Enhancement of cisplatin sensitivity in human breast cancer MCF-7 cell line through BiP and 14-3-3ζ co-knockdown

Cisplatin treatment confers the relative resistance to MCF-7 cells as compared to other breast cancer cell lines. One principal reason is that chemotherapeutic agents induce autophagy in these cells to inhibit apoptosis. Binding immunoglobulin protein (BiP), a master regulator of unfolded protein response (UPR) and 14-3-3ζ are two critical proteins upregulated in breast cancer rendering resistance to anticancer drugs. They also play pivotal roles in autophagy with crosstalk with the apoptotic pathways of UPR through certain regulators. Thus, BiP and 14-3-3ζ were selected as the candidate targets to enhance cell death and apoptosis. First, cisplatin resistance was induced and determined by MTT assay and qPCR in MCF-7 cells. Then, the apoptosis axis of UPR was activated by knocking down either BiP or 14-3-3ζ and overactivated by co-knockdown of BiP and 14-3-3ζ. Apoptosis assays were performed using flow cytometry, TUNEL assays utilized confocal microscopy followed by western blot analysis and caspase-3 and JNK activities were investigated to assess the outcomes. Finally, an autophagy assay followed by western blotting was performed to study the effects of co-knockdown genes on cell autophagy in the presence and absence of cisplatin. The present data indicated the enhancement of cisplatin sensitivity in MCF-7 cells co-knocked down in BiP and 14-3-3ζ compared with either gene knockdown. Upregulation of JNK and cleaved-PARP1 protein levels as well as caspase-3 and JNK overactivation confirmed the results. A marked attenuation of autophagy and Beclin1 as well as ATG5 downregulation were detected in co-knockdown cells compared to knockdown with either BiP or 14-3-3ζ. Cisplatin sensitization of MCF-7 cells through double-knockdown of BiP and 14-3-3ζ highlights the potential of targeting UPR and autophagy factors to increase the effect of chemotherapy.