[Isolation and characterization of a new placenta specific protein (PP12) (author's transl)]

New placental proteins: chemistry, physiology and clinical use

In the past decade, several new placental proteins have been isolated and studied. The 'pregnancy-specific' beta 1-glycoprotein (SP1) is a major placental product with unusual physicochemical properties that has been extensively investigated, but its biological function remains uncertain. Pregnancy-associated plasma protein A (PAPP-A), a glycoprotein of mol. wt 400,000, has effects in vitro on the coagulation and complement cascades, probably by its properties of protease inhibition. Placental protein 5 (PP5) may be involved in the coagulation and fibrinolytic systems, and in follicle maturation and semen liquefaction. 'Placental protein 12' (PP12) is not a product of the placenta at all; it appears to be produced in the female genital tract under the influence of progesterone and may also be produced by proliferating liver cells. Further study may reveal new roles for these placental proteins beyond their traditional roles as tumour markers.

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.

Pregnancy proteins in seminal plasma, seminal vesicles, preovulatory follicular fluid, and ovary

A number of proteins previously thought to be specific for the placenta or pregnancy have been identified in the fluids bathing both the oocyte and the sperm. In many cases their concentrations in follicular fluid and seminal plasma greatly exceeded those in the serum of nonpregnant women or men, and sometimes they even exceeded the levels in pregnancy sera. We report here the occurrence of PP5, PP12, PP14 and PAPP-A in follicular fluid and seminal plasma. In follicular fluid, the levels of PP5, PP12, and PAPP-A correlate with the estrogen concentration of the same fluid, and the PP12 and PAPP-A levels also bear a positive correlation to the progesterone concentration. The levels of PP12 and PAPP-A increase as the follicle grows, as do the levels of many steroid hormones. Therefore, the apparent correlations observed may be merely coincidental. However, circumstantial evidence from other reproductive organs indicates that the synthesis of PP12 and PAPP-A is stimulated by progesterone. Results of immunohistochemical staining show that PP12 and PAPP-A are localized in the luteinized granulosa cells and the corpus luteum. Previous studies indicate that PP5 and PAPP-A inhibit the action of proteolytic enzymes plasmin and elastase, which are believed to be involved in the mechanisms of ovulation. The study of the significance of these various placental proteins for human reproduction is only at its beginning. Clearly, elucidation of their function is the key to a more fundamental understanding of their role in the events governing ovulation and implantation.

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.

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) in menstrual fluid

In a previous study we found placental protein 12 (PP12) in the human endometrium. We now show that PP12-like immunoreactive material is released into menstrual fluid where it occurs at concentrations from 43 to 32 000 micrograms/1. The PP12 levels in menstrual fluid are 2- to 2000-fold higher than in serum of the same individuals thus suggesting that the protein either concentrates or is produced in the endometrium. The addition of protease inhibitors has no effect on the PP12 levels. In radioimmunoassay, the dose-response curves of menstrual fluid PP12 and placental PP12 are parallel. Experiments with fused rocket immuno-electrophoresis show that menstrual and placental PP12 are indistinguishable from each other. In gel filtration, menstrual PP12 has the same molecular weight as that of purified placental PP12. By immuno-peroxidase staining, PP12 is localized in the glandular epithelial cells of the menstrual endometrium. The glandular localization and high concentration of PP12 in menstrual fluid, as compared with PP12 levels in serum and endometrium, suggest that PP12 may be secreted by the endometrium.

Comparison of three methods for investigating placental protein 12(PP12)-like immunoreactive substance from preovulatory follicular fluid and purified PP12 from human placenta

Placental protein 12(PP12)-like immunoreactive fraction of preovulatory follicular fluid from Sephadex G-100 and purified placental PP12 were subjected to reverse phase high performance liquid chromatography (HPLC). The elution was carried out with acetonitrile gradient. PP12-like immunoreactivity of both samples had the same retention time. This fraction of follicular fluid from HPLC and placental PP12 were then run on a sodium dodecyl sulfate-polyacrylamide gel and transferred electrophoretically to a nitrocellulose (NC) sheet. Protein bands on the NC sheet were then detected immunologically with anti-PP12 antisera. After visualising the bands which had reacted with antisera it was obvious that PP12-like immunoreactive substance from follicular fluid and from placenta had an electrophoretic mobility corresponding to the same molecular mass.

