PTEN bridges protective autophagy and apoptosis induced by DNA damage mediated by reactive oxygen species(ROS)in response to cucurbitacin B in hepatocellular carcinoma cells

OBJECTIVE Reactive oxygen species(ROS)mediated both apoptosis and protective autophagy in response to natural products while the detailed mechanisms remain unclear.Cucurbitacin B(Cuc B),a natural tetracyclic triterpene,induced both protective autophagy and apoptosis mediated by ROS.This study was designed to explore the mechanism of Cuc B-induced apoptosis and autophagy in hepatocellular carcinoma BEL-7402cells.METHODS AND RESULTS Cuc B decreased cell viability in concentration-and time-dependent manners.Cuc B caused long comet tails and increased expression ofγHA2X,phosphorylation of ATM/ATR,and Chk1/Chk2.This DNA damage response was inhibited by KU55933 and caffeine.Cuc B induced autophagy as evidenced by monodansylcadaverine(MDC)staining,increased expression of LC3Ⅱ,phosphorylated ULK1and decreased expression of phosphorylated AKT,mT OR.Cuc B induced apoptosis mediated by Bcl-2 family proteins and caspase activation.Furthermore,Cuc B induced ROS formation,which was inhibited by N-acetylL-cysteine(NAC).NAC pretreatment dramatical y reversed Cuc B-induced DNA damage,autophagy,and apoptosis.Cuc B-induced apoptosis was reversed by NAC but enhanced by 3-methyladenine(3-MA),chloroquine(CQ),and silencing phosphatase and tensin homolog(PTEN).3-MA and CQ showed no effect on Cuc B-induced DNA damage.In addition,Cuc B increased PTEN phosphorylation.Silence PTEN restored Cuc B-induced autophagic protein expressions without affecting DNA damage.CONCLUSION Cuc B induced DNA damage,apoptosis and protective autophagy mediated by ROS.PTEN activation in response to DNA damage bridged apoptosis and pro-survival autophagy.These observations provide insights for better understanding the crosstalk between apoptosis and autophagy.