Transcription of testicular angiotensin-converting enzyme (ACE) is initiated within the 12th intron of the somatic ACE gene

Purification and characterization of angiotensin-converting enzyme (ACE) from sheep lung

Angiotensin-converting enzyme (ACE, EC 3.4.15.1) in the renin-angiotensin system regulates blood pressure by catalyzing angiotensin I to the vasoconstrictor angiotensin II. In this study, the ACE was purified and characterized from sheep lung. The kinetic properties of the ACE were designated. The inhibition effect of captopril, a specific ACE inhibitor, was determined. ACE was purified from sheep lung using the affinity chromatography method in one step. NHS-activated Sepharose 4 Fast Flow as column filler and lisinopril as a ligand in this method used. The molecular weight and purity of ACE were designated using the SDS-PAGE method. Optimum temperature and optimum pH were found for purified ACE. K_M and V_max values from Lineweaver–Burk charts determined. The inhibition type, IC₅₀, and K_i values of captopril on purified ACE were identified. ACE was 6405-fold purified from sheep lung by affinity chromatography in one step and specific activity was 16871 EU/mg protein. The purity and molecular weight of ACE were found with SDS-PAGE and observed two bands at around 60 kDa and 70 kDa on the gel. Optimum temperature and optimum pH were designated for purified ACE. Optimum temperature and pH were found as 40 °C and pH 7.4, respectively. V_max and K_M values were calculated to be 35.59 (µmol/min).mL⁻¹ and 0.18 mM, respectively. IC₅₀ value of captopril was found as 0.51 nM. The inhibition type of captopril was determined as non-competitive from the Lineweaver–Burk graph and the K_i value was 0.39 nM. As a result, it was observed in this study that the ACE enzyme can be successfully purified from sheep lungs in one step. Also, it was determined that captopril, which is a specific ACE inhibitor, has a significant inhibitory effect with a very low IC₅₀ value of 0.51 nM.

Regulation of Male Fertility by the Renin-Angiotensin System

The renin-angiotensin system (RAS) is a peptidic system known mainly for its roles in the maintenance of blood pressure and electrolyte and fluid homeostasis. However, several tissues and cells have been described to possess an intrinsic RAS that acts locally through different paracrine and autocrine mechanisms. In the male reproductive system, several components of this system have been observed in various organs and tissues, such as the testes, spermatozoa and seminal fluid. Some functions attributed to this local RAS are maintenance of seminal plasma electrolytes, regulation of steroidogenesis and spermatogenesis, and sperm functions. However, their specific actions in these locations are not fully understood. Therefore, a deep knowledge of the functions of the RAS at both the testicular and seminal levels could clarify its roles in male infertility and sperm physiology, and the different RAS elements could be used to design tools enabling the diagnosis and/or treatment of male infertility.

ACE2 receptor polymorphism: Susceptibility to SARS-CoV-2, hypertension, multi-organ failure, and COVID-19 disease outcome

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emerged in Chinese people in December 2019 and has currently spread worldwide causing the COVID-19 pandemic with more than 150,000 deaths. In order for a SARS-CoV like virus circulating in wild life for a very long time to infect the index case-patient, a number of conditions must be met, foremost among which is the encounter with humans and the presence in homo sapiens of a cellular receptor allowing the virus to bind. Recently it was shown that the SARS-CoV-2 spike protein, binds to the human angiotensin I converting enzyme 2 (ACE2). This molecule is a peptidase expressed at the surface of lung epithelial cells and other tissues, that regulates the renin-angiotensin-aldosterone system. Humans are not equal with respect to the expression levels of the cellular ACE2. Moreover, ACE2 polymorphisms were recently described in human populations. Here we review the most recent evidence that ACE2 expression and/or polymorphism could influence both the susceptibility of people to SARS-CoV-2 infection and the outcome of the COVID-19 disease. Further exploration of the relationship between the virus, the peptidase function of ACE2 and the levels of angiotensin II in SARS-CoV-2 infected patients should help to better understand the pathophysiology of the disease and the multi-organ failures observed in severe COVID-19 cases, particularly heart failure.

N-acetyl-seryl-aspartyl-lysyl-proline is a valuable endogenous antifibrotic peptide for kidney fibrosis in diabetes: An update and translational aspects

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is an endogenous peptide that has been confirmed to show excellent organ-protective effects. Even though originally discovered as a modulator of hemotopoietic stem cells, during the recent two decades, AcSDKP has been recognized as valuable antifibrotic peptide. The antifibrotic mechanism of AcSDKP is not yet clear; we have established that AcSDKP could target endothelial-mesenchymal transition program through the induction of the endothelial fibroblast growth factor receptor signaling pathway. Also, recent reports suggested the clinical significance of AcSDKP. The aim of this review was to update recent advances of the mechanistic action of AcSDKP and discuss translational research aspects.

How many human proteoforms are there?

Despite decades of accumulated knowledge about proteins and their post-translational modifications (PTMs), numerous questions remain regarding their molecular composition and biological function. One of the most fundamental queries is the extent to which the combinations of DNA-, RNA- and PTM-level variations explode the complexity of the human proteome. Here, we outline what we know from current databases and measurement strategies including mass spectrometry-based proteomics. In doing so, we examine prevailing notions about the number of modifications displayed on human proteins and how they combine to generate the protein diversity underlying health and disease. We frame central issues regarding determination of protein-level variation and PTMs, including some paradoxes present in the field today. We use this framework to assess existing data and to ask the question, "How many distinct primary structures of proteins (proteoforms) are created from the 20,300 human genes?" We also explore prospects for improving measurements to better regularize protein-level biology and efficiently associate PTMs to function and phenotype.

