title: Self-association mediated by the Ras association 1 domain of AF6 activates the oncogenic potential of MLL-AF6.
abstract: MLL is a common target for chromosomal translocations associated with acute leukemia resulting in its fusion with a large variety of nuclear or cytoplasmic proteins that may activate its oncogenic properties by distinct but poorly understood mechanisms. The MLL-AF6 fusion gene represents the most common leukemogenic fusion of mixed lineage leukemia (MLL) to a cytoplasmic partner protein. Here, we identified a highly conserved Ras association (RA1) domain at the amino-terminus of AF6 as the minimal region sufficient for MLL-AF6 mediated myeloid progenitor immortalization in vitro and short latency leukemogenesis in vivo. Moreover, the ability of RA1 to activate MLL oncogenesis is conserved with its Drosophila ortholog, Canoe. Although the AF6 RA1 domain has previously been defined as an interaction surface for guanosine triphosphate-bound Ras, single amino acid substitutions known to abolish the AF6-Ras interaction did not abrogate MLL-AF6-mediated oncogenesis. Furthermore, fusion of MLL to heterologous RA domains of c-Raf1 or RalGDS, or direct fusion of MLL to constitutively active K-RAS, H-RAS, or RAP1 was not sufficient for oncogenic activation of MLL. Rather, the AF6 RA1 domain efficiently mediated self-association, suggesting that constitutive MLL self-association is a more common pathogenic mechanism for MLL oncogenesis than indicated by previous studies of rare MLL fusion partners.
authors.affiliation: Department of Pathology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305, USA.
authors.forename: Michaela
authors.initials: M
authors.lastname: Liedtke
authors.forename: Paul M
authors.initials: PM
authors.lastname: Ayton
authors.forename: Tim C P
authors.initials: TC
authors.lastname: Somervaille
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Smith
authors.forename: Michael L
authors.initials: ML
authors.lastname: Cleary
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002478:Cells, Cultured; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D016547:Kinesins / Q000235:genetics / Q000378:metabolism*; D007942:Leukemia, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007951:Leukemia, Myeloid / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D009154:Mutation; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics / Q000378:metabolism*; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D009368:Neoplasm Transplantation; D012190:Retroviridae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014161:Transduction, Genetic; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C490657:Afdn protein, mouse; D051788:Myeloid-Lymphoid Leukemia Protein; D009218:Myosins; D016547:Kinesins; D018631:ras Proteins
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