, Volume 18, Issue 8, pp 963–979 | Cite as

Rac1 signaling protects monocytic AML cells expressing the MLL-AF9 oncogene from caspase-mediated apoptotic death

  • C. Hinterleitner
  • J. Huelsenbeck
  • C. Henninger
  • F. Wartlick
  • A. Schorr
  • B. Kaina
  • G. Fritz
Original Paper


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.


AML t(9;11)(p21;q23) Ras-homologous GTPases HMG-CoA reductase inhibitors (statins) DNA damage Apoptosis 



Protein kinase B


Acute lymphoblastic leukemia


Acute myeloid leukemia


Ataxia telangiectasia mutated


ATM and Rad3-related


Base excision repair


Breast cancer susceptibility protein


Checkpoint kinase


Cdc42/Rac interactive binding region


DNA damage response


DNA double-strand breaks


Guanine exchange factor


Inhibitory concentration 50 %


Epithelial-to-mesenchymal transition


3-Hydroxy-3-methyl-glutaryl coenzyme A


Histone H2AX


S139 phosphorylated H2AX


Inhibitory concentration 50 %


IC50 after EHT 1864 treatment


IC50 after lovastatin treatment


Mixed lineage leukemia

MLLT3 (=AF9)

Mixed lineage leukemia, tanslocated to, 3


Poly (ADP-ribose) polymerase


Ras-related C3 botulinum substrate 1




X-linked inhibitor of apoptosis



We would like to thank C. Brachetti for excellent technical assistance. This work was supported by the José Carreras Leukämie Stiftung (SP 10/07) and the Deutsche Krebshilfe (109188).

Conflict of interest

The authors declare no conflicts of interest.

Supplementary material

10495_2013_842_MOESM1_ESM.doc (49 kb)
Supplementary material 1 (DOC 49 kb)


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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • C. Hinterleitner
    • 2
  • J. Huelsenbeck
    • 2
  • C. Henninger
    • 1
  • F. Wartlick
    • 1
  • A. Schorr
    • 1
  • B. Kaina
    • 2
  • G. Fritz
    • 1
  1. 1.Institute of ToxicologyHeinrich-Heine University DüsseldorfDüsseldorfGermany
  2. 2.Institute of ToxicologyUniversity Medical Center of the Johannes Gutenberg University MainzMainzGermany

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