Progestin stimulates the biosynthesis of fibronectin and accumulation of fibronectin mRNA in human endometrial stromal cells

Pre-clinical models to study abnormal uterine bleeding (AUB)

Abnormal Uterine Bleeding (AUB) is a common debilitating condition that significantly reduces quality of life of women across the reproductive age span. AUB creates significant morbidity, medical, social, and economic problems for women, their families, workplace, and health services. Despite the profoundly negative effects of AUB on public health, advancement in understanding the pathophysiology of AUB and the discovery of novel effective therapies is slow due to lack of reliable pre-clinical models. This review discusses currently available laboratory-based pre-clinical scientific models and how they are used to study AUB. Human and animal in vitro, ex vivo, and in vivo models will be described along with advantages and limitations of each method.

Human versus non-human sex steroid use in hormone replacement therapies part 1: Preclinical data

Prior to 2002, hormone replacement therapy (HRT) was considered to be an important component of postmenopausal healthcare. This was based on a plethora of basic, epidemiological and clinical studies demonstrating the health benefits of supplementation with human sex steroids. However, adverse findings from the Women's Health Initiative (WHI) studies that examined the 2 major forms of HRT in use in the US at that time - Premarin (conjugated equine estrogens; CEE) and Prempro (CEE + medroxyprogesterone acetate; MPA), cast a shadow over the use of any form of HRT. Here we review the biochemical and physiological differences between the non-human WHI study hormones - CEE and MPA, and their respective human counterparts 17β-estradiol (E₂) and progesterone (P₄). Preclinical data from the last 30 years demonstrate clear differences between human and non-human sex steroids on numerous molecular, physiological and functional parameters in brain, heart and reproductive tissue. In contrast to CEE supplementation, which is not always detrimental although certainly not as optimal as E₂ supplementation, MPA is clearly not equivalent to P₄, having detrimental effects on cognitive, cardiac and reproductive function. Moreover, unlike P₄, MPA is clearly antagonistic of the positive effects of E₂ and CEE on tissue function. These data indicate that minor chemical changes to human sex steroids result in physiologically distinct actions that are not optimal for tissue health and functioning.

Induction of overt menstruation in intact mice

The complex tissue remodeling process of menstruation is experienced by humans and some primates, whereas most placental mammals, including mice, go through an estrous cycle. How menstruation and the underlying mechanisms evolved is still unknown. Here we demonstrate that the process of menstruation is not just species-specific but also depends on factors which can be induced experimentally. In intact female mice endogenous progesterone levels were raised by the induction of pseudopregnancy. Following an intrauterine oil injection, the decidualization of the endometrium was reliably induced as a prerequisite for menstruation. The natural drop of endogenous progesterone led to spontaneous breakdown of endometrial tissue within an average of 3 days post induction of decidualization. Interestingly, morphological changes such as breakdown and repair of the endometrial layer occurred in parallel in the same uterine horn. Most importantly, endometrial breakdown was accompanied by vaginally visible (overt) bleeding and flushing out of shed tissue comparable to human menstruation. Real-time PCR data clearly showed temporal changes in the expression of multiple factors participating in inflammation, angiogenesis, tissue modulation, proliferation, and apoptosis, as has been described for human menstruating endometrium. In conclusion, human menstruation can be mimicked in terms of extravaginally visible bleeding, tissue remodeling, and gene regulation in naturally non-menstruating species such as intact female mice without the need for an exogenous hormone supply.

Effects of tibolone on nuclear receptors in human endometrial cells

OBJECTIVE

Tibolone regulates estrogenic activity in a tissue-selective manner. The purpose of this study was to evaluate the effects of tibolone on the mRNA content of nuclear receptors, estrogen receptor-alpha and beta (ERalpha and ERbeta), progesterone receptor (PR), and androgen receptor (AR) in human endometrial stromal and glandular cells.

