The synthesis and fate of glycodelin in human ovary during folliculogenesis

The ontogeny of glycodelin in human ovarian follicles during folliculogenesis was studied. Glycodelin immunoreactivity began to be detected in the granulosa cells and thecal cells of late secondary follicles. Immunoreactivity was also found in both the luteinized granulosa cells and cumulus cells obtained from women undergoing the assisted reproduction treatment. However, only the luteinized granulosa cells, and not the cumulus cells, expressed glycodelin mRNA. Results also showed that the cumulus cells took up radiolabelled glycodelin and partially deglycosylated some of it. Glycodelin (and a partially deglycolsylated form of glycoldelin) appeared to complex with two cytoplasmic or membrane components of the cumulus cells. The data also demonstrated that ZIF-1, a glycoprotein isolated from human follicular fluid, was immunologically similar to glycodelin. In conclusion, we suggest that glycodelin is synthesized in the granulosa cells of ovarian follicles at late secondary follicle stage. It then may be released into the follicular fluid from where it is taken up and partially modified by the cumulus cells.

A rheostatic mechanism for T-cell inhibition based on elevation of activation thresholds

The activation of discrete T-cell responses depends on the triggering of individualized threshold numbers of T-cell receptors (TCRs). The results of this study indicate that the lipocalin placental protein 14 (PP14), a T-cell inhibitor produced by cells of the reproductive and hematopoietic systems, mediates its anti-inflammatory activity by elevating the T-cell activation threshold, thereby rendering T cells less sensitive to stimulation. Significantly, the data demonstrate hierarchical sensitivity of selected cytokine responses to PP14-mediated inhibition, with the hierarchy reflecting their respective activation thresholds. These findings suggest a novel paradigm for immunoinhibition wherein negative regulators can finely tune, rather than inactivate, T-cell responses, and thereby skew the cytokine output of immunologic responses.

Uterine-conceptus interactions and reproductive failure in cattle

The dialogue between trophectoderm cells of the conceptus and epithelial cells of the endometrium is critical to CL maintenance and embryo survival. The signal transduction mechanisms by which bovine interferon (IFN)-tau regulates cyclooxygenase (COX)-2 expression and secretion of prostaglandin F2alpha (PGF2alpha) in bovine endometrial (BEND) cells is examined. Stimulation of Protein Kinase C with a phorbol ester (phorbol 12, 13 dibutyrate [PDBu]) activates COX-2 gene expression and PGF2alpha secretion via the mitogen-activated protein kinase (MAPK) pathway. Interferon-tau attenuates PDBu activation of PGF2alpha secretion, but this inhibitory effect appears to be independent of the MAPK pathway. Embryonic IFN-tau, acting through a Type I IFN receptor, activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway resulting in activation or repression of interferon-stimulated genes. Experimental evidence is provided that IFN-tau regulation of STATs regulates gene expression of COX-2 in a manner that decreases secretion of PGF2alpha. Maternal regulation of the antiluteolytic pathway is discussed relative to the ability of the polyunsaturated fatty acid, eicosapentaenoic (EPA), to decrease endometrial secretion of PGF2alpha and progesterone to increase both conceptus development and IFN-tau secretion.

The role of chorionic gonadotropin (CG) in blastocyst implantation

Implantation is a complex spatio-temporal interaction between the genotypically different embryo and the mother. Success of this event requires the synchronization of development and effective biochemical communications from both sides. Chorionic gonadotropin (CG), which is a major embryonic signal in the primate, is a glycoprotein hormone synthesized and secreted by the trophoblast. Various isoforms exist in plasma, urine, and blastocyst culture medium, a result of posttranslational modifications. The exponential secretion of CG and its long circulatory half-life extends the life span of corpus luteum to maintain the supply of progesterone during the first 6-8 weeks of pregnancy. To study the direct effects of CG in the uterus, we used the baboon (Papio anubis) as a non-human primate model. In vivo stimulation with CG during the window of uterine receptivity results in further morphologic and biochemical modifications of the receptive endometrium. These are characterized by the plaque reaction in the luminal epithelium, an increase in glycodelin expression and secretion by the glandular epithelium, and the differentiation of subepithelial stromal fibroblasts characterized by expression of the alpha smooth muscle actin (alpha SMA). Pretreatment with progesterone receptor antagonist (PRa) completely or partially inhibits these effects. The signal transduction pathway activated by CG in primate endometrial epithelial cells involves the protein kinase A (PKA)-independent phosphorylation of extracellular signal regulated kinase (ERK 1/2). This alternate signal transduction pathway may prevent CG Receptor (R) downregulation at the implantation site and enhance epithelial cell proliferation and differentiation. Thus, our results suggest that CG plays an important role in implantation in addition to its luteotrophic role.

