Anti-metastatic potential of a proton beam is regulated by p38 MAPK/c-Fos signaling pathway in TPA-treated HepG2 human hepatocellular carcinoma

A proton beam therapy is considered the next generation radio-therapeutic tool for liver cancer treatments. However, its effect on metastasis has not been fully elucidated. Herein, we assessed the effects of a proton beam on the metastatic potential in HepG2, Hep3B and SK-Hep1 hepatocellular carcinomas. The result showed that a proton beam suppressed TPA-induced cell migration and invasion in HepG2 cells, but not in Hep3B and SK-Hep1 cells. In addition, matrix metalloproteinase-9 (MMP-9) activity and mRNA expressions were reversed by proton beam irradiation in TPA-treated HepG2 cells only. Furthermore, a proton beam suppressed TPA-induced gene expressions of urokinase plasminogen activator (uPA), uPA receptor (uPAR), Snail-1 and vascular endothelial growth factor (VEGF) in HepG2 cells in a dose-dependent manner. Moreover, we found that proton beam irradiation restrained p38 MAPK phosphorylation and c-Fos expression. Therefore, the result demonstrates that the anti-metastatic effects of a proton beam in TPA-treated HepG2 cells are associated with the inhibition of MMP-9 activity and the down-regulations of MMP-9, uPA, uPAR, Snail-1 and VEGF gene expression via the p38 MAPK/c-Fos signaling pathway. Taken together, this investigation suggests that the establishment of a customized proton beam therapeutic strategy for each liver cancer type is necessary to improve therapeutic efficiency.