STUDY DESIGN

Human endometrial stromal and glandular cells were isolated from endometrial tissue fragments and separately incubated with tibolone and its metabolites. Nuclear receptor mRNA was determined using real-time polymerase chain reaction (PCR).

RESULTS

In endometrial stromal cells, tibolone, Delta4-tibolone, and 3betaOH-tibolone, but not 3alphaOH-tibolone, significantly reduced ERalpha mRNA by approximately 60% and ERalpha protein by approximately 80%. No reduction of ERalpha was observed in endometrial glandular cells. Tibolone induced PR mRNAs to various extents and reached up to 6-fold in glandular cells, but only a moderate increase (approximately 1.5-fold) in stromal cells. Tibolone increased ERbeta and had little effect on AR mRNA in endometrial cells.

CONCLUSION

The results showed the majority of the nuclear receptors were not significantly altered. However, tibolone significantly reduced ERalpha in stromal cells and increased PR in glandular cells. These biological effects may play essential roles in averting stimulation of the endometrium in tibolone users.

Endocrine regulation of menstruation

In women, endometrial morphology and function undergo characteristic changes every menstrual cycle. These changes are crucial for perpetuation of the species and are orchestrated to prepare the endometrium for implantation of a conceptus. In the absence of pregnancy, the human endometrium is sloughed off at menstruation over a period of a few days. Tissue repair, growth, angiogenesis, differentiation, and receptivity ensue to prepare the endometrium for implantation in the next cycle. Ovarian sex steroids through interaction with different cognate nuclear receptors regulate the expression of a cascade of local factors within the endometrium that act in an autocrine/paracrine and even intracrine manner. Such interactions initiate complex events within the endometrium that are crucial for implantation and, in the absence thereof, normal menstruation. A clearer understanding of regulation of normal endometrial function will provide an insight into causes of menstrual dysfunction such as menorrhagia (heavy menstrual bleeding) and dysmenorrhea (painful periods). The molecular pathways that precipitate these pathologies remain largely undefined. Future research efforts to provide greater insight into these pathways will lead to the development of novel drugs that would target identified aberrations in expression and/or of local uterine factors that are crucial for normal endometrial function.

Expression of integrin alpha5 and integrin beta4 and their extracellular ligands fibronectin and laminin in human decidua during early pregnancy and its sex steroid-mediated regulation

The reorganization of the human endometrium is termed decidualization, which includes endometrial cell proliferation, differentiation, integrin switching and extracellular matrix (ECM) remodeling during early pregnancy. The present study aimed to investigate distribution patterns, staining intensity and sex steroid-mediated regulation of integrin alpha5 (CD49e), integrin beta4 (CD49f) expression and their ligands fibronectin and laminin during decidualization. Human tissue samples were evaluated in two groups, those collected in early days and those collected in advanced days of the first trimester. Correlating immunostaining was found between laminin and integrin beta4, and between fibronectin and integrin alpha5. The expression of fibronectin was higher than that of laminin in the early days (p < 0.05). Temporal and spatial immunostaining of integrin beta4 and alpha5 in the apical pole of luminal and glandular cells was observed as pregnancy progressed (p < 0.05). In vitro results showed that human chorionic gonadotropin (hCG) stimulated laminin expression, downregulated integrin beta4 expression, whereas estradiol decreased fibronectin expression by Ishikawa cells. hCG suppressed fibronectin expression in endometrial stromal cells in culture. Our results suggest that fibronectin is responsible for induction of decidual cell differentiation, and different temporal and spatial expression of the integrins may play a role in implantation. Our in vitro results suggest that regulation of extracellular matrix remodeling and integrin switching are at least partially regulated by reproductive hormones.

Progesterone induces the fibulin-1 expression in human endometrial stromal cells

BACKGROUND

By using microarray analysis with human endometrial stromal cells (ESCs), we previously reported that the mRNA for fibulin-1, an extracellular matrix as well as a plasma glycoprotein, is up-regulated by progesterone. In the present study, we tried to clarify the spatial and temporal regulation mechanism of fibulin-1 in the human endometrium.

