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