GAIT complex formation and Mycobacterium tuberculosis

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PROJECT SUMMARY Tuberculosis (TB) remains a major health concern, especially with the global emergence of drug resistant Mycobacterium tuberculosis (Mtb) strains. The World Health Organization estimated that nearly one third of the world's population is currently infected with Mtb, making this bacillus one of the most successful pathogens on earth. A key factor that contributes to the success of Mtb is its ability to survive inside macrophage, the host cell that has evolved the ability to capture and kill invading microbes. Following phagocytosis, Mtb must continuously monitor and appropriately respond to host bactericidal activities in order to establish a safe haven inside the macrophage's phagosome. The process by which Mtb survive inside macrophages is complex and still poorly understood. In this application, we propose to study a novel virulence mechanism by which Mtb hijacks the Interferon Gamma Activated Inhibitor of Translation (GAIT), a translational regulatory mechanism normally triggered in human macrophages by host kinases to prevent excessive reactions to interferon-gamma (IFNγ), a pro-inflammatory cytokine produced by T cells to activate antimicrobial activities in macrophages. Our preliminary data support the hypothesis that the eukaryotic-type Ser/Thr protein kinase G (PknG) from Mtb affects the phosphorylation status of the 60S-ribosomal subunit protein L13a, and the Glu/Pro-tRNA synthetase, EPRS, leading to the assembly of GAIT in an IFNγ-independent manner. Experiments in Specific Aim 1 are aimed to determine (i) the kinetics of GAIT assembly in response to mycobacterial infection, (ii) the role of PknG in Mtb-induced GAIT assembly and (iii) the impact of PknG kinase activity on Mtb growth inside human primary macrophages. Furthermore, experiments in Specific Aim 2 are designed to assess the impact of Mtb's PknG-induced GAIT assembly on the bacillus' intracellular survival. Together, these proposed experiments will elucidate the biological relevance of GAIT assembly for Mtb's survival in human macrophages, and establish the biological importance of Mtb's ability, through its PknG, to hijack GAIT assembly. This molecular tactic may allow Mtb to render the macrophage intracellular environment less anti- inflammatory and antimycobacterial, to promote its own survival. Understanding such an important virulence mechanism may help to develop novel therapeutic strategies that boost the innate anti-Mtb activities of our immune system.