INTERACTION OF THE V-REL ONCOPROTEIN WITH CELLULAR TRANSCRIPTION FACTOR SP1

We previously showed that v-Rel, the oncoprotein of the avian retrovir us Rev-T, can increase expression from promoters containing binding si tes for the cellular transcription factor Sp1 in chicken embryo fibrob lasts (S. Sif, A. J. Capobianco, and T. D. Gilmore, Oncogene 8:2501-25 09, 1993). In those experiments, v-Rel appeared to increase the transa ctivating function of Sp1; that is, v-Rel stimulated transactivation b y a GAL4-Sp1 protein that lacked the Sp1 DNA-binding domain, We have n ow shown that in vitro-synthesized v-Rel and GAL4-Sp1 form a complex t hat can be immunoprecipitated with either anti-Sp1 or anti-v-Rel antis erum. We have also shown that a glutathione S-transferase (GST)-Sp1 fu sion protein can specifically interact with in vitro-translated v-Rel and with in vivo-synthesized v-Rel from transformed chicken spleen cel ls. In addition, we have found that the abilities of wild-type and two mutant forms of v-Rel to increase transactivation by Sp1 in vivo corr elate with their abilities to interact with Sp1 in vitro. The sequence s important for the interaction of v-Rel with Sp1 in vitro have been m apped to the first 147 amino acids of v-Rel. Other Rel proteins, such as c-Rel, RelA, p52, and p50, were also able to form a complex,vith Sp 1 in vitro. These results suggest that v-Rel increases expression from Sp1 site-containing promoters by functionally interacting with Sp1 an d that cellular Rel proteins and Sp1 are likely to interact to influen ce transcription from natural promoters.