AP-2α reverses vincristine-induced multidrug resistance of SGC7901 gastric cancer cells by inhibiting the Notch pathway

Multidrug resistance (MDR) remains a major clinical obstacle in the treatment of gastric cancer (GC) since it causes tumor recurrence and metastasis. The transcription factor activator protein-2 alpha (AP-2 alpha) has been implicated in drug-resistance in breast cancer; however, its effects on MDR of gastric cancer are far from understood. In this study, we aimed to explore the effects of AP-2 alpha on the MDR in gastric cancer cells selected by vincristine (VCR). Decreased AP-2 alpha levels were markedly detected by RT-PCR and Western blot in gastric cancer cell lines (BGC-823, SGC-7901, AGS, MKN-45) compared with that in the gastric epithelial cell line (GES-1). Furthermore, we found that the expression of AP-2 alpha in SGC7901/VCR or SGC7901/adriamycin (ADR) cells was lower than in SGC7901 cells. Thus, a vector overexpressing AP-2 alpha was constructed and used to perform AP-2 alpha gain-of-function studies in SGC7901/VCR cells. The decreased IC50 values of the anti-cancer drugs in sensitive and resistant cells after transfect with pcDNA3.1/AP-2 alpha were determined in SGC7901/VCR cells by MTT assay. Moreover, flow cytometry analysis indicated that overexpressed AP-2 alpha induced cell cycle arrest in the G0/G1 phase and promoted cell apoptosis of VCR-selected SGC7901/VCR cells. RT-PCR and Western blot demonstrated that overexpressed AP-2 alpha can significantly induce the down-regulation of Notch1, Hes-1, P-gp and MRP1 in SGC7901/VCR cells. Similar effects can be observed when Numb (Notch inhibitor) was introduced. In addition, the intracellular ADR accumulation was markedly detected in AP-2 alpha overexpressed or Numb cells. In conclusion, our results indicate that AP-2 alpha can reverse the MDR of gastric cancer cells, which may be realized by inhibiting the Notch signaling pathway.