UBC Theses and Dissertations
Molecular analysis of Mycobacterium tuberculosis infection of human macrophages : the role of Protein tyrosine phosphatase A Poirier, Valérie
To survive in the human host macrophage, Mycobacterium tuberculosis, the etiological agent of Tuberculosis, infects human macrophages and inhibits two key cellular events required for the elimination of invading organisms; phagosome acidification and fusion with lysosomes. This is partially dependent on Protein tyrosine phosphatase A (PtpA) secreted into the cytosol of the macrophage. PtpA first disrupts phagosome acidification by binding to subunit H of the proton pump, and second, inhibits phagosome-lysosome fusion by dephosphorylating and inactivating the membrane fusion regulator, hVPS33B. The ability of M. tuberculosis to actively interfere with host trafficking events allows this pathogen to replicate and persist inside the macrophage and prevent antigen presentation required to initiate an adaptive immune response. In this work, we explored the global macrophage’s response to infection emphasizing on PtpA’s role in this process. We analyzed the macrophage global proteomic responses and focused on the activity of signalling pathways by determining the phosphorylation status of host proteins upon infection with M. tuberculosis strains. We found that PtpA affects the macrophage’s response by modulating various proteins involved in RNA metabolism, immunity and defence, and cellular respiration pathways. We further show that PtpA promotes M. tuberculosis survival by dephosphorylating the host kinase GSK3α on amino acid Y²⁷⁹ leading to inhibition of GSK3α and arrest of macrophage apoptosis. GSK3α has pro- and anti-apoptotic activities and dephosphorylation of Y²⁷⁹ inhibits its ability to initiate apoptosis. In this regard, activation of the host apoptosis executioner, caspase-3, is blocked in M. tuberculosis-infected macrophages compared to cells infected with ΔptpA mutant strain. Taken together, these findings reveal one of the long-sought effectors behind the inhibition of apoptosis of the host by virulent M. tuberculosis. Moreover, we are the first to simultaneously determine proteome-wide protein expression levels of human macrophages infected with M. tuberculosis and outline molecular signatures of the global and PtpA-dependent proteomic patterns of macrophages during infection. We have now established that PtpA significantly contributes to successful infection and survival of M. tuberculosis inside the macrophage. Understanding the mechanism of action of PtpA during M. tuberculosis infection may lead to the development of novel anti-mycobacterial drugs.
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