Osteopontin isoform c promotes the survival of cisplatin-treated NSCLC cells involving NFATc2-mediated suppression on calcium-induced ROS levels

Tumor microenvironment (TME) critically contributed to the malignant progression of transformed cells and the chemical responses to chemotherapy reagents. Osteopontin (OPN) is a secretory onco-protein with several splicing isoforms, all of which were known to regulate tumor growth and able to alter cell-cell or cell-TME communication. In this study using conditioned medium from the culture of OPNc (exon 4 excluded shorter form of OPN) overexpressing cells, we found that the survival of NSCLC cells treated with cisplatin was increased, where reduction of apoptosis by OPNc was associated with the activation of cellular calcium signals and subsequent translocation of nuclear factor of activated T cells c2 (NFATc2). The results revealed a mechanism of OPN and downstream signal for tumor cells to survive in chemo-stressed TME, which emphasized the importance of secretory proteins in alternative splicing isoforms. Our study not only demonstrated the importance of OPN neutralization for anti-tumor effects, but also implied that modulation in calcium/NFATc2/ROS axis could be a novel approach for improving the long-term outcome of NSCLC treatment. Overall design: Total RNA were obtained from A549 cells transfected with plasmid of NFATc2 or NFATc2M (deletion in the DNA binding domain) and induced with the conditioned medium from OPNc expressing cells. RNA-seq analysis was performed to find differentially expressed gene between NFATc2 and NFATc2M groups.