ISOLATION OF NOVEL, TRANSCRIPTIONALLY ACTIVE AP-1 BINDING-SITES - IMPLICATIONS FOR CELLULAR-TRANSFORMATION

Increased AP-1 DNA-binding activity, in the context of TRE-binding, is not a consequence of Fos transformation. In this report we investigat e the possibility of a change in binding site preference by vFosAP-1 c ompared with AP-1 from an untransformed cell. Fos binding sites mere i mmunoselected from random sequence oligonucleotides using a pan Fos an ti-serum with nuclear protein from quiescent FBRp75(v-fos)-transformed (FBR) and normal (208F) rat fibroblasts. The selected oligonucleotide s were aligned by computer and a consensus described for the sequences bound by AP-1 from the two cell lines. The vFos binding site is shown to be a consensus TRE, whereas the sequence ACCACATC is described as the cellular Fos protein family consensus. We demonstrate that sequenc es differing from the TRE consensus can bind AP-1 and direct transcrip tion. AP-1 DNA-binding activity differs between normal and transformed cells with several of the selected oligonucleotides. These sequences also demonstrate differential transcriptional activation between norma l and transformed cells. In particular, the 208F consensus has no tran scriptional activity in FBR cells. Further, EGF differentially influen ces the transcriptional activity of the oligonucleotides in 208F and F BR cells. Our results suggest that AP-1 may change its preferred bindi ng site depending on the proteins available at any given time, the seq uences flanking a non-consensus TRE or even the environment in which t he cell exists. These differences in binding site preference and trans criptional activation may result in the increased transforming ability . of the v-fos oncogene compared with the c-fos proto-oncogene and may extend the potential target genes beyond those with an AP-1 consensus binding site.