VEGFC/VEGFR3 axis mediates TGFβ1-induced epithelial-to-mesenchymal transition in non-small cell lung cancer cells

In the tumor progression, transforming growth factor β1 (TGFβ1) plays a critical role in tumorigenesis as well as metastasis. It is known that high plasma level of TGFβ1 in patients with advanced non-small cell lung cancer (NSCLC) is correlated with poor prognostics. In addition, the generation of cancer stem-like cells is associated with metastasis, drug resistance, and tumor recurrence, which also lead to poor outcomes in NSCLC patients. However, it remains unclear how TGFβ1 promotes NSCLC cells to acquire stem-like properties and accelerate tumor metastasis. In our study, we found that short term TGFβ1 treatment resulted in a significant epithelial-mesenchymal transition (EMT) morphological change in TGFβ1–sensitive NSCLC cells but not in insensitive cells. Western blotting confirmed increased Vimentin and reduced E-Cadherin protein expression after TGFβ1 treatment in A549, NCI-H1993, and NCI-H358 cells. TGFβ1 incubation dramatically decreased in vitro cell proliferation and increased cell invasion in TGFβ1–sensitive NSCLC cells but not in NCI-H1975, NCI-H1650, and HCC827 cells. Moreover, TGFβ1 was able to enhance the mRNA expression of Oct4, Nanog and Sox2 and drastically increased anchorage-independent colony formation in TGFβ1–sensitive NSCLC cells, suggesting the acquisition of cancer stem-like properties. Interestingly, we found that vascular endothelial growth factor receptor 3 (VEGFR3) mRNA expression was significantly elevated in TGFβ1–sensitive NSCLC cells compared to insensitive cells. And TGFβ1 was capable of inducing VEGF-C gene expression. Pharmacological blocking TGFβ type I receptor kinase (ALK5) significantly inhibited TGFβ1-induced VEGF-C expression. Silencing of ALK5 by siRNA also dramatically reduced TGFβ1-induced VEGF-C expression in TGFβ1–sensitive NSCLC cells. Therefore, TGFβ1 contributes for NSCLC metastasis through promoting EMT, generation of high invasive cancer cells with stem-like properties, and increasing VEGF-C expression. Blocking TGFβ pathway is a potential therapeutic target in human non-small cell lung cancer.