Heterodimerization of endothelin-converting enzyme-1 isoforms regulates the subcellular distribution of this metalloprotease

A non-canonical role of endothelin converting enzyme 1 (ECE1) in promoting lung cancer development via directly targeting protein kinase B (AKT)

BACKGROUND

Lung cancer is the second most common malignancy in the world, and lung adenocarcinoma (LUAD) in particular is the leading cause of cancer death worldwide. Endothelin converting enzyme 1 (ECE1) is a membrane-bound metalloprotease involved in endothelin-1 (ET-1) processing and regulates vasoconstriction. However, very few studies have reported the involvement of ECE1 in regulating tumor cell proliferation, and the mechanism remains poorly understood. Therefore, we aimed to determine the role of ECE1 in lung cancer development.

METHODS

The Cancer Genome Atlas database and Kaplan-Meier plotter were used to assess the association between ECE1 and lung cancer. The expression of ECE1 was detected using immunohistochemistry staining and western blotting. A variety of in vitro assays were performed to evaluate the effects of ECE1 on the colony formation, proliferation, migration and invasion using ECE1 knockdown lung cancer cells. The gene expression profiles regulated by ECE1 were investigated by RNA sequencing. An immunoprecipitation assay and immunofluorescence assay were used to evaluate the mechanism underlying the regulatory effect of ECE1 on protein kinase B (AKT). The effect of ECE1 on tumor development was assessed by xenografted lung cancer cells in either C57BL/6 mice or nude mice.

RESULTS

ECE1 was upregulated in LUAD and correlated with the poor prognosis of patients with LUAD. Functional studies showed that knockdown of ECE1 retarded the progression of tumors formed by lung cancer cells at least partly by inhibiting tumor cell proliferation. Moreover, ECE1 accelerated tumor cell proliferation through promoting AKT activation dispensable of its canonical target ET-1. Mechanically, ECE1 interacted with the pleckstrin homology (PH) domain of AKT and facilitated its translocation to the plasma membrane for activation. Furthermore, the inhibition of AKT activity counteracted the lung cancer cell growth inhibition observed both in vitro and in xenografts caused by ECE1 suppression.

CONCLUSIONS

The present study reveals a non-canonical function of ECE1 in regulating AKT activation and cell proliferation, which provides the basis for the development of a novel strategy for the intervention of cancer including LUAD by abrogating ECE1-AKT signaling.

Endothelin-converting enzyme-1 expression in acute and chronic liver injury in fibrogenesis

Endothelin-1 (ET-1) induces contraction, proliferation, and collagen synthesis of activated hepatic stellate cells and is a potent mediator of portal hypertension. Endothelin-converting enzyme-1 (ECE-1) generates ET-1 from the inactive precursor big-endothelin-1. The cellular distribution and activity of ECE-1 in the liver is unknown. Hepatic fibrogenesis was induced in rats by CCl₄ administration and secondary biliary cirrhosis after 6 weeks of complete bile duct occlusion (BDO). The tissue ET-1 and ET receptor protein levels were quantified, the ECE-1 isoform mRNAs were measured by RNase protection assay and ECE-1 activity was analyzed. ECE-1a and -b mRNA were upregulated in biliary cirrhosis and in CCl₄-injured livers, whereas ECE-1c mRNA remained unchanged. ECE-1 activity was increased after BDO and peaked at 12 h after acute CCl₄-intoxication. Tissue levels of ET-1, ET_A- and ET_B receptors were elevated 7-, 5-, and 4.6-fold in cirrhotic rats, respectively. ECE-1 activity increased following BDO and acute CCl₄-intoxication. In conclusion, ECE-1a and -b RNAs are upregulated in fibrogenesis, indicating that these isoforms play a central role in ET-1 generation during fibrogenesis and portal hypertension.

Intracellular metalloprotease activity controls intraneuronal Aβ aggregation and limits secretion of Aβ via exosomes

Accumulating evidence suggests that the abnormal aggregation of amyloid-β (Αβ) peptide in Alzheimer's disease (AD) begins intraneuronally, within vesicles of the endosomal-lysosomal pathway where Aβ is both generated and degraded. Metalloproteases, including endothelin-converting enzyme (ECE)-1 and -2, reside within these vesicles and normally limit the accumulation of intraneuronally produced Aβ. In this study, we determined whether disruption of Aβ catabolism could trigger Aβ aggregation within neurons and increase the amount of Aβ associated with exosomes, small extracellular vesicles derived from endosomal multivesicular bodies. Using cultured cell lines, primary neurons, and organotypic brain slices from an AD mouse model, we found that pharmacological inhibition of the ECE family of metalloproteases increased intracellular and extracellular Aβ levels and promoted the intracellular formation of Aβ oligomers, a process that did not require internalization of secreted Aβ. In vivo, the accumulation of intraneuronal Aβ aggregates was accompanied by increased levels of both extracellular and exosome-associated Aβ, including oligomeric species. Neuronal exosomes were found to contain both ECE-1 and -2 activities, suggesting that multivesicular bodies are intracellular sites of Aβ degradation by these enzymes. ECE dysfunction could lead to the accumulation of intraneuronal Aβ aggregates and their subsequent release into the extracellular space via exosomes.-Pacheco-Quinto, J., Clausen, D., Pérez-González, R., Peng, H., Meszaros, A., Eckman, C. B., Levy, E., Eckman, E. A. Intracellular metalloprotease activity controls intraneuronal Aβ aggregation and limits secretion of Aβ via exosomes.

ECE-1 overexpression in head and neck cancer is associated with poor tumor differentiation and patient outcome

BACKGROUND

Endothelin-converting enzyme-1 (ECE-1) primarily converts big endothelins (ETs) into active endothelin-1 (ET-1). However, the expression pattern and prognostication status of ECE-1 in head and neck cancer (HNC) are enigmatic. In this study, we investigated ECE-1 expression and assessed the roles of ECE-1 as a predictor for HNC differentiation and prognosis.

MATERIALS AND METHODS

ECE-1 expressions were evaluated by immunohistochemical analysis using a tissue microarray (TMA) composed of 100 cases of head and neck squamous cell carcinoma. The correlation of ECE-1 expression with clinicopathologic variables and patient outcomes was analyzed.

RESULTS

ECE-1 may be overexpressed in HNC carcinoma cells. Higher ECE-1 level was detected more frequently in moderately to poorly differentiated tumors and showed a lower differentiation category compared to the G1 cases (p = 0.015); this finding was further confirmed by an adjusted odds ratio (OR) of 4.071 (p = 0.042). Moreover, Kaplan-Meier survival analyses showed that a higher ECE-1 expression was associated with a poorer survival in patients with HNC (p < 0.0001). On multivariate Cox proportional hazards models analysis, ECE-1 of high expression proved to be an independent prognostic factor with a hazard ratio (HR) of 3.985 (p < 0.001).

CONCLUSION

Our data provide the first evidence that overexpression of ECE-1 in HNC is a predictor of poor tumor differentiation and prognosis.