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)

Placental protein 12 (PP12) is induced in the endometrium by progesterone

The occurrence of PP12 was studied by the biotin-avidin immunoperoxidase method in the endometrium of 106 premenopausal and postmenopausal women at various phases of the menstrual cycle or during estrogen and progestogen replacement therapy. No PP12 was found in the endometrium under the following conditions: (1) during the proliferative phase, (2) in cystic glandular hyperplasia, (3) during the first 3 postovulatory days in ovulatory cycles, (4) in atrophic postmenopausal endometrium, and (5) in estrogen-stimulated postmenopausal endometrium. PP12 was found in the endometrium under the following conditions: (1) in the secretory endometrium from the fourth postovulatory day onward, (2) in the endometrium during progestogen treatment of previously anovulatory premenopausal women, and (3) in the endometrium from postmenopausal women treated with estrogen followed by combined estrogen and progestogen replacement therapy. These results suggest that PP12 is a P-dependent protein which, in natural cycles, appears in the endometrium around the time of implantation and, in postmenopausal women, can be induced by progestogens after estrogen priming.

Placental protein 12 (PP12) in the human endometrium: tissue concentration in relation to histology and serum levels of PP12, progesterone and oestradiol

Placental protein 12 (PP12) was measured by radio-immuno-assay in serum and endometrial extracts of 25 women at various phases of the menstrual cycle, and in the decidua from six women undergoing legal abortion in early pregnancy. The results were analysed with respect to endometrial histology and serum oestradiol, progesterone and PP12 concentrations. PP12 was detected in the secretory phase endometrium and decidua, but not in the proliferative phase endometrium. The PP12 concentration in tissue increased from early (1.3-9.4 micrograms/g protein) to late secretory phase (5.3-155 micrograms/g), and considerably higher levels were found in decidua (282-3846 micrograms/g). There was a correlation (P less than 0.001) between endometrial PP12 and serum progesterone levels in non-pregnant women, and there also was a slight correlation (P less than 0.05) between endometrial and serum PP12 concentrations. These results show that PP12 is not pregnancy specific and suggest that the occurrence of PP12 is dependent on progesterone.

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).

Radioimmunoassay of placental protein 12: levels in amniotic fluid, cord blood, and serum of healthy adults, pregnant women, and patients with trophoblastic disease

A radioimmunoassay for placental protein 12 (PP12) is described and the levels in amniotic fluid, cord blood, and serum of nonpregnant individuals, pregnant women, and patients with trophoblastic disease are presented. During pregnancy, the highest PP12 levels were found at 22 to 23 weeks (mean +/- SD, 169 +/- 123 ng/ml), and there was a transient decline at 32 to 33 weeks (63 +/- 23 ng/ml). In amniotic fluid, the levels were 100 to 1,000 times higher than in maternal serum. In cord blood at birth, the values were of the same magnitude as in maternal serum. Also healthy nonpregnant women and men had PP12-like immunoreactivity in serum. Nonpregnant women (9 to 47 ng/ml) had higher levels than men (undetectable to 21 ng/ml). Elevated levels up to 84 ng/ml were occasionally observed in trophoblastic disease, both hydatidiform mole and choriocarcinoma, but they bore no correlation with the human chorionic gonadotropin levels. On the basis of these results PP12 is not a suitable marker for trophoblastic disease. PP12 values in normal pregnancy provide the basis for the evaluation of PP12 levels in abnormal pregnancy.

Ectopic production of placenta-"specific" tissue proteins (PP5 and PP11) by malignant breast tumors

With use of an enzyme-bridge immunoperoxidase (PAP) technique, an immunohistochemical localization of the two new placenta-"specific" tissue proteins, PP5 and PP11, was investigated in 16 cases of breast cancer. PP5 was localized in the cytoplasm of breast cancer cells in 62.5% of cases examined and PP11, in 46.7%. Thus PP5 and PP11 may be markers for breast cancer and the detection of these proteins in sera from breast cancer patients may be more reliable and useful in the detection and monitoring of breast cancer patients than the determination of SP1, PP10, or PP12, other pregnancy "specific" proteins.

Immunohistochemical location of proteins related to pregnancy-specific beta 1-glycoprotein (SP1) and placental tissue proteins (PP5, PP8, PP9, PP10, PP11, PP12) in the afterbirth of Cynomolgus monkeys (Macaca fascicularis)

The occurrence and location of proteins antigenically related to human pregnancy specific beta 1-glycoprotein (SP1) and to human placental tissue proteins (PP5, PP8, PP9, PP10, PP11, PP12) were studied in the afterbirth (placenta, membranes, decidua, and umbilical cord) of cynomolgus monkeys with use of an immunoglobulin enzyme bridge (PAP) technique. The results were basically the same throughout pregnancy. The syncytiotrophoblast of villi showed clear positive stainings for SP1, PP8, PP9, and PP11, whereas the cytotrophoblast (villi) was found to show clear positive staining for PP9 only. The main sources of proteins related to SP1, PP9, and PP11 were the syncytiotrophoblast cells of the villi and PP8, the syncytiotrophoblast cells of villi as well as the chorionic trophoblast cells. PP12 was mainly located in histiocytes found in the decidua, umbilical cord, amnion, and chorion. There were only traces of PP5 and PP10 in the placentae of cynomolgus monkeys throughout gestation. As in human placentae some granulocyte-like blood cells in the intervillous space were strongly positive for PP8, PP10, and PP12. The findings in the afterbirth of cynomolgus monkeys were similar to those in the human; the monkey could thus serve as a model for the investigation of the new placental proteins.

