HER2 promotes epithelial-mesenchymal transition through regulating osteopontin in gastric cancer

Aims: HER2 and osteopontin (OPN) are both important biomarkers in gastric cancer (GC). The relationships between them remain to be revealed. The purpose of this study is to explore the role of OPN in epithelialmesenchymal transition (EMT) in HER2 positive GCs. \Methods: Nanostring analysis was used to compare the mRNA levels of 730 cancer related genes between paired HER2 3+ and non-3+ areas in GC patients. Immunohistochemistry (IHC) staining was performed to analyze the expression levels of OPN, as well as EMT markers including E-cad, N-cad, twist and vimentin in both areas. To further verify the role of OPN in EMT, the expression levels of OPN and EMT markers, tumor invasion/migration were analyzed after down-regulating HER2 and OPN in GC cell lines MKN-45 and N-87. Results: Nanostring analysis identified 8 differential expression genes between HER2 3+ and non-3+ areas. Among them, the expression level of OPN was positively correlated with that of HER2. In GC specimens, OPN showed higher expression level in HER2 3+ areas where higher E-cad expression levels and lower N-cad and twist levels were also found. After knocking down OPN and HER2 by siRNA, both cell lines show decreased invasion/migration abilities, along with the down-regulation of the EMT phenotype, supporting by the decrease of E-cad, and the increase of N-cad and twist at both mRNA and protein levels. In addition, HER2 knock-down lead to a dramatic decrease of OPN expression. Conclusions: These findings indicate that HER2 may promote EMT via the regulation of OPN in GCs.