating Wnt-independent tumor organoids, which secreted the Wnt antagonist Sfrp1, Mosa et al found that Sfrp1 or genetic depletion of β-catenin strongly decreased the number of cancer-associated myofibroblasts (myCAFs: α-SMA + /Acta2 + ). 187 Coculture of this tumor organoid with inflammatory CAFs (iCAFs: IL-6 + /Tnfa + /IL-1a + ) resulted in the upregulation of Vim and Zeb1, while myCAFs reverse this upregulation, 187 indicating that the EMT process could be induced by Sfrp1 and that tumor behaviors were differentially regulated via Wnt signaling pathway in specific CAF subtypes.…”

“… 186 Similarly, in colorectal cancer, Mosa et al generated a Wnt3 HA/HA APC min/+ mouse model and demonstrated a direct role of Wnt signaling in fibroblast activation, contractility, and CAF phenotypic plasticity. 187 Importantly, β-catenin ablation reduced the expression of PDGFRα and FSP1 with no obvious cytoskeletal rearrangement in stromal fibroblasts, 188 noting that other signaling pathways might be implicated in the process of cytoskeletal rearrangement mediated by noncanonical Wnt signaling cascade. It has been shown that β-catenin also forms a β-catenin/E-cadherin complex that contributes to the motility and migration of fibroblasts.…”

Follistatin-Like 3 Correlates With Lymph Node Metastasis and Serves as a Biomarker of Extracellular Matrix Remodeling in Colorectal Cancer

“…To validate this speculation, correlation analyses were performed to explore the relationship between the FSTL3 expression and marker genes of those immune cells. CAFs, also the main cellular component in TME, are known to be involved in regulating inflammatory responses, tumor cell proliferation and migration, as well as TME remodeling by secreting matrix degrading enzymes, cytokines and growth factors (34)(35)(36). Correlation heatmap showed that FSTL3 was significantly positively correlated with CAF-associated genes and had a strong positive correlation with TGFB1 (gene encoding TGF-b) (Figure 10A).…”

Organoids and Colorectal Cancer

“…Mosa and colleagues reported that Wnt activity in CAFs is linked to distinct CAF subtypes: low or high Wnt levels induce inflammatory-like CAFs (iCAFs) or contractile myofibroblastic CAFs (myCAFs) subtypes, respectively. These authors showed that the co-culture of tumor organoids with iCAFs resulted in a significant upregulation of epithelial-to-mesenchymal markers, while myCAFs reverted this phenotype [ 159 ]. The co-culture of mouse intestinal organoids with macrophages and fibroblasts also revealed that these stromal cells can hyperactivate the PI3K signaling in colonic epithelial cells that already carry Kras and Tp53 mutations and that oncogenic mutations cell-autonomously mimic an epithelial signaling state normally induced by stromal cells [ 160 ].…”