RESUMO
Chromosomal translocations involving the immunoglobulin heavy chain (IGH) locus define common subgroups of B-cell lymphoma but are rare in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Recent fluorescent in situ hybridization and molecular cloning studies have identified several novel IGH translocations involving genes that play important roles in normal hemopoiesis, including the cytokine receptor genes CRLF2 and EPOR, all members of the CCAAT enhancer-binding protein gene family, as well as genes not normally expressed in hemopoietic cells including inhibitor of DNA binding 4. IGH translocation results in deregulated target gene expression because of juxtaposition with IGH transcriptional enhancers. However, many genes targeted by IGH translocations are also more commonly deregulated in BCP-ALL as a consequence of other genetic or epigenetic mechanisms. For example, interstitial genomic deletions also result in deregulated CRLF2 expression, whereas EPOR expression is deregulated as a consequence of the ETV6-RUNX1 fusion. The possible clinical importance of many of the various IGH translocations in BCP-ALL remains to be determined from prospective studies, but CRLF2 expression is associated with a poor prognosis. Despite their rarity, IGH chromosomal translocations in BCP-ALL therefore define not only new mechanisms of B-cell transformation but also clinically important subgroups of disease and suggest new targeted therapeutic approaches.
Assuntos
Linfócitos B/metabolismo , Transformação Celular Neoplásica/metabolismo , Cadeias Pesadas de Imunoglobulinas/metabolismo , Leucemia-Linfoma Linfoblástico de Células Precursoras B/metabolismo , Locos de Características Quantitativas , Translocação Genética , Doença Aguda , Animais , Transformação Celular Neoplásica/genética , Subunidade alfa 2 de Fator de Ligação ao Core/biossíntese , Subunidade alfa 2 de Fator de Ligação ao Core/genética , Regulação Leucêmica da Expressão Gênica/genética , Hematopoese/genética , Humanos , Cadeias Pesadas de Imunoglobulinas/genética , Proteínas Inibidoras de Diferenciação/biossíntese , Proteínas Inibidoras de Diferenciação/genética , Proteínas de Fusão Oncogênica/biossíntese , Proteínas de Fusão Oncogênica/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras B/diagnóstico , Leucemia-Linfoma Linfoblástico de Células Precursoras B/genética , Leucemia-Linfoma Linfoblástico de Células Precursoras B/terapia , Prognóstico , Receptores de Citocinas/biossíntese , Receptores de Citocinas/genética , Receptores da Eritropoetina/biossíntese , Receptores da Eritropoetina/genéticaRESUMO
Many subtypes of B-cell malignancy are characterized by chromosomal translocations that target the immunoglobulin loci. Molecular cloning of such translocations continues to allow the identification of genes whose deregulated expression plays a pivotal role in the pathogenesis of B-cell malignancy. The clustering of breakpoints within the immunoglobulin loci has allowed the development of rapid and robust polymerase chain reaction methods for cloning. We discuss in this chapter the use of long-distance inverse polymerase chain reaction methods to clone immunoglobulin chromosomal translocation breakpoints from clinical material. These methods have been successfully applied to several other types of chromosomal translocation including those involving other genes such as BCL6, ETV6, and MYC.
Assuntos
Quebra Cromossômica , Rearranjo Gênico , Genes de Imunoglobulinas , Reação em Cadeia da Polimerase/métodos , Translocação Genética , Cromossomos Humanos/genética , Clonagem Molecular , Proteínas de Ligação a DNA/genética , Genes myc/fisiologia , Humanos , Linfoma não Hodgkin/genética , Proteínas Nucleares/genética , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas c-bcl-6 , Proteínas Proto-Oncogênicas c-ets , Proteínas Repressoras/genética , Fatores de Transcrição/genética , Variante 6 da Proteína do Fator de Translocação ETSRESUMO
Members of the PRDM protein family have been shown to play important roles during embryonic development. Previous in vitro and in situ analyses indicated a function of Prdm6 in cells of the vascular system. To reveal physiological functions of Prdm6, we generated conditional Prdm6-deficient mice. Complete deletion of Prdm6 results in embryonic lethality due to cardiovascular defects associated with aberrations in vascular patterning. However, smooth muscle cells could be regularly differentiated from Prdm6-deficient embryonic stem cells and vascular smooth muscle cells were present and proliferated normally in Prdm6-deficient embryos. Conditional deletion of Prdm6 in the smooth muscle cell lineage using a SM22-Cre driver line resulted in perinatal lethality due to hemorrhage in the lungs. We thus identified Prdm6 as a factor that is essential for the physiological control of cardiovascular development.
