Mycobacterium tuberculosis Transfer RNA Induces IL-12p70 via Synergistic Activation of Pattern Recognition Receptors within a Cell Network.

Upon recognition of a microbial pathogen, the innate and adaptive immune systems are linked to generate a cell-mediated immune response against the foreign invader. The culture filtrate of Mycobacterium tuberculosis contains ligands, such as M. tuberculosis tRNA, that activate the innate immune response and secreted Ags recognized by T cells to drive adaptive immune responses. In this study, bioinformatics analysis of gene-expression profiles derived from human PBMCs treated with distinct microbial ligands identified a mycobacterial tRNA-induced innate immune network resulting in the robust production of IL-12p70, a cytokine required to instruct an adaptive Th1 response for host defense against intracellular bacteria. As validated by functional studies, this pathway contained a feed-forward loop, whereby the early production of IL-18, type I IFNs, and IL-12p70 primed NK cells to respond to IL-18 and produce IFN-γ, enhancing further production of IL-12p70. Mechanistically, tRNA activates TLR3 and TLR8, and this synergistic induction of IL-12p70 was recapitulated by the addition of a specific TLR8 agonist with a TLR3 ligand to PBMCs. These data indicate that M. tuberculosis tRNA activates a gene network involving the integration of multiple innate signals, including types I and II IFNs, as well as distinct cell types to induce IL-12p70.

Oxidation of phosphorothioate DNA modifications leads to lethal genomic instability.

Genomic modification by sulfur in the form of phosphorothioate (PT) is widespread among prokaryotes, including human pathogens. Apart from its physiological functions, PT sulfur has redox and nucleophilic properties that suggest effects on bacterial fitness in stressful environments. Here we show that PTs are dynamic and labile DNA modifications that cause genomic instability during oxidative stress. In experiments involving isotopic labeling coupled with mass spectrometry, we observed sulfur replacement in PTs at a rate of ∼2% h-1 in unstressed Escherichia coli and Salmonella enterica. Whereas PT levels were unaffected by exposure to hydrogen peroxide (H2O2) or hypochlorous acid (HOCl), PT turnover increased to 3.8-10% h-1 after HOCl treatment and was unchanged by H2O2, consistent with the repair of HOCl-induced sulfur damage. PT-dependent sensitivity to HOCl extended to cytotoxicity and DNA strand breaks, which occurred at HOCl doses that were orders of magnitude lower than the corresponding doses of H2O2. The genotoxicity of HOCl in PT-containing bacteria suggests reduced fitness in competition with HOCl-producing organisms and during infections in humans.

Quantitative analysis of ribonucleoside modifications in tRNA by HPLC-coupled mass spectrometry.

Post-transcriptional modification of RNA is an important determinant of RNA quality control, translational efficiency, RNA-protein interactions and stress response. This is illustrated by the observation of toxicant-specific changes in the spectrum of tRNA modifications in a stress-response mechanism involving selective translation of codon-biased mRNA for crucial proteins. To facilitate systems-level studies of RNA modifications, we developed a liquid chromatography-mass spectrometry (LC-MS) technique for the quantitative analysis of modified ribonucleosides in tRNA. The protocol includes tRNA purification by HPLC, enzymatic hydrolysis, reversed-phase HPLC resolution of the ribonucleosides, and identification and quantification of individual ribonucleosides by LC-MS via dynamic multiple reaction monitoring (DMRM). In this approach, the relative proportions of modified ribonucleosides are quantified in several micrograms of tRNA in a 15-min LC-MS run. This protocol can be modified to analyze other types of RNA by modifying the steps for RNA purification as appropriate. By comparison, traditional methods for detecting modified ribonucleosides are labor- and time-intensive, they require larger RNA quantities, they are modification-specific or require radioactive labeling.

A system for exposing molecules and cells to biologically relevant and accurately controlled steady-state concentrations of nitric oxide and oxygen.

Nitric oxide (NO) plays key roles in cell signaling and physiology, with diverse functions mediated by NO concentrations varying over three orders-of-magnitude. In spite of this critical concentration dependence, current approaches to NO delivery in vitro result in biologically irrelevant and poorly controlled levels, with hyperoxic conditions imposed by ambient air. To solve these problems, we developed a system for controlled delivery of NO and O(2) over large concentration ranges to mimic biological conditions. Here we describe the fabrication, operation and calibration of the delivery system. We then describe applications for delivery of NO and O(2) into cell culture media, with a comparison of experimental results and predictions from mass transfer models that predict the steady-state levels of various NO-derived reactive species. We also determined that components of culture media do not affect the steady-state levels of NO or O(2) in the device. This system provides critical control of NO delivery for in vitro models of NO biology and chemistry.