Epidermal growth factor receptors in rat placenta, amnion and yolk sac: characteristics of specific binding are dependent on gestational age

Stage-specific modification of G protein beta subunits in rat placenta

We previously analysed the plasma membrane proteins of rat placenta and prepared a database of 150 plasma membrane proteins, expressed in a stage-specific manner, utilizing two-dimensional gel electrophoresis (2D/E) [Mol. Cell. Endocrinol. 115(1995)149]. In this study, we focused on the proteins, tentatively named psL-I (MW 36.2 kDa, pI 5.3) and psL-II (35.9 kDa, 5.3), which were expressed mainly in late pregnancy. Close to psL-I and psL-II on 2D/E gels, we also recognized more abundant proteins [psC-I (36.2 kDa, 5.4) and psC-II (35.9 kDa, 5.4), respectively] arranged side by side with the same MW but different pI. Expression of psL-I and psL-II was detected only in junctional zone of placenta, whereas psC-I and psC-II were expressed in both labyrinth and junctional zones. In addition, psL-I and psL-II began to increase on day 16 of pregnancy and peaked at term, whereas expression of psC-I and psC-II was relatively constant. The analysis of these four proteins (psL-I, psL-II, psC-I and psC-II) by preparative 2D/E, peptide mapping, amino acid sequence and mass spectrometry (MALDI-TOF-MS) revealed that psC-I was a G protein beta1 subunit, and psC-II was a beta2 subunit, and showed that psL-I and psL-II were molecular modified forms of psC-I and psC-II, respectively. Expression of these G protein beta subunits (psL-I, psL-II, psC-I and psC-II) was also observed in rat choriocarcinoma cells, Rcho-1 cells. Expression of psC-I and psC-II was much higher than those of psL-I and psL-II, and their level was relatively constant regardless of the stage of differentiation in vitro. Interestingly, expression of psL-I and psL-II gradually increased in association with the differentiation. Since the expression of beta1 and beta2 subunit proteins and their mRNAs was constant during the process of differentiation in Rcho-1 cells, the expression of these lower pI forms of G protein subunits (psL-I and psL-II) was thought to be post-translationally regulated. In conclusion, there are modified forms of G protein beta1 and beta2 subunits, in the placenta and Rcho-1 cells, which are expressed in a pregnancy-stage or differentiation stage specific manner.

The presence of cortisol receptors in the human amnion

Cytosol extracts of human amnion tissue contained high affinity binding of cortisol (Ka=2.48+/-1.06 x 10(9) M(-1); n = 30) and low capacity binding of cortisol (Nmax=279+/-15.5 fmol mg(-1) protein). Kinetic studies of cortisol binding resulted in a similar value of Ka to that obtained by Scatchard analysis. Nuclear extracts of amnion tissue contained high affinity binding of cortisol (Ka=5.8+/-1.91 x 10(7) M[-1]) and low binding capacity (Nmax=91.4+/-21.4 fmol mg(-1) protein). Ka values were an order of magnitude higher in cytosol than in blood serum when amnion and blood were obtained from the same individuals. Differences in competitive ligand binding, especially dexamethasone, were observed between the amnion receptor and transcortin in serum. Gel permeation chromatography gave only one peak at 320 kDa for amnion receptor and only one peak at 48 kDa for transcortin from serum. When amnion tissue was incubated with or without cortisol, cytosol receptor activity was significantly lower in cortisol treated tissue than in control. The nuclear extracted receptor activity was significantly higher in cortisol treated tissue than control. The Ka values from cortisol treated tissue were significantly lower from control. Together the data support the presence of a specific cortisol receptor in the human amnion that is different from transcortin.

Epidermal growth factor reverses antiandrogen induced cryptorchidism and epididymal development

Epidermal growth factor, an androgen responsive paracrine factor, administered to pregnant mice has been reported to result in persistent wolffian ducts in female offspring. This fact led us to investigate whether epidermal growth factor can reverse the undescended testes and epididymal abnormalities associated with time specific flutamide administration. Timed pregnant Sprague-Dawley rats were treated with flutamide (undescended testes 74% and epididymal anomalies 53%) or flutamide plus epidermal growth factor (undescended testes 24% and epididymal anomalies 9%). The decrease in undescended testes and epididymal abnormalities following epidermal growth factor treatment was significant at p < 0.01. We performed immunohistological studies to evaluate whether flutamide alters epidermal growth factor expression in the paratesticular tissues during the time of maximal androgenic activity. These investigations revealed that antiandrogens did not alter epidermal growth factor expression in the fetal testes or epididymides. This finding suggests that epidermal growth factor does not reverse epididymal abnormalities or undescended testes by direct stimulation of the wolffian ducts or fetal testis.

