Dual function of polycomb group proteins in differentiated murine T helper (CD4⁺) cells

Abstract

BackgroundFollowing antigen recognition, naive T helper (Th; CD4+) cells can differentiate toward one of several effector lineages such as Th1 and Th2; each expressing distinctive transcriptional profiles of cytokine genes. These cytokines eventually instruct the strategy of the immune response. In our search for factors that propagate the transcriptional programs of differentiated Th cells, we previously found that Polycomb group (PcG) proteins, which are known as epigenetic regulators that maintain repressive chromatin states, bind differentially the signature cytokine genes. Unexpectedly, their binding to the Ifng (Interferon-g) in Th1 cells and Il4 (Interleukin-4) in Th2 cells, was correlated with transcriptional activation. Therefore, in this study we aimed to determine the functional role of PcG proteins in the regulation of the expression of the signature cytokine genes.MethodsPcG proteins were knocked down in primary and established murine Th cells using transduction of lentiviruses encoding short hairpin RNAs (shRNAs) directed to Mel-18, Ezh2, Eed and Ring1A, representative of two different PcG complexes. The chromatin structure and the binding activity of PcG proteins and transcription factors at the Ifng promoter were assessed by chromatin immunoprecipitation (ChIP) assays.ResultsDownregulation of PcG proteins was consistent with their function as positive regulators of the signature cytokine genes in primary and established Th1 and Th2 cells. Moreover, the PcG protein Mel-18 was necessary to recruit the Th1-lineage specifying transcription factor T-bet, and the T cell receptor (TCR)-inducible transcription factor NFAT1 to the Ifng promoter in Th1 cells. Nevertheless, our results suggest that PcG proteins can function also as conventional transcriptional repressors in Th cells of their known target the Hoxa7 gene.ConclusionsOur data support a model whereby the non-differentially expressed PcG proteins are recruited in a Th-lineage specific manner to their target genes to enforce the maintenance of specific transcriptional programs as transcriptional repressors or activators. Although our results suggest a direct effect of PcG proteins in the regulation of cytokine gene expression, indirect functions cannot be excluded.

Polycomb Repressive Complex 2-Dependent and -Independent Functions of Jarid2 in Transcriptional Regulation in Drosophila

“…5D). This is in agreement with previous reports (13,28,29,31) and demonstrates that PRC2 has cellular functions that extend beyond what we have learned from its role at Hox genes. Importantly, our studies also suggest that despite a very good correlation of Jarid2 and Su(z)12 occupancies (Fig.…”

The TRPM7 Chanzyme Is Cleaved to Release a Chromatin-Modifying Kinase

“…However, recent findings indicate that PRC2 (Jacob et al, 2011) and the Ezh2 methyltransferase subunit (Li et al, 2009) can also activate transcription (Simon and Kingston, 2013). In particular, H3K27me3 and H3S28p can coexist on the same histone molecule and H3K27me3S28 phosphorylation displaces PRC2 from the promoter (Gehani et al, 2010).…”

Ezh2 Regulates Transcriptional and Posttranslational Expression of T-bet and Promotes Th1 Cell Responses Mediating Aplastic Anemia in Mice

“…(2,41) Several studies point to an important role of Ezh2 and H3K27me3 in multiple lineages of effector T cells. (14,17,20,25) Genome-wide mapping analysis revealed that repressive H3K27me3 marked genes associated with differentiation and maintenance of effector and memory T cells. (1,51) Most recently, we have demonstrated new and essential roles of Ezh2 in regulating inflammatory T cell responses in mice after allogeneic BMT.…”