Browsing by Subject "Shp2"

Now showing 1 - 6 of 6
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    Frs2α and Shp2 signal independently of Gab to mediate FGF signaling in lens development
    (Company of Biologists, 2014-02-01) Li, Hongge; Tao, Chenqi; Cai, Zhigang; Hertzler-Schaefer, Kristina; Collins, Tamica N.; Wang, Fen; Feng, Gen-Sheng; Gotoh, Noriko; Zhang, Xin; Department of Medical and Molecular Genetics, IU School of Medicine
    Fibroblast growth factor (FGF) signaling requires a plethora of adaptor proteins to elicit downstream responses, but the functional significances of these docking proteins remain controversial. In this study, we used lens development as a model to investigate Frs2α and its structurally related scaffolding proteins, Gab1 and Gab2, in FGF signaling. We show that genetic ablation of Frs2α alone has a modest effect, but additional deletion of tyrosine phosphatase Shp2 causes a complete arrest of lens vesicle development. Biochemical evidence suggests that this Frs2α-Shp2 synergy reflects their epistatic relationship in the FGF signaling cascade, as opposed to compensatory or parallel functions of these two proteins. Genetic interaction experiments further demonstrate that direct binding of Shp2 to Frs2α is necessary for activation of ERK signaling, whereas constitutive activation of either Shp2 or Kras signaling can compensate for the absence of Frs2α in lens development. By contrast, knockout of Gab1 and Gab2 failed to disrupt FGF signaling in vitro and lens development in vivo. These results establish the Frs2α-Shp2 complex as the key mediator of FGF signaling in lens development.
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    Pharmacologic inhibition of PI3K p110δ in mutant Shp2E76K-expressing mice
    (Impact Journals, 2017-10-03) Deng, Lisa; Virts, Elizabeth L.; Kapur, Reuben; Chan, Rebecca J.; Pediatrics, School of Medicine
    Juvenile myelomonocytic leukemia is a childhood malignancy that lacks effective chemotherapies and thus has poor patient outcomes. PI3K p110δ has been found to promote hyperproliferation of cells expressing mutant Shp2. In this study, we tested the efficacy of a PI3Kδ inhibitor in mice expressing the Shp2 gain-of-function mutation, E76K. We found that in vivo treatment of mice led to significantly decreased splenomegaly, reduced frequency of bone marrow progenitor cells, and increased terminally differentiated peripheral blood myeloid cells. The survival of drug-treated mice was significantly prolonged compared to vehicle-treated controls, although mice from both groups ultimately succumbed to a similar myeloid cell expansion. PI3Kδ inhibitors are currently used to treat patients with relapsed lymphoid malignancies, such as chronic lymphocytic leukemia. The current findings provide evidence for using PI3Kδ inhibitors as a treatment strategy for JMML and potentially other myeloid diseases.
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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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    The protein tyrosine phosphate, SHP2, functions in multiple cellular compartments in FLT3-ITD+ Leukemia
    (2016-03-09) Richine, Briana Marie; Chan, Rebecca, J.; Carlesso, Nadia; Pollok, Karen E.; White, Kenneth E.
    FMS-like tyrosine receptor kinase-internal tandem duplications (FLT3-ITDs) are the most frequent deleterious mutations found in acute myeloid leukemia (AML) and portend a poor prognosis. Currently, AML patients typically achieve disease remission, yet undergo high rates of disease relapse, implying a residual post-treatment reservoir of resistant malignancy-initiating cells. This begs for new therapeutic approaches to be discovered, and suggests that targeting multiple cellular compartments is needed for improved therapeutic approaches. We have shown that the protein tyrosine phosphatase, Shp2, associates physically FLT3-ITD at tyrosine 599 (Y599) and positively regulates aberrant STAT5 activation and leukemogenesis. We also demonstrated that genetic disruption of Ptpn11, the gene encoding Shp2, increased malignancy specific survival of animals transplanted with FLT3-ITD-transduced cells, suggesting that Shp2 may regulate the function of the malignancy-initiating cell. Taken together, I hypothesized that inhibiting Shp2 can target both FLT3-ITD+ AML tumor cells as well as FLT3-ITD-expressing hematopoietic stem cells. To study this hypothesis, I employed two validation models including genetic inhibition of Shp2 interaction with FLT3-ITD in 32D cells or genetic disruption of Shp2 in FLT3-ITD-expressing HSCs. Using FLT3-ITD-expressing 32D cells as an AML tumor model, I found that mutating the Shp2 binding site on FLT3-ITD (Y599) reduced proliferation in vitro and increased latency to leukemia onset in vivo. Further, pharmacologic inhibition of Shp2 preferentially reduced proliferation of FLT3-ITD+ primary AML samples compared to FLT3-ITD- samples, and cooperated with inhibition of the lipid kinase, phospho-inositol-3-kinase (PI3K), and of the tyrosine kinase, Syk, to reduce proliferation of both FLT3-ITD+ and FLT3-ITD- AML samples. To evaluate the stem cell compartment, I crossed a murine locus-specific knock-in of FLT3-ITD with Shp2flox/flox; Mx1-Cre mice to generate FLT3-ITD; Shp2+/- mice and found that Shp2 heterozygosity dramatically inhibits hematopoietic stem cell engraftment in competitive transplant assays. Further, I found that lineage negative cells from FLT3-ITD; Shp2+/- mice demonstrated increased senescence compared to control mice, suggesting that Shp2 may regulate senescence in FLT3-ITD-expressing hematopoietic stem cells. Together, these findings indicate a cooperative relationship between the tyrosine phosphatase, Shp2, and the kinases PI3K and Syk in AML tumor cells, and indicate that Shp2 plays a positive role in the stem cell compartment to promote stem cell function of the malignancy-initiating cell in AML. Therefore, targeting Shp2 may hold therapeutic benefit for patients with FLT3-ITD+ AML.
