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Nf1 regulates hematopoietic progenitor cell growth and ras signaling in response to multiple cytokines
Y Y Zhang1, T A Vik, J W Ryder
1Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
Abstract:
Neurofibromin, the protein encoded by the NF1 tumor-suppressor gene, negatively regulates the output of p21(ras) (Ras) proteins by accelerating the hydrolysis of active Ras-guanosine triphosphate to inactive Ras-guanosine diphosphate. Children with neurofibromatosis type 1 (NF1) are predisposed to juvenile chronic myelogenous leukemia (JCML) and other malignant myeloid disorders, and heterozygous Nf1 knockout mice spontaneously develop a myeloid disorder that resembles JCML. Both human and murine leukemias show loss of the normal allele. JCML cells and Nf1-/- hematopoietic cells isolated from fetal livers selectively form abnormally high numbers of colonies derived from granulocyte-macrophage progenitors in cultures supplemented with low concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF). Taken together, these data suggest that neurofibromin is required to downregulate Ras activation in myeloid cells exposed to GM-CSF. We have investigated the growth and proliferation of purified populations of hematopoietic progenitor cells isolated from Nf1 knockout mice in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF), as well as to GM-CSF. We found abnormal proliferation of both immature and lineage-restricted progenitor populations, and we observed increased synergy between SCF and either IL-3 or GM-CSF in Nf1-/- progenitors. Nf1-/- fetal livers also showed an absolute increase in the numbers of immature progenitors. We further demonstrate constitutive activation of the Ras-Raf-MAP (mitogen-activated protein) kinase signaling pathway in primary c-kit+ Nf1-/- progenitors and hyperactivation of MAP kinase after growth factor stimulation. The results of these experiments in primary hematopoietic cells implicate Nf1 as playing a central role in regulating the proliferation and survival of primitive and lineage-restricted myeloid progenitors in response to multiple cytokines by modulating Ras output.
Insights
Neurofibromin loss in NF1 causes abnormal myeloid cell proliferation by dysregulating Ras signaling. This study shows Nf1 is crucial for controlling myeloid progenitor growth in response to cytokines.
Area of Science:
- Hematology
- Oncology
- Molecular Biology
Background:
- Neurofibromin, encoded by the NF1 tumor-suppressor gene, negatively regulates Ras proteins.
- Neurofibromatosis type 1 (NF1) predisposes individuals to myeloid malignancies, with loss of the normal NF1 allele observed in these cancers.
- Nf1 knockout mice exhibit myeloid disorders resembling human juvenile chronic myelogenous leukemia (JCML).
Purpose of the Study:
- To investigate the role of neurofibromin in regulating hematopoietic progenitor cell growth and proliferation.
- To elucidate the impact of Nf1 deficiency on Ras signaling pathways in response to cytokines.
- To understand the contribution of Nf1 to the development of myeloid disorders.
Main Methods:
- Purification and culture of hematopoietic progenitor cells from Nf1 knockout and wild-type mice.
- Assessment of cell proliferation and colony formation in response to cytokines like GM-CSF, IL-3, and SCF.
- Analysis of Ras-Raf-MAP kinase signaling pathway activation in Nf1-/- progenitors.
Main Results:
- Nf1-/- hematopoietic cells show abnormal proliferation and increased colony formation in response to low GM-CSF concentrations.
- Nf1-/- progenitors exhibit increased proliferation and enhanced synergy between SCF and other cytokines (IL-3, GM-CSF).
- Constitutive and hyperactivated Ras-Raf-MAP kinase signaling is observed in Nf1-/- progenitors.
Conclusions:
- Neurofibromin is essential for downregulating Ras activation in myeloid cells stimulated by GM-CSF.
- Nf1 plays a critical role in regulating the proliferation and survival of both primitive and lineage-restricted myeloid progenitors.
- Dysregulation of Ras signaling due to Nf1 loss contributes to myeloid malignancies.