J Biol Chem, Vol. 274, Issue 22, 15526-15532, May 28, 1999

An Upstream Regulator of the Glycoprotein Hormone -Subunit Gene Mediates Pituitary Cell Type Activation and Repression by Different Mechanisms

From the Division of Endocrinology, Metabolism and Diabetes, Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262

Targeting of -subunit gene expression within the pituitary is influenced by an upstream regulatory region that directs high level expression to thyrotropes and gonadotropes of transgenic mice. The same region also enhanced the activity of the proximal promoter in transfections of pituitary-derived -TSH and -T3 cells. We have localized the activating sequences to a 125-bp region that contains consensus sites for factors that also play a role in proximal promoter activity. Proteins present in -TSH and -T3 cells as well as those from GH3 somatotrope-derived cells interact with this region. The upstream area inhibited proximal -promoter activity by 80% when transfected into GH3 cells. Repression in GH3 cells was mediated through a different mechanism than enhancement, as supported by the following evidence. Reversing the orientation of the area resulted in a loss of proximal promoter activation in -TSH and -T3 cells but did not relieve repression in GH3 cells. Mutation of proximal sites shown to be important for activation had no effect on repression. Finally, bidirectional deletional analysis revealed that multiple elements are involved in activation and repression and, together with the DNA binding studies, suggests that these processes may be mediated through closely juxtaposed or even overlapping elements, thus perhaps defining a new class of bifunctional gene regulatory sequence.