RESUMO
The development of hematopoietic neoplasms is often associated with mutations, altered gene expression or chromosomal translocations. Recently, the t(5, 9)(q33;q22) translocation was found in a subset of peripheral T cell lymphomas and was shown to result in an IL-2-inducible kinase-spleen tyrosine kinase (ITK-Syk) fusion transcript. In this study, we show that T cell-specific expression of the ITK-Syk oncogene in mice leads to an early onset and aggressive polyclonal T cell lymphoproliferation with concomitant B cell expansion and systemic inflammation by 7-9 wk of age. Because this phenotype is strikingly different from previous work showing that ITK-Syk expression causes clonal T cell lymphoma by 20-27 wk of age, we investigated the underlying molecular mechanism in more detail. We show that the reason for the severe phenotype is the lack of B-lymphocyte-induced maturation protein-1 (Blimp-1) induction by low ITK-Syk expression. In contrast, high ITK-Syk oncogene expression induces terminal T cell differentiation in the thymus by activating Blimp-1, thereby leading to elimination of oncogene-expressing cells early in development. Our data suggest that terminal differentiation is an important mechanism to prevent oncogene-expressing cells from malignant transformation, as high ITK-Syk oncogene activity induces cell elimination. Accordingly, for transformation, a specific amount of oncogene is required, or alternatively, the induction of terminal differentiation is defective.
Assuntos
Inflamação/etiologia , Peptídeos e Proteínas de Sinalização Intracelular/fisiologia , Ativação Linfocitária/imunologia , Linfopoese/imunologia , Transtornos Linfoproliferativos/etiologia , Proteínas de Fusão Oncogênica/fisiologia , Proteínas Tirosina Quinases/fisiologia , Subpopulações de Linfócitos T/patologia , Fatores Etários , Animais , Subpopulações de Linfócitos B/imunologia , Subpopulações de Linfócitos B/patologia , Células Cultivadas , Quimera , Citocinas/sangue , DNA Complementar/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Hipergamaglobulinemia/etiologia , Inflamação/genética , Inflamação/imunologia , Inflamação/patologia , Peptídeos e Proteínas de Sinalização Intracelular/genética , Transtornos Linfoproliferativos/genética , Transtornos Linfoproliferativos/imunologia , Transtornos Linfoproliferativos/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas de Fusão Oncogênica/genética , Fosforilação , Fator 1 de Ligação ao Domínio I Regulador Positivo , Processamento de Proteína Pós-Traducional , Proteínas Tirosina Quinases/genética , Proteínas Recombinantes de Fusão , Fator de Transcrição STAT3/metabolismo , Quinase Syk , Subpopulações de Linfócitos T/imunologia , Subpopulações de Linfócitos T/metabolismo , Timo/imunologia , Timo/patologia , Fatores de Transcrição/biossíntese , Fatores de Transcrição/genética , Transdução Genética , Translocação GenéticaRESUMO
Peripheral T-cell lymphomas (PTCL) constitute a major treatment problem with high mortality rates due to the minimal effectiveness of conventional chemotherapy. Recent findings identified ITK-SYK as the first recurrent translocation in 17% of unspecified PTCLs and showed the overexpression of SYK in more than 90% of PTCLs. Here, we show that the expression of ITK-SYK in the bone marrow of BALB/c mice causes a T-cell lymphoproliferative disease in all transplanted mice within 8 weeks after transplantation. The disease was characterized by the infiltration of spleen, lymph nodes, bone marrow, and skin with CD3+CD4+CD8- and CD3+CD4-CD8- ITK-SYK-positive T-cells accompanied by a systemic inflammatory reaction with upregulation of interleukin 5 and INF-gamma. ITK-SYK-positive T-cells showed enhanced apoptosis resistance and INF-gamma production in vitro. The disease was serially transplantable, inducing clonal T-cell expansion in secondary recipients. The action of ITK-SYK in vivo was dependent on SYK kinase activity and disease development could be inhibited by the treatment of mice with SYK inhibitors. Interestingly, the translocation of ITK-SYK from the membrane to the cytoplasm, using a point mutation in the pleckstrin homology domain (ITK-SYK R29C), did not abolish, but rather, enhanced disease development in transplanted mice. CBL binding was strongly enhanced in membrane-associated ITK-SYK E42K and was causative for delayed disease development. Our results show that ITK-SYK causes a T-cell lymphoproliferative disease in mice, supporting its role in T-cell lymphoma development in humans. Therefore, pharmacologic inhibition of SYK in patients with U-PTCLs carrying the ITK-SYK fusion protein might be an effective treatment strategy.
Assuntos
Peptídeos e Proteínas de Sinalização Intracelular/imunologia , Linfoma de Células T/imunologia , Transtornos Linfoproliferativos/imunologia , Proteínas de Fusão Oncogênica/imunologia , Proteínas Tirosina Quinases/imunologia , Animais , Linfócitos B/imunologia , Transplante de Medula Óssea , Modelos Animais de Doenças , Feminino , Humanos , Imunofenotipagem , Peptídeos e Proteínas de Sinalização Intracelular/genética , Ativação Linfocitária , Linfoma de Células T/enzimologia , Linfoma de Células T/genética , Linfoma de Células T/patologia , Transtornos Linfoproliferativos/genética , Transtornos Linfoproliferativos/patologia , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Proteínas de Fusão Oncogênica/biossíntese , Proteínas de Fusão Oncogênica/genética , Mutação Puntual , Proteínas Tirosina Quinases/biossíntese , Proteínas Tirosina Quinases/genética , Proteínas Proto-Oncogênicas c-cbl/metabolismo , Quinase Syk , Linfócitos T/imunologiaRESUMO
In lysine biosynthesis, dihydrodipicolinate reductase (DHDPR) catalyses the formation of tetrahydrodipicolinate. Unlike DHDPR enzymes from Escherichia coli and Mycobacterium tuberculosis, which have dual specificity for both NADH and NADPH as co-factors, the enzyme from Thermotoga maritima has a significantly greater affinity for NADPH. Despite low sequence identity with the E. coli and M. tuberculosis DHDPR enzymes, DHDPR from T. maritima has a similar catalytic site, with many conserved residues involved in interactions with substrates. This suggests that as the enzyme evolved, the co-factor specificity was relaxed. Kinetic studies show that the T. maritima DHDPR enzyme is inhibited by high concentrations of its substrate, DHDP, and that at high concentrations NADH also acts as an inhibitor of the enzyme, suggesting a novel method of regulation for the lysine biosynthetic pathway. Increased thermal stability of the T. maritima DHDPR enzyme may be associated with the lack of C-terminal and N-terminal loops that are present in the E. coli DHDPR enzyme.
