K-RasG12D expression induces hyperproliferation and aberrant signaling in primary hematopoietic stem/progenitor cells

Abstract

Defining how cancer-associated mutations perturb signaling networks in stem/progenitor populations that are integral to tumor formation and maintenance is a fundamental problem with biologic and clinical implications. Point mutations in RAS genes contribute to many cancers, including myeloid malignancies. We investigated the effects of an oncogenic Kras^G12D allele on phosphorylated signaling molecules in primary c-kit⁺ lin^−/low hematopoietic stem/progenitor cells. Comparison of wild-type and Kras^G12D c-kit⁺ lin^−/low cells shows that K-Ras^G12D expression causes hyperproliferation in vivo and results in abnormal levels of phosphorylated STAT5, ERK, and S6 under basal and stimulated conditions. Whereas Kras^G12D cells demonstrate hyperactive signaling after exposure to granulocyte-macrophage colony-stimulating factor, we unexpectedly observe a paradoxical attenuation of ERK and S6 phosphorylation in response to stem cell factor. These studies provide direct biochemical evidence that cancer stem/progenitor cells remodel signaling networks in response to oncogenic stress and demonstrate that multi-parameter flow cytometry can be used to monitor the effects of targeted therapeutics in vivo. This strategy has broad implications for defining the architecture of signaling networks in primary cancer cells and for implementing stem cell–targeted interventions.