EZH2

Primary Author(s)*

Paul De Fazio, MSc, Monash Health

Synonyms

• Enhancer Of Zeste Homolog 2
• Enhancer Of Zeste 2 Polycomb Repressive Complex 2 Subunit
• ENX1
• EZH1
• KMT6
• KMT6A

Genomic Location

Cytoband: 7q36.1

Genomic Coordinates:

chr7:148,504,464-148,581,441 [hg19]

chr7:148,807,372-148,884,349 [hg38]

Cancer Category/Type

Diffuse Large B-Cell Lymphoma

EZH2 gain-of-function mutations affecting residue Tyr646 (NM_004456.4) occur in up to 22% of diffuse large B-cell lymphoma (DLBCL) of the germinal center B-cell (GCB) subtype, but not the activated B-cell (ABC) subtype (Morin et al., 2010; Reddy et al., 2017). Less commonly, mutations in Ala677 (NM_004456.4) and Ala687 (NM_004456.4) among other residues have also been described (Majer et al., 2012; McCabe et al., 2012). EZH2 Tyr646 mutations are more common in BCL2-rearranged GCB DLBCL (Ryan et al., 2011). The EZH2 inhibitor tazemetostat is undergoing clinical trials for use in relapsed or refractory B-cell lymphoma (Italiano et al., 2018).

Follicular Lymphoma

EZH2 Tyr646 (NM_004456.4) gain-of-function mutations affect 7-27% of follicular lymphomas (FL) (Bödör et al., 2013; Morin et al., 2010). Other mutations observed include Lys634, Val637, Val679, Ala682, and Ala692 (all NM_004456.4) (Bödör et al., 2013). Mutational status does not appear to affect overall survival (Bödör et al., 2013). Most mutations are monoallelic, predominantly clonal rather than subclonal events, and persist during transformation of FL and so are likely early events in this malignancy (Bödör et al., 2013).

Natural Killer/T-cell Lymphoma

EZH2 is highly expressed in many natural killer/T-cell lymphomas (Abdalkader et al., 2016; Kim et al., 2016), but gain-of-function mutations are not observed. EZH2 overexpression confers growth advantage in nasal-type natural killer/T-cell lymphomas independently of its histone methyltransferase activity, partly due to MYC-mediated inhibition of microRNAs that target EZH2 (Yan et al., 2013).

T-cell Acute Lymphoblastic Leukemia

Loss of function mutations and deletions affecting EZH2 occur in 25% of T-cell acute lymphoblastic leukemia (Ntziachristos et al., 2012).

Acute Myeloid Leukemia

EZH2 is highly expressed in AML, particularly in patients with complex karyotypes (Grubach et al., 2008), and is associated with extramedullary infiltration (Zhu et al., 2016). EZH2 somatic mutations in AML are specific for secondary AML after an antecedent myeloid malignancy (Lindsley et al., 2015), although loss of EZH2 attenuates leukemogenicity (Sashida et al., 2014; Tanaka et al., 2012). EZH2 mutations are found with a frequency of ~2% in AML and are associated with lower blast percentage and -7/del(7q) karyotype, although they have no prognostic impact (Wang et al., 2013).

Myelodysplastic/Myeloproliferative Neoplasms, Myelodysplastic Syndrome, Myelofibrosis

EZH2 is often overexpressed in myelodysplastic syndrome (MDS) (Xu et al., 2011). Mono- and biallelic EZH2 inactivating mutations are found in 12% of myelodysplastic/myeloproliferative neoplasms and 13% of myelofibrosis (Ernst et al., 2010). They are associated with poor prognosis in myelofibrosis (Guglielmelli et al., 2011) and MDS (Bejar et al., 2011). Loss of EZH2 promotes the development of myelodysplastic syndrome in a mouse model (Khan et al., 2013; Sashida et al., 2014).