Angiotensin-converting enzyme in innate and adaptive immunity

Angiotensin-converting enzyme (ACE) - a zinc-dependent dicarboxypeptidase with two catalytic domains - plays a major part in blood pressure regulation by converting angiotensin I to angiotensin II. However, ACE cleaves many peptides besides angiotensin I and thereby affects diverse physiological functions, including renal development and male reproduction. In addition, ACE has a role in both innate and adaptive responses by modulating macrophage and neutrophil function - effects that are magnified when these cells overexpress ACE. Macrophages that overexpress ACE are more effective against tumours and infections. Neutrophils that overexpress ACE have an increased production of superoxide, which increases their ability to kill bacteria. These effects are due to increased ACE activity but are independent of angiotensin II. ACE also affects the display of major histocompatibility complex (MHC) class I and MHC class II peptides, potentially by enzymatically trimming these peptides. Understanding how ACE expression and activity affect myeloid cells may hold great promise for therapeutic manipulation, including the treatment of both infection and malignancy.

Angiotensin-converting enzyme in innate and adaptive immunity

Angiotensin-converting enzyme (ACE) - a zinc-dependent dicarboxypeptidase with two catalytic domains - plays a major part in blood pressure regulation by converting angiotensin I to angiotensin II. However, ACE cleaves many peptides besides angiotensin I and thereby affects diverse physiological functions, including renal development and male reproduction. In addition, ACE has a role in both innate and adaptive responses by modulating macrophage and neutrophil function - effects that are magnified when these cells overexpress ACE. Macrophages that overexpress ACE are more effective against tumours and infections. Neutrophils that overexpress ACE have an increased production of superoxide, which increases their ability to kill bacteria. These effects are due to increased ACE activity but are independent of angiotensin II. ACE also affects the display of major histocompatibility complex (MHC) class I and MHC class II peptides, potentially by enzymatically trimming these peptides. Understanding how ACE expression and activity affect myeloid cells may hold great promise for therapeutic manipulation, including the treatment of both infection and malignancy.

Classical Renin-Angiotensin system in kidney physiology

The renin-angiotensin system has powerful effects in control of the blood pressure and sodium homeostasis. These actions are coordinated through integrated actions in the kidney, cardiovascular system and the central nervous system. Along with its impact on blood pressure, the renin-angiotensin system also influences a range of processes from inflammation and immune responses to longevity. Here, we review the actions of the "classical" renin-angiotensin system, whereby the substrate protein angiotensinogen is processed in a two-step reaction by renin and angiotensin converting enzyme, resulting in the sequential generation of angiotensin I and angiotensin II, the major biologically active renin-angiotensin system peptide, which exerts its actions via type 1 and type 2 angiotensin receptors. In recent years, several new enzymes, peptides, and receptors related to the renin-angiotensin system have been identified, manifesting a complexity that was previously unappreciated. While the functions of these alternative pathways will be reviewed elsewhere in this journal, our focus here is on the physiological role of components of the "classical" renin-angiotensin system, with an emphasis on new developments and modern concepts.

Hypertensive epigenetics: from DNA methylation to microRNAs

The major epigenetic features of mammalian cells include DNA methylation, posttranslational histone modifications and RNA-based mechanisms including those controlled by small non-coding RNAs (microRNAs (miRNAs)). An important aspect of epigenetic mechanisms is that they are potentially reversible and may be influenced by nutritional-environmental factors and through gene-environment interactions. Studies on epigenetic modulations could help us understand the mechanisms involved in essential hypertension and further prevent it's progress. This review is focused on new knowledge on the role of epigenetics, from DNA methylation to miRNAs, in essential hypertension.

The biological significance of angiotensin-converting enzyme inhibition to combat kidney fibrosis

Both angiotensin-converting enzyme inhibitor (ACE-I) and angiotensin II receptor blocker have been recognized as renin-angiotensin system (RAS) inhibitors. These two RAS inhibitors are rarely recognized as drugs with distinct pharmacological effects in the clinic or most clinical trials. Some preclinical basic research and clinical trials indicate that ACE-I might display superior organ-protective effects, especially anti-fibrotic effects. Such anti-fibrotic effects of ACE-I could be associated with an endogenous anti-fibrotic peptide, N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP). In this review, we focused on the anti-fibrotic effects of RAS inhibition and the endogenous anti-fibrotic peptide AcSDKP.

N-acetyl-seryl-aspartyl-lysyl-proline: a valuable endogenous anti-fibrotic peptide for combating kidney fibrosis in diabetes

Fibroproliferative diseases are responsible for 45% of deaths in the developed world. Curing organ fibrosis is essential for fibroproliferative diseases. Diabetic nephropathy is a common fibroproliferative disease of the kidney and is associated with multiorgan dysfunction. However, therapy to combat diabetic nephropathy has not yet been established. In this review, we discuss the novel therapeutic possibilities for kidney fibrosis in diabetes focusing on the endogenous anti-fibrotic peptide, N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), which is the substrate for angiotensin-converting enzyme and exhibits meaningful anti-fibrotic effects in various experimental models of fibrotic disease.

Tissue-specific expression of transgenic secreted ACE in vasculature can restore normal kidney functions, but not blood pressure, of Ace-/- mice

Angiotensin-converting enzyme (ACE) regulates normal blood pressure and fluid homeostasis through its action in the renin-angiotensin-system (RAS). Ace-/- mice are smaller in size, have low blood pressure and defective kidney structure and functions. All of these defects are cured by transgenic expression of somatic ACE (sACE) in vascular endothelial cells of Ace-/- mice. sACE is expressed on the surface of vascular endothelial cells and undergoes a natural cleavage secretion process to generate a soluble form in the body fluids. Both the tissue-bound and the soluble forms of ACE are enzymatically active, and generate the vasoactive octapeptide Angiotensin II (Ang II) with equal efficiency. To assess the relative physiological roles of the secreted and the cell-bound forms of ACE, we expressed, in the vascular endothelial cells of Ace-/- mice, the ectodomain of sACE, which corresponded to only the secreted form of ACE. Our results demonstrated that the secreted form of ACE could normalize kidney functions and RAS integrity, growth and development of Ace-/- mice, but not their blood pressure. This study clearly demonstrates that the secreted form of ACE cannot replace the tissue-bound ACE for maintaining normal blood pressure; a suitable balance between the tissue-bound and the soluble forms of ACE is essential for maintaining all physiological functions of ACE.

