Placental protein 12 is a decidual protein that binds somatomedin and has an identical N-terminal amino acid sequence with somatomedin-binding protein from human amniotic fluid

Placental protein 12 (PP12) was originally isolated from term human placenta and adjacent membranes. Recently we found that the site of PP12 synthesis is decidua but not placenta. In this work, the purity of PP12 was first tested by sodium dodecyl sulfate polyacrylamide slab-gel electrophoresis and by reverse phase HPLC, and the N-terminal amino acid sequence of 15 residues was determined by a liquid-phase sequencer. A single amino acid sequence of Ala-Pro-Trp-Gln-Cys-Ala-Pro-Cys-Ser-Ala-Asp-Glu-Leu-Ala-Leu was obtained showing identity to the known N-terminal amino acid sequence of somatomedin-binding protein from human amniotic fluid. Like the latter, PP12 bound somatomedin (insulin-like growth factor I) as demonstrated in gel chromatography by a shift in the elution pattern of [125I]iodo-insulin-like growth factor I after incubation with PP12. These data show that PP12 is a somatomedin-binding protein and extend through previous literature on PP12 the existing knowledge on the physiology and pathophysiology of somatomedin-binding protein(s) in human reproduction and cancer.

Synthesis of placental protein 12 by human endometrium

We have previously shown that placental protein 12 (PP12) is synthesized and secreted by human term pregnancy decidua in vitro. In the present study, fragments of proliferative and secretory phase endometrium were cultured in media in the presence and absence of progesterone (P) and 17 beta-estradiol (E2) for 96 h. The PP12 concentrations in the media and tissues were measured by RIA, and de novo synthesis was investigated by measuring the incorporation of [35S]methionine into PP12. Before culture, PP12 could not be detected in any proliferative endometria, whereas all secretory endometria contained PP12. All secretory endometria released PP12 into the medium in the presence and absence of added P and E2. Secretory endometria released significantly more PP12 than proliferative endometria. Three of seven proliferative endometria did not release PP12 in the absence of P, but all did so after P had been added. The addition of P to culture medium caused a 2.4-to over 71-fold increase in PP12 secretion over control values in proliferative endometria and up to a 3.5-fold increase in secretory endometrium. E2 had no significant effect. Cycloheximide totally inhibited the PP12 release induced by P from proliferative endometrium, and in secretory endometrium, it either totally blocked PP12 release or inhibited the stimulation due to P. [35S]Methionine was incorporated into immunoprecipitable PP12 in cultures of secretory and P-treated proliferative phase endometria. These results demonstrate de novo synthesis of PP12 by nonpregnant endometrium in tissue culture and suggest that the biosynthesis and secretion of PP12 by nonpregnant endometrium are regulated by P.

Placental protein 14 and progestagen-dependent endometrial protein are immunologically indistinguishable

Placental protein 14 isolated from the human placenta and its adjacent membranes, and progestagen-dependent endometrial protein (PEP) isolated from the endometrium have been described independently by two groups. We report results of the radioimmunological and immunodiffusion tests which show that the proteins are immunologically indistinguishable from each other.

Serum levels of placental protein 14 reflect ovulation in nonconceptional menstrual cycles

Placental protein 14 (PP14), originally isolated from the human placenta and its adjacent membranes, was detected in the serum of nonpregnant women. The levels were measured by radioimmunoassay in 218 serum samples from 19 women throughout the menstrual cycle. In 13 women with a normal ovulatory cycle, the levels showed consistent variation. They were highest (up to 172 ng/ml) in the late secretory phase and remained high for the first days of the next cycle. Low concentrations were found from the midproliferative to the early luteal phase of the cycle. No similar variation was seen in anovulatory cycles of six other women. Compared with ovulatory cycles, anovulatory cycles exhibited lower PP14 levels in the latter part of the cycle (P less than 0.001) and in the beginning of the next cycle (P less than 0.01). In ovulatory cycles, the sustained elevation of serum PP14 concentration over the following period may be explained by the fairly long half-life (42 hours) of PP14 in serum: once the level has increased, it declines slowly. These results suggest that PP14 measurement may become a novel means to distinguish between ovulatory and anovulatory cycles even after the onset of the next period.

