title: GPHN, a novel partner gene fused to MLL in a leukemia with t(11;14)(q23;q24).
abstract: We report a novel MLL-associated chromosome translocation t(11;14)(q23;q24) in a child who showed signs of acute undifferentiated leukemia 3 years after intensive chemotherapy that included the topoisomerase-II inhibitor VP 16. Screening of a cDNA library of the patient's leukemic cells showed a novel fusion transcript between MLL and the Gephyrin (GPHN) gene on 14q24. The resulting MLL-GPHN fusion gene encodes MLL AT hook motifs and a DNA methyltransferase homology domain fused to the C-terminal half of Gephyrin, including a presumed tubulin binding site and a domain homologous to the Escherichia coli molybdenum cofactor biosynthesis protein MoeA. Genomic breakpoint analysis showed potential in vitro topoisomerase-II DNA-binding sites spanning the breakpoints in both MLL and GPHN but no flanking sequences that might mediate homologous recombination. This suggests that MLL-GPHN may have been generated by VP 16/topoisomerase-II-induced DNA double-strand breaks, followed by error-prone DNA repair via non-homologous end joining. Gephyrin was originally identified as a submembraneous scaffold protein that anchors and immobilizes postsynaptic membrane neurotransmitter receptors to underlying cytoskeletal elements. It also is reported to bind to phosphatidylinositol 3,4,5-triphosphate binding proteins involved in actin dynamics and downstream signaling and interacts with ATM-related family member RAFT1. Gephyrin domains in the chimeric protein therefore could contribute novel signal sequences or might modify MLL activity by oligomerization or intracellular redistribution.
authors.affiliation: Leukaemia Research Fund Centre, Institute of Cancer Research, London, United Kingdom. maeguchi@icr.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Eguchi
authors.forename: M
authors.initials: M
authors.lastname: Eguchi-Ishimae
authors.forename: M
authors.initials: M
authors.lastname: Seto
authors.forename: K
authors.initials: K
authors.lastname: Morishita
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: R
authors.initials: R
authors.lastname: Ueda
authors.forename: K
authors.initials: K
authors.lastname: Ueda
authors.forename: N
authors.initials: N
authors.lastname: Kamada
authors.forename: M
authors.initials: M
authors.lastname: Greaves
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D002675:Child, Preschool; D019457:Chromosome Breakage / Q000235:genetics; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics*; D002883:Chromosomes, Human, Pair 14 / Q000235:genetics*; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics*; D005260:Female; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D007948:Leukemia, Monocytic, Acute / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D051788:Myeloid-Lymphoid Leukemia Protein; D015514:Oncogene Proteins, Fusion / Q000235:genetics*; D011519:Proto-Oncogenes; D014157:Transcription Factors; D014178:Translocation, Genetic
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C497422:KMT2A protein, human; D008565:Membrane Proteins; D015514:Oncogene Proteins, Fusion; D014157:Transcription Factors; C073441:gephyrin; D051788:Myeloid-Lymphoid Leukemia Protein; D011495:Histone-Lysine N-Methyltransferase