Stat5 is critical for the development and maintenance of myeloproliferative neoplasm initiated by Nf1 deficiency.

Juvenile myelomonocytic leukemia is a rare myeloproliferative neoplasm characterized by hyperactive RAS signaling. Neurofibromin1 (encoded by the NF1 gene) is a negative regulator of RAS activation. Patients with neurofibromatosis type 1 harbor loss-of-function mutations in NF1 and have a 200- to 500-fold increased risk of juvenile myelomonocytic leukemia.

Nf1 mutant mice with p19ARF gene loss develop accelerated hematopoietic disease resembling acute leukemia with a variable phenotype.

Juvenile Myelomonocytic Leukemia (JMML) is a relentlessly progressive myeloproliferative/myelodysplastic (MPD/MDS) hematopoietic disorder more common in patients with any one of at least three distinct genetic lesions, specifically NF1 gene loss and PTPN11 and NRAS mutations. NF1 and PTPN11 are molecular lesions associated with Neurofibromatosis Syndrome Type I (NF1 Syndrome) and Noonan's Syndrome, respectively. The occurrence of JMML is rare; even among those predisposed with these syndromes to development of disease, and secondary genetic events likely contribute to the development and progression of disease.

Hedgehog signaling is dispensable for adult murine hematopoietic stem cell function and hematopoiesis.

We report the unexpected finding that loss of Hh signaling through conditional deletion of Smoothened (Smo) in the adult hematopoietic compartment has no apparent effect on adult hematopoiesis, including peripheral blood count, number or cell-cycle status of stem or progenitor cells, hematopoietic colony-forming potential, long-term repopulating activity in competitive repopulation assays, or stress response to serial 5-fluorouracil treatment. Furthermore, pharmacologic inhibition of Hh signaling with a potent and selective small molecule antagonist has no substantive effect on hematopoiesis in the mouse. In addition, Hh signaling is not required for the development of MLL-AF9-mediated acute myeloid leukemia (AML).

A role for JAK2 mutations in myeloproliferative diseases.

Myeloproliferative disorders (MPDs) are characterized by a clonal expansion of myeloid cells. Over the past two years, the identification of the JAK2V617F mutation in most cases of polycythemia vera (PV) as well as approximately 50% of patients with essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF) has greatly advanced our understanding of MPDs. The JAK2V617F mutation alters the JAK2 tyrosine kinase to confer constitutive activation and affect downstream signaling pathways.

The GAP-related domain of neurofibromin attenuates proliferation and downregulates N- and K-Ras activation in Nf1-negative AML cells.

Inactivation of the NF1 tumor suppressor causes myeloproliferative diseases. NF1 encodes a GTPase activating protein (GAP) for Ras. Myeloid cells with loss of NF1 have high levels of Ras-GTP, functionally equivalent to the effects of RAS oncogenes.