Fig. 4

CD26 is important for apigenin (API)-modulated motility and positively correlates with invasiveness of non-small cell lung cancer (NSCLC) cells. a Changes in expressions of different proteases in CL1–5 cells following 24 h of treatment with API. b CL1–5 cells (upper panel) were treated with various concentrations of API or H1975, and A549 cells (lower panel) were treated with 40 μM API for 24 h, after which a Western blot analysis was performed. Quantitative results of indicated proteins were adjusted to β-actin protein levels. c NSCLC cells were treated with 40 μM API for 24 h and then subjected to an RT-PCR to analyze CD26 mRNA expression. d Upper panel, protein and mRNA levels of CD26 in NSCLC cell lines. Lower panel, quantitative results of CD26 protein and mRNA levels which were respectively normalized to β-actin and GAPDH levels. e In vitro invasive abilities of NSCLC cell lines. Quantitative results by counting invaded cells in a 200× field. Values are presented as the mean ± SD of three independent experiments. Scare bar, 200 μm. f Correlations between CD26 protein expression levels and the invasiveness of NSCLC cell lines. Spearman correlation coefficient = 0.773; p = 0.042. g A549, CL1–5, and H1975 cells were transiently transfected with CD26-specific siRNA or control siRNA and subjected to invasion assays. Left panel, Western blot analysis of CD26 expression. Right panel, CD26-specific siRNA suppresses the invasive abilities of NSCLC cells. Quantitative results by counting invaded cells in a 100× field. Multiples of differences are presented as the mean ± SD of three independent experiments. * p < 0.05, compared to the control group. Scare bar, 500 μm. h Invasive ability in CL1–0 cells which were transiently transfected with a vector control (CL1–0/Neo) or pENTER-CD26 (CL1–0/CD26) followed by API or vehicle treatment for an additional 24 h. Quantitative results by counting invaded cells in a 100× field. Values are presented as the mean ± SD of three independent experiments. ** p < 0.01, compared to the vehicle groups. Scare bar, 500 μm. i Kaplan-Meier analysis of CD26 gene expression in lung cancer tissues. The lung cancer dataset was retrieved from TCGA