Identification of autophagy inhibiting factors of Mycobacterium tuberculosis by high throughput loss of function screening
Emily J Strong1, Kristen L. Jurcic Smith2, Neeraj K. Saini3, Tony W. Ng3, Steven A. Porcelli3, 4 and Sunhee Lee1, 2, 3
1Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA; 2Human Vaccine Institute and Department of Medicine, Duke University, Durham, North Carolina, USA; 3Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA; 4Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA; 5Department of Molecular Genetics and Microbiology, Duke University, Durham, North Carolina, USA
The interaction of host cells with mycobacteria is complex and can lead to multiple outcomes ranging from bacterial clearance to progressive or latent infection. Autophagy is recognized as one component of host cell responses that has an essential role in both innate and adaptive immunity to intracellular bacteria. Many microbes, including M. tuberculosis, have evolved mechanisms to evade or exploit autophagy, but the precise mechanisms are mostly unknown1. Through a loss of function screening of a transposon mutagenized M. tuberculosis library, we identified 16 genes that contribute to autophagy inhibition, six of which encoded proteins belonging to the PE/PPE family2. We hypothesize these PE/PPE factors mediate autophagy evasion in order to ensure survival within the host. Their expression in M. smegmatis and deletion in M. tuberculosis confirmed these PE/PPE proteins’ function in inhibiting infection-induced autophagy resulting in increased intracellular bacterial burden in vitro. These PE/PPE effects were associated with increased activity of the mammalian target of rapamycin (mTOR) and decreased production of TNF-α and IL-1β. The differential upregulation of these PE/PPE proteins in response to different stress conditions was observed, which may be advantageous for M. tuberculosis by modulating host/microbe interactions under various conditions. Our findings demonstrated that multiple M. tuberculosis PE/PPE proteins are involved in inhibiting autophagy during infection of host phagocytes and may provide strategic targets developing therapeutics or vaccines against tuberculosis.
1 Saini et al (2016) https://doi.org/10.1038/nmicrobiol.2016.133
2 Strong et al (2020) https://doi.org/a0.1128/IAI.00269-20 (In-Press)
Funding: NIAID 1RO1AII27711-01