title: Unraveling the Activation Mechanism of Taspase1 which Controls the Oncogenic AF4-MLL Fusion Protein.
abstract: We have recently demonstrated that Taspase1-mediated cleavage of the AF4-MLL oncoprotein results in the formation of a stable multiprotein complex which forms the key event for the onset of acute proB leukemia in mice. Therefore, Taspase1 represents a conditional oncoprotein in the context of t(4;11) leukemia. In this report, we used site-directed mutagenesis to unravel the molecular events by which Taspase1 becomes sequentially activated. Monomeric pro-enzymes form dimers which are autocatalytically processed into the enzymatically active form of Taspase1 (αββα). The active enzyme cleaves only very few target proteins, e.g., MLL, MLL4 and TFIIA at their corresponding consensus cleavage sites (CSTasp1) as well as AF4-MLL in the case of leukemogenic translocation. This knowledge was translated into the design of a dominant-negative mutant of Taspase1 (dnTASP1). As expected, simultaneous expression of the leukemogenic AF4-MLL and dnTASP1 causes the disappearance of the leukemogenic oncoprotein, because the uncleaved AF4-MLL protein (328 kDa) is subject to proteasomal degradation, while the cleaved AF4-MLL forms a stable oncogenic multi-protein complex with a very long half-life. Moreover, coexpression of dnTASP1 with a BFP-CSTasp1-GFP FRET biosensor effectively inhibits cleavage. The impact of our findings on future drug development and potential treatment options for t(4;11) leukemia will be discussed.
authors.affiliation: Institute of Pharmaceutical Biology, Goethe-University of Frankfurt, Biocenter, Max-von-Laue-Str. 9, D-60438 Frankfurt/Main, Germany.
authors.forename: Samaneh
authors.initials: S
authors.lastname: Sabiani
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland.
authors.forename: Tim
authors.initials: T
authors.lastname: Geppert
authors.affiliation: Institute of Pharmaceutical Biology, Goethe-University of Frankfurt, Biocenter, Max-von-Laue-Str. 9, D-60438 Frankfurt/Main, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Engelbrecht
authors.affiliation: Institute of Pharmaceutical Biology, Goethe-University of Frankfurt, Biocenter, Max-von-Laue-Str. 9, D-60438 Frankfurt/Main, Germany.
authors.forename: Eric
authors.initials: E
authors.lastname: Kowarz
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland.
authors.forename: Gisbert
authors.initials: G
authors.lastname: Schneider
authors.affiliation: Institute of Pharmaceutical Biology, Goethe-University of Frankfurt, Biocenter, Max-von-Laue-Str. 9, D-60438 Frankfurt/Main, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Marschalek
mesh_terms: D018360:Crystallography, X-Ray; D004252:DNA Mutational Analysis; D010450:Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D057075:Enzyme Assays; D031541:Fluorescence Resonance Energy Transfer; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D006868:Hydrolysis; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000378:metabolism; D051788:Myeloid-Lymphoid Leukemia Protein / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion / Q000378:metabolism*; D055503:Protein Multimerization; D015203:Reproducibility of Results
chemical_list: C113855:MLL-AF4 fusion protein, human; D050505:Mutant Proteins; D015514:Oncogene Proteins, Fusion; D051788:Myeloid-Lymphoid Leukemia Protein; D010450:Endopeptidases; C480823:taspase1, human
keywords: AF4–MLL; Oncoprotein activation; Taspase1; t(4;11) leukemia