Legumain from bovine kidney: its purification, molecular cloning, immunohistochemical localization and degradation of annexin II and vitamin D-binding protein

Immune modulation of goat monocytes by Fasciola gigantica Legumain-1 protein (Fg-LGMN-1)

Legumains belonging to C_13 peptidase family of proteins, and are ubiquitously disseminated among all vertebrate and invertebrate organisms, and have been implicated in innumerable biological and cellular functionality. Herein, we characterized and evaluated immunoregulatory characteristics of Legumain-1 from Fasciola gigantica (Fg-LGMN-1) during its interaction with host immune cells. The isopropyl-ß-d-thiogalactopyranoside (IPTG) stimulated RFg-LGMN-1 protein was positively detected by rat serum containing anti-RFg-LGMN-1 polyclonal antibodies. Furthermore, the uptake of RFg-LGMN-1 by goat monocytes was successfully confirmed using Immunofluorescence Assay (IFA). The immunohistochemical analysis revealed the native localization of LGMN-1 protein on the periphery and internal structures such as suckers, pharynx, and genital pore of the adult parasite, thereby validating its presence in excretory-secretory (ES) products of F. gigantica. The RFg-LGMN-1 co-incubated with concanavalin-A (Con-A) stimulated the increase of interleukin 2 (IL-2), IL-10, and IL-17 in monocytes derived from peripheral blood mononuclear cells (PBMCs) in the concentration-dependent manner. However, the IL-4 cytokine in response to the RFg-LGMN-1 protein declined. These results illuminated the role of LGMN-1 during the parasite-host interface. Our findings elaborated additional evidence that Legumain protein play a role in the manipulating host immune responses during parasite infections. However, further evaluation of RFg-LGMN-1 protein in context of its immunomodulatory roles should be conducted to enhance our understandings of the mechanisms employed by F. gigantica to evade host immune responses.

The Cysteine Protease Legumain Is Upregulated by Vitamin D and Is a Regulator of Vitamin D Metabolism in Mice

Legumain is a lysosomal cysteine protease that has been implicated in an increasing amount of physiological and pathophysiological processes. However, the upstream mechanisms regulating the expression and function of legumain are not well understood. Here, we provide in vitro and in vivo data showing that vitamin D3 (VD3) enhances legumain expression and function. In turn, legumain alters VD3 bioavailability, possibly through proteolytic cleavage of vitamin D binding protein (VDBP). Active VD3 (1,25(OH)2D3) increased legumain expression, activity, and secretion in osteogenic cultures of human bone marrow stromal cells. Upregulation of legumain was also observed in vivo, evidenced by increased legumain mRNA in the liver and spleen, as well as increased legumain activity in kidneys from wild-type mice treated with 25(OH)D3 (50 µg/kg, subcutaneously) for 8 days compared to a control. In addition, the serum level of legumain was also increased. We further showed that active legumain cleaved purified VDBP (55 kDa) in vitro, forming a 45 kDa fragment. In vivo, no VDBP cleavage was found in kidneys or liver from legumain-deficient mice (Lgmn-/-), whereas VDBP was cleaved in wild-type control mice (Lgmn+/+). Finally, legumain deficiency resulted in increased plasma levels of 25(OH)D3 and total VD3 and altered expression of key renal enzymes involved in VD3 metabolism (CYP24A1 and CYP27B1). In conclusion, a regulatory interplay between VD3 and legumain is suggested.

Role of LGMN in tumor development and its progression and connection with the tumor microenvironment

Legumain (LGMN) has been demonstrated to be overexpressed not just in breast, prostatic, and liver tumor cells, but also in the macrophages that compose the tumor microenvironment. This supports the idea that LGMN is a pivotal protein in regulating tumor development, invasion, and dissemination. Targeting LGMN with siRNA or chemotherapeutic medicines and peptides can suppress cancer cell proliferation in culture and reduce tumor growth in vivo. Furthermore, legumain can be used as a marker for cancer detection and targeting due to its expression being significantly lower in normal cells compared to tumors or tumor-associated macrophages (TAMs). Tumor formation is influenced by aberrant expression of proteins and alterations in cellular architecture, but the tumor microenvironment is a crucial deciding factor. Legumain (LGMN) is an in vivo-active cysteine protease that catalyzes the degradation of numerous proteins. Its precise biological mechanism encompasses a number of routes, including effects on tumor-associated macrophage and neovascular endothelium in the tumor microenvironment. The purpose of this work is to establish a rationale for thoroughly investigating the function of LGMN in the tumor microenvironment and discovering novel tumor early diagnosis markers and therapeutic targets by reviewing the function of LGMN in tumor genesis and progression and its relationship with tumor milieu.