Expression of the antiviral protein Mx in peripheral blood mononuclear cells of pregnant and bred, non-pregnant ewes

Interferon-tau (IFN tau) acts locally on the endometrium to suppress estrogen and oxytocin receptor expression and block luteolysis in ruminants. Systemic administration of conceptus homogenates or recombinant ovine IFN tau does not block luteolysis or enhance pregnancy rates in sheep or cattle, respectively. However, IFN tau up-regulates expression of the antiviral protein Mx throughout the entire uterine wall during early pregnancy. These studies determined if conceptus-derived IFN tau also up-regulates Mx expression in components of the circulating immune system that migrate through the endometrial wall. In experiment one, peripheral blood mononuclear cells (PBMC) were isolated from ewes at D26 post-artificial insemination (AI) and Mx mRNA levels examined by Northern and slot-blot hybridization. Pregnancy resulted in a two-fold increase in Mx mRNA levels compared to bred, non-pregnant ewes at D26. In experiment two, PBMC were isolated from ewes at AI, and every three days from D9 to D30. Results showed a four-fold increase in Mx mRNA levels in PBMC from pregnant versus bred, non-pregnant ewes at D15. Increased Mx mRNA, which remained elevated through D30, was accompanied by increased levels of Mx protein. These results show that pregnancy recognition signaling rapidly induces Mx gene expression in PBMC, and are the first to suggest that IFN tau activates gene expression in components of the circulating immune system.

Angiogenic role for glycodelin in tumorigenesis

Angiogenesis plays an important role in neovascularization in tumors. Glycodelin, a hormone-responsive protein, has been detected in tumors of reproductive organs and is found in high levels in the plasma of subjects with gynecological malignancies. Glycodelin is also found in the endothelial cells of the umbilical cord and in the blood vessels of tumors. In this study, we tested whether glycodelin-rich amniotic fluid and a synthetic peptide derived from the sequence of glycodelin peptide (Gp) might promote angiogenic response by examining the migration and tube formation in human umbilical cord vein endothelial cells (HUVECs). Increased migration and tube formation of HUVECs were found in the presence of amniotic fluid and Gp, and this increase was blocked by antibody to Gp and by an anti-vascular endothelial growth factor (VEGF) antibody, suggesting that the angiogenic effects of glycodelin might be mediated by VEGF. The results also showed that Gp significantly increased the release of VEGF protein and mRNA expression in HUVECs, RL-95 (human endometrial carcinoma cells), OVCAR-3 (human ovarian adenocarcinoma cells), EM42 (human endometrial epithelial cells), THP-1 (human monocyte), and MCF-7 and MDA-MB-231 (human breast adenocarcinoma cells) cell lines. VEGF receptor Fit-1 mRNA expression in HUVECs was also increased in the presence of Gp. These findings, together with the suggestion from the literature that glycodelin may have immunosuppressive properties, suggest that glycodelin might play an important role in neovascularization during embryogenesis and tumor development.

Placental protein 14 induces apoptosis in T cells but not in monocytes

Substantial evidence exists in literature to suggest that placental protein 14 (PP14) (recently renamed glycodelin A), exhibits immunosuppressive properties and is an indispensable macromolecule in the maternal system for the establishment, maintenance, and progression of pregnancy. Though there are several reports substantiating the above, the mechanism of its action at the molecular level has not been elucidated as yet. In this paper we provide data that suggest that amniotic fluid PP14 and recombinant PP14 expressed in Pichia pastoris induce apoptosis in human peripheral blood lymphocytes upon activation, independent of monocytes. That PP14 has a direct apoptotic action on T cells but not on monocytes was also demonstrated by utilizing human cell lines. PP14 was shown to induce apoptosis in the human T cell lines, Jurkat and MOLT-4 cells, but not in the human monocytic cell line, U937.