METHODS AND RESULTS

Quantitative analysis with real-time PCR experiments on human endometrial tissues showed significantly higher fibulin-1 mRNA expressions in secretory phase endometria than in proliferative phase. Immunohistochemical studies revealed that the fibulin-1 protein is expressed in the glandular epithelium in proliferative phase endometria, and that expression switched to the stroma in secretory phase endometria. In culture experiments with ESCs, a significant increase of fibulin-1 mRNA expression was observed in cells treated with 6 alpha-methyl-17 alpha-hydroxy-progesterone acetate (MPA) or 8 bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP). MPA stimulated the fibulin-1 mRNA expression in a dose-dependent manner, and a progesterone antagonist, RU-486, inhibited the stimulatory effect almost completely. By contrast, beta-estradiol alone did not increase the fibulin-1 mRNA expression.

CONCLUSIONS

These results suggest that fiblin-1 is an important molecule that mediates progesterone action in human ESC differentiation towards implantation.

Human embryo implantation: current knowledge and clinical implications in assisted reproductive technology

A pregnancy rate of approximately 15% per cycle renders the process of human reproduction inefficient. The cycle-dependent expression of molecules involved in the embryo-endometrial dialogue has lead to the identification of a 'window of implantation'. This is the unique temporal and spatial expression of factors that allows the embryo to implant (via signalling, appositioning, attachment and invasion) in a specific time frame of 48 h, 7-10 days after ovulation. Integrin molecules, L-selectin ligands, mucin-1, heparin-binding epidermal growth factor and pinopodes are involved in appositioning and attachment. The embryo produces cytokines and growth factors [interleukins, prostaglandins, vascular endothelial growth factor (VEGF)] and receptors for endometrial signals (leukaemia inhibitory factor receptor, colony stimulating factor receptor, insulin-like growth factors and heparin binding epidermal growth factor receptor). The immune system plays an important role. Immunomodulatory factors such as glycodelin, inhibin and interleukin prevent a graft-versus-host reaction. Angiogenesis controlled by VEGF and prostaglandins is needed for formation of a receptive endometrium and a placenta. Identification of these factors has led to their use as markers of implantation that may identify defects causing subfertility. An ideal marker of implantation is sensitive and specific, and easy to obtain without disturbing implantation. Glycodelin and leukaemia inhibitory factor (serum) and integrins and pinopodes (biopsies) are promising candidates.

Microarray Expression Profiling Reveals Candidate Genes for Human Uterine Receptivity

The endometrium undergoes cyclic changes in response to circulating ovarian steroid hormones as it prepares for implantation. This dynamic tissue is well suited to microarray expression profiling for elucidation of molecular players participating in the maturation of the endometrium and during the process of implantation. Recent advances in sequencing the human and mouse genomes and the availability of microarray technology and bioinformatic analyses have made elucidating these molecular participants and dialogs a reality. Analysis of the window of implantation, a temporal and spatially unique period in which the endometrium is receptive to embryonic implantation, has revealed numerous processes to be occurring simultaneously or sequentially. These include cell cycle regulation, angiogenesis, immune modulation of implantation, defense mechanisms put into place by antibacterial agents and detoxicants, secretion of unique products, transport of ions and water, growth factor actions, steroid hormone action and metabolism, and production of extracellular matrix proteins, unique cell surface glycoproteins, and a variety of transcription factors, to name a few. Several groups have recently conducted studies with human endometrium, and remarkable similarities exist with mouse. Also, many genes and gene families involved in the unique differentiation process of stromal cell decidualization are conserved. In addition, infertility associated with endometriosis is partly implantation-based, and gene profiling of such tissue during the window of implantation has revealed additional insight into mechanisms underlying infertility in this disorder. Global profiling of genes in the endometrium, decidua, and at the interface between the trophoblast and the decidua, has provided remarkable in sight into endometrial maturation and implantation.

