title: Mammalian target of Rapamycin inhibition and mycobacterial survival are uncoupled in murine macrophages.
abstract: BACKGROUND
  Autophagy is a cellular response to intracellular pathogens including mycobacteria and is induced by the direct inhibitors of mammalian target of Rapamycin (mTOR), a major negative regulator of autophagy. Autophagy induction by mTOR inhibition (mTOR dependent autophagy), through chemical means or starvation, leads to mycobacterial killing in infected cells. However, previous work by our group has shown that mycobacterial infection of macrophages naturally induces both autophagy and mammalian target of Rapamycin (mTOR) activity (mTOR independent autophagy). In the current work, we further explore the relationship between mTOR activity and mycobacterial killing in macrophages.
  
  
  RESULTS
  While low concentrations of the mTOR inhibitors, Rapamycin, Torin 1, and Torin 2, can effectively reduce or block mTOR activity in response to lipopolysaccharides (LPS) or mycobacteria, higher concentrations (10 uM) are required to observe Mycobacterium smegmatis killing. The growth of M. smegmatis was also inhibited by high concentrations of Rapamycin in LC3B and ATG5 deficient bone marrow derived macrophages, suggesting that non-autophagic mechanisms might contribute to killing at high doses. Since mycobacterial killing could be observed only at fairly high concentrations of the mTOR inhibitors, exceeding doses necessary to inhibit mTOR, we hypothesized that high doses of Rapamycin, the most commonly utilized mTOR inhibitor for inducing autophagic killing, may exert a direct bactericidal effect on the mycobacteria. Although a short-term treatment of mycobacteria with Rapamycin did not substantially affect mycobacterial growth, a long-term exposure to Rapamycin could impact mycobacterial growth in vitro in select species.
  
  
  CONCLUSIONS
  This data, coupled with previous work from our laboratory, further indicates that autophagy induction by mTOR inhibition is an artificial means to increase mycobacterial killing and masks more relevant endogenous autophagic biochemistry that needs to be understood.
authors: Alfred J
authors: AJ
authors: Zullo
authors: Kristen L
authors: KL
authors: Jurcic Smith
authors: Human Vaccine Institute and Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA. sunhee.lee@duke.edu.
authors: Sunhee
authors: S
authors: Lee
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects; D000071187:Autophagy-Related Protein 5; D002460:Cell Line; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D020102:Mycobacterium smegmatis / Q000187:drug effects*; D009287:Naphthyridines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: C553294:1-(4-(4-propionylpiperazin-1-yl)-3-(trifluoromethyl)phenyl)-9-(quinolin-3-yl)benzo(h)(1,6)naphthyridin-2(1H)-one; C558529:9-(6-aminopyridin-3-yl)-1-(3-(trifluoromethyl)phenyl)benzo(h)(1,6)naphthyridin-2(1H)-one; D000900:Anti-Bacterial Agents; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D009287:Naphthyridines; D047428:Protein Kinase Inhibitors; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus