Type I insulin-like growth factor receptors in the BeWo choriocarcinoma cell (b30 clone) during cell differentiation

The effects of high-density lipoprotein and oxidized high-density lipoprotein on forskolin-induced syncytialization of BeWo cells

INTRODUCTION

The negative relationship between maternal high-density lipoprotein-cholesterol (HDL-c) level during pregnancy and infant birth weight has been found. Syncytialization (differentiation and fusion) of trophoblast cells is important to fetal development. HDL has an antioxidant effect, and has been proved to protect trophoblast functions including hormone secretion and invasion. However, HDL is susceptible to oxidation, and high concentrations of HDL impair cell growth and oxidized HDL (oxHDL) inhibits cell proliferation and migration. Moreover, the effects of HDL and oxHDL on trophoblast syncytialization have not been characterized. The aim of this study was to investigate the effects of HDL and oxHDL on trophoblast syncytialization.

METHODS

Human choriocarcinoma trophoblasts (BeWo cells) were treated with human HDL or oxHDL and then induced to differentiate by forskolin in syncytialization assays. Expression levels of mRNAs and proteins regulating syncytialization were detected by real-time PCR and western blotting, respectively.

RESULTS

Treatments of HDL at high concentrations reduced human chorionic gonadotropin (hCG) secretion, placental alkaline phosphatase activity and fusion rates, and decreased the expressions of GCM1 and ERVW-1 mRNA as well as phospho-MAPK1/3 (p-MAPK1/3) and total MAPK1/3 protein in the forskolin-induced syncytialization of BeWo cells. Furthermore, treatment of oxHDL (20 μg/ml) decreased hCG secretion, but increased the expression of p-MAPK1/3 protein.

DISCUSSION

These data suggested that both HDL at high concentrations and oxHDL inhibited BeWo cells syncytialization, and might be harmful to placental and fetal development.

Placental phenotype and the insulin-like growth factors: resource allocation to fetal growth

The placenta is the main determinant of fetal growth and development in utero. It supplies all the nutrients and oxygen required for fetal growth and secretes hormones that facilitate maternal allocation of nutrients to the fetus. Furthermore, the placenta responds to nutritional and metabolic signals in the mother by altering its structural and functional phenotype, which can lead to changes in maternal resource allocation to the fetus. The molecular mechanisms by which the placenta senses and responds to environmental cues are poorly understood. This review discusses the role of the insulin-like growth factors (IGFs) in controlling placental resource allocation to fetal growth, particularly in response to adverse gestational environments. In particular, it assesses the impact of the IGFs and their signalling machinery on placental morphogenesis, substrate transport and hormone secretion, primarily in the laboratory species, although it draws on data from human and other species where relevant. It also considers the role of the IGFs as environmental signals in linking resource availability to fetal growth through changes in the morphological and functional phenotype of the placenta. As altered fetal growth is associated with increased perinatal morbidity and mortality and a greater risk of developing adult-onset diseases in later life, understanding the role of IGFs during pregnancy in regulating placental resource allocation to fetal growth is important for identifying the mechanisms underlying the developmental programming of offspring phenotype by suboptimal intrauterine growth.

Regulation of human trophoblast GLUT1 glucose transporter by insulin-like growth factor I (IGF-I)

