High expression of trimethylated histone H3 lysine 4 is associated with poor prognosis in hepatocellular carcinoma.

Tumor-associated epigenetic alterations including DNA methylation and histone modifications are important determinants in the initiation and progression of hepatocellular cancer (HCC) and represent promising biomarkers and therapeutic targets. Locus-specific trimethylation of histone H3 lysine 4 (H3K4me) is a well-known modification linked to the enhanced transcriptional expression of many genes activated in HCC. Our aim was to assess the cellular expression pattern of H3K4me3 in HCC and its association with clinicopathologic variables and outcome. Expression of H3K4me3 and the histone methyltransferase (HMT) SET and MYND domain-containing protein 3 (SMYD3) was studied by Western blotting and immunohistochemistry in cell lines and tumor tissue microarray from a well-characterized series of HCC patients (n = 168). The optimal cut-point of H3K4me3 expression for prognosis was determined by the X-tile program. The prognostic significance was evaluated using Kaplan-Meier survival estimates and log-rank tests. Tumor tissue microarray from another independent HCC patients cohort (n = 147) was used for validation studies. Expression of H3K4me3 and SMYD3 were enhanced in HCC cell lines. In tumor specimens, enhanced expression of H3K4me3 was correlated with reduced overall survival (P < .0001), especially in early-stage HCC patients (TNM I/II). Furthermore, both univariate and multivariate analyses revealed that H3K4me3 level was a significant and independent predictor of poor survival (hazard ratio, 3.592; 95% confidence interval, 2.302-5.605). In addition, H3K4m3 expression was positively correlated with SMYD3 expression in both testing and validation cohorts (P < .0001). In conclusion, H3K4me3 level defines unrecognized subsets of HCC patients with distinct epigenetic phenotype and clinical outcome and can thus be a novel predictor for poor prognosis of HCC patients, especially at TNM I/II stage.