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

Renin-angiotensin system (RAS) enzymes and placental trophoblast syncytialisation

Placental renin-angiotensin system (RAS) components; prorenin, angiotensinogen, and angiotensin (Ang) II type 1 receptor (AT₁R) are upregulated during syncytialisation. This study examined whether angiotensin-converting enzyme (ACE), ACE2 and neprilysin (NEP) are also altered during syncytialisation. Two in vitro models of syncytialisation were used: forskolin-treated BeWo cells and spontaneously syncytialising primary human trophoblast cells. Term placentae and primary trophoblasts had the highest levels of ACE, ACE2 and NEP mRNA. In primary trophoblasts, ACE mRNA levels significantly increased with syncytialisation, ACE2 and NEP mRNA levels decreased. ACE, ACE2 and NEP protein levels and ACE2 activity did not change. Syncytialisation of primary trophoblasts decreased soluble (s)ACE and sNEP but not sACE2 levels. In primary trophoblasts, the balance between the enzymes controlling the two opposing pathways of the RAS was maintained. These findings were unable to be reproduced in BeWo cells. Future studies exploring placental levels of these enzymes in pregnancies complicated by placental insufficiency are warranted.

Induction Effects of Apigenin, Luteolin and Vinpocetin on Neutral Endopeptidase (NEP) and Angiotensin-Converting Enzyme Activity (ACE) of SK-N-SH Cells

The long-term effects of a number of flavonoids (such as apigenin, luteolin and amentoflavone) and vinpocetine on the neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE) were investigated. It was shown that apigenin, luteolin and vinpocetin are able to induce the activity of both NEP and ACE associated with the inhibition of the proliferation of the neuroblastoma cell line SK-N-SH. Amentoflavone has no effect on either NEP or ACE activity. An additional enhancement of cellular NEP activity could be detected after the treatment of the cells with a combination of both arabinosylcytosine and either apigenin or luteolin. This effect supports the assumption that apigenin and luteolin influence directly the gene expression of NEP. Taking into account the significant role of NEP and ACE in the degradation of amyloid beta peptides, the induction of both enzymes by long-term treatment with apigenin, luteolin and vinpocetine may have a beneficial effect regarding the prevention of the formation of amyloid plaques and the effect of these substances may be discussed as neuroprotective.

Protein kinases orchestrate cell cycle regulators in differentiating BeWo choriocarcinoma cells

Choriocarcinoma, a trophoblastic neoplasia, occurs in women as an incidence of abnormal pregnancy. BeWo choriocarcinoma cells derived from the abnormal placentation are a suitable model system to study the factors associated with differentiation, invasion and other cellular events as an alternative to clinical samples. Many protein kinases orchestrate the complex events of cell cycle and in case of malignancy such regulators are found to be mutated. In the present study, BeWo cells treated with forskolin (Fo) and phorbol 12-myristate 13-acetate (PMA) were used to study the role of PKA (protein kinase A) and PKC (protein kinase C), respectively, on the expression pattern of differentiation-related genes, membrane markers, PKC isoforms and cell cycle regulators. The effect of Fo and PMA on the cell proliferation was assessed. Progressive induction of alkaline phosphatase level and formation of multinucleated differentiated cells were observed in the cells treated with Fo. Exposure of cells to Fo and PMA induced the mRNA transcripts of α-hCG, β-hCG and endoglin and down-regulates E-cadherin at mRNA and protein levels. Synergistic levels of both up- and down-regulated genes/proteins were observed when cells were treated with the combination of Fo and PMA. The mRNA levels of cyclin D1, cyclin E1, p21, Rb, p53, caspase-3 and caspase-8 decreased gradually during differentiation. Fo significantly inhibited the protein levels of PCNA, Rb, PKC-α and PMA stimulated mRNA expression of PKC-ε and PKC-δ. Further, failure in the activation of essential components of the cell cycle machinery caused G2/M phase arrest in differentiating BeWo cells.