The Mammalian Cysteine Protease Legumain in Health and Disease

The cysteine protease legumain (also known as asparaginyl endopeptidase or δ-secretase) is the only known mammalian asparaginyl endopeptidase and is primarily localized to the endolysosomal system, although it is also found extracellularly as a secreted protein. Legumain is involved in the regulation of diverse biological processes and tissue homeostasis, and in the pathogenesis of various malignant and nonmalignant diseases. In addition to its proteolytic activity that leads to the degradation or activation of different substrates, legumain has also been shown to have a nonproteolytic ligase function. This review summarizes the current knowledge about legumain functions in health and disease, including kidney homeostasis, hematopoietic homeostasis, bone remodeling, cardiovascular and cerebrovascular diseases, fibrosis, aging and senescence, neurodegenerative diseases and cancer. In addition, this review addresses the effects of some marketed drugs on legumain. Expanding our knowledge on legumain will delineate the importance of this enzyme in regulating physiological processes and disease conditions.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

Target Enzymes Considered for the Treatment of Alzheimer's Disease and Parkinson's Disease

Various amyloidogenic proteins have been suggested to be involved in the onset and progression of neurodegenerative diseases (ND) such as Alzheimer's disease (AD) and Parkinson's disease (PD). Particularly, the aggregation of misfolded amyloid-β and hyperphosphorylated tau and α-synuclein are linked to the pathogenesis of AD and PD, respectively. In order to care the diseases, multiple small molecules have been developed to regulate the aggregation pathways of these amyloid proteins. In addition to controlling the aggregation of amyloidogenic proteins, maintaining the levels of the proteins in the brain by amyloid degrading enzymes (ADE; neprilysin (NEP), insulin-degrading enzyme (IDE), asparagine endopeptidase (AEP), and ADAM10) is also essential to cure AD and PD. Therefore, numerous biological molecules and chemical agents have been investigated as either inducer or inhibitor against the levels and activities of ADE. Although the side effect of enhancing the activity of ADE could occur, the removal of amyloidogenic proteins could result in a relatively good strategy to treat AD and PD. Furthermore, since the causes of ND are diverse, various multifunctional (multitarget) chemical agents have been designed to control the actions of multiple risk factors of ND, including amyloidogenic proteins, metal ions, and reactive oxygen species. Many of them, however, were invented without considerations of regulating ADE levels and actions. Incorporation of previously created molecules with the chemical agents handling ADE could be a promising way to treat AD and PD. This review introduces the ADE and molecules capable of modulating the activity and expression of ADE.

Lansoprazole inhibits the cysteine protease legumain by binding to the active site

Proton pump inhibitors (PPIs) are prodrugs used in the treatment of peptic ulcer diseases. Once activated by acidic pH, the PPIs subsequently inhibit the secretion of gastric acid by covalently forming disulphide bonds with the SH groups of the parietal proton pump, that is the H⁺ /K⁺ -ATPase. Long-term use of PPIs has been associated with numerous adverse effects, including bone fractures. Considering the mechanism of activation, PPIs could also be active in acidic micro-environments such as in lysosomes, tumours and bone resorption sites. We suggested that the SH group in the active site of cysteine proteases could be susceptible for inhibition by PPIs. In this study, the inhibition by lansoprazole was shown on the cysteine proteases legumain and cathepsin B by incubating purified proteases or cell lysates with lansoprazole at different concentrations and pH conditions. The mechanism of legumain inhibition was shown to be a direct interaction of lansoprazole with the SH group in the active site, and thus blocking binding of the legumain-selective activity-based probe MP-L01. Lansoprazole was also shown to inhibit both legumain and cathepsin B in various cell models like HEK293, monoclonal legumain over-expressing HEK293 cells (M38L) and RAW264.7 macrophages, but not in human bone marrow-derived skeletal (mesenchymal) stem cells (hBMSC-TERT). During hBMSC-TERT differentiation to osteoblasts, lansoprazole inhibited legumain secretion, alkaline phosphatase activity, but had no effects on in vitro mineralization capacity. In conclusion, lansoprazole acts as a direct covalent inhibitor of cysteine proteases via disulphide bonds with the SH group in the protease active site. Such inhibition of cysteine proteases could explain some of the off-target effects of PPIs.

