Amniotic fluid concentrations of secreted pregnancy-associated endometrial alpha 1- and alpha 2-globulins (alpha 1- and alpha 2-PEG)

KLF11 epigenetically regulates glycodelin-A, a marker of endometrial biology via histone-modifying chromatin mechanisms

Endometrial biology is characterized by programmed proliferation and differentiation that is synchronous with ovarian folliculogenesis to maximize the chance of pregnancy. Glycodelin-A, an endometrial secretory protein, promotes pregnancy mostly through immunomodulatory mechanisms. Glycodelin-A is repressed during the proliferative and early secretory phase and activated thereafter. Progesterone activates glycodelin via the Sp1 (Specificity Protein 1) transactivator. We identify a novel role for Kruppel-like transcription factor 11 (KLF11) as a glycodelin-A repressor. Although KLF11 bound 2 distinct regulatory elements, it regulated glycodelin promoter activity differentially through each element. Whereas KLF11 weakly activated glycodelin promoter activity via a region that also bound Sp1, the dominant effect of KLF11 was repression of promoter activity, messenger RNA (mRNA), and protein expression via a novel, specific binding element. KLF11 mediated this repression by recruiting the SIN3/histone deacetylase (HDAC) corepressor complex to the glycodelin promoter. KLF11 may solely, or by competing with Sp1, repress glycodelin-A levels and thereby influence its role in the endometrium.

Glycodelin in reproduction

To achieve a successful pregnancy in humans, sperm is required for capacitation, followed by binding to and entry into an oocyte. Maternal endometrial epithelial cells (EECs) prepare the appropriate implantation environment through regulation of immune cells and endometrial cells. After acquiring endometrial receptivity, a successful pregnancy consists of complex and finely regulated steps involving apposition, adhesion, invasion, and penetration. Glycodelin is a secretory glycoprotein that affects cell proliferation, differentiation, adhesion, and motility. Glycodelin has four glycoforms (glycodelin-A, -S, -F. and -C); differences in glycosylation affect each characteristic function. Glycodelin has a unique temporospatial pattern of expression, primarily in the reproductive tract where glycodelin is mid-secretory phase-dominant. Recent studies have demonstrated that glycodelin protein has the potential to regulate various processes, including immunosuppression, fertilization, and implantation. This review details the orchestrated regulation of successful pregnancy by glycodelin as well as a discussion of the basic characteristics of glycodelin.

Ligand activated relaxin receptor increases the transcription of IGFBP-1 and prolactin in human decidual and endometrial stromal cells

The aim of this study was to investigate relaxin (RLX) receptor-mediated gene activation in human endometrium. We determined the promoter activities of insulin-like growth factor binding protein-1 (IGFBP-1) and prolactin (PRL) and identified sequence(s) that mediate RLX activated transcription in human decidual cells and endometrial stromal cells. In human decidual cells, the promoter activity of IGFBP-1 was increased significantly in cells incubated with RLX. In endometrial stromal cells, the RLX mediated activation was enhanced only when stromal cells were co-transfected with RLX-receptor (LGR7) expression vector and RLX alone had little effect (Mazella et al., 2004). Deletion and mutation analysis showed that the cAMP regulatory element (CRE, -263 to -259 bp) in the IGFBP-1 promoter was essential for the activation. In addition, RLX increased the phosphorylation of CRE binding protein (CREB to p-CREB) and p-CREB resided in the nucleus, indicating that RLX activates the protein kinase (PKA) system in decidual cells. Gel shift assay showed that nuclear extracts prepared from RLX treated decidual cells increased the binding to the CRE site of the IGFBP-1 promoter. RLX increased the PRL promoter activity mediated through the region containing multiple CCAAT/enhancer-binding proteins (C/EBP) binding sites that have been shown to mediate the PRL gene activation by cAMP analogue (Pohnke et al., 1999). RLX enhanced IGFBP-1 promoter activity was inhibited by cAMP dependent PKA inhibitor, H-89. PRL promoter activity was inhibited by both H-89 and U0126 indicating multiple signalling pathways are activated by RLX in endometrial cells for different target gene activation.

