FGF2-mediated regulation of TGF-β-induced endothelial-to-myofibroblast transition

Tumor microenvironment contains various components including cancer cells, tumor vessels, and cancer associated fibroblasts (CAFs), comprising of tumor-promoting myofibroblasts and tumor-suppressing fibroblasts. Multiple lines of evidence indicated that transforming growth factor-β (TGF-β) induces the formation of myofibroblasts and other types of mesenchymal (non-myofibroblastic) cells from endothelial cells. Recent reports showed that fibroblast growth factor 2 (FGF2) modulates TGF-β-induced mesenchymal transition of endothelial cells, but the molecular mechanisms regarding the signals that control the transcriptional networks during the formation of different groups of fibroblasts remain largely unclear. Here, we studied the roles of FGF2 during the regulation of TGF-β-induced mesenchymal transition of tumor endothelial cells (TECs). We demonstrated that auto/paracrine FGF signals in TECs inhibit TGF-β-induced endothelial-to-myofibroblast transition (End-MyoT), leading to suppressed formation of contractile myofibroblast cells, but on the other hand can also collaborate with TGF-β in promoting the formation of active fibroblastic cells which have migratory and proliferative properties. FGF2 modulated TGF-β-induced formation of myofibroblastic and non-myofibroblastic cells from TECs via transcriptional regulation of the array of various mesenchymal markers and growth factors. Furthermore, we observed that TECs treated with TGF-β were more competent in promoting in vivo tumor growth than TECs treated with TGF-β and FGF2. Mechanistically, we showed that Elk1 mediated this FGF2-induced inhibition of End-MyoT via inhibition of TGF-β-induced transcriptional activation of α-SMA promoter by myocardin-related transcription factor (MRTF)-A. Our data suggest that TGF-β and FGF2 oppose and cooperate with each other during the formation of myofibroblastic and non-myofibroblastic cells from TECs to determine the characteristics of the mesenchymal cells in tumor microenvironment. Identification of marker genes for TGF-β-induced endothelial-to-myofibroblast transition Samples 1..4: The effect of FGF2 on TGF-β-induced endothelial-to-myofibroblast transition was examined. Tumor endothelial cells were cultured in the absence or presence of 1 ng/mL of TGF-β2 in combination with 50 ng/mL of FGF2 for 72 h. Samples 5..8: The effect of FGF2 and infigratinib (a pan-inhibitor of FGF receptors) on TGF-β-induced endothelial-to-myofibroblast transition was examined. Tumor endothelial cells were cultured in the absence or presence of 1 ng/mL of TGF-β2 in combination with 50 ng/mL of FGF2 or 3 mM infigratinib for 72 h.