Tryptophan Biosynthesis Protects Mycobacteria from CD4 T-Cell-Mediated Killing

“We created conditionally required gene sets as well as ranked gene lists for each condition, which allowed us to compare gene sets using the running-sum enrichment analysis in the GSEA tool (Subramanian et al., 2005).”

“…shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“…shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“In human disease, progressive CD4 T cell loss due to HIV infection also increases the risk for TB disease and death (Pawlowski et al., 2012; Selwyn et al., 1989).”

“Infection triggers host responses that sequester important compounds such as amino acids and iron (Hood and Skaar, 2012; Zhang and Rubin, 2013).”

“Mtb in particular relies upon cholesterol and fatty acid catabolism, gluconeogenesis, and the glyoxylate shunt to survive the host environment (Lee et al., 2013; Marrero et al., 2010; McKinney et al., 2000; Muñoz-Elı́as and McKinney, 2005; Pandey and Sassetti, 2008).”

“01), it also includes more than 400 newly discovered genes required for in vivo growth (Figure S2A) (Sassetti and Rubin, 2003).”

“Mtb in particular relies upon cholesterol and fatty acid catabolism, gluconeogenesis, and the glyoxylate shunt to survive the host environment (Lee et al., 2013; Marrero et al., 2010; McKinney et al., 2000; Muñoz-Elı́as and McKinney, 2005; Pandey and Sassetti, 2008).”

“Most transposon insertionsequencing techniques currently use insertion count totals summed across all sites in a gene (Goodman et al., 2009; Griffin et al., 2011).”

“…transport mechanisms (that have not been defined) or direct access to the cytoplasm through either partial or complete loss of vacuolar integrity, a model consistent with recent observations of Mtb escape into the cytoplasm (Hagedorn et al., 2009; McDonough et al., 1993; van der Wel et al., 2007).”

“The CD4-deficient MHC class II knockout (KO) mice, and other mice that lack CD4 T cells, cannot stop mycobacterial growth and rapidly succumb to disease and death (Cosgrove et al., 1991; Grusby et al., 1991; Mogues et al., 2001; Scanga et al., 2000).”

“Mtb in particular relies upon cholesterol and fatty acid catabolism, gluconeogenesis, and the glyoxylate shunt to survive the host environment (Lee et al., 2013; Marrero et al., 2010; McKinney et al., 2000; Muñoz-Elı́as and McKinney, 2005; Pandey and Sassetti, 2008).”

“Most transposon insertionsequencing techniques currently use insertion count totals summed across all sites in a gene (Goodman et al., 2009; Griffin et al., 2011).”

“The CD4-deficient MHC class II knockout (KO) mice, and other mice that lack CD4 T cells, cannot stop mycobacterial growth and rapidly succumb to disease and death (Cosgrove et al., 1991; Grusby et al., 1991; Mogues et al., 2001; Scanga et al., 2000).”

“Humans and mice generally cannot clear Mtb during infection, but both are able to limit bacterial growth, and in the case of immunocompetent humans, prevent disease (Ernst, 2012; Flynn, 2006).”

“The CD4-deficient MHC class II knockout (KO) mice, and other mice that lack CD4 T cells, cannot stop mycobacterial growth and rapidly succumb to disease and death (Cosgrove et al., 1991; Grusby et al., 1991; Mogues et al., 2001; Scanga et al., 2000).”

“As with previous reports, we observed that IFN-g alone does not measurably inhibit WT Mtb growth (Fabri et al., 2011).”

“…ability to survive host defenses is directly responsible for the large reservoir of infected people, whereas its ability to subvert bactericidal mechanisms 1296 Cell 155, 1296–1308, December 5, 2013 ª2013 Elsevier Inc. allows it to replicate in vivo and cause disease (Ehrt and Schnappinger, 2009).”

“Mtb in particular relies upon cholesterol and fatty acid catabolism, gluconeogenesis, and the glyoxylate shunt to survive the host environment (Lee et al., 2013; Marrero et al., 2010; McKinney et al., 2000; Muñoz-Elı́as and McKinney, 2005; Pandey and Sassetti, 2008).”

“Reports have shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“This could occur through specific host or bacterial transport mechanisms (that have not been defined) or direct access to the cytoplasm through either partial or complete loss of vacuolar integrity, a model consistent with recent observations of Mtb escape into the cytoplasm (Hagedorn et al., 2009; McDonough et al., 1…”

“A host of other Mtb amino acid auxotrophs are attenuated for growth in mice; it is possible that this is due to immune-driven starvation mechanisms (Hondalus et al., 2000; Pavelka et al., 2003; Price et al., 2011; Tattoli et al., 2012; Zhang and Rubin, 2013).”