Glycodelin: a major lipocalin protein of the reproductive axis with diverse actions in cell recognition and differentiation

Glycodelin is a glycoprotein that belongs to the lipocalin superfamily. Depending on glycosylation, glycodelin appears in various isoforms. In the uterus, glycodelin-A is the major progesterone-regulated glycoprotein secreted into uterine luminal cavity by secretory/decidualized endometrial glands. The other tissues expressing glycodelin include fallopian tubes, ovary, breast, seminal vesicle, bone marrow, and eccrine glands. Glycodelin-A potently and dose-dependently inhibits human sperm-egg binding, whereas differently glycosylated glycodelin-S from seminal plasma has no such effect. Absence of contraceptive glycodelin-A in the uterus during periovulatory midcycle is consistent with an open "fertile window." Glycodelin induced by local or systemic administration of progestogens may potentially reduce the fertilizing capacity of sperm in any phase of the menstrual cycle. Glycodelin also has immunosuppressive activity. Its high concentration at the fetomaternal interface may contribute to protection of the embryonic semiallograft. Besides being an epithelial differentiation marker, glycodelin appears to play a role in glandular morphogenesis, as transfection of glycodelin cDNA into a glycodelin-negative breast cancer cells resulted in formation of gland-like structures, restricted proliferation, and induction of other epithelial markers. These various properties, as well as the chemistry, biology, and clinical aspects of glycodelin, continue to be areas of active investigation reviewed in this communication.

Ligand activated hPR modulates the glycodelin promoter activity through the Sp1 sites in human endometrial adenocarcinoma cells

Human endometrium produces glycodelin-A (GdA). The GdA mRNA is highly expressed in progestin-sensitized human endometrial glandular epithelial cells. The mechanism of GdA gene expression, however, is not clear. To understand the cell specific GdA gene transcription, our first approach was to identify the cis-element in the GdA promoter using transfection assay in a human endometrial adenocarcinoma cell line (HEC-1B, a cell line originally derived from the glandular component of the endometrium). The GdA promoter (-1900 to +20 bp) was linked to the luciferase reporter gene to construct p1900Luc, along with two shorter promoter constructs, p1100Luc and p304Luc. Deletion analysis showed that the basal promoter activity was derived from the region between -304 to +20 bp. This region contains three putative Sp1 binding sites (Sp1-1, -243 to -238 bp; Sp1-2, -207 to -202 bp; and Sp1-3, -56 to -49 bp). Mutation analysis at the Sp1 sites showed that p304Spm2Luc and p304Spm3Luc reduced the activity by 80%, while p304Spm1-2-3Luc reduced the activity by 95%. Sp1-1 mutation, however, had no effect. These results showed that two of the three Sp1 cis-elements mediate the basal promoter activity of the GdA gene. Electrophoretic gel mobility shift showed that at least two specific binding proteins in the nuclear extracts of HEC-1B cells bound to the oligo containing Sp1-2 or Sp1-3 cis-element. Sp1 antibody reduced the specific binding complex by 70% suggesting that Sp1 transcription factor regulates GdA gene expression. In addition, over expression of Sp1 increased the promoter activity. To determine whether progestin would modulate the promoter activity, HEC-1B cells were transfected with p304Luc and with progesterone receptor (either hPR-A or hPR-B) expression vector. Medroxyprogesterone acetate increased the promoter activity (3-fold) derived from p304Luc but not from the mutant, p304Spm1-2-3Luc. In contrast, the promoter activity was slightly reduced in cells treated with estradiol and co-transfected with estrogen receptor expression vector. These data indicate that ligand-activated PR stimulates GdA gene expression mediated through the functional Sp1 sites.

