An upstream regulator of the glycoprotein hormone cu-subunit gene mediatespituitary cell type activation and repression by different mechanisms

Targeting of alpha-subunit gene expression within the pituitary is influenc ed by an upstream regulatory region that directs high level expression to t hyrotropes and gonadotropes of transgenic mice. The same region also enhanc ed the activity of the proximal promoter in transfections of pituitary-deri ved alpha-TSH and alpha-T3 cells. We have localized the activating sequence s to a 125-bp region that contains consensus sites for factors that also pl ay a role in proximal promoter activity. Proteins present in alpha-TSH and alpha-T3 cells as well as those from GH3 somatotrope-derived cells interact with this region. The upstream area inhibited proximal alpha-promoter acti vity by 80% when transfected into GH3 cells. Repression in GH3 cells was me diated through a different mechanism than enhancement, as supported by the following evidence. Reversing the orientation of the area resulted in a los s of proximal promoter activation in alpha-TSH and alpha-T3 cells but did n ot relieve repression in GH3 cells. Mutation of proximal sites shown to be important for activation had no effect on repression. Finally, bidirectiona l deletional analysis revealed that multiple elements are involved in activ ation and repression and, together with the DNA binding studies, suggests t hat these processes may be mediated through closely juxtaposed or even over lapping elements, thus perhaps defining a new class of bifunctional gene re gulatory sequence.