Progesterone receptor (hPR) upregulates the fibronectin promoter activity in human decidual fibroblasts

Previous studies have shown that progestin induces the production of fibronectin (FN) and its mRNA content in human endometrial stromal cells. The mechanism of the upregulation was unclear. In the present study, we provide evidence that hPR regulates the FN promoter activity mainly through the CRE/AP1 site located in the proximal region of the promoter in human decidual fibroblasts. Various lengths of the proximal region of the FN promoter were linked to the reporter vector to construct promoter-reporter plasmids and were then transfected into human decidual fibroblasts. Deletion and mutation analysis showed that CRE/AP1 and Sp1 sites in the proximal region mediated the basal promoter activity. To evaluate progestin-mediated transcriptional activation, decidual fibroblasts were transfected with p300 (FN promoter-reporter construct) and hPR expression vector. Cells treated with medroxyprogesterone acetate (MPA) increased the promoter activity ranging from 2.5- to 9-fold determined in 10 decidual specimens. hPRA enhanced activation was stronger than that of hPRB. Structural analysis of hPR showed that DNA and ligand binding domains are essential for the activation, and missing the TAF1 domain weakens the activation. The proximal promoter region of the FN gene lacks a canonical PRE site. Mutation at the CRE/AP1 site eliminated the upregulation by progestin. To evaluate the interaction of hPR with the CRE/AP1 site, the CRE/AP1 site was mutated to the consensus AP1 cis-element (TGACGTCA, -172 to -165 bp, mutated to TGAC_TCA) which eliminated the CREB binding. FN promoter activity derived from p300AP1 mutant was found to be higher than that of p300. These results showed that hPR interacts with the AP1 binding proteins, but not with CREB. Progestin treatment or overexpression hPR did not alter appreciably the content of c-jun or c-fos in decidual fibroblasts nuclear extracts. Antibody to hPR (hPRa3), which precipitated hPR also coprecipitated c-jun and c-fos, whereas CREB was not precipitated by hPRa3. The observation implies that hPRs are brought to the FN promoter region by AP1 proteins to enhance the transcription. In summary, this study provides molecular evidence that the CRE/AP1 site and c-jun/c-fos in decidual fibroblasts mediate the hPR-enhanced activation of FN transcription.

Progestin-regulated expression of tissue factor in decidual cells: implications in endometrial hemostasis, menstruation and angiogenesis

Expression of tissue factor (TF), the primary initiator of hemostasis via thrombin formation, is induced during progesterone (P4)-stimulated decidualization of human endometrial stromal cells (HESCs), and remains elevated in decidualized HESCs of luteal and gestational endometrium. In HESC monolayers, progestins elevate TF mRNA and protein levels and estradiol (E2) plus progestin further enhance TF levels for weeks despite no response to E2 alone. This in vitro model mimics the chronic differential ovarian steroid upregulation of TF levels associated with in vivo decidualization. After incubation of HESCs with E2 plus progestin to elevate TF expression, the antiprogestin RU486 completely reversed this upregulation. Thus, progesterone withdrawal transformed decidualization-associated hemostasis of the luteal phase endometrium to the hemorrhagic milieu of menstruation. Transient transfections with TF promoter constructs containing SP and EGR-1 binding sites before and after inactivation by site-directed mutagenesis revealed that Sp1 mediates basal and progestin-enhanced TF transcriptional activity. Progesterone receptor involvement in TF expression was further confirmed since RU486 was a pure antagonist of progestin-enhanced TF mRNA and protein expression, and progestin-enhanced, but not basal, Sp1-mediated transcriptional activity. Enhanced TF mRNA and protein levels in HESCs require co-incubation with progestin and epidermal growth factor receptor (EGFR) agonist indicating that the EGFR mediates progestin-enhanced TF expression. A peak in the primary angiogenic agent, vascular endothelial growth factor (VEGF) in luteal phase endometrium may be indirectly regulated by P4. Neither E2, nor progestin, nor E2 plus progestin affected VEGF expression in glandular epithelial and stromal cells, whereas thrombin enhanced VEGF mRNA and protein levels in decidualized HESCs, but not in the epithelial cells. Transudation of clotting factors to perivascular decidual cell TF in the luteal phase would generate thrombin, enabling it to act as an autocrine enhancer of VEGF in decidualized HESCs. Abnormal uterine bleeding complicates long-term progestin only contraceptive use. After Norplant administration, endometrial VEGF levels are elevated and TF levels are selectively enhanced in decidualized HESCs at bleeding sites. Over-expressed VEGF causes blood vessels to become leaky, increasing clotting factor access to decidualized HESC-expressed TF to promote feed-forward thrombin and VEGF formation. Since thrombin and VEGF induce angiogenesis via separate endothelial cell receptors, they may synergize to elicit aberrant angiogenesis, and ultimately lead to focal bleeding.