Assuntos
Sistema Cardiovascular/embriologia , Proteínas Repressoras/fisiologia , Animais , Sequência de Bases , Northern Blotting , Southern Blotting , Padronização Corporal , Diferenciação Celular , Proliferação de Células , Primers do DNA , Camundongos , Camundongos Knockout , Músculo Liso/citologia , Neovascularização Fisiológica , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase , Proteínas Repressoras/genéticaRESUMO
Integrative genomic and gene-expression analyses have identified amplified oncogenes in B-cell non-Hodgkin lymphoma (B-NHL), but the capability of such technologies to localize tumor suppressor genes within homozygous deletions remains unexplored. Array-based comparative genomic hybridization (CGH) and gene-expression microarray analysis of 48 cell lines derived from patients with different B-NHLs delineated 20 homozygous deletions at 7 chromosome areas, all of which contained tumor suppressor gene targets. Further investigation revealed that only a fraction of primary biopsies presented inactivation of these genes by point mutation or intragenic deletion, but instead some of them were frequently silenced by epigenetic mechanisms. Notably, the pattern of genetic and epigenetic inactivation differed among B-NHL subtypes. Thus, the P53-inducible PIG7/LITAF was silenced by homozygous deletion in primary mediastinal B-cell lymphoma and by promoter hypermethylation in germinal center lymphoma, the proapoptotic BIM gene presented homozygous deletion in mantle cell lymphoma and promoter hypermethylation in Burkitt lymphoma, the proapoptotic BH3-only NOXA was mutated and preferentially silenced in diffuse large B-cell lymphoma, and INK4c/P18 was silenced by biallelic mutation in mantle-cell lymphoma. Our microarray strategy has identified novel candidate tumor suppressor genes inactivated by genetic and epigenetic mechanisms that substantially vary among the B-NHL subtypes.
Assuntos
Proteínas Reguladoras de Apoptose/genética , Proteínas de Transporte/genética , Inibidor de Quinase Dependente de Ciclina p18/genética , Genes Supressores de Tumor , Proteínas de Homeodomínio/genética , Linfoma de Células B/genética , Proteínas de Membrana/genética , Proteínas Nucleares/genética , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas/genética , Deleção de Sequência , Fatores de Transcrição/genética , Proteínas de Transporte Vesicular/genética , Proteínas Adaptadoras de Transdução de Sinal , Apoptose/genética , Proteína 11 Semelhante a Bcl-2 , Biópsia , Linhagem Celular Tumoral , Mapeamento Cromossômico , Cromossomos Humanos/genética , Cromossomos Humanos/ultraestrutura , Metilação de DNA , Análise Mutacional de DNA , DNA de Neoplasias/genética , Epigênese Genética , Dosagem de Genes , Regulação Neoplásica da Expressão Gênica , Inativação Gênica , Homozigoto , Humanos , Linfoma de Células B/classificação , Linfoma de Células B/imunologia , Linfoma de Células B/patologia , Hibridização de Ácido Nucleico , Análise de Sequência com Séries de Oligonucleotídeos , Mutação Puntual , Regiões Promotoras Genéticas/genética , Proteínas de Ligação a RNA , Nexinas de ClassificaçãoRESUMO
CCAAT enhancer-binding protein (CEBP) transcription factors play pivotal roles in proliferation and differentiation, including suppression of myeloid leukemogenesis. Mutations of CEBPA are found in a subset of acute myeloid leukemia (AML) and in some cases of familial AML. Here, using cytogenetics, fluorescence in situ hybridization (FISH), and molecular cloning, we show that 5 CEBP gene family members are targeted by recurrent IGH chromosomal translocations in BCP-ALL. Ten patients with t(8;14)(q11;q32) involved CEBPD on chromosome 8, and 9 patients with t(14;19)(q32;q13) involved CEBPA, while a further patient involved CEBPG, located 71 kb telomeric of CEBPA in chromosome band 19q13; 4 patients with inv(14)(q11q32)/t(14;14)(q11;q32) involved CEBPE and 3 patients with t(14;20)(q32;q13) involved CEBPB. In 16 patients the translocation breakpoints were cloned using long-distance inverse-polymerase chain reaction (LDI-PCR). With the exception of CEBPD breakpoints, which were scattered within a 43-kb region centromeric of CEBPD, translocation breakpoints were clustered immediately 5' or 3' of the involved CEBP gene. Except in 1 patient with t(14;14)(q11;q32), the involved CEBP genes retained germ-line sequences. Quantitative reverse transcription (RT)-PCR showed overexpression of the translocated CEBP gene. Our findings implicate the CEBP gene family as novel oncogenes in BCP-ALL, and suggest opposing functions of CEBP dysregulation in myeloid and lymphoid leukemogenesis.