Modulation of steroidogenesis in choriocarcinoma cells by cholera toxin, phorbol ester, epidermal growth factor and insulin-like growth factor I

Contributions of Drug Transporters to Blood-Placental Barrier

The placenta is the only organ linking two different individuals, mother and fetus, termed as blood-placental barrier. The functions of the blood-placental barrier are to regulate material transfer between the maternal and fetal circulation. The main functional units are the chorionic villi within which fetal blood is separated by only three or four cell layers (placental membrane) from maternal blood in the surrounding intervillous space. A series of drug transporters such as P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), multidrug resistance-associated proteins (MRP1, MRP2, MRP3, MRP4, and MRP5), organic anion-transporting polypeptides (OATP4A1, OATP1A2, OATP1B3, and OATP3A1), organic anion transporter 4 (OAT4), organic cation transporter 3 (OCT3), organic cation/carnitine transporters (OCTN1 and OCTN2), multidrug and toxin extrusion 1 (MATE1), and equilibrative nucleoside transporters (ENT1 and ENT2) have been demonstrated on the apical membrane of syncytiotrophoblast, some of which also expressed on the basolateral membrane of syncytiotrophoblast or fetal capillary endothelium. These transporters are involved in transport of most drugs in the placenta, in turn, affecting drug distribution in fetus. Moreover, expressions of these transporters in the placenta often vary along with the gestational ages and are also affected by pathophysiological factor. This chapter will mainly illustrate function and expression of these transporters in placentas, their contribution to drug distribution in fetus, and their clinical significance.

Multiple functions of syncytiotrophoblast mitochondria

The human placenta plays a central role in pregnancy, and the syncytiotrophoblast cells are the main components of the placenta that support the relationship between the mother and fetus, in apart through the production of progesterone. In this review, the metabolic processes performed by syncytiotrophoblast mitochondria associated with placental steroidogenesis are described. The metabolism of cholesterol, specifically how this steroid hormone precursor reaches the mitochondria, and its transformation into progesterone are reviewed. The role of nucleotides in steroidogenesis, as well as the mechanisms associated with signal transduction through protein phosphorylation and dephosphorylation of proteins is discussed. Finally, topics that require further research are identified, including the need for new techniques to study the syncytiotrophoblast in situ using non-invasive methods.

Role of OAT4 in Uptake of Estriol Precursor 16α-Hydroxydehydroepiandrosterone Sulfate Into Human Placental Syncytiotrophoblasts From Fetus

Estriol biosynthesis in human placenta requires the uptake of a fetal liver-derived estriol precursor, 16α-hydroxydehydroepiandrosterone sulfate (16α-OH DHEAS), by placental syncytiotrophoblasts at their basal plasma membrane (BM), which faces the fetal circulation. The aim of this work is to identify the transporter(s) mediating 16α-OH DHEAS uptake at the fetal side of syncytiotrophoblasts by using human placental BM-enriched vesicles and to examine the contribution of the putative transporter to estriol synthesis at the cellular level, using choriocarcinoma JEG-3 cells. Organic anion transporter (OAT)-4 and organic anion transporting polypeptide 2B1 proteins were enriched in human placental BM vesicles compared with crude membrane fraction. Uptake of [(3)H]16α-OH DHEAS by BM vesicles was partially inhibited in the absence of sodium but was significantly increased in the absence of chloride and after preloading glutarate. Uptake of [(3)H]16α-OH DHEAS by BM vesicles was significantly inhibited by OAT4 substrates such as dehydroepiandrosterone sulfate, estrone-3-sulfate, and bromosulfophthalein but not by cyclosporin A, tetraethylammonium, p-aminohippuric acid, or cimetidine. These characteristics of vesicular [(3)H]16α-OH DHEAS uptake are in good agreement with those of human OAT4-transfected COS-7 cells as well as forskolin-differentiated JEG-3 cells. Estriol secretion from differentiated JEG-3 cells was detected when the cells were incubated with 16α-OH DHEAS for 8 hours but was inhibited in the presence of 50 μM bromosulfophthalein. Our results indicate that OAT4 at the BM of human placental syncytiotrophoblasts plays a predominant role in the uptake of 16α-OH DHEAS for placental estriol synthesis.