New pregnancy and placental proteins and their possible diagnostic significance

In our laboratory a large number of, for the most part, new proteins have been detected by immunochemical methods in extracts from human term placentae: namely 3 pregnancy proteins (SP1, SP2 and SP3), around 40 soluble placental tissue proteins (PPs) and at least 11 different solubilized, apparently membrane-associated, tissue proteins. A great deal of the new proteins has been already isolated to purity and characterized. The treatise gives an overview of what is known of the physico-chemical properties and of the possible biological role of these proteins as well as of their occurrence in tissues and body fluids. It also summarizes the possible diagnostic significance of detection and measurement of these proteins on the one hand in pregnant women, on the other hand in patients with tumours and other diseases, as far as this has been already investigated.

Placental protein 10 (PP10) in normal pregnancy and cholestasis of pregnancy

The circulating concentrations of placental protein 10 (PP10) were measured by radioimmunoassay in 288 women with normal pregnancy and ten women (55 samples) with cholestasis of pregnancy. Serum PP10 levels were not affected by changes in incubation and storage temperature, and no diurnal variation was observed. The highest PP10 levels (36-85 micrograms/l) in normal pregnancy were found at 34 weeks. The postpartum decline of serum PP10 concentration corresponded to an average half-life of 18 h. In cholestasis of pregnancy at 32-39 weeks, the serum PP10 levels were found to be lower than normal. Negative correlation was observed between aminotransferase and PP10 levels in serum and between the bile acid levels and the PP10 concentration. These results suggest that the severity of maternal liver disorder is reflected in the circulating PP10 concentration.

Placental protein 12 (PP12): a new test for the prediction of the small-for-gestational-age infant

The circulating levels of placental protein 12 (PP12) and placental lactogen (hPL) were measured in 501 women between 36 and 41 weeks gestation. There was a significant positive association between hPL levels and infant birthweight and a significant negative association in the case of PP12 levels. The clinical efficiency of elevated PP12 levels in the prediction of low-birthweight infant at term compared favourably with that of reduced hPL levels.

Distribution of placental protein 14 in tissues and body fluids during pregnancy

Placental protein 14 (PP14) levels were measured in serum samples from non-pregnant and pregnant women, amniotic fluid, cord blood, and extracts of placenta, decidua and fetal membranes. The levels were low (15-40 micrograms/l) in serum of non-pregnant women. In four pregnancies following in-vitro fertilization, the serum PP14 levels started to rise 2-12 days after embryo replacement. In normal pregnancy, the highest serum PP14 concentrations (up to 2200 micrograms/l) were detected between 6 and 12 weeks. After 16 weeks the level decreased and plateaued at 24 weeks to around 200 micrograms/l. In amniotic fluid, the highest PP14 levels (232 mg/l) were found between 12 and 20 weeks, being considerably higher than those in maternal serum throughout pregnancy. In cord blood, the levels were low (15-22 micrograms/l) or undetectable. In early pregnancy decidua, the PP14 content was higher (41-160 mg/g total protein) than in late pregnancy decidua (60-2700 micrograms/g total protein). In amnion and chorion laeve, the PP14 concentration varied from 50 to 750 and 50 to 1000 micrograms/g protein, respectively. Early pregnancy placenta contained 0.25-15 mg/g and late pregnancy placenta 3-430 micrograms/g protein of PP14. These results show that the levels of PP14 in pregnancy serum have a similar profile to hCG, but in contrast to other placental proteins, the amniotic fluid PP14 levels are remarkably high. This may be explained by suggesting that decidua is a source of PP14.

