Far Upstream Sequences Regulate the Human Prolactin Promoter Transcription

Abstract

The human prolactin gene is mainly expressed in pituitary lactotrope cells, but transcription from an alternative, far upstream promoter was detected in lymphoid, placental and mammary cells. We describe the transcriptional activity in rat pituitary cells of the complete region separating the two promoters, using transient transfection experiments. A far upstream activating region was only functional in combination with the prolactin promoter. DNaseI protection experiments revealed, in addition to binding sites for the pituitary-specific factor Pit-1, sites (e.g. SD1) for several ubiquitous factors and one lymphoid-specific factor (SD4). A single copy of the ubiquitous site SD1 or the lymphoid-specific site SD4 was unable to activate transcription of a heterologous promoter in pituitary cells. However, SD1 activated transcription in nonpituitary cells and SD4 was functional specifically in lymphoid cells. Five copies of a distal site (D8) activated transcription in each cell type tested. Gel retardation experiments show that this site binds the specific factor C/EBP in liver and a distinct factor in other cell types. Our results suggest that different elements within this large region direct specific expression from each promoter via a complex interplay between cell-specific and ubiquitous transcription factors.