Polymorphic forms of expressed bovine interferon-tau genes: relative transcript abundance during early placental development, promoter sequences of genes and biological activity of protein products

Multiple interferon (IFN)-tau genes exist in cattle, but it has remained unclear how many are expressed, the extent of their variation, and whether different genes exhibit similar patterns of expression and code for proteins with similar biological activities. A total of 118 complementary DNA (cDNA) were bi-directionally sequenced from reverse-transcribed bovine (bo) conceptus RNA over the period from blastocyst formation until day 25 of pregnancy. Fourteen different cDNAs, encoding eight different IFN-tau, were confirmed unique. All showed high sequence conservation (>98% nucleotide identity; >96% amino acid identity). The cDNA fell into three, recently evolved, phylogenetic groups (tau1, 2, and 3). Mean concentrations of IFN-tau messenger RNA were greater at day 17 and day 19 than at day 14 and day 25, with different genes showing comparable expression patterns, although there appeared to be a major bias in expression of two genes (for boIFN-tau1c and tau3a) in blastocysts. Genes representing members of the three boIFN-tau groups were cloned. Their promoter regions were conserved over regions considered important for transcriptional activation. Recombinant protein generated in Escherichia coli from representative genes in the three groups had similar but not identical antiviral activities. In summary, many IFN-tau genes, which are probably under similar transcriptional control, are expressed in bovine trophoblast during the peri-implantation period of development.

Cloning of the ovine estrogen receptor-alpha promoter and functional regulation by ovine interferon-tau

Interferon-tau (IFNtau), the ruminant pregnancy recognition signal, inhibits transcription of the estrogen receptor alpha (ERalpha) gene in the endometrial lumenal epithelium of the sheep uterus, thereby abrogating production of luteolytic PGF(2alpha) pulses. The effects of IFNtau are mediated in part by IFN-stimulated response elements (ISREs) and IFN regulatory factor elements (IRFEs). The promoter/enhancer region of the ovine ERalpha gene was cloned, sequenced, and predicted to contain four IRFEs and one ISRE. Electrophoretic mobility shift assays indicated that the -2110 IRFE bound only IRF-1, whereas the -1877 IRFE and the -1284 ISRE were functional in binding IRF-1 and IRF-2. IFNtau inhibited transcriptional activity of the 2.7-kb ovine ERalpha promoter in transfection assays using ovine lumenal epithelium cells. Analyses of sequential 5'-deletion mutants of the ovine ERalpha promoter indicated that the effects of IFNtau may be mediated by IRFEs as well as other elements. Overexpression of ovine IRF-2, but not IRF-1, inhibited transcriptional activity of several regions of the ovine ERalpha promoter containing an IRFE or an ISRE as well as some, but not all, regions lacking these elements.

Progesterone as an immunomodulatory molecule

Increased progesterone sensitivity of pregnancy lymphocytes is due to activation-induced appearance of progesterone binding sites in the lymphocytes. Following recognition of fetally derived antigens gamma/delta TCR+ cells develop progesterone receptors. Progesterone binding results in the synthesis of a mediator protein named the progesterone-induced blocking factor (PIBF). PIBF by acting on the phospholipase A2 enzyme interferes with arachidonic acid metabolism, induces a Th2 biased immune response, and by controlling NK activity exerts an anti-abortive effect.

Glycodelin: a pane in the implantation window

Glycodelin is an endometrial protein with proposed immunomodulatory activity during human embryonic nidation. In this review we describe the effects of ovarian hormones on glycodelin transcription, synthesis, and secretion by human epithelial cells and focus on the importance of glycodelin in implantation. We demonstrate that glycodelin transcription, synthesis, and secretion by human epithelial cells are stimulated by progestins and antiprogestins but not by estrogen. Sequences localized within a 403-base-pair region flanking the 5' human glycodelin gene promoter appear to be responsible for transcriptional activation of this gene mediated by progesterone receptor-ligand complexes. Relaxin, purported to enhance glycodelin production in vivo and in prior in vitro studies, had no stimulatory effect on the expression of this gene in vitro in our models.

