title: Proton-shuttling lichen compound usnic acid affects mitochondrial and lysosomal function in cancer cells.
abstract: The lichen compound usnic acid (UA) is a lipophilic weak acid that acts as a proton shuttle and causes loss of mitochondrial inner membrane potential. In the current study we show that UA treatment induced the formation of autophagosomes in human cancer cells, but had minimal effects on normal human fibroblasts. However, autophagic flux was incomplete, degradation of autophagosomal content did not occur and acidification was defective. UA-treated cells showed reduced ATP levels and activation of AMP kinase as well as signs of cellular stress. UA is thus likely to trigger autophagosome formation both by energy depletion and stress conditions. Our findings indicate that the H(+)-shuttling effect of UA operates not only in mitochondria as previously shown, but also in lysosomes, and have implications for therapeutic manipulation of autophagy and pH-determined drug distribution.
authors.affiliation: Faculty of Medicine, University of Iceland, Reykjavik, Iceland.
authors.forename: Margret
authors.initials: M
authors.lastname: Bessadottir
authors.forename: Mar
authors.initials: M
authors.lastname: Egilsson
authors.forename: Eydis
authors.initials: E
authors.lastname: Einarsdottir
authors.forename: Iris H
authors.initials: IH
authors.lastname: Magnusdottir
authors.forename: Margret H
authors.initials: MH
authors.lastname: Ogmundsdottir
authors.forename: Sesselja
authors.initials: S
authors.lastname: Omarsdottir
authors.forename: Helga M
authors.initials: HM
authors.lastname: Ogmundsdottir
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000263:Adenylate Kinase / Q000378:metabolism; D001572:Benzofurans / Q000494:pharmacology*; D004354:Drug Screening Assays, Antitumor; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008011:Lichens / Q000737:chemistry*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009369:Neoplasms / Q000378:metabolism* / Q000473:pathology; D010588:Phagosomes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D011522:Protons; D015398:Signal Transduction / Q000187:drug effects; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D001572:Benzofurans; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D011522:Protons; C073339:usnic acid; D000255:Adenosine Triphosphate; D000263:Adenylate Kinase