Browsing by Subject "PTPN11"

Now showing 1 - 4 of 4
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    Hematopoietic-restricted Ptpn11E76K reveals indolent MPN progression in mice
    (Impact Journals, 2018-04-24) Tarnawsky, Stefan P.; Yu, Wen-Mei; Qu, Cheng-Kui; Chan, Rebecca J.; Yoder, Mervin C.; Biochemistry and Molecular Biology, School of Medicine
    Juvenile Myelomonocytic Leukemia (JMML) is a pediatric myeloproliferative neoplasm (MPN) that has a poor prognosis. Somatic mutations in Ptpn11 are the most frequent cause of JMML and they commonly occur in utero. Animal models of mutant Ptpn11 have probed the signaling pathways that contribute to JMML. However, existing models may inappropriately exacerbate MPN features by relying on non-hematopoietic-restricted Cre-loxP strains or transplantations into irradiated recipients. In this study we generate hematopoietic-restricted models of Ptpn11E76K-mediated disease using Csf1r-MCM and Flt3Cre. We show that these animals have indolent MPN progression despite robust GM-CSF hypersensitivity and Ras-Erk hyperactivation. Rather, the dominant pathology is pronounced thrombocytopenia with expanded extramedullary hematopoiesis. Furthermore, we demonstrate that the timing of tamoxifen administration in Csf1r-MCM mice can specifically induce recombinase activity in either fetal or adult hematopoietic progenitors. We take advantage of this technique to show more rapid monocytosis following Ptpn11E76K expression in fetal progenitors compared with adult progenitors. Finally, we demonstrate that Ptpn11E76K results in the progressive reduction of T cells, most notably of CD4+ and naïve T cells. This corresponds to an increased frequency of T cell progenitors in the thymus and may help explain the occasional emergence of T-cell leukemias in JMML patients. Overall, our study is the first to describe the consequences of hematopoietic-restricted Ptpn11E76K expression in the absence of irradiation. Our techniques can be readily adapted by other researchers studying somatically-acquired blood disorders.
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    The origin of Juvenile Myelomonocytic Leukemia : Insights from developmental hematopoiesis
    (2017-06) Tarnawsky, Stefan Pasichnyk; Yoder, Mervin C.; Chan, Rebecca J.
    Hematopoiesis proceeds through three developmental phases, each with a unique and indispensable function. The individual roles of these phases in the pathogenesis of blood disorders is unknown. We have adapted murine lineage trace models to identify the relative contributions of embryonic, fetal, and adult hematopoietic phases to the origin of Juvenile Myelomonocytic Leukemia. We hypothesized that the fetal phase would have the most pronounced contribution to the development of JMML, a pediatric myeloproliferative disorder whose disease-initiating somatic mutations occur in utero. Progenitors expressing PTPN11E76K from all three waves were growth hypersensitive to GM-CSF due to hyperactive RAS-ERK signaling. However, fulminant myeloproliferation was only seen in fetal and adult cohorts. We observed equal disease severity in FLT3Cre; PTPN11E76K; ROSA26mTmG and CSF1R-MCM; PTPN11E76K; ROSA26YFP cohorts, which had high and low mutant allele frequencies, respectively. This led to the revelation that all progenitors in the BM niche of mutant animals have equal growth hypersensitivity and RAS-ERK hyperactivation due to non-cell autonomous effects of PTPN11E76K. We further identified that FLT3Cre has hematopoietic-restricted expression, and thereby circumvented morbidity from PTPN11E76K expression in endothelial and stromal cells. This led us to hypothesize that FLT3Cre; KrasG12D; ROSA26mTmG would be the first faithful model of JMML to express this disease-initiating mutation. Indeed, FLT3Cre; KrasG12D mice were born at expected Mendelian ratio and showed normal weight gain to 2 weeks of age. Thereafter, they acquired defining features of JMML including monocytosis, anaemia, thrombocytopenia, and hepatosplenomegaly. All FLT3Cre; KrasG12D mice succumb to a JMML-like disease, which was propagated following transplantation. This is in contrast with CSF1R-MCM; KrasG12D; ROSA26YFP mice, in which low mutant allele frequencies in either fetal or adult HSCs uniformly resulted in T-ALL. Our models reveal previously underappreciated features of JMML including an expansion of dendritic cells and a pronounced defect in T-lymphocyte development. We are the first to demonstrate non-cell autonomous effects of hematopoietic-restricted PTPN11E76K expression. Most importantly, we have shown that both the spatial and the temporal origin of JMML-initiating mutations will affect disease manifestations. Each of our findings suggest novel strategies to treat this intractable disease.