Presence of a 31-kD protein band in human cumulus--corona radiata--conditioned media and pregnancy outcome

OBJECTIVE

To investigate relationships between cumulus-oocyte complex (COC) morphology, protein patterns of cumulus-corona (CC) cell-conditioned media, and pregnancy outcome in IVF-ET cycles.

DESIGN

Retrospective study.

SETTING

Private university IVF center.

PATIENT(S)

One hundred twenty infertile women who underwent IVF-ET procedures.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

COC grading, analysis of CC cell morphology and conditioned media, and pregnancy rate (PR).

RESULT(S)

After IVF and embryo transfer, cultured CC cells were classified as high (HA) or low (LA) on the basis of their adhesive properties. Neither adhesion activity nor fertilization rates and embryo quality were correlated with COC grading. PR in cycles with HA cells was 38%, but 14% of cycles showing LA activity also had positive outcome. To find more meaningful parameters of CC cells useful to predict fertilization and pregnancy, the electrophoretic protein patterns of media conditioned by HA or LA cells were studied. Retrospective analysis showed that all cycles in which replaced embryos were associated with the presence of a 31-kD band in conditioned media failed implantation, whereas 83% of cycles lacking this band resulted in positive, ongoing pregnancy.

CONCLUSION(S)

Pregnancy prediction cannot rely simply on CC cell morphological analysis. Screening of conditioned media may provide more reliable parameters.

Synergism between vascular endothelial growth factor and placental growth factor contributes to angiogenesis and plasma extravasation in pathological conditions

Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.

The crystal structure of human placenta growth factor-1 (PlGF-1), an angiogenic protein, at 2.0 A resolution

The angiogenic molecule placenta growth factor (PlGF) is a member of the cysteine-knot family of growth factors. In this study, a mature isoform of the human PlGF protein, PlGF-1, was crystallized as a homodimer in the crystallographic asymmetric unit, and its crystal structure was elucidated at 2.0 A resolution. The overall structure of PlGF-1 is similar to that of vascular endothelial growth factor (VEGF) with which it shares 42% amino acid sequence identity. Based on structural and biochemical data, we have mapped several important residues on the PlGF-1 molecule that are involved in recognition of the fms-like tyrosine kinase receptor (Flt-1, also known as VEGFR-1). We propose a model for the association of PlGF-1 and Flt-1 domain 2 with precise shape complementarity, consider the relevance of this assembly for PlGF-1 signal transduction, and provide a structural basis for altered specificity of this molecule.

Glycodelins

Glycodelin is a major glycoprotein that is synthesized in the endometrium in response to progesterone and relaxin exposure. Endometrium-derived glycodelin-A has contraceptive and immunosuppressive properties. Glycodelin is absent from the endometrium during the fertile periovulatory phase, but is synthesized in this tissue during the peri-implantation phase and is abundant during the last week of the luteal phase. Changes in local and/or circulating glycodelin concentrations have been observed in women with reproductive disorders. The chemical modification of glycodelins has resulted in compounds with antiviral activity.

Interferon-tau suppresses prostaglandin F2alpha secretion independently of the mitogen-activated protein kinase and nuclear factor kappa B pathways

Pregnancy is established in ruminants through inhibitory actions of interferon (IFN)-tau on the release of prostaglandin F2alpha (PGF), which allows the corpus luteum to survive and continue to produce progesterone. Experiments were designed to 1) delineate the signal transduction pathway coordinating the synthesis of PGF, 2) determine how rapidly recombinant bovine (rb) IFN-tau attenuated phorbol ester (PDBu)-induced secretion of PGF, and 3) establish the site at which rbIFN-tau attenuates the secretion of PGF in cultured bovine endometrial (BEND) cells. BEND cells were untreated (control) or treated for 5, 10, 60, 180, or 300 min with PDBu (100 ng/ml), rbIFN-tau (50 or 500 ng/ml), PDBu + rbIFN-tau, or PDBu + PD98059 (MEK-1 inhibitor; 50 microM). Secretion of PGF was induced (P < 0.0001) by PDBu within 180 min, but induction was inhibited 74% by the addition of rbIFN-tau (P < 0.0001) and was ablated completely by PD98059. Parallel results were obtained for cyclooxygenase (COX)-2 protein expression. PDBu induced (P < 0.05) activation of the Raf-1/MEK-1/ERK-1/2 pathway, which was obligatory for the expression of COX-2 and secretion of PGF but was not altered by cotreatment with rbIFN-tau. PDBu induced (P < 0.05) transcription of c-jun and c-fos mRNAs within 30 min; induction was inhibited (P < 0.05) by cotreatment with PD98059 but not by cotreatment with rbIFN-tau. Treatment of BEND cells with rbIFN-tau also did not attenuate PDBu-induced degradation of IkappaBalpha, suggesting that the IkappaBalpha/NFkappaB pathway is not a site of IFN-tau inhibition of PGF. However, rbIFN-tau did block transcription of the COX-2 gene induced by PDBu within 30 min. In conclusion, COX-2 expression and PGF secretion induced by PDBu is mediated through the Raf-1/MEK-1/ERK-1/2 pathway, but this pathway is not disrupted by rbIFN-tau. Because rbIFN-tau inhibits COX-2 mRNA within 30 min, we hypothesized that transcription factors activated by rbIFN-tau rapidly and directly attenuate COX-2 gene expression, thereby suppressing secretion of PGF.