Alterations in maternal epidermal growth factor (EGF) effect testicular descent and epididymal development

OBJECTIVE

(1) To determine the ability of epidermal growth factor (EGF) to reverse antiandrogen-induced cryptorchidism and epididymal abnormalities; (2) to evaluate whether alterations in maternal EGF would result in abnormal testicular descent or mal development of the epididymis.

METHODS

Experiment 1: Timed pregnant ICR mice were treated with either flutamide, flutamide plus EGF, or vehicle alone on gestational days 11 through birth. Experiment 2: Maternal EGF was abolished by removing the submandibular glands. Following timed mating, dams were treated with either flutamide, anti-EGF, DHT, or vehicle alone on gestational days 11 through birth.

RESULTS

Experiment 1: Treatment with flutamide resulted in a 36 percent (26/72) incidence of undescended testes (UDT), and a 43 percent (31/72) incidence of abnormal epididymides. Rats treated simultaneously with flutamide plus EGF had a reduced incidence of UDT (14%, 6/42) and epididymal anomalies (19%, 8/42); p < 0.01. Experiment 2: The absence of maternal EGF resulted in a significant incidence of cryptorchidism in 11/50 (22%) testes, and epididymal anomalies in 19/50 (38%); p < 0.01.

CONCLUSIONS

Our findings suggest that EGF stabilizes the wolffian duct system and partially mediates testicular descent.

Effects of epidermal growth factor on mouse fetal growth

The effects of epidermal growth factor (EGF) on fetal growth were examined in mice. EGF is synthesized in large amounts by the mouse submandibular glands. On the 18th day of gestation, the body weight of fetuses whose mothers had undergone sialoadenectomy (excision of the submandibular glands) was significantly lower than that of controls. However, the maternal-plasma EGF concentration was not significantly affected by sialoadenectomy. The body weight of fetuses whose mothers were injected with EGF for 7 days during pregnancy was significantly higher than that of controls. Sialoadenectomy altered the blood amino acid concentrations in adult female animals, especially the levels of leucine and isoleucine. These results suggest that EGF influences fetal growth mainly by regulating maternal nutrition.

Epidermal growth factor stimulates mouse placental lactogen I but inhibits mouse placental lactogen II secretion in vitro

This study was undertaken to determine whether epidermal growth factor (EGF) regulates the secretion of mouse placental lactogen (mPL)-I and mPL-II. Primary cell cultures were prepared from placentas from days 7, 9, and 11 of pregnancy and cultured for up to 5 days. Addition of EGF (20 ng/ml) to the medium resulted in significant stimulation of mPL-I secretion by the second day of culture in cells from days 7 and 9 of pregnancy and significant inhibition of mPL-II secretion by the third or fourth day of culture in cells from days 7, 9, and 11. Dose-response studies carried out with cells from day 7 of pregnancy demonstrated that the minimum concentration of EGF that stimulated mPL-I secretion and inhibited mPL-II secretion was 1.0 ng/ml. EGF did not affect the DNA content of the cells or cell viability, assessed by trypan blue exclusion, nor did it have a general effect on protein synthesis. There are three types of PL-containing giant cells in mouse placental cell cultures: cells that contain either mPL-I or mPL-II and cells that contain both hormones. Immunocytochemical analysis and the reverse hemolytic plaque assay indicated that EGF treatment was accompanied by a significant increase in the number of cells that produce mPL-I, but among the PL cells that contained mPL-I, there was no change in the fraction of cells that contained only mPL-I or the fraction that contained both mPL-I and mPL-II. In contrast, EGF treatment did affect the distribution of mPL-II among PL cells. In control cultures, about 75% of the cells that contained mPL-II also contained mPL-I, but in EGF-treated cultures, all of the cells that contained mPL-II also contained mPL-I. These data suggest that EGF regulates mPL-I and mPL-II secretion at least partly by regulating PL cell differentiation.