Platelet immunoregulatory factors

A number of soluble and membrane-associated proteins are known to mediate platelet:leukocyte interactions. Platelet-derived factors that have attracted the most attention to date include transforming growth factor beta, interleukin 1 and platelet factor 4. Recently, we have uncovered another protein within platelets that has leukocyte modulatory activity. It was previously characterized as an endometrial glycoprotein named placental protein 14 (PP14) with suppressive effects upon lymphocyte proliferation, pro-inflammatory cytokine production and natural killer cell function. The "hematopoietic" PP14 derived from cells of the megakaryocytic lineage shares this immunosuppressive property, as evaluated by two-way mixed lymphocyte cultures. Interestingly, two alternatively spliced hematopoietic PP14 mRNAs have been cloned which differ in their encoded proteins. Cell-free translation and transfection analyses have verified the translatability of both PP14 mRNA species and allowed for the analysis of their glycosylation properties. PP14, a member of the lipocalin structural superfamily of proteins, now offers an intriguing new link between the coagulation and immune systems.

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.

Activation of the human IGFBP-1 gene promoter by progestin and relaxin in primary culture of human endometrial stromal cells

We have studied the activity for the insulin-like growth factor binding protein-1 (IGFBP-1) gene promoter in human endometrial stromal cells by transient transfection. The promoter activity derived from p3.6CAT or p3.6Luc (3400 bp IGFBP-1 promoter 5' to the reporter gene chloramphenicol acetyltransferase or luciferase) was minimal in unstimulated cells. A time study over 13 days of culture showed that the promoter activity increased exponentially to > 10(4) fold in cells treated with medroxyprogesterone acetate (MPA) and relaxin (RLX). Induction of the IGFBP-1 gene promoter activity by hormones was similar to the secretion pattern of IGFBP-1 in endometrial stromal cells. MPA alone caused a moderate induction, 3-40-fold increase over the control. Deletion analysis showed that two regions in the IGFBP-1 gene promoter were responsible for the activation of the IGFBP-1 gene. The basal promoter region, termed bp1-A (+68 bp to -1.205 kb), contains multiple sections of regulatory sequence including a cis-element CCAAT (-72 bp). A DNase I protection assay in the bp-1A region revealed four distinct binding regions, one of which contained the CCAAT box region. Another promoter region, termed bp1-B (-2.6 to -3.4 kb), mediated 95% of the total promoter activity in endometrial stromal cells. The bp1-B region also contains multiple regulatory sequences. Mutation and DNase I protection assay suggest that Sp1-like binding site at -2.63 kb was a regulatory site responsible for the activation of IGFBP-1 gene promoter.

Identification of a distal regulatory sequence of the human IGFBP-1 gene promoter and regulation by the progesterone receptor in a human endometrial adenocarcinoma cell line

The activity of the insulin-like growth factor binding protein-1 (IGFBP-1) gene promoter was studied in the human endometrial adenocarcinoma cell line HEC-1B. Basal promoter activity was directed by the region +68 to -207 bp, similar to observations in the hepatoma HepG2 cell line. A distal regulatory sequence approximately -2.6 kb from the transcription initiation site strongly enhanced the activity of the IGFBP-1 gene promoter in HEC-1B cells, but not in HepG2 cells. Sequence analysis revealed that this active region resides in 105 bp between -2,628 to -2,732 bp (the Rsa I-Cla I fragment). This region contains many putative active motifs homologous to known cis elements. Additional deletion and mutation in the Rsa I-Cla I fragment showed that the activity was confined to a 58-bp DNA fragment. In cells treated with progestin and co-transfected with progesterone receptor vector hPR1, the CAT activity derived from constructs containing the Rsa I-Cla I fragment was reduced in a dose-dependent manner. The active DNA fragment also stimulated the activity of the heterologous TK/CAT promoter in HEC-1B cells, while the PR complex inhibited this activity by 50%. These observations indicate that most of the regulation of the IGFBP-1 gene in HEC-1B cells is derived from the distal promoter region confined to the Rsa I-Cla I fragment and that the same region mediates an inhibitory effect from the progesterone receptor.

