Osteopontin-c isoform inhibition modulates ovarian cancer cell cisplatin resistance, viability and plasticity

Osteopontin (OPN) is upregulated in several types of tumor and has been associated with chemoresistance. However, the contribution of OPN splicing isoforms (OPN-SIs) to chemoresistance requires further investigation. The present study aimed to evaluate the expression patterns of each tested OPN-SI in cisplatin (CDDP)-resistant ovarian carcinoma cell lines, focusing on the role of the OPN-c isoform (OPNc) in drug resistance. ACRP ovarian cancer cells resistant to CDDP, as well as their parental cell line A2780, were used. Analyses of the transcriptional expression of OPN-SIs, epithelial-mesenchymal transition (EMT) markers and EMT-related cytokines were performed using reverse transcription-quantitative PCR. OPNc was silenced in ACRP cells using anti-OPNc DNA oligomers and stably overexpressed by transfecting A2780 cells with a mammalian expression vector containing the full length OPNc cDNA. Functional assays were performed to determine cell proliferation, viability and colony formation. The results demonstrated that among the three tested OPN-SIs, OPNc was the most upregulated transcript in the ACRP cells compared with the parental A2780 cells. In addition, the expression levels of P-glycoprotein multidrug transporter were upregulated in CDDP-resistant ACRP cells compared with those in A2780 cells. OPNc knockdown sensitized ACRP cells to CDDP treatment and downregulated P-gp expression levels compared with those in the negative control group. Additionally, silencing of OPNc impaired cell proliferative and colony formation abilities, as well as reversed the expression levels of EMT markers and EMT-related cytokines compared with those in the negative control cells. Notably, although stable OPNc overexpression resulted in increased A2780 cell proliferation, it notably increased CDDP sensitivity compared with that in the cells transfected with a control vector. These results suggested that OPNc silencing may represent a putative approach to sensitize resistant ovarian cancer cells to chemotherapeutic agents.