Approximately one-third of the world's population is infected with Mycobacterium tuberculosis (M.tb), and the World Health Organization estimates that in 2007 there were 9.27 million new cases and more than 1.7 million people died of tuberculosis. M.tb is able to establish this enormous worldwide burden of disease by subverting innate and adaptive defenses of the host. One way in which it does this is to convert the normally hostile environment of a macrophage into a niche in which it can effectively replicate. Normally during phagosome maturation, the bacterial vacuole is transformed from a comparatively inert compartment to a phagolysosome, an effective microbicidal and degradative compartment. However, a variety of mycobacterial species prevent the normal maturation of the phagosome, residing in a replicative niche that resembles an early endosome, although exactly how they do this is not clear. We hypothesize that to promote its intracellular survival M.tb secrete EsxH in order to inhibit the endosomal sorting complex required for transport (ESCRT), cellular machinery of the macrophage involved in protein trafficking. We found that the ESCRT machinery represents a major vulnerability of the cell, as it is required to control growth of non-pathogens, like Mycobacterium smegmatis, as well as of M.tb. Moreover, we identified a novel host-pathogen interaction between the M.tb protein, EsxH, and the host protein hepatocyte growth factor-regulated tyrosine kinase substrate (Hgs/Hrs), which is a component of the ESCRT machinery. In this proposal, we seek to extend our preliminary studies in order to characterize the mechanism by which ESCRT protects against bacterial infection. In addition, we will investigate the interaction between EsxH and Hgs and evaluate its importance to the outcome of infection. These studies will provide important insight into how M.tb subverts the normal anti-microbial capacity of macrophages. If we understood how M.tb does this, we might be able to improve the mycobacterial killing capacity of the infected macrophage, enabling development of novel therapeutics that have the potential to significantly shorten therapy and change the face of the global epidemic.

Public Health Relevance

The success of Mycobacterium tuberculosis (M.tb) as a pathogen is due to its ability to survive within macrophages, cells that normally eradicate bacteria. How it does this is poorly understood. We found that ESCRT, a host cell protein complex, protects macrophages against non-pathogenic mycobacteria, and we intend to characterize its role in M.tb infection. This will advance our understanding of how M.tb survives in macrophages, which might enable the creation of much needed, new therapies.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IDM-T (02))
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Jacobs, Gail G
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New York University
Internal Medicine/Medicine
Schools of Medicine
New York
United States
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Siegrist, M Sloan; Steigedal, Magnus; Ahmad, Rushdy et al. (2014) Mycobacterial Esx-3 requires multiple components for iron acquisition. MBio 5:e01073-14
Mehra, Alka; Zahra, Aleena; Thompson, Victor et al. (2013) Mycobacterium tuberculosis type VII secreted effector EsxH targets host ESCRT to impair trafficking. PLoS Pathog 9:e1003734
Philips, Jennifer A; Ernst, Joel D (2012) Tuberculosis pathogenesis and immunity. Annu Rev Pathol 7:353-84