PROXIMAL PROMOTER REGION OF THE JUNB GENE MEDIATES ATTENUATION OF SERUM INDUCIBILITY IN SRC-TRANSFORMED CELLS

Transcription of the junB gene is rapidly and transiently induced foll owing stimulation of susceptible cells by growth factors in serum. Our previous studies demonstrated that serum inducibility of junB and oth er immediate-early genes is markedly attenuated in fibroblasts chronic ally transformed by the viral Src oncoprotein. Moreover, attenuation o f junB induction occurs at the transcriptional level. To characterize further the molecular mechanisms of this attenuation, various full-len gth and recombinant junB constructs were transfected into normal and v iral Src-transformed rat fibroblasts. A stable transfection system was used to faithfully reproduce regulation of the junB gene. Analyses of pooled populations of stably transfected cells demonstrate that seque nces between -89 and +32 (relative to the transcriptional start site) are sufficient to confer both serum inducibility of the junB gene in n ormal cells and its attenuation in viral Src-transformed cells. By con trast, attenuation of c-fos serum inducibility by Src transformation i nvolves element(s) distinct from regulatory elements identified previo usly in the c-fos promoter. These results identify a proximal promoter region of the junB gene that is involved in a novel negative regulati on of its transcription.