RESUMEN
RNA binding proteins drive proliferation and tumorigenesis by regulating the translation and stability of specific subsets of messenger RNAs (mRNAs). We have investigated the role of eukaryotic initiation factor 4B (eIF4B) in this process and identify 10-fold more RNA binding sites for eIF4B in tumour cells from patients with diffuse large B-cell lymphoma compared to control B cells and, using individual-nucleotide resolution UV cross-linking and immunoprecipitation, find that eIF4B binds the entire length of mRNA transcripts. eIF4B stimulates the helicase activity of eIF4A, thereby promoting the unwinding of RNA structure within the 5' untranslated regions of mRNAs. We have found that, in addition to its well-documented role in mRNA translation, eIF4B additionally interacts with proteins associated with RNA turnover, including UPF1 (up-frameshift protein 1), which plays a key role in histone mRNA degradation at the end of S phase. Consistent with these data, we locate an eIF4B binding site upstream of the stem-loop structure in histone mRNAs and show that decreased eIF4B expression alters histone mRNA turnover and delays cell cycle progression through S phase. Collectively, these data provide insight into how eIF4B promotes tumorigenesis.
Asunto(s)
Factores Eucarióticos de Iniciación , Histonas , Estabilidad del ARN , ARN Mensajero , Proteínas de Unión al ARN , Humanos , ARN Mensajero/metabolismo , ARN Mensajero/genética , Histonas/metabolismo , Proteínas de Unión al ARN/metabolismo , Proteínas de Unión al ARN/genética , Sitios de Unión , Factores Eucarióticos de Iniciación/metabolismo , Factores Eucarióticos de Iniciación/genética , Línea Celular Tumoral , Regiones no Traducidas 5' , Transactivadores/metabolismo , Transactivadores/genética , Linfoma de Células B Grandes Difuso/genética , Linfoma de Células B Grandes Difuso/metabolismo , Unión Proteica , Factor 4A Eucariótico de Iniciación/metabolismo , Factor 4A Eucariótico de Iniciación/genética , ARN HelicasasRESUMEN
We show that a common polymorphic variant in the ERCC5 5' untranslated region (UTR) generates an upstream ORF (uORF) that affects both the background expression of this protein and its ability to be synthesized following exposure to agents that cause bulky adduct DNA damage. Individuals that harbor uORF1 have a marked resistance to platinum-based agents, illustrated by the significantly reduced progression-free survival of pediatric ependymoma patients treated with such compounds. Importantly, inhibition of DNA-PKcs restores sensitivity to platinum-based compounds by preventing uORF1-dependent ERCC5 expression. Our data support a model in which a heritable 5' noncoding mRNA element influences individuals' responses to platinum-based chemotherapy.
Asunto(s)
Regiones no Traducidas 5'/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Resistencia a Antineoplásicos/genética , Endonucleasas/genética , Endonucleasas/metabolismo , Ependimoma/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Sistemas de Lectura Abierta/genética , Polimorfismo Genético/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Antineoplásicos/farmacología , Antineoplásicos/uso terapéutico , Proteínas de Unión al Calcio/metabolismo , Línea Celular , Línea Celular Tumoral , Cisplatino/farmacología , Cisplatino/uso terapéutico , Daño del ADN , Ependimoma/tratamiento farmacológico , Ependimoma/mortalidad , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Regulación Neoplásica de la Expresión Génica/genética , Células HeLa , HumanosRESUMEN
B-cell lymphomas are a heterogeneous group of diseases that can arise at different stages of B-cell development, often as a result of errors in the cells' unique ontogeny. Common oncogenic features are often observed, including chromosomal rearrangements, somatic mutations and transcriptional change. Disruption of translation regulation is also frequently implicated in both B-cell lymphoma development and progression. Deregulation of translation in lymphomagenesis can arise through changes to the proteins constituting the translational machinery or to their regulators, and to changes in miRNA (microRNA) expression.
