Extracellular M. tuberculosis DNA Targets Bacteria for Autophagy by Activating the Host DNA-Sensing Pathway

Robert O. Watson, et al. Cell 150, 803–815, August 17, 2012

Speaker: Cheng-Lun Hsu (徐政倫)            )                              Time: 13:00~14:00, Dec. 12, 2012

Commentator: Dr. I Hsiu Huang (黃一修 博士)  )            Place: Room 601

Abstract:

Autophagy has been implicated in acute M. tuberculosis restriction by macrophage. Previous studies showed that M. tuberculosis extracellular DNA is exposed to the host cytosol during macrophage infection, activating TBK1 to elicit production of type I interferon., However,but howautophagy targets and limits M. tuberculosis replication is still unclear. To determine whether M. tuberculosis is targeted by autophagy, BMDM derived from GFP-LC3 mice was infected with wild-type M. tuberculosis and ESX-1 mutants strain, Δesat-6., and The mutantΔesat-6 failed tocolocalize with LC3 and ATG12. Next, they examined which autophagy receptor is required for autophagy targeting., using shRNA to Kknockdown p62 or NDP52 in GFP-LC3 Raw cells showed the reduced co-localization of infected with M. tuberculosis andto see the cololization rate betweenGFP-LC3 and M. tuberculosis reduced. Because both p62 and NDP52 could be recruited to ubiquitinated substrates, BMDMs immunostaining ed with anti-Ub Ab were was performed to determine whether M. tuberculosis is colocalized with host ubiquitins, which could coat allowing M. tuberculosis for coated with Ub targeted to autophagosome. In addition, Here the author suggested that DNA sensing is necessary to activate Ub-mediated autophagy. targeting by using transfected Transfection of dsDNA into GFP-LC3 RAW cells led to see the increased colocalization of rate between dsDNA, and Ub, ATG12, LAMP-1, andor NDP52. Because STING is involved in DNA sensing pathway, Accordingly, the author tested whether STING is also required for Ub-mediated autophagy, and Sting-/-STING-/- or knockdown NDP52 knockdown lead to lowered thecolocalization between LC3/Ub with DNA. Accordingly, Increased bacterial survival rate in Sting-/- , and Atg5-/- BMDMs showed the increased survival rate of M. tuberculosis, suggesting promoted that STING and ATG5 are required for targeting -dependent delivery of M. tuberculosis toautophagosomey lysosome indeed limit bacterial replication. To this end, the author performed low-dose aerosol infections of Atg5-/- mice and found that Atg5-/- mice were extremely sensitive to M. tuberculosis, suggesting that ATG5-mediated autophagy in monocytes plays a major role in eliciting innate immune response to M. tuberculosis infection.

Reference:

1.      Paolo S. Manzanillo. et al. Mycobacterium Tuberculosis Activates the DNA-Dependent Cytosolic Surveillance Pathway within Macrophages. Cell Host & Microbe 11, 469–480, May 17, 2012

2.      Jennifer Smith. Et al. Evidence for Pore Formation in Host Cell Membranes by ESX-1-Secreted ESAT-6 and Its Role in Mycobacterium marinum Escape from the Vacuole. INFECTION AND IMMUNITY, Vol. 76, No. 12, p. 5478–5487, Dec, 2008.