“This is consistent with the reactive nitrogen species and low pH of Mtb’s in vivo niche (Ehrt and Schnappinger, 2009; Vandal et al., 2008).”

“Mtb in particular relies upon cholesterol and fatty acid catabolism, gluconeogenesis, and the glyoxylate shunt to survive the host environment (Lee et al., 2013; Marrero et al., 2010; McKinney et al., 2000; Muñoz-Elı́as and McKinney, 2005; Pandey and Sassetti, 2008).”

“Reports have shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“Humans and mice generally cannot clear Mtb during infection, but both are able to limit bacterial growth, and in the case of immunocompetent humans, prevent disease (Ernst, 2012; Flynn, 2006).”

“A host of other Mtb amino acid auxotrophs are attenuated for growth in mice; it is possible that this is due to immune-driven starvation mechanisms (Hondalus et al., 2000; Pavelka et al., 2003; Price et al., 2011; Tattoli et al., 2012; Zhang and Rubin, 2013).”

“Trp starvation, through IDO-mediated depletion of cytoplasmic pools of this amino acid, appears to be a mechanism that has the added benefit of leading to kynurenine production and prevention of immunopathology (Desvignes and Ernst, 2009).”

“An Mtb strain carrying a deletion of the trpD gene has been shown to be a Trp auxotroph (Figure 3B) (Parish, 2003; Smith et al., 2001).”

“In order to define the set of Mtb genes required for surviving the CD4 T cell response, we infected both wild-type (WT) and MHC class II KO (MHCII / ) mice with a library of Mtb transposon mutants (Zhang et al., 2012).”

“This could occur through specific host or bacterial transport mechanisms (that have not been defined) or direct access to the cytoplasm through either partial or complete loss of vacuolar integrity, a model consistent with recent observations of Mtb escape into the cytoplasm (Hagedorn et al., 2009; McDonough et al., 1…”

“We focused on anthranilate analogs, compounds that have been shown to inhibit the synthesis of quorum-sensing molecules in Pseudomonas aeruginosa that, like Trp synthesis, also have an anthranilate intermediate (Lesic et al., 2007).”

“Reports have shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“A host of other Mtb amino acid auxotrophs are attenuated for growth in mice; it is possible that this is due to immune-driven starvation mechanisms (Hondalus et al., 2000; Pavelka et al., 2003; Price et al., 2011; Tattoli et al., 2012; Zhang and Rubin, 2013).”

“Reports have shown that the Th1 subset is especially effective in limiting Mtb growth, and cytokines such as IFN-g and TNF-a are needed in some, but not all, models of CD4 T cell-mediated defenses (Bold et al., 2011; Flynn et al., 1993, 1995; Gallegos et al., 2011; Nandi and Behar, 2011; Scanga et al., 2000).”

“Infection triggers host responses that sequester important compounds such as amino acids and iron (Hood and Skaar, 2012; Zhang and Rubin, 2013).”

“Small-molecule inhibitors of Trp and other aromatic amino acid biosynthesis exist for other organisms, suggesting that certain enzymes in these pathways might be ‘‘druggable,’’ or suitable for chemical inhibition (Coggins et al., 2003).”

“One of the transcriptionally induced genes in response to IFN-g is a Trp-catabolizing enzyme: indoleamine-2,3-dioxygenase (IDO) (Alberati-Giani et al., 1997).”

“We cloned and purified bothWT and the F68I mutant form of TrpE and assayed their activity by measuring the fluorescent product, anthranilate (Baker and Crawford, 1966).”

“A host of other Mtb amino acid auxotrophs are attenuated for growth in mice; it is possible that this is due to immune-driven starvation mechanisms (Hondalus et al., 2000; Pavelka et al., 2003; Price et al., 2011; Tattoli et al., 2012; Zhang and Rubin, 2013).”

“Interestingly, the trpE deletion strains die far more rapidly than a trpD deletion (Parish, 2003).”

“IDO is thus required for IFN-g-mediated growth inhibition of Chlamydia and other Trp auxotrophic intracellular pathogens (Ibana et al., 2011; Zelante et al., 2009).”

“Some bacteria, such as Mycobacterium tuberculosis, escape CD4-mediated defense by synthesizing their own Trp under stress conditions (Zhang et al., 2013).”

“tuberculosis is able to synthesize tryptophan, and thus IFN-c-inducible activation of IDO and subsequent reduction in tryptophan availability fails to exert an anti-mycobacterial effect, whereas blockage of mycobacterial tryptophan synthesis increased the efficacy of this host defense mechanism (97).”