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Kevin Shannon

Publications and source records attributed to Kevin Shannon.

At least 19 recordsLinked to original sources
PubMed2007

Deregulated Ras signaling in developmental disorders: new tricks for an old dog.

Ras proteins regulate cell proliferation, survival and differentiation and are constitutively activated by somatic point mutations in many cancers. Previous studies of neurofibromatosis type 1 and Noonan syndrome also implicated hyperactive Ras in developmental disorders. Recently, germline mutations in H-RAS and K-RAS and in genes encoding other molecules in the Ras-Raf-MEK-ERK cascade were shown to underlie cases of Noonan, cardio-facio-cutaneous, and Costello syndromes. These disorders share phenotypic traits that include abnormal facial features, heart defects, and impaired growth and development. Many of these germline, disease-associated mutations encode novel Ras, Raf and MEK proteins. These studies underscore a crucial role of Ras signaling in human development.

Germ-Line Mutation↗
PubMed2006

K-RasG12D expression induces hyperproliferation and aberrant signaling in primary hematopoietic stem/progenitor cells.

Defining how cancer-associated mutations perturb signaling networks in stem/progenitor populations that are integral to tumor formation and maintenance is a fundamental problem with biologic and clinical implications. Point mutations in RAS genes contribute to many cancers, including myeloid malignancies. We investigated the effects of an oncogenic Kras(G12D) allele on phosphorylated signaling molecules in primary c-kit(+) lin(-/low) hematopoietic stem/progenitor cells. Comparison of wild-type and Kras(G12D) c-kit(+) lin(-/low) cells shows that K-Ras(G12D) expression causes hyperproliferation in vivo and results in abnormal levels of phosphorylated STAT5, ERK, and S6 under basal and stimulated conditions. Whereas Kras(G12D) cells demonstrate hyperactive signaling after exposure to granulocyte-macrophage colony-stimulating factor, we unexpectedly observe a paradoxical attenuation of ERK and S6 phosphorylation in response to stem cell factor. These studies provide direct biochemical evidence that cancer stem/progenitor cells remodel signaling networks in response to oncogenic stress and demonstrate that multi-parameter flow cytometry can be used to monitor the effects of targeted therapeutics in vivo. This strategy has broad implications for defining the architecture of signaling networks in primary cancer cells and for implementing stem cell-targeted interventions.

Animals↗
PubMed2006

Beta common receptor inactivation attenuates myeloproliferative disease in Nf1 mutant mice.

Neurofibromatosis type 1 (NF1) syndrome is caused by germline mutations in the NF1 tumor suppressor, which encodes neurofibromin, a GTPase activating protein for Ras. Children with NF1 are predisposed to juvenile myelomonocytic leukemia (JMML) and lethally irradiated mice given transplants with homozygous Nf1 mutant (Nf1-/-) hematopoietic stem cells develop a fatal myeloproliferative disorder (MPD) that models JMML. We investigated the requirement for signaling through the GM-CSF receptor to initiate and sustain this MPD by generating Nf1 mutant hematopoietic cells lacking the common beta chain (Beta c) of the GM-CSF receptor. Mice reconstituted with Nf1-/-, beta c-/- stem cells did not develop evidence of MPD despite the presence of increased number of immature hematopoietic progenitors in the bone marrow. Interestingly, when the Mx1-Cre transgene was used to inactivate a conditional Nf1 mutant allele in hematopoietic cells, concomitant loss of beta c-/- reduced the severity of the MPD, but did not abrogate it. Whereas inhibiting GM-CSF signaling may be of therapeutic benefit in JMML, our data also demonstrate aberrant proliferation of Nf1-/-myeloid progenitors that is independent of signaling through the GM-CSF receptor.

Animals↗
PubMed2006

Somatic activation of a conditional KrasG12D allele causes ineffective erythropoiesis in vivo.

