Proteomic analysis of selective cytotoxic anticancer properties of flavonoids isolated from Citrus platymamma on A549 human lung cancer cells

Abstract

Citrus platymamma Hort. ex Tanaka (Byungkyul in Korean) has been used in Korean folk medicine for the treatment of inflammatory disorders and cancer. However, the molecular mechanism underlying the anticancer properties of flavonoids isolated from C. platymamma (FCP) remains to be elucidated. Therefore, the present study attempted to identify the key proteins, which may be important in the anticancer effects of FCP on A549 cells using a proteomic approach. FCP showed a potent cytotoxic effect on the A549 human lung cancer cells, however, it had no effect on WI-38 human fetal lung fibroblasts at the same concentrations. Furthermore, 15 differentially expressed protein spots (spot intensities 2-fold change; P<0.05) were obtained from comparative proteome analysis of two-dimensional gel electrophoresis maps of the control (untreated) and FCP-treated A549 cells. Finally, eight differentially expressed proteins, one of which was upregulated and seven of which were downregulated, were successfully identified using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry and peptide mass fingerprinting analysis. Specifically, proteins involved in signal transduction were significantly downregulated, including annexin A1 (ANXA1) and ANXA4, whereas 14-3-3 epsilon was upregulated. Cytoskeletal proteins, including cofilin-1 (CFL1), cytokeratin 8 (KRT8) and KRT79, and molecular chaperones/heat shock proteins, including endoplasmin, were downregulated. Proteins involved in protein metabolism, namely elongation factor Ts were also downregulated. Consistent with results of the proteome analysis, the immunoblotting results showed that 14-3-3 epsilon was upregulated, whereas CFL1, ANXA4 and KRT8 were downregulated in the FCP-treated A549 cells. The majority of the proteins were involved in tumor growth, cell cycle, apoptosis, migration and signal transduction. These findings provide novel insights into the molecular mechanisms underlying FCP-induced anticancer effects on A549 cells.