RESUMEN
Endemic, sporadic and HIV-associated Burkitt lymphoma (BL) all have a B-cell phenotype and a MYC translocation, but a variable association with the Epstein-Barr virus (EBV). However, there is still no satisfactory explanation of how EBV participates in the pathogenesis of BL. A recent investigation suggested that EBV-positive and EBV-negative BL have different cells of origin. In particular, according to immunoglobulin gene mutation analysis, EBV-negative BLs may originate from early centroblasts, whereas EBV-positive BLs seem to arise from postgerminal center B cells or memory B cells. The appearance of a germinal center phenotype in EBV-positive cells might thus derive from a block in B-cell differentiation. The exit from the germinal center involves a complex series of events, which require the activation of BLIMP-1, and the consequent downregulation of several target genes. Here, we investigated the expression of specific miRNAs predicted to be involved in B-cell differentiation and found that hsa-miR-127 is differentially expressed between EBV-positive and EBV-negative BLs. In particular, it was strongly upregulated only in EBV-positive BL samples, whereas EBV-negative cases showed levels of expression similar to normal controls, including microdissected germinal centers (GC) cells. In addition, we found evidence that hsa-miR-127 is involved in B-cell differentiation process through posttranscriptional regulation of BLIMP1 and XBP1. The overexpression of this miRNA may thus represent a key event in the lymphomagenesis of EBV positive BL, by blocking the B-cell differentiation process.
Asunto(s)
Linfocitos B/metabolismo , Linfoma de Burkitt/genética , Diferenciación Celular , MicroARNs/genética , Procesamiento Postranscripcional del ARN , Adolescente , Adulto , Linfocitos B/patología , Linfocitos B/virología , Western Blotting , Linfoma de Burkitt/metabolismo , Linfoma de Burkitt/patología , Línea Celular Tumoral , Niño , Preescolar , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Femenino , Perfilación de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Herpesvirus Humano 4/crecimiento & desarrollo , Humanos , Masculino , Persona de Mediana Edad , Factor 1 de Unión al Dominio 1 de Regulación Positiva , Factores de Transcripción del Factor Regulador X , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Proteína 1 de Unión a la X-Box , Adulto JovenRESUMEN
Cdk9/Cyclin T1 complex is very important in controlling specific differentiative pathways of several cell types. Limited data are available regarding the expression of Cdk9/Cyclin T1 in hematopoietic and lymphoid tissues. Cdk9/Cyclin T1 expression seems to be related to particular stages of lymphoid differentiation/activation. In this study, we observed that the expression level of Cdk9/Cyclin T1 in vivo increases in memory B cells compared to naïve B cells, and in activated B cells, compared to non-activated ones. The expression level of the Cdk9/Cyclin T1 complex does not increase in cells induced to differentiate in vitro. In addition, we showed that Cdk9 interacts with E12 and E47, specifically activated during Germinal Center (GC) reaction. Taken together this data suggests an active role for the Cdk9/Cyclin T1 complex during lymphoid differentiation through germinal center reaction.
Asunto(s)
Linfocitos B/citología , Linfocitos B/enzimología , Diferenciación Celular , Quinasa 9 Dependiente de la Ciclina/metabolismo , Ciclinas/metabolismo , Activación de Linfocitos/inmunología , Linfocitos B/metabolismo , Supervivencia Celular , Ciclina T , Quinasa 9 Dependiente de la Ciclina/genética , Ciclinas/genética , Regulación de la Expresión Génica , Centro Germinal/enzimología , Humanos , Células Jurkat , Ganglios Linfáticos/enzimología , Microscopía Confocal , Unión Proteica , Transporte de Proteínas , Factores de Transcripción TCF/metabolismo , Proteína 1 Similar al Factor de Transcripción 7RESUMEN
Burkitt lymphoma (BL) is a B-cell tumor whose characteristic gene aberration is the translocation t(8;14), which determines c-myc overexpression. Several genetic and epigenetic alterations other than c-myc overexpression have also been described in BL. It has been demonstrated that the RBL2/p130 gene, a member of the retinoblastoma family (pRbs), is mutated in BL cell lines and primary tumors. The aim of this study was to investigate the biologic effect of RBL2/p130 in BL cells and its possible role in lymphomagenesis. Therefore, we reintroduced a functional RBL2/p130 in BL cell lines where this gene was mutated. Our results demonstrated that RBL2/p130-transfected cells regain growth control. This suggests that RBL2/p130 may control the expression of several genes, which may be important for cell growth and viability. Gene-expression analysis revealed a modulation of several genes, including CGRRF1, RGS1, BTG1, TIA1, and PCDHA2, upon RBL2/p130 reintroduction. We then monitored their expression in primary tumors of endemic BL as well, demonstrating that their expression resembled those of the BL cell lines. In conclusion, these data suggest that, as RBL2/p130 modulates the expression of target genes, which are important for cell growth and viability, its inactivation may be relevant for the occurrence of BL.
Asunto(s)
Biomarcadores de Tumor/genética , Linfoma de Burkitt/genética , Perfilación de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Mutación/genética , Proteína p130 Similar a la del Retinoblastoma/genética , Adolescente , Linfoma de Burkitt/clasificación , Linfoma de Burkitt/metabolismo , Proliferación Celular , Niño , Preescolar , Femenino , Humanos , Masculino , Análisis de Secuencia por Matrices de Oligonucleótidos , Pronóstico , Proteína p130 Similar a la del Retinoblastoma/metabolismo , Células Tumorales CultivadasAsunto(s)
Silenciador del Gen , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Proteína p130 Similar a la del Retinoblastoma/deficiencia , Proteína p130 Similar a la del Retinoblastoma/genética , Línea Celular , Humanos , Neoplasias/genética , Neoplasias/metabolismo , Reproducibilidad de los Resultados , Fase de Descanso del Ciclo Celular , Proteína p130 Similar a la del Retinoblastoma/biosíntesis , TransfecciónRESUMEN
The Cdk9/Cyclin T1 complex is very important in controlling specific differentiative pathways of several cell types, including muscle cells and neurons. We recently demonstrated the involvement of this complex in B cell activation/differentiation. To check whether the Cdk9/Cyclin T1 complex is also involved in the T cell activation/differentiation process, we isolated different T cell populations by magnetic separation, based on their surface antigens. We observed that the expression level of Cdk9/Cyclin T1 increases in effector T cells (CD27(+)), as well as in activated T cells (CD25(+)) and memory T cells (CD45RA(-)), thus suggesting a specific upregulation of the Cdk9/Cyclin T1 complex following antigen encounter. We have previously demonstrated that in B cells, Cdk9 interacts in vivo with the E2A gene products E12/E47 (members of the basic helix-loop-helix family) which are involved in differentiation. In this article, we show that this interaction also occurs in T cells. This suggests an active role for the Cdk9/Cyclin T1 complex during lymphoid differentiation, through physical binding with E12 and E47. These preliminary results suggest that the Cdk9/Cyclin T1 complex may be important in the activation and differentiation program of lymphoid cells and that its upregulation, which is due to still unknown mechanisms, may contribute to malignant transformation.