Nobiletin, a flavone from Citrus depressa, induces gene expression and increases the protein level and activity of neprilysin in SK-N-SH cells

Neprilysin (NEP) is one of the candidate amyloid β protein (Aβ) degrading enzymes affecting brain Aβ clearance. This enzyme declines in the brain with age, which leads to the increased Aβ deposition in Alzheimer's disease (AD). Pharmacological activation of NEP during the aging process, therefore, represents a potential strategy to prevent the development of AD. To examine the influence of nobiletin on neprilysin activity, we measured cellular NEP activity in SK-N-SH cells. Moreover, NEP expression was examined by using reverse transcription - polymerase chain reaction and Western blotting. Measurement of cellular NEP activity showed that nobiletin stimulated this in a dose- and time-dependent manner in SK-N-SH cells. Moreover, nobiletin increased the expression of NEP mRNA, and then the levels of NEP protein, also in a dose- and time-dependent manner. Our findings showed that nobiletin promoted NEP gene and protein expression, resulting in enhancement of cellular NEP activity in SK-N-SH cells. This compound could be a novel Aβ-degrading compound for use in the development of disease-modifying drugs to prevent and (or) cure AD.

Squelching of ETS2 transactivation by POU5F1 silences the human chorionic gonadotropin CGA subunit gene in human choriocarcinoma and embryonic stem cells

The subunit genes encoding human chorionic gonadotropin, CGA, and CGB, are up-regulated in human trophoblast. However, they are effectively silenced in choriocarcinoma cells by ectopically expressed POU domain class 5 transcription factor 1 (POU5F1). Here we show that POU5F1 represses activity of the CGA promoter through its interactions with ETS2, a transcription factor required for both placental development and human chorionic gonadotropin subunit gene expression, by forming a complex that precludes ETS2 from interacting with the CGA promoter. Mutation of a POU5F1 binding site proximal to the ETS2 binding site does not alter the ability of POU5F1 to act as a repressor but causes a drop in basal promoter activity due to overlap with the binding site for DLX3. DLX3 has only a modest ability to raise basal CGA promoter activity, but its coexpression with ETS2 can up-regulate it 100-fold or more. The two factors form a complex, and both must bind to the promoter for the combination to be transcriptionally effective, a synergy compromised by POU5F1. Similarly, in human embryonic stem cells, which express ETS2 but not CGA, ETS2 does not occupy its binding site on the CGA promoter but is found instead as a soluble complex with POU5F1. When human embryonic stem cells differentiate in response to bone morphogenetic protein-4 and concentrations of POU5F1 fall and hCG and DLX3 rise, ETS2 then occupies its binding site on the CGA promoter. Hence, a squelching mechanism underpins the transcriptional silencing of CGA by POU5F1 and could have general relevance to how pluripotency is maintained and how the trophoblast lineage emerges from pluripotent precursor cells.

The loss of endoglin promotes the invasion of extravillous trophoblasts

Endoglin is a coreceptor for TGF-β, which is expressed in syncytiotrophoblasts. The soluble form of endoglin (sEng) has been observed to increase in the serum of preeclamptic patients. Several studies have shown that endoglin is involved in cancer invasion. However, the role of endoglin in extravillous trophoblasts (EVT), which have an invasive phenotype, remains unknown. The present study was designed to investigate the expression and role of endoglin in human EVT. We found that endoglin was mainly expressed on cytotrophoblasts within the cell column during the first trimester and its expression decreased in the EVT by immunohistochemistry and immunocytochemistry. The expression of endoglin significantly increased after treatment with TGF-β1 and TGF-β3 in the human EVT cell line, HTR-8/SVneo, as detected by semiquantitative RT-PCR. To investigate the role of endoglin in EVT, the stable knockdown of endoglin was performed by lentiviral short hairpin RNA transfection into the HTR-8/SVneo cells. Although proliferation was not affected, the motility and invasiveness of the HTR-8/SVneo cells significantly increased by the knockdown of endoglin. Both the mRNA expression and secretion of urokinase-type plasminogen activator significantly increased in endoglin knockdown cells. The secretion of sEng was very low in HTR-8/SVneo, and the treatment of endoglin knockdown cells with 10 ng/ml sEng had no effect on their invasiveness. Therefore, the suppression of sEng was not involved in the increased invasiveness of endoglin knockdown cells. These results suggested that EVT increased their invasive function as a result of decreasing expression of transmembrane endoglin.