Somatic activation of a conditional targeted Kras(G12D) allele induces a fatal myeloproliferative disease in mice that closely models juvenile and chronic myelomonocytic leukemia. These mice consistently develop severe and progressive anemia despite adequate numbers of clonogenic erythroid progenitors in the bone marrow and expanded splenic hematopoiesis. Ineffective erythropoiesis is characterized by impaired differentiation. These results demonstrate that endogenous levels of oncogenic Ras have cell lineage-specific effects and support efforts to modulate Ras signaling for therapy of anemia in patients with myelodysplastic syndromes and myeloproliferative disorders.

Alleles↗
PubMed2006

Inherited predispositions and hyperactive Ras in myeloid leukemogenesis.

Identifying the molecular basis for inherited cancer predispositions reveals genes that when mutated, play a critical role in the earliest stages of tumorigenesis. Although rare, inherited predispositions to myeloid leukemias have led to a greater understanding of pathways important for myeloid proliferation and maturation. In particular, elucidating why children with neurofibromatosis type 1 (NF1) and Noonan syndrome (NS) are predisposed to juvenile myelomonocytic leukemia (JMML) has uncovered a critical role of hyperactive Ras signaling in normal myeloid growth and leukemogenesis. Here, we review studies of human samples and experiments performed in genetically engineered strains of mice investigating the molecular and biochemical basis of aberrant growth in JMML. These strains model human disease features and provide an opportunity to investigate novel therapeutic strategies that may ultimately cure JMML and other myeloid malignancies characterized by hyperactive Ras.

Animals↗
PubMed2006

Germline KRAS mutations cause Noonan syndrome.

Noonan syndrome (MIM 163950) is characterized by short stature, facial dysmorphism and cardiac defects. Heterozygous mutations in PTPN11, which encodes SHP-2, cause approximately 50% of cases of Noonan syndrome. The SHP-2 phosphatase relays signals from activated receptor complexes to downstream effectors, including Ras. We discovered de novo germline KRAS mutations that introduce V14I, T58I or D153V amino acid substitutions in five individuals with Noonan syndrome and a P34R alteration in a individual with cardio-facio-cutaneous syndrome (MIM 115150), which has overlapping features with Noonan syndrome. Recombinant V14I and T58I K-Ras proteins show defective intrinsic GTP hydrolysis and impaired responsiveness to GTPase activating proteins, render primary hematopoietic progenitors hypersensitive to growth factors and deregulate signal transduction in a cell lineage-specific manner. These studies establish germline KRAS mutations as a cause of human disease and infer that the constellation of developmental abnormalities seen in Noonan syndrome spectrum is, in large part, due to hyperactive Ras.

Adolescent↗
PubMed2005

Safety and efficacy of gemtuzumab ozogamicin in pediatric patients with advanced CD33+ acute myeloid leukemia.

This open-label, dose-escalation study evaluated the safety and efficacy of single-agent gemtuzumab ozogamicin, a humanized anti-CD33 antibody-targeted chemotherapeutic agent, for pediatric patients with multiple relapsed or primary refractory acute myeloid leukemia (AML). Twenty-nine children 1 to 16 years of age (relapsed disease, 19; refractory disease, 10) received gemtuzumab ozogamicin ranging from 6 to 9 mg/m2 per dose for 2 doses (separated by 2 weeks) infused over 2 hours. All patients had anticipated myelosuppression. Other toxicities included grade 3/4 hyperbilirubinemia (7%) and elevated hepatic transaminase levels (21%); the incidence of grade 3/4 mucositis (3%) or sepsis (24%) was relatively low. One patient treated at 9 mg/m2 developed veno-occlusive disease (VOD) of the liver and defined the dose-limiting toxicity. Thirteen patients underwent hematopoietic stem-cell transplantation less than 3.5 months after the last dose of gemtuzumab ozogamicin; 6 (40%) developed VOD. Eight of 29 (28%) patients achieved overall remission. Remissions were comparable in patients with refractory (30%) and relapsed (26%) disease. Mean multidrug resistance-protein-mediated drug efflux was significantly lower in the leukemic blasts of patients achieving remission (P < .005). Gemtuzumab ozogamicin was relatively well tolerated at 6 mg/m2 for 2 doses and was equally effective in patients with refractory and relapsed disease. Further studies in combination with standard induction therapy for childhood AML are warranted.

Acute Disease↗
PubMed2005

Granulocyte/macrophage colony-stimulating factor and accessory cells modulate radioprotection by purified hematopoietic cells.

Granulocyte/macrophage colony-stimulating factor (GM-CSF) promotes the survival, proliferation, and differentiation of myeloid lineage cells and regulates chemotaxis and adhesion. However, mice in which the genes encoding GM-CSF (Gmcsf) or the beta common subunit of the GM-CSF receptor (betac) are inactivated display normal steady-state hematopoiesis. Here, we show that host GM-CSF signaling strongly modulates the ability of donor hematopoietic cells to radioprotect lethally irradiated mice. Although bone marrow mononuclear cells efficiently rescue Gmcsf mutant recipients, fetal liver cells and Sca1(+) lin(-/dim) marrow cells are markedly impaired. This defect is partially attributable to accessory cells that are more prevalent in bone marrow. In contrast, Gmcsf-deficient hematopoietic stem cells demonstrate normal proliferative potentials. Short-term survival is also impaired in irradiated betac mutant recipients transplanted with fetal liver or bone marrow. These data demonstrate a nonredundant function of GM-CSF in radioprotection by donor hematopoietic cells that may prove relevant in clinical transplantation.

Animals↗
PubMed2005

JAKing up hematopoietic proliferation.

Mutations that deregulate proliferation and survival pathways have emerged as a common molecular theme in the pathogenesis of myeloproliferative disorders (MPDs). Three studies now report an amino acid substitution in the JAK2 kinase in most patients with polycythemia vera as well as in some cases of essential thrombocythemia and chronic idiopathic myelofibrosis. Functional analysis demonstrates that this mutation confers erythropoietin-independent growth in vitro, deregulates signaling pathways downstream of JAK2, and causes polycythemia in mice. These results open new avenues for diagnosing and classifying patients with these disorders, and identify a new molecular target for drug discovery.

Animals↗
PubMed2004

Percutaneous epicardial mapping during ablation of difficult accessory pathways as an alternative to cardiac surgery.

OBJECTIVES: The aim of this study was to define the role of percutaneous epicardial mapping for the ablation of previous failed ablation of accessory pathways. BACKGROUND: Cardiac surgery is the only curative option for failed radiofrequency (RF) catheter ablation of accessory pathway (AP)-mediated tachycardias. We investigated a combined percutaneous epicardial and endocardial approach for failed AP ablations. METHODS: We present our experience in a series of 6 cases (7 APs) with previous failed attempts at catheter ablation (median 2 attempts, range 1-4) and persistent symptomatic tachycardias. Endocardial mapping of the APs was performed using conventional techniques. Sites with local electrograms suggestive of AP location were selected. When initial endocardial mapping was not successful for ablation of the pathway, percutaneous transthoracic pericardial puncture was performed via a subxiphoid approach, and an ablation catheter was positioned at the epicardial aspect of the putative AP location for epicardial-endocardial electrogram comparison. Endocardial RF energy was applied to locations considered appropriate. Epicardial RF applications were delivered when endocardial applications failed. Coronary arteriography was performed to assess the proximity of coronary arteries to the ablation catheter. RESULTS: APs were located in the right free wall (4 patients, 5 APs) and the right (1 patient) and left (1 patient) posteroseptal regions. In all patients, epicardial mapping assisted in identifying successful ablation sites. In 3 patients, the earliest atrial activation during orthodromic tachycardia was present in an epicardial electrogram. Successful AP ablation was achieved with an epicardial RF application in 2 patients, either alone or with simultaneous endocardial-epicardial delivery. In the remaining 4 patients, APs were successfully ablated endocardially after epicardial mapping. These patients represent 18% of all cases referred to our institution for ablation of previously failed accessory pathways (6/32 patients). CONCLUSIONS: A combined endocardial-epicardial approach to mapping and RF ablation can facilitate successful endocardial ablation in most cases. In selected cases, APs can be ablated by epicardial delivery of RF. Epicardial mapping is an effective alternative to cardiac surgery for patients in whom prior attempts at AP ablation have failed.