Placental protein 5 (PP5) inhibits thrombin-induced coagulation of fibrinogen

The effect of Placental Protein 5 (PP5) on thrombin-induced coagulation of diluted fibrinogen is described. In contrast to previous reports which failed to demonstrate antithrombin-like activity for PP5 on synthetic substrates, we show in this study that PP5 inhibits thrombin activity in a dose-dependent manner. PP5 acts thus in a very similar way to antithrombin III (ATIII). Although PP5 binds to heparin, it does not show any heparin-cofactor activity. Whereas catalytic amounts of heparin accelerate greatly the inhibitory effect of ATIII, no accelerating effect of heparin on PP5 could be observed under the same conditions. In spite of its anti-thrombin activity, PP5 cannot be considered as a pregnancy-analogue of ATIII, as it lacks the heparin-cofactor activity.

Isolation and characterization of two membrane-associated placental tissue proteins

Two membrane associated placental tissue proteins (PP4 and MP1) have been isolated and characterized. Both proteins are found in the soluble as well as solubilized protein fractions of the human placenta and thus appear to be at least partly associated with placental membranes. PP4 has a molecular weight of 35000 and apparently consists of a single peptide chain. It has an electrophoretic mobility in between the alpha 1- and alpha 2-globulins, an isoelectric point of 4.85 and a sedimentation coefficient of 3.3 S. The carbohydrate content of PP4 amounts to 2.4%. MP1 was isolated from placental protein fractions solubilized with Triton X-100. It has a molecular weight of around 18000 and appears to be composed of two identical subunits which are non-covalently linked. MP1 was found to have an electrophoretic mobility in between the alpha 2- and beta 1-globulins, an isoelectric point of 4.75 and a sedimentation coefficient of 6.65 S. MP1 is a glycoprotein which contains 9.6% carbohydrates. Immunochemical methods were used to detect and quantitate PP4 and MP1 in extracts of placentae and other human tissues. MP1 appears to be specific to the placenta, whereas PP4 was found to occur also in certain other human tissues. The diagnostic significance of detection and measurement of these proteins in tissues and body fluids is presently under investigation.

Isolation and characterization of four new placental tissue proteins (PP18, PP19, PP20, PP21)

Four new soluble placental tissue proteins (PP18, PP19, PP20, PP21) have been isolated to purity from saline extracts of human term placentas. Two of the new proteins appear to be partly associated with placental membranes; they also could be detected in placental protein fractions obtained by extracting the insoluble part of the placental tissue with solubilizing agents after the soluble material had been removed by washing with saline. The new placental proteins were characterized by their physical properties as well as by their carbohydrate and aminoacid compositions. Specific antisera to the new proteins were obtained by immunizing animals with the corresponding purified proteins. They were used to detect and quantitate the new proteins in extracts of placentas and other human tissues by immunochemical methods. From one human term placenta an average of 2 mg PP18, 90 mg PP19, 0.5 mg PP20, and around 7 mg PP21 could be extracted. None of these new proteins is specific to the placenta; they also were found to occur in extracts of certain other human tissues. The immunohistochemical localization of these proteins as well as measurement of their concentrations in body fluids by sensitive radioimmunoassays are presently under investigation.

Synthesis of placental protein 12 by human decidua

The synthesis and secretion of placental protein 12 (PP12) were studied in tissue culture using explants of decidua, amnion, chorion, and placenta from seven full term pregnancies. The total amounts of PP12 in media and tissues were measured by RIA, and new protein synthesis and secretion by decidual explants were demonstrated by the incorporation of [35S]methionine into PP12 after 20 h of incubation with 12.5 microCi/ml [35S]methionine. Cycloheximide was used to study the effect of a protein synthesis inhibitor on the secretion of PP12 by decidua. Significantly more PP12 (P less than 0.001) was released into the medium from decidual explants than from chorion and amnion explants throughout the experimental period of 24 h. When incubated under identical conditions, placental explants released no detectable PP12. In decidual tissues and their culture media, the total amount of PP12 was 127.4% higher after incubation than before incubation (P less than 0.001). No increase was found when chorion and amnion were cultured. The addition of cycloheximide into cultures decreased the total amount of PP12 in the decidua and in its culture medium by more than 50%, indicating that one part of PP12 in decidua was performed and another part was newly synthesized. Decidual explants incorporated [35S]methionine into immunoprecipitable PP12 indicating new PP12 synthesis. In gel filtration, 77% of decidual [35S] PP12 eluted in the same position as purified PP12. In sodium dodecyl sulfate polyacrylamide gel electrophoresis, the migration mobility of [35S]PP12 was identical with that of purified PP12. Our results clearly demonstrate that PP12 is a decidual rather than a placental protein.

