Abstract
Leukemic relapse is believed to be driven by transformed hematopoietic stem cells that harbor oncogenic mutations or have lost tumor suppressor function. Recent comprehensive sequencing studies have shown that mutations predicted to activate Ras signaling are highly prevalent in hematologic malignancies and, notably, in refractory and relapsed cases. To better understand what drives this clinical phenomenon, we expressed oncogenic NrasG12D within the hematopoietic system in mice and interrogated its effects on hematopoietic stem cell (HSC) survival. N-RasG12D conferred a survival benefit to HSC and progenitors following metabolic and genotoxic stress. This effect was limited to HSC and early progenitors and was independent of autophagy and cell proliferation. N-RasG12D-mediated HSC survival was not affected by inhibition of the canonical Ras effectors such as MEK and PI3K. However, inhibition of the non-canonical Ras effector pathway protein kinase C (PKC) ameliorated the protective effects of N-RasG12D. Mechanistically, N-RasG12D lowered levels of reactive oxygen species (ROS), which correlated with reduced mitochondrial membrane potential and ATP levels. Inhibition of PKC restored the levels of ROS to that of control HSC and abrogated the protective effects granted by N-RasG12D. Thus, N-RasG12D activation within HSC promote cell survival through the mitigation of ROS, and targeting this mechanism may represent a viable strategy to induce apoptosis during malignant transformation of HSC.