Enhancement of gene expression by transcription factor AP-1 is dependent on orientation of AP-1 element

Transcription factor AP-1 induced by 12-O-tetradecanoylphorbol-13-acetate treatment of LLC-PK1 cells binds specifically to an AP-1 oligonucleotide. To study the effect of interaction of transcription factor AP-1 with its AP-1 element on gene expression, an AP-1 consensus sequence was cloned into a reporter vector. Expression of the reporter gene in transfected cells was greatly enhanced in the presence of the reverse-oriented AP-1 element upstream of a SV40 promoter. Mutation (G to C) of the central base in the AP-1 motif (TGAGTCA) abolished the enhancement for the reporter gene expression. These results indicate that the orientation of AP-1 element relative to the transcription machinery is important for its regulatory function. Moreover, sequences that flank the AP-1 motif are also required for its regulatory function.