Different in vivo functions of the two catalytic domains of angiotensin-converting enzyme (ACE)

Angiotensin-converting enzyme (ACE) can cleave angiotensin I, bradykinin, neurotensin and many other peptide substrates in vitro. In part, this is due to the structure of ACE, a protein composed of two independent catalytic domains. Until very recently, little was known regarding the specific in vivo role of each ACE domain, and they were commonly regarded as equivalent. This is not true, as shown by mouse models with a genetic inactivation of either the ACE N- or C-domain. In vivo, most angiotensin II is produced by the ACE C-domain. Some peptides, such as the anti-fibrotic peptide AcSDKP, are substrates only of the ACE N-domain. Knowing the in vivo role of each ACE domain has great significance for developing ACE domain-specific inhibitors and for understanding the full effects of the anti-ACE pharmaceuticals in widespread clinical use.

Zinc metalloproteinases and amyloid Beta-Peptide metabolism: the positive side of proteolysis in Alzheimer's disease

Alzheimer's disease is a neurodegenerative condition characterized by an accumulation of toxic amyloid beta- (Aβ-)peptides in the brain causing progressive neuronal death. Aβ-peptides are produced by aspartyl proteinase-mediated cleavage of the larger amyloid precursor protein (APP). In contrast to this detrimental "amyloidogenic" form of proteolysis, a range of zinc metalloproteinases can process APP via an alternative "nonamyloidogenic" pathway in which the protein is cleaved within its Aβ region thereby precluding the formation of intact Aβ-peptides. In addition, other members of the zinc metalloproteinase family can degrade preformed Aβ-peptides. As such, the zinc metalloproteinases, collectively, are key to downregulating Aβ generation and enhancing its degradation. It is the role of zinc metalloproteinases in this "positive side of proteolysis in Alzheimer's disease" that is discussed in the current paper.

Cell signaling, internalization, and nuclear localization of the angiotensin converting enzyme in smooth muscle and endothelial cells

The angiotensin converting enzyme (ACE) catalyzes the extracellular formation of angiotensin II, and degradation of bradykinin, thus regulating blood pressure and renal handling of electrolytes. We have previously shown that exogenously added ACE elicited transcriptional regulation independent of its enzymatic activity. Because transcriptional regulation generates from protein-DNA interactions within the cell nucleus we have investigated the initial cellular response to exogenous ACE and the putative internalization of the enzyme in smooth muscle cells (SMC) and endothelial cells (EC). The following phenomena were observed when ACE was added to cells in culture: 1) it bound to SMC and EC with high affinity (K(d) = 361.5 +/- 60.5 pM) and with a low binding occupancy (B(max) = 335.0 +/- 14.0 molecules/cell); 2) it triggered cellular signaling resulting in late activation of focal adhesion kinase and SHP2; 3) it modulated platelet-derived growth factor receptor-beta signaling; 4) it was endocytosed by SMC and EC; and 5) it transited through the early endosome, partially occupied the late endosome and the lysosome, and was localized to the nuclei. The incorporation of ACE or a fragment of it into the nuclei reached saturation at 120 min, and was preceded by a lag time of 40 min. Internalized ACE was partially cleaved into small fragments. These results revealed that extracellular ACE modulated cell signaling properties, and that SMC and EC have a pathway for delivery of extracellular ACE to the nucleus, most likely involving cell surface receptor(s) and requiring transit through late endosome/lysosome compartments.

A small region in the angiotensin-converting enzyme distal ectodomain is required for cleavage-secretion of the protein at the plasma membrane

Both germinal and somatic isoforms of ACE are type I ectoproteins expressed on the cell surface from where the enzymatically active ectodomains are released to circulation by a regulated cleavage-secretion process. Our previous studies have shown that ACE-secretase activity is regulated by the ACE distal ectodomain and not by sequences at or around the cleavage site. In the current study we have identified that the ACE residues encompassing 343 to 655 of the germinal form are needed for its cleavage-secretion. To narrow down this region further, we have examined the cleavage-secretion of ACE-CD4 chimeric proteins in mammalian cells and Pichia pastoris. These experiments identified five residues (HGEKL) in the ACE region of the chimeric proteins that were essential for their cleavage-secretion. When the corresponding residues were substituted by alanine in native germinal and somatic ACE, the mutant proteins were not cleaved, although they were displayed on the cell surface and enzymatically active. These results demonstrated that a small region in the ectodomain of ACE is required for its cleavage at the juxtamembrane domain. This conclusion was further supported by our observation that secreted ACE inhibited cell-bound ACE cleavage-secretion, although the secreted form did not contain the cleavage site.

New insights into the role of angiotensin-converting enzyme obtained from the analysis of genetically modified mice

Angiotensin-converting enzyme (ACE) has been well-recognized for its role in blood pressure regulation. ACE is made by many tissues, though it is most abundantly expressed on the luminal surface of vascular endothelium. ACE knockout mice show a profound phenotype with low blood pressure, but also with hemopoietic and developmental defects, which complicates understanding the biological functions of ACE in individual tissue types. Using a promoter-swapping strategy, several mouse lines with unique ACE tissue expression patterns were studied. These include mice with ACE expression in the liver (ACE 3/3), the heart (ACE 8/8), and macrophages (ACE 10/10). We also investigated mice with a selective inactivation of either the N- or C-terminal ACE catalytic domain. Our studies indicate that ACE plays a role in many other physiologic processes beyond simple blood pressure control.