Microarray analysis of genes controlled by progesterone in human endometrial stromal cells in vitro

The steroid hormone progesterone is a key factor in establishment and maintenance of pregnancy in the human endometrium. To obtain a global view and identify new target genes for progesterone in human endometrial stromal cells in short-term (3 days) culture, we used a screening strategy to analyze the expression of nearly 1000 human genes by DNA microarray analysis. The results showed that six genes were up-regulated (at least a two-fold increase), and 27 genes were down-regulated (at least a two-fold decrease) after progesterone treatment compared with control. Progesterone stimulated the expression of the interleukin (IL)-1 receptor type 1, fibulin-1, fibulin-2, microsomal glutathione S-transferase 1, fumarylacetoacetate hydrolase and orphan G protein-coupled receptor (RDC1). Progesterone inhibited the expression of insulin-like growth factor binding protein-5, heparin-binding epidermal growth factor-like growth factor, and IL-13 receptor alpha2. In addition, progesterone inhibited the expression of genes involved in immune modulators, DNA/chromatin-related proteins, signal transduction, transcription factors, transport proteins, enzyme, receptor and structural proteins. Our results demonstrate that microarray analysis can be used to identify progesterone-regulated genes in endometrial stromal cells, thus contributing to a more detailed understanding of the molecular mechanisms in response to progesterone in the endometrium during the preparatory period for implantation.

Decidual cell-expressed tissue factor maintains hemostasis in human endometrium

We showed that decidualized stromal cells of luteal phase and pregnant human endometrium express tissue factor (TF), the primary initiator of hemostasis, thereby suggesting a mechanism by which perivascular decidual cells can mitigate the risk of hemorrhage during endovascular trophoblast invasion. Progestins enhanced TF mRNA and protein levels in monolayers of human endometrial stromal cells (HESCs), with estradiol (E2) + progestin, further enhancing TF levels despite a lack of response to E2 alone. This differential ovarian steroid response has been found for several decidualization markers. Further studies with cultured HESCs established that elevated TF levels are mediated by the progesterone receptor and are maintained for weeks in response to E2 plus progestin, thus simulating the chronic upregulation of TF levels observed in decidualized HESCs in vivo. Recent studies revealed that elevated TF expression during in vitro decidualization of HESCs involved both the EGFR and progesterone receptor. Thus, enhancement of TF mRNA and protein levels in the HESCs required co-incubation with a progestin (MPA) and an EGFR agonist such as EGF or TGF-alpha. In correspondence with co-elevation of EGFR and TF in decidualized HESCs in sections of luteal phase and pregnant endometrium, EGFR levels proved to be progestin-enhanced in the cultured HESCs. We established that progestin-enhanced TF expression in HESCs was trancriptionally regulated, then evaluated the relative roles of SP and EGR-1 sites on the TF promoter in regulating this expression. Transient transfections with a series of promoter constructs containing overlapping SP and EGR-1 sites and with constructs in which the EGR-1 and SP sites were systematically inactivated by site-directed mutagenesis established the dominance of SP sites in both basal and progestin-enhanced TF transcriptional activity. Additional experiments involving transient transfections with SPloverexpressing vectors and with a specific blocker of if Sp1 binding to its corresponding GC box specified the importance of the Sp1 transcription factor. These results were further validated by immunostaining, which revealed that the ratio of Sp1 to Sp3 increased during progestin-regulated decidualization of HESCs in vitro and in vivo. The absence of canonical estrogen and progesterone response elements from either the TF or Sp1 gene promoters suggests that the EGFR may help to mediate progestin-enhanced TF expression during decidualization of HESCs.