Glucose transport to the fetus across the placenta takes place via glucose transporters in the opposing faces of the barrier layer, the microvillous and basal membranes of the syncytiotrophoblast. While basal membrane content of the GLUT1 glucose transporter appears to be the rate-limiting step in transplacental transport, the factors regulating transporter expression and activity are largely unknown. In view of the many studies showing an association between IGF-I and fetal growth, we investigated the effects of IGF-I on placental glucose transport and GLUT1 transporter expression. Treatment of BeWo choriocarcinoma cells with IGF-I increased cellular GLUT1 protein. There was increased basolateral (but not microvillous) uptake of glucose and increased transepithelial transport of glucose across the BeWo monolayer. Primary syncytial cells treated with IGF-I also demonstrated an increase in GLUT1 protein. Term placental explants treated with IGF-I showed an increase in syncytial basal membrane GLUT1 but microvillous membrane GLUT1 was not affected. The placental dual perfusion model was used to assess the effects of fetally perfused IGF-I on transplacental glucose transport and syncytial GLUT1 content. In control perfusions there was a decrease in transplacental glucose transport over the course of the perfusion, whereas in tissues perfused with IGF-I through the fetal circulation there was no change. Syncytial basal membranes from IGF-I perfused tissues showed an increase in GLUT1 content. These results demonstrate that IGF-I, whether acting via microvillous or basal membrane receptors, increases the basal membrane content of GLUT1 and up-regulates basal membrane transport of glucose, leading to increased transepithelial glucose transport. These observations provide a partial explanation for the mechanism by which IGF-I controls nutrient supply in the regulation of fetal growth.

MicroRNA-378a-5p targets cyclin G2 to inhibit fusion and differentiation in BeWo cells

MicroRNAs are expressed abundantly in the placenta throughout pregnancy. We have previously reported that microRNA (miR)-378a-5p promoted trophoblast migration and invasion. To further understand the role of miR-378a-5p during placental development, we investigated whether it may regulate the differentiation of syncytiotrophoblast (STB). Using a choriocarcinoma cell line, BeWo, we found that miR-378a-5p was down-regulated during forskolin-induced STB differentiation. Transfection of a miR-378a-5p mimic into BeWo cells decreased the formation of multinucleated STB, increased E-cadherin, and decreased the expression level of STB marker genes. On the other hand, transfection of anti-miR-378a-5p resulted in an increase in formation of multinucleated STB and expression of STB marker genes, as well as the loss of E-cadherin. Bioinformatic analysis revealed that miR-378a-5p has four potential binding sites at the 3' untranslated region (UTR) of cyclin G2 (CCNG2). Using luciferase reporter assays, we showed that miR-378a-5p decreased the luciferase activity of reporter constructs that contain CCNG2 3' UTR. In addition, miR-378a-5p decreased, whereas anti-miR-378a-5p increased, CCNG2 mRNA levels. Overexpression of CCNG2 increased the expression of syncytin-1 and fusion index and reversed the inhibitory effects of miR-378a-5p. In contrast, silencing of CCNG2 using siRNA increased E-cadherin and decreased syncytin-1 levels. These findings provide initial evidence that CCNG2 promotes STB differentiation and suggest that miR-378a-5p exerts an inhibitory role in STB differentiation, in part, by down-regulating CCNG2 expression, in the BeWo cell model.

The cAMP-responsive element binding protein (CREB) transcription factor regulates furin expression during human trophoblast syncytialization

INTRODUCTION

The multinucleated syncytiotrophoblast is formed and maintained by cytotrophoblast cell fusion and serves multiple functions to ensure a successful pregnancy. We have previously reported that the proprotein convertase furin is required for trophoblast syncytialization by processing type 1 insulin-like growth factor receptor (IGF1R).

METHODS

Utilizing trophoblast cell fusion models including induced fusion of choriocarcinoma BeWo cells and spontaneous fusion of primary cultured term cytotrophoblast cells, the expression of furin was evaluated by quantitative real-time PCR, Western blotting and immunofluorescence. The key transcription factor regulating the FUR gene promoter and critical responsive elements were identified by luciferase reporter assays, truncated mutants analysis, site-directed mutagenesis and ChIP.

RESULTS

We demonstrated that the levels of FUR mRNA were significantly stimulated by cAMP/PKA signaling pathway during spontaneous fusion of cytotrophoblast cells and forskolin-induced fusion of BeWo cells. cAMP-responsive element binding protein (CREB) was proven to be the key transcription factor which regulated the FUR P1 promoter during forskolin-induced BeWo cell fusion, and two critical cAMP-responsive elements (CREs) in the P1 promoter were further identified. Finally, we showed that CREB mediated endogenous furin activation and that CREB siRNA attenuated forskolin-induced furin expression and cell fusion in BeWo cells.

