Hematopoietic Cell Fate and the Initiation of Leukemic Properties in Primitive Primary Human Cells Are Influenced by Ras Activity and Farnesyltransferase Inhibition

Abstract

The Ras pathway transduces divergent signals determining normal cell fate and is frequently activated in hematopoietic malignancies, but the manner in which activation contributes to human leukemia is poorly understood. We report that a high level of activated H-Ras signaling in transduced primary human hematopoietic progenitors reduced their proliferation and enhanced monocyte/macrophage differentiation. However, the exposure of these cells to a farnesyltransferase inhibitor and establishment of a moderate level of Ras activity showed increased proliferation, an elevated frequency of primitive blast-like cells, and progenitors with enhanced self-renewal capacity. These results suggest that the amplitude of Ras pathway signaling is a determinant of myeloid cell fate and that moderate Ras activation in primitive hematopoietic cells can be an early event in leukemogenesis.

This work was supported by the National Cancer Institute of Canada with funds from the Canadian Cancer Society, the Canadian Institutes for Health Research, the Stem Cell Network of the National Centres of Excellence, the Canadian Genetic Diseases Network of the National Centres of Excellence, and a Canada Research Chair.

We thank Ljilijana Petrovic of Mount Sinai Hospital (Toronto, Ontario, Canada) for obtaining CB samples, Gisele Knowles and Sherry Zhao (Department of Immunology, Hospital for Sick Children, Toronto) for fluorescence-activated cell sorting of CB subfractions, and Teresa Hawley (Holland Laboratory, American Red Cross, Rockville, Md.) for creating the PG13/MSCV-H-Ras producer line. We are also grateful to Dwayne Barber (Princess Margaret Hospital, Toronto) for his gift of antibodies and Ras effector inhibitors, to Bruce Patterson (Princess Margaret Hospital) for his valuable assistance in interpreting cell morphology, to David Hedley for antibodies and advice regarding intracellular flow cytometry, and to Robert Bishop (Schering-Plough) for the generous gift of FTI compounds which made this project possible. Finally, we thank Sean Egan, Dwayne Barber, Robert Bishop, and Atsushi Miyajima for their critical reading of the manuscript.