Cancerous inhibitor of protein phosphatase 2A enhances chemoresistance of gastric cancer cells to oxaliplatin

BACKGROUND: Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a newly discovered oncogene. It is an active cell proliferation regulatory factor that inhibits tumor apoptosis in gastric cancer (GC) cells. CIP2A is functionally related to chemoresistance in various types of tumors according to recent studies. The underlying mechanism, however, is unknown. Further, the primary treatment regimen for GC is oxaliplatin-based chemotherapy. Nonetheless, it often fails due to chemoresistance of GC cells to oxaliplatin. AIM: The goal of this study was to examine CIP2A expression and its association with oxaliplatin resistance in human GC cells. METHODS: Immunohistochemistry was used to examine CIP2A expression in GC tissues and adjacent normal tissues. CIP2A expression in GC cell lines was reduced using small interfering RNA. After confirming the silencing efficiency, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tetrazolium and flow cytometry assays were used to evaluate cell proliferation and apoptosis caused by oxaliplatin treatment. Further, the key genes and protein changes were verified using real-time quantitative reverse transcription PCR and Western blotting, respectively, before and after intervention. For bioinformatics analysis, we used the R software and Bioconductor project. For statistical analysis, we used GraphPad Prism 6.0 and the Statistical Package for the Social Sciences software version 20.0 (IBM, Armonk, United States). RESULTS: A high level of CIP2A expression was associated with tumor size, T stage, lymph node metastasis, Tumor Node Metastasis stage, and a poor prognosis. Further, CIP2A expression was higher in GC cells than in normal human gastric epithelial cells. Using small interfering RNA against CIP2A, we discovered that CIP2A knockdown inhibited cell proliferation and significantly increased GC cell sensitivity to oxaliplatin. Moreover, CIP2A knockdown enhanced oxaliplatin-induced apoptosis in GC cells. Hence, high CIP2A levels in GC may be a factor in chemoresistance to oxaliplatin. In human GC cells, CIP2A regulated protein kinase B phosphorylation, and chemical inhibition of the protein kinase B signaling pathway was significantly associated with increased sensitivity to oxaliplatin. Therefore, the protein kinase B signaling pathway was correlated with CIP2A-enhanced chemoresistance of human GC cells to oxaliplatin. CONCLUSION: CIP2A expression could be a novel therapeutic strategy for chemoresistance in GC.