mTOR-independent autophagy counteracts apoptosis in herpes simplex virus type 1-infected U251 glioma cells

• DOI: 10.1016/j.micinf.2013.04.012
• Publication Date: 2013-05-10T10:30:55Z
• Authors: Gordana Tovilovic; Biljana Ristic; Marina Siljic; Valentina Nikolic; Tamara Kravic-Ste...; Marija Dulovic; Marina Milenkovic; Aleksandra Knezevic; Mihajlo Bosnjak; Vladimir Bumbasir...; Maja Stanojevic; Vladimir Trajkovic
• Keywords: 0301 basic medicine; 570; 0303 health sciences; AMP-activated protein kinase; Cell Survival; Akt; TOR Serine-Threonine Kinases; 610; Apoptosis; Herpesvirus 1, Human; HSV-1; Cell Line; 3. Good health; 03 medical and health sciences; Gene Expression Regulation; Host-Pathogen Interactions; mTOR; Autophagy; Humans; Neuroglia

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.