Oncogenic and transcriptional cooperation with Ha-Ras requires phosphorylation of c-Jun on serines 63 and 73.
Recent advances indicate a link between tumour promoters, transformation, and AP-1 activity. Protein kinase C activation increases AP-1 DNA-binding activity independently of new protein synthesis. AP-1 is also stimulated by transforming oncoproteins and growth factors. These proteins are thought to participate in a signalling cascade affecting the nuclear AP-1 complex composed of the Jun and Fos proteins. Because c-Jun is the most potent transactivator in the AP-1 complex and is elevated in Ha-ras-transformed cells, in which c-Fos is downregulated, we focused on it as a potential target. c-Jun could convert input from an oncogenic signalling cascade into changes in gene expression. Indeed, transformation of rat embryo fibroblasts by c-Jun requires an intact transcriptional activation domain and cooperation with oncogenic Ha-ras. Expression of oncogenic Ha-ras augments transactivation by c-Jun and stimulates its phosphorylation. Here we describe the mapping of the Ha-ras-responsive phosphorylation sites to serines 63 and 73 of c-Jun. Site-directed mutagenesis indicates that phosphorylation of these serines is essential for stimulation of c-Jun activity and for cooperation with Ha-ras in ocogenic transformation.
Smeal
T
T
Department of Pharmacology, University of California San Diego, School of Medicine, La Jolla 92093-0636.
Binetruy
B
B
Mercola
D A
DA
Birrer
M
M
Karin
M
M
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002471:Cell Transformation, Neoplastic; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015689:Oncogene Protein p21(ras) / Q000502:physiology*; D010766:Phosphorylation; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012694:Serine / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D016755:Proto-Oncogene Proteins c-jun; D012694:Serine; D015689:Oncogene Protein p21(ras)