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    PI3K in juvenile myelomonocytic leukemia
    (2013-11-20) Goodwin, Charles B.; Chan, Rebecca, J.; Herbert, Brittney-Shea; White, Kenneth E.; Yoder, Mervin C.
    Juvenile Myelomonocytic Leukemia (JMML) is rare, fatal myeloproliferative disease (MPD) affecting young children, and is characterized by expansion of monocyte lineage cells and hypersensitivity to Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) stimulation. JMML is frequently associated with gain-of-function mutations in the PTPN11 gene, which encodes the protein tyrosine phosphatase, Shp2. Activating Shp2 mutations are known to promote hyperactivation of the Ras-Erk signaling pathway, but Akt is also observed to have enhanced phosphorylation, suggesting a potential role for Phosphatidylinositol-3-Kinase (PI3K)-Akt signaling in mutant Shp2-induced GM-CSF hypersensitivity and leukemogenesis. Having demonstrated that Class IA PI3K is hyperactivated in the presence of mutant Shp2 and contributes to GM-CSF hypersensitivity, I hypothesized the hematopoietic-specific Class IA PI3K catalytic subunit p110δ is a crucial mediator of mutant Shp2-induced PI3K hyperactivation and GM-CSF hypersensitivity in vitro and MPD development in vivo. I crossed gain-of-function mutant Shp2 D61Y inducible knockin mice, which develop fatal MPD, with mice expressing kinase-dead mutant p110δ D910A to evaluate p110δ’s role in mutant Shp2-induced GM-CSF hypersensitivity in vitro and MPD development in vivo. As a comparison, I also crossed Shp2 D61Y inducible knockin mice with mice bearing inducible knockout of the ubiquitously expressed Class IA PI3K catalytic subunit, p110α. I found that genetic interruption of p110δ, but not p110α, significantly reduced GM-CSF-stimulated hyperactivation of both the Ras-Erk and PI3K-Akt signaling pathways, and as a consequence, resulted in reduced GM-CSF-stimulated hyper-proliferation in vitro. Furthermore, I found that mice bearing genetic disruption of p110δ, but not p110α, in the presence of gain-of-function mutant Shp2 D61Y, had on average, smaller spleen sizes, suggesting that loss of p110δ activity reduced MPD severity in vivo. I also investigated the effects of three PI3K inhibitors with high specificity for p110δ, IC87114, GDC-0941, and GS-9820 (formerly known as CAL-120), on mutant Shp2-induced GM-CSF hypersensitivity. These inhibitors with high specificity for p110δ significantly reduced GM-CSF-stimulated hyperactivation of PI3K-Akt and Ras-Erk signaling and reduced GM-CSF-stimulated hyperproliferation in cells expressing gain-of-function Shp2 mutants. Collectively, these findings show that p110δ-dependent PI3K hyperactivation contributes to mutant Shp2-induced GM-CSF hypersensitivity and MPD development, and that p110δ represents a potential novel therapeutic target for JMML.
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    Yolk sac erythromyeloid progenitors expressing gain of function PTPN11 have functional features of JMML but are not sufficient to cause disease in mice
    (Wiley, 2017-12) Tarnawsky, Stefan P.; Yoshimoto, Momoko; Deng, Lisa; Chan, Rebecca J.; Yoder, Mervin C.; Biochemistry and Molecular Biology, School of Medicine
    BACKGROUND: Accumulating evidence suggests the origin of juvenile myelomonocytic leukemia (JMML) is closely associated with fetal development. Nevertheless, the contribution of embryonic progenitors to JMML pathogenesis remains unexplored. We hypothesized that expression of JMML-initiating PTPN11 mutations in HSC-independent yolk sac erythromyeloid progenitors (YS EMPs) would result in a mouse model of pediatric myeloproliferative neoplasm (MPN). RESULTS: E9.5 YS EMPs from VavCre+;PTPN11D61Y embryos demonstrated growth hypersensitivity to granulocyte-macrophage colony-stimulating factor (GM-CSF) and hyperactive RAS-ERK signaling. Mutant EMPs engrafted the spleens of neonatal recipients, but did not cause disease. To assess MPN development during unperturbed hematopoiesis we generated CSF1R-MCM+;PTPN11E76K ;ROSAYFP mice in which oncogene expression was restricted to EMPs. Yellow fluorescent protein-positive progeny of mutant EMPs persisted in tissues one year after birth and demonstrated hyperactive RAS-ERK signaling. Nevertheless, these mice had normal survival and did not demonstrate features of MPN. CONCLUSIONS: YS EMPs expressing mutant PTPN11 demonstrate functional and molecular features of JMML but do not cause disease following transplantation nor following unperturbed development. Developmental Dynamics 246:1001-1014, 2017. © 2017 Wiley Periodicals, Inc.