Breast Cancer

Meta-analysis shows that EZH2 overexpression is associated with estrogen receptor negativity, progesterone receptor negativity, human epidermal growth factor receptor type 2 positivity, invasive ductal cancer, Caucasian race, high histological grade, triple-negative status, and poor patient survival (Wang et al., 2015). Phosphorylation of EZH2 at residue Thr416 by CDK2 appears to play a role in malignancy of triple negative breast cancers, meaning CDK2 inhibitors could be effective in this context (Yang et al., 2015).

Prostate Cancer

High EZH2 expression is associated with an aggressive subset of prostate cancers (Varambally et al., 2002). It is correlated with a high Gleason grade, advanced tumor stage, positive nodal status, elevated PSA, early PSA recurrence, and increased cell proliferation (Melling et al., 2015). TMPRSS2-ERG rearrangements and ERG expression are also correlated (Melling et al., 2015). High EZH2 expression is linked to deletions of PTEN, 6q15, 5q21, and 3p13, particularly in ERG-negative cancers (Melling et al., 2015). High EZH2 expression is also associated with lower 5- and 10-year survival (Bachmann et al., 2006).

Endometrial Cancer

High EZH2 expression is associated with reduced progression-free and overall survival in endometrial cancer (Oki et al., 2017) and contributes to the proliferation of endometrial carcinoma (Jia et al., 2014). In vitro evidence supports inhibition of EZH2 as a viable therapeutic strategy in this cancer, possibly in combination with standard therapy (Oki et al., 2017).

Bladder Cancer

Although EZH2 provides no prognostic information, it is highly expressed in bladder cancer and higher expression is associated with higher grade invasive cancers (Warrick et al., 2016; Weikert et al., 2005).

Liver Cancer

Overexpression of EZH2 is associated with vascular invasion, histological grade, and increased cell proliferation in hepatocellular carcinoma (HCC) and combined hepatocellular and cholangiocarcinoma (Sasaki et al., 2008). The increased proliferation of HCC cells may be due to activation of Wnt/β-catenin signalling as a result of EZH2-mediated gene silencing (Cheng et al., 2011). EZH2 silences multiple tumor suppressor microRNAs in liver cancer (Au et al., 2012). The long noncoding RNA high expression in hepatocellular carcinoma (HEIH) associates with EZH2 to cause repression of EZH2 targets in liver cancer cell lines (Yang et al., 2011). Certain germline single nucleotide polymorphisms (SNPs) may confer decreased HCC risk (Yu et al., 2013).

Glioblastoma

Increased EZH2 expression correlates with higher glioma grade and confers a poor prognosis in glioblastoma patients (Zhang et al., 2015). Repression of EZH2 inhibits tumor growth in glioma cell lines (Zhang et al., 2015) and diminishes glioblastoma cancer stem cell self-renewal, possibly due to direct transcriptional regulation of MYC by EZH2 (Suvà et al., 2009). However, prolonged reduction in EZH2 expression causes cell fate switching leading to tumor progression and resistance to the drug temozolomide (de Vries et al., 2015; Fan et al., 2014). There is a positive feedback loop between EZH2 expression and β-catenin/TCF4 and STAT3 signaling in glioblastoma cells (Zhang et al., 2015). EZH2 is a direct target of microRNA-137 in glioblastoma (Sun et al., 2015).

Lung Cancer

Meta-analysis of EZH2 expression in non-small cell lung cancer (NSCLC) indicates that EZH2 overexpression is associated with poor overall survival in Asian patients, patients with lung adenocarcinoma, and stage I NSCLC patients (Wang et al., 2016). EZH2 expression increases with lung cancer development and metastasis (Wan et al., 2013) and is correlated with high promoter methylation in small cell lung cancer (Poirier et al., 2015). EZH2 inhibition in NSCLC with mutated BRG1 and EGFR sensitizes the tumor to topoisomerase II inhibition in a mouse model, while inhibiting EZH2 in BRG1 and EGFR wild-type NSCLC has the opposite effect (Fillmore et al., 2015)

