title: mTOR-independent autophagy counteracts apoptosis in herpes simplex virus type 1-infected U251 glioma cells.
abstract: We investigated the role of autophagy, a stress-inducible lysosomal self-digestion of cellular components, in modulation of herpes simplex virus type 1 (HSV-1)-triggered death of U251 human glioma cells. HSV-1 caused apoptotic death in U251 cells, characterized by phosphatidylserine externalization, caspase activation and DNA fragmentation. HSV-1-induced apoptosis was associated with the induction of autophagic response, as confirmed by the conversion of cytosolic LC3-I to autophagosome-associated LC3-II, increase in intracellular acidification, presence of autophagic vesicles, and increase in proteolysis of the selective autophagic target p62. HSV-1-triggered autophagy was not associated with the significant increase in the expression of proautophagic protein beclin-1 or downregulation of the major autophagy suppressor mammalian target of rapamycin (mTOR). Moreover, the phosphorylation of mTOR and its direct substrate p70 S6 kinase was augmented by HSV-1 infection, while the mTOR stimulator Akt and inhibitor AMPK-activated protein kinase (AMPK) were accordingly activated and suppressed, respectively. An shRNA-mediated knockdown of the autophagy-essential LC3β, as well as pharmacological inhibition of autophagy with bafilomycin A1 or 3-methyladenine, markedly accelerated apoptotic changes and ensuing cell death in HSV-1-infected glioma cells. These data indicate that AMPK/Akt/mTOR-independent autophagy could prolong survival of HSV-1-infected U251 glioma cells by counteracting the coinciding apoptotic response.
authors.affiliation: Institute for Biological Research, University of Belgrade, Despota Stefana Blvd.142, 11000 Belgrade, Serbia.
authors.forename: Gordana
authors.initials: G
authors.lastname: Tovilovic
authors.forename: Biljana
authors.initials: B
authors.lastname: Ristic
authors.forename: Marina
authors.initials: M
authors.lastname: Siljic
authors.forename: Valentina
authors.initials: V
authors.lastname: Nikolic
authors.forename: Tamara
authors.initials: T
authors.lastname: Kravic-Stevovic
authors.forename: Marija
authors.initials: M
authors.lastname: Dulovic
authors.forename: Marina
authors.initials: M
authors.lastname: Milenkovic
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Knezevic
authors.forename: Mihajlo
authors.initials: M
authors.lastname: Bosnjak
authors.forename: Vladimir
authors.initials: V
authors.lastname: Bumbasirevic
authors.forename: Maja
authors.initials: M
authors.lastname: Stanojevic
authors.forename: Vladimir
authors.initials: V
authors.lastname: Trajkovic
mesh_terms: D017209:Apoptosis; D001343:Autophagy; D002460:Cell Line; D002470:Cell Survival; D005786:Gene Expression Regulation; D018259:Herpesvirus 1, Human / Q000276:immunology* / Q000472:pathogenicity; D054884:Host-Pathogen Interactions; D006801:Humans; D009457:Neuroglia / Q000276:immunology* / Q000821:virology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases
keywords: AMP-activated protein kinase; Akt; Apoptosis; Autophagy; HSV-1; mTOR