Influence of osteopontin silencing on survival and migration of lung cancer cells

Osteopontin (OPN) is a multifunctional protein overexpressed in many cancers and is involved in tumor progression and metastasis. In lung cancer, elevated OPN expression is associated with an unfavorable prognosis. Therefore, inhibition of OPN is an attractive approach for improving survival. We used siRNA to specifically downregulate OPN expression in A549 lung cancer cells. OPN silencing was evaluated with quantitative reverse transcriptase polymerase chain reaction (RT-PCR) for mRNA levels and with Western blotting for protein levels. Effects on cell proliferation were measured by cell counting. The influence on tumor cell migration was detected using a modified Boyden chamber. Changes in cell cycle distribution were assessed by flow cytometry. Using the colony formation assay, we determined changes in radiosensitivity. A specific and effective downregulation of OPN expression was detected in both RNA and protein levels. Cell proliferation and cell migration were significantly reduced by OPN silencing after 24 h and the effects were further increased by the addition of irradiation. The cell cycle distribution showed a reduction in S phase and an increase in cells arrested in both G(0)/G(1) and G(2)/M phases. Specific enhancement of radiosensitivity was clearly shown after OPN knockdown. The combination of OPN silencing and irradiation showed a synergistic effect leading to reduced cell survival.