title: Impaired chromatin remodelling at STAT1-regulated promoters leads to global unresponsiveness of Toxoplasma gondii-infected macrophages to IFN-γ.
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.
authors.affiliation: Institute for Medical Microbiology, University Medical Center, Georg-August-University, Göttingen, Germany.
authors.forename: Christine
authors.initials: C
authors.lastname: Lang
authors.forename: Anke
authors.initials: A
authors.lastname: Hildebrandt
authors.forename: Franziska
authors.initials: F
authors.lastname: Brand
authors.forename: Lennart
authors.initials: L
authors.lastname: Opitz
authors.forename: Hassan
authors.initials: H
authors.lastname: Dihazi
authors.forename: Carsten G K
authors.initials: CG
authors.lastname: Lüder
mesh_terms: D000818:Animals; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects / Q000235:genetics*; D005260:Female; D015870:Gene Expression / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006655:Histone Deacetylases / Q000187:drug effects; D006790:Host-Parasite Interactions; D007371:Interferon-gamma / Q000494:pharmacology; D008264:Macrophages / Q000276:immunology / Q000378:metabolism* / Q000469:parasitology; D051379:Mice; D008807:Mice, Inbred BALB C; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics*; D055503:Protein Multimerization; D050794:STAT1 Transcription Factor / Q000235:genetics*; D015398:Signal Transduction / Q000187:drug effects; D014122:Toxoplasma / Q000502:physiology*; D014123:Toxoplasmosis / Q000276:immunology* / Q000469:parasitology; D059467:Transcriptome / Q000187:drug effects
chemical_list: D056572:Histone Deacetylase Inhibitors; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; D007371:Interferon-gamma; D006655:Histone Deacetylases