A stress-enhanced model for discovery of disease-modifying gene: Ece1-suppresses the toxicity of α-synuclein A30P

Parkinson's disease (PD) is a progressive motor neurodegenerative disorder, characterized by a selective loss of dopaminergic neurons in the substantia nigra. The complexity of disease etiology includes both genetic and environmental factors. No effective drug that can modify disease progression and protect dopamine neurons from degeneration is presently available. Human α-Synuclein A30P (A30P) is a mutant gene identified in early onset PD and showed to result selective dopamine neuron loss in transgenic A30P flies and mice. Paraquat (PQ) is an herbicide and an oxidative stress generator, linked to sporadic PD. We hypothesized that vital PD modifier genes are conserved across species and would show unique transcriptional changes to oxidative stress in animals expressing a PD-associated gene, such as A30P. We also hypothesized that manipulation of PD modifier genes would provide neuroprotection across species. To identify disease modifier genes, we performed two independently-duplicated experiments of microarray, capturing genome-wide transcriptional changes in A30P flies, chronically fed with PQ-contaminated food. We hypothesized that the best time point of identifying a disease modifier gene is at time when flies showed maximal combined toxicity of A30P transgene and PQ treatment during an early stage of disease and that effective disease modifiers gene are those showing transcriptional changes to oxidative stress in A30P expressing and not in wild type animals. Fly Neprilysin3 (Nep3) is one identified gene that is highly conserved. Its mouse and human homolog is endothelin-converting enzyme-1 (Ece1). To investigate the neuroprotective effect of Ece1, we used NS1 cells and mouse midbrain neurons expressing A30P, treated with or without PQ. We found that ECE1 expression protected against A30P toxicity on cell viability, on neurite outgrowth and ameliorated A30P accumulation in vitro. Expression of ECE1 in vivo suppressed dopamine neuron loss and alleviated the corresponding motor deficits in mice with A30P-expression. Our study leverages a new approach to identify disease modifier genes using a stress-enhanced PD animal model.

Androgen alleviates neurotoxicity of β-amyloid peptide (Aβ) by promoting microglial clearance of Aβ and inhibiting microglial inflammatory response to Aβ

AIMS

Lower androgen level in elderly men is a risk factor of Alzheimer's disease (AD). It has been reported that androgen reduces amyloid peptides (Aβ) production and increases Aβ degradation by neurons. Activated microglia are involved in AD by either clearing Aβ deposits through uptake of Aβ or releasing cytotoxic substances and pro-inflammatory cytokines. Here, we investigated the effect of androgen on Aβ uptake and clearance and Aβ-induced inflammatory response in microglia, on neuronal death induced by Aβ-activated microglia, and explored underlying mechanisms.

METHODS

Intracellular and extracellular Aβ were examined by immunofluorescence staining and Western blot. Amyloid peptides (Aβ) receptors, Aβ degrading enzymes, and pro-inflammatory cytokines were detected by RT-PCR, real-time PCR, and ELISA. Phosphorylation of MAP kinases and NF-κB was examined by Western blot.

RESULTS

We found that physiological concentrations of androgen enhanced Aβ42 uptake and clearance, suppressed Aβ42 -induced IL-1β and TNFα expression by murine microglia cell line N9 and primary microglia, and alleviated neuronal death induced by Aβ42 -activated microglia. Androgen administration also reduced Aβ42 -induced IL-1β expression and neuronal death in murine hippocampus. Mechanistic studies revealed that androgen promoted microglia to phagocytose and degrade Aβ42 through upregulating formyl peptide receptor 2 and endothelin-converting enzyme 1c expression, and inhibited Aβ42 -induced pro-inflammatory cytokines expression via suppressing MAPK p38 and NF-κB activation by Aβ42 , in an androgen receptor independent manner.

CONCLUSION

Our study demonstrates that androgen promotes microglia to phagocytose and clear Aβ42 and inhibits Aβ42 -induced inflammatory response, which may play an important role in reducing the neurotoxicity of Aβ.

Regulation of the turnover of ACC synthases by phytohormones and heterodimerization in Arabidopsis

Ethylene influences many aspects of plant growth and development. The biosynthesis of ethylene is highly regulated by a variety of internal and external cues. A key target of this regulation is 1-aminocyclopropane-1-carboxylic acid (ACC) synthases (ACS), generally the rate-limiting step in ethylene biosynthesis, which is regulated both transcriptionally and post-transcriptionally. Prior studies have demonstrated that cytokinin and brassinosteroid (BR) act as regulatory inputs to elevate ethylene biosynthesis by increasing the stability of ACS proteins. Here, we demonstrate that several additional phytohormones also regulate ACS protein turnover. Abscisic acid, auxin, gibberellic acid, methyl jasmonic acid, and salicylic acid differentially regulate the stability of ACS proteins, with distinct effects on various isoforms. In addition, we demonstrate that heterodimerization influences the stability of ACS proteins. Heterodimerization between ACS isoforms from distinct subclades results in increased stability of the shorter-lived partner. Together, our study provides a comprehensive understanding of the roles of various phytohormones on ACS protein stability, which brings new insights into crosstalk between ethylene and other phytohormones, and a novel regulatory mechanism that controls ACS protein stability through a heterodimerization of ACS isoforms.

Endothelin-converting enzymes degrade α-synuclein and are reduced in dementia with Lewy bodies

We have examined the roles of the endothelin-converting enzyme-1 and -2 (ECE-1 and ECE-2) in the homeostasis of α-synuclein (α-syn) and pathogenesis of Lewy body disease. The ECEs are named for their ability to convert inactive big endothelin to the vasoactive peptide endothelin-1 (EDN1). We have found that ECE-1 and ECE-2 cleave and degrade α-syn in vitro and siRNA-mediated knockdown of ECE-1 and ECE-2 in SH-SY5Y neuroblastoma cells significantly increased α-syn both intracellularly (within the cell lysate) (p < 0.05 for both ECE-1 and -2) and extracellularly (in the surrounding medium) (p < 0.05 for ECE-1 and p = 0.07 for ECE-2). Double immunofluorescent labelling showed co-localization of ECE-1 and ECE-2 with α-syn within the endolysosomal system (confirmed by a proximity ligation assay). To assess the possible relevance of these findings to human Lewy body disease, we measured ECE-1 and ECE-2 levels by sandwich ELISA in post-mortem samples of cingulate cortex (a region with a predilection for Lewy body pathology) in dementia with Lewy bodies (DLB) and age-matched controls. ECE-1 (p < 0.001) and ECE-2 (p < 0.01) levels were significantly reduced in DLB and both enzymes correlated inversely with the severity of Lewy body pathology as indicated by the level of α-syn phosphorylated at Ser129 (r = -0.54, p < 0.01 for ECE-1 and r = -0.49, p < 0.05 for ECE-2). Our novel findings suggest a role for ECEs in the metabolism of α-syn that could contribute to the development and progression of DLB.

Endothelin-1: Biosynthesis, Signaling and Vasoreactivity

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide originally isolated from endothelial cells. Its synthesis, mainly regulated at the gene transcription level, involves processing of a precursor by a furin-type proprotein convertase to an inactive intermediate, big ET-1. The latter peptide can then be cleaved directly by an endothelin-converting enzyme (ECE) into ET-1 or reach the active metabolite through a two-step process involving chymase hydrolyzing big ET-1 to ET-1 (1-31), itself needing conversion to ET-1 by neprilysin (NEP) to exert physiological activity. ET-1 signals through two G protein-coupled receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB). Both receptors induce an increase in intracellular Ca(2+), mainly from the extracellular space through voltage-independent mechanisms, the receptor-operated channels and store-operated channels. ET-1 also induces signaling through epidermal growth factor receptor transactivation, oxidative stress induction, rho-kinase, and the activation (ETA) or inhibition (ETB) of the adenylate cyclase/cyclic adenosine monophosphate pathway. Arterial vasoconstriction is mediated mainly by the ETA receptor. ET-1, via endothelium-located ETB, relaxes arteries or constricts vessels following activation of the same receptor type on the smooth muscle, where it can interact with ETA. In addition, ETB-dependent vasoconstriction seems more prominent in the venous vasculature. A better understanding of how ET-1 is synthesized and how ETA and ETB receptors interact could help design better pharmacological agents in the treatment of cardiovascular diseases where targeting the ET-1 system is indicated.

