ABSTRACT
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.
Subject(s)
5' Untranslated Regions/genetics , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Drug Resistance, Neoplasm/genetics , Endonucleases/genetics , Endonucleases/metabolism , Ependymoma/genetics , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Open Reading Frames/genetics , Polymorphism, Genetic/genetics , Transcription Factors/genetics , Transcription Factors/metabolism , Antineoplastic Agents/pharmacology , Antineoplastic Agents/therapeutic use , Calcium-Binding Proteins/metabolism , Cell Line , Cell Line, Tumor , Cisplatin/pharmacology , Cisplatin/therapeutic use , DNA Damage , Ependymoma/drug therapy , Ependymoma/mortality , Gene Expression Regulation, Neoplastic/drug effects , Gene Expression Regulation, Neoplastic/genetics , HeLa Cells , HumansABSTRACT
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.
ABSTRACT
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.
Subject(s)
Lymphoma, B-Cell/genetics , MicroRNAs/metabolism , Protein Biosynthesis , B-Lymphocytes/pathology , B-Lymphocytes/physiology , Gene Expression Regulation, Neoplastic , Humans , Lymphoma, B-Cell/classification , Lymphoma, B-Cell/diagnosis , MicroRNAs/genetics , PrognosisABSTRACT
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.
Subject(s)
DNA-Binding Proteins/metabolism , Gene Expression Regulation, Neoplastic , Neuroblastoma/genetics , Nuclear Proteins/genetics , Nuclear Proteins/metabolism , Oncogene Proteins/genetics , RNA Stability , RNA, Messenger/metabolism , Tumor Suppressor Proteins/metabolism , Cell Line, Tumor , Genes, myc , Humans , N-Myc Proto-Oncogene Protein , Neuroblastoma/metabolism , Nuclear Proteins/biosynthesis , Oncogene Proteins/biosynthesis , Oncogene Proteins/metabolism , Promoter Regions, Genetic , Protein Isoforms/metabolism , Transcriptional Activation , Tumor Protein p73ABSTRACT
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.
Subject(s)
Neuroblastoma/genetics , Sequence Deletion , Tumor Suppressor Protein p53/genetics , Base Sequence , Cell Line, Tumor , Cyclin-Dependent Kinase Inhibitor p21/biosynthesis , Cyclin-Dependent Kinase Inhibitor p21/genetics , Gene Dosage , Gene Expression , Humans , Molecular Sequence Data , Neuroblastoma/metabolism , Protein Isoforms/genetics , Protein Isoforms/metabolism , Transcriptional Activation , Tumor Suppressor Protein p53/metabolism , Yeasts/geneticsABSTRACT
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.
