Regulation of rat growth hormone gene expression in tissue culture: influence of cell growth phase.

Regions of the rat growth hormone gene (rGH) upstream of the transcription initiation site were cloned upstream of the firefly luciferase reporter gene to study promoter activity in GH3 rat pituitary cells during lag, logarithmic and plateau phase cell growth. The region -1751bp to -1329 activated gene expression in lag phase cells, but was neutral during logarithmic and plateau phase cell growth. Sequences between -1329bp and -553 were inhibitory during lag and plateau phase growth, but activated promoter activity when introduced into cells during logarithmic growth. We conclude that the rGH 5' flanking DNA provides an interesting model to study DNA sequences involved in growth-related changes in promoter activity.