Inhibition of cytoplasmic GSK-3β increases cisplatin resistance through activation of Wnt/β-catenin signaling in A549/DDP cells

Cisplatin-based chemotherapy is recommended as the first-line therapy for advanced non-small cell lung cancer (NSCLC). However, acquired cisplatin resistance is ubiquitous in patients with NSCLC, but the molecular mechanism of such resistance remains ambiguous. The present study sought to examine the role of the Wnt/β-catenin signaling pathway in cisplatin resistance by assessing the phosphorylation and subcellular distribution of GSK-3β in a human lung adenocarcinoma cell line, A549, and its cisplatin-resistant subline, A549/DDP. Total GSK-3β, phosphorylated GSK-3βser9 and phosphorylated GSK-3βtyr216 in cytoplasmic and nuclear fractions of A549/DDP and A549 cells were examined by western blot analysis. The regulation of cisplatin resistance, apoptosis, β-catenin and survivin protein expression by inhibition of cytoplasmic GSK-3β were determined by MTT assay, flow cytometry analysis, immunofluorescence technique and western blot analysis. In the present study, cytoplasmic levels of p-GSK-3βser9 were significantly increased in A549/DDP cells as compared with A549 cells (P < 0.01), and these levels were further increased by cisplatin treatment in A549/DDP cells (P < 0.01). In contrast, cytoplasmic levels of p-GSK-3βser9 were reduced in A549 cells after treatment with cisplatin (P < 0.01). However, cytoplasmic levels of p-GSK-3βtyr216 were significantly decreased in A549/DDP cells as compared with A549 cells (P < 0.01), and these levels were further decreased by cisplatin treatment in A549/DDP cells (P < 0.01). Conversely, cytoplasmic levels of p-GSK-3βtyr216 were raised in A549 cells after treatment with cisplatin (P < 0.01). Analysis of downstream effectors of the Wnt/β-catenin signaling pathway revealed upregulation of β-catenin and survivin expression in A549/DDP cells treated with cisplatin as compared to untreated cells. In A549 cells, cisplatin treatment decreased the expression of β-catenin and survivin. Furthermore, phosphorylation of GSK-3β at serine 9 by LiCl and transient interference of GSK-3β by siRNA increased β-catenin and survivin protein expression in A549/DDP cells. Low exogenous and endogenous cytoplasmic GSK-3β expression enhanced the IC50 and inhibited apoptosis. In conclusion, activation of the Wnt/β-catenin signaling pathway and upregulated survivin expression due to cytoplasmic GSK-3β inhibition might lead to cisplatin resistance in NSCLC.