Structural and functional analysis of cystatin E reveals enzymologically relevant dimer and amyloid fibril states

Protein activity is often regulated by altering the oligomerization state. One mechanism of multimerization involves domain swapping, wherein proteins exchange parts of their structures and thereby form long-lived dimers or multimers. Domain swapping has been specifically observed in amyloidogenic proteins, for example the cystatin superfamily of cysteine protease inhibitors. Cystatins are twin-headed inhibitors, simultaneously targeting the lysosomal cathepsins and legumain, with important roles in cancer progression and Alzheimer's disease. Although cystatin E is the most potent legumain inhibitor identified so far, nothing is known about its propensity to oligomerize. In this study, we show that conformational destabilization of cystatin E leads to the formation of a domain-swapped dimer with increased conformational stability. This dimer was active as a legumain inhibitor by forming a trimeric complex. By contrast, the binding sites toward papain-like proteases were buried within the cystatin E dimer. We also showed that the dimers could further convert to amyloid fibrils. Unexpectedly, cystatin E amyloid fibrils contained functional protein, which inhibited both legumain and papain-like enzymes. Fibril formation was further regulated by glycosylation. We speculate that cystatin amyloid fibrils might serve as a binding platform to stabilize the pH-sensitive legumain and cathepsins in the extracellular environment, contributing to their physiological and pathological functions.

Secretion of Legumain Increases in Conditioned Medium from DJ-1-Knockout Cells and in Serum from DJ-1-Knockout Mice

Background

Asparaginyl endopeptidase, also known as legumain (EC 3.4.22.34) shows strong activity in the mouse kidney. Legumain is also highly expressed in tumors. DJ-1/PARK7 is a Parkinson's disease- and cancer-associated protein. DJ-1 is a coactivator of various transcription factors. Recently, we reported that transcription of the legumain gene is regulated by p53 through DJ-1.

Methods

We measured the secretion levels of legumain in a conditioned medium of DJ-1 knockout cells and in serum from DJ-1 knockout mice using Western blotting and ELISA. We performed immunocytochemical staining of legumain to examine the localization of legumain in DJ-1-knockout cells.

Results

We found that the secretion levels of legumain were increased in the conditioned medium of DJ-1-knockout cells and in serum from DJ-1-knockout mice. Dot structures of legumain were also increased in DJ-1-knockout cells.

Conclusion

The results suggest that legumain secretion from DJ-1-knockout cells and in mice increases through its increased expression and accumulation in membrane-associated vesicles.

Biological function of Dictyocaulus viviparus asparaginyl peptidase legumain-1 and its suitability as a vaccine target

The present study characterized the biological function of the asparaginyl peptidase legumain-1 (LEG-1) of the bovine lungworm Dictyocaulus viviparus and its suitability as a recombinant vaccine against dictyocaulosis. Quantitative real-time PCR and immunoblot analysis revealed LEG-1 to be almost exclusively transcribed and expressed in parasitic lungworm stages. Immunohistochemistry localized the enzyme in the parasite's gut, which was confirmed by immunoblots detecting LEG-1 in the gut as well as male testes. LEG-1 was recombinantly (rLEG-1) expressed in the yeast Pichia pastoris and subsequently analysed in activity assays for its enzyme functions and substrate specificity. For sufficient functionality, rLEG-1 needed trans-activation through D. viviparus cathepsin L-2, indicating a novel mechanism of legumain activation. After trans-activation, rLEG-1 worked best at pH 5·5 and 35-39 °C and cleaved a legumain-specific artificial substrate as well as the natural substrates bovine collagen types I and II. In a clinical vaccination trial, rLEG-1 did not protect against challenge infection. Results of in vitro characterization, transcription pattern and localization enhance the presumption that LEG-1 participates in digestion processes of D. viviparus. Since rLEG-1 needs trans-activation through a cathepsin, it is probably involved in an enzyme cascade and therefore remains interesting as a candidate in a multi-component vaccine.

