Antitumor effects of Tubeimoside-1 in NCI-H1299 cells are mediated by microRNA-126-5p-induced inactivation of VEGF-A/VEGFR-2/ERK signaling pathway

Tubeimoside-1 (TBMS1), a triterpenoid saponin isolated from the tuber of Bolbostemma paniculatum (Maxim) Franquet, serves an universal suppressive role in multiple cancer types, including lung cancer. However, the mechanism involved in non-small cell lung cancer (NSCLC) cells by which TBMS1 elicits its antitumor effects is not yet completely understood. The present study indicated that 10 µmol/l TBMS1 significantly enhanced apoptosis and notably blocked the migration and invasion of NCI-H1299 cells. These effects were reversed following transfection with miR-126-5p inhibitor into TBMS1-treated NCI-H1299 cells. Vascular endothelial growth factor-A (VEGF-A) is a target gene for miR-126-5p. Notably, results suggested that the downregulated VEGF-A and VEGFR-2 in TBMS1-treated NCI-H1299 cells were upregulated after inhibiting miR-126-5p, and overexpression of VEGF-A or VEGFR-2 could significantly reduce apoptosis and promote the migration and invasion of TBMS1-treated NCI-H1299 cells. Furthermore, TBMS1 combined with TBHQ (an ERK activator) dramatically suppressed TBMS1-induced apoptosis and stimulated TBMS1-reduced migration and invasion in NCI-H1299 cells, suggesting that TBMS1 inhibits the ERK signaling pathway and represses the growth and metastasis of NCI-H1299 cells. Further study demonstrated that either inhibiting miR-126-5p or overexpressing VEGF-A and VEGFR-2 in TBMS1-treated NCI-H1299 cells elevated the mRNA expression levels and phosphorylation levels of MEK1, as well as ERK. To conclude, TBMS1 increases miR-126-5p expression, whereas overexpressing miR-126-5p inactivates VEGF-A/VEGFR-2/ERK signaling pathway, which ultimately actuates the pro-apoptotic and anti-metastatic effects in NCI-H1299 cells. Therefore, the present findings provide a theoretical foundation for TBMS1 as a potential candidate in NSCLC treatment.