Cadherin-11 is a hormonally regulated cellular marker of decidualization in human endometrial stromal cells

Cultured human endometrial stromal cells respond to the gonadal steroids, progesterone and 17beta-estradiol, with morphological and biochemical changes that are characteristic of decidualization in vivo. To date, the cellular mechanisms involved in the terminal differentiation of human endometrial stromal cells into decidual cells remain poorly understood. We have recently determined that the novel cadherin subtype, known as cadherin-11, is expressed by endometrial stromal cells undergoing decidualization during the luteal phase of the menstrual cycle and the decidua of pregnancy. In these studies, we have examined cadherin-11 mRNA and protein expression levels in human endometrial stromal cells undergoing steroid-mediated decidualization in vitro. Progesterone or a combination of progesterone and 17beta-estradiol increased stromal cadherin-11 mRNA and protein expression levels with time in culture. Maximum levels of cadherin-11 expression in these cell cultures correlated with a marked increase in IGFBP-1 mRNA levels, a biochemical marker of decidualization. In contrast, 17beta-estradiol had no effect on stromal cad-11 mRNA and protein expression or the levels of the IGFBP-1 mRNA transcript. Taken together, these observations demonstrate that cadherin-11 mRNA and protein expression levels are up-regulated during the terminal differentiation of endometrial stromal cells-suggesting that this cell adhesion molecule may serve as a useful cellular marker for decidualization.

17Beta-estradiol potentiates the stimulatory effects of progesterone on cadherin-11 expression in cultured human endometrial stromal cells

Cadherin-11 (cad-11) is a novel member of the cadherin gene superfamily of calcium-dependent cell adhesion molecules. To date, the factors capable of regulating this cell adhesion molecule remain poorly characterized. We have recently determined that cad-11 expression in the human endometrium is tightly regulated during the menstrual cycle. The spatiotemporal expression of cad-11 in the stromal cells of the human endometrium during the menstrual cycle suggests that gonadal steroids regulate the expression of this endometrial cell adhesion molecule. In view of these observations, we have examined the ability of progestins, estrogens, and androgens, alone or in combination, to regulate cad-11 expression in isolated human endometrial stromal cells using Northern and Western blot analyses. In these studies, we have determined that progesterone, but not 17beta-estradiol or dihydrotestosterone, is capable of regulating cad-11 messenger RNA and protein expression levels in isolated endometrial stromal cells. In addition, 17beta-estradiol, but not dihydrotestosterone, was capable of potentiating the stimulatory effects of progesterone in a dose-dependent manner. Taken together, these observations suggest that both 17beta-estradiol and progesterone are required for maximal cad-11 expression in human endometrial stromal cells in vitro.

Differentiation-dependent and cell-specific regulation of the hIGFBP-1 gene in human endometrium

We analyzed IGFBP-1 gene promoter activity by transient transfection during the progressive decidualization of human endometrial stromal cells. A time study over a 13-day culture period showed that the promoter activity increased exponentially to > 10(4) fold in cells treated with MPA and RLX correlating with the secretion rate and steady-state mRNA levels of the endogenous gene. Deletion analysis showed that two regions in the IGFBP-1 gene promoter are responsible for the activation of the IGFBP-1 gene. The basal promoter region between -1 and -300 bp contains multiple sections of functional elements homologous either to CRE, PRE, or CCAAT. The major difference of IGFBP-1 gene activation in endometrium and the hepatic system lies in the distal promoter region, between -2.6 and -3.4 kb, which mediates 95% of the total promoter activity derived from -3.3 kb to +68 bp. Functional and binding analysis in the distal promoter region showed that multiple Sp1 elements interacting with a novel Sp3 transcription factor activates the hIGFBP-1 gene promoter.

Fibronectinase activity in cultured human trophoblasts is mediated by urokinase-type plasminogen activator

OBJECTIVE

Human trophoblast proteolytic activity is believed to have implications for early implantation events and maintenance of chorionic structural integrity later in gestation. Abnormal release of chorion-derived extracellular matrix proteins such as fibronectin may identify patients at risk for preterm labor and delivery. The aim of this study was to characterize the enzyme(s) potentially responsible for trophoblast-mediated proteolysis of fibronectin.

STUDY DESIGN

Human term cytotrophoblasts were analyzed for their capacity to cleave fibronectin into discrete proteolytic fragments. Selective protease inhibitors were used to characterize trophoblast-derived enzymes with fibronectinase activity. Analysis and quantitation of fibronectin fragment release was determined by Western immunoblots and enzyme-linked immunosorbent assays.

RESULTS

Fibronectinase activity in trophoblast cultures was found to be both cell mediated and secreted, with the release of discrete fibronectin fragments into the media. Cell-mediated proteolytic activity could be partially inhibited by serum, whereas conditioned media containing fibronectinase activity was completely inhibited by serum, a serine protease inhibitor, and a selective inhibitor of urokinase-type plasminogen activator. Digestion of fibronectin with pure urokinase produced a similar pattern of fibronectin fragments compared with fibronectinase-generated fragments. Immunodepletion of urokinase from trophoblast media abolished fibronectinase activity.

CONCLUSIONS

Trophoblast-derived urokinase-type plasminogen activator has significant proteolytic activity in vitro with the capability of cleaving fibronectin into discrete fragments. In early pregnancy this activity could be part of the enzymatic cascade leading to uterine extracellular matrix remodeling and implantation. Later in pregnancy trophoblast derived urokinase could promote normal or inflammation-induced changes in the chorionic extracellular matrix.

Fibronectin is an estrogen-repressed protein in RUCA-I rat endometrial adenocarcinoma cells

We recently established and characterized two rat endometrial adenocarcinoma cell lines which we called RUCA-I and RUCA-II. Despite high estrogen receptor levels neither cell line responded to estradiol in conventional cell culture conditions on plastic and in the presence of charcoal stripped fetal calf serum. We further demonstrated that culturing of these cells on a reconstituted basement membrane induced the estrogen responsiveness for both proliferation and gene expression. Particularly, the expression of components of the complement C3 system, which represent major estradiol inducible proteins in the rat uterus in vivo, were found to be under the control of estrogens and antiestrogens. In this paper the search for estrogen repressed proteins is reported. For this purpose secretory proteins of RUCA-I cells were metabolically labelled with 35S-methionine and tested for the presence of estrogen-repressed, antiestrogen-inducible protein species. Analyzing cell culture supernatants of RUCA-I cells by polyacrylamide gel electrophoresis under reducing conditions a protein with an apparent size of approx. 250-270 kDa became conspicuous. The formation and secretion of this protein was suppressed by estradiol and induced by the antiestrogen ICI 164384. Gel electrophoresis performed under non-reducing conditions and hyaluronidase digestion showed that this estrogen-repressed protein represents a dimeric glycoprotein. By immunoprecipitation this glycoprotein was identified as fibronectin. Investigations of steady state mRNA levels of fibronectin by rtPCR suggested a post-transcriptional regulation of this molecule by estradiol. This is the first report on repression of components of the extracellular matrix by estradiol and induction by the complete antiestrogen ICI 164384. The consequences of this finding in regard to growth and invasion of endometrial tumors are discussed.