Protease activity of legumain is inhibited by an increase of cystatin E/M in the DJ-1-knockout mouse spleen, cerebrum and heart

Legumain (EC 3.4.22.34) is an asparaginyl endopeptidase. Legumain activity has been detected in various mouse tissues including the kidney, spleen and epididymis. Legumain is overexpressed in the majority of human solid tumors and transcription of the legumain gene is regulated by the p53 tumor suppressor in HCT116 cells. The legumain activity is also increased under acid conditions in Alzheimer's disease brains. DJ-1/PARK7, a cancer- and Parkinson's disease-associated protein, works as a coactivator to various transcription factors, including the androgen receptor, p53, PSF, Nrf2, SREBP and RREB1. Recently, we found that legumain expression, activation and cleavage of annexin A2 are regulated by DJ-1 through p53. In this study, we found that the expression levels of legumain mRNA were increased in the cerebrum, kidney, spleen, heart, lung, epididymis, stomach, small intestine and pancreas from DJ-1-knockout mice, although legumain activity levels were decreased in the cerebrum, spleen and heart from DJ-1-knockout mice. Furthermore, we found that cystatin E/M expression was increased in the spleen, cerebrum and heart from DJ-1-knockout mice. These results suggest that reduction of legumain activity is caused by an increase of cystatin E/M expression in the spleen, cerebrum and heart from DJ-1-knockout mice.

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Legumain is strongly activated in the epididymis from DJ-1-knockout mice.

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Expression level of legumain mRNA is increased but activity is decreased in the spleen, cerebrum and heart from DJ-1-knockout mice.

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Expression level of cystatin E/M is increased in the spleen, cerebrum and heart from DJ-1-knockout mice.

Clinicopathologic significance of legumain overexpression in cancer: a systematic review and meta-analysis

Since reports on the clinical significance of legumain in cancer have shown inconsistent results, we systematically evaluated clinical indicators of legumain in cancer. We searched the Cochrane Library, PubMed, Embase, and EBSCO databases and the Wangfang and CNKI databases in China by using "legumain" and ("neoplasms" OR "cancer") as search terms. We included case-controlled studies of legumain and cancer. The quality of the studies was evaluated by using Lichtenstein's guidelines, and valid data was extracted for analysis. In total, 10 articles were included in this study. Meta-analysis showed that legumain was overexpressed in cancer compared with in normal tissue and was higher in stage III-IV disease than in I-II disease. Moreover, legumain overexpression was correlated with poor prognosis and clinical stage. Furthermore, Cancer Genome Atlas data showed that among patients with rectal cancer, those with tumors overexpressing legumain had shorter overall survival than those in the low expression group (P < 0.05). Legumain appears to be involved in tumor development and deterioration; thus, it can potentially be developed into both a marker for monitoring and diagnosing tumors and a therapeutic target.

Expression and protease activity of mouse legumain are regulated by the oncogene/transcription co-activator, DJ-1 through p53 and cleavage of annexin A2 is increased in DJ-1-knockout cells

Legumain (EC 3.4.22.34) is an asparaginyl endopeptidase. Strong legumain activity was observed in the mouse kidney, and legumain was highly expressed in tumors. We previously reported that bovine kidney annexin A2 was co-purified with legumain and that legumain cleaved the N-terminal region of annexin A2 at an Asn residue in vitro and in vivo. Recently, we found that transcription of the legumain gene is regulated by the p53 tumor suppressor in HCT116 cells. We and others reported that DJ-1/PARK7, a cancer- and Parkinson's disease-associated protein, works as a coactivator to various transcription factors, including the androgen receptor, p53, PSF, Nrf2, SREBP and RREB1. In this study, we found that expression levels of legumain mRNA and protein and legumain activity were increased in DJ-1-knockout cells. Furthermore, we found that DJ-1 binds to the p53-binding site on intron 1 of the mouse legumain gene in wild-type cells and that cleavage of annexin A2 was increased in DJ-1-knockout cells. These results suggest that legumain expression and activation and cleavage of annexin A2 are regulated by DJ-1 through p53.

