Global uterine genomics in vivo: microarray evaluation of the estrogen receptor alpha-growth factor cross-talk mechanism

Cross-talk between growth factor receptors and the estrogen receptor (ER) has been proposed as a signaling mechanism in estrogen target tissues, with ER(alpha) as a direct target of growth factor receptor-activated signals, leading to regulation of estrogen target genes and estrogen-like biological responses to growth factors. We evaluated whether global genomic changes in the mouse uterus in response to epidermal growth factor or IGF-I mimic those of estradiol (E2), reflecting the cross-talk mechanism. Overlapping responses to growth factors and E2 were expected in the wild type (WT) whereas no response was expected in mice lacking ER(alpha) (ER(alpha) knockout). Surprisingly, although most of the E2 response in the WT also occurred after growth factor treatment, some genes were induced only by E2. Second, although E2 did not induce gene changes in the ER(alpha) knockout, the growth factor response was almost indistinguishable from that of the WT. Differences in response of some genes to IGF-I or epidermal growth factor indicated selective regulation mechanisms, such as phosphatidylinositol 3-kinase or MAPK-dependent responses. The robust ER(alpha)-independent genomic response to growth factor observed here is surprising considering that the biological growth response is ER(alpha) dependent. We propose two mechanisms as alternatives to the cross-talk mechanism for uterine gene regulation. First, E2 increases uterine growth factors, which activate downstream signaling cascades, resulting in gene regulation. Second, growth factors and estrogen regulate similar genes. Our results suggest that the estrogen response in the uterus involves E2-specific ER(alpha)-mediated responses as well as responses resulting from convergence of growth factor and ER-initiated activities.     

Differential effects of estrogen and raloxifene on messenger RNA and matrix metalloproteinase 2 activity in the rat uterus

A detailed analysis of the differential effects of estrogen (E) compared to raloxifene (Ral), a selective estrogen receptor modulator (SERM), following estrogen receptor (ER) binding in gynecological tissues was conducted using gene microarrays, Northern blot analysis, and matrix metalloproteinase (MMP) 2 activity studies. We profiled gene expression in the uterus following acute (1 day) and prolonged daily (5 wk) treatment of E and Ral in ovariectomized rats. Estrogen regulated twice as many genes as Ral, largely those associated with catalysis and metabolism, whereas Ral induced genes associated with cell death and negative cell regulation. Follow-up studies confirmed that genes associated with matrix integrity were differentially regulated by Ral and E at various time points in uterine and vaginal tissues. Additional experiments were conducted to determine the levels of MMP2 activity in uterus explants from ovariectomized rats following 2 wk of treatment with E, Ral, or one of two additional SERMs: lasofoxifene, and levormeloxifene. Both E and lasofoxifene stimulated uterine MMP2 activity to a level twofold that of Ral, whereas levormeloxifene elevated MMP2 activity to a level 12-fold that of Ral. These data show that one of the significant differences between E and Ral signaling in the uterus is the regulation of genes and proteins associated with matrix integrity. This may be a potential key difference between the action of SERMs in the uterus of postmenopausal women.     

Tissue-specific regulation of rat estrogen receptor mRNAs

The estrogen receptor (ER) is present in a wide variety of mammalian tissues and is required for physiological estrogen responses, including estrogen-induced tissue-specific changes in gene expression. We studied the estrogen regulation of the mRNAs encoding the ER in rat uterus, liver, and pituitary. Ovariectomized (21-28 day post surgery) female CD-1 rats were injected daily with 17 beta-estradiol (E2, 10 micrograms/100 g BW) for 0, 1, or 4 h, 1, 3, or 7 days and compared with intact controls. Steady-state levels of ER mRNA were quantified using a human ER cDNA probe. Only one hybridizing species of approximately 6.2 kilobase (kb) was detected in uterine and liver RNA, similar to that observed in MCF7 human breast cancer cells. However, the ER mRNA regulation by E2 differed in direction depending on the tissue examined. In uterus, ER mRNA increased 3- to 6-fold after ovariectomy, and returned to intact levels within 24 h of E2 replacement. In contrast, liver ER mRNA declined 1.5- to 3-fold after ovariectomy and returned to intact levels after 1-3 days of E2. In pituitary tissue two hybridizing forms of ER mRNA were observed, with one species migrating at 6.2 kb, equivalent to the form in other tissues, and a second smaller species at approximately 5.5 kb. The lower molecular weight species varied somewhat in abundance from animal to animal, averaging about 20% of the intensity of the 6.2 kb band. The ER mRNA forms were regulated positively with E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunological analysis of the biochemical properties of the uterine estrogen receptor