Endothelin-Receptor Antagonists beyond Pulmonary Arterial Hypertension: Cancer and Fibrosis

The endothelin axis and in particular the two endothelin receptors, ETA and ETB, are targets for therapeutic intervention in human diseases. Endothelin-receptor antagonists are in clinical use to treat pulmonary arterial hypertension and have been under clinical investigation for the treatment of several other diseases, such as systemic hypertension, cancer, vasospasm, and fibrogenic diseases. In this Perspective, we review the molecules that have been evaluated in human clinical trials for the treatment of pulmonary arterial hypertension, as well as other cardiovascular diseases, cancer, and fibrosis. We will also discuss the therapeutic consequences of receptor selectivity with regard to ETA-selective, ETB-selective, or dual ETA/ETB antagonists. We will also consider which chemical characteristics are relevant to clinical use and the properties of molecules necessary for efficacy in treating diseases against which known molecules displayed suboptimal efficacy.

Protective effects of grape seed proanthocyanidins on cardiovascular remodeling in DOCA-salt hypertension rats

Cardiovascular remodeling, as a hallmark of hypertension-induced pathophysiology, causes substantial cardiovascular morbidity and mortality. There is increasing evidence that has demonstrated a broad spectrum of pharmacological and therapeutic benefits of grape seed proanthocyanidins (GSP) against oxidative stress and cardiovascular diseases. In this study, 180- to 200-g SD rats treated with DOCA (120 mg/week sc with 1% NaCl and 0.2% KCl in drinking water) and GSP (150, 240, 384 mg/kg) or amlodipine (ALM) (5 mg/kg) for 4 weeks were recruited. The protective effects of GSP on blood pressure and cardiovascular remodeling in rats with DOCA-salt-induced hypertension were investigated. Our results indicated that DOCA-salt could induce hypertension, cardiovascular remodeling and dysfunction, oxidative stress and the release of endothelin-1 (ET-1) and could increase JNK1/2 and p38MAPK phosphorylation. GSP or ALM treatments significantly improved hypertension, cardiovascular remodeling and dysfunction and oxidative stress, restrained the release of ET-1 and down-regulated the JNK1/2 and p38MAPK phosphorylation. These findings demonstrate that GSP has protective effects against increase of blood pressure induced by DOCA-salt hypertension and cardiovascular remodeling by inhibiting the reactive oxygen species/mitogen-activated protein kinase pathway via restraining the release of ET-1.

Amyloid-beta protein clearance and degradation (ABCD) pathways and their role in Alzheimer's disease

Amyloid-β proteins (Aβ) of 42 (Aβ42) and 40 aa (Aβ40) accumulate as senile plaques (SP) and cerebrovascular amyloid protein deposits that are defining diagnostic features of Alzheimer's disease (AD). A number of rare mutations linked to familial AD (FAD) on the Aβ precursor protein (APP), Presenilin-1 (PS1), Presenilin- 2 (PS2), Adamalysin10, and other genetic risk factors for sporadic AD such as the ε4 allele of Apolipoprotein E (ApoE-ε4) foster the accumulation of Aβ and also induce the entire spectrum of pathology associated with the disease. Aβ accumulation is therefore a key pathological event and a prime target for the prevention and treatment of AD. APP is sequentially processed by β-site APP cleaving enzyme (BACE1) and γ-secretase, a multisubunit PS1/PS2-containing integral membrane protease, to generate Aβ. Although Aβ accumulates in all forms of AD, the only pathways known to be affected in FAD increase Aβ production by APP gene duplication or via base substitutions on APP and γ-secretase subunits PS1 and PS2 that either specifically increase the yield of the longer Aβ42 or both Aβ40 and Aβ42. However, the vast majority of AD patients accumulate Aβ without these known mutations. This led to proposals that impairment of Aβ degradation or clearance may play a key role in AD pathogenesis. Several candidate enzymes, including Insulin-degrading enzyme (IDE), Neprilysin (NEP), Endothelin-converting enzyme (ECE), Angiotensin converting enzyme (ACE), Plasmin, and Matrix metalloproteinases (MMPs) have been identified and some have even been successfully evaluated in animal models. Several studies also have demonstrated the capacity of γ-secretase inhibitors to paradoxically increase the yield of Aβ and we have recently established that the mechanism is by skirting Aβ degradation. This review outlines major cellular pathways of Aβ degradation to provide a basis for future efforts to fully characterize the panel of pathways responsible for Aβ turnover.

Agonist-biased trafficking of somatostatin receptor 2A in enteric neurons

Somatostatin (SST) 14 and SST 28 activate somatostatin 2A receptors (SSTR2A) on enteric neurons to control gut functions. SST analogs are treatments of neuroendocrine and bleeding disorders, cancer, and diarrhea, with gastrointestinal side effects of constipation, abdominal pain, and nausea. How endogenous agonists and drugs differentially regulate neuronal SSTR2A is unexplored. We evaluated SSTR2A trafficking in murine myenteric neurons and neuroendocrine AtT-20 cells by microscopy and determined whether agonist degradation by endosomal endothelin-converting enzyme 1 (ECE-1) controls SSTR2A trafficking and association with β-arrestins, key regulators of receptors. SST-14, SST-28, and peptide analogs (octreotide, lanreotide, and vapreotide) stimulated clathrin- and dynamin-mediated internalization of SSTR2A, which colocalized with ECE-1 in endosomes and the Golgi. After incubation with SST-14, SSTR2A recycled to the plasma membrane, which required active ECE-1 and an intact Golgi. SSTR2A activated by SST-28, octreotide, lanreotide, or vapreotide was retained within the Golgi and did not recycle. Although ECE-1 rapidly degraded SST-14, SST-28 was resistant to degradation, and ECE-1 did not degrade SST analogs. SST-14 and SST-28 induced transient interactions between SSTR2A and β-arrestins that were stabilized by an ECE-1 inhibitor. Octreotide induced sustained SSTR2A/β-arrestin interactions that were not regulated by ECE-1. Thus, when activated by SST-14, SSTR2A internalizes and recycles via the Golgi, which requires ECE-1 degradation of SST-14 and receptor dissociation from β-arrestins. After activation by ECE-1-resistant SST-28 and analogs, SSTR2A remains in endosomes because of sustained β-arrestin interactions. Therapeutic SST analogs are ECE-1-resistant and retain SSTR2A in endosomes, which may explain their long-lasting actions.

Endothelin-converting enzyme-1 gene ablation attenuates pulmonary fibrosis via CGRP-cAMP/EPAC1 pathway

Endothelin-1 (ET-1) has been shown to be involved in human pulmonary fibrosis. However, recent clinical trials targeting the ET-1 pathway with ET-1 receptor antagonists failed to achieve beneficial outcomes. Another strategy opposing the actions of ET-1 involves the inhibition of endothelin-converting enzyme-1 (ECE-1). We hypothesize that ECE-1 inhibition exerts beneficial effects on pulmonary fibrosis. Pulmonary fibrosis was induced by instilling bleomycin intratracheally into ECE-1 heterozygous knockout mice (ECE-1(+/-)) and their wild-type control mice (ECE-1(+/+)). Lung inflammation and fibrosis were assessed on Days 7, 14, and 28 after bleomycin instillation. The activity of ECE-1 and the concentrations of its related peptides, ET-1, bradykinin, atrial natriuretic peptide (ANP), and calcitonin gene-related peptide (CGRP), were determined. ECE-1(+/-) mice demonstrated less lung inflammation and limited fibrosis compared with control mice. ECE-1 activity was half-reduced in ECE-1(+/-) mice, and this activity also altered ET-1 and CGRP concentrations, but not concentrations of bradykinin and ANP. ET-1 concentrations were found to be lower in ECE-1(+/-) mice after the development of fibrosis, in contrast to the unaltered concentrations during inflammation. Reduced ECE-1 activity resulted in higher CGRP concentrations, which altered the pathological functionality of the lung, indicating the activation of the CGRP pathway involving cyclic adenosine monophosphate (cAMP)/exchange protein directly activated by cAMP and cAMP/protein kinase A in ECE-1(+/-) mice. Bleomycin instillation on Day 14 induced the accumulation of M2 macrophages expressing CGRP receptors in ECE-1(+/-) mice. Our results emphasize that the in vivo ECE-1-mediated degradation of CGRP promotes the transition from lung inflammation to fibrosis. Further, our study identified M2 macrophages as the target cells of CGRP action during this transition.

