title: HIF-1α-dependent autophagy protects HeLa cells from fenretinide (4-HPR)-induced apoptosis in hypoxia.
abstract: Novel therapeutic strategies are needed to address and to solve the emerging problem of hypoxia-induced resistance to anticancer drugs. N-(4-Hydroxyphenyl)retinamide (4-HPR) exhibits potent anticancer and chemopreventive activities, but its inefficiency under hypoxia, through undetermined mechanisms, may contribute to its lack of activity in clinical trials. In this study, we showed that under normoxia, 4-HPR resulted in apoptosis and ultimate cell death; in contrast, under hypoxia, autophagy was preferentially induced by 4-HPR at an equivalent concentration, accompanied by microtubule associated protein light-chain 3 (LC3) conversion and acidic vesicular organelle formation. Under hypoxia, autophagy inhibition by 3-methyladenine or chloroquine significantly enhanced apoptosis and decreased cell viability in 4-HPR-exposed cells, indicating that autophagy prevents cancer cell death and presumably leads to hypoxia-induced resistance to 4-HPR. Importantly, knockdown of hypoxia-inducible factor-1α (HIF-1α) inhibited autophagy but promoted 4-HPR-induced apoptosis under hypoxia, demonstrating its critical role as a mediator of this protective autophagy. The present study provides the first evidence supporting the hypothesis that autophagy and apoptosis can be differentially induced by 4-HPR under different oxygen conditions; mediated by HIF-1α, 4-HPR-induced autophagy under hypoxia confers a survival advantage to HeLa cells, protects them from 4-HPR-induced death signals, and thus contributes to their hypoxia-induced resistance to this agent. Our data suggest that autophagy inhibition is a potential alternative strategy to overcome hypoxia-induced resistance to 4-HPR and enhance the anticancer activities of this agent.
authors.affiliation: Institute of Pharmacology and Toxicology, College of Pharmaceutical Sciences, Zhejiang University, #388 Yuhangtang Road, Hangzhou, Zhejiang 310058, China.
authors.forename: Xiao-Wen
authors.initials: XW
authors.lastname: Liu
authors.forename: Yi
authors.initials: Y
authors.lastname: Su
authors.forename: Hong
authors.initials: H
authors.lastname: Zhu
authors.forename: Ji
authors.initials: J
authors.lastname: Cao
authors.forename: Wan-Jing
authors.initials: WJ
authors.lastname: Ding
authors.forename: Yu-Chen
authors.initials: YC
authors.lastname: Zhao
authors.forename: Qiao-Jun
authors.initials: QJ
authors.lastname: He
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D016923:Cell Death; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D005260:Female; D017313:Fenretinide / Q000378:metabolism / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D017313:Fenretinide