Isolation of amniotic fluid proteins of non-maternal serum origin by negative immuno-affinity chromatography

Although several proteins of non-maternal serum origin are known to exist in amniotic fluid, the predominance of serum proteins has hampered the isolation of all but a very few. This report describes the removal of large amounts contaminating serum proteins from amniotic fluid with anti-human serum antibody coupled to a solid matrix, leaving behind small amounts of proteins of interest, about 3% of the total amniotic fluid proteins. An antibody raised against the non-adsorbed proteins and used in immunoelectrophoretic methods permitted detection of more, probably unknown, proteins in amniotic fluid of potential biological and diagnostic interest.

Multiple forms of mRNA encoding human pregnancy-associated endometrial alpha 2-globulin, a beta-lactoglobulin homologue

Human pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG) is the major secretory protein product of the endometrium during embryo implantation and the first few weeks of pregnancy. It is a homologue of beta-lactoglobulin, a retinol binding protein, but unlike beta-lactoglobulin it is not found in the mammary gland. The cloning and sequencing of 34 alpha 2-PEG clones has revealed several minor variant forms indicative of alternatively spliced alpha 2-PEG pre-mRNA. These minor forms have also been detected amongst uncloned cDNA after PCR amplification. Some of these mRNAs would give rise to forms of alpha 2-PEG protein lacking internal sequences, whereas others affect the mRNA sequences on the 3' boundary of the presumed termination codon. Sequences within the cDNA clones are consistent with the existence of splice sites, and together with similarities found between alpha 2-PEG cDNA and beta-lactoglobulin gene sequences there is good evidence in support of an unusual scheme for the alternative splicing of alpha 2-PEG pre-mRNA involving both alternative 5' splice sites and alternative 3' splice sites. This scheme suggests that the alpha 2-PEG and beta-lactoglobulin genes share a similar structure in at least two regions, and it is likely that beta-lactoglobulin pre-mRNA would show a similar pattern of alternative splicing for one of these regions.

Monoclonal antibodies to human secretory "pregnancy-associated endometrial alpha 1-globulin," an insulin-like growth factor binding protein: characterization and use in radioimmunoassay, Western blots, and immunohistochemistry

Monoclonal antibodies were raised against pregnancy-associated endometrial alpha 1-globulin (alpha 1-PEG), a 32 KD insulin-like growth factor binding protein (IGF-BP), which represents a major secretory product of the human decidualized endometrium during pregnancy. This class of IGF-BP has been implicated in the modulation of action, inhibitory and stimulatory, of insulin-like growth factors. Immunization with the protein purified from pregnancy endometrium resulted after myeloma fusion in the isolation of six hybridoma clones and the antibodies produced were characterized. The Ka of the antibodies ranged between 4.75 x 10(9) M-1 and 0.7 x 10(8) M-1. In Western blots all monoclonal antibodies reacted with purified protein of molecular weight 32 KD and specifically detected this IGF-BP species in culture medium and cytosolic extracts of pregnancy endometrium and amniotic fluid. The monoclonal antibodies appear to define three epitope-bearing regions as evidenced by their reactivity to polypeptide fragments of the protein. After synthesis and secretion by tissue explants in vitro the protein is susceptible to cleavage into fragments possessing different monoclonal antibody-defined reactivity. Employing immunohistochemical techniques the protein was principally localized to decidual cells in tissue sections of pregnancy endometrium and solely to these cells after enzymic digestion of the tissue. The implications of these results are discussed with respect to potential role of IGF-BP in the action of IGF upon the IGF-1 receptor-bearing populations, including lymphocytes and trophoblast cells, D in the decidua.

Secretory proteins of the endometrium--potential markers for endometrial dysfunction