Asunto(s)
Linfoma de Células B/genética , MicroARNs/metabolismo , Biosíntesis de Proteínas , Linfocitos B/patología , Linfocitos B/fisiología , Regulación Neoplásica de la Expresión Génica , Humanos , Linfoma de Células B/clasificación , Linfoma de Células B/diagnóstico , MicroARNs/genética , PronósticoRESUMEN
MYCN activation, mainly by gene amplification, is one of the most frequent molecular events in neuroblastoma (NB) oncogenesis, and is associated with increased malignancy and decreased neuronal differentiation propensity. The frequency of concomitant loss of heterozygosity at the 1p36.3 locus, which harbours the p53 anti-oncogene homologue TP73, indicates that MYCN and p73 alterations may cooperate in the pathogenesis of NB. We have previously shown that p73 isoforms are deregulated in NB tumours and that TAp73 co-operates synergistically with p53 for apoptosis of NB cells, whereas DeltaNp73 activates the expression of neuronal differentiation genes such as BTG2. Herein, using both ectopic expression and RNA interference-mediated silencing of p73 in MYCN amplified NB cells, we show that p73alpha isoforms inhibit MYCN expression at both transcript and protein levels, in spite of transactivator effects on MYCN promoter. To explain this paradox, we found that TAp73alpha exerts negative post-transcriptional effects leading to reduced MYCN mRNA stability. RNA immunoprecipitation experiments suggest that this dominant inhibitory post-transcriptional effect could be due to an interaction between the p73 protein and MYCN mRNA, a hypothesis also raised for the regulation of certain genes by the p53 protein.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Regulación Neoplásica de la Expresión Génica , Neuroblastoma/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas Oncogénicas/genética , Estabilidad del ARN , ARN Mensajero/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Línea Celular Tumoral , Genes myc , Humanos , Proteína Proto-Oncogénica N-Myc , Neuroblastoma/metabolismo , Proteínas Nucleares/biosíntesis , Proteínas Oncogénicas/biosíntesis , Proteínas Oncogénicas/metabolismo , Regiones Promotoras Genéticas , Isoformas de Proteínas/metabolismo , Activación Transcripcional , Proteína Tumoral p73RESUMEN
The tumor suppressor gene, p53, is rarely mutated in neuroblastomas (NB) at the time of diagnosis, but its dysfunction could result from a nonfunctional conformation or cytoplasmic sequestration of the wild-type p53 protein. However, p53 mutation, when it occurs, is found in NB tumors with drug resistance acquired over the course of chemotherapy. As yet, no study has been devoted to the function of the specific p53 mutants identified in NB cells. This study includes characterization and functional analysis of p53 expressed in eight cell lines: three wild-type cell lines and five cell lines harboring mutations. We identified two transcription-inactive p53 variants truncated in the C-terminus, one of which corresponded to the p53beta isoform recently identified in normal tissue by Bourdon et al. [J. C. Bourdon, K. Fernandes, F. Murray-Zmijewski, G. Liu, A. Diot, D. P. Xirodimas, M. K. Saville and D. P. Lane (2005) Genes Dev., 19, 2122-2137]. Our results show, for the first time, that the p53beta isoform is the only p53 species to be endogenously expressed in the human NB cell line SK-N-AS, suggesting that the C-terminus truncated p53 isoforms may play an important role in NB tumor development.
Asunto(s)
Neuroblastoma/genética , Eliminación de Secuencia , Proteína p53 Supresora de Tumor/genética , Secuencia de Bases , Línea Celular Tumoral , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/biosíntesis , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Dosificación de Gen , Expresión Génica , Humanos , Datos de Secuencia Molecular , Neuroblastoma/metabolismo , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Activación Transcripcional , Proteína p53 Supresora de Tumor/metabolismo , Levaduras/genéticaRESUMEN
The present study aims to investigate the role of p73 in response to cisplatin treatment in p53 wild-type neuroblastoma SH-SY5Y cells. Results showed that cisplatin induced a dose-dependent up-regulation of p53, p73, and a number of p53-responsive genes. Interestingly, endogenous Deltaexon2p73-expression was down-regulated by cisplatin treatment. Neither p21 nor GADD45 induction was observed in p53-deficient Lan-1 cells, although endogenous TAp73 expression was markedly induced. In the presence of cisplatin, exogenous TAp73 overexpression in SH-SY5Y cells induced p21 up-regulation without altering the apoptotic sub-G1 cell population. Moreover, siRNA-mediated suppression of TAp73 expression did not alter the sub-G1 population. Collectively, our results suggest that wt-p53 SH-SY5Y cells respond to cisplatin by inducing p73 isoform regulation and sustaining p53-dependent apoptosis that is independent of TAp73alpha.
Asunto(s)
Antineoplásicos/farmacología , Cisplatino/farmacología , Proteínas de Unión al ADN/metabolismo , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Proteínas Nucleares/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Empalme Alternativo , Apoptosis , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Línea Celular Tumoral , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/genética , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Proteínas de Unión al ADN/genética , Relación Dosis-Respuesta a Droga , Humanos , Neuroblastoma , Proteínas Nucleares/genética , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Interferencia de ARN , Estabilidad del ARN , ARN Mensajero/metabolismo , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Factores de Tiempo , Transfección , Proteína Tumoral p73 , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismo , Proteínas Supresoras de Tumor/genéticaRESUMEN
Hematological malignancies are a heterogeneous group of diseases deriving from blood cells progenitors. Although many genes involved in blood cancers contain internal ribosome entry sites (IRESes), there has been only few studies focusing on the role of cap-independent translation in leukemia and lymphomas. Expression of IRES trans-acting factors can also be altered, and interestingly, BCL-ABL1 fusion protein expressed from "Philadelphia" chromosome, found in some types of leukemia, regulates several of them. A mechanism involving c-Myc IRES and cap-independent translation and leading to resistance to chemotherapy in multiple myeloma emphasize the contribution of cap-independent translation in blood cancers and the need for more work to be done to clarify the roles of known IRESes in pathology and response to chemotherapeutics.