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    The role of Bruton's tyrosine kinase and PI3K p110δ in mutant SHP2-induced juvenile myelomonocytic leukemia
    (2018) Deng, Lisa; Chan, Rebecca, J.; Kapur, Reuben; Herbert, Brittney-Shea; Ware, Stephanie M.; Yoder, Mervin
    Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm that lacks effective chemotherapies. Most commonly, patients have gain-of-function (GOF) oncogenic mutations in SHP2, leading to hyperactivation of ERK and AKT and hyperproliferation of cells in response to granulocyte macrophage-colony stimulating factor (GM-CSF). Our lab previously showed that p110δ, the hematopoietic-specific catalytic subunit of phosphoinositide 3-kinase, is a crucial mediator of mutant Shp2-induced GM-CSF hypersensitivity in vitro. We treated oncogenic Shp2-expressing mice with a p110δ inhibitor and showed that the strong effect our lab observed in vitro translated into reduced splenomegaly and prolonged survival in vivo. We investigated molecules potentially cooperating with p110δ signaling and discovered that Bruton’s tyrosine kinase (BTK) is hyperphosphorylated in GOF Shp2 myeloid cells. We used specific BTK and p110δ inhibitors to demonstrate that BTK cooperates with p110δ to hyperactivate Akt/Erk and to promote hyperproliferation. GOF Shp2-expressing mice treated in vivo with the drug combination targeting p110δ and BTK have significantly decreased splenomegaly and WBC counts. We also explored the mechanism of BTK signaling and hypothesized that B cell adaptor for PI3K (BCAP) mediated BTK upregulation of PI3K activity. In mutant Shp2 macrophages, we observed BCAP phosphorylation specifically in the larger isoforms needed for PI3K activation, and BTK inhibition led to a dose-dependent reduction in this phosphorylation. We also demonstrated reduced interaction between BCAP and the PI3K regulatory p85α subunit bearing mutated SH2 domains. Finally, we investigated the effects of mutated DNA methyltransferase 3A (Dnmt3a) in conjunction with GOF Shp2. Double mutant mice quickly became moribund with pronounced splenomegaly and leukocytosis. There was an expansion of mature myeloid cells in the periphery and myeloid progenitors in the bone marrow, plus anemia with evidence of compensatory erythropoiesis in the spleen. Our findings show that the myeloproliferative neoplasm caused by GOF Shp2 is due to hyperactive p110δ, and this is further promoted by BTK, which forms a positive feedback loop with PI3K and BCAP, thus leading to more Akt/Erk hyperphosphorylation and more hyperproliferation in response to GM-CSF. The dual inhibition of p110δ and BTK represents a novel effective treatment strategy for JMML and other diseases induced by oncogenic Shp2.
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    Shp2 deletion in post-migratory neural crest cells results in impaired cardiac sympathetic innervation
    (2014-05) Lajiness, Jacquelyn D.; Ingram, David A., Jr.; Harrington, Maureen A.; Mirmira, Raghavendra G.; Payne, Mark; Rubart, Michael
    Autonomic innervation of the heart begins in utero and continues during the neonatal phase of life. A balance between the sympathetic and parasympathetic arms of the autonomic nervous system is required to regulate heart rate as well as the force of each contraction. Our lab studies the development of sympathetic innervation of the early postnatal heart in a conditional knockout (cKO) of Src homology protein tyrosine phosphatase 2 (Shp2). Shp2 is a ubiquitously expressed non-receptor phosphatase involved in a variety of cellular functions including survival, proliferation, and differentiation. We targeted Shp2 in post-migratory neural crest (NC) lineages using our novel Periostin-Cre. This resulted in a fully penetrant mouse model of diminished cardiac sympathetic innervation and concomitant bradycardia that progressively worsen. Shp2 is thought to mediate its basic cellular functions through a plethora of signaling cascades including extracellular signal-regulated kinases (ERK) 1 and 2. We hypothesize that abrogation of downstream ERK1/2 signaling in NC lineages is primarily responsible for the failed sympathetic innervation phenotype observed in our mouse model. Shp2 cKOs are indistinguishable from control littermates at birth and exhibit no gross structural cardiac anomalies; however, in vivo electrocardiogram (ECG) characterization revealed sinus bradycardia that develops as the Shp2 cKO ages. Significantly, 100% of Shp2 cKOs die within 3 weeks after birth. Characterization of the expression pattern of the sympathetic nerve marker tyrosine hydroxylase (TH) revealed a loss of functional sympathetic ganglionic neurons and reduction of cardiac sympathetic axon density in Shp2 cKOs. Shp2 cKOs exhibit lineage-specific suppression of activated pERK1/2 signaling, but not of other downstream targets of Shp2 such as pAKT (phosphorylated-Protein kinase B). Interestingly, restoration of pERK signaling via lineage-specific expression of constitutively active MEK1 (Mitogen-activated protein kinase kinase1) rescued TH-positive cardiac innervation as well as heart rate. These data suggest that the diminished sympathetic cardiac innervation and the resulting ECG abnormalities are a result of decreased pERK signaling in post-migratory NC lineages.