FUNCTIONAL AND MECHANISTIC ANALYSES OF HISTONE DEACETYLASES (HDAC3) IN INFLAMMATORY GENE CONTROL

In this study, we investigated the role of individual class I histone deacetylases (HDACs) namely Hdac1, -2 and -3 using retroviral RNA interference to define their specific contribution to control an inducible gene expression program, namely inflammatory gene expression in 3T3 fibroblasts and primary macrophages. In addition to genes showing the expected transcriptional de-repression, we observed 8/20 genes in a test set being down-regulated following individual HDAC depletion. The requirement for HDACs function in gene induction as opposed to the more commonly observed role as transcriptional repressors may either underlie an indirect consequence of impaired HDAC mediated repression or a direct involvement of Hdac1 and Hdac3 in inducible gene activity. Therefore, we extended both the in vitro and in vivo analyses using conditional knockout (KO) mice. Genetic deletion of Hdac3 indicates that Hdac3 is required for the activation of 45% of the lipopolysaccharides (LPS)-induced genes. Global analysis of histone H4 acetylation showed that transcriptional down-regulation in Hdac3-/- cells did not correlate with increased histone acetylation, suggesting the possible involvement of indirect or secondary effects. We found that the LPS-inducible, Hdac3-dependent genes include a large group of interferon-β (IFNβ)-inducible genes (eg. IP10, Irf1) and another group (eg. Il-6) that may be regulated by AP-1 family proteins. In addition, gene expression analyses identified interferon-signalling pathway as being impaired in Hdac3-/- cells. Basal and inducible Ifnβ transcriptions require cJun/AP-1 and the decreased amount of AP-1 family proteins in Hdac3-/- cells may explain the lack of Ifnβ activation and the increased acetylation in genomic regions.