Endothelin-converting enzymes degrade intracellular β-amyloid produced within the endosomal/lysosomal pathway and autophagosomes

Impairments in Aβ removal are increasingly being considered as a possible cause for the abnormal Aβ build-up typical of Alzheimer disease. Of particular interest is a pool of Aβ that accumulates intraneuronally and may contribute to neuronal toxicity. The mechanism for intraneuronal accumulation, however, is not well understood and is commonly attributed to impaired removal of extracellular Aβ by neurons. Based on the intracellular distribution of the well established Aβ degrading enzymes, ECE-1 and ECE-2, we tested whether impairments in their catalytic activity could lead to intracellular Aβ accumulation. Using SH-SY5Y cells overexpressing wild-type amyloid precursor protein and pharmacological inhibition of endogenous ECE activity, we found that ECEs participate in the degradation of at least two distinct pools of Aβ; one destined for secretion and the other being produced and degraded within the endosomal-autophagic-lysosomal pathways. Although ECE-1 regulates both pools of Aβ, ECE-2 regulates mainly the intracellular pool of the peptide. Consistent with this result, ECE-2 was found to co-localize with markers of the endosomal/lysosomal pathway but not with a trans-Golgi network marker. Furthermore, ECE-2 was detected in autophagic vesicles in cells treated with chloroquine. Under these conditions, ECE inhibition produced significantly higher elevations in intracellular Aβ than chloroquine treatment alone. This study highlights the existence of Aβ clearance mechanisms by ECEs at intracellular sites of production. Alterations in ECE activity may be considered as a cause for increased intraneuronal Aβ in Alzheimer disease.

The role of ECE1 variants in cognitive ability in old age and Alzheimer's disease risk

The β-amyloid peptide may play a central role in Alzheimer's disease (AD) pathogenesis. We have evaluated variants in seven Aβ-degrading genes (ACE, ECE1, ECE2, IDE, MME, PLAU, and TF) for association with AD risk in the Genetic and Environmental Risk in Alzheimer's Disease Consortium 1 (GERAD1) cohort, and with three cognitive phenotypes in the Lothian Birth Cohort 1936 (LBC1936), using 128 and 121 SNPs, respectively. In GERAD1, we identified a significant association between a four-SNP intragenic ECE1 haplotype and risk of AD in individuals that carried at least one APOE ε4 allele (P = 0.00035, odds ratio = 1.61). In LBC1936, we identified a significant association between a different two-SNP ECE1 intragenic haplotype and non-verbal reasoning in individuals lacking the APOE ε4 allele (P = 0.00036, β = -0.19). Both results showed a trend towards significance after permutation (0.05 < P < 0.10). A follow-up cognitive genetic study evaluated the association of ECE1 SNPs in three additional cohorts of non-demented older people. Meta-analysis of the four cohorts identified the significant association (Z < 0.05) of SNPs in the ECE-1b promoter with non-verbal reasoning scores, particularly in individuals lacking the APOE ε4 allele. Our genetic findings are not wholly consistent. Nonetheless, the AD associated intronic haplotype is linked to the 338A variant of known ECE1b promoter variant, 338C>A (rs213045). We observed significantly less expression from the 338A variant in two human neuroblastoma cell lines and speculate that this promoter may be subject to tissue-specific regulation.

Neurotensin-induced proinflammatory signaling in human colonocytes is regulated by β-arrestins and endothelin-converting enzyme-1-dependent endocytosis and resensitization of neurotensin receptor 1

The neuropeptide/hormone neurotensin (NT) mediates intestinal inflammation and cell proliferation by binding of its high affinity receptor, neurotensin receptor-1 (NTR1). NT stimulates IL-8 expression in NCM460 human colonic epithelial cells by both MAP kinase- and NF-κB-dependent pathways. Although the mechanism of NTR1 endocytosis has been studied, the relationship between NTR1 intracellular trafficking and inflammatory signaling remains to be elucidated. In the present study, we show that in NCM460 cells exposed to NT, β-arrestin-1 (βARR1), and β-arrestin-2 (βARR2) translocate to early endosomes together with NTR1. Endothelin-converting enzyme-1 (ECE-1) degrades NT in acidic conditions, and its activity is crucial for NTR1 recycling. Pretreatment of NCM460 cells with the ECE-1 inhibitor SM19712 or gene silencing of βARR1 or βARR2 inhibits NT-stimulated ERK1/2 and JNK phosphorylation, NF-κB p65 nuclear translocation and phosphorylation, and IL-8 secretion. Furthermore, NT-induced cell proliferation, but not IL-8 transcription, is attenuated by the JNK inhibitor, JNK(AII). Thus, NTR1 internalization and recycling in human colonic epithelial cells involves βARRs and ECE-1, respectively. Our results also indicate that βARRs and ECE-1-dependent recycling regulate MAP kinase and NF-κB signaling as well as cell proliferation in human colonocytes in response to NT.

Nitric oxide decreases the expression of endothelin-converting enzyme-1 through mRNA destabilization

OBJECTIVE

Endothelial function depends on the equilibrium in the synthesis of vasoactive endothelial factors. It is well known that endothelin and nitric oxide (NO) exhibit reciprocal regulation. We assessed the ability of NO to regulate endothelin-converting enzyme-1 (ECE-1) expression in vascular endothelial cells.

METHODS AND RESULTS

Bovine aortic endothelial cells were incubated with 2 different NO donors as well as with a cyclic-GMP analog, dibutyryl-cGMP (dB-cGMP). ECE-1 protein content and mRNA expression were evaluated by Western blot and Northern blot, respectively, promoter activity by transfection experiments, ECE-1 activity by ELISA, and cGMP production by radioimmunoassay. Both NO donors decreased ECE-1 protein content, mRNA expression, and ECE-1 activity. ODQ, an inhibitor of soluble guanylyl cyclase, blocked those effects. NO donors raised cGMP levels, and dB-cGMP mimicked their effects on ECE-1 expression, which were blocked by KT5823, a nonspecific PKG inhibitor. The changes on ECE-1 expression were due to a destabilization on 3'-untranslated region (3'-UTR) of this mRNA, because the activity of a luciferase reporter construct containing the 3'-UTR of the ECE-1 gene was reduced by dB-cGMP in a PKG-dependent manner. The biological relevance of this regulation was confirmed in bovine aortic endothelial cells coincubated with macrophages in the presence of lipopolysaccharide, in eNOS-deficient mice, and in Wistar rats treated with NO donors. In every case, an inverse relationship was observed between NO and ECE-1 protein content.

CONCLUSION

Our results support that NO regulates ECE-1 expression through a cGMP/PKG-dependent regulatory mechanism at the post-transcriptional level via the 3'-UTR of the ECE-1 gene.

