Proteomic Analysis of the cellular responses to bioactive triterpenoid saponin astragaloside IV from Radix Astragalus in human liver cancer HepG2 cells

Abstract

Chemoprevention of oncogenic transformation is recognized as a cost-effective strategy to reduce the incidence of various cancers. Most of the chemoprevetive agents are derived from the natural resources. Radix Astragalus is one of the most important chemopreventive medicinal herbs in traditional Chinese medicine. This study was designed to investigate the biological effects of astragaloside IV, a major active triterpenoid glycoside in the herb, on the protein expression in human liver cancer HepG2 cells. Following the treatment with astragaloside IV, the protein extracts of HepG2 cells were resolved by twodimensional electrophoresis (2-DE) and visualized by silver staining. The protein spots were quantitatively compared and ranked according to the changes induced by astragaloside IV. Fifteen top up-regulated and 13 top down-regulated spots were excised from the gels and analyzed by matrix-assisted laser desorption/ionization timeof-flight mass spectrometry (MALDI-TOF-MS). Of the astragaloside IV-regulated proteins, oncogene Vav3b was suppressed up to 1.70-fold and in a dose dependent manner. Vav3 protein as the third member of oncogene Vav family is known to be involved in the regulation of several key signal transduction pathways leading to cell malignant transformation. Vav3b is only composed of the C-terminal two SH3 domains and one SH2 domain of Vav protein, suggesting an uncharacterized role in regulating cell signal transduction. Astragaloside IV-mediated regulation of Vav3b protein expression was verified by Western blot analysis using specific antibody. Thus, our results suggest that downregulation of Vav3b expression by astragaloside IV may represent a novel strategy for cancer therapy.