title: Targeting MLL-AF4 with short interfering RNAs inhibits clonogenicity and engraftment of t(4;11)-positive human leukemic cells.
abstract: The chromosomal translocation t(4;11) marks infant acute lymphoblastic leukemia associated with a particularly dismal prognosis. The leukemogenic role of the corresponding fusion gene MLL-AF4 is not well understood. We show that transient inhibition of MLL-AF4 expression with small interfering RNAs impairs the proliferation and clonogenicity of the t(4; 11)-positive human leukemic cell lines SEM and RS4;11. Reduction of mixed-lineage leukemia (MLL)-ALL-1 fused gene from chromosome 4 (AF4) levels induces apoptosis associated with caspase-3 activation and diminished BCL-X(L) expression. Suppression of MLL-AF4 is paralleled by a decreased expression of the homeotic genes HOXA7, HOXA9, and MEIS1. MLL-AF4 depletion inhibits expression of the stem-cell marker CD133, indicating hematopoietic differentiation. Transfection of leukemic cells with MLL-AF4 siRNAs reduces leukemia-associated morbidity and mortality in SCID mice that received a xenotransplant, suggesting that MLL-AF4 depletion negatively affects leukemia-initiating cells. Our findings demonstrate that MLL-AF4 is important for leukemic clonogenicity and engraftment of this highly aggressive leukemia. Targeted inhibition of MLL-AF4 fusion gene expression may lead to an effective and highly specific treatment of this therapy-resistant leukemia.
authors.affiliation: Department of Molecular Biology, Interfaculty Institute for Cell Biology, Eberhard Karls University of Tuebingen, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Thomas
authors.forename: Andreas
authors.initials: A
authors.lastname: Gessner
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Vornlocher
authors.forename: Philipp
authors.initials: P
authors.lastname: Hadwiger
authors.forename: Johann
authors.initials: J
authors.lastname: Greil
authors.forename: Olaf
authors.initials: O
authors.lastname: Heidenreich
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015973:Gene Expression Regulation, Leukemic / Q000235:genetics*; D006085:Graft Survival / Q000235:genetics*; D006801:Humans; D007938:Leukemia / Q000235:genetics* / Q000378:metabolism / Q000628:therapy; D051379:Mice; D016513:Mice, SCID; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics* / Q000378:metabolism; D009368:Neoplasm Transplantation / Q000379:methods; D015514:Oncogene Proteins, Fusion / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*; D014183:Transplantation, Heterologous; D014410:Tumor Stem Cell Assay / Q000379:methods
chemical_list: C113855:MLL-AF4 fusion protein, human; D015514:Oncogene Proteins, Fusion; D034741:RNA, Small Interfering; D051788:Myeloid-Lymphoid Leukemia Protein