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Upstream ORF affects MYCN translation depending on exon 1b alternative splicing.

ABSTRACT: The MYCN gene is transcribed into two major mRNAs: one full-length (MYCN) and one exon 1b-spliced (MYCNDelta1b) mRNA. But nothing is known about their respective ability to translate the MYCN protein.Plasmids were prepared to enable translation from the upstream (uORF) and major ORF of the two MYCN transcripts. Translation was studied after transfection in neuroblastoma SH-EP cell line. Impact of the upstream AUG on translation was evaluated after directed mutagenesis. Functional study with the two MYCN mRNAs was conducted by a cell viability assay. Existence of a new protein encoded by the MYCNDelta1b uORF was explored by designing a rabbit polyclonal antibody against a specific epitope of this protein.Both are translated, but higher levels of protein were seen with MYCNDelta1b mRNA. An upstream ORF was shown to have positive cis-regulatory activity on translation from MYCN but not from MYCNDelta1b mRNA. In transfected SH-EP neuroblastoma cells, high MYCN dosage obtained with MYCNDelta1b mRNA translation induces an antiapoptotic effect after serum deprivation that was not observed with low MYCN expression obtained with MYCN mRNA. Here, we showed that MYCNOT: MYCN Overlap Transcript, a new protein of unknown function is translated from the upstream AUG of MYCNDelta1b mRNA.Existence of upstream ORF in MYCN transcripts leads to a new level of MYCN regulation. The resulting MYCN dosage has a weak but significant anti-apoptotic activity after intrinsic apoptosis induction.

SUBMITTER: Besancon R

PROVIDER: S-EPMC2810302 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Upstream ORF affects MYCN translation depending on exon 1b alternative splicing.

Besançon Roger R Valsesia-Wittmann Sandrine S Locher Clara C Delloye-Bourgeois Céline C Furhman Lydie L Tutrone Giovani G Bertrand Christophe C Jallas Anne-Catherine AC Garin Elisabeth E Puisieux Alain A

BMC cancer 20091217

<h4>Background</h4>The MYCN gene is transcribed into two major mRNAs: one full-length (MYCN) and one exon 1b-spliced (MYCNDelta1b) mRNA. But nothing is known about their respective ability to translate the MYCN protein.<h4>Methods</h4>Plasmids were prepared to enable translation from the upstream (uORF) and major ORF of the two MYCN transcripts. Translation was studied after transfection in neuroblastoma SH-EP cell line. Impact of the upstream AUG on translation was evaluated after directed muta ...[more]

PMID: 20017904

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Project description:BackgroundNeuroblastoma (NB) tumors are well known for their pronounced clinical and molecular heterogeneity. The global gene expression and DNA copy number alterations have been shown to have profound differences in tumors of low or high stage and those with or without MYCN amplification. RNA splicing is an important regulatory mechanism of gene expression, and differential RNA splicing may be associated with the clinical behavior of a tumor.MethodsIn this study, we used exon array profiling to investigate global alternative splicing pattern of 47 neuroblastoma samples in stage 1 and stage 4 with normal or amplified MYCN copy number (stage 1-, 4- and 4+). The ratio of exon-level expression to gene-level expression was used to detect alternative splicing events, while the gene-level expression was applied to characterize whole gene expression change.ResultsPrincipal component analysis (PCA) demonstrated distinct splicing pattern in three groups of samples. Pairwise comparison identified genes with splicing changes and/or whole gene expression changes in high stage tumors. In stage 4- compared with stage 1- tumors, alternatively spliced candidate genes had little overlap with genes showing whole gene expression changes, and most of them were involved in different biological processes. In contrast, a larger number of genes exhibited either exon-level splicing, gene-level expression or both changes in stage 4+ versus stage 1- tumors. Those biological processes involved in stage 4- tumors were disrupted to a greater extent by both splicing and transcription regulations in stage 4+ tumors.ConclusionsOur results demonstrated a significant role of alternative splicing in high stage neuroblastoma, and suggested a MYCN-associated splicing regulation pathway in stage 4+ tumors. The identification of differentially spliced genes and pathways in neuroblastoma tumors of different stages and molecular subtypes may be important to the understanding of cancer biology and the discovery of diagnostic markers or therapeutic targets in neuroblastoma.

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Upstream ORF affects MYCN translation depending on exon 1b alternative splicing.

Publications

Upstream ORF affects MYCN translation depending on exon 1b alternative splicing.

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