DISCUSSION

This provides the first evidence of the upstream regulator of furin during trophoblast cell fusion.

CONCLUSIONS

The above results suggest that the FUR transcription is activated by CREB-dependent stimulation of the FUR P1 promoter during human trophoblast syncytialization.

The proprotein convertase furin is required for trophoblast syncytialization

The multinucleated syncytial trophoblast, which forms the outermost layer of the placenta and serves multiple functions, is differentiated from and maintained by cytotrophoblast cell fusion. Deficiencies in syncytial trophoblast differentiation or maintenance likely contribute to intrauterine growth restriction and pre-eclampsia, two common gestational diseases. The cellular and molecular mechanisms governing trophoblast syncytialization are poorly understood. We report here that the proprotein convertase furin is highly expressed in syncytial trophoblast in the first trimester human placentas, and expression of furin in the syncytiotrophoblast is significantly lower in the placentas from pre-eclamptic patients as compared with their gestational age-matched control placentas. Using multiple experimental models including induced fusion of choriocarcinoma BeWo cells and spontaneous fusion of primary cultured cytotrophoblast cells or placental explants, we demonstrate that cytotrophoblast cell fusion and syncytialization are accompanied by furin expression. Furin-specific siRNAs or inhibitors inhibit cell fusion in BeWo cells, as well as trophoblast syncytialization in human placental explants. Furthermore, type 1 IGF receptor (IGF1R) is indicated in this study as a substrate of furin, and processing of IGF1R by furin is an essential mechanism for syncytialization. Finally, using lentivirus-mediated RNAi targeting to mouse trophectoderm, we demonstrate that furin function is required for the development of syncytiotrophoblast structure in the labyrinth layer, as well as for normal embryonic development.

Relevance of syndecan-1 in the trophoblastic BeWo cell syncytialization

PROBLEM

To investigate the role of syndecan-1 in the differentiation of the BeWo cells into syncytiotrophoblast.

METHOD OF STUDY

BeWo cells were stimulated with forskolin to form syncytia, and the expression of syndecan-1, desmoplakin I+II, human chorionic gonadotrophin (hCG) and angiogenesis-associated factors was analyzed. Syndecan-1 was silenced by siRNA to evaluate its involvement in the forskolin-mediated syncytia formation.

RESULTS

Treatment of the BeWo cells with forskolin led to a significant increase in the syncytia formation. It was associated with an increase in the expression of syndecan-1 with a concomitant decrease in the expression of desmoplakin I+II. Forskolin treatment of the BeWo cells also led to an increase in the secretion of soluble endoglin, whereas no change was observed in the soluble fms-like tyrosine kinase-1. Silencing of the syndecan-1 expression in BeWo cells led to a significant decrease in cell fusion both in the presence and in the absence of forskolin. It was associated with a significant decrease in hCG level in the conditioned medium.

CONCLUSION

Syndecan-1 is up-regulated in BeWo cells during differentiation and its silencing inhibits syncytialization and thus could be a useful biomarker for syncytiotrophoblast formation.

Regulation of pregnancy-associated plasma protein A2 (PAPPA2) in a human placental trophoblast cell line (BeWo)

BACKGROUND

Pregnancy-associated plasma protein A2 (PAPPA2) is an insulin-like growth factor-binding protein (IGFBP) protease expressed at high levels in the placenta and upregulated in pregnancies complicated by preeclampsia and HELLP (Hemolytic anemia, Elevated Liver enzymes, and Low Platelet count) syndrome. However, it is unclear whether elevated PAPPA2 expression causes abnormal placental development, or whether upregulation compensates for placental pathology. In the present study, we investigate whether PAPPA2 expression is affected by hypoxia, oxidative stress, syncytialization factors or substances known to affect the expression of PAPPA2's paralogue, PAPPA.