The content of placental protein 12 in decidua and fetal membranes is greater than in placenta

Radioimmunoassay, gel filtration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis were used to study the content and properties of placental protein 12 (PP12) in the placenta, decidua and fetal membranes. The tissues were obtained from early pregnancy in 12 cases, and after normal term delivery in eight cases in seven of which chorion and amnion laeve were also studied. There was more PP12 in decidua and fetal membranes than in placenta. The decidua/placenta ratio of PP12 content ranged from 2 to 1154 (mean 193, SEM 66). These results suggest that PP12 is a decidual rather than placental protein.

Pregnancy-specific beta-1 glycoprotein (SP-1) in breast carcinoma. Pathologic and clinical considerations

Ectopic production of placental proteins by a variety of nontrophoblastic epithelial tumors is well recognized. Pregnancy-specific beta-1 glycoprotein (SP-1), a recently described placental protein, has been detected both in the serum and tumors of patients with breast carcinoma. To assess the significance of SP-1 in breast carcinoma, we stained 139 cases of primary breast carcinoma for SP-1 using the immunoperoxidase technique. Overall, 55 (40%) of breast cancers were positive for SP-1; focal positivity was also noted in normal breast epithelium and fibrocystic disease. Both intraductal (32%) and infiltrating duct (43%) carcinomas were more often positive than either in situ (5%) or infiltrating (26%) lobular carcinomas. SP-1 positivity in tumors of infiltrating duct morphology less than 3 cm in diameter, correlated highly (P less than 0.01) with the presence of axillary lymph node metastases. The presence of SP-1 in normal breast epithelium and fibrocystic disease and the low rate of positivity in lobular carcinoma casts doubt on the usefulness of SP-1 as a tumor marker. However, these findings suggest that immunopositivity for SP-1 in small infiltrating duct carcinomas may be an indicator of poor prognosis.

Serum levels of placenta-specific tissue protein 12 (PP12) in pregnancies complicated by pre-eclampsia, diabetes or twins

PP12 is one of the recently discovered soluble tissue antigens of the placenta. During normal pregnancy maternal serum PP12 levels rise during the first 18 weeks reaching a mean peak value of 139.9 +/- 40.26 micrograms/l; after that there is a fall to a mean value of 111.9 +/- 42.39 micrograms/l between 28 and 40 weeks. Significantly higher mean serum PP12 levels were found in the third trimester in two high risk pregnancy groups (281.09 +/- 117.08 micrograms/l in pre-eclamptic toxaemia and 203.71 +/- 73.77 micrograms/l in diabetes) while serum PP12 levels remained normal (114.94 +/- 58.06 micrograms/l) in twin pregnancy. The increase of serum PP12 concentration in toxaemia and in diabetes may be of considerable diagnostic significance.

Placental protein 12 (PP12): Factors affecting levels in late pregnancy

The circulating concentration of placental protein 12 was measured by radioimmunoassay in 109 pregnant women. The effect on the serum PP12 level of temperature, repeat freezing and thawing, and day-to-day and diurnal variation were assessed and the post partum changes of levels were studied. On average, PP12 levels in plasma are about one-half of those in serum in the same individual. PP12 immunoreactivity is destroyed by heating but not by repeated freezing and thawing. Changes in serum PP12 levels at various times of day showed a significant and consistent diurnal variation (F = 7.21; d.f.24; 96; P less than 0.001). The peak mean (+/- s.e.m.) value at 0800 h (80.8 +/- 8.7 ng/ml) was 41 per cent higher than the 24-h mean (P less than 0.05), and the nadir concentration at 1400 h (40.4 +/- 5.4 ng/ml) was 29 per cent lower than the 24-h mean (P less than 0.025). There is also considerable day-to-day variation (up to 72 per cent) in serum PP12 levels. If serum samples are taken at 0700 h, there is a slight negative correlation between PP12 concentration and placental weight (P less than 0.05), but not between PP12 level and birthweight of the child. In term pregnancy, the levels taken at 0700 h are higher (163.7 +/- 12.4 ng/ml) than at 0900 to 1300 h (115.7 +/- 11.4 ng/ml, P less than 0.001). The PP12 level is not affected by labour.(ABSTRACT TRUNCATED AT 250 WORDS)