Characterization of the first angiotensin-converting like enzyme in bacteria: Ancestor ACE is already active

Angiotensin-converting enzyme (ACE) is a metallopeptidase that converts angiotensin I into angiotensin II. ACE is crucial in the control of cardiovascular and renal homeostasis and fertility in mammals. In vertebrates, both transmembrane and soluble ACE, containing one or two active sites, have been characterized. So far, only soluble, single domain ACEs from invertebrates have been cloned, and these have been implicated in reproduction in insects. Furthermore, an ACE-related carboxypeptidase was recently characterized in Leishmania, a unicellular eukaryote, suggesting the existence of ACE in more distant organisms.

Interestingly, in silico databank analysis revealed that bacterial DNA sequences could encode putative ACE-like proteins, strikingly similar to vertebrates' enzymes. To gain more insight into the bacterial enzymes, we cloned the putative ACE from the phytopathogenic bacterium, Xanthomonas axonopodis pv. citri, named XcACE. The 2 kb open reading frame encodes a 672-amino-acid soluble protein containing a single active site. In vitro expression and biochemical characterization revealed that XcACE is a functional 72 kDa dipeptidyl-carboxypeptidase. As in mammals, this metalloprotease hydrolyses angiotensin I into angiotensin II. XcACE is sensitive to ACE inhibitors and chloride ions concentration. Variations in the active site residues, highlighted by structural modelling, can account for the different substrate selectivity and inhibition profile compared to human ACE. XcACE characterization demonstrates that ACE is an ancestral enzyme, provoking questions about its appearance and structure/activity specialisation during the course of evolution.

Roles of the juxtamembrane and extracellular domains of angiotensin-converting enzyme in ectodomain shedding

Angiotensin-converting enzyme (ACE) is one of a growing number of integral membrane proteins that is shed from the cell surface through proteolytic cleavage by a secretase. To investigate the requirements for ectodomain shedding, we replaced the glycosylphosphatidylinositol addition sequence in membrane dipeptidase (MDP) - a membrane protein that is not shed - with the juxtamembrane stalk, transmembrane (TM) and cytosolic domains of ACE. The resulting construct, MDP-STM(ACE), was targeted to the cell surface in a glycosylated and enzymically active form, and was shed into the medium. The site of cleavage in MDP-STM(ACE) was identified by MS as the Arg(374)-Ser(375) bond, corresponding to the Arg(1203)-Ser(1204) secretase cleavage site in somatic ACE. The release of MDP-STM(ACE) and ACE from the cells was inhibited in an identical manner by batimastat and two other hydroxamic acid-based zinc metallosecretase inhibitors. In contrast, a construct lacking the juxtamembrane stalk, MDP-TM(ACE), although expressed at the cell surface in an enzymically active form, was not shed, implying that the juxtamembrane stalk is the critical determinant of shedding. However, an additional construct, ACEDeltaC, in which the N-terminal domain of somatic ACE was fused to the stalk, TM and cytosolic domains, was also not shed, despite the presence of a cleavable stalk, implying that in contrast with the C-terminal domain, the N-terminal domain lacks a signal required for shedding. These data are discussed in the context of two classes of secretases that differ in their requirements for recognition of substrate proteins.

Molecular cloning and biochemical characterization of a new mouse testis soluble-zinc-metallopeptidase of the neprilysin family

Because of their roles in controlling the activity of several bio-active peptides, members of the neprilysin family of zinc metallopeptidases have been identified as putative targets for the design of therapeutic agents. Presently, six members have been reported, these are: neprilysin, endothelin-converting enzyme (ECE)-1 and ECE-2, the Kell blood group protein, PHEX (product of the phosphate-regulating gene with homologies to endopeptidase on the X chromosome) and X-converting enzyme (XCE). In order to identify new members of this important family of peptidases, we designed a reverse transcriptase-PCR strategy based on conserved amino acid sequences of neprilysin, ECE-1 and PHEX. We now report the cloning from mouse testis of a novel neprilysin-like peptidase that we called NL1. NL1 is a glycoprotein that, among the members of the family, shows the strongest sequence identity with neprilysin. However, in contrast with neprilysin and other members of the family which are type II integral membrane proteins, NL1 was secreted when expressed in cultured mammalian cells, likely due to cleavage by a subtilisin-like convertase at a furin-like site located 22 amino acid residues in the C-terminus of the transmembrane domain. The recombinant enzyme exhibited neprilysin-like peptidase activity and was efficiently inhibited by phosphoramidon and thiorphan, two inhibitors of neprilysin. Northern blot analysis and in situ hybridization showed that NL1 mRNA was found predominantly in testis, specifically in round and elongated spermatids. This distribution of NL1 mRNA suggests that it could be involved in sperm formation or other processes related to fertility.

Selective restoration of male fertility in mice lacking angiotensin-converting enzymes by sperm-specific expression of the testicular isozyme

Although angiotensin-converting enzyme (ACE) has been studied primarily in the context of its role in blood pressure regulation, this widely distributed enzyme has many other physiological functions. The ACE gene encodes two isozymes. The somatic isozyme is expressed in many tissues, including vascular endothelial cells, renal epithelial cells, and testicular Leydig cells, whereas the testicular or germinal angiotensin-converting enzyme is expressed only in sperm. The ACE gene knockout mice lack both isozymes and they exhibit low blood pressure, kidney dysfunctions, and male infertility. Here, we report the use of a sperm-specific promoter and interbreeding of transgenic and gene knockout mice for generating a mouse strain that expressed ACE only in sperm. The experimental mice maintained the kidney defects of ACE-/- mice, but unlike the knockout strain, the males were fertile. Thus, we established that the role of ACE in male fertility is completely dependent on its exclusive expression in sperm. Our study clearly demonstrated how transgenic and knockout techniques can be combined for ascribing a specific physiological function to the expression of a multifunctional protein in a given tissue.

