A progestagen-associated protein of the human endometrium: basic studies and potential clinical applications.
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Two proteins, designated as PP12 and PP14 were originally isolated from soluble extracts of the human placenta and its adjacent membranes. We have shown that they are synthesized by decidualized/secretory endometrium and not by placenta. Both proteins occur at high concentrations in human amniotic fluid, which is therefore an excellent source for purification. PP12 is a 34-kDa glycoprotein, which has an N-terminal amino acid sequence of Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala. This is identical with that of somatomedin-binding protein purified from the amniotic fluid. PP12 too binds somatomedin-C, or IGF-I (insulin-like growth factor-I). Human secretory endometrium synthesizes and secretes PP12, and progesterone stimulates its secretion. PP14 is a 28-kDa glycoprotein. Its N-terminal sequence shows homology to that of beta-lactoglobulins from various species. We have found PP14 in the human endometrium, serum and milk. Immunologically, PP14 is related to progestagen-associated endometrial protein (PEP), alpha-2 pregnancy-associated endometrial protein (alpha-2, PEG), endometrial protein 15 (EP15), alpha-uterine protein (AUP) and chorionic alpha-2 microglobulin (CAG-2). In ovulatory menstrual cycles, the concentration of PP14 increases in endometrial tissue as the secretory changes advance. In serum, the PP14 concentration begins to rise later than the progesterone levels, and high serum PP14 levels are maintained for the first days of the next cycle. By contrast, no elevation of serum PP14 level is seen in anovulatory cycles. Our results show that progesterone-associated proteins are synthesized by the human endometrium and appear in the peripheral circulation, where they can be quantitatively measured using immunochemical techniques.
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.
Monospecific antisera against two fetal antigens (FA-1 and FA-2), alphafetoprotein (AFP) and two endometrial proteins (PP12 and PP14) were used to examine the distribution of these proteins and antigens in human trophoblast and gestational endometrium in first and third trimesters of pregnancy, normal human ovary and fetal tissues by indirect immunoperoxidase histochemical localisation techniques. Fetal liver stained exclusively for FA-1 and AFP which was used as a reference protein. Staining for FA-2 was seen in fetal connective tissue, in particular the basement membrane. FA-1 and FA-2 did not stain positively in decidua, trophoblast or ovarian tissue. Gestational endometrium stained positively for PP14 exclusively in the glandular epithelium, whilst staining for PP12 was seen only in the stromal cells. Trophoblast, both early and late, and ovarian tissue did not stain positively for any of the four substances tested.
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This study was conducted to assess endometrial protection in women on a cyclical combined hormone replacement regimen with 1 mg norethisterone BP, and to evaluate the use of the bleeding pattern and serum alpha 2-PEG in monitoring the endometrial response to exogenous hormone therapy. Fifty-one postmenopausal women attending the Menopause Research Unit at Leicester Royal Infirmary, UK, completed the study. All patients were at least 1 year after the menopause, with an average of 26 months since the last menstrual period. All women were prescribed a regimen of two tablets of Hormonin (oestriol 0.27 mg, oestrone 1.4 mg, and oestradiol 0.6 mg) continuously, with 1 mg of norethisterone added for 12 days out of each 28-day treatment cycle. Menstrual diaries were collected and analysed. The secretory changes were assessed by histology, menstrual bleeding pattern and a biological marker of secretory activity (alpha 2-PEG). Withdrawal bleeding occurred on average on days 11, 12, 11, 12 and 13 on months 2, 3, 6, 9 and 12, respectively. There was a poor degree of consistency in the bleeding pattern. The level of alpha 2-PEG increased from the average baseline measurement of 2.7 ng/ml (S.D., 4.12) to 8.5 ng/ml (S.D., 4.16) after progestogen treatment. This rise, although significant, did not correlate with the uterine bleeding pattern. There was no statistically significant correlation between the level of alpha 2-PEG and endometrial histology. The findings highlight the fact that cycle predictability on HRT, as exemplified in this regimen, is poor. The level of alpha 2-PEG is a poor predictor of the endometrial histology and has a poor correlation with the day of onset of bleeding.
A novel combination of two conventional techniques (autoradiography, AR and line immunoelectrophoresis, LIE; ARLIE) for identification of specific proteins synthesized de novo by explants is described. The incorporation rate of [35S]-methionine was linear in proteins derived from cytosol fractions and supernatants of first trimester human trophoblast and gestational endometrium for up to 18 h. SDS-PAGE analysis of these fractions provided further evidence of the protein synthesis and secretion by the tissue explants. The ARLIE system was evaluated by investigating the synthesis and secretion of five test proteins (PP12, PP14, hPL, FA-1 and FA-2) by trophoblast and gestational endometrium. The synthesis P12 and PP14 could be demonstrated by gestational endometrium only. Similarly the synthesis of hPL could be demonstrated by the trophoblast alone. The synthesis of the fetal proteins (FA-1 and FA-2) could not be demonstrated by either tissue. The control procedure, Protein A assisted immunoprecipitation, yielded similar results for PP14 but not hPL. This novel combination (ARLIE) provides a simple technique with which to study the de novo synthesis of several proteins simultaneously which is independent of the subclass and species of origin of antibodies.
