Serum-, TPA-, and Ras-induced expression from Ap-1/Ets-driven promoters requires Raf-1 kinase.

  1. J T Bruder,
  2. G Heidecker, and
  3. U R Rapp
  1. Laboratory of Viral Carcinogenesis, National Cancer Institute, Frederick Cancer Research and Development Center, Maryland 21702-1201.

Abstract

Raf-1 serine-threonine protein kinase has the hallmarks of a critical switch that connects growth factor receptor activation at the cell membrane with transcriptional events in the nucleus. We show by use of Raf-1 dominant-negative mutants that Raf-1 is required for serum-, TPA-, and Ras-induced expression from the oncogene-responsive element in the polyomavirus enhancer. The minimal region of Raf-1 that displays this dominant-negative phenotype (Raf-C4) contains a cysteine finger motif. Raf-C4 appears to function by titrating out a Raf-1-activating factor that is induced by Ras following serum or TPA treatment of NIH-3T3 cells. In addition, we show that Raf-1 and Ras cooperate in trans-activation through the oncogene-responsive element and that the cysteine-rich region is necessary for this effect.

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