Angiotensin-converting enzyme and male fertility

The angiotensin-converting enzyme (ACE; EC 3.4.15.1) gene (Ace) encodes both a somatic isozyme found in blood and several other tissues, including the epididymis, and a testis-specific isozyme (testis ACE) found only in developing spermatids and mature sperm. We recently used gene targeting to disrupt the gene coding for both ACE isozymes in mice and reported that male homozygous mutants mate normally but have reduced fertility; the mutant females are fertile. Here we explore the male fertility defect. We demonstrate that ACE is important for achieving in vivo fertilization and that sperm from mice lacking both ACE isozymes show defects in transport within the oviducts and in binding to zonae pellucidae. Males generated by gene targeting that lack somatic ACE but retain testis ACE are normally fertile, establishing that somatic ACE in males is not essential for their fertility. Furthermore, male and female mice lacking angiotensinogen have normal fertility, indicating that angiotensin I is not a necessary substrate for testis ACE. Males heterozygous for the mutation inactivating both ACE isozymes sire wild-type and heterozygous offspring at an indistinguishable frequency, indicating no selection against sperm carrying the mutation.

The distal ectodomain of angiotensin-converting enzyme regulates its cleavage-secretion from the cell surface

Angiotensin-converting enzyme (ACE) is a type I ectoprotein that is cleaved off the cell surface by a plasma membrane-bound metalloprotease. However, CD4, another type I ectoprotein does not undergo such cleavage-secretion. In this study, we investigated the structural determinants of the ACE protein that regulate the cleavage-secretion process. Substitution and deletion mutations revealed that the cytoplasmic domain, the transmembrane domain, and the juxtamembrane region encompassing the major and the minor cleavage sites of ACE do not regulate its cleavage. Moreover, a chimeric protein containing the distal extracellular domain of CD4 and the juxtamembrane, transmembrane, and the cytoplasmic domains of ACE, although transported to the cell surface, was not cleavage-secreted. In contrast, the distal extracellular domain of ACE was shown to be the important determinant: a protein containing the distal extracellular domain of ACE and the juxtamembrane, transmembrane, and cytoplasmic domain of CD4 was efficiently cleaved off the cell surface. The chimeric protein was cleaved within the CD4 sequence and the responsible enzymatic activity was inhibited by Compound 3, a relatively specific inhibitor of the ACE secretase activity. These results demonstrate that, in a chimeric protein, the distal extracellular domain of a cleavable protein, such as ACE, can induce a proteolytic cleavage within the juxtamembrane domain of an uncleaved protein such as CD4.

The critical role of tissue angiotensin-converting enzyme as revealed by gene targeting in mice

Angiotensin-converting enzyme (ACE) generates the vasoconstrictor angiotensin II, which plays a critical role in maintenance of blood pressure in mammals. Although significant ACE activity is found in plasma, the majority of the enzyme is bound to tissues such as the vascular endothelium. We used targeted homologous recombination to create mice expressing a form of ACE that lacks the COOH-terminal half of the molecule. This modified ACE protein is catalytically active but entirely secreted from cells. Mice that express only this modified ACE have significant plasma ACE activity but no tissue-bound enzyme. These animals have low blood pressure, renal vascular thickening, and a urine concentrating defect. The phenotype is very similar to that of completely ACE-deficient mice previously reported, except that the renal pathology is less severe. These studies strongly support the concept that the tissue-bound ACE is essential to the control of blood pressure and the structure and function of the kidney.

cAMP-response element modulator tau is a positive regulator of testis angiotensin converting enzyme transcription

Testis angiotensin-converting enzyme (ACE) is a unique form of ACE, only produced by male germ cells, and results from a testis-specific promoter found within the ACE gene. We have investigated the role of cAMP-response element modulator (CREM)tau in testis ACE transcription. In gel shift experiments, testes nuclear proteins retard an oligonucleotide containing the cAMP-response element (CRE) found at position -55 in the testis ACE promoter. Anti-CREM antibody supershifts this complex. Competitive gel shift shows that recombinant CREM tau protein and testis nuclear proteins have a similar specificity of binding to the tests ACE CRE. Functional analysis using in vitro transcription and transfection studies also demonstrate that CREM tau protein is a transcriptional activator of the testis ACE promoter. Western blot analysis identifies CREM tau protein in the protein-DNA complex formed between nuclear proteins and the testis ACE CRE motif. This analysis also identified other CREM isoforms in the gel-shifted complex, which are thought to be CREM tau 1/2, CREM alpha/beta, and S-CREM. These data indicate that CREM tau isoforms play an important role as a positive regulator in the tissue-specific expression of testis ACE.