METHODS

BeWo cells, a model of placental trophoblasts, were treated with one of the following: hypoxia (2% O2), oxidative stress (20 microM hydrogen peroxide), forskolin (10 microM and 100 microM), TGF-beta (10 and 50 ng/mL), TNF-alpha (100 ng/mL), IL-1beta (100 ng/mL) or PGE2 (1 microM). We used quantitative RT-PCR (qRT-PCR) to quantify the mRNA levels of PAPPA2, as well as those of PAPPA and ADAM12 since these proteases have similar substrates and are also highly expressed in the placenta. Where we observed significant effects on PAPPA2 mRNA levels, we tested for effects at the protein level using an in-cell Western assay.

RESULTS

Hypoxia, but not oxidative stress, caused a 47-fold increase in PAPPA2 mRNA expression, while TNF-alpha resulted in a 6-fold increase, and both of these effects were confirmed at the protein level. PGE2 resulted in a 14-fold upregulation of PAPPA2 mRNA but this was not reflected at the protein level. Forskolin, TGF-beta and IL-1beta had no significant effect on PAPPA2 mRNA expression. We observed no effects of any treatment on PAPPA or ADAM12 expression.

CONCLUSION

Our study demonstrates that factors previously known to be highly expressed in preeclamptic placentae (PGE2 and TNF-alpha), contribute to the upregulation of PAPPA2. Hypoxia, known to occur in preeclamptic placentae, also increased PAPPA2 expression. These results are consistent with the hypothesis that PAPPA2 is upregulated as a consequence of placental pathology, rather than elevated PAPPA2 levels being a cause of preeclampsia.

Regulation of placental growth hormone secretion in a human trophoblast model--the effects of hormones and adipokines

Placental growth hormone (PGH) is secreted from the human placental syncytiotrophoblast into the maternal circulation. PGH levels in pregnant women correlate with the birth weight of their offspring. We hypothesized that metabolic regulators may alter PGH secretion. BeWo cells as human trophoblast models were treated for 24, 48, and 72 h with insulin, insulin-like growth factor (IGF)-1, cortisol, ghrelin, leptin and visfatin. Cyclic-adenosinmonophosphate treatment served as positive control. PGH concentrations in culture media were measured. Insulin reduced (p < 0.008; analysis of variance) PGH secretion from BeWo cells after 72 h. No effect was found when treating cells with IGF-1. Cortisol reduced PGH secretion after 48 h (p < 0.00118; analysis of variance) and 72 h (p < 0.015). Leptin and ghrelin both suppressed (p < 0.027 and p < 0.017, paired t test) whereas visfatin increased (p < 0.014, paired t test) PGH secretion at 72 h. Cyclic adenosinmonophosphate increased (p < 0.003) PGH secretion at 72 h. Our results indicate that in vitro PGH secretion by BeWo cells is regulated by hormonal factors and adipokines. We speculate on the existence of a maternal-placental regulatory loop, in which elevated insulin and leptin levels might down-regulate PGH secretion.

IGF regulation of neutral amino acid transport in the BeWo choriocarcinoma cell line (b30 clone): evidence for MAP kinase-dependent and MAP kinase-independent mechanisms

OBJECTIVE

IGF-1 and IGF-1 receptors are major determinants of fetal growth and are expressed primarily on the maternal-facing surface of the syncytiotrophoblast cell membrane in the human placenta. IGF-1 regulates fetal growth, in part, by regulating amino acid transport across the placenta. The objective of these studies was to study the role of IGF-1 and its signaling pathway in regulating neutral amino acid transport in a human trophoblast cell culture model.

DESIGN

The regulation of neutral amino acid transport by IGF-1 was studied in cultured BeWo(b30) choriocarcinoma cells using the non-metabolizing amino acid analog, [(3)H]-alpha-aminoisobutyric acid (AIB). Transport in the absence of Na was used to distinguish system L from total AIB transport. Similarly, Na-dependent transport in the presence of excess methyl-AIB (MeAIB) permitted discrimination of systems A (MeAIB-sensitive) and ASC (MeAIB-insensitive). Specific inhibitors of intracellular signaling pathways were then used to determine the signaling pathway utilized by IGFs to regulate each amino acid transport system. Specificity of inhibition was assessed using specific markers of p70 S6 kinase activity and MAP kinase activation.

