SUMMARY Activation of the TLR4 signaling pathway by lipopoly-saccharide (LPS) leads to induction of both inflammatory and interferon-stimulated genes, but the mechanisms through which these coordinately activated transcriptional programs are balanced to promote an optimal innate immune response remain poorly understood. In a genome-wide small interfering RNA (siRNA) screen of the LPS-induced tumor necrosis factor α (TNF-α) response in macrophages, we identify the interferon-stimulated protein IFIT1 as a negative regulator of the inflammatory gene program. Transcriptional profiling further identifies a positive regulatory role for IFIT1 in type I interferon expression, implicating IFIT1 as a reciprocal modulator of LPS-induced gene classes. We demonstrate that these effects of IFIT1 are mediated through modulation of a Sin3A-HDAC2 transcriptional regulatory complex at LPS-induced gene loci. Beyond the well-studied role of cytosolic IFIT1 in restricting viral replication, our data demonstrate a function for nuclear IFIT1 in differential transcriptional regulation of separate branches of the LPS-induced gene program.

All living things on this planet interact in one way or another with other living things. We use different terms to describe the interactions between two different species. If both species benefit from interacting with each other, that is, if each species relies on the other one for its well-being, then the relationship is called mutualism. In contrast, antagonism is the term used to describe a relationship that benefits only one of the species, while causing harm to the other one. In this article, we discuss a specific type of antagonism called parasitism. We will provide an overview of the diversity of parasitic species, discuss their role in major tropical diseases, and highlight the importance of the study of parasites to the medical field.

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Activation of the TLR4 signaling pathway by LPS leads to activation of both inflammatory and interferon stimulated genes, however the mechanisms through which these coordinately activated transcriptional programs are balanced to promote an optimal innate immune response remains poorly understood. In a genome-wide siRNA screen of the LPS-induced TNF-a response in macrophages, we identified the interferon-stimulated protein IFIT1 as a negative regulator of the inflammatory gene program. Transcriptional profiling further identified an unexpected positive regulatory role for IFIT1 in type I interferon expression, implicating IFIT1 as a reciprocal modulator of LPS-induced inflammatory and interferon gene expression. We demonstrate that these effects of IFIT1 are mediated through modulation of a Sin3a-HDAC2 transcriptional regulatory complex at LPS-induced gene loci. Beyond the well-studied role of cytosolic IFIT1 in restricting viral replication, our data demonstrate an unappreciated function for nuclear IFIT1 in differential transcriptional regulation of separate branches of the LPS-induced gene program. IFIT1 depletion led to a significant increase in the replication of B. cenocepacia. Prior treatment of IFIT1 depleted cells with recombinant IFN-β reversed the enhanced replication of B. cenocepacia, indicating a role for autocrine IFN-β in controlling B. cenocepacia infection and a requirement for IFIT1 in interferon induction in response to bacterial infection. We also observed reduced expression of IFNβ1 in response to viral and bacterial infection in IFIT1 depleted cells, suggesting a broad role for IFIT1 in supporting IFNβ1 expression.

Objective Toxoplasma gondii is a ubiquitous parasite of medical and veterinary importance; however, there exists no cure for chronic toxoplasmosis. Metabolic enzymes required for the production and maintenance of tissue cysts represent promising targets for novel therapies. Here, we use reverse genetics to investigate the role of Toxoplasma phosphoglucomutase 1, PGM1, in Toxoplasma growth and cystogenesis. Results We found that disruption of pgm1 did not significantly affect Toxoplasma intracellular growth and the lytic cycle. pgm1-defective parasites could differentiate into bradyzoites and produced cysts containing amylopectin in vitro. However, cysts produced in the absence of pgm1 were significantly smaller than wildtype. Together, our findings suggest that PGM1 is dispensable for in vitro growth but contributes to optimal Toxoplasma cyst development in vitro, thereby necessitating further investigation into the function of this enzyme in Toxoplasma persistence in its host.