Structure and function of legumain in health and disease

The last years have seen a steady increase in our understanding of legumain biology that is driven from two largely uncoupled research arenas, the mammalian and the plant legumain field. Research on legumain, which is also referred to as asparaginyl endopeptidase (AEP) or vacuolar processing enzyme (VPE), is slivered, however. Here we summarise recent important findings and put them into a common perspective. Legumain is usually associated with its cysteine endopeptidase activity in lysosomes where it contributes to antigen processing for class II MHC presentation. However, newly recognized functions disperse previously assumed boundaries with respect to their cellular compartmentalisation and enzymatic activities. Legumain is also found extracellularly and even translocates to the cytosol and the nucleus, with seemingly incompatible pH and redox potential. These different milieus translate into changes of legumain's molecular properties, including its (auto-)activation, conformational stability and enzymatic functions. Contrasting its endopeptidase activity, legumain can develop a carboxypeptidase activity which remains stable at neutral pH. Moreover, legumain features a peptide ligase activity, with intriguing mechanistic peculiarities in plant and human isoforms. In pathological settings, such as cancer or Alzheimer's disease, the proper association of legumain activities with the corresponding cellular compartments is breached. Legumain's increasingly recognized physiological and pathological roles also indicate future research opportunities in this vibrant field.

The polar high molecular weight fraction of the Agaricus blazei Murill extract, AndoSan™, reduces the activity of the tumor-associated protease, legumain, in RAW 264.7 cells

AndoSan™ is an extract of Agaricus blazei Murill (AbM; 82.4%), Hericium erinaceum (14.7%), and Grifola frondosa (2.9%). The main ingredient of AndoSan, AbM, is rich in different forms of β-glucans. Since these exhibit potent antitumor activity and have immunomodulatory effects, the stimulatory effect of AndoSan on the production of different cytokines, chemokines, and leukocyte growth factors has predominantly been attributed to β-glucans. AndoSan has been claimed to consist of 90% carbohydrate, of which 2.8% is β-glucans, but in this study, we show that the carbohydrate content is only 2% of the dry weight, corresponding to 0.09% β-glucan per mL of AndoSan. Fractionation of AndoSan, followed by carbohydrate analysis and HPLC analysis revealed that most of the glucose was concentrated in the polar high molecular weight fraction of AndoSan (ethanol insoluble water extract [EIWE]-A) and that this extract was able to significantly inhibit the activity of the tumor-associated protease, legumain, in RAW 264.7 cells. Legumain is synthesized as a zymogen and undergoes pH-dependent autoactivation of the proform to reach an enzymatically active form. In this study, we demonstrate that both the polar and nonpolar AndoSan fractions are able to inhibit the autoactivation of prolegumain, and that the polar fractions of AndoSan are the most potent inhibitors of the active form of the enzyme.

The asparaginyl endopeptidase legumain is essential for functional recovery after spinal cord injury in adult zebrafish

Unlike mammals, adult zebrafish are capable of regenerating severed axons and regaining locomotor function after spinal cord injury. A key factor for this regenerative capacity is the innate ability of neurons to re-express growth-associated genes and regrow their axons after injury in a permissive environment. By microarray analysis, we have previously shown that the expression of legumain (also known as asparaginyl endopeptidase) is upregulated after complete transection of the spinal cord. In situ hybridization showed upregulation of legumain expression in neurons of regenerative nuclei during the phase of axon regrowth/sprouting after spinal cord injury. Upregulation of Legumain protein expression was confirmed by immunohistochemistry. Interestingly, upregulation of legumain expression was also observed in macrophages/microglia and neurons in the spinal cord caudal to the lesion site after injury. The role of legumain in locomotor function after spinal cord injury was tested by reducing Legumain expression by application of anti-sense morpholino oligonucleotides. Using two independent anti-sense morpholinos, locomotor recovery and axonal regrowth were impaired when compared with a standard control morpholino. We conclude that upregulation of legumain expression after spinal cord injury in the adult zebrafish is an essential component of the capacity of injured neurons to regrow their axons. Another feature contributing to functional recovery implicates upregulation of legumain expression in the spinal cord caudal to the injury site. In conclusion, we established for the first time a function for an unusual protease, the asparaginyl endopeptidase, in the nervous system. This study is also the first to demonstrate the importance of legumain for repair of an injured adult central nervous system of a spontaneously regenerating vertebrate and is expected to yield insights into its potential in nervous system regeneration in mammals.