Induction of neutral endopeptidase (NEP) activity of SK-N-SH cells by natural compounds from green tea

Deposition of amyloid β-peptide as senile plaques in the brain is one of the neuropathological hallmarks of Alzheimer's disease, which is the most prevalent progressive neurodegenerative disease leading to dementia. Neutral endopeptidase is one of the major β-amyloid-degrading enzymes in the brain. To examine the influence of different polyphenols and other natural products from green tea extract (from Camellia sinensis, Theaceae), we used the neuroblastoma cell line SK-N-SH and studied the changes in the specific cellular neutral endopeptidase activity after long-term treatment with these substances. We have shown that caffeine leads to an increase in specific cellular neutral endopeptidase activity more than theophylline, theobromine or theanine. We have also shown that the combination of epicatechin, epigallocatechin and epigallocatechingallate with caffeine, theobromine or theophylline induced cellular neutral endopeptidase activity. It is suggested that the enhancement of cellular neutral endopeptidase activity by green tea extract and its natural products might be correlated with an elevated level of intracellular cyclic adenosine monophosphate.

Induction of neutral endopeptidase activity in PC-3 cells by an aqueous extract of Epilobium angustifolium L. and oenothein B

An aqueous extract of Epilobium angustifolium and its main compound oenothein B (OeB), a dimeric macrocyclic ellagitannin, are specifically able to induce the neutral endopeptidase (NEP) in prostate cancer cells. The angiotensin-converting enzyme (ACE) is not influenced. Additionally, a weak but statistically significant inhibition of cell proliferation is observed. Simultaneous treatment of the cells with arabinosylcytosine and the extract as well as the OeB, leads to an additional enhancement of NEP activity. Taking into account the role of this peptidase in prostate cancer progression, our results might offer a pharmacological explanation for the use of Epilobium in folk medicine.

Cell specific expression of CD10/neutral endopeptidase 24.11 gene in human prostatic tissue and cells

BACKGROUND

Neutral endopeptidase (NEP/CD10) is a cell surface zinc metalloproteinase that functions as part of a regulatory loop controlling local concentrations of peptide substrates and associated peptide-mediated signal transduction processes. In contrast to the encouraging data dealing with NEP activity and regulation in prostate epithelial cells, only a few studies are available on the cellular expression and localization of neutral endopeptidase in the prostatic stromal and cancer cells. Here, we describe the cellular localization of NEP in human prostatic tissue and cells using in situ RT-PCR as a novel molecular biological approach.

METHODS

Immunofluorescence and Western blot experiments were performed to control the expression and distribution of the NEP in normal and malignant human prostatic tissues and cell lines. NEP gene expression was monitored by RT-PCR, NEP mRNA was detected in paraffin tissue sections and cultured cells of human prostate by the highly sensitive method of one step-in situ reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

NEP mRNA was detected in human prostatic tissue and in cultured cells by means of in situ RT-PCR. Prostatic tissue showed strong signals in the glandular epithelium and weak signals in the stroma, cultured cells displayed strong signals in prostate cancer cells (LNCaP) and weak signals in stromal cells (hPCPs). Western blot experiments were performed using whole cell extracts to proof the presence of NEP protein in LNCaP and hPCPs. The experiments confirm the expression of NEP by both cell types, however, the experiment with hPCPs cells showed two bands. NEP-immunofluorescence was strong in normal prostatic epithelium and confined to the apical plasma membrane. In dedifferentiated prostate cancer specimens, immunofluorescence of apical plasma membranes was lost, and both the cytoplasm and portions of the plasma membrane were immunoreactive for NEP. Prostate cancer cells (LNCaP) showed a strong immunoreaction of the plasma membrane and the cytoplasm. In comparison with LNCaP cells, only a weak cytoplasmic immunofluorescence was found in some stromal cells (hPCPs).

