3,[73] which has been reported to destabilize nucleosomes.[74] A concomitant decline in H2A.Z was also observed at the promoter, particularly of the CD69 gene.[73] Enrichment of H2A.Z near the transcription start Angiogenesis inhibitor site and depletion concomitant with induction have also been reported for other inducible genes,[55, 75] the suggestion being that

incorporation of H2A.Z decreases the stability of the nucleosome. Complex programmes of transcriptional regulation orchestrate the carefully co-ordinated expression of signature immune-responsive genes in response to T-cell activation. The molecular switches that mediate such precise and intricate control have been best characterized for the key T-cell cytokine, IL-2. Given its cell-specific expression, rapid transcription response and importance in T-cell biology, IL2 is considered as a model gene for unravelling epigenetic switches. As summarized in Fig. 3, extensive analysis of the IL2 gene allows us to put forward a model of the complex multilayered hierarchy of gene regulatory processes that are likely to drive immune-responsive genes. In resting T cells, when no IL2 transcription occurs, the IL2 gene exhibits low levels of chromatin accessibility and is decorated by H3/H2A.Z mTOR inhibitor nucleosomes

with H2A.Z flanking its transcription start site.[66, 73] Moreover, silent IL2 transcription is reinforced by the repressive activity of the microRNA, mir-200c and transcription factor, Zeb-1.[21] Chromatin remodelling accompanies high levels of IL2 transcription in activated T cells and histone variant exchange takes place in the promoter regions with a loss of histone H3 and a gain of H3.3. In addition, a concomitant decline of H2A.Z levels accompanied gene induction. H3.3 carries active histone post-translational modifications such as K9ac across the IL2 gene.[73] The accessible chromatin state across the IL2 promoter in activated BCKDHB T cells exposes the binding sites for transcription

factors such as c-Rel for chromatin remodelling and Pol II to initiate IL2 expression.[48, 66, 76, 77] Transcription of IL2 is dependent on the formation of the active transcription complex with PKCθ, MSK1 and LSD1 as well as the adapter protein 14-3-3ζ with Pol II[21] and increase in the elongation marker H3K36me3.[48] Overall, as illustrated in Fig. 3, IL2 regulation perfectly depicts the multi-layered process from all levels of the chromatin, ranging from chromatin accessibility, histone modifications, microRNAs and transcription factors. This holds particular significance in T-cell biology as the level of IL2 dictates the outcome of the T-cell immune response. In summary, to understand the multi-layered process of transcriptional regulation, it is necessary to combine research from the systematic approach of bioinformatics and bench top experiments.