Roles of SET7/9 and LSD1 in the Pathogenesis of Arsenicinduced Hepatocyte Apoptosis

Background and Aims:Multiple regulatory mechanisms play an important role in arsenic-induced liver injury.To investigate whether histone H3 lysine 4(H3K4)methyltransferase(SET7/9)and histone H3K4 demethyltransferase(LSD1/KDM1A)can regulate endoplasmic reticulum stress(ERS)-related apoptosis by modulating the changes of H3K4 methylations in liver cells treated with arsenic.Methods:Apoptosis,proliferation and cell cycles were quantified by flow cytometry and real-time cell analyzer.The expression of ERS-and epigenetic-related proteins was detected by Western blot analysis.The antisense SET7/9 expression vector and the overexpressed LSD1 plasmid were used for transient transfection of LO_(2) cells.The effects of NaAsO_(2) on the methylation of H3 in the promoter regions of 78 kDa glucose-regulated protein,activating transcription factor 4 and C/EBP-homologous protein were evaluated by chromatin immunoprecipitation assay.Results:The protein expression of LSD1(1.25±0.08 vs.1.77±0.08,p=0.02)was markedly decreased by treatment with 100μM NaAsO_(2),whereas the SET7/9(0.68±0.05 vs.1.10±0.13,p=0.002)expression level was notably increased,which resulted in increased H3K4me1/2(0.93±0.64,1.19±0.22 vs.0.71±0.13,0.84±0.13,p=0.03 and p=0.003).After silencing SET7/9 and overexpressing LSD1 by transfection,apoptosis rate(in percentage:3.26±0.34 vs.7.04±0.42,4.80±0.32 vs.7.52±0.38,p=0.004 and p=0.02)was significantly decreased and proliferation rate was notably increased,which is reversed after inhibiting LSD1(in percentage:9.31±0.40 vs.7.52±0.38,p=0.03).Furthermore,the methylation levels of H3 in the promoter regions of GRP78(20.80±2.40 vs.11.75±2.47,20.46±2.23 vs.14.37±0.91,p=0.03 and p=0.01)and CHOP(48.67±4.04 vs.16.67±7.02,59.33±4.51 vs.20.67±3.06,p=0.004 and p=0.001)were significantly increased in LO_(2) cells exposed to 100μM NaAsO_(2) for 24 h.Conclusions:Histone methyltransferase SET7/9 and histone demethyltransferase LSD1 jointly regulate the changes of H3K4me1/me2 levels in arsenic-induced apoptosis.NaAsO_(2) induces apoptosis in LO_(2) cells by activating the ERS-mediated apoptotic signaling pathway,at least partially by enhancing the methylation of H3 on the promoter regions of ERS-associated genes,including GRP78 and CHOP.