Human preovulatory follicular fluid, luteinized cells of hyperstimulated preovulatory follicles, and corpus luteum contain placental protein 12

RIA gel filtration, isoelectric focusing; and immunoperoxidase staining were employed to study the occurrence and physicochemical characteristics of placental protein 12 (PP12) in the human ovary, corpus luteum, and preovulatory follicular fluid. Fluid aspirated from 75 follicles from 22 women hyperstimulated for in vitro fertilization contained 6-230 micrograms/liter PP12-like immunoreactive material. The dose-response curves of follicular fluid PP12, amniotic fluid PP12, and purified human placental PP12 were parallel in the PP12 RIA. In gel filtration, follicular fluid PP12 eluted in the same volume as purified PP12. The isoelectric point of follicular fluid PP12 was 4.9 and that of purified placental PP12 4.6-4.7. A positive correlation was found between follicular fluid estradiol and PP12, progesterone and PP12, and follicular fluid volume and PP12 concentrations. By immunoperoxidase staining, PP12 was not detectable in unstimulated ovarian tissue before ovulation. In hyperstimulated preovulatory follicles biopsied in connection with follicle aspiration, PP12 was found in the granulosa cells which were luteinized (n = 3), whereas in those hyperstimulated follicles (n = 5) with no luteinization, no PP12 was found either. PP12 was seen in all corpora lutea (n = 5) from unstimulated menstrual cycles. These results show that the occurrence of PP12 is not limited to the placenta. The correlation between follicular fluid steroid and PP12 levels and the findings by immunoperoxidase staining suggest that PP12 is related to endocrine phenomena of the ovary, possibly to the luteinization process.

The radioimmunoassay of human placental protein 14 (PP14)

The development and validation of a radioimmunoassay for the measurement of human placental protein 14 in maternal serum is described. The mean concentration of this protein in serum from 22 normal pregnant women showed a decline during the third trimester from 120 micrograms/l at 27 weeks gestation to 65 micrograms/l at term. Serum samples from 16 patients with intra-uterine growth retardation tended to contain lower concentrations of placental protein 14, these results reaching significance at weeks 36-38 of gestation. Of seven patients with pre-eclampsia from whom two or more blood samples were taken, four showed increases in concentration of this protein as pregnancy proceeded, compared with the normal pattern of decreasing values.

Immunologic and biological properties and clinical significance of placental proteins PP5 and PP12

Among the number of newly isolated placental proteins, PP5 and PP12 share some common characteristics: Both are present in the syncytiotrophoblast of normal placenta and hydatidiform mole, but less frequently, if at all, in choriocarcinoma. The levels in heparinized plasma of both proteins are lower than those in serum, and both are heat-labile. The function of PP12 is completely unknown, whereas PP5 appears to be related to the blood coagulation and fibrinolytic systems at the placental site through its antiplasmin activity. Many exciting avenues of research have been opened to uncover the biological role of these proteins in fetal development and cancer. We are pursuing this research with the immediate goal of assessing the role of PP12 in the blood coagulation system and of studying the expression of both proteins in various forms of cancer.

