Lung cancer cell lines (A549, CL1-5, H23, H460, and PC13), a nasopharyngeal carcinoma cell line (NPC-TW01), an oral cancer cell line (SAS), and human normal nasal mucosal epithelial (NNM) cells were used in this study. The NNM cells were a primary culture derived from a nasal polyp [27] . The A549, H23, and H460 lines were obtained from the American Type Culture Collection. The CL1-5 line was established by Chu et al. [47] . The A549, CL1-5, H23 and H460 cells were grown in RPMI 1640 (Gibco, CA, USA) containing 10% fetal bovine serum (FBS, Gibco, CA, USA) at 37uC in a 5% CO 2 incubator. The NPC-TW01, PC13, SAS, and NNM cells were grown in DMEM (Gibco, CA, USA) containing 10% FBS at 37uC in a 10% CO 2 incubator.