VEGF-C induced by TGF- ß1 signaling in gastric cancer enhances tumor-induced lymphangiogenesis.

ABSTRACT

BACKGROUND: The role of TGF-ß1 in lymph node metastasis and lymphangiogenesis, one of the most important steps of gastric cancer dissemination, is largely unknown. The goal of this study was to investigate the role of TGF-ß1 signaling and its molecular mechanisms involved in lymphangiogenesis of gastric cancer. METHODS: Two gastric cell line models, MKN45 and KATOIII, were selected for this study. The protein expression of TGF-ß1 pathway molecules and VEGF-C were examined with western blot, or ELISA according to TGF-ß1 treatment. To explore whether Smad3 binds to the specific DNA sequences in the VEGFC promoter, we performed an electrophoretic mobility shift assay. Lymphatic tube forming assay and gastric cancer xenograft mouse models were also used to elucidate the effect of TGF-ß1 on lymphangiogenesis. RESULTS: TGF-ß1 induced the activation of Smad2/3 and Smad pathway-modulated VEGF-C expression in gastric cancer cell line models. Phosphorylated and activated Smad3 in the nucleus bound to the promoter of VEGFC in KATO III cells. Of note, in MKN45 cells, the Smad-independent AKT pathway was also activated in response to TGF-ß1 and induced VEGF-C expression. Inhibition of TGF-ß1 signaling down-regulated the expression of VEGF-C. We also confirmed, through tube forming assay and tumor xenograft mouse model, that TGF-ß1 increased lymphatic formation, while TGF-ß1 inhibition blocked lymphangiogenesis. CONCLUSION: Smad-dependent and -independent TGF-ß1 pathways induce VEGF-C, which make lymphangiogenesis around tumor. These findings suggest that TGF-ß might be a potential therapeutic target for preventing gastric cancer progression and dissemination.