Levels of placenta-specific tissue protein 12 (PP12) in serum during normal pregnancy and in patients with trophoblastic tumour

A sensitive radioimmunoassay method has been developed to measure soluble placental protein 12. Using this method trace amounts of PP12 have also been detected in the sera of healthy non-pregnant subjects (24.0 +/- 6.15 micrograms/l). During normal pregnancy serum PP12 levels rose rapidly reaching a peak value of 139.90 +/- 40.26 micrograms/l at 18 weeks. Serial determinations of PP12 have been made in 31 patients with trophoblastic tumours (16 hydatidiform moles, 10 invasive moles and five choriocarcinomas). It has been found that in patients with hydatidiform and invasive moles its initial values are extremely high (342.9 +/- 257.9 micrograms/l and 279.3 +/- 103.1 micrograms/l, respectively), much exceeding the non-pregnant and normal pregnant values. After evacuation of hydatidiform moles serum-PP12 rapidly fell to the upper limit of normal at 21-28 days, and to normal values at 8-12 weeks after operation. In patients with invasive mole requiring chemotherapy the rate of fall of PP12 level was slower. In patients with choriocarcinoma serum-PP12 levels were moderately raised (59-132 micrograms/l) and followed the clinical course of the disease. Serum-PP12 levels would seem to be of less value in monitoring patients with trophoblastic tumours than other tumour-markers (hCG, and SP1).

Serum levels of placental protein 10 (PP10) in women with breast cancer and genital carcinoma and in healthy male and female subjects

PP10, a recently characterized glycoprotein from human placenta, was studied using a specific double-antibody radioimmunoassay in the serum of about 100 volunteers and 200 cancer patients. Elevated levels (greater than 20 nU/ml) were found in 87% of patients with primary breast cancer, in 100% of those with primary genital tumours and in 78% of patients with recurrent disease. PP10 was also measured in tumour extracts and in some patients with benign tumours. The serum concentration decreased within a few weeks after removal of the tumour. There were no significant correlations of the PP10 level with age, tumour size, histological grading or lymph node involvement. Sequential determinations of PP10 during cytostatic therapy sometimes showed rising levels accompany the development of metastases. PP10 can be regarded as a tumour associated protein and a tumour marker in gynaecological practice.

Concentration of placental protein 10 (PP10) in maternal serum and amniotic fluid throughout normal gestation and in pregnancy complicated by fetal growth retardation

PP10, a new placental glycoprotein, was studied by a specific and sensitive double-antibody radioimmunoassay in maternal serum and other body fluids throughout pregnancy. The mean value of serum PP10 in healthy nonpregnant individuals was approximately 10 microU/l. During normal pregnancy it rose to 3,500 microU/l. The rate of rise was obtained from 78 normal pregnancies with 279 single assay values from weeks 6-40. The shape of the curve resembled that for other placental proteins (HPL, SP1). PP10 levels in amniotic fluid were measured in 145 samples from weeks 13-55 of normal pregnancies and at term. The mean concentration was 500 microU/l until week 18 and then rose slowly. Cord blood contained only trace amounts. PP10 was not found in maternal urine. The concentration in maternal serum and amniotic fluid was higher in twin pregnancies than in singleton pregnancies. In 46 cases with low birth weights the PP10 levels in maternal serum were significantly lower than normal. Simultaneous measurements of PP10 and E3, HPL and SP1 were made in 17 individual follow-up's. PP10 was comparable with E3 and appeared to be better than HPL and SP1 in predicting intrauterine fetal growth retardation.

Purification of pregnancy-specific beta 1-glycoprotein with a monoclonal antibody immunoadsorbent

Hybrid cell lines secreting monoclonal antibodies against pregnancy-specific beta 1-glycoprotein (SP1) were produced by fusion of a mouse myeloma cell line with spleen cells from BALB/c mice immunized with purified placental SP1. The clones were further grown intraperitoneally in mice, and the ascites fluids contained anti-SP1 antibodies in high titers. One of the monoclonal antibodies was coupled to cyanogen-bromide-activated Sepharose and used for affinity chromatography of SP1 using late pregnancy serum as starting material. The purification of SP1 by means of immunoadsorption utilizing monoclonal antibodies offers remarkable advantages compared with the purification procedures used so far.