RESULTS

Maximal stimulating concentrations of IGF-I (100 ng/ml) stimulated AIB transport by 30-40% exclusively through system A. Wortmannin (100 nM), an inhibitor of PI-3-kinase activity, inhibited all IGF-I-stimulated transport. Rapamycin (100 ng/ml), an inhibitor of p70 S6 kinase, and bisindolylmaleimide, an inhibitor of protein kinase C (PKC), had no effect. PD-098059 (50 miccroM), an inhibitor of MAP kinase activation, inhibited 20-30% of basal AIB transport but did not inhibit IGF-I-stimulated transport under the conditions studied. IGF-1 did not increase steady state mRNA levels of the system A transporters, SNAT1 and SNAT2, suggesting IGF-1 stimulates transport via post-transcriptional mechanisms.

CONCLUSIONS

These data demonstrate that IGF-I stimulates neutral amino acid transport system A by a PI3-kinase dependent, post-transcriptional pathway in the BeWo(b30) cell line. Additionally, system A activity appear to be sensitive to MAP kinase-dependent pathways not regulated by IGFs.

PLAC1 expression increases during trophoblast differentiation: evidence for regulatory interactions with the fibroblast growth factor-7 (FGF-7) axis

PLAC1 is a recently described, trophoblast-specific gene that localizes to a region of the X-chromosome important in placental development. Immunohistochemical analysis demonstrated that PLAC1 polypeptide localizes to the differentiated syncytiotrophoblast throughout gestation (8-41 weeks) as well as a small population of villous cytotrophoblasts. Consistent with these observations, quantitative RT-PCR demonstrated that PLAC1 mRNA increases more than 300-fold during cytotrophoblast differentiation in culture to form syncytiotrophoblasts. Agents known to be relevant to trophoblast differentiation were then tested for the ability to influence PLAC1 expression. Fibroblast growth factor-7 (FGF-7), also known as keratinocyte growth factor (KGF), stimulated PLAC1 mRNA expression approximately two-fold in the BeWo(b30) trophoblast cell line. FGF-7 stimulation was significantly inhibited by PD-98059 and wortmannin suggesting mediation via MAP kinase and PI-3 kinase-dependent signaling pathways. Interestingly, epidermal growth factor (EGF) treatment of trophoblasts had no effect on PLAC1 expression alone, but potentiated the effect of FGF-7, suggesting the presence of a regulatory interaction of the two growth factors. FGF-7 and its receptor, FGFR-2b, exhibited spatial overlap with PLAC1 suggesting these regulatory interactions are physiologically relevant during gestation. These data demonstrate PLAC1 expression is upregulated during trophoblast differentiation, localizing primarily to the differentiated syncytiotrophoblast. Furthermore PLAC1 expression is specifically regulated by peptide growth factors relevant to trophoblast differentiation.

PLAC1, a trophoblast-specific gene, is expressed throughout pregnancy in the human placenta and modulated by keratinocyte growth factor

Plac1, a placenta-specific gene, is expressed exclusively by cells of trophoblastic lineage in the mouse, and maps to a region of the X chromosome known to be important in placental growth. These studies were undertaken to define the cellular location of the mRNA for the human orthologue, PLAC1, within the human placenta, and to examine its expression throughout gestation. By Northern analysis, PLAC1 mRNA was detected in term human placenta, migrating as a single 1.7 kb transcript, but in no other fetal or adult tissues tested. Expression was observed throughout gestation, whereas mouse Plac1 is significantly reduced after 12.5 dpc. Using an (35)S-labeled riboprobe, PLAC1 expression was trophoblast-specific at all stages of gestation (8-41 weeks); no expression was seen in cells within the stromal compartment or decidua. Using BeWo choriocarcinoma cells as a trophoblast model, keratinocyte growth factor (KGF) stimulated steady-state PLAC1 mRNA expression approximately twofold by Northern analysis and quantitative real-time PCR. Stimulation was observed only after 24 hr of exposure, suggesting that the stimulatory effect of KGF is secondary to the promotion of trophoblast growth or differentiation. No change in mRNA levels resulted from exposure to insulin-like growth factor II (IGF-II). Trophoblast-specific expression throughout gestation and responsiveness to KGF are consistent with a fundamental role for PLAC1 at the maternal-fetal interface.

