Involvement of RFX proteins in transcriptional activation from a Ras-responsive enhancer element.

The B10.RRE element has previously been shown to mediate induced transcription in response to an activated Ha- ras gene and epidermal growth factor in keratinocytes but not in fibroblasts. We report the identification of regulatory factor for X box 3 (RFX-3) as a B10.RRE-binding protein, using the yeast one-hybrid assay. We showed that in vitro-translated RFX3, as well as RFX1 and RFX2, was able to bind B10.RRE in a sequence-specific manner. Furthermore, RFX proteins are part of the protein complex in HeLa and HepG2 cells that binds the B10.RRE element. Functional analysis in cell culture demonstrated that a truncated version of RFX1 (*RFX1) lacking the repressor domain was able to activate transcription from B10.RRE. Conversely, a dominant-negative form of RFX1 was able to block Ras-induced transcription. Taken together, these results suggest a novel role for the RFX family of transcription factors as modulators of Ras signalling in epithelial cells. Such an interaction is of potential relevance for cell growth and carcinogenesis in the skin.