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Insulin-like growth factor binding protein-1 (IGFBP-1) [also known as placental protein 12(PP12)] and placental protein 14 (PP14) have been identified by specific immunostaining in early pregnancy specimens obtained 13-35 days of gestation. PP12 was evident in a discrete number of stromal decidual cells at the deciduotrophoblastic interface and under the endometrial surface epithelium. These cells did not have the rounded appearance of classic decidual cells but most often displayed cytoplasmic expansions. Staining for PP14 was strictly localized to the glandular epithelium of the endometrium. Implantation of the conceptus may be an important mechanism in the early expression of PP12 but not PP14.
Crude human decidual extracts containing up to 26.6 mg/l of placental protein 14 (PP14) and purified PP14 were assessed for their effects on the in vitro lymphocyte reactivity to phytohemagglutinin (PHA). Both decidual extract and purified PP14 suppressed the mitogenic response to PHA with the suppression being dose-dependent over the range of PP14 concentrations investigated (0-26.6 mg/l). On the specific reduction of the PP14 content by a monoclonal anti-PP14 immunoadsorbant the suppression was reduced. The suppressive activity of PP14 was related to the degree of proliferation of the stimulated lymphocytes. These results suggest that PP14, which is present at peak levels in the first trimester of pregnancy and constitutes up to 10% of the soluble protein content of decidual tissue, may be an immunomodulator important for the survival of the implanting embryo and maintenance of early pregnancy.
Concentrations of placental protein 14 (PP14) were measured by radioimmunoassay in 103 amniotic fluid samples from 10 to 20 weeks of pregnancy. Low levels of PP14 were present at 10-12 weeks (median values 82-280 micrograms/l). After 12 weeks, the levels increased by two orders of magnitude to reach a peak at 18 weeks (median 11 mg/l). This pattern may reflect the obliteration of the extraembryonic coelom and direct apposition of the decidua with the chorio-amnion.
In view of the increasing use of oestrogen-progestogen therapy in post-menopausal women the availability of possible biochemical marker of endometrial response to progestogen would be highly desirable. Placental protein 14 (PP14) has recently been shown to be excreted from the endometrium during the secretory phase of the menstrual cycle. In the present study we examined the concentration of serum PP14 (S-PP14) in 15 pre-menopausal women during the menstrual cycle and in 30 early post-menopausal women receiving three different doses of 17 beta-oestradiol (E2), cyclically combined with norethisterone acetate (NETA). S-PP14 levels peaked on day 1 following the onset of menstrual bleeding and on day 7 during NETA administration. It was possible to estimate the area under the S-PP14 curve reliably from one or two blood samples taken at optimal times. In the post-menopausal women, S-PP14 varied in a highly significant dose-dependent manner, i.e., the higher the E2 dose (in relation to the fixed NETA dose) the higher the S-PP14 response was found to be. We suggest that S-PP14 measurements might reflect the quantitative development of the endometrium in the secretory phase in both pre-menopausal and post-menopausal women.
The secretory endometrial protein PP14 was measured in serum from 49 healthy, early post-menopausal women receiving continuous combined oestradiol valerate/cyproterone acetate (2 mg E2V + 1 mg CPA daily) or placebo over a period of 2 years. In the hormone group, serum PP14 increased from 2.1 micrograms/l to a maximum of 8.1 micrograms/l after 1 month of treatment, then fell after 3 months to 3.8 micrograms/l and remained at that level for the rest of the 2-year period. After the first month, the occurrence of uterine bleeding was associated with significantly increased serum PP14 levels. Bleeding was not correlated with the serum concentration of 17 beta-oestradiol (E2) or CPA, or the CPA/E2 ratio. Serum PP14 was significantly dependent on the serum concentration of E2, but not on that of CPA. The present data confirm that serum PP14 levels reflect the secretory phase of the endometrium and that bleeding during continuous combined hormone replacement therapy is probably caused by a sub-optimal hormonal balance.
