Divergent roles of histone deacetylase 6 (HDAC6) and histone deacetylase 11 (HDAC11) on the transcriptional regulation of IL10 in antigen presenting cells

Highlights

• HDAC6 interacts with HDAC11 in antigen presenting cells.

• HDAC6 is a positive regulator of IL10 production.

• Nuclear role of HDAC6 as transcriptional regulator.

• HDACs as modulators of the APC plasticity to trigger T-cell activation.

Abstract

The anti-inflammatory cytokine IL-10 is a key modulator of immune responses. A better understanding of the regulation of this cytokine offers the possibility of tipping the balance of the immune response toward either tolerance, or enhanced immune responses. Histone deacetylases (HDACs) have been widely described as negative regulators of transcriptional regulation, and in this context, the primarily nuclear protein HDAC11 was shown to repress il-10 gene transcriptional activity in antigen-presenting cells (APCs). Here we report that another HDAC, HDAC6, primarily a cytoplasmic protein, associates with HDAC11 and modulates the expression of IL-10 as a transcriptional activator. To our knowledge, this is the first demonstration of two different HDACs being recruited to the same gene promoter to dictate divergent transcriptional responses. This dynamic interaction results in dynamic changes in the expression of IL-10 and might help to explain the intrinsic plasticity of the APC to determine T-cell activation versus T-cell tolerance.

Introduction

Antigen presenting cells (APCs) play a central role in the induction of T-cell activation as well as T-cell tolerance (Rabinovich et al., 2007). IL-10, a cytokine with immunosuppressive properties, has been shown to be critical in the generation of APCs with tolerogenic properties (Grütz, 2005, Wakkach et al., 2003) and in the prevention of self-tissue damage (Li and Flavell, 2008, Murai et al., 2009, Rubtsov et al., 2008). As such, a better understanding of the regulation of this cytokine in APCs might unveil novel molecular targets to tip the balance of an immune response towards either tolerance or immune activation.

A major regulatory mechanism for IL-10 production occurs at the transcriptional level, and it is dictated by negative and positive feedback loops involving several transcriptional regulators and signaling pathways that are cell-type specific. Important transcriptional regulators of il-10 include STAT3, Sp1, AP-1, NFκB, C/EBPβ, and GATA3 (Saraiva and O’Garra, 2010). While some of them are required for transcriptional activation of the il-10 gene (STAT3, Sp1) others (PU.1) exert an opposite effect. The molecular mechanism(s) dictating the balance between these divergent pathways remain to be fully elucidated (Saraiva and O’Garra, 2010).

Recent studies have demonstrated that in addition to genetic regulation, epigenetic modifications of specific genes influences the inflammatory status of the APC and T-cell activation versus T-cell tolerance (Medzhitov and Horng, 2009, Woan et al., 2012). Histone acetyl transferases (HATs) and histone deacetylases (HDACs) mediate chromatin modification by acetylation and deacetylation of histone tails respectively, a well-known mechanism of transcriptional regulation in the inflammatory response (Foster et al., 2007). Along these lines, important changes in chromatin have been observed during the activation of the il-10 gene promoter, including acetylation of specific promoter regions (Villagra et al., 2009, Zhang et al., 2006).

HDACs are enzymes that are recruited by co-repressors or by multi-protein transcriptional complexes to gene promoters where they regulate gene expression through chromatin modifications (de Ruijter et al., 2003, Yang and Seto, 2008). Recently, by over-expressing or knocking down specific HDACs in murine and human APCs we found that among all the members of this family of enzymes, the primarily nuclear HDAC11 (Gao et al., 2002) is recruited to the il-10 gene promoter to negatively regulate its expression (Villagra et al., 2009). Those earlier studies also suggested that another member of this family, HDAC6, which is primarily found in the cytoplasm, might exert an opposite effect to that of HDAC11 upon il-10 gene transcriptional activity. These divergent effects led us to explore whether a “cross-talk” or interaction might exist between these two HDACs. Here we have shown that unlike HDAC11, which is a transcriptional repressor of il-10, HDAC6 is required for il-10 gene transcriptional activation in APCs. Furthermore, we have found that these two HDACs physically interact with each other in the cytoplasm and nuclei of APCs. The additional demonstration that il-10 gene expression is abrogated in the absence of HDAC6, but not rescued upon additional knockdown of HDAC11, points to HDAC6 as the “driver” within this molecular complex and as a such a potential therapeutic target to disrupt the tolerogenic properties of IL-10 on the APC.