Regulation of telomerase during human placental differentiation: a role for TGFbeta1

The transient tumor-like attributes of the first-trimester placenta anchor the developing embryo to the uterine wall thus establishing a vital link between the mother and the fetus. Dysregulation of this invasive behavior and/or controlled proliferation of the placenta is associated with abnormal pregnancies. Several of these diseased states also exhibit aberrant telomerase activity, among other pathophysiological manifestations. Considering the strong correlation between telomerase activity and tumorigenesis, it was of interest to see whether the crucial processes of trophoblast proliferation and differentiation were brought about through the modulation of telomerase. Using two in vitro model systems of trophoblast differentiation, we demonstrate here that telomerase activity is negatively regulated during placental differentiation. We further show that this modulation is at the level of transcription of hTERT. We also propose a role for TGF beta1 in regulating telomerase activity in differentiating trophoblasts by down-regulating the expression of hTERT at the transcriptional level.

Upregulation of neutral endopeptidase expression and enzymatic activity during the differentiation of human choriocarcinoma cells

Neutral endopeptidase (NEP)/CD10, a cell-surface peptidase degrading various bioactive peptides, is mainly present in syncytiotrophoblasts in the human placenta. However, the change in NEP expression upon trophoblast differentiation remains to be clarified. In the present study, we examined the expression of NEP in the differentiating trophoblast using the BeWo choriocarcinoma cell line as a model system. Under the normal culture conditions, NEP was very weakly expressed on most proliferating cytotrophoblastic BeWo cells, while a minority of the cell population (less than 5 per cent ), consisting of giant, multinucleated cells, clearly expressed NEP at the cell membrane. Treatment of BeWo cells with forskolin (FSK) for 48-72 h resulted in an 11- to 44-fold increase in the level of hCG secretion and induced cell fusion leading to the formation of multinucleated syncytiotrophoblasts, indicating functional and morphological differentiation. Fluorescence-activated cell sorting (FACS) analysis revealed that treatment with FSK significantly increased the cell-surface protein expression of NEP on differentiating BeWo cells. Consistently, there was a significant increase in the NEP enzymatic activity after FSK treatment. The level of hCG secretion from the FSK-treated cells was further enhanced when the cells were treated in the presence of the NEP inhibitor phosphoramidon. Immunohistochemical analysis of normal chorionic villi and choriocarcinoma tissues revealed the localization of NEP in syncytiotrophoblastic cells, as opposed to weak or negative staining in cytotrophoblastic cells. These data demonstrate that induction of choriocarcinoma cell differentiation is associated with an increase of NEP/CD10 expression at the cell surface, suggesting a role of this enzyme in regulating differentiated trophoblast functions such as hCG secretion. NEP/CD10 may also be a new cellular differentiation marker of both the normal and neoplastic trophoblast.

