Modulation of activated T cells by transient EZH2 inhibition [ChIP-Seq]

The histone methyltransferase enhancer of zeste homolog 2 (EZH2)-mediated epigenetic regulation of T cell differentiation in acute infection has been extensively investigated. However, the role of EZH2 in T cell exhaustion remains under-explored. Here, using in vitro exhaustion models, we demonstrate that transient inhibition of EZH2 in T cells prior to the phenotypic onset of exhaustion with a clinically approved inhibitor, Tazemetostat, delays their dysfunctional progression and preserves T cell stemness and polyfunctionality while having no negative impact on cell proliferation. Tazemetostat induces T-cell epigenetic reprogramming and increases the expression of the self-renewal T cell transcription factor TCF1 by reducing its promoter H3K27 methylation preferentially in rapidly dividing T cells. Transcriptomic profiling revealed a cell division-dependent upregulation of genes associated with thymocytes, memory and effector T cell subsets. Mapping of EZH2-associated genomic regions by ChIP-seq showed an enrichment of promoters among H2K27me3 loci reduced in abundance by tazemetostat, including those genes upregulated in taz-treated T cells. In brief, cells were fixed with 1% formaldehyde for 15 min and quenched with 0.125 M glycine. Chromatin was isolated by adding lysis buffer, followed by disruption with a Dounce homogenizer. Lysates were sonicated and the DNA sheared to an average length of 300-500 bp with Active Motif’s EpiShear probe sonicator (cat# 53051). Genomic DNA (Input) was prepared by treating aliquots of chromatin with RNase, proteinase K and heat for de-crosslinking, followed by SPRI beads clean up (Beckman Coulter) and quantitation by Clariostar (BMG Labtech). Extrapolation to the original chromatin volume allowed determination of the total chromatin yield. An aliquot of chromatin (40 ug) was precleared with protein A agarose beads (Invitrogen). Genomic DNA regions of interest were isolated using 4 ug of antibody against H3K27me3 (Active Motif, 39155, Lot 11822023). Complexes were washed, eluted from the beads with SDS buffer, and subjected to RNase and proteinase K treatment. Crosslinks were reversed by incubation overnight at 65 C, and ChIP DNA was purified by phenol-chloroform extraction and ethanol precipitation.