Inhibition of CCAAT/enhancer-binding protein alpha and beta translation by upstream open reading frames.
CCAAT/enhancer-binding protein (C/EBP) alpha is a bZIP transcription factor whose expression is restricted to specific cell types. Analysis of C/EBPalpha mRNA and protein levels in various mammalian cells indicates that expression of this gene is controlled both transcriptionally and post-transcriptionally. We report here that C/EBPalpha translation is repressed in several cell lines by an evolutionarily conserved upstream open reading frame (uORF), which acts in cis to inhibit C/EBPalpha translation. Mutations that disrupt the uORF completely abolished translational repression of C/EBPalpha. The related c/ebpbeta gene also contains an uORF that suppresses translation. The length of the spacer sequence between the uORF terminator and the ORF initiator codon (7 bases in all c/ebpalpha genes and 4 bases in c/ebpbeta homologs) is precisely conserved. The effects of insertions, deletions, and base substitutions in the C/EBPalpha spacer showed that both the length and nucleotide sequence of the spacer are important for efficient translational repression. Our data indicate that the uORFs regulate translation of full-length C/EBPalpha and C/EBPbeta and do not play a role in generating truncated forms of these proteins, as has been suggested by start site multiplicity models.
Lincoln
A J
AJ
Advanced BioScience Laboratories-Basic Research Program, NCI-Frederick Cancer Research and Development Center, National Institutes of Health, Frederick, Maryland 21702-1201, USA.
Monczak
Y
Y
Williams
S C
SC
Johnson
P F
PF
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002417:Cattle; D002460:Cell Line; D002645:Chickens; D004275:DNA, Ribosomal / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D051381:Rats; D012045:Regulatory Sequences, Nucleic Acid; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000096:biosynthesis; D014162:Transfection; D014982:Xenopus laevis
D022762:CCAAT-Enhancer-Binding Proteins; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors