Abstract
Intracellular pathogens including the apicomplexan and opportunistic parasite Toxoplasma gondii profoundly modify their host cells in order to establish infection. We have shown previously that intracellular T. gondii inhibit up-regulation of regulatory and effector functions in murine macrophages (MΦ) stimulated with interferon (IFN)-γ, which is the cytokine crucial for controlling the parasites' replication. Using genome-wide transcriptome analysis we show herein that infection with T. gondii leads to global unresponsiveness of murine macrophages to IFN-γ. More than 61% and 89% of the transcripts, which were induced or repressed by IFN-γ in non-infected MΦ, respectively, were not altered after stimulation of T. gondii-infected cells with IFN-γ. These genes are involved in a variety of biological processes, which are mostly but not exclusively related to immune responses. Analyses of the underlying mechanisms revealed that IFN-γ-triggered nuclear translocation of STAT1 still occurred in Toxoplasma-infected MΦ. However, STAT1 bound aberrantly to oligonucleotides containing the IFN-γ-responsive gamma-activated site (GAS) consensus sequence. Conversely, IFN-γ did not induce formation of active GAS-STAT1 complexes in nuclear extracts from infected MΦ. Mass spectrometry of protein complexes bound to GAS oligonucleotides showed that T. gondii-infected MΦ are unable to recruit non-muscle actin to IFN-γ-responsive DNA sequences, which appeared to be independent of stimulation with IFN-γ and of STAT1 binding. IFN-γ-induced recruitment of BRG-1 and acetylation of core histones at the IFN-γ-regulated CIITA promoter IV, but not β-actin was diminished by >90% in Toxoplasma-infected MΦ as compared to non-infected control cells. Remarkably, treatment with histone deacetylase inhibitors restored the ability of infected macrophages to express the IFN-γ regulated genes H2-A/E and CIITA. Taken together, these results indicate that Toxoplasma-infected MΦ are unable to respond to IFN-γ due to disturbed chromatin remodelling, but can be rescued using histone deacetylase inhibitors.
Highlights
Toxoplasma gondii is a protozoan parasite that is highly prevalent in humans and warm-blooded animals throughout the world
We and others have previously shown that intracellular Toxoplasma parasites inhibit expression of several IFN-c-regulated genes including those encoding the major histocompatibility complex (MHC) class II, inducible nitric oxide synthase, p47 GTPases and monokine induced by gamma interferon (MIG) in macrophages (MW) [15,16,17,18,19,20]
In order to determine the global effect of T. gondii infection on IFN-c responsiveness of macrophages, we performed whole genome microarray analyses of murine bone marrow-derived MW (BMMW), infected or not with T. gondii, and stimulated or not with IFN-c (Figure 1A)
Summary
Toxoplasma gondii is a protozoan parasite that is highly prevalent in humans and warm-blooded animals throughout the world. We and others have previously shown that intracellular Toxoplasma parasites inhibit expression of several IFN-c-regulated genes including those encoding the major histocompatibility complex (MHC) class II, inducible nitric oxide synthase (iNOS), p47 GTPases and monokine induced by gamma interferon (MIG) in macrophages (MW) [15,16,17,18,19,20]. IFN-c-regulated gene expression is impaired in other cell types infected with Toxoplasma such as astrocytes and microglia [21] as well as human fibroblasts [22]. Interference with MW function may be relevant, because these cells are critical for the course of infection.
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