Overexpression of tissue factor pathway inhibitor-2 (TFPI-2), decreases the invasiveness of prostate cancer cells in vitro

Human tissue factor pathway inhibitor-2 (TFPI-2) is a 32-kDa serine protease inhibitor that inhibits plasmin, trypsin, chymotrypsin, cathepsin G, and plasma kallikrein but not urokinase and tissue-type plasminogen activators or thrombin. After discovering that TFPI-2 expression is down-regulated or lost during tumor progression, we investigated the role of TFPI-2 in the invasiveness of the prostate cancer cell line (LNCaP). We stably transfected LNCaP cells with a 0.7-kb vector expressing TFPI-2 in the sense orientation and measured the expression of TFPI-2 protein and mRNA by these cells by western and northern blotting. Neither TFPI-2 protein nor mRNA was expressed by parental LNCaP cells or vector-transfected controls, but levels of both protein and mRNA were significantly increased in the sense-TFPI-2 clones. The sense clones were less invasive than the control cells in Matrigel invasion and spheroid migration assays. This is the first demonstration that upregulation of TFPI-2 plays a significant role in the invasive behavior of human prostate cancer cells.

Pregnancy-specific glycoprotein (PSG) in baboon (Papio hamadryas): family size, domain structure, and prediction of a functional region in primate PSGs

Pregnancy-specific glycoprotein (PSG) constitutes a major component of serum of pregnant women and appears to be essential for a successful pregnancy. Its function is, however, still unknown. Because of the evolutionary divergence between human and rodent PSG, functional studies may require a primate animal model. We have characterized PSG transcripts in a baboon placenta cDNA library and analyzed baboon genomic DNA. The main PSG isoform had the domain structure N-A1-B2-C similar to the human type IIa isoform. The type I isoform (N-A1-A2-B2-C) was also expressed. Fifteen similar PSG genes were identified of which at least nine were simultaneously expressed in third trimester baboon placenta. Thus, the baboon PSG family was as complex as that of humans. Recombinant baboon PSG (isoform IIa) had a molecular weight of 38 kDa and reacted with antibodies against human PSG. Comparative analysis of 43 N-domain amino acid sequences of PSG from four species and nine primate carcinoembryonic antigen subgroup N domain sequences identified a number of residues in the GFCC'C" ss-sheet and FG loop that are probable candidates for PSG binding to its putative ligand.

Interferon-tau activates multiple signal transducer and activator of transcription proteins and has complex effects on interferon-responsive gene transcription in ovine endometrial epithelial cells

