Mm. Montano et al., IDENTIFICATION OF A NOVEL TRANSFERABLE CIS-ELEMENT IN THE PROMOTER OFAN ESTROGEN-RESPONSIVE GENE THAT MODULATES SENSITIVITY TO HORMONE ANDANTIHORMONE, Molecular endocrinology, 11(3), 1997, pp. 330-341
The estrogen receptor (ER) is a ligand-regulated transcription factor
that acts at the promoters of estrogen-regulated genes to modulate the
ir expression. In the present study, we examined three estrogen-regula
ted promoters, namely the rat progesterone receptor gene distal (PR(D)
) and proximal (PR(P)) promoters and the human pS2 gene promoter, and
observed marked differences in their sensitivity to stimulation by est
rogen and repression of estrogen-stimulated transcription by antiestro
gen (AE)-occupied ER. ER-containing MCF-7 human breast cancer cells we
re transfected with reporter gene constructs containing estrogen respo
nse elements upstream of the three gene promoters. In this system, PR(
P) and PR(D) showed similar dose-response curves for stimulation by es
tradiol whereas pS2 was activated by even lower concentrations of estr
adiol. By contrast, PR(D) was much less sensitive to repression of est
rogen-stimulated activity by all AEs studied, relative to the PR(P) an
d the pS2 promoters. Using deletion and mutational analysis, we have i
dentified a transferable cis element at -131 to -94 bp in PR(D) that i
s involved in modulating the sensitivity of this promoter to both estr
ogens and AEs. The element reduced the magnitude of estrogen-stimulate
d activity, enhanced the ability of AEs to repress estrogen-stimulated
activity, and elicited similiar effects when transferred to the promo
ter of another estrogen-responsive gene. Thus, removal of this region
from PR(D) further accentuated the insensitivity of this promoter to A
E while enhancing its sensitivity (both EC(50) and fold induction) to
estrogen. Gel mobility shift assays showed that proteins from nuclear
extracts of MCF-7 cells interact with this element and that the bindin
g of these proteins is inversely correlated with the transcriptional e
ffectiveness of the ER. The findings demonstrate that a specific cis e
lement from the promoter of an estrogen-responsive gene can alter the
transcriptional activity of hormone and antihormone-occupied receptor
bound at its response element near the promoter. Such ligand response
modulatory elements, and changes in the levels and activity of factors
that bind to such elements, may underlie the different sensitivities
of steroid hormone-regulated genes to both hormones and antihormones.