Modulation of estradiol synthesis and aromatase activity in human choriocarcinoma JEG-3 cells exposed to tetrabromobisphenol A

The goal of the present study was to investigate the impact of tetrabromobisphenol A (TBBPA) on human choriocarcinoma-derived placental JEG-3 cells in vitro. We determined the effect of this compound on estradiol secretion, aromatase protein expression and activity in vitro in the JEG-3 cell line. We assessed the ability of TBBPA to increase intracellular levels of cAMP as well as its effect on cell viability and proliferation. Our results indicated that TBBPA, at a wide range of concentrations (1×10(-8)-5×10(-5)M), significantly induced estradiol secretion by JEG-3 cells compared to that of controls after 24, 48 or 72 h of exposure. This effect was accompanied by an increase in the aromatase protein expression in JEG-3 cells treated with 100 nM and 10 μM of TBBPA for 24 h. Additionally, in our study, we confirmed that TBBPA-induced changes in aromatase protein expression were associated w ith the up-regulation of aromatase activity and cAMP levels. No tested doses of TBBPA inhibited JEG-3 cell proliferation, except for the highest dose of 100 μM, which had a toxic effect on cell viability at all time points. The present study clearly indicates that TBBPA alters JEG-3 cells estrogen synthesis due to its action on CYP19 protein expression and thus this compound may interfere with normal placental development during early pregnancy.

PKA tightly bound to human placental mitochondria participates in steroidogenesis and is not modified by cAMP

INTRODUCTION

Protein phosphorylation plays an important role in the modulation of steroidogenesis and it depends on the activation of different signaling cascades. Previous data showed that PKA activity is related to steroidogenesis in mitochondria from syncytiotrophoblast of human placenta (HPM). PKA localization and contribution in progesterone synthesis and protein phosphorylation of HPM was assessed in this work.

METHODS

Placental mitochondria and submitochondrial fractions were used. Catalytic and regulatory PKA subunits were identified by Western blot. PKA activity was determined by the incorporation of (32)P into proteins in the presence or absence of specific inhibitors. The effect of PKA activators and inhibitors on steroidogenesis and protein phosphorylation in HPM was tested by radioimmunoassay and autoradiography.

RESULTS

The PKAα catalytic subunit was distributed in all the submitochondrial fractions whereas βII regulatory subunit was the main isoform observed in both the outer and inner membranes of HPM. PKA located in the inner membrane showed the highest activity. Progesterone synthesis and mitochondrial protein phosphorylation are modified by inhibitors of PKA catalytic subunit but are neither sensitive to inhibitors of the regulatory subunit nor to activators of the holoenzyme.

DISCUSSION

The lack of response in the presence of PKA activators and inhibitors of the regulatory subunit suggests that the activation of intramitochondrial PKA cannot be prevented or further activated.

CONCLUSIONS

The phosphorylating activity of PKA inside HPM could be an important component of the steroidogenesis transduction cascade, probably exerting its effects by direct phosphorylation of its substrates or by modulating other kinases and phosphatases.

Oestradiol and FSH in gestational trophoblastic disease: a prospective analysis of their predictive value

OBJECTIVE

To determine whether oestradiol or follicle-stimulating hormone (FSH) measured prior to treatment could improve the predictive value of the risk score used to determine treatment in cases of persistent gestational trophoblastic disease (GTD).

DESIGN

Prospective observational study.

SETTING

Tertiary referral centre for GTD.

POPULATION

All women referred to Weston Park Hospital, Sheffield, with GTD between 1st January 1996 and 31st December 2000.

