AP-1 Factors Play an Important Role in Transformation Induced by the v- rel Oncogene

Abstract

ABSTRACT v- rel is the oncogenic member of the Rel/NF-κB family of transcription factors. The mechanism by which v-Rel induces transformation of avian lymphoid cells and fibroblasts is not precisely known. However, most models propose that v- rel disrupts the normal transcriptional regulatory network. In this study we evaluated the role of AP-1 family members in v-Rel-mediated transformation. The overexpression of v-Rel, c-Rel, and c-RelΔ resulted in a prolonged elevation of c- fos and c- jun expression and in a sustained repression of fra-2 at both the mRNA and protein levels in fibroblasts and lymphoid cells. Moreover, the transforming abilities of these Rel proteins correlated with their ability to alter the expression of these AP-1 factors. v-Rel exhibited the most pronounced effect, whereas c-Rel, with poor transforming ability, elicited only moderate changes in AP-1 levels. Furthermore, c-RelΔ, which exhibits enhanced transforming potential relative to c-Rel, induced intermediate changes in AP-1 expression. To directly evaluate the role of AP-1 family members in the v-Rel transformation process, a sup jun -1 transdominant mutant was used. The sup jun -1 mutant functions as a general inhibitor of AP-1 activity by inhibiting AP-1-mediated transactivation and by reducing AP-1 DNA-binding activity. Coinfection or sequential infection of fibroblasts or lymphoid cells with viruses carrying rel oncogenes and sup jun -1 resulted in a reduction of the transformation efficiency of the Rel proteins. The expression of sup jun -1 inhibited the ability of v-Rel transformed lymphoid cells and fibroblasts to form colonies in soft agar by over 70%. Furthermore, the expression of sup jun -1 strongly interfered with the ability of v-Rel to morphologically transform avian fibroblasts. This is the first report showing that v-Rel might execute its oncogenic potential through modulating the activity of early response genes.