Induction of endothelin-2 expression by luteinizing hormone and hypoxia: possible role in bovine corpus luteum formation

The pattern and regulation of endothlin-2 (EDN2) expression and its putative roles in bovine ovaries were investigated. EDN2 mRNA was determined in corpus luteum (CL) and during folliculoluteal transition induced by GnRH in vivo. EDN2 was elevated only in the early CL and was not present in older CL. In the young CL, EDN2 mRNA was identified mainly in luteal cells but not endothelial cells that expressed the EDN1 gene. Similarly, in preovulatory follicles, EDN2 was expressed in the granulosa cells (GCs) and not in the vascular theca interna. LH and hypoxia are two major stimulants of CL formation. Therefore, GCs were cultured with bovine LH, under hypoxic conditions. GCs incubated with bovine LH resulted in increased EDN2 mRNA 42 h later. CoCl2, a hypoxia-mimicking agent, elevated EDN2 in GCs in a dose-dependent manner. Incubation of the human GC line (Simian virus 40 large T antigen) under low oxygen tension (1%) augmented EDN2 6 and 24 h later. In these two cell types, along with EDN2, hypoxia augmented VEGF. EDN2 induced in GCs changes that characterize the developing CL: cell proliferation as well as up-regulation of vascular endothelial growth factor and cyclooxygenase-2 (mRNA and protein levels). Human chorionic gonadotropin also up-regulated these two genes. Small interfering RNA targeting EDN-converting enzyme-1 effectively reduced its mRNA levels. This treatment, expected to lower the mature EDN2 peptide production, inhibited VEGF mRNA levels and GC numbers. Together these data suggest that elevated EDN2 in the early bovine CL, triggered by LH surge and hypoxia, may facilitate CL formation by promoting angiogenesis, cell proliferation, and differentiation.

Endothelin evokes distinct calcium transients in neuronal and non-neuronal cells of rat olfactory mucosa primary cultures

The olfactory system is regulated by several nervous and hormonal factors, and there is a growing body of evidence that some of these modulations already take place in the olfactory mucosa (OM). We recently suggested that, among others, vasoactive peptides might play multifaceted roles in different OM cells. Here we studied the effect of the vasoconstrictive peptide endothelin (ET) in the rat OM. We identified different components of the ET system both in the olfactory mucosa and in long-term primary culture of OM cells, composed of olfactory sensory neurons (OSNs) lying on a blend of non-neuronal OM cells (nNCs). We demonstrated that ET receptors are differentially expressed on OM cells, and that ET might be locally matured by the endothelin-converting enzyme ECE-1 located in OSNs. Using calcium imaging, we showed that ET triggers robust dose-dependent Ca(2+) responses in most OM cells, which consist of a transient phase, followed, in nNCs, by a sustained plateau phase. All transient responses depended on intracellular calcium release, while the sustained plateau phase also depended on subsequent external calcium entry. Using both pharmacology and spotting lethal (sl/sl) mutant rats, lacking functional ET(B) receptors, we finally demonstrated that these effects of ET are mediated through ET(B) receptors in OSNs and ET(A) receptors in nNCs.The present study therefore identifies endothelin as a potent endogenous modulator of the olfactory mucosa; specific endothelin-mediated Ca(2+) signals may serve distinct signaling functions, and thereby suggest differential functional roles of endothelin in both neuronal and non-neuronal OM cells.

Identification of novel proteins in isolated polyphosphate vacuoles in the primitive red alga Cyanidioschyzon merolae

Plant vacuoles are organelles bound by a single membrane, and involved in various functions such as intracellular digestion, metabolite storage, and secretion. To understand their evolution and fundamental mechanisms, characterization of vacuoles in primitive plants would be invaluable. Algal cells often contain polyphosphate-rich compartments, which are thought to be the counterparts of seed plant vacuoles. Here, we developed a method for isolating these vacuoles from Cyanidioschyzon merolae, and identified their proteins by MALDI TOF-MS. The vacuoles were of unexpectedly high density, and were highly enriched at the boundary between 62 and 80% w/v iodixanol by density-gradient ultracentrifugation. The vacuole-containing fraction was subjected to SDS-PAGE, and a total of 46 proteins were identified, including six lytic enzymes, 13 transporters, six proteins for membrane fusion or vesicle trafficking, five non-lytic enzymes, 13 proteins of unknown function, and three miscellaneous proteins. Fourteen proteins were homologous to known vacuolar or lysosomal proteins from seed plants, yeasts or mammals, suggesting functional and evolutionary relationships between C. merolae vacuoles and these compartments. The vacuolar localization of four novel proteins, namely CMP249C (metallopeptidase), CMJ260C (prenylated Rab receptor), CMS401C (ABC transporter) and CMT369C (o-methyltransferase), was confirmed by labeling with specific antibodies or transient expression of hemagglutinin-tagged proteins. The results presented here provide insights into the proteome of C. merolae vacuoles and shed light on their functions, as well as indicating new features.

Therapeutic potential of endothelin receptor modulators: lessons from human clinical trials

The endothelin system, and in particular endothelin receptors, are targets for therapeutic intervention in human diseases. Endothelin receptor antagonists have reached clinical use for treating pulmonary arterial hypertension, and are under clinical investigation for several other diseases, such as cancer, vasospasm or fibrogenic diseases. We review the molecules that have been evaluated in the main clinical trials, from the point of view of receptor selectivity and of their chemical characteristics which were important for efficacy in pulmonary hypertension. We will also discuss future use of antagonists to endothelin receptor(s) in several human diseases and what should be the necessary properties of the future molecules for efficacy in diseases where the presently tested molecules displayed suboptimal efficacy.

Regulation of vascular contractility and blood pressure by the E2F2 transcription factor

BACKGROUND

Recent studies have identified a polymorphism in the endothelin-converting enzyme (ECE)-1b promoter (-338C/A) that is strongly associated with hypertension in women. The polymorphism is located in a consensus binding sequence for the E2F family of transcription factors. E2F proteins are crucially involved in cell-cycle regulation, but their roles in cardiovascular function are poorly understood. Here, we investigated the potential role of E2F2 in blood pressure regulation.

METHODS AND RESULTS

Tail-cuff measurements of systolic and diastolic blood pressures were significantly higher in E2F2-null (E2F2(-/-)) mice than in their wild-type littermates, and in ex vivo ring assays, aortas from the E2F2(-/-) mice exhibited significantly greater contractility in response to big endothelin-1. Big endothelin-1 is activated by ECE-1, and mRNA levels of ECE-1b, the repressive ECE-1 isoform, were significantly lower in E2F2(-/-) mice than in wild-type mice. In endothelial cells, chromatin immunoprecipitation assays confirmed that E2F2 binds the ECE-1b promoter, and promoter-reporter assays indicated that E2F2 activates ECE-1b transcription. Furthermore, loss or downregulation of E2F2 led to a decline in ECE-1b levels, to higher levels of the membranous ECE-1 isoforms (ie, ECE-1a, -1c, and -1d), and to deregulated ECE-1 activity. Finally, Sam68 coimmunoprecipitated with E2F2, occupied the ECE-1b promoter (chromatin immunoprecipitation), and repressed E2F2-mediated ECE-1b promoter activity (promoter-reporter assays).

CONCLUSIONS

Our results identify a cell-cycle-independent mechanism by which E2F2 regulates endothelial function, arterial contractility, and blood pressure.