METHODS

Blood was taken prior to the initiation of treatment to measure oestradiol and FSH. The results were analysed with respect to the time taken for the beta-hCG to return to normal.

MAIN OUTCOME MEASURES

Time taken to reach a normal beta-hCG.

RESULTS

Data on 118 women were collected. Three women died of GTD during follow up. Using Cox's proportional hazards regression analysis, division of the risk scores into high and low risk groups (</=7, >7) demonstrated a significant difference with regard to the length of time taken to reach a normal beta-hCG level (hazard ratio 0.32; 95% CI: 0.18, 0.57) comparing high risk relative to low risk. However, addition of neither oestradiol nor FSH to the Cox regression analysis produced a significant hazard ratio (Ln oestradiol, 0.95; FSH 0.99). Division of the patients' risk scores into three groups of low (0-4), intermediate (5-7) and high (>7) risk groups produced similar results.

CONCLUSIONS

The measurement of neither oestradiol nor FSH appears to improve the prediction of outcome in persistent GTD when added to the risk score.

Effects of some persistent halogenated environmental contaminants on aromatase (CYP19) activity in the human choriocarcinoma cell line JEG-3

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5-pentachlorobiphenyl (PCB126), a technical PCB mixture (Aroclor 1016), and a technical toxaphene mixture (Camphechlor) on aromatase (CYP19) activity were investigated in human choriocarcinoma JEG-3 cells. After 18 h incubation with TCDD, PCB126, Aroclor 1016 or toxaphene, ethoxyresorufin-O-deethylase (EROD), and aromatase activity were determined. To exclude serum effects, incubations were carried out with or without fetal calf serum in the medium. EROD activity was induced by both TCDD and PCB126 in the presence or absence of serum, which indicates that JEG-3 cells are responsive toward dioxin-like chemicals. Neither Aroclor 1016 nor toxaphene affected EROD activity in these cells. Calculated EC50 values for induction of EROD activity were 0.71 and 0.40 nM for TCDD, and 48 and 20 nM for PCB126 in presence or absence of serum, respectively. Incubation with TCDD or PCB126 with or without serum caused a concentration-dependent decrease in the aromatase activity of up to 4.9-fold. Calculated EC50 values for this effect were 52 pM and 13 nM for TCDD, and 75 and 48 nM for PCB126 in the presence and absence of serum, respectively. Aroclor 1016 and toxaphene had no effect on aromatase activity at concentrations up to 1.0 microM for Aroclor 1016 or 3.0 microM for toxaphene. These results show that aromatase activity can be decreased in a concentration dependent way within the same range where EROD activity is increased. In view of these results, possible effects of dioxin-like compounds on estrogen producing and androgen target cells should be studied in more detail.

Regulation of cytochrome P450 cholesterol side-chain cleavage, 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase type 1 and estradiol-17 beta-hydroxysteroid dehydrogenase mRNA levels by calcium in human choriocarcinoma JEG-3 cells