CONCLUSIONS

In normal prostatic tissue and specimens derived from human prostate cancer, NEP mRNA and protein are expressed mainly by the epithelial cells and to a minor extent by the stromal cells of human prostate glands. In situ RT-PCR is a powerful and straightforward approach for the routine and rapid detection of cellular specific expression of low copy genes.

Regulatory role of membrane-bound peptidases in the progression of gynecologic malignancies

Membrane-bound peptidases play a key role in the control of growth, differentiation, and signal transduction of many cellular systems by degrading bioactive peptides. Thus, abnormal changes in their expression pattern and catalytic function result in altered peptide activation, which contributes to neoplastic transformation or progression. In this review, we describe our recent findings along with work from other groups on the expression and biological functions of membrane-bound peptidases in cancer, focusing on the regulatory roles of three peptidases, aminopeptidase A (APA), neutral endopeptidase (NEP) and placental leucine aminopeptidase (P-LAP), in the progression of gynecologic malignancies. APA, NEP and P-LAP are differentially expressed and localized in various gynecologic malignancies including cervical cancer, endometrial cancer, ovarian cancer and choriocarcinoma in a tumor-type specific pattern. The expression levels are up- or down-regulated depending on histological grade or disease progression. These peptidases play regulatory roles in tumor cell proliferation, invasion or angiogenesis via degradation/inactivation of target peptides such as angiotensin II, endothelin-1 and oxytocin, which act on cancer cells as stimulatory or inhibitory factors. Thus, membrane-bound peptidases may become not only a new diagnostic/prognostic marker, but also a novel molecular target for the treatment of gynecologic malignancies.

Expression of placental leucine aminopeptidase and adipocyte-derived leucine aminopeptidase in human normal and malignant invasive trophoblastic cells

We recently identified two novel aminopeptidases, placental leucine aminopeptidase (P-LAP) and adipocyte-derived leucine aminopeptidase (A-LAP). Enzymatically, P-LAP degrades oxytocin, vasopressin, and angiotensin III, while A-LAP degrades angiotensin II and kallidin. In this study we investigated the expression and localization of P-LAP and A-LAP in human trophoblastic cells in the normal placenta (n = 26), gestational choriocarcinoma (n = 8), and placental site trophoblastic tumor (n = 3). On immunoblot analysis both P-LAP and A-LAP proteins were detected in normal placenta and five choriocarcinoma tissues, as well as in two choriocarcinoma cell lines. Immunohistochemical staining of normal placental tissues demonstrated that P-LAP was not only localized in villous syncytiotrophoblasts but also highly expressed in extravillous trophoblasts (EVTs) invading the decidua or maternal spiral arteries. The expression level of P-LAP on these invasive EVTs reached a maximum during the late first to second trimesters of pregnancy, and it decreased in the third trimester. Similarly, A-LAP was strongly expressed in EVTs invading the decidua or spiral arteries in the second trimester of pregnancy, while it was weakly or moderately expressed in villous cytotrophoblasts or EVTs located in the cell columns. These two aminopeptidases were more strongly expressed in all eight choriocarcinomas and three placental site trophoblastic tumors and mainly localized to the intermediate-type trophoblastic tumor cells invading the uterine myometrium or stromal vessels. In summary P-LAP and A-LAP were predominantly expressed in the invasive phenotype of EVTs during placentation, as well as in the invasive tumor cells of trophoblastic neoplasms. These results suggest the involvement of these aminopeptidases in invasiveness of both normal and malignant intermediate-type trophoblasts possibly through degradation of specific peptide substrates.