The endopeptidase activity and the activation by Cl- of angiotensin-converting enzyme is evolutionarily conserved: purification and properties of an an angiotensin-converting enzyme from the housefly, Musca domestica

A soluble 67 kDa angiotensin-converting enzyme (ACE) has been purified by lisinopril-Sepharose affinity column chromatography from adult houseflies, Musca domestica. The dipeptidyl carboxypeptidase activity towards benzoyl-Gly-His-Leu was inhibited by captopril (IC50 50 nM) and fosinoprilat (IC50 251 nM), two inhibitors of mammalian ACE, and was activated by Cl- (optimal Cl- concentration 600 mM). Musca ACE removed C-terminal dipeptides from angiotensin I, bradykinin [Leu5]enkephalin and [Met5]enkephalin and also functioned as an endopeptidase by hydrolysing dipeptideamides from [Leu5]enkephalinamide and [Met5]enkephalinamide, and a dipeptideamide and a tripeptideamide from substance P. Musca ACE was also able to cleave a tripeptide from both the N-terminus and C-terminus of luteinizing hormone-releasing hormone, with C-terminal hydrolysis predominating. Maximal N-terminal tripeptidase activity occurred at 150 mM NaCl, whereas the C-terminal tripeptidase activity continued to rise with increasing concentration of Cl- (0-0.5 M). Musca ACE displays properties of both the N- and C-domains of human ACE, indicating a high degree of conservation during evolution of the substrate specificity of ACE and its response to Cl-.

An alternative, nonkinase product of the brain-specifically expressed Ca2+/calmodulin-dependent kinase II alpha isoform gene in skeletal muscle

The gene for the alpha isoform of Ca2+/calmodulin-dependent kinase II (alpha CaMKII) codes for a multifunctional protein kinase that is found exclusively in the brain. Here we show that in skeletal muscle, an alternative nonkinase product, hereafter referred to as alpha KAP (alpha CaMKII association protein), is expressed from the same gene. alpha KAP consists of a C-terminal region that is identical to the association domain of alpha CaMKII, with the exception of 11 amino acids inserted in the variable region. The N-terminal sequence of alpha KAP is highly hydrophobic and not present in any known CaMKII protein. The catalytic and regulatory domains of alpha CaMKII are missing in alpha KAP. Analysis of the exon-intron structure revealed that the alpha KAP transcript is derived from the alpha CaMKII gene by alternative promoter usage and RNA splicing. The transcriptional start site of alpha KAP mRNA is located within an intron of the alpha CaMKII gene. Therefore, the relationship between alpha KAP and alpha CaMKII is that of a gene within a gene. Immunostaining using anti-alpha KAP antibodies suggests that alpha KAP is associated with sarcomeres of skeletal muscle fibers. On the basis of its primary structure and specific location, the possible function of alpha KAP as an anchoring protein for CaMKII is discussed.

Angiotensin II: biosynthesis, molecular recognition, and signal transduction

1. Angiotensin II is a well-known vasopressive octapeptide that is the principal end-product of the renin-angiotensin system. In addition to its tonic effect on vascular smooth muscle cells, it also stimulates aldosterone secretion from the adrenals and promotes sodium reabsorption through renal tubular cells. 2. These physiological functions have been appreciated for some time, but as details of the molecular and cell biology of the angiotensin response mechanism become understood, it is increasingly apparent that the hormone has a much broader repertoire. Its functional variability is made possible by (i) different enzymatic routes for its generation, (ii) different receptors distributed in different tissues, (iii) different mechanisms for receptor regulation, and (iv) different signal transduction pathways. 3. This insight is the direct consequence of advances in pharmacology that led first to inhibitors of angiotensin converting enzyme and later to angiotensin II receptor antagonists. This review looks at the current status of angiotensin biochemistry and physiology and provides a basis for anticipation of future developments.

Naturally occurring active N-domain of human angiotensin I-converting enzyme

Angiotensin I-converting enzyme (ACE, kininase II) is a single-chain protein containing two active site domains (named N- and C-domains according to position in the chain). ACE is bound to plasma membranes by its C-terminal hydrophobic transmembrane anchor. Ileal fluid, rich in ACE activity, obtained from patients after surgical colectomy was used as the source. Column chromatography, including modified affinity chromatography on lisinopril-Sepharose, yielded homogeneous ACE after only a 45-fold purification. N-terminal sequencing of ileal ACE and partial sequencing of CNBr fragments revealed the presence of an intact N terminus but only a single N-domain active site, ending between residues 443 and 559. Thus, ileal-fluid ACE is a unique enzyme differing from the widely distributed two-domain somatic enzyme or the single C-domain testicular (germinal) ACE. The molecular mass of ileal ACE is 108 kDa and when deglycosylated, the molecular mass is 68 kDa, indicating extensive glycosylation (37% by weight). In agreement with the results reported with recombinant variants of ACE, the ileal enzyme is less Cl(-)-dependent than somatic ACE; release of the C-terminal dipeptide from a peptide substrate was optimal in only 10 mM Cl-. In addition to hydrolyzing at the C-terminal end of peptides, ileal ACE efficiently cleaved the protected N-terminal tripeptide from the luteinizing hormone-releasing hormone and its congener 6-31 times faster, depending on the Cl- concentration, than the C-domain in recombinant testicular ACE. Thus we have isolated an active human ACE consisting of a single N-domain. We suggest that there is a bridge section of about 100 amino acids between the active N- and C-domains of somatic ACE where it may be proteolytically cleaved to liberate the active N-domain. These findings have potential relevance and importance in the therapeutic application of ACE inhibitors.

