N-myc translation is initiated via an internal ribosome entry segment that displays enhanced activity in neuronal cells.
Eukaryotic translation can be initiated either by a cap-dependent mechanism or by internal ribosome entry, a process by which ribosomes are directly recruited to structured regions of mRNA upstream of the initiation codon. We analysed the 5' untranslated region (UTR) of the proto-oncogene N-myc, and demonstrated by transfections in a dicistronic vector system that it contains a potent internal ribosome entry segment (IRES). The IRES is similar in length to the c-myc IRES and the activities of these IRESs are comparable in non-neuronal cells. Transfections were also carried out in cell lines derived from neuroblastomas, in which N-myc is expressed, and in a neuronal precursor cell line. In these cells the N-myc IRES is up to seven times more active than that of c-myc, suggesting that neuronal-specific non-canonical trans-acting factors are used by the N-myc but not the c-myc IRES. N-myc expression is increased by gene amplification in many neuroblastomas, but this is the first example of a translational mechanism by which N-myc expression could be further increased. The discovery of an IRES that displays enhanced activity in neuronal cell lines has important potential as a tool for protein expression in neural tissue.
Jopling
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CL
Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH, UK.
Willis
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AE
D020121:5' Untranslated Regions / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D016259:Genes, myc / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D009474:Neurons / Q000502:physiology*; D010442:Peptide Chain Initiation, Translational / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics*; D000090063:Proto-Oncogene Mas; D012326:RNA Splicing / Q000235:genetics; D012270:Ribosomes / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured
D020121:5' Untranslated Regions; D018076:DNA, Complementary; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas