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DOT1L and EZH2 cooperatively repress PRC2 targets to maintain the GC B cell identity in DLBCL [RNA-seq]

ABSTRACT: Previous published data suggested that DOT1L indirectly represses PRC2 target genes in murine B cell model. To address whether this relationship persists in human GCB-DLBCL, by integration of transcriptomic and epigenetic analysis, we defined the candidate direct targets of PRC2. GSEA of this genes list showed that DOT1L inhibition was able to significantly derepress candidate PRC2-target genes in Oci-Ly7 and Oci-Ly8. This effect was also observed upon combination treatment of DOT1Li and EZH2i, suggesting that DOT1L indirectly regulates the repression of PRC2 target genes. Moreover, it has been established that in the absence of Dot1l or Ezh2, GC B cells cannot maintain their identity and instead differentiate into a dysfunctional plasma cell-like state. We therefore, investigated whether the combined inhibition of DOT1L and EZH2 enhances plasma cell differentiation. We first established differentiation-state specific signatures unique for NBC, CB, MBC, PB, and BMPC using the GenomicScape database. Unsupervised clustering of the GSVA scores revealed that all the cell lines treated with the combination treatment were clustered together and gained a BMPC signature at the expense of a CB-signature. This crosstalk between DOT1L and EZH2 appeared to be conserved among different GCB-DLBCL cell lines and was independent of their responsiveness to the treatments.

ORGANISM(S): Homo sapiens

PROVIDER: GSE277665 | GEO | 2025/01/22

REPOSITORIES: GEO

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Project description:We studied transcriptional changes by Affymetrix human microarrays in DLBCL cell lines as a result of treatment with GSK126, a potent, highly-selective, SAM-competitive, small molecule inhibitor of EZH2 In eukaryotes, epigenetic post-translational modification of histones is critical for regulation of chromatin structure and gene expression. EZH2 is the catalytic subunit of the Polycomb Repressive Complex 2 (PRC2) and is responsible for repressing target gene expression through methylation of histone H3 on lysine 27 (H3K27). Over-expression of EZH2 is implicated in tumorigenesis and correlates with poor prognosis in multiple tumor types. Recent reports have identified somatic heterozygous mutations of Y641 and A677 residues within the catalytic SET domain of EZH2 in diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL). The Y641 residue is the most frequently mutated residue, with 22% of GCB (Germinal Cell B-cell) DLBCL and FL harboring mutations at this site. These lymphomas exhibit increased H3K27 tri-methylation (H3K27me3) due to altered substrate preferences of the mutant enzymes. However, it is unknown whether direct inhibition of EZH2 methyltransferase activity alone will be effective in treating lymphomas carrying activating EZH2 mutations. Herein, we demonstrate that GSK126, a potent, highly-selective, SAM-competitive, small molecule inhibitor of EZH2 methyltransferase activity, decreases global H3K27me3 levels and reactivates silenced PRC2 target genes. GSK126 effectively inhibits the proliferation of EZH2 mutant DLBCL cell lines and dramatically inhibits the growth of EZH2 mutant DLBCL xenografts in mice. Together, these data demonstrate that pharmacological inhibition of EZH2 activity may provide a promising treatment for EZH2 mutant lymphoma. 10 DLBCL cell lines (7 mutant and 3 wild type EZH2), that were differentially sensitive to GSK126 in proliferation assays, were treated for 72 hours, in duplicate (n=2), with either DMSO (vehicle) or 500nM of GSK126, a potent selective EZH2 inhibitor. EZH2 mutant cell lines are Pfeiffer, KARPAS-422, WSU-DLCL2, SU-DHL-10, SU-DHL-6, DB and SU-DHL-4. EZH2 wildtype cell lines are HT, OCI-LY-19 and Toledo.

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DOT1L and EZH2 cooperatively repress PRC2 targets to maintain the GC B cell identity in DLBCL [RNA-seq]

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