Phorbol ester-induced amino-terminal phosphorylation of human JUN but not JUNB regulates transcriptional activation.
Phorbol ester tumor promoters activate gene transcription by regulating both the synthesis and posttranslational modification of the activator protein 1 (AP-1) transcription factor, c-Jun and JunB are components of the mammalian AP-1 complex. Here we demonstrate that in U-937 human leukemic cells, phorbol esters stimulate the phosphorylation of the amino terminus of human c-Jun (JUN) but not human JunB (JUNB). Mutational analysis indicates that serine-63 and -73, which reside within the putative regulatory domain of JUN, are required for both constitutive and phorbol 12-myristate 13-acetate-inducible N-terminal JUN phosphorylation. To determine the functional role of this N-terminal phosphorylation, we prepared several chimeric proteins containing the N-terminal 84 amino acids (positions 5-89) of human JUN or murine JUNB fused to the yeast GAL4 DNA-binding domain. This region was found to be sufficient for the phorbol ester-inducible transcriptional activity of JUN, but not JUNB. This induction was abolished by the mutation of serine-63 and -73 to leucine residues. Thus, we propose that phorbol esters enhance the trans-activation potential of JUN, but not JUNB, by the phosphorylation of the N-terminal regulatory domain of JUN.
Franklin
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CC
Division of Hematology/Oncology, University of Alabama, Birmingham 35294.
Sanchez
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V
Wagner
F
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Woodgett
J R
JR
Kraft
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AS
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D016758:Genes, jun; D006801:Humans; D008715:Methionine / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010710:Phosphates / Q000378:metabolism; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid; D013462:Sulfur Radioisotopes; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D010710:Phosphates; D010761:Phosphorus Radioisotopes; D016755:Proto-Oncogene Proteins c-jun; D011993:Recombinant Fusion Proteins; D013462:Sulfur Radioisotopes; D008715:Methionine; D013755:Tetradecanoylphorbol Acetate