Laminin decreases PRL and IGFBP-1 expression during in vitro decidualization of human endometrial stromal cells

The expression of laminin, a major constituent of endometrial cell basement membranes, is increased during differentiation of human endometrial stromal cells (decidualization). To determine whether laminin plays a role in decidualization, we studied the effects of laminin substrate on the synthesis and release of prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1), two major secretory proteins of decidualized stromal cells. Endometrial stromal cells were plated on laminin as well as several other extracellular matrix (ECM) proteins (types 1 and IV collagen or fibronectin) and on plastic, and cultured in media containing medroxyprogesterone acetate (MPA) and estradiol. Cells cultured on plastic or ECM proteins displayed similar morphological changes indicative of decidualization. However, the release of PRL and IGFBP-1 from cells cultured on plastic and ECM proteins (types 1 and IV collagen and fibronection) was approximately 2.1-fold and 2.8-fold greater respectively, than from cells cultured on laminin. The decrease in PRL and IGFBP-1 expression in cells cultured on laminin was not due to differences in initial cell attachment efficiency or final DNA content. In addition, laminin had no effect on the content of laminin protein or fibronectin mRNA levels, indicating that the effects of laminin on PRL and IGFBP-1 were specific. PGE2 stimulated the release of PRL and IGFBP-1 from cells cultured on laminin to levels comparable to those from cells cultured on plastic or other ECM proteins. This indicates that the decrease in PRL and IGFBP-1 release by laminin was not due to a generalized unresponsiveness. In contrast to the effects of laminin during decidualization, PRL expression was not altered by laminin in terminally differentiated decidual cells isolated at term. Our results support a role for laminin in selectively regulating PRL and IGFBP-1 gene expression during in vitro decidualization of human endometrial stromal cells.

Steroid regulation of oncofetal fibronectin expression in human cytotrophoblasts

Oncofetal fibronectin (onfFN) is a uniquely glycosylated form of FN suggested to play a critical role in uterine/placental adherence during pregnancy. In the present study we have examined steroid regulation of onfFN in highly purified preparations (> or = 95%) of cytotrophoblasts isolated from human term placentas. Based on immunoassays, relative to controls, treatment of cytotrophoblasts with 10(-6) M medroxyprogesterone acetate (MPA) down-regulated media levels of onfFN 25, 53, 59, and 62% on days 1, 2, 3 and 4, respectively. The pattern of steroid regulation and levels of total FN were nearly identical to that of onfFN suggesting that chronic steroid treatment regulates synthesis of FN and not its oncofetal glycosylation. MPA treatment induced a 2-fold stimulation in media levels of hCG indicating that increased placental function was associated with steroid-mediated changes in FN expression. Steroid specificity experiments demonstrated that MPA, cortisol, and dexamethasone were potent inhibitors of onfFN expression whereas estradiol (E2), deoxycorticosterone, testosterone, progesterone, and the synthetic progestin OD-14, were not. This suggested that glucocorticoids and not progestins may be the physiologic regulators of placental FN expression and that MPA may mediate its matrix-modifying activity through a glucocorticoid-like mechanism. Treatment of cells with dexamethasone (10(-7) M) did not affect the levels of total protein synthesis or the release of human placental lactogen to the culture medium. This indicated that steroid-mediated down-regulation of onfFN expression in cytotrophoblasts did not result from a general reduction of protein synthesis. Based on densitometric scanning of Western blots, MPA and dexamethasone treatments down-regulated media levels of onfFN 70% relative to control levels. Northern blotting revealed that MPA and dexamethasone mediated a 60-90% reduction in steady state levels of FN mRNA in the presence or absence of E2. Our in vitro model may provide a unique system to evaluate steroidal effects on extracellular matrix (ECM) protein expression. In addition, we suggest that steroids may critically regulate placental ECM protein synthesis, and thus affect trophoblast/uterine adherence throughout pregnancy and expulsion of the placenta and membranes following delivery of the fetus.