Interferon-tau (IFNtau), a type I IFN produced by sheep conceptus trophectoderm, is the signal for maternal recognition of pregnancy. Although it is clear that IFNtau suppresses transcription of the estrogen receptor alpha and oxytocin receptor genes and induces expression of various IFN-stimulated genes within the endometrial epithelium, little is known of the signal transduction pathway activated by the hormone. This study determined the effects of IFNtau on signal transducer and activator of transcription (STAT) activation, expression, DNA binding, and transcriptional activation using an ovine endometrial epithelial cell line. IFNtau induced persistent tyrosine phosphorylation and nuclear translocation of STAT1 and -2 (10 min to 48 h), but transient phosphorylation and nuclear translocation of STAT3, -5a/b, and -6 (10 to <60 min). IFNtau increased expression of STAT1 and -2, but not STAT3, -5a/b, and -6. IFN-stimulated gene factor-3 and STAT1 homodimers formed and bound an IFN-stimulated response element (ISRE) and gamma-activated sequence (GAS) element, respectively. IFNtau increased transcription of GAS-driven promoters at 3 h, but suppressed their activity at 24 h. In contrast, the activity of an ISRE-driven promoter was increased at 3 and 24 h. These results indicate that IFNtau activates multiple STATs and has differential effects on ISRE- and GAS-driven gene transcription.

Trophoblast interferon and pregnancy

The maternal recognition of pregnancy in ruminants requires the production of interferons by the preimplantation blastocyst. These proteins, the trophoblast interferons (IFN-tau), are the products of a number of similar genes, the expression of which is controlled by characteristic promoter regions. They are expressed for a short period in high concentrations, and have antiluteolytic, antiviral, antiproliferative and immunomodulatory effects, through receptors on the endometrial epithelium. The antiluteolytic effects of IFN-tau result from inhibition of endometrial expression of the oxytocin receptor, through which circulating oxytocin stimulates episodic prostaglandin F2a production. Some of the properties of IFN-tau differ from those of other type I interferons, and they may have novel therapeutic effects. Because of their central role in early gestation, these proteins have excited the interest of reproductive physiologists. However, their other properties, and the fact that their expression is controlled so precisely, have made them of interest to a wide range of biologists.

Embryo maternal dialogue: From pregnancy recognition to proliferation control

Embryo-maternal dialogue starts shortly after fertilization and is exerted through both local and systemic signaling. We have discovered specific embryo derived pre-implantation factors (PIF), novel peptides that are secreted already at the two cell stage and which modulate cellular immunity. In the fallopian tube the embryo, a partial allograft, is tolerated by the mother. Embryo derived peripheral signaling (PIF) is also detected prior to implantation in maternal sera. This signal may also help prime the endometrium to facilitate implantation. Upon implantation, embryo-endometrial communication becomes direct and highly amplified. When the immune privilege appears to be secured, embryogenesis proper initiates. This requires proliferation/differentiation to be tightly controlled. Knowledge of proliferation promoters is ample while the factors involved in its control remain less understood. We have identified a class of novel proteins/peptides, developmental proteins (DPs), that are present in the embryo before a mature immune system has developed. Their role is to create a balance between pro and antiproliferative forces, to promote normal proliferation while controlling abnormal cell proliferation (i.e. due to carcinogens, toxins, viruses, and ionic radiation). DPs, may also redirect growth towards functionality through differentiation. DPs appear to act through a specific receptor negating growth factors action through promotion of tumor suppressors and inhibition of tumor promoters at 2 minutes, blocking DNA synthesis at ~24 hours, and promoting apoptosis at ~48 hours. When an embryo becomes incompatible with life, DPs may lead to growth arrest, PIF-like compounds decline, the immune system to be restored and the pregnancy is rejected. Final identification and use of PIF and DPs is likely to help both managing early pregnancy disorders and aid in treatment of proliferative disorders due to cancer and viral infection.

Inhibition of tumor growth by the antiangiogenic placental hormone, proliferin-related protein

Proliferin-related protein (PRP) is a potent placental antiangiogenic hormone. To test the antiangiogenic potential of PRP to block tumor growth, we engineered tumor cells to express this hormone. Both SV40-transformed BALB/c mouse 3T3 fibroblasts and rat C6 glioma cells have markedly reduced growth rates as tumors in mice if they express high levels of PRP. In both models, the small tumors that form are largely avascular, whereas control tumors are rich in blood vessels, consistent with PRP limiting tumor growth by preventing neovascularization of the tumors. The antiangiogenic effects of PRP are also detected on human endothelial cells, suggesting that the receptor and signaling pathway of this mouse hormone are conserved between mouse and human and may represent useful targets for the development of antiangiogenic therapeutics. That signaling pathway appears to involve an inhibition of arachidonic acid release, based on the ability of arachidonic acid to overcome the antiangiogenic effects of PRP.