title: Mechanisms involved in spontaneous and Viscum album agglutinin-I-induced human neutrophil apoptosis: Viscum album agglutinin-I accelerates the loss of antiapoptotic Mcl-1 expression and the degradation of cytoskeletal paxillin and vimentin proteins via caspases.
abstract: Viscum album agglutinin-I (VAA-I) is a plant lectin that possesses interesting potential therapeutic properties and immunomodulatory activities. We have recently found that VAA-I is a potent inducer of human neutrophil apoptosis, but the mechanism(s) involved require further elucidation. In this study, we found that VAA-I alters mitochondrial transmembrane potential and increases intracellular levels of reactive oxygen species (ROS). Despite these observations, treatment with the mitochondrial stabilizer, bongkrekic acid, or with catalase, known to degrade H(2)O(2), fails to reverse VAA-I-induced apoptosis. Moreover, VAA-I was found to induce apoptosis in PLB-985 cells deficient in gp91(phox), indicating that the lectin acts via an ROS-independent mechanism. Pretreatment of neutrophils with brefeldin A, an inhibitor of vesicular transport, was found to reverse VAA-I-induced apoptosis. Protein expression of Mcl-1 was decreased by VAA-I. The role of caspases in the degradation of cytoskeletal proteins during both spontaneous and VAA-I-induced neutrophil apoptosis was also investigated. Paxillin and vimentin were markedly degraded by VAA-I when compared with neutrophils that undergo spontaneous apoptosis, but not vinculin or alpha- and beta-tubulin. Caspases were involved in cytoskeletal protein degradation because preincubation with the pan-caspase inhibitor N-benzyloxycarbonyl-V-A-D-O-methylfluoromethyl ketone was found to reverse protein cleavage. We conclude that VAA-I needs to be internalized to mediate apoptosis and that its activity is not dependent on a cell surface receptor-mediated pathway. Also, we conclude that VAA-I induces apoptosis by ROS-independent and Mcl-1-dependent mechanisms and that caspases are involved in cytoskeletal protein degradation in both spontaneous and VAA-I-induced neutrophil apoptosis.
authors.affiliation: Institut National de la Recherche Scientifique-Institut Armand-Frappier/Santé Humaine, Universite du Quebec, 245 boulevard Hymus, Pointe-Claire, Quebec, Canada H9R 1G6.
authors.forename: Valérie
authors.initials: V
authors.lastname: Lavastre
authors.forename: Martin
authors.initials: M
authors.lastname: Pelletier
authors.forename: Reinhard
authors.initials: R
authors.lastname: Saller
authors.forename: Katarina
authors.initials: K
authors.lastname: Hostanska
authors.forename: Denis
authors.initials: D
authors.lastname: Girard
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D020126:Brefeldin A / Q000494:pharmacology; D020169:Caspases / Q000502:physiology*; D003598:Cytoskeletal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D007382:Intermediate Filaments / Q000187:drug effects / Q000378:metabolism; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D014784:Mistletoe; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D051419:Paxillin; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D028321:Plant Preparations; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species / Q000378:metabolism; D054788:Ribosome Inactivating Proteins; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D014746:Vimentin / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D003598:Cytoskeletal Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; C496061:PXN protein, human; D051419:Paxillin; D010750:Phosphoproteins; D028321:Plant Preparations; D010940:Plant Proteins; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D054790:Ribosome Inactivating Proteins, Type 2; D014118:Toxins, Biological; C488865:VAA-I protein, Viscum album; D014746:Vimentin; C009674:ribosome inactivating protein, Viscum; D020126:Brefeldin A; D054788:Ribosome Inactivating Proteins; D020169:Caspases