Normal hematopoiesis and neurofibromin-deficient myeloproliferative disease require Erk
Karl Staser, Su-Jung Park, Steven D. Rhodes, Yi Zeng, Yong Zheng He, Matthew A. Shew, Jeffrey R. Gehlhausen, Donna Cerabona, Keshav Menon, Shi Chen, Zejin Sun, Jin Yuan, David A. Ingram, Grzegorz Nalepa, Feng-Chun Yang, D. Wade Clapp
Karl Staser, Su-Jung Park, Steven D. Rhodes, Yi Zeng, Yong Zheng He, Matthew A. Shew, Jeffrey R. Gehlhausen, Donna Cerabona, Keshav Menon, Shi Chen, Zejin Sun, Jin Yuan, David A. Ingram, Grzegorz Nalepa, Feng-Chun Yang, D. Wade Clapp
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Brief Report

Normal hematopoiesis and neurofibromin-deficient myeloproliferative disease require Erk

Abstract

Neurofibromatosis type 1 (NF1) predisposes individuals to the development of juvenile myelomonocytic leukemia (JMML), a fatal myeloproliferative disease (MPD). In genetically engineered murine models, nullizygosity of Nf1, a tumor suppressor gene that encodes a Ras-GTPase–activating protein, results in hyperactivity of Raf/Mek/Erk in hematopoietic stem and progenitor cells (HSPCs). Activated Erk1/2 phosphorylate kinases and transcription factors with myriad mitogenic roles in diverse cell types. However, genetic studies examining Erk1/2’s differential and/or combined control of normal and Nf1-deficient myelopoiesis are lacking. Moreover, prior studies relying on chemical Mek/Erk inhibitors have reached conflicting conclusions in normal and Nf1-deficient mice. Here, we show that while single Erk1 or Erk2 disruption did not grossly compromise myelopoiesis, dual Erk1/2 disruption rapidly ablated granulocyte and monocyte production in vivo, diminished progenitor cell number, and prevented HSPC proliferation in vitro. Genetic disruption of Erk1/2 in the context of Nf1 nullizygosity (Mx1Cre+Nf1flox/floxErk1–/–Erk2flox/flox) fully protects against the development of MPD. Collectively, we identified a fundamental requirement for Erk1/2 signaling in normal and Nf1-deficient hematopoiesis, elucidating a critical hematopoietic function for Erk1/2 while genetically validating highly selective Mek/Erk inhibitors in a leukemia that is otherwise resistant to traditional therapy.

Authors

Karl Staser, Su-Jung Park, Steven D. Rhodes, Yi Zeng, Yong Zheng He, Matthew A. Shew, Jeffrey R. Gehlhausen, Donna Cerabona, Keshav Menon, Shi Chen, Zejin Sun, Jin Yuan, David A. Ingram, Grzegorz Nalepa, Feng-Chun Yang, D. Wade Clapp

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Figure 2

Granulocytopoiesis and monocytopoiesis require Erk.

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Granulocytopoiesis and monocytopoiesis require Erk. (A and B) Erk1/2-KO ...
(A and B) Erk1/2-KO cells form few colonies in LPPC-HPPC assays. **P < 0.01; ***P < 0.001, Erk1 /2-KO vs. all, 1-way ANOVA with Bonferroni’s correction. (C) Single Erk1/2-KO SLAM-LS cells fail to produce colonies and show no evidence of expansion using Hoechst-based cell detection (not shown). *P < 0.05 Erk1/2-KO vs. all, 1-way ANOVA with Bonferroni’s correction. (D) Lethally irradiated CD45.1/2+ mice received mixed CD45.2+ (Erk mutant) and CD45.1+ (WT) marrow cells at a one-to-one ratio. (E and F) After Cre induction (4 months following transplantation), the WT CD45.2+ recipients demonstrated stable chimerism, but the Erk1/2-KO recipients experienced rapid and progressive loss of CD45.2+ cells, as measured in the peripheral blood (for WT vs. Erk1/2-KO 45.2+ chimerism, data not significant at –0.5 months, P < 0.001 at 1 and 6 months, 2-way ANOVA with Bonferroni’s correction). (G–I) Peripheral blood flow cytometric analyses after Cre induction demonstrate ablated Erk1/2-KO-derived CD45.2+ circulating nonlymphoid cells (CD3–B220–), granulocytes (CD3–B220–Gr1+Mac1+), and monocytes (CD3–B220–Gr1–Mac1+). P < 0.0001, WT vs. Erk1/2-KO, Student’s 2-tailed unpaired t test.