Identification and properties of a peptidyl dipeptidase in the housefly, Musca domestica, that resembles mammalian angiotensin-converting enzyme

[D-Ala2,Leu5]Enkephalin was readily metabolized by membranes (40,000 g pellet) prepared from heads of the housefly, Musca domestica, with Gly3-Phe4 being the major site of cleavage. This hydrolysis was only partially inhibited (40%) by 10 microM phosphoramidon, an inhibitor of endopeptidase-24.11, but was almost totally abolished in the presence of a mixture of 10 microM phosphoramidon and 10 microM captopril, a potent inhibitor of mammalian angiotensin-converting enzyme (ACE). An assay for ACE employing Bz-Gly-His-Leu as the substrate was used to confirm the presence of an ACE-like peptidyl dipeptidase activity in fly head membranes. The peptidase had a Km of 1.91 mM for Bz-Gly-His-Leu and a pH optimum of 8.2. The activity was inhibited by 100 microM EDTA and was greatly activated by ZnCl2 but not other bivalent metal ions. Captopril, lisinopril, fosinoprilat and enalaprilat, all selective inhibitors of mammalian ACE, were also good inhibitors of the insect enzyme with IC50 values of 400 nM, 130 nM, 16 nM and 290 nM respectively. An M(r) value of around 87,000 was obtained for this enzyme from gel-filtration chromatography, indicating that the insect enzyme is similar in size to mammalian testicular ACE (M(r) = 90,000-110,000) and not the larger form of the enzyme (M(r) = 150,000-180,000) found in mammalian somatic tissues. The fly peptidyl dipeptidase was released from membranes into a soluble fraction by incubating the head membranes at 37 degrees C but not at 0 degree C, suggesting that the insect ACE-like enzyme can be solubilized from cell surfaces through the activity of a membrane-bound enzyme activity. In conclusion, we have shown the existence of a peptidyl dipeptidase in membranes from the heads of M. domestica, which has similar properties to those of mammalian ACE.

Identification of positive and negative transcriptional regulatory elements of the rabbit angiotensin-converting enzyme gene

The two tissue-specific mRNAs encoding the isozymes of rabbit angiotensin-converting enzyme (ACE) are generated from the same gene by alternative choice of two transcription initiation sites 5.7 kb apart. In the current study, we have characterized the regulatory sites controlling the transcription of the larger pulmonary isozyme mRNA. For this purpose, reporter genes driven by varying lengths of upstream region of the ACE gene were transfected into ACE-producing cells. Our results demonstrated that the transcription of this gene is primarily driven by positive elements within the first 274 bp DNA upstream of the transcription initiation site. The reporter gene driven by this region was expressed in two ACE-producing cells but not in two ACE-non-producing cells thereby establishing its tissue specificity. Our experiments also revealed the existence of a strong negative element located between -692 and -610 positions. This element suppressed the expression of the reporter gene in a dose-dependent and position and orientation-independent fashion thus suggesting that it is a true silencer element. It could also repress the expression of a reporter gene driven by the heterologous strong promoter of the beta-actin gene. The repressing effects of the negative element could be partially overcome by cotransfecting the isolated negative element along with the reporter gene containing the negative element. This result was possibly due to the functional removal of a limiting trans-acting factor which binds to this element. Electrophoretic mobility shift assays revealed that the negative element can form several complexes with proteins present in the nuclear extract of an ACE-producing cell line. At least part of the negative element is strongly conserved in the upstream regions of the human and mouse ACE genes.

Functional analysis of the human somatic angiotensin I-converting enzyme gene promoter

Angiotensin I-converting enzyme (ACE) is a key enzyme in the regulation of systemic blood pressure and plays a major role in the renin-angiotensin and bradykinin-kinin systems, at the luminal surface of the vascular endothelia. To identify the promoter region, the transcription regulatory elements and the cell specificity of the ACE gene, five successive DNA deletions of the 5' upstream region (-1214, -754, -472, -343, -132 bp relative to the start site of transcription) were isolated and fused in sense and antisense orientations to the bacterial chloramphenicol acetyltransferase (CAT) reporter gene in the promoterless plasmid pBLCAT3. Promoter activities were measured in transient transfection assays using three different cell lines from rabbit endothelium (RE), human embryocarcinoma (Tera-1) and hepatocarcinoma cells (HepG2). All five fragments of the ACE promoter region directed expression of the CAT gene when transfected into the endothelial and the embryocarcinoma cells, which contain endogenous ACE mRNA and express ACE activity. In contrast only minimal levels of promoter activity were obtained on transfection into hepatocarcinoma cells in which endogenous ACE mRNA and ACE activity were not detected. Transfection of RE and Tera-1 cells demonstrated that promoter activity was defined by the length of the ACE promoter sequence inserted into the construct. The 132 bases located upstream from the transcription start site were sufficient to confer ACE promoter activity, whereas the sequences upstream from -472 bp and between -343 bp and -132 bp were responsible for a decrease of promoter activity. Furthermore, the minimal 132 bp of the ACE promoter contains elements which direct cell-specific CAT expression. In addition, the DNA transfection study in the presence of dexamethasone suggested that the potential glucocorticoid regulatory elements, located in the sequence of the ACE promoter, are not functional.

Sperm-specific expression of angiotensin-converting enzyme (ACE) is mediated by a 91-base-pair promoter containing a CRE-like element

The gene encoding the testis isozyme of angiotensin-converting enzyme (testis ACE) is one example of the many genes expressed uniquely during spermatogenesis. This protein is expressed by developing germ cells late in their development and results from the activation of a sperm-specific promoter that is located within intron 12 of the gene encoding the somatic isozyme of ACE. In vitro transcription, DNase footprinting, gel shift assays, and transgenic mouse studies have been used to define the minimal testes ACE promoter and to characterize DNA-protein interactions mediating germ cell-specific expression. These studies show that proper cell- and stage-specific expression of testis ACE requires only a small portion of the immediate upstream sequence extending to -91. A critical motif within this core promoter is a cyclic AMP-responsive element sequence that interacts with a testis-specific transactivating factor. Since this putative cyclic AMP-responsive element has been conserved within the testis ACE promoters of different species and is found at the same site in other genes that are expressed specifically in the testis, it may provide a common mechanism for the recognition of sperm-specific promoters.

