Histone lysine methyltransferase EHMT2 is involved in proliferation, apoptosis, cell invasion and DNA methylation of human neuroblastoma cells

Background: Neuroblastoma (NB), a childhood neoplasm arising from neural crest cells, is characterized by a diversity of clinical behaviors ranging from spontaneous remission to rapid tumor progression and death. In addition to genetic abnormalities, recent studies have indicated that epigenetic aberrations also contribute to NB pathogenesis. However, the epigenetic mechanisms underlying the pathogenesis of NB are largely unknown. Methods: Inhibition of euchromatic histone-lysine N-methyltransferase 2 (EHMT2) was evaluated through the measurement of H3K9Me2 levels. Cell proliferation was examined by the use of cell counting in human NB cell lines (LA1-55n, IMR-5 and NMB). The RNA expression of EHMT2, MYCN, and p21 was measured by real-time PCR. The expression of PCNA, MYCN, p53, cyclinD1, H3, H3K27M2, and H3K9Me2 was examined by Western blot analysis. In vitro invasion and the effects of the EHMT2 inhibitor (BIX-01294) were assessed in the Transwell chamber assay. Caspase-3 and -8 activities were measured by a Caspase-Glo assay kit. The level of global DNA methylation was measured by liquid chromatography-mass spectroscopy. Results: BIX-01294, a specific inhibitor of EHMT2 (a key enzyme for histone H3 dimethylation at lysine-9), specifically decreases global H3K9Me2 level but not H3K27Me2. The inhibition of EHMT2 decreased proliferation of NB cells and induced apoptosis by increasing caspase 8/caspase 3 activity. BIX-01294 inhibited NB cell mobility and invasion. This was accompanied with a decreased expression of the MYCN oncogene. Inhibition of EHMT2 enhanced a doxorubicin induced inhibitory effect on cell proliferation. Finally EHMT2 inhibition modulated global DNA methylation levels in NB cells. Conclusion: Our results demonstrate that histone lysine methylation is involved in cell proliferation, apoptosis, cell invasion, and global DNA methylation in human NB cells. Further understanding of this mechanism may provide insight into the pathogenesis of NB progression and lead to novel treatment strategies.