title: Beclin 1-mediated autophagy in hepatocellular carcinoma cells: implication in anticancer efficiency of oroxylin A via inhibition of mTOR signaling.
abstract: Autophagy is a tightly-regulated catabolic process that involves the degradation of intracellular components via lysosomes. Although the pivotal role of autophagy in cell growth, development, and homeostasis has been well understood, its function in cancer prevention and intervention remains to be delineated. The aim of this study was to investigate the function and mechanism of autophagy induced by oroxylin A, a natural mono-flavonoid extracted from Scutellariae radix. We found for the first time that oroxylin A induced Beclin 1-mediated autophagy in human hepatocellular carcinoma HepG2 cells. Time-lapse video microscopy and western blotting studies showed that treatment of cells with 80 μM oroxylin A resulted in the conversion of water soluble MAP-LC3 (LC3-I) to the lipidated and autophagosome-associated form (LC3-II) after 12hours; then autophagosome-lysosome fusion and lysosome degradation after 24 hours was required in oroxylin A-mediated cell death. This induction was associated with the suppressing of PI3K-PTEN-Akt-mTOR signaling pathway by oroxylin A. Our results also showed that autophagy took place before noticeable apoptosis can be observed. It was further demonstrated that oroxylin A-triggered autophagy contributed to cell death using over-expression of autophagy-related gene (Atg5 and Atg7) and inhibition of autophagy by siBeclin 1 and 3-methyladenine (3-MA). In vivo study, oroxylin A inhibited xenograft tumor growth and induced obvious autophagy in tumors. Taken together, we conclude that oroxylin A exhibits autophagy-mediated antitumor activity in a dose and time-dependent manner in vivo and in vitro. These findings define and support a novel function of autophagy in promoting death of hepatocellular carcinoma cells.
authors.affiliation: State Key Laboratory of Natural Medicines, Jiangsu Key Laboratory of Carcinogenesis and Intervention (China Pharmaceutical University), Nanjing, People's Republic of China.
authors.forename: Meijuan
authors.initials: M
authors.lastname: Zou
authors.forename: Na
authors.initials: N
authors.lastname: Lu
authors.forename: Chen
authors.initials: C
authors.lastname: Hu
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Yajing
authors.initials: Y
authors.lastname: Sun
authors.forename: Xiaotang
authors.initials: X
authors.lastname: Wang
authors.forename: Qidong
authors.initials: Q
authors.lastname: You
authors.forename: Cong
authors.initials: C
authors.lastname: Gu
authors.forename: Tao
authors.initials: T
authors.lastname: Xi
authors.forename: Qinglong
authors.initials: Q
authors.lastname: Guo
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D001343:Autophagy / Q000187:drug effects*; D000071186:Beclin-1; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D005419:Flavonoids / Q000494:pharmacology*; D056945:Hep G2 Cells; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013329:Structure-Activity Relationship; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; D005419:Flavonoids; D008565:Membrane Proteins; C080669:5,7-dihydroxy-6-methoxy-2-phenylchromen-4-one; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases