p90RSK Activation Promotes Epithelial-Mesenchymal Transition in Cisplatin-Treated Triple-Negative Breast Cancer Cells

ABSTRACT

p90 ribosomal S6 kinase (p90RSK), one of the downstream effectors in ERK1/2 pathways, shows high expression in human breast cancer tissues. However, its role in breast cancer development and drug resistance is not fully understood. Here, we demonstrate that Cis-DDP treatment failed to increase cytotoxicity in MDA-MB-231 cells compared to MCF-7 cells and p90RSK activation was involved in Cis-DDP-resistance to MDA-MB-231 cells. In the study, we found that inhibition of p90RSK expression or activation using a small interfering RNA (siRNA) or dominant-negative kinase mutant (DN-p90RSK) plasmid overexpression increased Cis-DDP-induced cytotoxicity of MDA-MB-231 cells, respectively. Mechanistically, we found that Cis-DDP resistance was associated with up-regulation of epithelial growth factor (EGF) expression and EGF treatment induced cancer survival signaling pathway including activation of ERK1/2, p90RSK, and Akt. We also examined the expression of epithelial-mesenchymal transition (EMT)-associated proteins using a reverse transition-quantitative PCR analysis. Cis-DDP treatment induced EMT by increasing the expression levels of N-cadherin, Snail, and Twist, while decreasing the expression levels of E-cadherin. Furthermore, we examined the epithelial marker, Zonula occludens-1 (ZO-1) using immunofluorescence analysis and found that Cis-DDP-inhibited ZO-1 expression was recovered by p90RSK deactivated condition. Therefore, we conclude that Cis-DDP resistance is involved in EMT via regulating the EGF-mediated p90RSK signaling pathway in MDA-MB-231 cells.