NRP1 regulates radiation-induced EMT via TGF-β/Smad signaling in lung adenocarcinoma cells

Purpose Radiation has been shown to promote the epithelial-mesenchymal transition (EMT) in tumor cells, and TGF-beta/Smad and PI3K-Akt signaling pathways play an important role in the EMT. In this study, we investigated the effects of neuropilin-1 (NRP1) on radiation-induced TGF-beta/Smad and non-classical Smad signaling pathways in lung cancer cells, as well as the effects of NRP1 on invasion and migration. Materials and methods Changes in the expression levels of EMT markers (beta-catenin, N-cadherin, and vimentin) and related transcription factors (Twist and ZEB1) in stably transfected cells were detected by Western blotting and qPCR, and changes were assessed by TGF-beta/Smad and non-classical Smad signaling. Immunofluorescence was used to detect the expression of the cytoskeletal protein F-actin. Expression of TGF-beta 1 and CXCL-12 was detected by ELISA. Transwell and scratch assays were used to detect the invasive ability and migration of lung cancer cells, respectively. Results Our results showed that ionizing radiation could induce the EMT as well as morphological changes in lung adenocarcinoma cells (A549); however, the effects were not significant in lung squamous carcinoma cells (SK-MES-1). Moreover, we showed that NRP1 promotes the EMT induced by ionizing radiation in A549 cells, which may be related to the increased expression of EMT-related transcription factors. NRP1 may promote the radiation-induced EMT of A549 cells mainly through TGF-beta 1/Smad2/3 signaling. NRP1 also enhanced radiation-induced invasion, migration, and CXCL-12 expression in A549 cells. Conclusions We conclude that NRP1 promotes radiation-induced EMT in lung adenocarcinoma cells via TGF-beta 1/Smad signaling and not non-classical Smad signaling, and enhances the invasion and migration of lung adenocarcinoma cells.