title: Rac1 signaling protects monocytic AML cells expressing the MLL-AF9 oncogene from caspase-mediated apoptotic death.
abstract: We investigated the relevance of signaling mechanisms regulated by the Ras-homologous GTPase Rac1 for survival of acute myeloid leukemia (AML) cells harbouring the MLL-AF9 oncogene due to t(9;11)(p21;q23) translocation. Monocytic MLL-AF9 expressing cells (MM6, THP-1) were hypersensitive to both small-molecule inhibitors targeting Rac1 (EHT 1864, NSC 23766) (IC50EHT ~12.5 μM) and lipid lowering drugs (lovastatin, atorvastatin) (IC50Lova ~7.5 μM) as compared to acute myelocytic leukemia (NOMO-1, HL60) and T cell leukemia (Jurkat) cells (IC50EHT >30 μM; IC50Lova >25 μM). Hypersensitivity of monocytic cells following Rac1 inhibition resulted from caspase-driven apoptosis as shown by profound activation of caspase-8,-9,-7,-3 and substantial (~90 %) decrease in protein expression of pro-survival factors (survivin, XIAP, p-Akt). Apoptotic death was preceded by S139-posphorylation of histone H2AX (γH2AX), a prototypical surrogate marker of DNA double-strand breaks (DSBs). Taken together, abrogation of Rac1 signaling causes DSBs in acute monocytic leukemia cells harbouring the MLL-AF9 oncogene, which, together with downregulation of survivin, XIAP and p-Akt, results in massive induction of caspase-driven apoptotic death. Apparently, Rac1 signaling is required for maintaining genetic stability and maintaining survival in specific subtypes of AML. Hence, targeting of Rac1 is considered a promising novel strategy to induce lethality in MLL-AF9 expressing AML.
authors.affiliation: Institute of Toxicology, University Medical Center of the Johannes Gutenberg University Mainz, Obere Zahlbacher Str 67, 55131 Mainz, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hinterleitner
authors.forename: J
authors.initials: J
authors.lastname: Huelsenbeck
authors.forename: C
authors.initials: C
authors.lastname: Henninger
authors.forename: F
authors.initials: F
authors.lastname: Wartlick
authors.forename: A
authors.initials: A
authors.lastname: Schorr
authors.forename: B
authors.initials: B
authors.lastname: Kaina
authors.forename: G
authors.initials: G
authors.lastname: Fritz
mesh_terms: D017209:Apoptosis; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D006801:Humans; D007948:Leukemia, Monocytic, Acute / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D009000:Monocytes / Q000166:cytology / Q000378:metabolism*; D051788:Myeloid-Lymphoid Leukemia Protein / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D015514:Oncogene Proteins, Fusion / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C474558:MLL-AF9 fusion protein, human; C489901:MLLT3 protein, human; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion; D051788:Myeloid-Lymphoid Leukemia Protein; D020169:Caspases; D020830:rac1 GTP-Binding Protein