In human placenta the cytochrome P450 side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase type 1 (3 beta-HSD-1) convert cholesterol and pregnenolone producing progesterone, whereas 17 beta-hydroxysteroid dehydrogenase type 1 (17 beta-HSD-1) mediates the interconversion of estrone and estradiol. We have examined the effects of calcium on phorbol ester- and cAMP-induced P450scc, 3 beta-HSD-1 and 17 beta-HSD-1 mRNAs in human JEG-3 cells. A23187 increased in a dose-dependent fashion in the 1.3 kb 17 beta-HSD-1 mRNA whereas a weaker increase followed by a gradual depletion effect of A23187 was observed on 3 beta-HSD-1 mRNA. No significant effect of A23187 on P450scc mRNA was observed. Using 0.50 microM of A23187 the induction of 3 beta-HSD-1 and 17 beta-HSD-1 mRNAs was maximum within about 6 h whereas P450scc mRNA levels stayed unaffected throughout the time-course period. The action of A23187 was synergistic on cAMP-stimulated 17 beta-HSD-1 mRNA levels, while in a dose-dependent manner A23187 progressively depleted 3 beta-HSD-1 and P450scc mRNA abundance probably by activation of a calcium-/calmodulin-dependent phosphodiesterase. On the phorbol 12-myristate, 13-acetate (PMA)-stimulated 3 beta-HSD-1, 17beta-HSD-1 and P450scc mRNA levels only the lowest concentration of A23187 potentialized the PMA effect on the 17 beta-HSD-1 mRNA levels. Using thapsigargin (TG), a cell-permeable sesquiterpene lactone that releases calcium by inhibiting sarco/endoplasmic reticular calcium-ATPase, our data indicated the presence in JEG-3 cells of TG-sensitive and TG-insensitive calcium-ATPases regulating 3 beta-HSD-1 and 17 beta-HSD-1 mRNA levels. These results emphasized the complexity of calcium contribution with the protein kinase A and C pathways in the regulation of P450scc, 3 beta-HSD-1 and 17 beta-HSD-1 mRNA levels. In addition, the different sensitivity of these genes to calcium suggest they could be activated by different subclasses of PKCs.

Ethanol modulates the hormone secretory responses induced by epidermal growth factor in choriocarcinoma cells

Analysis of clinical data has implicated ethanol (EtOH) as an embryotoxic agent and as an agent that disrupts normal placental structure and function. Because epidermal growth factor (EGF) is an important regulator of placental function, we have studied the effects of EtOH on EGF-induced hormone secretion using JEG-3 choriocarcinoma cells that serve as a model for trophoblast cells. EtOH at physiological (5-100 mM) concentrations modulated effects of EGF in a time and dose-dependent manner. EGF-induced P4 secretion was increased by 20-100 mM EtOH after a 2-day pretreatment of cells with EtOH, but not after a 6-day pretreatment. Preincubation with 50 mM EtOH doubled the P4 responses to 50 and 100 ng/ml EGF. Although a 2- or 4-day preincubation of cells with 10-50 mM EtOH increased the secretion of E2 in response to 20 ng/ml EGF, a 6-day preincubation inhibited the secretory response to EGF. Pretreatment of cells with 10-50 mM, but not 100 mM EtOH for 2 to 6 days enhanced the human chorionic gonadotropin (hCG) secretory response to EGF. At 50 mm EtOH, the secretion of hCG in response to EGF was increased 2-fold. EtOH also increased basal hCG secretion in a dose-dependent manner between 10-50 mM EtOH. These results suggest that EtOH may modulate EGF-stimulated hormone secretion from cells of placental origin. Such alterations, if they occur in vivo, may impact on the function of the placenta and could potentially explain the pathophysiology of alcohol toxicity during pregnancy.

Characterization of 17 beta-hydroxysteroid dehydrogenase type 1 in choriocarcinoma cells: regulation by basic fibroblast growth factor

17 beta-Hydroxysteroid dehydrogenase type 1 (17-HSD type 1) is a steroidogenic enzyme catalyzing reversible interconversion of estradiol and estrone. 17-HSD type 1 is actively expressed in human placenta. We characterized 17-HSD type 1 expression and its regulation by basic fibroblast growth factor (bFGF) in JAR, JEG-3 and BeWo choriocarcinoma cell lines. Based on Southern and Northern analysis, as well as measurement of catalytic activity and immunoreactive protein, all the choriocarcinoma cell lines contained and expressed the gene coding for 17-HSD type 1, identical to that of normal human cells. However, the cell lines showed marked quantitative differences in the levels of expression of the enzyme, being lowest in JAR cells and highest in BeWo cells, as measured by immunofluorometric assay, Northern analysis and catalytic activity. These differences in the basal level of expression were most probably not based on any sequence differences in the putative proximal promoter area of the gene in different cell lines, since no dissimilarities were observed in the 806 bp region upstream from the transcription start site of 1.3 kb mRNA coding for 17-HSD type 1 except for frequent polymorphism characteristic of normal human cells using polymerase chain reaction/single-strand conformation polymorphism (PCR-SSCP) analysis. The reductive (estrone-->estradiol) activity was about 4-7 times higher compared with the oxidative activity (estradiol-->estrone) in all the cell lines studied, indicating that in these choriocarcinoma cell lines, 17-HSD activity favours estradiol formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue-specific expression of the human aromatase cytochrome P-450 gene by alternative use of multiple exons 1 and promoters, and switching of tissue-specific exons 1 in carcinogenesis

