Effect of STAT-3-mediated non-dependent VEGFR-2 pathway on radiosensitivity of non-small cell lung cancer cells

Abstract

Objective To investigate the effect of signal transducer and activator of transcription-3(STAT-3)-mediated non-dependent vascular endothelial growth factor receptor-2(VEGFR-2) pathway on the radiosensitivity of non-small cell lung cancer (NSCLC) cells and its possible mechanism. Methods NSCLC cells were divided into control group, apatinib (VEGFR-2 inhibitor) group, apatinib+ S3I-201(STAT-3 inhibitor) group, radiation (RT) group, RT+ apatinib group, and RT+ apatinib+ S3I-201 group. Q-PCR and Western blot were used to measure the mRNA and protein expression of VEGFR-2, STAT-3, other proteins involved in the signaling pathway, hypoxia-inducible factor 1α(HIF-1α), and cyclin D1. The cellular radiosensitivity was determined by colony-forming assay and cell apoptosis and cell cycle distribution were evaluated by flow cytometry. Results For Calu-1 cells, there was no significant difference in the expression of VEGFR-2 mRNA and STAT-3 mRNA between the apatinib group and the control group (P>0.05); the apatinib group had significantly lower expression of HIF-1α mRNA and cyclin D1 mRNA than the control group (P<0.05); the apatinib+ S3I-201 group had significantly lower mRNA and phosphorylated protein expression of VEGFR-2, STAT-3, and related downstream target proteins than the control group (F=304.54, P<0.01; F=118.99, P<0.01, F=144.34, P<0.01; F=529.66, P<0.01); compared with the control group, the apatinib+ S3I-201 group and the apatinib group showed increases in apoptosis rate and proportion of cells in G2+ M phase, and the apatinib+ S3I-201 group had significantly greater increases than the apatinib group (F=72.37, P<0.01). Compared with Calu-1 cells, the radiosensitizing effect of apatinib on A549 cells was limited (SER[sensitizer enhancement ratio]=1.39). The radiosensitizing effect of apatinib+ S3I-201 on A549 cells was significantly higher than that of apatinib (SER: 1.72 vs. 1.39, P=0.000). Conclusions The inhibition of STAT-3 can enhance the radiosensitivity of NSCLC cells. When VEGFR-2 is inhibited by apatinib, activated STAT-3 regulates the expression of cyclin D1 directly or indirectly to affect the radiosensitivity of NSCLC cells. The inhibition of VEGFR-2 and STAT-3 has a good radiosensitizing effect on NSCLC cells. Key words: Protein express; Lung meoplasms cell line; Radiosensitivity