Oncogenic Ras can induce transcriptional activation through a variety of promoter elements, including tandem c-Ets-2 binding sites

Abstract

Oncogenic Ras activates the transcription of a variety of viral and cellular genes through promoter elements consisting of two closely linked binding sites for transcription factors from several distinct families. To better understand what constitutes a promoter oncogene response element (ORE), various transcription factor binding site configurations were inserted into a reporter gene, and transactivation by oncogenic Ras was measured by cotransfection assays in NIH3T3 cells. We show that a single copy of two closely linked binding sites for either AP-1, Ets, NF-kappa B, or single closely linked Ets and AP-1 binding sites, are sufficient to confer at least 10-fold transactivation by similar amounts of oncogenic Ras. Single binding sites for these factors, or several other pairings of binding sites, are not sufficient to confer Ras responsiveness. The effect of altered ORE binding site spacing and orientation was systematically analysed, and limited flexibility was observed. The novel observation that two adjacent c-Ets-2 binding sites are sufficient to act as an ORE, indicates that Ets family proteins are a target of the Ras pathway distinct from AP-1. This ORE also mediates equivalent transactivation by c-Ets-2, and mutant OREs show a parallel decrease in Ras and c-Ets-2 responsiveness. Together, these data help to define transcriptional targets of the Ras signal transduction pathway.