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* Department of Immunology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261; and
Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109
Little is known about the transcriptional regulators that control the proliferation of multipotent bone marrow progenitors. Understanding the mechanisms that restrict proliferation is of significant interest since the loss of cell cycle integrity can be associated with hematopoietic exhaustion, bone marrow failure, or even oncogenic transformation. Herein, we show that multipotent LSKs (lineage–Scahighc-kit+) from E47-deficient mice exhibit a striking hyperproliferation associated with a loss of cell cycle quiescence and increased susceptibility to in vivo challenge with a mitotoxic drug. Total LSKs contain long-term self-renewing hematopoietic stem cells and downstream multipotential progenitors (MPPs) that possess very limited or no self-renewal ability. Within total LSKs, we found specific developmental and functional deficits in the MPP subset. E47 knockout mice have grossly normal numbers of self-renewing hematopoietic stem cells but a 50–70% reduction in nonrenewing MPPs and downstream lineage-restricted populations. The residual MPPs in E47 knockout mice fail to fully up-regulate flk2 or initiate V(D)J recombination, hallmarks of normal lymphoid lineage progression. Consistent with the loss of normal cell cycle restraints, we show that E47-deficient LSKs have a 50% decrease in p21, a cell cycle inhibitor and known regulator of LSK proliferation. Moreover, enforced expression studies identify p21 as an E47 target gene in primary bone marrow LSKs. Thus, E47 appears to regulate the developmental and functional integrity of early hematopoietic subsets in part through effects on p21-mediated cell cycle quiescence.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work is supported by National Institutes of Health Grant R03 AR054529, the Elsa U. Pardee Foundation, U.S. Immune Deficiency Network, and the Winters Foundation (to L.B.); and National Institutes of Health Grants R01 CA086433 (to C.M.) and NIH P01 HL084205 (to I.D.B.). I.D.B. is an American Cancer Society Clinical Research Professor.
2 Address correspondence and reprint requests to Dr. Lisa Borghesi, Department of Immunology, University of Pittsburgh School of Medicine, 200 Lothrop Street, Pittsburgh, PA 15261. E-mail address: borghesi{at}pitt.edu
3 Abbreviations used in this paper: BM, bone marrow; CLP, common lymphoid progenitor; ETP, early T lineage progenitor; 5-FU, 5-fluorouracil; 4-OHT, 4-hydroxytamoxifen; HET, heterozygous; HSC, hematopoietic stem cell; KO, knockout; LRP, lineage-restricted progenitor; LSK, lineage–Scahighc-kit+; LT, long-term; MPP, multipotential progenitor; WT, wild type.
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