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Blood, 15 June 2007, Vol. 109, No. 12, pp. 5238-5241.
Prepublished online as a Blood First Edition Paper on February 22, 2007; DOI 10.1182/blood-2006-09-047050.
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HEMATOPOIESIS
Brief Report
Expression of oncogenic K-ras from its endogenous promoter leads to a partial block of erythroid differentiation and hyperactivation of cytokine-dependent signaling pathways
Jing Zhang1,
Yangang Liu1,
Caroline Beard1,
David A. Tuveson2,3,
Rudolf Jaenisch1,2,
Tyler E. Jacks2, and
Harvey F. Lodish1,2
1 Whitehead Institute for Biomedical Research, Cambridge, MA;
2 Center for Cancer Research and Department of Biology, Massachusetts Institute of Technology, Cambridge, MA;
3 Department of Medicine, University of Pennsylvania, Philadelphia, PA
When overexpressed in primary erythroid progenitors, oncogenic Ras leads to the constitutive activation of its downstream signaling pathways, severe block of terminal erythroid differentiation, and cytokine-independent growth of primary erythroid progenitors. However, whether high-level expression of oncogenic Ras is required for these phenotypes is unknown. To address this issue, we expressed oncogenic K-ras (K-rasG12D) from its endogenous promoter using a tetracycline-inducible system. We show that endogenous K-rasG12D leads to a partial block of terminal erythroid differentiation in vivo. In contrast to results obtained when oncogenic Ras was overexpressed from retroviral vectors, endogenous levels of K-rasG12D fail to constitutively activate but rather hyperactivate cytokine-dependent signaling pathways, including Stat5, Akt, and p44/42 MAPK, in primary erythroid progenitors. This explains previous observations that hematopoietic progenitors expressing endogenous K-rasG12D display hypersensitivity to cytokine stimulation in various colony assays. Our results support efforts to modulate Ras signaling for treating hematopoietic malignancies.

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