We investigated the potential signaling molecules that regulate EZH2 overexpression in aggressive B-cell lymphomas and found that 80% of cases of EZH2-positive diffuse large B-cell lymphoma show high p-ERK1/2 expression (average ~57% tumor cell positivity).
We detected EZH2 mutations in 12/55 (22%) follicular lymphomas (FL), 5/35 (14%) diffuse large B cell lymphomas with a germinal center immunophenotype (GCB-DLBCL), and 2/11 (18%) high grade B cell lymphomas with concurrent rearrangements of BCL2 and MYC.
Univariate analyses revealed that EZH2/Bcl-2 coexpression correlated to worse objective response rate (ORR), shorter OS and PFS in DLBCL patients treated with RCHOP while multivariate analysis indicated that only elevated LDH level (<i>P</i>=0.001) and presence of B symtom (<i>P</i>=0.008) rather than EZH2/Bcl-2 coexpression were associated with worse OS.
These mutations, which result in the replacement of a single tyrosine in the SET domain of the EZH2 protein (Tyr641), occur in 21.7% of GCB DLBCLs and 7.2% of FLs and are absent from ABC DLBCLs.
Recurrent somatic heterozygous gain-of-function mutations of EZH2 have been identified in DLBCL, most notably affecting tyrosine 641 (Y641), inducing hyper-trimethylation of H3K27 (H3K27me3).
Prioritized alterations in epigenetic modulators were common and included gain-of-function EZH2 and loss-of-function ARID1A mutations (14% of diffuse large B-cell lymphomas and 22% of follicular lymphomas contained alterations in each of these two genes).
Next-generation sequencing of follicular lymphoma and diffuse-large B-cell lymphoma has revealed frequent somatic, heterozygous Y641 mutations in the histone methyltransferase EZH2.
Mutations in EZH2 (Y646) and CD79B (Y196) were detected in 13.2% and 8% of the samples, respectively, almost exclusively in follicular lymphomas and diffuse large B-cell lymphomas.
Moreover, oncogenic BCL6 and EZH2 cooperate to accelerate diffuse large B cell lymphoma (DLBCL) development and combinatorial targeting of these repressors results in enhanced anti-lymphoma activity in DLBCLs.
In this study, we treated Burkitt lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) cell lines with 3-deazaneplanocin-A (DZNep), an indirect EZH2 inhibitor which possesses anticancer properties both in-vitro and in-vivo.
In particular, recurrent gain-of-function mutations targeting EZH2 Y641 occur most frequently in follicular lymphoma and aggressive diffuse large B-cell lymphoma and are associated with H3K27me3 hyperactivation, which contributes to lymphoma pathogenesis.
Here, we discuss the function of histone acetyltransferases (CREBBP, EP300), histone methyltransferases (KDM2C/D, EZH2) and regulators of higher order chromatin structure (HIST1H1C/D/E, ARID1A and SMARCA4) that have been reported to be mutated in ⩾5% of DLBCL, FL or BL.
HDAC1,2 inhibition impairs EZH2- and BBAP-mediated DNA repair to overcome chemoresistance in EZH2 gain-of-function mutant diffuse large B-cell lymphoma.
GSK126 effectively inhibits the proliferation of EZH2 mutant DLBCL cell lines and markedly inhibits the growth of EZH2 mutant DLBCL xenografts in mice.
Germinal center-like DLBCL is enriched for activating EZH2 mutations, and encouraging activity has been observed for the EZH2 inhibitor tazemetostat, which now has a fast-track US Food and Drug Administration designation.