RESUMO
Lymphomas are assumed to originate at different stages of lymphocyte development through chromosomal aberrations. Thus, different lymphomas resemble lymphocytes at distinct differentiation stages and show characteristic morphologic, genetic, and transcriptional features. Here, we have performed a microarray-based DNA methylation profiling of 83 mature aggressive B-cell non-Hodgkin lymphomas (maB-NHLs) characterized for their morphologic, genetic, and transcriptional features, including molecular Burkitt lymphomas and diffuse large B-cell lymphomas. Hierarchic clustering indicated that methylation patterns in maB-NHLs were not strictly associated with morphologic, genetic, or transcriptional features. By supervised analyses, we identified 56 genes de novo methylated in all lymphoma subtypes studied and 22 methylated in a lymphoma subtype-specific manner. Remarkably, the group of genes de novo methylated in all lymphoma subtypes was significantly enriched for polycomb targets in embryonic stem cells. De novo methylated genes in all maB-NHLs studied were expressed at low levels in lymphomas and normal hematopoietic tissues but not in nonhematopoietic tissues. These findings, especially the enrichment for polycomb targets in stem cells, indicate that maB-NHLs with different morphologic, genetic, and transcriptional background share a similar stem cell-like epigenetic pattern. This suggests that maB-NHLs originate from cells with stem cell features or that stemness was acquired during lymphomagenesis by epigenetic remodeling.
Assuntos
Transformação Celular Neoplásica/genética , Epigênese Genética/fisiologia , Perfilação da Expressão Gênica , Genômica/métodos , Linfoma de Células B/genética , Análise de Sequência com Séries de Oligonucleotídeos , Transformação Celular Neoplásica/patologia , Metilação de DNA/fisiologia , Células-Tronco Embrionárias/metabolismo , Células-Tronco Embrionárias/fisiologia , Feminino , Perfilação da Expressão Gênica/métodos , Regulação Neoplásica da Expressão Gênica , Células-Tronco Hematopoéticas/metabolismo , Células-Tronco Hematopoéticas/fisiologia , Humanos , Linfoma de Células B/patologia , Masculino , Invasividade Neoplásica , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Transcrição Gênica/fisiologia , Células Tumorais CultivadasRESUMO
Classical Hodgkin's lymphoma (cHL) is a distinct malignancy of the immune system. Despite the progress made in the understanding of the pathology of cHL, the transforming events remain to be elucidated. It has been proposed that mutations in the TP53 gene in biopsy material as well as cell lines derived from cHL are rare and therefore not notably involved in the pathogenesis of the malignant H&RS cells. Re-evaluating the expression in cHL-derived cell lines, we found that in 3/6 of these cell lines, TP53 transcripts are characterized by deletions within exon 4 (L428 cells) and nearly a complete loss of exons 10 - 11 (L1236) or exons 8 - 11 (HDLM-2), respectively. These changes were found in otherwise rarely mutated regions of TP53. Cell lines L1236 and HDLM-2 harbour fusions with alu-repeats in their TP53 mRNA 3'-ends, resulting in the carboxyterminal truncation and loss of the transcriptional activity of p53. Transcriptional inactivity was also found for p53 in L428 cells. This study characterizes mutations in TP53 transcripts within cHL cell lines with associated functional defects in the resulting p53 proteins and therefore reintroduces the concept that mutations of TP53 might be involved in the pathogenesis of Hodgkin's lymphoma.