Placental leucine aminopeptidase/oxytocinase gene regulation by activator protein-2 in BeWo cell model of human trophoblast differentiation

Placental leucine aminopeptidase (P-LAP) is located preferentially in syncytiotrophoblasts in human placenta. Here we investigated P-LAP expression and the regulatory mechanisms in BeWo choriocarcinoma cells with forskolin (FSK)-induced differentiation. Morphologically differentiated cells revealed enhanced P-LAP staining. FSK significantly increased P-LAP activity and mRNA. Deletion or mutation of activator protein-2 (AP-2) binding site in the footprint-3 (-216 to -172) of P-LAP promoter abrogated the stimulatory effects of FSK on luciferase activity of the construct -216/+49. In AP-2-deficient Hep-G2 cells, FSK failed to stimulate luciferase activity of the construct -216/+49. Among the isoforms, BeWo expressed AP-2alpha and AP-2gamma, while FSK increased only AP-2alpha. These results suggest differentiation-dependent P-LAP expression in trophoblasts, which involves increased AP-2alpha binding.

VEGF-, KIT protein- and neutral endopeptidase (NEP/CD10)-positive myofibroblasts-precursors of angiogenesis in chorioangiomas?

Chorioangiomas are benign angiomatous tumours of the placenta occurring with a frequency of approximately one per cent of all examined placentae. Hypoxia and genetic factors are discussed to be predisposing factors for chorioangiomas. However, not much is known about the tumorigenesis of these benign tumours. Screening with various antibodies in a rare case of chorangiomatosis, we found disseminated spindle cells coexpressing vascular epithelial growth factor (VEGF), neutral endopeptidase 24.11 (NEP/CD10), and KIT protein (CD117) within the tumour stroma. A possible involvement of such factors in angiogenesis and tumorigenesis of chorioangiomas/chorangiomatosis has not been studied so far.Seven placentae with chorioangiomas (n=6) or chorangiomatosis (n=1), six normal placentae, and four cutaneous haemangiomas were analysed immunohistochemically (ABC and APAAP methods) using antibodies against VEGF, NEP, KIT protein, as well as endothelial markers like PECAM-1 (CD31), CD34, v. Willebrand factor (factor VIII), and ulex europaeus. In addition, analysis of c-kit 'gain of function' mutation Asp 816 to Val by means of Hinfl digestion and direct sequencing of semi-nested polymerase chain reaction products was performed. All chorioangiomas and haemangiomas strongly expressed the endothelial markers CD34, CD31, and FVIII, while only weak expression of ulex lectin was noted. Disseminated groups of VEGF-, NEP-, and KIT protein-positive spindle cells, which coexpressed vimentin and smooth-muscle actin were identified as myofibroblasts in the stroma of four chorioangiomas. These spindle cells were quantified as numerous in two and as rare in two other cases. No VEGF-positive myofibroblasts, however, were detected in the villous stroma of normal control placentae and haemangiomas. Only scattered perivascular myofibroblasts expressing KIT protein and NEP were detected in early gestational placenta controls. In all chorioangiomas and chorangiomatosis PCR analysis failed to unveil c-kit 'gain of function' mutation Asp 816 to Val in KIT protein-positive spindle cells. Moreover, a significant increase in mast cells was observed only in the haemangiomas. As expected, endothelial origin of chorioangiomas/chorangiomatosis was verified by CD31, CD34, FVIII expression. Myofibroblastic spindle cells expressing VEGF and NEP may be precursor cells in these peculiar angiomatous tumours. Although activating c-kit mutation Asp 816 to Val was not detected by PCR, the presence of KIT protein (CD117)-positive intratumoral myofibroblastic spindle cells in chorioangiomas and chorangiomatosis might suggest involvement of the stem cell factor (SCF)-receptor in pathologically enhanced angiogenesis.

