Mycobacterium tuberculosis Infection Induces HDAC1-Mediated Suppression of IL-12B Gene Expression in Macrophages.

Aneesh Chandran,Sathish Mundayoor,Cecil Antony,Krishnamurthy Natarajan,R Ajay Kumar,Leny Jose

doi:10.3389/fcimb.2015.00090

Abstract

Downregulation of host gene expression is one of the many strategies employed by intracellular pathogens such as Mycobacterium tuberculosis (MTB) to survive inside the macrophages and cause disease. The underlying molecular mechanism behind the downregulation of host defense gene expression is largely unknown. In this study we explored the role of histone deacetylation in macrophages in response to infection by virulent MTB H37Rv in manipulating host gene expression. We show a significant increase in the levels of HDAC1 with a concomitant and marked reduction in the levels of histone H3-acetylation in macrophages containing live, but not killed, virulent MTB. Additionally, we show that HDAC1 is recruited to the promoter of IL-12B in macrophages infected with live, virulent MTB, and the subsequent hypoacetylation of histone H3 suppresses the expression of this gene which plays a key role in initiating Th1 responses. By inhibiting immunologically relevant kinases, and by knockdown of crucial transcriptional regulators, we demonstrate that protein kinase-A (PKA), CREB, and c-Jun play an important role in regulating HDAC1 level in live MTB-infected macrophages. By chromatin immunoprecipitation (ChIP) analysis, we prove that HDAC1 expression is positively regulated by the recruitment of c-Jun to its promoter. Knockdown of HDAC1 in macrophages significantly reduced the survival of intracellular MTB. These observations indicate a novel HDAC1-mediated epigenetic modification induced by live, virulent MTB to subvert the immune system to survive and replicate in the host.

Highlights

Mycobacterium tuberculosis (MTB) is the causative agent of tuberculosis (TB) in humans and is responsible for approximately 1.4 million deaths a year across the world (World Health Organization, 2012)
We observed that at 12 h PI, HDAC1 and HDAC2 were marginally downregulated in macrophages infected with live, virulent MTB (Figures 1A,B) whereas at 24 h PI, the expression of HDAC1 was found to be significantly upregulated by about five-fold (Figure 1C), and no marked change was observed in HDAC2 expression (Figure 1D) when compared to uninfected macrophages and those infected with heat-killed MTB
To compare HDAC1 at the protein level, we carried out immunocytochemical imaging and observed that at 12 h, the fluorescence signal for HDAC1 from macrophages infected with live, virulent MTB was equal to that from macrophages infected with heat-killed MTB, but lower than that from uninfected macrophages (Figure 2A)

Summary

Introduction

Mycobacterium tuberculosis (MTB) is the causative agent of tuberculosis (TB) in humans and is responsible for approximately 1.4 million deaths a year across the world (World Health Organization, 2012). A fundamental step in eukaryotic gene expression and repression is the exposure or concealment of regulatory DNA sequences to transcriptional regulators These two processes are dependent on highly specific, MTB-Induced HDAC1 Suppresses Immune Responses reversible covalent post-translational modifications of histones by chromatin modifying enzymes, or on physical rearrangement of nucleosomes by chromatin remodeling factors. The status of acetylation of histones plays a key role in gene expression and is maintained by two classes of enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs) (Garcia-Garcia et al, 2009a) Chromatin modifications such as acetylation, methylation, and phosphorylation of histones are employed by intracellular pathogens to survive and cause disease in their host. A number of host genes, many of which are implicated in the production of molecules involved in host immune responses, are positively or negatively regulated by MTB upon infection (van Crevel et al, 2002; Hossain and Norazmi, 2013)

Methods

Results

Conclusion