Pleurotus nebrodensis polysaccharide(PN50G) evokes A549 cell apoptosis by the ROS/AMPK/PI3K/AKT/mTOR pathway to suppress tumor growth

Abstract

Since the strong antineoplastic potential against A549 cells of Pleurotus nebrodensis polysaccharide (PN50G) in vitro has been proven previously, the definitive mechanism of PN50G-induced apoptosis in A549 cells in vivo was further investigated. All the results indicated that PN50G significantly suppressed tumor growth in A549 tumor-bearing mice. Tumor cells treated with PN50G were arrested in the G0/G1 phase, and marked changes in the expression of cell cycle-related proteins, including cyclin D1, cyclin A and cyclin B1, were observed. Moreover, western blotting anaylsis indicated that PN50G triggered the mitochondrial apoptotic pathway, for an increased Bax/Bcl-2 ratio, release of cytochrome c, cleavage of caspase-3 and PRPP in A549 tumor cells were observed. And the decrease in the expression of the translation related protein P70S6K was observed, because PN50G activated AMPK phosphorylation, but inhibited PI3K/AKT phosphorylation and suppressed the activation of the mammalian target of rapamycin (mTOR) induced by PN50G. In vivo imaging was performed on tumor-bearing mice, and the results indicated that PN50G significantly increased the intracellular levels of reactive oxygen species (ROS). Furthermore, it indicated that PN50G promoted the protein expression of Beclin 1 and LC-3 in a dose-dependent manner. All the results suggested that PN50G-mediated apoptosis and autophagy of A549 tumor cells in vivo mainly involved in the mitochondrial pathway and the AMPK/PI3K/mTOR pathway.