Impaired chromatin remodelling at STAT1-regulated promoters leads to global unresponsiveness of Toxoplasma gondii-infected macrophages to IFN-γ

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. © 2012 lang et al.