In contrast to our detailed knowledge of endometrial structure, the study of endometrial function is still in its infancy. It seems likely that most of the changes that occur in the endometrium during the cycle are directed towards the promotion of implantation, and that the proteins secreted by the tissue have a role to play in the maintenance of pregnancy. One approach to the study of these proteins has been the incubation of endometrium in vitro with labelled amino acid precursors, and this method has revealed that in early pregnancy two proteins are quantitatively more important than the others synthesized and secreted by the endometrium. One of these proteins is a homologue of beta-lactoglobulin, also known as alpha 2-PEG, PP14 or PEP. It is synthesized by endometrial glands and no other source has been identified. Its synthesis is induced in the luteal phase of the menstrual cycle, rises to a peak in the early weeks of pregnancy and then rapidly declines as the decidua spongiosa is replaced by decidua compacta. The direction of its secretion appears to be into the amniotic fluid, and its function may be to transport a vitamin or other essential substance to the early conceptus: another possible function is immunosuppression. The protein can be measured in peripheral blood and may be useful as a marker of the effect of progesterone-or its lack of effect, as in the inadequate luteal phase. The other quantitatively important endometrial protein is IGF binding protein, which is produced mainly by stromal fibroblasts in the late luteal phase of the cycle. During the cycle the contribution of the endometrium to serum levels of IGF-BP is slight, but in pregnancy, as the amount of decidua compacta increases, levels in peripheral blood rise, with peaks at 18-24 weeks and at 36-40 weeks. The function of the protein may be to protect the mother by inhibiting IGF, or to enable IGF to stimulate the growth of endometrial stroma. Links between this protein and disorders of fetal growth have been suggested. The diversity of the possible functions of these proteins, and the continuing uncertainty over their roles, underline the complexity of endometrial functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Two fetal antigens (FA-1 and FA-2) and endometrial proteins (PP12 and PP14) isolated from amniotic fluid; preliminary observations in fetal and maternal tissues

Rabbit antihuman antibodies were derived by the injection of fractions of second trimester amniotic fluid known to contain proteins of endometrial/decidual origin. Using standard separation and absorption procedures, two antibody preparations were generated which demonstrated specificities against two and three proteins, respectively, in line immunoelectrophoresis and crossed immunoelectrophoresis. Analysis against proteins of fetal, maternal, endometrial and placental origin revealed that the bispecific antiserum reacted only with placental protein 14 (PP14; also known as progestagen-dependent endometrial protein, PEP) and one other hitherto undescribed antigen referred to as Fetal Antigen 1 (FA-1) molecular mass 60 kDa; electrophoretic mobility: slow; alpha 1-alpha 2; fast, albumin. The trispecific antiserum demonstrated specifities against placental protein 12 (PP12), alpha-fetoprotein (AFP) and another previously undescribed antigen referred to as Fetal Antigen 2 (FA-2) molecular mass 35 and 140 kDa; electrophoretic mobility: albumin. Following purification, monospecific antisera against each of these proteins (with the exception of AFP) were derived in new rabbits. Maternal and fetal blood, amniotic fluid and aqueous extracts from endometrial/decidual and placental tissues were analysed in rocket immunoelectrophoresis using these antisera to examine the distribution in these tissues. The analyses demonstrated a pattern of distribution typical for proteins of endometrial/decidual origin in these compartments in the case of PP12 and PP14, but suggested that the primary source of origin of FA-1 and FA-2 may be the fetus.

Detection and characterization of human secretory "pregnancy-associated endometrial alpha 2-globulin" in uterine luminal fluid

Pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the major secretory protein of the human endometrium as assessed by in vitro de novo synthesis and secretion, during the mid- to late-luteal phase of the menstrual cycle and early first trimester pregnancy, has now been detected immunochemically in uterine luminal flushings during the luteal phase of the menstrual cycle. Physicochemical characterization of this immunoreactive alpha 2-PEG demonstrated that it exhibited identical properties to the protein isolated from either the cytosol of pregnancy endometrium or medium from in vitro cultures of pregnancy endometrium, i.e. native Mr 56 K, subunit Mr 28 K, eluted from an anion exchange column at 0.11 M NaCl and bound to concanavalin A. These findings, together with other evidence, suggest that a major route of secretion of alpha 2-PEG during the luteal phase of the menstrual cycle in vivo is into the lumen of the uterus. These results are discussed with reference to the hypothesis that alpha 2-PEG, derived from the endometrial glandular epithelium, may represent the human functional analogue of uteroglobin and to the implications for the human of the hypothesized immunosuppressive role of uteroglobin and transglutaminase (Factor XIII) in masking Class I MHC antigens on gametes and the conceptus.