Role of protein kinase C in the expression of endothelin converting enzyme-1

Increased expression of endothelin converting enzyme-1 (ECE-1) is associated with diabetic nephropathy. The molecular mechanisms underlying this association, as yet unknown, possibly involve protein kinase C (PKC) pathways. In the present study, we examined the effects of high glucose and PKC activation on ECE-1 expression in primary human umbilical vein endothelial cells (HUVECs) and in HUVEC line (EA.hy926). Increasing glucose concentration, but not mannitol, from 5.5-22.2 mmol/liter for 3 d, enhanced prepro endothelin-1 (ET-1) mRNA expression, ET-1 levels, ECE-1 protein, and mRNA expressions by 7, 4, 20, and 2.6-fold, respectively. High glucose increased ECE-1 protein expression dose and time dependently. By Western blot analysis, PKC-beta1, -beta2, and -delta isoform levels were significantly increased relative to other isoforms when glucose level was increased. Treatment with Rottlerin, a PKC-delta isoform inhibitor, reduced significantly the glucose-induced ET-1 secretion, and ECE-1 protein expression, but (S)-13-[(dimethylamino)methyl]-10,11,14,15-tetrahydro-4,9:16,21-dimetheno 1H,1(3)H-dibenzo[e,k]pyrrolo[3,4-h] (1, 4, 3) oxadiaza-cyclohexadecene-1,3(2H)-dione or Gö6976, specific PKC-beta and -alpha inhibitors, respectively, did not. Overexpression of PKC-delta but not PKC-alpha or -beta1 isoforms by adenovirus vector containing the respective cDNA in HUVECs incubated with 5.5 mmol/liter glucose, increased in parallel PKC proteins, and glucose-induced endothein-1 and ECE-1 protein expression by 4- to 6-fold. These results show that enhanced ECE-1 expression induced by hyperglycemia is partly due to activation of the PKC-delta isoform. Thus, inhibition of this PKC isoform may prevent diabetes-related increase in ET-1.

Endothelin-converting enzyme 1 promotes re-sensitization of neurokinin 1 receptor-dependent neurogenic inflammation

BACKGROUND AND PURPOSE

The metalloendopeptidase endothelin-converting enzyme 1 (ECE-1) is prominently expressed in the endothelium where it converts big endothelin to endothelin-1, a vasoconstrictor peptide. Although ECE-1 is found in endosomes in endothelial cells, the role of endosomal ECE-1 is unclear. ECE-1 degrades the pro-inflammatory neuropeptide substance P (SP) in endosomes to promote recycling and re-sensitization of its neurokinin 1 (NK(1)) receptor. We investigated whether ECE-1 regulates NK(1) receptor re-sensitization and the pro-inflammatory effects of SP in the endothelium.

EXPERIMENTAL APPROACH

We examined ECE-1 expression, SP trafficking and NK(1) receptor re-sensitization in human microvascular endothelial cells (HMEC-1), and investigated re-sensitization of SP-induced plasma extravasation in rats.

KEY RESULTS

HMEC-1 expressed all four ECE-1 isoforms (a-d), and fluorescent SP trafficked to early endosomes containing ECE-1b/d. The ECE-1 inhibitor SM-19712 prevented re-sensitization of SP-induced Ca2+ signals in HMEC-1 cells. Immunoreactive ECE-1 and NK(1) receptors co-localized in microvascular endothelial cells in the rat. SP-induced extravasation of Evans blue in the urinary bladder, skin and ears of the rat desensitized when the interval between two SP injections was 10 min, and re-sensitized after 480 min. SM-19712 inhibited this re-sensitization.

CONCLUSIONS AND IMPLICATIONS

By degrading endocytosed SP, ECE-1 promotes the recycling and re-sensitization of NK(1) receptors in endothelial cells, and thereby induces re-sensitization of the pro-inflammatory effects of SP. Thus, ECE-1 inhibitors may ameliorate the pro-inflammatory actions of SP.

Isoforms of endothelin-converting enzyme-1 (ECE-1) have opposing effects on prostate cancer cell invasion

Cross-talk between tumour and stromal cells can profoundly influence cancer cell invasion by increasing the availability of mitogenic peptides such as endothelin-1 (ET-1). Endothelin-1 is elevated in men with metastatic prostate cancer (PC), and can exert both an autocrine (epithelial) and a paracrine (stromal) influence on growth. Endothelin-1 is generated from its inactive precursor big-ET-1 by endothelin-converting enzyme 1 (ECE-1). We and others have demonstrated that ECE-1 expression is significantly elevated in tumours and surrounding stromal tissue. Our current data show siRNA-mediated knockdown of stromal ECE-1 reduces epithelial (PC-3) cell invasion in coculture. Interestingly, readdition of ET-1 only partially recovers this effect suggesting a novel role for ECE-1 independent of ET-1 activation. Parallel knockdown of ECE-1 in both stromal and epithelial compartments results in an additive decrease in cell invasion. We extrapolated this observation to the four recognised isoforms ECE-1a, ECE-1b, ECE-1c and ECE-1d. Only ECE-1a and ECE-1c were significant but with reciprocal effects on cell invasion. Transient ECE-1c overexpression increased PC-3 invasiveness through matrigel, whereas transient ECE-1a expression suppressed invasion. Furthermore, transient ECE-1a expression in stromal cells strongly counteracts the effect of transient ECE-1c expression in PC-3 cells. The ECE-1 isoforms may, therefore, be relevant targets for antiinvasive therapy in prostate and other cancers.

Adeno-associated viral (AAV) serotype 5 vector mediated gene delivery of endothelin-converting enzyme reduces Abeta deposits in APP + PS1 transgenic mice

Reduction of Abeta deposition is a major therapeutic strategy in Alzheimer's disease (AD). The concentration of Abeta in the brain is modulated not only by Abeta production but also by its degradation. One of the proteases involved in the degradation of Abeta peptides is endothelin-converting enzyme (ECE). In this study, we investigated the effects of an intracranial administration of a seroptype 5 recombinant adeno-associated viral vector (rAAV) containing the ECE-1 synthetic gene on amyloid deposition in amyloid precursor protein (APP) plus presenilin-1 (PS1) transgenic mice. The rAAV vector was injected unilaterally into the right anterior cortex and hippocampus of 6-month-old mice, while control mice received an AAV vector expressing green fluorescent protein (GFP). Immunohistochemical testing for the hemagglutinin (HA) tag appended to ECE revealed strong expression in areas surrounding the injection sites but minimal expression in the contralateral regions. Immunohistochemical tests showed that Abeta decreases in the anterior cortex and hippocampus in mice receiving the ECE synthetic gene. Further, decreases in Congo red positive deposits were also observed in both regions. These results indicate that increasing the expression of beta-amyloid degrading enzymes through gene therapy is a promising approach to the treatment of AD.

The ovarian endothelin network: an evolving story

The endothelin (ET) system consists of three ET isopeptides, several converting enzyme isoforms and two G-protein-coupled receptors, ETA and ETB, which are linked to multiple signaling pathways. Less than 20 years after the initial detection of ET-1 in granulosa cells, the ovarian ET network continues to expand with the discovery of new members and functions. ETs influence a broad range of essential reproductive processes, such as ovulation, steroidogenesis and luteolysis. Therefore, a more comprehensive understanding of the ovarian ET network might provide new strategies for controlling reproduction. This review presents up-to-date findings on the ET network in the ovary.

Endothelin-converting enzyme-1 regulates endosomal sorting of calcitonin receptor-like receptor and beta-arrestins

Although cell surface metalloendopeptidases degrade neuropeptides in the extracellular fluid to terminate signaling, the function of peptidases in endosomes is unclear. We report that isoforms of endothelin-converting enzyme-1 (ECE-1a–d) are present in early endosomes, where they degrade neuropeptides and regulate post-endocytic sorting of receptors. Calcitonin gene-related peptide (CGRP) co-internalizes with calcitonin receptor-like receptor (CLR), receptor activity-modifying protein 1 (RAMP1), β-arrestin2, and ECE-1 to early endosomes, where ECE-1 degrades CGRP. CGRP degradation promotes CLR/RAMP1 recycling and β-arrestin2 redistribution to the cytosol. ECE-1 inhibition or knockdown traps CLR/RAMP1 and β-arrestin2 in endosomes and inhibits CLR/RAMP1 recycling and resensitization, whereas ECE-1 overexpression has the opposite effect. ECE-1 does not regulate either the resensitization of receptors for peptides that are not ECE-1 substrates (e.g., angiotensin II), or the recycling of the bradykinin B₂ receptor, which transiently interacts with β-arrestins. We propose a mechanism by which endosomal ECE-1 degrades neuropeptides in endosomes to disrupt the peptide/receptor/β-arrestin complex, freeing internalized receptors from β-arrestins and promoting recycling and resensitization.

