c-Jun transcriptional activity is augmented by expression of oncogenic Ras and Raf proteins. This study demonstrates a direct correlation between Ras transforming activity and c-Jun activation, supporting an important role for c-Jun in transformation by Ras. Since we observed that Ras activated c-Jun transcriptional activity by increasing phosphorylation of the c-Jun activation domain at residues Ser-63/Ser-73 and that oncogenic Ras proteins activated extracellular signal-regulated protein kinases (ERK1 and ERK2) (also known as mitogen-activated protein kinases), we evaluated the possibility that ERKs were directly responsible for c-Jun activation. Coexpression of wild-type ERKs with oncogenic Ras proteins potentiated, while kinase-defective ERKs inhibited, Ras-induced transcriptional activation from the Ras-responsive element (Ets-1/AP-1) present in the NVL-3 enhancer and the serum-response element in the c-fos promoter. In contrast, coexpression of either wild-type or kinase-defective ERKs inhibited Ras and Raf activation of c-Jun transcriptional activity. Thus, although activation of both ERK and c- Jun are downstream consequences of activation of the Ras signal transduction pathway, our results suggest that Ras-induced c-Jun phosphorylation and transcriptional activation are not a direct consequence of ERK1 and ERK2 activation.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jun 21 1994|
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