Glucose transporters in the human placenta

The availability of antibodies and cDNA probes specific for the various members of the facilitated-diffusion glucose transporter (GLUT) family has enabled researchers to obtain a much clearer picture of the mechanisms for placental uptake and transplacental transport of glucose. This review examines studies of human placental glucose transport with the aim of providing a model which describes the transporter isoforms present in the placenta, their cellular localization and functional significance. The GLUT1 glucose transporter, present on both the microvillous and basal membranes of the syncytial barrier, is the primary isoform involved in the transplacental movement of glucose. Although GLUT3 mRNA is widely distributed, GLUT3 protein is localized to the arterial component of the vascular endothelium, where it may play a role in enhancing transplacental glucose transport. This data is in contrast to the situation in other mammalian species, such as the mouse, rat and sheep, where GLUT3 protein is not only present in those epithelial cells which carry out transplacental transport but becomes an increasingly prominent isoform as gestation progresses. The asymmetric distribution of GLUT1 in the human syncytiotrophoblast (microvillous>basal) means that basal GLUT1 acts as the rate limiting step in transplacental transfer. Changes in basal GLUT1 therefore have the potential to cause alterations in transplacental transport of glucose. Although there appear to be no changes in syncytial GLUT1 expression in intrauterine growth retardation, in diabetic pregnancies increases in basal GLUT1 expression and activity have been observed, with significant consequences for the maternal-fetal flux of glucose. Little is known of glucose transporter regulation in the placenta save for the effects of hyper- and hypoglycemia. GLUT1 expression and activity appear to be inversely related to extracellular glucose concentration, however within the physiological range, GLUT1 expression is relatively refractory to glucose concentration. Information is still needed on gestational development, on the expression and activity in well-defined conditions of intrauterine growth retardation, on the mechanisms and consequences of the changes observed in diabetic pregnancy and on the role of external agents other than glucose in regulating placental glucose transport.

Identification of a stress-induced protein during human trophoblast differentiation by differential display analysis

Differentiation of human placental trophoblast is characterized by a process during which mononuclear villous cytotrophoblasts fuse to form a multinucleate syncytium. This event is associated with dramatic changes in gene expression. In the present study, we have applied a sensitive approach-differential display analysis-to evaluate changes in gene expression during in vitro forskolin-induced differentiation of a model of human trophoblast, the choriocarcinoma BeWo. We identified seven genes that were up-regulated; their expression and function have not previously been reported in trophoblast. Four up-regulated genes were novel upon comparison of their sequences to the GenBank database. The other three genes encode human cytochrome p450 IIC, inosine monophosphate dehydrogenase type II, and reducing agent and tunicamycin-responsive protein (RTP). Northern blot analysis revealed that RTP mRNA expression was induced to 3-fold in BeWo after 24-h incubation with forskolin and increased up to 11-fold by 72 h of forskolin treatment. The expression pattern of RTP was further investigated by in situ hybridization on second trimester and term placenta tissues. RTP mRNA was predominantly expressed in syncytiotrophoblasts in both second trimester and term placentae. The expression of RTP gene in BeWo cells was protein kinase C dependent. This is the first description of RTP gene expression in placenta and the first study elucidating the signaling pathway involved in the regulation of RTP gene expression. These results suggest that RTP may play a role in trophoblast cell proliferation and differentiation.

Antagonistic analogs of growth hormone releasing hormone (GHRH) inhibit cyclic AMP production of human cancer cell lines in vitro

Antagonistic analogs of growth hormone-releasing hormone (GHRH) inhibit growth of various human cancers both in vivo and in vitro. GHRH, vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating peptide stimulate cyclic AMP (cAMP) release from various human cancer cell lines in vitro. Thus, in the present study, we investigated the effects of antagonistic analogs of GHRH on the GHRH- and VIP-induced cAMP release from cultured human cancer cells in a superfusion system. Various human cancer cell lines were exposed to human GHRH(1-29)NH2 (2-20 nM) or VIP (0.1-5 nM) repeatedly for 12 min or continuously for 96 min. GHRH antagonist MZ-5-156 at 100 to 200 nM concentration inhibited the GHRH- or VIP-induced cAMP release from mammary (MDA-MB-468), prostatic (PC-3), and pancreatic (SW-1990 and CAPAN-2) cancer cells. These results show that antagonistic analogs of GHRH suppress the stimulatory effects of GHRH and VIP on the cAMP production of various cancer cells. Because cAMP is a potent second messenger controlling many intracellular functions, including the stimulation of cell growth, an inhibition of autocrine/paracrine action of GHRH by the GHRH antagonists may provide the basis for the development of new methods for cancer treatment.