Tandem histone methyltransferase upregulation defines a unique aggressive prostate cancer phenotype.

Background: Histone modifications alter transcriptional gene function and participate in cancer progression. Enhancer-of-Zeste-Homologue-2 (EZH2) and Nuclear-Receptor-Binding-SET-domain2 (NSD2) methylate H3K27 and H3K36, respectively, to regulate transcription. Given the therapeutic interest in these enzymes, we investigated expression and coregulation in hormone-sensitive (HS) and castrate-resistant (CR) prostate cancer (PC).

Methods: EZH2 and NSD2 levels were quantified using VECTRA analysis in HS and CRPC tissue microarrays (n = 105 + 66). Expression data from The Cancer Genome Atlas (n = 498), Memorial Sloan Kettering Cancer Center (n = 240), and Stand Up to Cancer/Prostate Cancer Foundation (n = 444) cBioportal datasets were queried, and associations between EZH2 and NSD2 and clinicopathologic variables determined.

Results: Tumour expression of NSD2, but not EZH2, increased in CRPC (p = 0.05, 0.09). Epithelial nuclei co-expressing NSD2 and EZH2 increased in CRPC compared to HSPC (69 vs 42%, p = 0.02), and in metastatic tissue relative to benign (55 vs 35%, p = 0.02). cBioportal analysis revealed collinear NSD2/EZH2 expression (Spearman = 0.57, 0.58, 0.58, all p < 0.001). NSD2/EZH2 co-expression significantly associates with clinicopathologic characteristics including grade group, stage and seminal vesicle involvement. On univariate and multivariate analysis tumours co-expressing NSD2 and EZH2 conferred increased risk of recurrence (hazard ratio: 2.6, 95% confidence inerval: 1.2-5.4, p = 0.01). Kaplan-Meier analysis revealed reduced progression-free-survival of NSD2 and EZH2 co-expression patients in datasets (p < 0.001, 0.002).

Conclusions: Increased EZH2/NSD2 co-expression is overrepresented in CRPC, metastases and associates with shorter disease-free survival in PC patients. Coregulation of these two histone methyltransferases is a biomarker for aggressive PC and licenses them as therapeutic targets.