The aim of this study was to elucidate the bioactive components and anti-tumor mechanism of poplar propolis extract obtained from North China (CP) in human hepatocellular carcinoma HepG2 cells in vitro.

Cell viability and proliferation were measured by SRB assay and EdU proliferation test kit, respectively. Cell migration was evaluated by scratching test. Reactive oxygen species (ROS) production and mitochondrial membrane potential were investigated with the fluorescent probes, DCHF and JC-1, respectively. The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were inspected by measurement kits. Apoptosis was assessed by acridine orange (AO) and Hoechst 33258 staining. Levels of Bax, Bcl-2, caspase 9, caspase 3, PARP, MMP-2, MMP-9, PI3K/p-PI3K, AKT/p-AKT, p38MAPK/p-p38 MAPK, ERK/p-ERK, LATS2, YAP, TAZ and TEAD1 were assessed by western blotting, respectively.

The bioactive components of CP inhibiting HepG2 cells were mainly flavonoids, and esters. CP induced HepG2 apoptosis through a mitochondrial-dependent intrinsic pathway with elevated the levels of cleaved PARP, cleaved caspase 3, and Bax and decreased the expressions of Bcl-2 and procaspase 9. It seemed that CP triggered apoptosis by activation of the p38 MAPK and inactivation of p-ERK. More importantly, we found that CP suppressed the Hippo pathway, leading to inactivation of YAP/TAZ and TEAD1 and inhibition of PI3K/AKT signaling molecules.

CP exerted excellent anti-proliferation and pro-apoptosis actions in HepG2 cells by inactivation of the loop between the Hippo/YAP and PI3K/AKT pathways, and may be a promising therapy for HCC.