Sperm-specific expression of angiotensin-converting enzyme (ACE) is mediated by a 91-base-pair promoter containing a CRE-like element

The gene encoding the testis isozyme of angiotensin-converting enzyme (testis ACE) is one example of the many genes expressed uniquely during spermatogenesis. This protein is expressed by developing germ cells late in their development and results from the activation of a sperm-specific promoter that is located within intron 12 of the gene encoding the somatic isozyme of ACE. In vitro transcription, DNase footprinting, gel shift assays, and transgenic mouse studies have been used to define the minimal testes ACE promoter and to characterize DNA-protein interactions mediating germ cell-specific expression. These studies show that proper cell- and stage-specific expression of testis ACE requires only a small portion of the immediate upstream sequence extending to -91. A critical motif within this core promoter is a cyclic AMP-responsive element sequence that interacts with a testis-specific transactivating factor. Since this putative cyclic AMP-responsive element has been conserved within the testis ACE promoters of different species and is found at the same site in other genes that are expressed specifically in the testis, it may provide a common mechanism for the recognition of sperm-specific promoters.

Use of alternative polyadenylation sites for tissue-specific transcription of two angiotensin-converting enzyme mRNAs

The pulmonary isozyme of rabbit angiotensin-converting enzyme (ACE) is encoded by an mRNA of about 5 kb. cDNA clones corresponding to different parts of this mRNA have been isolated and the complete nucleotide sequences of both the coding and non-coding regions of the mRNA have been determined. The encoded protein has 1309 residues with a 33 amino acids-long signal peptide at the amino terminus and a potential membrane-anchoring domain near the carboxyl terminus. There is a strong sequence homology between two regions of the rabbit cDNA and between the rabbit, human, and mouse cDNAs. Comparison of the nucleotide sequences of the 3' untranslated regions of rabbit pulmonary and testicular ACE cDNAs revealed that the testicular cDNA is nested within the pulmonary cDNA at the 3' end. A rabbit genomic clone encompassing this region was isolated and partially sequenced. It was shown that the gene contains two potential polyadenylation sites 628 bp apart within one exon. Northern analyses with an appropriate oligonucleotide probe confirmed that the proximal polyadenylation site is used exclusively for terminating the testicular mRNA whereas the distal one is used exclusively for the pulmonary mRNA. These results demonstrated that the transcription of the two mRNAs encoding the two ACE isozymes not only initiates at two alternative tissue-specific sites which are 5.7 kb apart but the mRNAs also get polyadenylated at two alternative sites which are 628 bp apart.

An analysis of vertebrate mRNA sequences: intimations of translational control

Five structural features in mRNAs have been found to contribute to the fidelity and efficiency of initiation by eukaryotic ribosomes. Scrutiny of vertebrate cDNA sequences in light of these criteria reveals a set of transcripts--encoding oncoproteins, growth factors, transcription factors, and other regulatory proteins--that seem designed to be translated poorly. Thus, throttling at the level of translation may be a critical component of gene regulation in vertebrates. An alternative interpretation is that some (perhaps many) cDNAs with encumbered 5' noncoding sequences represent mRNA precursors, which would imply extensive regulation at a posttranscriptional step that precedes translation.

A novel Ca2+/calmodulin-dependent protein kinase and a male germ cell-specific calmodulin-binding protein are derived from the same gene

A cDNA representing a unique Ca2+/calmodulin-dependent protein kinase has been cloned and sequenced from a rat brain cDNA library. This enzyme, expressed in brain, testis, and spleen, is only 32% identical to the various isoforms of Ca2+/calmodulin-dependent protein kinase II. The sequence of the COOH-terminal 169 amino acids is identical to that of a previously described male germ cell-specific calmodulin-binding protein called calspermin (T. Ono, G.R. Slaughter, R.G. Cook, and A.R. Means, J. Biol. Chem. 264:2081-2087, 1989). This identity extends to the nucleic acid sequence and includes all but the first 130 nucleotides of the calspermin cDNA. Primer extension and sequence of a genomic fragment containing the unique calspermin sequence reveals that this mRNA is derived from the kinase transcription unit by germ cell-specific use of a unique exon. In situ hybridization was used to demonstrate that both kinase and calspermin mRNAs are expressed during spermatogenesis. The kinase mRNA is first detected in early meiotic cells and declines to a low level in haploid cells. Calspermin mRNA first appears in pachytene primary spermatocytes and continues to increase as cells complete meiosis and undergo terminal differentiation. These results show that differential utilization of a single gene during spermatogenesis is used to generate mRNAs that encode proteins with distinct functions.

A novel Ca2+/calmodulin-dependent protein kinase and a male germ cell-specific calmodulin-binding protein are derived from the same gene

A cDNA representing a unique Ca2+/calmodulin-dependent protein kinase has been cloned and sequenced from a rat brain cDNA library. This enzyme, expressed in brain, testis, and spleen, is only 32% identical to the various isoforms of Ca2+/calmodulin-dependent protein kinase II. The sequence of the COOH-terminal 169 amino acids is identical to that of a previously described male germ cell-specific calmodulin-binding protein called calspermin (T. Ono, G.R. Slaughter, R.G. Cook, and A.R. Means, J. Biol. Chem. 264:2081-2087, 1989). This identity extends to the nucleic acid sequence and includes all but the first 130 nucleotides of the calspermin cDNA. Primer extension and sequence of a genomic fragment containing the unique calspermin sequence reveals that this mRNA is derived from the kinase transcription unit by germ cell-specific use of a unique exon. In situ hybridization was used to demonstrate that both kinase and calspermin mRNAs are expressed during spermatogenesis. The kinase mRNA is first detected in early meiotic cells and declines to a low level in haploid cells. Calspermin mRNA first appears in pachytene primary spermatocytes and continues to increase as cells complete meiosis and undergo terminal differentiation. These results show that differential utilization of a single gene during spermatogenesis is used to generate mRNAs that encode proteins with distinct functions.