The Mechanism Of LSD1 Mediated Epigenetic Modification Regulation On Cell Differentiation In Human Acute Myeloid Leukemia

Lysine-specific demethylase 1(LSD1)was the first histone demethylase identified by Dr.Yang Shi from Harvard Medical School in 2004.LSD1 catalyzes the removal of mono-and di-methylation marks on histone 3 lysine 4(H3K4)and lysine 9(H3K9)via a flavin adenine dinucleotide(FAD)-dependent oxidative reaction.The potential link between cancer and LSD1 activity is underscored by the observation that loss of H3K4 methylation and enrichment of H3K9 methylation are associated with several types of tumors.Recent reports indicate that LSD1 may regulate the balance between cell differentiation and proliferation to sustain oncogenic potential of leukemia stem cells in primary human leukemia cells.However,the pro-differentiation and anti-proliferation effects of LSD1 inhibition in acute myeloid leukemia(AML)are not fully understood yet.Here,we first systemically report that small hairpin RNA(shRNA)mediated LSD1 inhibition causes a remarkable transcriptional activation of myeloid lineage marker genes(CD11b/ITGAM and CD86),reduction of cell proliferation and decrease of clonogenic ability of human AML cell lines.Cell surface expression of CD11 b and CD86 increases significantly and dynamically in human AML cells upon sustained LSD1 inhibition.To further investigate the mechanism underlying these effects in human AML cells,Chromatin immunoprecipitation and quantitative PCR(ChIP-qPCR)analyses of histone marks were carried out and revealed that there is a specific increase of H3K4Me2 modification and an accompanied increase of H3K4Me3 modification at the respective CD11 b and CD86 promoter region,whereas the global H3K4Me2 level remains constant.To further confirm the in vivo mechanism of action,we chose a representative AML cell line THP-1 with MLL-AF9 translocation and generated LSD1 conditional knockdown cell line followed by injection of these cells in the mouse xenograft models.Doxycycline induced inhibition of LSD1 significantly blocked tumor growth and induced a prominent increase of CD11 b and CD86 in vivo.Taken together,our results demonstrate the anti-tumor properties of LSD1 inhibition on human AML cell lines and mouse xenograft models.Our findings provide mechanistic insights into the LSD1 functions in controlling both differentiation and proliferation in AML.It underlines the possible therapeutic potential of genetic inhibition of LSD1 in MLL-AF9 AML.