The enhancement of propyl gallate-induced apoptosis in HeLa cells by a proteasome inhibitor MG132

Propyl gallate (PG) used in processed food and medicinal preparations has been shown to induce cell death in normal and cancer cells. The inhibition of proteasome function has emerged as a useful strategy to maneuver apoptosis. Here, we investigated the combined effects of PG and MG132 (a proteasome inhibitor) on He La cells in relation to cell growth, cell death, reactive oxygen species (ROS) and glutathione (GSH). PG induced growth inhibition and apoptosis in He La cells, accompanied by the loss of mitochondrial membrane potential (MMP; Delta Psi(m)), activation of caspase 3 and PARP cleavage. The levels of ROS and GSH depletion were increased in PG-treated He La cells. MG132 intensified apoptosis and PARP cleavage in PG-treated He La cells. MG132 also increased ROS levels including mitochondrial O-2(center dot-), MMP (Delta Psi(m)) loss and GSH depletion in PG-treated He La cells. PG induced a G1 phase arrest of the cell cycle in He La cells, which was significantly prevented by MG132. MG132 alone inhibited He La cell growth via inducing the cell cycle arrests and triggering apoptosis. Conclusively, the inhibition of proteasome by MG132 plays a role as an enhancement factor in PG-induced apoptosis of He La cells via increasing ROS levels and GSH depletion.