CXCR4/TGF-β1 mediated self-differentiation of human mesenchymal stem cells to carcinoma-associated fibroblasts and promoted colorectal carcinoma development.

Background: Tumor microenvironment (TME) is a crucial part of tumor hallmarks. Mesenchymal stem cells (MSCs), important components of TME, are the main source of Carcinoma-associated fibroblasts (CAFs), but the mechanism of transformation regulation is still unclear. Transforming growth factor-β1 (TGF-β1), chemokine Stromal cell-derived factor-1 (SDF-1) and its endogenous receptor CXCR4 may play important roles during this process.
Methods: Co-culture technique was used to explore the effects of MSCs on the proliferation, migration and invasion of colorectal carcinoma (CRC) cells and how they induced MSCs to differentiate into CAFs. The expression of α-SMA, Vimentin, S100A4 and FAP were detected as CAFs markers. Inhibitors AMD3100 and cyclophosphamide (Cy) were pre-treated in MSCs to verify the functions of CXCR4/TGF-β1. Finally, the xenograft models in nude mice were generated to further verify this process in vivo.
Results: MSCs promoted the CRCs proliferation, invasion and migration, and induced SDF-1 expression and secretion, which dramatically up-regulated CXCR4 and TGF-β1 expression in MSCs. The levels of CAFs markers elevated in MSCs, indicating CAFs differentiation occurred in MSCs. AMD3100 and Cy treatment significantly blocked this differentiation process of MSCs by suppressing CXCR4 expression and TGF-β1 secretion. In vivo xenograft experiments also demonstrated that MSCs promoted differentiation into CAFs through CXCR4/TGF-β1 signaling in either primary tumor tissues or hepatic metastatic tissues of CRC.
Conclusion: Our studies have revealed the essential role of CXCR4/TGF-β1 axis playing in the transformation of tumor microenvironment by mediating MSCs differentiation into CAFs, promoting CRCs growth and metastasis.