Assuntos
Regulação Neoplásica da Expressão Gênica , Doença de Hodgkin/genética , Mutação/genética , Deleção de Sequência , Proteína Supressora de Tumor p53/genética , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Análise Mutacional de DNA , DNA de Neoplasias/genética , DNA de Neoplasias/metabolismo , Éxons/genética , Doença de Hodgkin/metabolismo , Humanos , Immunoblotting , Reação em Cadeia da Polimerase , Proteínas Proto-Oncogênicas c-mdm2/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA Neoplásico/genética , RNA Neoplásico/metabolismo , Transcrição Gênica , Células Tumorais Cultivadas , Proteína Supressora de Tumor p53/metabolismoRESUMO
BACKGROUND: The distinction between Burkitt's lymphoma and diffuse large-B-cell lymphoma is unclear. We used transcriptional and genomic profiling to define Burkitt's lymphoma more precisely and to distinguish subgroups in other types of mature aggressive B-cell lymphomas. METHODS: We performed gene-expression profiling using Affymetrix U133A GeneChips with RNA from 220 mature aggressive B-cell lymphomas, including a core group of 8 Burkitt's lymphomas that met all World Health Organization (WHO) criteria. A molecular signature for Burkitt's lymphoma was generated, and chromosomal abnormalities were detected with interphase fluorescence in situ hybridization and array-based comparative genomic hybridization. RESULTS: We used the molecular signature for Burkitt's lymphoma to identify 44 cases: 11 had the morphologic features of diffuse large-B-cell lymphomas, 4 were unclassifiable mature aggressive B-cell lymphomas, and 29 had a classic or atypical Burkitt's morphologic appearance. Also, five did not have a detectable IG-myc Burkitt's translocation, whereas the others contained an IG-myc fusion, mostly in simple karyotypes. Of the 176 lymphomas without the molecular signature for Burkitt's lymphoma, 155 were diffuse large-B-cell lymphomas. Of these 155 cases, 21 percent had a chromosomal breakpoint at the myc locus associated with complex chromosomal changes and an unfavorable clinical course. CONCLUSIONS: Our molecular definition of Burkitt's lymphoma clarifies and extends the spectrum of the WHO criteria for Burkitt's lymphoma. In mature aggressive B-cell lymphomas without a gene signature for Burkitt's lymphoma, chromosomal breakpoints at the myc locus were associated with an adverse clinical outcome.
Assuntos
Linfoma de Burkitt/genética , Perfilação da Expressão Gênica , Expressão Gênica , Linfoma de Células B/genética , Algoritmos , Linfoma de Burkitt/diagnóstico , Linfoma de Burkitt/patologia , DNA de Neoplasias/análise , Diagnóstico Diferencial , Feminino , Seguimentos , Genes de Imunoglobulinas , Genes bcl-2 , Genes myc , Humanos , Linfoma de Células B/classificação , Linfoma de Células B/diagnóstico , Linfoma de Células B/mortalidade , Masculino , Pessoa de Meia-Idade , Análise de Sequência com Séries de Oligonucleotídeos , Proteínas de Fusão Oncogênica/genética , Prognóstico , RNA Neoplásico/análise , Taxa de Sobrevida , Transcrição Gênica , Translocação GenéticaRESUMO
Recently, comparative genomic hybridization (CGH)- and fluorescence in situ hybridization (FISH)-analyses of native Hodgkin and Reed-Sternberg (H&RS) cells extracted from Hodgkin lymphoma (HL) revealed a recurrent amplification of the HDM2 locus on chromosome 12. HDM2 is known to target, inactivate and to degrade p53. Wild type (wt) p53 protein is detected in high levels in HL. Simultaneously, stabilized wt p53 and spliced hdm2 transcripts have been observed in different tumors. Therefore, we examined the expression and structure of HDM2 in HL cell lines and possible effects on components of the p53 pathway. DNA integrity and induction potential of p53 was verified by DNA sequencing and detection of potential effector proteins (p21(WAF/CIP), HDM2) using immunofluorescence, respectively. All HL cell lines show an overexpression of HDM2 protein. Furthermore, several different spliced hdm2 transcripts (mdm-sv) including five new variants lacking a functional p53 binding site were characterized. If expressed, corresponding proteins were shown to be not restricted to the nucleus. Co-localization of the potential binding partners HDM2/p14(ARF) and HDM2/p53 was found in HL cell lines. We suggest that HDM2-sv have no significant disturbing influence on the interaction of these proteins.