Analysis of legumain and cystatin 6 expression at the maternal-fetal interface in pigs

Cathepsins (CTSs), a family of lysosomal cysteine proteases, and their inhibitors, cystatins (CSTs), play a critical role in endometrial and placental tissue remodeling during the establishment and maintenance of pregnancy in many species including rodents, sheep, cow, and pigs. In this study, we determined expression of legumain (LGMN), a cathepsinmember, and its inhibitor, CST6, at the maternal-fetal interface in pigs. Expression of both LGMN and CST6 mRNAs increased during mid- to late pregnancy in the uterine endometrium. LGMN and CST6 mRNAs localized to luminal epithelial cells (LE) and glandular epithelial cells (GE) and to the chorionic membrane (CM), with a strong intensity in GE and the CM for LGMN and in the CM for CST6 during pregnancy. LGMN protein was detected at molecular weights (MW) of approximately 50,000 and 37,000, and the abundance of the37,000-MW LGMN protein increased during mid- to latepregnancy. CST6 protein was also highly expressed in the uterine endometrium in mid- to latepregnancy. LGMN protein localized to LE, GE, and the CM during pregnancy. LGMN and CST6 were aberrantly expressed in the uterine endometrium from gilts with somatic cell nuclear transfer-derived conceptuses at term compared to those of gilts carrying conceptuses derived from natural mating. These results demonstrated that LGMN and CST6 were expressed in the uterine endometrium in a cell-type and stage-specific manner, suggesting that the LGMN and CST6 system at the maternal-fetal interface may play an important role in the establishment and maintenance of pregnancy in pigs.

Stabilization, characterization, and selective removal of cystatin C amyloid oligomers

The pathophysiological process in amyloid disorders usually involves the transformation of a functional monomeric protein via potentially toxic oligomers into amyloid fibrils. The structure and properties of the intermediary oligomers have been difficult to study due to their instability and dynamic equilibrium with smaller and larger species. In hereditary cystatin C amyloid angiopathy, a cystatin C variant is deposited in arterial walls and cause brain hemorrhage in young adults. In the present investigation, we use redox experiments of monomeric cystatin C, stabilized against domain swapping by an intramolecular disulfide bond, to generate stable oligomers (dimers, trimers, tetramers, decamers, and high molecular weight oligomers). These oligomers were characterized concerning size by gel filtration, polyacrylamide gel electrophoresis, and mass spectrometry, shape by electron and atomic force microscopy, and, function by assays of their capacity to inhibit proteases. The results showed the oligomers to be highly ordered, domain-swapped assemblies of cystatin C and that the oligomers could not build larger oligomers, or fibrils, without domain swapping. The stabilized oligomers were used to induce antibody formation in rabbits. After immunosorption, using immobilized monomeric cystatin C, and elution from columns with immobilized cystatin C oligomers, oligomer-specific antibodies were obtained. These could be used to selectively remove cystatin C dimers from biological fluids containing both dimers and monomers.

Nuclear legumain activity in colorectal cancer

The cysteine protease legumain is involved in several biological and pathological processes, and the protease has been found over-expressed and associated with an invasive and metastatic phenotype in a number of solid tumors. Consequently, legumain has been proposed as a prognostic marker for certain cancers, and a potential therapeutic target. Nevertheless, details on how legumain advances malignant progression along with regulation of its proteolytic activity are unclear. In the present work, legumain expression was examined in colorectal cancer cell lines. Substantial differences in amounts of pro- and active legumain forms, along with distinct intracellular distribution patterns, were observed in HCT116 and SW620 cells and corresponding subcutaneous xenografts. Legumain is thought to be located and processed towards its active form primarily in the endo-lysosomes; however, the subcellular distribution remains largely unexplored. By analyzing subcellular fractions, a proteolytically active form of legumain was found in the nucleus of both cell lines, in addition to the canonical endo-lysosomal residency. In situ analyses of legumain expression and activity confirmed the endo-lysosomal and nuclear localizations in cultured cells and, importantly, also in sections from xenografts and biopsies from colorectal cancer patients. In the HCT116 and SW620 cell lines nuclear legumain was found to make up approximately 13% and 17% of the total legumain, respectively. In similarity with previous studies on nuclear variants of related cysteine proteases, legumain was shown to process histone H3.1. The discovery of nuclear localized legumain launches an entirely novel arena of legumain biology and functions in cancer.

