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

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 TRENRAS ^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 forAMLand attenuating aggressiveness of relapsed AML.