title: Ursolic acid promotes cancer cell death by inducing Atg5-dependent autophagy.
abstract: Ursolic acid (UA) has been reported to possess anticancer activities. Although some of the anticancer activities of UA have been explained by its apoptosis-inducing properties, the mechanisms underlying its anticancer actions are largely unknown. We have found that UA-activated autophagy induced cytotoxicity and reduced tumor growth of cervical cancer cells TC-1 in a concentration-dependent manner. UA did not induce apoptosis of TC-1 cells in vitro as determined by annexin V/propidium iodide staining, DNA fragmentation, and Western blot analysis of the apoptosis-related proteins. We found that UA increased punctate staining of light chain 3 (LC3), which is an autophagy marker. LC3II, the processed form of LC3I which is formed during the formation of double membranes, was induced by UA treatment. These results were further confirmed by transmission electron microscopy. Wortmannin, an inhibitor of autophagy, and a small interfering RNA (siRNA) for autophagy-related genes (Atg5) reduced LC3II and simultaneously increased the survival of TC-1 cells treated with UA. We also found that LC3II was significantly reduced and that survival was increased in Atg5-/- mouse embryonic fibroblast (MEF) cells compared to Atg5+/+ MEF cells under UA treatment. However, silencing BECN1 by siRNA affected neither the expression of LC3II nor the survival of TC-1 cells under UA treatment. These results suggest that autophagy is a major mechanism by which UA kills TC-1 cells. It is Atg5 rather than BECN1 that plays a crucial role in UA-induced autophagic cell death in TC-1 cells. The activation of autophagy by UA may become a potential cancer therapeutic strategy complementing the apoptosis-based therapies. Furthermore, regulation of Atg5 may improve the efficacy of UA in cancer treatment.
authors.affiliation: Department of Human Anatomy, Guangzhou Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: Shuilong
authors.initials: S
authors.lastname: Leng
authors.forename: Yanli
authors.initials: Y
authors.lastname: Hao
authors.forename: Daobing
authors.initials: D
authors.lastname: Du
authors.forename: Shanyan
authors.initials: S
authors.lastname: Xie
authors.forename: Lepeng
authors.initials: L
authors.lastname: Hong
authors.forename: Haigang
authors.initials: H
authors.lastname: Gu
authors.forename: Xiao
authors.initials: X
authors.lastname: Zhu
authors.forename: Jinfang
authors.initials: J
authors.lastname: Zhang
authors.forename: Daping
authors.initials: D
authors.lastname: Fan
authors.forename: Hsiang-fu
authors.initials: HF
authors.lastname: Kung
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000502:physiology; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D005260:Female; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D014315:Triterpenes / Q000494:pharmacology*; D000097245:Ursolic Acid
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D014315:Triterpenes; D000097245:Ursolic Acid; C502778:ATG5 protein, human; C491997:BECN1 protein, human
keywords: Atg5; TC-1; apoptosis; autophagy; ursolic acid