Extensive screening of aromatase cDNA was carried out in cDNA libraries from various human tissues. The DNA sequences of all the isolated cDNA clones were identical in the region encoded by exons 2-10 of the aromatase gene. However, tissue-specific sequences, which were classified into four groups, were observed in the 5' portions of the clones corresponding to the region encoded by exon 1. All of them were also found in clones isolated from a human genomic library and mapped between exons 1 and 2 of the human aromatase gene reported previously, suggesting the presence of multiple exons 1 and promoters in the gene. Reverse transcription-PCR analyses of aromatase mRNAs in various tissues revealed that aromatase transcripts are tissue-specifically spliced by alternative use of multiple exons 1, although minor forms of the transcripts were also present in each tissue. Aromatase mRNA is spliced from 10 exons in most tissues, but from 9 exons in the prostate and from 10 or 11 exons in the placenta. This suggests that tissue-specific regulation of the aromatase gene in various tissues may be explained by alternative use of multiple exons 1 flanked with tissue-specific promoters. The alternative use of multiple exons 1 for liver transcripts was found to change developmentally. Furthermore, switch from an adipose-specific exon 1 to another type of exon 1 was observed in aromatase transcripts of adipose tissues of three of five breast cancer patients.

Regulation of the cholesterol side-chain cleavage cytochrome P-450 and adrenodoxin mRNAs in cultured choriocarcinoma cells

Cytochrome P-450scc (P-450scc) catalyzes the cholesterol side-chain cleavage reaction, a rate-limiting enzymatic step for progesterone synthesis in trophoblastic and other steroidogenic cells. Adrenodoxin is the iron/sulfur protein donating electrons to P-450scc during this reaction. We examined the effects of cholera toxin (CT), an activator of adenylate cyclase, and 12-O-tetradecanoylphorbol acetate (TPA), a phorbol ester protein kinase C activator, on the levels of mRNAs encoding P-450scc and adrenodoxin in JEG-3 choriocarcinoma cells. CT induced in a concentration- and time-dependent manner P-450scc and adrenodoxin mRNA levels to 8-fold and 1.5-fold above that of control, respectively. TPA also increased P-450scc and adrenodoxin mRNA levels about 3-fold and 1.5-fold above that of control, respectively. Epidermal growth factor (EGF) was found to weakly induce P-450scc mRNA accumulation with a maximal 20% stimulation above basal levels. The effects of CT and TPA were apparently additive on both mRNAs. The protein synthesis inhibitor cycloheximide diminished basal, CT-, TPA-, and EGF-stimulated P-450scc mRNA accumulation whereas the opposite was observed for the adrenodoxin mRNA. Insulin-like growth factor I (IGF-I) appeared to have no effect on either mRNA. These data indicate that: (1) the accumulation of P-450scc and adrenodoxin mRNAs is mainly controlled by the cyclic adenosine 3',5'-monophosphate (cAMP)-dependent pathway but their stimulation by TPA- and EGF-induced signals may also play a weaker synergistic role; (2) the protein synthesis inhibitor cycloheximide inhibits basal, CT-, TPA- and EGF-stimulated P-450scc mRNA levels while it increases the expression of adrenodoxin mRNA suggesting that in the malignant trophoblasts these two enzyme mRNAs are differentially controlled.