Transcriptional activation of the immediate early gene pip92 by serum growth factors requires both Ets and CArG-like elements.

pip92 is an immediate early gene that is transcriptionally activated in mouse 3T3 fibroblasts upon treatment with serum growth factors or the tumor promoter 12-O-tetradecanoylphorbol-13-acetate. Here we show that a 73-base pair pip92 promoter fragment located between base pairs 1231 and 1158 upstream of the transcription start site is sufficient to mediate transcriptional activation. This promoter fragment contains two binding sites for transcription factors of the Ets family and a low affinity binding site for the serum response factor. The minimal sequence that mediates serum induction includes at least one copy of the Ets-binding site and a low affinity binding site for the serum response factor. This sequence can interact with at least two proteins in a fibroblast nuclear extract that have binding characteristics of an Ets family protein and a serum response factor-like protein. These proteins can bind the pip92-inducible element simultaneously, thus forming a ternary complex. Furthermore, the same element interacts with recombinant serum response factor and Elk1 proteins individually as well as simultaneously to form a ternary complex. This mode of ternary complex formation is in contrast to the one seen in the promoter of the c-fos protooncogene, where formation of the ternary complex is dependent on the prior assembly of the serum response factor-DNA binary complex. The activation of a number of immediate early genes appears to be mediated through a ternary complex involving members of the Ets family of transcription factors and the serum response factor. We propose that different mechanisms can lead to the formation of such ternary complexes.