Oncogenic N-Ras and Tet2 haploinsufficiency collaborate to dysregulate hematopoietic stem and progenitor cells

Concurrent genetic lesions exist in a majority of patients with hematologic malignancies. Among these, somatic mutations that activate RAS oncogenes and inactivate the epigenetic modifier ten-eleven translocation 2 (TET2) frequently co-occur in human chronic myelomonocytic leukemias (CMMLs) and acute myeloid leukemias, suggesting a cooperativity in malignant transformation. To test this, we applied a conditional murine model that endogenously expressed oncogenic Nras(G12D) and monoallelic loss of Tet2 and explored the collaborative role specifically within hematopoietic stem and progenitor cells (HSPCs) at disease initiation. We demonstrate that the 2 mutations collaborated to accelerate a transplantable CMML-like disease in vivo, with an overall shortened survival and increased disease penetrance compared with single mutants. At preleukemic stage, N-Ras(G12D) and Tet2 haploinsufficiency together induced balanced hematopoietic stem cell (HSC) proliferation and enhanced competitiveness. Nras(G12D/+)/Tet2(+/-) HSCs displayed increased self-renewal in primary and secondary transplantations, with significantly higher reconstitution than single mutants. Strikingly, the 2 mutations together conferred long-term reconstitution and selfrenewal potential to multipotent progenitors, a pool of cells that usually have limited selfrenewal compared with HSCs. Moreover, HSPCs from Nras(G12D/+)/Tet2(+-/-) mice displayed increased cytokine sensitivity in response to thrombopoietin. Therefore, our studies establish a novel tractable CMML model and provide insights into how dysregulated signaling pathways and epigenetic modifiers collaborate to modulate HSPC function and promote leukemogenesis.