Translational Regulation of the JunD Messenger RNA

• Published in: The Journal of biological chemistry Vol. 277; no. 36; pp. 32697 - 32705
• Main Authors: Short, John D., Pfarr, Curt M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 06-09-2002; American Society for Biochemistry and Molecular Biology
• Subjects: 5' Untranslated Regions; Animals; Base Sequence; Binding Sites; Cell Line; Codon; COS Cells; Gene Expression Regulation; HeLa Cells; Humans; Luciferases - metabolism; Mice; Models, Genetic; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Open Reading Frames; Phosphorylation; Protein Biosynthesis; Protein Isoforms; Proto-Oncogene Proteins c-jun - chemistry; Proto-Oncogene Proteins c-jun - genetics; Proto-Oncogene Proteins c-jun - metabolism; Rats; Ribosomes - metabolism; RNA, Messenger - metabolism; Sequence Homology, Amino Acid; Transfection; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M204553200

JunD, a member of the Jun family of nuclear transcription proteins, dimerizes with Fos family members or other Jun proteins (c-Jun or JunB) to form the activator protein 1 (AP-1) transcription factor. The junD gene contains no introns and generates a single mRNA. Here we show that two predominant JunD isoforms are generated by alternative initiation of translation, a 39-kDa full-length JunD protein (JunD-FL) by initiation at the first AUG codon downstream of the mRNA 5′ cap and a shorter, 34-kDa JunD protein (ΔJunD) by initiation at a second in-frame AUG codon. The JunD mRNA contains a long, G/C-rich 5′-untranslated region that is predicted to be highly structured and is important for regulating the ratio of JunD-FL and ΔJunD protein expression. A third functional out-of-frame AUG directs translation from a short open reading frame positioned between the JunD-FL and ΔJunD start sites. In addition, three non-AUG codons also support translation, an ACG codon (in-frame with JunD) and a CUG are positioned in the 5′-untranslated region, and a CUG codon (also in-frame with JunD) is located downstream of the short open reading frame . Mutation of these start sites individually had no affect on ΔJunD protein levels, but mutation of multiple upstream start sites led to an increase in ΔJunD protein levels, indicating that these codons can function cumulatively to suppress ΔJunD translation. Finally, we show that the JunD mRNA does not possess an internal ribosome entry site and is translated in a cap-dependent manner.