A promoter-linked coupling region required for stimulation of α-fetoprotein transcription by distant enhancers

Open Access
Publisher Website
Google Scholar
Abstract
We previously demonstrated that the rat α-fetoproteln (AFP) gene has three upstream enhancers that stimulate the AFP promoter addltively in HepG2 cells (1). In this paper, deletion analysis demonstrated that a promoter-linked segment from −178 to −155 was required for full activity when the enhancers were distant from the promoter, even at less than their normal genomlc distances, but dispensable when the enhancers were moved close to the promoter. This ‘promoter-coupling element’ appears to interact simultaneously with all three enhancers. Deletion analysis also localized a transcription stimulatory and a negative region In the promoter. Though these latter regions controlled the strength of the isolated promoter, they did not affect ‘coupling’ to the distant enhancers, and transcription stimulation by these distal promoter elements was small compared to the distant enhancers. Overall, the distant enhancers, acting through the promoter-coupling element, accounted for 70% of the activity of the transfected AFP gene. Footprint analysis with HepG2 nuclear extracts demonstrated protein binding at two sites near the promoter-coupling element. The data Indicate a positive transcription control mechanism by which distant enhancers stimulate the AFP promoter through a specific promoter-linked element.