RESUMO
Tumorigenesis in rodents, as well as in humans, has been shown to be a multistep process, with each step reflecting an altered gene product or gene regulatory process leading to autonomy of cell growth. Initial genetic mutations are often associated with dysfunctional growth regulation, as is demonstrated in several transgenic mouse models. These changes are often followed by alterations in tumor suppressor gene function, allowing unchecked cell cycle progression and, by genomic instability, additional genetic mutations responsible for tumor metastasis. Here we show that reduced transforming growth factor-beta signaling in T lymphocytes leads to a rapid expansion of a CD8+ memory T-cell population and a subsequent transformation to leukemia/lymphoma as shown by multiple criteria, including peripheral blood cell counts histology, T-cell receptor monoclonality, and host transferability. Furthermore, spectral karyotype analysis of the tumors shows that the tumors have various chromosomal aberrations. These results suggest that reduced transforming growth factor-beta signaling acts as a primary carcinogenic event, allowing uncontrolled proliferation with consequent accumulation of genetic defects and leukemic transformation.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Leucemia de Células T/imunologia , Transtornos Linfoproliferativos/imunologia , Fator de Crescimento Transformador beta/imunologia , Animais , Linfócitos T CD8-Positivos/patologia , Transformação Celular Neoplásica/imunologia , Transformação Celular Neoplásica/patologia , Aberrações Cromossômicas , Memória Imunológica , Leucemia de Células T/genética , Leucemia de Células T/patologia , Transtornos Linfoproliferativos/genética , Transtornos Linfoproliferativos/patologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Proteínas Serina-Treonina Quinases , Receptor do Fator de Crescimento Transformador beta Tipo II , Receptores de Antígenos de Linfócitos T/imunologia , Receptores de Fatores de Crescimento Transformadores beta/imunologia , Transdução de SinaisRESUMO
We examined the MLL translocation in two cases of infant AML with X chromosome disruption. The G-banded karyotype in the first case suggested t(X;3)(q22;p21)ins(X;11)(q22;q13q25). Southern blot analysis showed one MLL rearrangement. Panhandle PCR approaches were used to identify the MLL fusion transcript and MLL genomic breakpoint junction. SEPTIN6 from chromosome band Xq24 was the partner gene of MLL. MLL exon 7 was joined in-frame to SEPTIN6 exon 2 in the fusion transcript. The MLL genomic breakpoint was in intron 7; the SEPTIN6 genomic breakpoint was in intron 1. Spectral karyotyping revealed a complex rearrangement disrupting band 11q23. FISH with a probe for MLL confirmed MLL involvement and showed that the MLL-SEPTIN6 junction was on the der(X). The MLL genomic breakpoint was a functional DNA topoisomerase II cleavage site in an in vitro assay. In the second case, the karyotype revealed t(X;11)(q22;q23). Southern blot analysis showed two MLL rearrangements. cDNA panhandle PCR detected a transcript fusing MLL exon 8 in-frame to SEPTIN6 exon 2. MLL and SEPTIN6 are vulnerable to damage to form recurrent translocations in infant AML. Identification of SEPTIN6 and the SEPTIN family members hCDCrel and MSF as partner genes of MLL suggests a common pathway to leukaemogenesis.
Assuntos
Cromossomos Humanos Par 11/genética , DNA Topoisomerases Tipo II/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação ao GTP/genética , Leucemia Mieloide/genética , Proto-Oncogenes , Fatores de Transcrição , Translocação Genética/genética , Cromossomo X/genética , Doença Aguda , Sequência de Bases , Quebra Cromossômica/genética , Mapeamento Cromossômico , Cromossomos Humanos Par 3/genética , Proteínas do Citoesqueleto , Histona-Lisina N-Metiltransferase , Humanos , Hibridização in Situ Fluorescente , Lactente , Leucemia Mielomonocítica Aguda/genética , Dados de Sequência Molecular , Proteína de Leucina Linfoide-Mieloide , SeptinasRESUMO
Few t(9;11) translocations in DNA topoisomerase II inhibitor-related leukemias have been studied in detail and the DNA damage mechanism remains controversial. We characterized the der(11) and der(9) genomic breakpoint junctions in a case of AML following etoposide and doxorubicin. Etoposide-, etoposide metabolite- and doxorubicin-induced DNA topoisomerase II cleavage was examined in normal homologues of the MLL and AF-9 breakpoint sequences using an in vitro assay. Induction of DNA topoisomerase II cleavage complexes in CEM and K562 cell lines was investigated using an in vivo complex of enzyme assay. The translocation occurred between identical 5'-TATTA-3' sequences in MLL intron 8 and AF-9 intron 5 without the gain or loss of bases. The 5'-TATTA-3' sequences were reciprocally cleaved by DNA topoisomerase II in the presence of etoposide, etoposide catechol or etoposide quinone, creating homologous 4-base 5' overhangs that would anneal to form both breakpoint junctions without any processing. der(11) and der(4) translocation breakpoints in a treatment-related ALL at the same site in MLL are consistent with a damage hotspot. Etoposide and both etoposide metabolites induced DNA topoisomerase II cleavage complexes in the hematopoietic cell lines. These results favor the model in which the chromosomal breakage leading to MLL translocations in DNA topoisomerase II inhibitor-related leukemias is a consequence of DNA topoisomerase II cleavage.
Assuntos
DNA Topoisomerases Tipo II/metabolismo , Proteínas de Ligação a DNA/metabolismo , Leucemia Mieloide Aguda/metabolismo , Proteínas Nucleares/metabolismo , Processamento de Proteína Pós-Traducional , Proto-Oncogenes , Fatores de Transcrição , Adolescente , DNA Topoisomerases Tipo II/genética , Proteínas de Ligação a DNA/genética , Histona-Lisina N-Metiltransferase , Humanos , Hibridização in Situ Fluorescente , Leucemia Mieloide Aguda/genética , Masculino , Dados de Sequência Molecular , Proteína de Leucina Linfoide-Mieloide , Proteínas Nucleares/genética , Recombinação Genética , Translocação GenéticaRESUMO
Cytogenetic data have significantly contributed to our understanding of the heterogeneity of acute myeloid leukemia (AML). In AML, numerous recurrent chromosomal aberrations have been identified, and several of them, e.g. t(8;21)(q22;q22), t(15;17)(q22;q11-12), inv(16)(p13q22), are specific for distinct subgroups. Furthermore, chromosomal aberrations have proved to be of paramount prognostic importance for remission induction and survival. Chromosome analysis using classical cytogenetic banding techniques often fails to completely resolve complex karyotypes and cryptic translocations not identifiable by these techniques have been detected using molecular cytogenetic methods. While fluorescence in situ hybridization (FISH) has become an indispensable tool for screening and follow-up of known aberrations, the techniques of spectral karyotyping (SKY) and multiplex-fluorescence in situ hybridization (M-FISH) allow for the simultaneous visualization of all chromosomes of a metaphase in a single hybridization step, and thereby enable screening for the aberrations present without their prior knowledge. Therefore, with the introduction of these techniques in 1996 the comprehensive analysis of complex karyotypes and the identification of new, hitherto cryptic translocations and, ultimately, the identification of new disease subgroups seemed possible. Since, more than 600 cases of AML and MDS have been analyzed. Herein, we attempt to summarize the data published and discuss what has been achieved towards realization of these goals.