Abstract
Initiation of translation of the proto-oncogene c-myc can occur by either the cap-dependent scanning mechanism or by internal ribosome entry. The latter mechanism requires a complex RNA structural element that is located in the 5' untranslated region of c-myc, termed an internal ribosome entry segment (IRES). Recent work has shown that IRESs are used to maintain protein expression under conditions when cap-dependent translation initiation is compromised; for example, during mitosis, apoptosis and under conditions of cell stress, such as hypoxia or heat shock. Induction of genotoxic stress also results in a large reduction in global protein synthesis rates and therefore we investigated whether the c-myc IRES was active following DNA damage. As expected, in cells treated with either ethylmethane sulphonate or mitomycin C there was a large reduction in protein synthesis, although this was brought about by two different mechanisms. However, in each case the c-myc IRES was active and c-Myc protein expression was maintained. Finally we showed that the proteins required for this process are downstream of the p38 mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated protein kinase (ERK)/MEK(MAPK/ERK kinase) signalling pathways, since pre-treatment of cells with inhibitors of these pathways before DNA damage is initiated inhibits both c-myc IRES activity and expression of c-Myc protein.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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5' Untranslated Regions / genetics
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Blotting, Northern
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Blotting, Western
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Cell Survival / drug effects
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Cell Survival / physiology*
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DNA Damage / drug effects*
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DNA-Binding Proteins / metabolism
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Electrophoresis, Polyacrylamide Gel
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Enzyme Inhibitors / pharmacology
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Ethyl Methanesulfonate / pharmacology
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HeLa Cells / metabolism*
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HeLa Cells / pathology
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Humans
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Immunosuppressive Agents / pharmacology
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Luciferases / metabolism
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Mitogen-Activated Protein Kinases / antagonists & inhibitors
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Mitogen-Activated Protein Kinases / metabolism
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Mitomycin / pharmacology
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Peptide Chain Initiation, Translational / genetics*
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Phosphorylation
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Precipitin Tests
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Protein Biosynthesis / genetics*
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Protein Kinases / metabolism
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Protein Synthesis Inhibitors / pharmacology
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Proto-Oncogene Mas
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Proto-Oncogene Proteins c-myc / genetics
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Proto-Oncogene Proteins c-myc / metabolism*
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Ribosomes / metabolism*
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Sirolimus / pharmacology
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TOR Serine-Threonine Kinases
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Transcription Factors / metabolism
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p38 Mitogen-Activated Protein Kinases
Substances
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5' Untranslated Regions
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DNA-Binding Proteins
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Enzyme Inhibitors
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Immunosuppressive Agents
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MAS1 protein, human
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Protein Synthesis Inhibitors
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Proto-Oncogene Mas
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Proto-Oncogene Proteins c-myc
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RNA, Messenger
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Transcription Factors
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Mitomycin
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Ethyl Methanesulfonate
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Luciferases
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Protein Kinases
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MTOR protein, human
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TOR Serine-Threonine Kinases
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Mitogen-Activated Protein Kinases
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p38 Mitogen-Activated Protein Kinases
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Sirolimus