RESUMO
Chronic myelomonocytic leukemia (CMML) is a pre-leukemic syndrome that displays both myelodysplastic and myeloproliferative features. The t(5;12) chromosomal translocation, present in a subset of CMML patients with myeloproliferation fuses the amino terminal portion of the ets family member, Tel, with the transmembrane and tyrosine kinase domains of platelet-derived growth factor receptor beta (PDGFRbeta) gene. To investigate the role of this fusion protein in the pathogenesis of CMML, we expressed the Tel-PDGFRbeta fusion cDNA in hematopoietic cells of transgenic mice under the control of the human CD11a promoter. Transgenic founders and their offspring express the transgene specifically in hematopoietic tissues and develop a myeloproliferative syndrome characterized by: overproduction of mature neutrophils and megakaryocytes in the bone marrow; splenomegaly with effacement of splenic architecture by extramedullary hematopoiesis; an abnormal population of leukocytes co-expressing lymphoid and myeloid markers; and increased numbers of colonies in in vitro bone marrow CFU assays. All mice expressing the transgene exhibited at least one of these features of dysregulated myelopoiesis, and 20% progressed to a myeloid or lymphoid malignancy. This murine model of CMML parallels a myeloproliferative syndrome in humans and implicates the Tel-PDGFRbeta fusion protein in its pathogenesis.
Assuntos
Proteínas de Ligação a DNA/genética , Leucemia Mielomonocítica Crônica/genética , Transtornos Mieloproliferativos/genética , Proteínas de Fusão Oncogênica/genética , Receptor beta de Fator de Crescimento Derivado de Plaquetas/genética , Proteínas Repressoras , Fatores de Transcrição/genética , Animais , Medula Óssea/metabolismo , Medula Óssea/patologia , Ensaio de Unidades Formadoras de Colônias , Proteínas de Ligação a DNA/metabolismo , Feminino , Citometria de Fluxo , Hematopoese , Células-Tronco Hematopoéticas/metabolismo , Células-Tronco Hematopoéticas/patologia , Leucemia Mielomonocítica Crônica/patologia , Leucemia Mielomonocítica Crônica/fisiopatologia , Leucócitos/metabolismo , Leucócitos/patologia , Masculino , Megacariócitos/metabolismo , Megacariócitos/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Transtornos Mieloproliferativos/patologia , Transtornos Mieloproliferativos/fisiopatologia , Proteínas de Fusão Oncogênica/metabolismo , Regiões Promotoras Genéticas/genética , Proteínas Proto-Oncogênicas c-ets , Receptor beta de Fator de Crescimento Derivado de Plaquetas/metabolismo , Baço/metabolismo , Baço/patologia , Fatores de Transcrição/metabolismo , Transgenes/genética , Variante 6 da Proteína do Fator de Translocação ETSRESUMO
Purine nucleoside phosphorylase (PNP) deficiency is an inherited autosomal recessive disorder resulting in severe combined immunodeficiency. The purpose of this study was to determine the molecular defects responsible for PNP deficiency in one such patient. The patient's PNP cDNA was amplified by PCR and sequenced. Point mutations leading to amino acid substitutions were found in both alleles. One point mutation led to a Ser-to-Gly substitution at amino acid 51 and was common to both alleles. In addition, an Asp-to-Gly substitution at amino acid 128 and an Arg-to-Pro substitution at amino acid 234 were found in the maternal and paternal alleles, respectively. In order to prove that these mutations were responsible for the disease state, each of the three mutations was constructed separately by site-directed mutagenesis of the normal PNP cDNA, and each was transiently expressed in COS cells. Lysates from cells transfected with the allele carrying the substitution at amino acid 51 retained both function and immunoreactivity. Lysates from cells transfected with PNP alleles carrying a substitution at either amino acid 128 or amino acid 234 contained immunoreactive material but had no detectable human PNP activity. In summary, molecular analysis of this patient identified point mutations within the PNP gene which are responsible for the enzyme deficiency.