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

Abstract

Acquired aplastic anemia (AA) is a potentially fatal bone marrow (BM) failure syndrome. IFN-γ-producing T helper (Th)1 CD4+ T cells mediate the immune destruction of hematopoietic cells, and are central to the pathogenesis. However, the molecular events that control the development of BM-destructive Th1 cells remain largely unknown. Ezh2 is a chromatin-modifying enzyme that regulates multiple cellular processes primarily by silencing gene expression. We recently reported that Ezh2 is crucial for inflammatory T cell responses after allogeneic BM transplantation. To elucidate whether Ezh2 mediates pathogenic Th1 responses in AA and the mechanism of Ezh2 action in regulating Th1 cells, we studied the effects of Ezh2 inhibition in CD4+ T cells using a mouse model of human AA. Conditionally deleting Ezh2 in mature T cells dramatically reduced the production of BM-destructive Th1 cells in vivo, decreased BM-infiltrating Th1 cells, and rescued mice from BM failure. Ezh2 inhibition resulted in significant decrease in the expression of Tbx21 and Stat4 (which encode transcription factors T-bet and STAT4, respectively). Introduction of T-bet but not STAT4 into Ezh2-deficient T cells fully rescued their differentiation into Th1 cells mediating AA. Ezh2 bound to the Tbx21 promoter in Th1 cells, and directly activated Tbx21 transcription. Unexpectedly, Ezh2 was also required to prevent proteasome-mediated degradation of T-bet protein in Th1 cells. Our results identify T-bet as the transcriptional and post-translational Ezh2 target that acts together to generate BM-destructive Th1 cells, and highlight the therapeutic potential of Ezh2 inhibition in reducing AA and other autoimmune diseases.

Ezh2 regulates differentiation and function of natural killer cells through histone methyltransferase activity

“…Histone modifications are reversible, making them suitable targets for therapeutic intervention. Alterations in histone lysine methyltranferases are frequently associated with physiological and pathological processes, including cancer (36,37) and autoimmune disease (38). Increased expression of Ezh2 or Ezh2 mutations that enhance methyltransferase activity are observed in cancer and often correlate with poor prognosis (36).…”

Hsp90 inhibition destabilizes Ezh2 protein in alloreactive T cells and reduces graft-versus-host disease in mice

“…To determine the effect of AUY922 on Ezh2 in alloreactive T cells in vivo, we measured the expression of Ezh2 and T-bet, a transcription factor regulated by Ezh2 in T cells, 15,16 in donor T cells isolated from those undergoing allogeneic HSCT. As compared with untreated controls, AUY922 decreased the protein levels of Ezh2, Akt, and p-Akt and transcription of Tbx21 (encoding T-bet) in alloreactive CD8 1 T cells (supplemental Figure 7A-B), without altering their production of H3K27me3, H3K4me3, H3K9me3, or H3K36me3 (supplemental Figure 7A).…”

“…[12][13][14] Our studies and others suggest that Ezh2 plays an important role in regulating effector survival and lineage differentiation of CD4 1 Th1 and Th2 cells. [15][16][17] Using mouse models of allogeneic HSCT, we discovered that loss of T-cell Ezh2 led to GVHD inhibition. 16 Thus, targeting Ezh2 may represent an effective therapeutic strategy for GVHD prevention and treatment.…”

“…These results are in contradictory to our previous reports that genetic deletion of Ezh2 inhibited the production of alloreactive T cells. 15,16,26 Thus, Ezh2 may have additional effects on regulating GVH reaction via a noncanonical mechanism.…”

Histone Lysine Methyltransferase Ezh1 Promotes TLR-Triggered Inflammatory Cytokine Production by Suppressing Tollip

“…In adaptive immunity, genespecific histone H3 lysine 27 (H3K27) methylation markers were considered a signature of different CD4 + Th cell subsets (15). Recently, Th1 lineage-specific transcription factor T-bet was shown to be under the regulation of the H3K27 methyltransferase Ezh2 (16). Ezh2 also was found to specifically enhance Th cell differentiation and plasticity via transcriptional regulation of other lineage-specifying genes (17).…”