Endothelin-converting enzyme 1 degrades neuropeptides in endosomes to control receptor recycling

Neuropeptide signaling requires the presence of G protein-coupled receptors (GPCRs) at the cell surface. Activated GPCRs interact with beta-arrestins, which mediate receptor desensitization, endocytosis, and mitogenic signaling, and the peptide-receptor-arrestin complex is sequestered into endosomes. Although dissociation of beta-arrestins is required for receptor recycling and resensitization, the critical event that initiates this process is unknown. Here we report that the agonist availability in the endosomes, controlled by the membrane metalloendopeptidase endothelin-converting enzyme 1 (ECE-1), determines stability of the peptide-receptor-arrestin complex and regulates receptor recycling and resensitization. Substance P (SP) binding to the tachykinin neurokinin 1 receptor (NK1R) induced membrane translocation of beta-arrestins followed by trafficking of the SP-NK1R-beta-arrestin complex to early endosomes containing ECE-1a-d. ECE-1 degraded SP in acidified endosomes, disrupting the complex; beta-arrestins returned to the cytosol, and the NK1R, freed from beta-arrestins, recycled and resensitized. An ECE-1 inhibitor, by preventing NK1R recycling in endothelial cells, inhibited resensitization of SP-induced inflammation. This mechanism is a general one because ECE-1 similarly regulated NK3R resensitization. Thus, peptide availability in endosomes, here regulated by ECE-1, determines the stability of the peptide-receptor-arrestin complex. This mechanism regulates receptor recycling, which is necessary for sustained signaling, and it may also control beta-arrestin-dependent mitogenic signaling of endocytosed receptors. We propose that other endosomal enzymes and transporters may similarly control the availability of transmitters in endosomes to regulate trafficking and signaling of GPCRs. Antagonism of these endosomal processes represents a strategy for inhibiting sustained signaling of receptors, and defects may explain the tachyphylaxis of drugs that are receptor agonists.

Mechanisms of reduced luteal sensitivity to prostaglandin F2alpha during maternal recognition of pregnancy in ewes

During maternal recognition of pregnancy, the conceptus stimulates endometrial secretion of PGF2alpha and PGE2. However, PGF2alpha is less effective in causing luteal regression in pregnant than in non-pregnant ewes. Experiments were conducted to elucidate mechanisms for reduced luteal sensitivity to PGF2alpha during maternal recognition of pregnancy. Corpora lutea (CL) were collected from pregnant and non-pregnant ewes 0, 4, or 12h following treatment with PGF2alpha on day 12 after estrus. Luteal PTGHS2 mRNA did not differ due to PGF2alpha or pregnancy status. Luteal PTGES mRNA was reduced in both pregnant and non-pregnant ewes after PGF2alpha treatment; while, luteal PTGFS mRNA was reduced 4h after PGF2alpha in pregnant, but not non-pregnant ewes. The result was a greater ratio of PTGES to PTGFS mRNA in pregnant ewes. Luteal mRNA for HPGD did not differ between pregnant and non-pregnant ewes on day 12. Luteal END1 mRNA was reduced in pregnant as compared to non-pregnant ewes prior to PGF2alpha challenge. Luteal END1 mRNA was increased after PGF2alpha in pregnant and non-pregnant ewes; however, ECE1 mRNA was reduced 4h after PGF2alpha in pregnant, but not non-pregnant ewes. The in vitro conversion of PGF2alpha to PGFM was greater in CL of pregnant than non-pregnant ewes at day 14. Luteal conversion of PGF2alpha to PGFM appears to be regulated post-transcriptionally. During maternal recognition of pregnancy, mechanisms of reduced luteal sensitivity to PGF2alpha may include a shift in prostaglandin production to the luteotropin PGE2, a reduction of ECE1 mRNA, and increased catabolism of PGF2alpha.

A novel signal transduction cascade involving direct physical interaction of the renin/prorenin receptor with the transcription factor promyelocytic zinc finger protein

A human renin/prorenin receptor (RER) has recently been cloned. To gain insight into the molecular function of the RER, we studied its signal transduction mechanisms. Initially, we found a ubiquitous and intracellular expression pattern of the human RER. Consistently, we observed several transcriptional start sites and a high promoter activity of the human RER. We could identify the transcription factor promyelocytic zinc finger (PLZF) protein as a direct protein interaction partner of the C-terminal domain of the RER by yeast 2-hybrid screening and coimmunoprecipitation. Coimmunoprecipitation experiments also indicated homodimerization of the RER. On activation of the RER by renin, PLZF is translocated into the nucleus and represses transcription of the RER itself, thereby creating a very short negative feedback loop, but activates transcription of the p85alpha subunit of the phosphatidylinositol-3 kinase (PI3K-p85alpha). Small interfering RNA against the RER abolished these effects. A PLZF cis-element in the RER promoter was identified by site-directed mutagenesis and electrophoretic mobility-shift assay. Renin stimulation caused a 6-fold recruitment of PLZF to this promoter region as shown by chromatin immunoprecipitation. Moreover, renin stimulation of rat H9c2 cardiomyoblasts induced an increase of cell number and a decrease of apoptosis. These effects were partly abolished by PI3K inhibition and completely abrogated by small interfering RNA against PLZF. Finally, experiments in PLZF knockout mice confirmed the role of PLZF as an upstream regulator of RER and PI3K-p85alpha. Our data demonstrate the existence of a novel signal transduction pathway involving the ligand renin, RER, and the transcription factor PLZF, which is of physiological and putative pathophysiological relevance.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

The influence of the endothelin-converting enzyme-1 gene polymorphism on the progression of autosomal dominant polycystic kidney disease

BACKGROUND; A significant phenotypical variability is observed in autosomal dominant polycystic kidney disease (ADPKD), the most common renal hereditary disease. Endothelin-1 (ET-1) has been suggested to be an important disease-promoting factor of the kidney. Endothelin-converting enzyme-1 (ECE-1) is the main protease responsible for ET-1 generation by cleavage of its functionally inactive precursor. We examined the influence of the ECE-1b C-338A polymorphism on the progression of ADPKD toward end-stage renal disease (ESRD). The A allele was suggested to be associated with higher plasma level of ET-1.

METHODS

200 ADPKD patients (107 males, 93 females) who had reached ESRD were analyzed. Patients were divided into three groups: (1) 47 patients (23 males, 24 females) with ESRD later than in 63 yr (slow progressors); (2) 71 patients (38 males, 33 females) with ESRD before 45 yr (rapid progressors); and (3) 82 patients (46 males, 36 females) with ESRD between 45-63 yr. Moreover, we analyzed 160 genetically unrelated healthy Czech subjects as the control group (82 males, 78 females, mean age 51.4 +/- 8.2 yr). DNA samples from collected blood were genotyped for ECE-1b C-338A polymorphism using described polymerase chain reaction (PCR) followed by restriction enzyme digestion. We compared the frequencies of different genotypes between the groups of slow and rapid progressors and the ages of ESRD with regard to different genotypes.

RESULTS

The ECE-1b C-338A genotype distribution showed no differences among the groups of slow progressors, rapid progressors, ADPKD group with ESRD between 45-63 yr and control group. Comparing the ages of ESRD of all patients, we did not find significant differences in the ages with regard to different genotypes: CC (51.5 +/- 10.1 yr), AC (51.6 +/- 11.4 yr), AA (48.2 +/- 5.9 yr). There was a tendency to lower age of ESRD in AA homozygotes in comparison with other genotypes (t-test, p = 0.12). We found no influence of gender.