Adolescent↗
PubMed2004

The sum is greater than the FGFR1 partner.

Cancer-associated chromosomal translocations create chimeric oncoproteins that contribute to aberrant growth by dominant or dominant negative mechanisms. Interestingly, genes such as MLL, RARA, and EWS are fused to multiple partners. This molecular promiscuity can provide important functional information, as specific translocations may be associated with discrete clinical and molecular features. In this issue of Cancer Cell, use a murine retroviral transduction/transplantation system to analyze two FGFR1 fusions found in hematologic malignancies. Their results show that these chromosomal rearrangements play a central role in pathogenesis, underscore the role of partner genes in modulating disease phenotypes, and uncover potential therapeutic targets.

Bone Marrow↗
PubMed2004

Evaluation of safety and efficacy of pacemaker and defibrillator implantation by axillary incision in pediatric patients.

We successfully implanted 11 pacemakers, 6 defibrillators, and 1 biventricular pacemaker in 18 pediatric patients (15 female; 4 to 15 years, average age: 9) using the retropectoral transvenous approach with a hidden axillary incision. The average follow-up period was 24 months (range 49 months). Eight patients had congenital structural heart conditions (d-transposition of great arteries S/P Mustard operation, d-transposition of great arteries S/P arterial switch operation, truncus arteriosus, right ventricular diverticula, ventricular septal defect, hypertrophic cardiomyopathy). Four patients had acquired heart conditions (dilated cardiomyopathy, myocarditis). Excellent sensing and pacing thresholds were achieved in all attempted implantations. There was no pneumothorax. There was one lead dislodgement. One lead fracture distant from the subclavian vein occurred 4 months after implantation. Implantation of pacemakers and defibrillators via axillary incisions can be safe and effective in pediatric patients. This approach avoids skin erosion when implanting large devices such as defibrillators or biventricular devices in small patients with limited muscle mass while achieving superior aesthetic results. The axillary or extrathoracic venous entry site avoids subclavian crush syndrome.

Adolescent↗
PubMed2003

IL-3 receptor signaling is dispensable for BCR-ABL-induced myeloproliferative disease.

BCR-ABL expression led to a dramatic up-regulation of the IL-3, IL-5, and granulocyte-macrophage colony-stimulating factor receptor beta common (IL-3Rbetac) and IL-3 receptor beta (IL-3Rbeta) chains in murine embryonic stem cell-derived hematopoietic cells coincident with an expansion of multipotent progenitors and myeloid elements. This up-regulation required BCR-ABL tyrosine kinase activity and led to IL-3Rbetac/beta chain tyrosine phosphorylation in the absence of detectable IL-3 production. These results suggested that cytokine-independent IL-3 receptor activation could be a dominant signaling component in BCR-ABL-induced leukemogenesis. To unambiguously define the significance of IL-3 receptor-dependent signaling in BCR-ABL-induced leukemogenesis, BCR-ABL-transduced bone marrow cells deficient in either IL-3Rbetac chain or both IL-3Rbetac/beta chain expression were examined for their ability in generating myeloproliferative disease (MPD). These BCR-ABL-expressing knockout cells were capable of generating MPD similar to control cells, demonstrating that IL-3 receptor activation is not essential for BCR-ABL-induced MPD. However, the IL-3Rbetac/beta chain could act as a cofactor in BCR-ABL-induced leukemogenesis by activation of its many known oncogenic signaling pathways.

Animals↗
PubMed2003

Mouse cancer models as a platform for performing preclinical therapeutic trials.