Ovarian Cancer

EZH2 is overexpressed in two-thirds of ovarian carcinoma and correlates with high stage and high grade disease, and decreased overall survival (Lu et al., 2010). EZH2 is involved in angiogenesis (Lu et al., 2010) and in suppressing apoptosis (Li et al., 2010) in ovarian cancer cells. Accordingly, knockdown of EZH2 induces apoptosis and reduces invasion in these cells (Li et al., 2010). EZH2 expression, possibly mediated by microRNA-101, contributes to acquired cisplatin resistance in ovarian cancer (Hu et al., 2010; Liu et al., 2014). ARD1A mutations sensitize ovarian tumors to EZH2 inhibitors (Bitler et al., 2015).

Melanoma

High EZH2 expression in melanoma is associated with thicker primary melanomas, Clark’s level of invasion V, increased proliferation, and expression of cyclin D1 (Bachmann et al., 2006). EZH2 is able to suppress cellular senescence in melanoma cells by inhibiting p21/CDKN1A expression (Fan et al., 2011). High EZH2 expression is associated with reduced 5-year survival (Bachmann et al., 2006). Tyr646 (NM_004456.4) gain-of-function mutations have been identified in melanomas, and cell lines with these mutations form larger tumors compared to control cells in a xenograft mouse model (Barsotti et al., 2015; Hodis et al., 2012).

Gene Overview

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Common Alteration Types

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Copy Number Loss	Copy Number Gain	LOH	Loss-of-Function Mutation	Gain-of-Function Mutation	Translocation/Fusion
EXAMPLE: X	EXAMPLE: X	EXAMPLE: X	EXAMPLE: X	EXAMPLE: X	EXAMPLE: X

Internal Pages

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EXAMPLE Germline Cancer Predisposition Genes

External Links

Put your text here - Include as applicable links to: 1) Atlas of Genetics and Cytogenetics in Oncology and Haematology, 2) COSMIC, 3) CIViC, 4) St. Jude ProteinPaint, 5) Precision Medicine Knnowledgebase (Weill Cornell), 6) Cancer Index, 7) OncoKB, 8) My Cancer Genome, 9) UniProt, 10) Pfam, 11) GeneCards, 12) GeneReviews, and 13) Any gene-specific databases.

EXAMPLES

TP53 by Atlas of Genetics and Cytogenetics in Oncology and Haematology - detailed gene information

TP53 by COSMIC - sequence information, expression, catalogue of mutations

TP53 by CIViC - general knowledge and evidence-based variant specific information

TP53 by IARC - TP53 database with reference sequences and mutational landscape

TP53 by St. Jude ProteinPaint mutational landscape and matched expression data.

TP53 by Precision Medicine Knowledgebase (Weill Cornell) - manually vetted interpretations of variants and CNVs

TP53 by Cancer Index - gene, pathway, publication information matched to cancer type

TP53 by OncoKB - mutational landscape, mutation effect, variant classification

TP53 by My Cancer Genome - brief gene overview

TP53 by UniProt - protein and molecular structure and function

TP53 by Pfam - gene and protein structure and function information

TP53 by GeneCards - general gene information and summaries

GeneReviews - information on Li Fraumeni Syndrome

References

EXAMPLE Book

1. Arber DA, et al., (2008). Acute myeloid leukaemia with recurrent genetic abnormalities, in World Health Organization Classification of Tumours of Haematopoietic and Lymphoid Tissues, 4th edition. Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J, Vardiman JW, Editors. IARC Press: Lyon, France, p117-118.

EXAMPLE Journal Article

1. Li Y, et al., (2001). Fusion of two novel genes, RBM15 and MKL1, in the t(1;22)(p13;q13) of acute megakaryoblastic leukemia. Nat Genet 28:220-221, PMID 11431691.

Notes

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