[New placental protein (PP15) with immunosuppressive properties (author's transl)]

The isolation and characterization of a new placental protein (PP15) which has immunosuppressive properties are described. The protein was purified from extracts of human term placentae by rivanol and ammonium sulfate fractionation, gel filtration, ion exchange chromatography, preparative zone electrophoresis, and chromatography on hydroxyapatite. PP15 was found to have a sedimentation coèfficient of 2.9 S and a molecular weight of 30,700 daltons as determined by ultracentrifugation; its molecules apparently are composed of two identical subunits which are held together by non-covalent bonds. The electrophorectic mobility of PP15 corresponds to that of albumin. PP15 is a glycoprotein and contains 3.3% carbohydrates (hexoses 2.8%, hexosamines 0.3%, sialic acid 0.2%). The amino acid composition of this protein was also determined: the most abundant amino acids in the peptide chain were found to be glutamic acid, aspartic acid, isoleucine, and leucine. PP15 has immunosuprressive properties: on testing its effect on the lymphoycte transformation in the MLC-test in vitro a significant inhibitory activity could be demonstrated.

Immunohistochemical location of placental proteins (PP8, 9, 10, 11, 12) in human term placentae

By using an immunoglobulin enzyme bridge (PAP) technique, the location of two ubiquitous tissue proteins (PP8, PP9) and three placental specific tissue proteins (PP10, PP11, PP12) was investigated in ethanol/acetic acid-fixed paraffin-embedded human term placentae. PP8 was found mainly in both the cytoplasm and the nucleus of trophoblast cells (chorion) and syncytiotrophoblast (villi). PP9 was found in the cytoplasm of trophoblast cells (chorion), the fibrous part of interstitial connective tissues (villi), and the cytoplasm of histiocytes (villi, amnion, and decidua). PP10 was found in the cytoplasm of epithelium (amnion) and in both the cytoplasm and the nucleus of syncytiotrophoblast (villi). PP12 was found in the cytoplasm of histiocytes in decidua, amnion, and chorion and the cytoplasm of syncytiotrophoblast (villi). In addition, stains for PP8, PP10, and PP12 were taken up by the cytoplasm of histiocytes found in amnion, villi, the intervillous space, and decidua, in contrast to PP11, which was found to be specific to the cytoplasm of trophoblast cells (chorion and villi). Possible clinical applications of these findings are discussed.

Ectopic synthesis of pregnancy specific beta 1-glycoprotein (SP1) and placental specific tissue proteins (PP5, PP10, PP11, PP12) in nontrophoblastic malignant tumours. Possible markers in oncology

By using an enzyme-bridge immunoperoxidase (PAP) technique, localization of so-called pregnancy-specific beta 1-glycoprotein (SP1) and placental-specific tissue proteins (PP5, PP10, PP11, PP12) was investigated in 19 cases of breast cancer, 24 cases of testicular malignant tumours, 12 cases of gastric cancer and some cases of other malignant tumours. These five glycoproteins isolated from human term placentae and characterized by Bohn are localised mainly in the cytoplasm, or nucleus of syncytiotrophoblast and appear to be specific for the trophoblast. But to a certain percentage these proteins could also be detected in the cytoplasma of malignant cells: In breast cancer, SP1 was present in 52.6% of cases, PP5 in 63.2%, PP10 in 68.4%, PP11 in 55.6% and PP12 in 31.6%. In testicular malignant tumours the detection rates of these proteins varied from 20.8 to 75.0% and in gastric cancer from 41.7 to 66.7%. In total 50% of the tumours tested were SP1-positive, 58.3% PP5-positive, 55.6% PP10-positive, 38.0% PP11-positive and 31.9% PP12-positive. In addition, it was found that mononuclear histiocytes showed a strong cytoplasmic staining for PP10 and PP12 and that a few other non-cancerous cells (i.e. striated cells in gastric metaplasia, gastric polyps etc.) stained for PP5, PP10, PP11 and/or PP12. All control sections were negative in malignant cells as well as in other tissue cells. This study confirms the reports that some kinds of malignant tumours produce SP1 and indicates that the ectopic production of proteins normally produced by the trophoblast is a common finding in malignant tumours. It furthermore suggests that such proteins may be useful as markers in monitoring patients with malignant diseases. The possible mechanisms of ectopic production of these inappropriate proteins in malignant tumours are discussed.