OBJECTIVE: Our purpose was to investigate the diagnostic accuracy of single or summed measurements of progesterone and placental protein 14, a progestin-dependent endometrial glycoprotein, in the evaluation of luteal function. STUDY DESIGN: Forty-five healthy women had daily blood measurements of luteinizing hormone, progesterone, and placental protein 14 during one menstrual cycle. RESULTS: Thirty-nine women had normal and six had deficient luteal function on the basis of serial progesterone determinations. Luteal insufficiency was not accurately diagnosed by single progesterone or placental protein 14 values or by integrated placental protein 14 measurements. In contrast, the condition was correctly identified in all but one cycle when the sum of progesterone on days 4 and 7 was < 49 nmol/L (15.4 ng/ml). A poor correlation was found between peak or integrated measurements of progesterone and placental protein 14. CONCLUSION: Measurement of serum progesterone, but not placental protein 14, on 2 days of the midluteal phase provides a convenient and reliable test of luteal function.
OBJECTIVE: Our objective was to determine if a progesterone antagonist might interdict the development of a secretory endometrium. STUDY DESIGN: Eleven normally cycling women not at risk for pregnancy received RU 486 (1 mg/day orally) or placebo throughout one menstrual cycle in a randomized, double-blind, crossover fashion. Estradiol, progesterone, and placental protein 14 were measured every 3 days; luteinizing hormone was measured until the midcycle surge was detected. An endometrial biopsy was performed on luteal phase day 7 to 9 and interpreted with Noyes' criteria. Differences between treatment groups were analyzed by the Student t test. RESULTS: RU 486 delayed ovulation, retarded endometrial maturation, and reduced peak levels of placental protein 14 without affecting gonadal steroid production. The abnormalities in endometrial morphology and function are similar to those seen in infertile women with luteal phase defects. CONCLUSION: We hypothesize that this regimen of antiprogestin administration may prevent implantation and offer a novel strategy for fertility control.
The presence of a progestogen-dependent endometrial protein (PEP) in women was previously described. The present study was undertaken to determine whether the occurrence or the concentration of PEP in endometria is related to the developmental stage of tissues and/or to the levels of endogenous progesterone (P) or 17 beta-estradiol (E) to which the tissues are exposed. Samples of serum and endometrial tissue in different developmental stages were obtained from pregnant women and women with normal menstrual cycles and were analyzed for PEP. In addition, the sera were analyzed for P and E. The occurrence of PEP in the endometrium of all of the women who were studied was found to be correlated with the heightened secretory activity and with the decidual change in the tissue. Furthermore, in women with normal cycles, the detection of PEP was associated with high serum levels of P. Comparison of serum levels of P with endometrial levels of PEP in pregnant women and in women in the mid-secretory phase of the menstrual cycle indicated that a 2.8-fold rise in serum levels of P during pregnancy was accompanied by a comparable (about threefold) rise in tissue levels of PEP. Therefore, we conclude that, in pregnant women and women with normal cycles, the levels of PEP in the endometrium reflect developmental changes within the endometrium, and that those levels are directly related to serum levels of P.
OBJECTIVE: The aim of the study was to assess the dose-response effects on the postmenopausal endometrium of 3 sequential combined hormone replacement regimens and 1 continuous combined hormone replacement regimen of estradiol and gestodene. STUDY DESIGN: In this 2-year double-blind, placebo-controlled study, 278 healthy postmenopausal women received either 2 mg estradiol sequentially combined with 50 microg or 25 microg gestodene, 1 mg estradiol sequentially or continuously combined with 25 microg gestodene, or placebo. RESULTS: All 4 hormone treatment regimens produced a safe endometrial histologic appearance. The regimens that were based on the lower dose of 1 mg estradiol was associated with less uterine bleeding than were those that were based on 2 mg estradiol. For sequentially opposing the 2 mg dose of estradiol, the dose of 25 microg gestodene was less efficient in producing secretory activity than was the dose of 50 microg gestodene. The measurement of placental protein 14 in serum reflected the secretory transformation of the endometrial buildup. CONCLUSION: The reduction in bleeding episodes associated with regimens with lower estradiol doses may lead to improved long-term therapy compliance by menopausal women. The potency of progestogens can be assessed by measuring the serum concentration of placental protein 14.
Placental protein 14 (PP14) is a glycoprotein of the lipocalin family that acts as a negative regulator in T cell receptor-mediated activation. In this study, we investigated PP14s potential role in regulating B cell activation. While PP14-inhibited B cell proliferation, IgM secretion and the surface expression of MHC class II, the expression of other surface molecules, such as CD69 and CD86, were unaffected. These observed effects were independent of the anti-IgM concentration used for stimulation, regardless of the presence of either T cells or IL-4, and persisted when B cells were stimulated by stimuli, which circumvent early events during B cell Ag receptor (BCR) activation, namely, protein kinase C activators in combination with Ca(2+) ionophore. Interestingly, we demonstrated that PP14s inhibitory characteristics are reminiscence of that achieved by independent ligation of CD19 using anti-CD19 mAb. Together with our previously reported effects on T cells, these findings identify PP14 as a soluble regulatory factor capable of interacting with both T and B cells in a carbohydrate-dependent manner and as a result it can affect both cellular and humoral immune responses.