title: Inhibition of histone methyltransferase EZH2 depletes leukemia stem cell of mixed lineage leukemia fusion leukemia through upregulation of p16.
abstract: Leukemia stem cells (LSC) are resistant to conventional chemotherapy and persistent LSC after chemotherapy are supposed to be a major cause of relapse. However, information on genetic or epigenetic regulation of stem cell properties is still limited and LSC-targeted drugs have scarcely been identified. Epigenetic regulators are associated with many cellular processes including maintenance of stem cells. Of note are polycomb group proteins, because they potentially control stemness, and can be pharmacologically targeted by a selective inhibitor (DZNep). Therefore, we investigated the therapeutic potential of EZH2 inhibition in mixed lineage leukemia (MLL) fusion leukemia. Intriguingly, EZH2 inhibition by DZNep or shRNA not only suppressed MLL fusion leukemia proliferation but also reduced leukemia initiating cells (LIC) frequency. Expression analysis suggested that p16 upregulation was responsible for LICs reduction. Knockdown of p16 canceled the survival advantage of mice treated with DZNep. Chromatin immunoprecipitation assays demonstrated that EZH2 was highly enriched around the transcription-start-site of p16, together with H3K27 methylation marks in MLL/ENL and Hoxa9/Meis1 transduced cells but not in E2A/HLF transduced cells. Although high expression of Hoxa9 in MLL fusion leukemia is supposed to be responsible for the recruitment of EZH2, our data also suggest that there may be some other mechanisms independent of Hoxa9 activation to suppress p16 expression, because expression levels of Hoxa9 and p16 were not inversely related between MLL/ENL and Hoxa9/Meis1 transduced cells. In summary, our findings show that EZH2 is a potential therapeutic target of MLL fusion leukemia stem cells.
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Koki
authors.initials: K
authors.lastname: Ueda
authors.forename: Akihide
authors.initials: A
authors.lastname: Yoshimi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kagoya
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nishikawa
authors.forename: Victor E
authors.initials: VE
authors.lastname: Marquez
authors.forename: Masahiro
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Mineo
authors.initials: M
authors.lastname: Kurokawa
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics; D045744:Cell Line, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000096:biosynthesis* / Q000235:genetics; D000071221:Enhancer of Zeste Homolog 2 Protein; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D007938:Leukemia / Q000188:drug therapy* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells / Q000187:drug effects*; D063151:Polycomb Repressive Complex 2 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D015533:Transcriptional Activation; D014183:Transplantation, Heterologous; D015854:Up-Regulation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D019941:Cyclin-Dependent Kinase Inhibitor p16; D000071221:Enhancer of Zeste Homolog 2 Protein; D018398:Homeodomain Proteins; D000075064:Myeloid Ecotropic Viral Integration Site 1 Protein; D009363:Neoplasm Proteins; D063151:Polycomb Repressive Complex 2; D034741:RNA, Small Interfering; C490671:HLF protein, human; C000616391:MEIS1 protein, human; C000616392:Meis1 protein, mouse; C407909:TCF3 protein, human; C097899:homeobox protein HOXA9; C498409:EZH2 protein, human
keywords: 3-Deazaneplanocin; histones; homeobox proteins; mixed-lineage acute leukemias; polycomb repressive complex 2