Study On The Epigenetic Mechanism Of MLL Complexes Regulate C-myc Transcription In Hepatocellular Carcinoma Cells

Hepatocellular carcinoma(HCC)is the fourth leading cause of cancer in the world.HCC is a complex disease with high aggressiveness and poor prognosis.It's important to explore the mechanism as well as the critical path of liver cancer and develop new efficient therapeutic targets.Abnormal histone modification associated with the occurrence of HCC.The MLL gene encodes a histone methyltransferase that methylate histone H3,Menin and Dot1L inhibitors MI-2 and EPZ004777 inhibited malignant proliferation in tumors,however the effect on HCC is still unknown.Here we report the effects of MI-2 or EPZ004777 on malignant phenotype of HCC,the epigenetic regulatory mechanisms on transcription of c-Myc and c-Myc target genes,show the potential application prospect of small molecule targeting histone modification.In our study,the effects of MI-2 and EPZ004777 on malignant proliferation phenotypes of HepG2 were observed.Then we tested the effects of MI-2 or EPZ004777 on the protein expression and transcription of c-Myc and c-Myc target genes.ChIP assay showed the effect of MI-2 or EPZ004777 on the level of H3K4me3 and H3K79me2 at the promoter of c-Myc.With siRNA transfection,the role of MLL fusion protein complexes in the transcription of c-Myc was discussed.Furthermore,two inhibitors were combined in HCC to explore their interrelationship.The result showed that:firstly,MI-2 and EPZ004777 inhibited HCC cell proliferation;secondly,MI-2 and EPZ004777 down-regulated the transcription of c-Myc and c-Myc target genes;thirdly,H3K4me3 regulated by Menin-MLL is an important epigenetic mechanism that inhibited the transcription of c-Myc by MI-2,H3K79me2 regulated by MLL-Dot1L play an important rolein the transcription of c-Myc;Fourthly,complementary activities of MI-2 and EPZ004777 in HCC.All the results indicate that the transcription of c-Myc is repressed by MI-2 and EPZ004777 through MLL fusion complexes-mediated H3K4me3 and H3K79me2 at the promoter of c-Myc.We illustrate the epigenetic regulatory mechanism of MI-2 and EPZ004777 on transcription of c-Myc and the therapeutic significance of the combined application,our work highlight the role of MLL fusion complexes in anti-HCC and provides a novel target for liver cancer therapy.