Engineering cancer-associated mutations into the mouse germline is an important tool for biological studies of growth control and tumorigenesis. Tractable models of many human cancers now exist in which the initiating genetic lesions have been elucidated and, in some instances, where the cooperating lesions are also known. The urgent need for more effective strategies for treating human cancer has stimulated interest in harnessing these models to test therapeutic agents. Although the ultimate value of genetically engineered mouse models for cancer drug discovery is unknown, several encouraging experiments provide proof of principle.

Animals↗
PubMed2002

Leukemic potential of doubly mutant Nf1 and Wv hematopoietic cells.

The development of molecularly targeted treatments of adult leukemias warrants investigation of these targets in similar pediatric leukemias. The NF1 tumor suppressor gene, which encodes a GTPase activating protein for p21(ras), is frequently inactivated in juvenile myelomonocytic leukemia (JMML). Other patients with JMML acquire activating RAS gene mutations. Recipient mice reconstituted with Nf1-/- fetal hematopoietic cells develop a myeloproliferative disease (MPD) that models the human disease. JMML arises from clonal expansion of a hematopoietic stem cell, and JMML cells and murine Nf1-/- hematopoietic cells are hypersensitive to granulocyte macrophage-colony stimulating factor and KitL, the ligand for c-kit. We generated embryos doubly mutant for the Wv allele of c-kit and Nf1 to ask if reduction of c-kit activity would delay or prevent the development of MPD. Despite a reduction in c-kit activity to approximately 10% of wild-type levels, Nf1-/-;Wv/Wv cells induced MPD in recipient mice.

Alleles↗
PubMed2002

HIV type 1 glycoprotein 120 inhibits cardiac myocyte contraction.

Cardiomyopathy is a common, life-threatening, but poorly understood complication of HIV infection. The purpose of the present study is to study the effects of an HIV surface envelope protein, glycoprotein 120 (gp120), on cell contraction and L-type Ca(2+) current in rabbit ventricular myocytes. Rabbit ventricular cells were isolated by an enzyme dissociation method. Cell contractions were induced by electric field stimulation. Whole cell L-type Ca(2+) channel currents were measured by the whole cell voltage-clamp technique. We found that perfusion with solution containing gp120 (0.1 microg/ml) derived from HIV-1(SF2) significantly inhibited field-stimulated contractions and L-type Ca(2+) current in rabbit ventricular myocytes as compared with perfusion with buffer alone. These results suggest that HIV-1 gp120 may directly contribute to cardiac dysfunction as seen in many HIV patients.

Animals↗
PubMed2002

Clonal evolution in marrows of patients with Shwachman-Diamond syndrome: a prospective 5-year follow-up study.

OBJECTIVES: Shwachman-Diamond syndrome (SDS) is characterized by varying degrees of marrow failure. Retrospective studies suggested a high propensity for malignant myeloid transformation into myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). The study's aims were to determine the cellular and molecular characteristics as well as the clinical course of malignant myeloid transformation and clonal marrow disease in patients with SDS. METHODS: This is a longitudinal prospective study of 14 patients recruited for annual hematological evaluations. Results of baseline and serial hematological assessments for up to 5 years are reported. RESULTS: Clonal marrow cytogenetic abnormalities (CMCA) were detected in 4 patients (29%) on first testing or at follow-up. The abnormalities were del(20q) in two patients, i(7q) in one, and combined del(20q) and i(7q) in one. The following tests did not distinguish patients with CMCA from other SDS patients: severity of peripheral cytopenia, fetal hemoglobin levels, percentage of marrow CD34+ cells, colony growth from marrow CD34+ cells, cluster-to-colony ratio, marrow stromal function, percentage of marrow apoptosis cells, and granulocyte colony-stimulating factor receptor expression. RAS and p53 mutation analysis and AML blast colony assays were uniformly negative. No patients showed progression into more advanced stages of MDS or into AML. In one patient, the abnormal clone became undetectable after 2 years of follow-up. CONCLUSIONS: We conclude that although CMCA in SDS is high, progression into advanced stages of MDS or to overt AML may be slow and difficult to predict. Treatment should be cautious since some abnormal clones can regress.

Acute Disease↗