The effects of phosphoramidon on the expression of human endothelin-converting enzyme-1 (ECE-1) isoforms

Endothelin-1 (ET-1) is generated from big ET-1 by endothelin converting enzyme-1 (ECE-1). This process is inhibited by phosphoramidon through binding to the catalytic domain of ECE-1. There are four isoforms of human ECE-1 (ECE-1a, ECE-1b, ECE-1c and ECE-1d) which possess a conserved catalytic domain. Interestingly, a recent study has shown that in ECE-1b-transfected CHO cells phosphoramidon increases the expression and activity of ECE-1b. It is not known, however, whether phosphoramidon has similar effects on the expression of other ECE-1 isoforms. To address this point, we have established recombinant CHO cell lines that permanently express either human ECE-1a, ECE-1b or ECE-1c. Incubation of CHO/ECE-1a, -1b, and -1c with phosphoramidon (100 microM) for 16 hours markedly elevated the intracellular expression of ECE-1a and ECE-1b, but not ECE-1c protein, as indicated by Western blotting and immunocytochemistry. These increases appear to be due to inhibition of intracellular degradation of the protein because metabolic labeling followed by immunoprecipitation showed ECE-1a and ECE-1b proteins had prolonged half-lives in the phosphoramidon-treated cells. This is further supported by the finding that ECE-1 mRNA levels were unchanged following phosphoramidon treatment. Taken together, our results demonstrate that phosphoramidon differentially affects the expression of three human ECE-1 isoforms.

Enhancement of neutral endopeptidase activity in SK-N-SH cells by green tea extract

Green tea extract (EFLA85942) is able to induce specifically the neutral endopeptidase (NEP) activity and to inhibit the proliferation of SK-N-SH cells; the angiotensin-converting enzyme (ACE) activity is not influenced under the same conditions. The treatment of the cells with arabinosylcytosine and green tea extract results in a strong enhancement of cellular NEP activity whereas cellular ACE activity was not changed significantly, indicating a green tea extract-specific regulation of NEP expression. Because of its role in the degradation of amyloid beta peptides this enzyme induction of NEP by long term treatment with green tea extract may have a beneficial effect regarding the prevention of forming amyloid plaques.

Neutral endopeptidase/CD10 expression during phorbol ester-induced differentiation of choriocarcinoma cells through the protein kinase C- and extracellular signal-regulated kinase-dependent signalling pathway

Neutral endopeptidase 24.11 (NEP) is identical to CD10, which is a differentiation antigen for early B-lymphoid progenitors in the B-cell differentiation pathway. This ectoenzyme is known to have a key role in the control of growth, differentiation, and signal transduction of many cellular systems by regulating bioactive peptides and cytokines. Recently, we demonstrated that NEP/CD10 is upregulated during forskolin-induced choriocarcinoma cell differentiation, suggesting that NEP/CD10 is a trophoblast differentiation marker. The purpose of this study was to clarify the enhancement of NEP/CD10 expression and its signal transduction pathway during phorbol ester (PMA)-induced differentiation of BeWo choriocarcinoma cells. PMA-induced differentiation of BeWo cells was confirmed by morphological change and human chorionic gonadotropin (hCG) secretion, which was completely blocked by a protein kinase C (PKC) inhibitor, Bisindolylmaleimide I (Bis I). On immunoblot analysis, PMA enhanced NEP/CD10 expression in a dose- and time-dependent manner, which was completely abolished by Bis I and a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor, PD98059. PMA also induced phosphorylation of p44/p42 extracellular signal-regulated kinases (ERK) 1 and 2. These observations indicated that activation of PKC by PMA induced differentiation of BeWo cells, and that PMA activated MAPK/ERK, which resulted in the enhancement of NEP/CD10 expression. Furthermore, immunocytochemical analysis showed that NEP/CD10 expression was detected on the membranes of PMA-treated differentiated BeWo cells. In summary, we demonstrated that NEP/CD10 was enhanced during PMA-induced differentiation of BeWo choriocarcinoma cells through a PKC-dependent MEK/ERK signalling pathway. Our findings also suggest that NEP/CD10 may play a functional role in the process of trophoblast differentiation.