RESUMO
TEL-JAK2 fusion proteins, which are a result of t(9;12)(p24;p13) translocations associated with human leukemia, activate Stat5 in vitro and in vivo and cause a myelo- and lymphoproliferative disease in a murine bone marrow transplant model. We report that Socs-1, a member of the SOCS family of endogenous inhibitors of JAKs and STATs, inhibits transformation of Ba/F3 cells by TEL-JAK2 but has no effect on Ba/F3 cells transformed by BCR-ABL, TEL-ABL, or TEL-platelet-derived growth factor receptor beta. TEL-JAK2, in addition to activating Stat5, associates with Shc and Grb2 and induces activation of Erk2, and expression of Socs-1 inhibits engagement of each of these signaling molecules. TEL-JAK2 kinase activity is inhibited by Socs-1, as assessed by in vitro kinase assays. In addition, Socs-1 induces proteasomal degradation of TEL-JAK2. Mutational analysis indicates that the SOCS box of Socs-1 is required for proteasomal degradation and for abrogation of growth of TEL-JAK2-transformed cells. Furthermore, murine bone marrow transplant assays demonstrate that expression of Socs-1 prolongs latency of TEL-JAK2-mediated disease in vivo. Collectively, these data indicate that Socs-1 inhibits TEL-JAK2 in vitro and in vivo through inhibition of kinase activity and induction of TEL-JAK2 protein degradation.
Assuntos
Proteínas de Transporte/fisiologia , Cisteína Endopeptidases/fisiologia , Células-Tronco Hematopoéticas/fisiologia , Complexos Multienzimáticos/fisiologia , Proteínas de Fusão Oncogênica/fisiologia , Proteínas Tirosina Quinases/fisiologia , Proteínas Proto-Oncogênicas , Proteínas Repressoras , Animais , Linhagem Celular , Transformação Celular Neoplásica , Ativação Enzimática , Células-Tronco Hematopoéticas/patologia , Janus Quinase 2 , Camundongos , Complexo de Endopeptidases do Proteassoma , Transdução de Sinais/fisiologia , Proteína 1 Supressora da Sinalização de Citocina , Proteínas Supressoras da Sinalização de CitocinaRESUMO
STAT5 is activated in a broad spectrum of human hematologic malignancies. We addressed whether STAT5 activation is necessary for the myelo- and lymphoproliferative disease induced by TEL/JAK2 using a genetic approach. Whereas mice transplanted with bone marrow transduced with retrovirus expressing TEL/JAK2 develop a rapidly fatal myelo- and lymphoproliferative syndrome, reconstitution with bone marrow derived from Stat5ab-deficient mice expressing TEL/JAK2 did not induce disease. Disease induction in the Stat5a/b-deficient background was rescued with a bicistronic retrovirus encoding TEL/JAK2 and Stat5a. Furthermore, myeloproliferative disease was induced by reconstitution with bone marrow cells expressing a constitutively active mutant, Stat5a, or a single Stat5a target, murine oncostatin M (mOSM). These data define a critical role for Stat5a/b and mOSM in the pathogenesis of TEL/JAK2 disease.
Assuntos
Proteínas de Ligação a DNA/genética , Transtornos Linfoproliferativos/fisiopatologia , Proteínas do Leite , Transtornos Mieloproliferativos/fisiopatologia , Proteínas de Fusão Oncogênica/genética , Transativadores/genética , Animais , Southern Blotting , Células da Medula Óssea/patologia , Transplante de Medula Óssea , Ensaio de Unidades Formadoras de Colônias , DNA de Neoplasias/análise , Fibrose , Citometria de Fluxo , Técnicas de Transferência de Genes , Transtornos Linfoproliferativos/genética , Camundongos , Camundongos Mutantes , Mutagênese/fisiologia , Transtornos Mieloproliferativos/genética , Transplante de Neoplasias , Oncostatina M , Peptídeos/genética , Fenótipo , Retroviridae/genética , Fator de Transcrição STAT5RESUMO
Recent reports have demonstrated fusion of the TEL gene on 12p13 to the JAK2 gene on 9p24 in human leukemias. Three variants have been identified that fuse the TEL pointed (PNT) domain to (i) the JAK2 JH1-kinase domain, (ii) part of and (iii) all of the JH2 pseudokinase domain. We report that all of the human TEL/JAK2 variants, and a human/mouse chimeric hTEL/mJAK2(JH1) fusion gene, transform the interleukin-3 (IL-3)-dependent murine hematopoietic cell line Ba/F3 to IL-3-independent growth. Transformation requires both the TEL PNT domain and JAK2 kinase activity. Furthermore, all TEL/JAK2 variants strongly activated STAT 5 by phosphotyrosine Western blots and by electrophoretic mobility shift assays (EMSA). Mice (n = 40) transplanted with bone marrow infected with the MSCV retrovirus containing either the hTEL/mJAK2(JH1) fusion or its human counterpart developed a fatal mixed myeloproliferative and T-cell lymphoproliferative disorder with a latency of 2-10 weeks. In contrast, mice transplanted with a TEL/JAK2 mutant lacking the TEL PNT domain (n = 10) or a kinase-inactive TEL/JAK2(JH1) mutant (n = 10) did not develop the disease. We conclude that all human TEL/JAK2 fusion variants are oncoproteins in vitro that strongly activate STAT 5, and cause lethal myelo- and lymphoproliferative syndromes in murine bone marrow transplant models of leukemia.