RAS oncogene suppression induces apoptosis followed by more differentiated and less myelosuppressive disease upon relapse of acute myeloid leukemia

Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, USA.
Blood (Impact Factor: 10.45). 11/2008; 113(5):1086-96. DOI: 10.1182/blood-2008-01-132316
Source: PubMed


To study the oncogenic role of the NRAS oncogene (NRAS(G12V)) in the context of acute myeloid leukemia (AML), we used a Vav promoter-tetracycline transactivator (Vav-tTA)-driven repressible TRE-NRAS(G12V) transgene system in Mll-AF9 knock-in mice developing AML. Conditional repression of NRAS(G12V) expression greatly reduced peripheral white blood cell (WBC) counts in leukemia recipient mice and induced apoptosis in the transplanted AML cells correlated with reduced Ras/Erk signaling. After marked decrease of AML blast cells, myeloproliferative disease (MPD)-like AML relapsed characterized by cells that did not express NRAS(G12V). In comparison with primary AML, the MPD-like AML showed significantly reduced aggressiveness, reduced myelosuppression, and a more differentiated phenotype. We conclude that, in AML induced by an Mll-AF9 transgene, NRAS(G12V) expression contributes to acute leukemia maintenance by suppressing apoptosis and reducing differentiation of leukemia cells. Moreover, NRAS(G12V) oncogene has a cell nonautonomous role in suppressing erythropoiesis that results in the MPD-like AML show significantly reduced ability to induce anemia. Our results imply that targeting NRAS or RAS oncogene-activated pathways is a good therapeutic strategy for AML and attenuating aggressiveness of relapsed AML.

Download full-text


Available from: Ilze Matise, Oct 01, 2015
35 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mixed-lineage-leukemia (MLL) fusion oncogenes are closely involved in infant acute leukemia, which is frequently accompanied by mutations or overexpression of FMS-like receptor tyrosine kinase 3 (FLT3). Earlier studies have shown that MLL fusion proteins induced acute leukemia together with another mutation, such as an FLT3 mutant, in mouse models. However, little has hitherto been elucidated regarding the molecular mechanism of the cooperativity in leukemogenesis. Using murine model systems of the MLL-fusion-mediated leukemogenesis leading to oncogenic transformation in vitro and acute leukemia in vivo, this study characterized the molecular network in the cooperative leukemogenesis. This research revealed that MLL fusion proteins cooperated with activation of Ras in vivo, which was substitutable for Raf in vitro, synergistically, but not with activation of signal transducer and activator of transcription 5 (STAT5), to induce acute leukemia in vivo as well as oncogenic transformation in vitro. Furthermore, Hoxa9, one of the MLL-targeted critical molecules, and activation of Ras in vivo, which was replaceable with Raf in vitro, were identified as fundamental components sufficient for mimicking MLL-fusion-mediated leukemogenesis. These findings suggest that the molecular crosstalk between aberrant expression of Hox molecule(s) and activated Raf may have a key role in the MLL-fusion-mediated-leukemogenesis, and may thus help develop the novel molecularly targeted therapy against MLL-related leukemia.
    Leukemia: official journal of the Leukemia Society of America, Leukemia Research Fund, U.K 09/2009; 23(12):2197-209. DOI:10.1038/leu.2009.177 · 10.43 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Sleeping Beauty (SB) transposon system has been used as a somatic mutagen to identify candidate cancer genes. In previous studies, efficient leukemia/lymphoma formation on an otherwise wild-type genetic background occurred in mice undergoing whole-body mobilization of transposons, but was accompanied by high levels of embryonic lethality. To explore the utility of SB for large-scale cancer gene discovery projects, we have generated mice that carry combinations of different transposon and transposase transgenes. We have identified a transposon/transposase combination that promotes highly penetrant leukemia/lymphoma formation on an otherwise wild-type genetic background, yet does not cause embryonic lethality. Infiltrating gliomas also occurred at lower penetrance in these mice. SB-induced or accelerated tumors do not harbor large numbers of chromosomal amplifications or deletions, indicating that transposon mobilization likely promotes tumor formation by insertional mutagenesis of cancer genes, and not by promoting wide-scale genomic instability. Cloning of transposon insertions from lymphomas/leukemias identified common insertion sites at known and candidate novel cancer genes. These data indicate that a high mutagenesis rate can be achieved using SB without high levels of embryonic lethality or genomic instability. Furthermore, the SB system could be used to identify new genes involved in lymphomagenesis/leukemogenesis.
    Cancer Research 11/2009; 69(21):8429-37. DOI:10.1158/0008-5472.CAN-09-1760 · 9.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mixed lineage leukemia (MLL) gene rearrangement is commonly observed in human leukemias. Many of the resultant MLL fusion proteins are found correlated with Ras signaling. Nevertheless, Ras mutations have only been reported in a small subset of MLL-rearranged leukemia. With the potential of developing new therapeutic regimens targeting Ras signaling pathway, we studied the role of MLL-AF4 family fusions and MLL-septin family fusions in the activation of Ras signaling in leukemogenesis. Elk-1-driven luciferase reporter system was used to study the role of MLL-AF4, MLL-AF5q31, MLL-LAF4, MLL-CDCrel, MLL-MSF, and MLL-Septin 6 in the activation of Ras signaling. Dominant negative Ras S17N mutant and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor U0126 were employed to demonstrate the involvement of Ras and MEK in this transactivation event. The activation of endogenous Ras/MEK signaling pathway by MLL fusion proteins in leukemia cell lines was also addressed by immunoblot analysis and small interfering RNA knockdown approach. We demonstrated that MLL-AF4, MLL-AF5q31, and MLL-LAF4 activated Elk-1 transcription factor, one of the major downstream effectors of Ras. This activation was abolished in the presence of dominant negative Ras or MEK inhibitor U0126, indicating the requirements of Ras and MEK. We further showed that endogenous MEK is phosphorylated in a MLL-AF4-expressing leukemia cell line, whereas depletion of MLL-AF4 by small interfering RNA reduced the phospho-MEK level. Our findings suggest that MLL-AF4 family fusion oncoproteins can activate Elk-1 through Ras/MEK/extracellular signal-regulated kinase (ERK) pathway and strongly support the role of Ras signaling in the pathogenesis of MLL-rearranged leukemia.
    Experimental hematology 03/2010; 38(6):481-8. DOI:10.1016/j.exphem.2010.03.014 · 2.48 Impact Factor
Show more