CONCLUSION

We excluded the effect of ECE-1b C-338A polymorphism on the progression of ADPKD. We could observe a mild tendency toward faster decline of renal function in AA homozygous individuals.

Protein Kinase C Regulates the Cell Surface Activity of Endothelin-Converting Enzyme-1

The potent vasoconstrictor endothelin is a 21 amino acid peptide whose principal physiological function is to regulate vascular tone. The generation of endothelin is crucially dependent on the local presence and activity of endothelin converting enzyme-1 (ECE-1) expressed on the surface of vascular endothelial cells. In this study, we have shown in endothelial cells that the enzyme is phosphorylated, and that phosphorylation is increased by phorbol ester stimulation of protein kinase C (PKC). Furthermore, by monitoring specific ECE-1 activity on the surface of live cells, we also show that following PKC activation, enzyme activity is significantly increased at the cell surface, where it is positioned to catalyse the generation of active endothelin. We believe this novel finding is unprecedented for a peptide processing enzyme. Indeed, this new knowledge regarding the control of endothelin production by regulating ECE-1 activity at the cell surface opens up a new area of endothelin biology and will provide novel insights into the physiology and pathophysiology of endothelin and endothelin-associated diseases. In addition, the information generated in these studies may provide valuable new insights into potential extra- and intracellular targets for the pharmacological and perhaps even therapeutic regulation of endothelin production and thus vascular tone.

Genomic organisation of the mouse gene encoding endothelin-converting enzyme-1 (ECE-1) and mRNA expression of ECE-1 isoforms in murine tissues

Mouse knockout-models have previously revealed important biological functions of endothelin-converting enzyme-1 (ECE-1) in normal cardiac and craniofacial development. Since human ECE-1 is expressed in various isoforms, termed a, b, c, and d, expression of which is controlled by alternative promoters, we postulated that corresponding isoforms may also be transcribed from the murine Ece1 gene. By comparative sequence analysis using exon-specific sequences of human and rat ECE-1 we have resolved the complete exon-intron structure of the murine Ece1 locus on chromosome 4. The murine Ece1 gene comprises 23 exons distributed over 100 kb of genomic DNA and was found to be structurally highly conserved when compared to the human ECE1 gene. As with the human gene, the exons containing isoform-specific sequences were localised in the 5' terminal region of the murine Ece1 gene. Using specific sense primers, isoform-specific expression of murine ECE-1 mRNA in various mouse tissues was confirmed by RT-PCR. Using real-time PCR we demonstrated that ECE-1c was the most abundantly expressed isoform in most tissues, except for heart and aorta displaying a more even isoform distribution. We detected an additional isoform-specific exon, designated c2, which was apparently constitutively spliced and expressed only as minor fraction of ECE-1c transcripts. Our results provide evidence of structural conservation of mammalian genes encoding ECE-1 and will facilitate a more refined analysis of ECE-1 mRNA expression in the mouse model organism.

Increased immunoreactivities against endothelin-converting enzyme-1 and monocyte chemotactic protein-1 in hepatic stellate cells of rat fibrous liver induced by thioacetamide

The progression of rat liver fibrosis induced by intraperitoneal administration of thioacetamide (TAA) was evaluated by immunocytochemistry using anti-alpha-smooth muscle actin (alpha-SMA), antiendothelin-converting enzyme (ECE)-1, and anti-monocyte chemotactic protein (MCP)-1 antibodies. The fibrous septal spaces gradually increased after administration of TAA, and pseudolobules were established in the 7-week TAA-treated groups. Immunoreactivities against alpha-SMA were not detected in hepatic stellate cells (HSCs) of the control group without TAA treatment, although they were observed in the HSCs around the fibrous septal spaces in all TAA-treated groups, indicating that activation of HSCs occurs during the establishment of pseudolobules. Immunoreactivities against ECE-1 and MCP-1 were seen in such HSCs of the TAA-treated groups, but few or no immunoreactivities were detected in the HSCs of the control group. The most significant increase in the ECE-1 immunoreactivities was detected in the 1-week TAA-treated group, whereas that in MCP-1 was observed in the 7-week TAA-treated group. The present immunocytochemistry indicated a difference in the accelerated expression period between immunoreactivities against ECE-1 and MCP-1 in the HSCs during the progression of TAA-induced liver fibrosis, suggesting that ECE-1 is involved in the early phase of liver fibrosis and that MCP-1 plays a role during the later phase.

Endothelin-converting Enzyme-1, Abundance of Isoforms a-d and Identification of a Novel Alternatively Spliced Variant Lacking a Transmembrane Domain

Endothelin-converting enzyme-1 (ECE-1) cleaves big endothelins, as well as bradykinin and beta-amyloid peptide. Several isoforms of ECE-1 (a-d) have been identified to date; they differ only in their NH(2) terminus but share the catalytic domain located in the COOH-terminal end. Using quantitative PCR, we found ECE-1d to be the most abundant type in several endothelial cells (EC) types. In addition to full-length ECE-1 forms we have identified novel, alternatively spliced mRNAs of ECE-1 b-d. These splice variants (SVs) lack exon 3', which codes for the transmembrane region and is present in full-length forms. SVs mRNA were highly expressed in EC derived from macro and microvascular beds but much less so in other, non-endothelial cells expressing ECE-1, which suggests that the splicing mechanism is cell-specific. Analyses of ECE-1d and its SV form in stably transfected HEK-293 cells revealed that both proteins were recognized by anti COOH-terminal ECE-1 antibodies, but anti NH(2)-terminal antibodies only bound ECE-1d. The novel protein, designated ECE-1 sv, has an apparent molecular mass of 75 kDa; by using site-directed mutagenesis its start site was identified in a region common to all ECE-1 forms suggesting that ECE-1 b-d SV mRNAs are translated into the same protein. In agreement with the findings demonstrating common COOH terminus for ECE-1sv and ECE-1d, both exhibited a similar catalytic activity. However, immunofluorescence staining and differential centrifugation revealed a distinct intracellular localization for these two proteins. The presence of ECE-1sv in different cellular compartments than full-length forms of the enzyme may suggest a distinct physiological role for these proteins.

Vascular endothelin in hypertension

Endothelins are powerful vasoconstrictor peptides that also play numerous other functions in many different organs. Endothelin-1 (ET-1) is the most abundant and important of this family of peptides in blood vessels. Production of ET-1 is increased in the endothelium and the kidney in salt-dependent models of hypertension (e.g.: DOCA-salt rats and Dahl salt-sensitive rats, in salt-loaded SHR-SP, in angiotensin II-infused and in diabetic rats). ET-1 elicits an inflammatory response by increasing oxidant stress in the vascular wall, which induces vascular remodeling and endothelial dysfunction found in the hypertensive models that exhibit an endothelin-mediated component. Endothelin receptor antagonism reduces blood pressure and vascular hypertrophic remodeling present in these hypertensive models. Patients with stage 2 hypertension have enhanced vascular expression of ET-1. Endothelin receptor antagonists lower blood pressure in hypertensive patients. They could become therapeutic agents for prevention of target organ damage in hypertension and in type 2 diabetes, chronic renal failure and congestive heart failure. Side effects of endothelin receptor blockers have prevented up to the present their development for these indications. New endothelin antagonists devoid of these side effects, or alternatively inhibitors of the endothelin converting enzymes that generate ET-1 may in the future become available to block the endothelin system. However, to date endothelin antagonists have been approved only for the treatment of primary pulmonary hypertension, a rapidly fatal condition in which the endothelin system plays an important role and endothelin antagonists exert favorable effects.