Immunohistochemical and immunochemical analysis using Western blot techniques were carried out with estrogen receptor (ER) monoclonal antibody H-222 to 1) clarify the "nuclear translocation" phenomenon of ER, 2) elucidate the primary nuclear binding site of ER, and 3) to evaluate the binding force between ER and its nuclear binding site in the uterus of ovariectomized adult mice. Exclusive nuclear localization of ER was recognized in the epithelial cells, stroma cells, and smooth muscle cells. Uterine tissues prepared from animals injected with saline, 17 beta-estradiol (E2), estriol (E3), and diethylstilbestrol (DES) exhibited almost the same ER immunostaining when they were fixed prior to sectioning (prefixation method) and frozen sections were used. On the other hand, when fresh-frozen sections were fixed before or after incubation with various solutions (postfixation method) and then treated with various salt solutions, greater differences were seen in immunostaining of ER between saline-injected and hormone-treated animals. Immunostaining of ER in control animals was low after incubation with PBS (0.01 M phosphate buffer containing 0.16 M NaCl, pH 7.2), whereas uterine tissue from hormone-injected mice showed strong nuclear immunostaining after this treatment. After treatment with 0.4 M KCl or 0.5 M NaCl, immunostaining in the uterus of both hormone-injected and control animals was completely abolished. DNase treatment caused an almost complete loss of immunostaining of ER; however, RNase digestion slightly increased immunoreactivity in both E2-injected and control animals. Quantitative analysis using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot techniques showed that after incubation of tissue sections for 30 min with PBS, 0.4 M KCl, or DNase, 60%, 10%, and 30% of ER were present, respectively, compared to amount of ER present in unincubated sections. These findings suggest the following for the ER in uterine tissue; nuclear occupancy is a phenomenon that occurs due to a differential affinity between occupied and unoccupied receptors in the nucleus; after hormone treatment, the receptor levels do not fluctuate in the nucleus to the extent demonstrated by binding assays; and the properties of the ER detected in the immunohistochemical analysis are identical to those observed in biochemical studies.     

Regulation of progesterone receptors and decidualization in uterine stroma of the estrogen receptor-alpha knockout mouse

Regulation of progesterone receptor (PR) in uterine stroma (endometrial stroma plus myometrium) by estrogen was investigated in estrogen receptor-alpha (ERalpha) knockout (alphaERKO) mice. 17 beta-Estradiol (E(2)) increased PR levels in uterine stroma of ovariectomized alphaERKO mice, and ICI 182 780 (ICI) inhibited this E(2)-induced PR expression. Estrogen receptor-beta(ER beta) was detected in both uterine epithelium and stroma of wild-type and alphaERKO mice by immunohistochemistry. In organ cultures of alphaERKO uterus, both E(2) and diethylstilbestrol induced stromal PR, and ICI inhibited this induction. These findings suggest that estrogen induces stromal PR via ERbeta in alphaERKO uterus. However, this process is not mediated exclusively by ERbeta+, because in ERbeta knockout mice, which express ERalpha, PR was up-regulated by E(2) in uterine stroma. In both wild-type and alphaERKO mice, progesterone and mechanical traumatization were essential and sufficient to induce decidual cells, even though E(2) and ERalpha were also required for increase in uterine weight. Progesterone receptor was strongly expressed in decidual cells in alphaERKO mice, and ICI did not inhibit decidualization or PR expression. This study suggests that up-regulation of PR in endometrial stroma is mediated through at least three mechanisms: 1) classical estrogen signaling through ERalpha, 2) estrogen signaling through ERbeta, and 3) as a result of mechanical stimulation plus progesterone, which induces stromal cells to differentiate into decidual cells. Each of these pathways can function independently of the others.