Hypovitaminosis D as predisposing factor for atrophic type A gastritis: a case-control study and review of the literature on the interaction of Vitamin D with the immune system

1,25-Dihydroxyvitamin D displays immunoregulatory and anti-inflammatory properties, and the cells involved in innate and adaptive immune response express the vitamin D receptor and can both produce and respond to this hormone. This article aims at describing the complex immune regulatory role of vitamin D and depicting whether a correlation exists between atrophic type A gastritis and hypovitaminosis. We studied 62 autoimmune gastritis (AIG) patients and compared them to 54 lymphocytic gastritis patients, 21 Helicobacter pylori gastritis patients and 212 healthy subjects. We also statistically analyzed vitamin D concentration in 36,384 outpatients referred to our clinical laboratories. 25-Hydroxyvitamin D levels, the measurable metabolite used to determine vitamin D status in plasma, were measured by a chemiluminescent method. Average level of 25-OHD in AIG subjects was 9.8 ± 5.6 ng/mL (95% confidence interval (CI) 8.4-11.2), 11.1 ± 8.4 (CI 7.5-14.7) in H. pylori gastritis patients, 22.2 ± 13.5 (CI 18.6-25.8) in nonspecific lymphocytic gastritis patients, 21.3 ± 12.2 (CI 19.7-22.9) in healthy subjects, and 21.8 ± 13.1 (CI 21.7-21.9) in the 36,384 outpatients. Vitamin D levels in AIG patients were significantly lower than in patients with nonspecific gastritis or in the general population, supporting the hypothesis that hypovitaminosis D might be a risk factor for the development of autoimmune diseases. The low vitamin D concentration in H. pylori gastritis patients might act as predisposing factor for a more severe Th1-type aggression to the stomach epithelium.

Intra- and extracellular regulation of activity and processing of legumain by cystatin E/M

Legumain, an asparaginyl endopeptidase, is up-regulated in tumour and tumour-associated cells, and is linked to the processing of cathepsin B, L, and proMMP-2. Although legumain is mainly localized to the endosomal/lysosomal compartments, legumain has been reported to be localized extracellularly in the tumour microenvironment and associated with extracellular matrix and cell surfaces. The most potent endogenous inhibitor of legumain is cystatin E/M, which is a secreted protein synthesised with an export signal. Therefore, we investigated the cellular interplay between legumain and cystatin E/M. As a cell model, HEK293 cells were transfected with legumain cDNA, cystatin E/M cDNA, or both, and over-expressing monoclonal cell lines were selected (termed M38L, M4C, and M3CL, respectively). Secretion of prolegumain from M38L cells was inhibited by treatment with brefeldin A, whereas bafilomycin A1 enhanced the secretion. Cellular processing of prolegumain to the 46 and 36 kDa enzymatically active forms was reduced by treatment with either substance alone. M38L cells showed increased, but M4C cells decreased, cathepsin L processing suggesting a crucial involvement of legumain activity. Furthermore, we observed internalization of cystatin E/M and subsequently decreased intracellular legumain activity. Also, prolegumain was shown to internalize followed by increased intracellular legumain processing and activation. In addition, in M4C cells incomplete processing of the internalized prolegumain was observed, as well as nuclear localized cystatin E/M. Furthermore, auto-activation of secreted prolegumain was inhibited by cystatin E/M, which for the first time shows a regulatory role of cystatin E/M in controlling both intra- and extracellular legumain activity.

Autophagic activity measured in whole rat hepatocytes as the accumulation of a novel BHMT fragment (p10), generated in amphisomes by the asparaginyl proteinase, legumain

To investigate the stepwise autophagic-lysosomal processing of hepatocellular proteins, the abundant cytosolic enzyme, betaine:homocysteine methyltransferase (BHMT) was used as a probe. Full-length (45 kDa) endogenous BHMT was found to be cleaved in an autophagy-dependent (3-methyladenine-sensitive) manner in isolated rat hepatocytes to generate a novel N-terminal 10-kDa fragment (p10) identified and characterized by mass spectrometry. The cleavage site was consistent with cleavage by the asparaginyl proteinase, legumain and indeed a specific inhibitor of this enzyme (AJN-230) was able to completely suppress p10 formation in intact cells, causing instead accumulation of a 42-kDa intermediate. To prevent further degradation of p10 or p42 by the cysteine proteinases present in autophagic vacuoles, the proteinase inhibitor leupeptin had to be present. Asparagine, an inhibitor of amphisome-lysosome fusion, did not detectably impede either p42 or p10 formation, indicating that BHMT processing primarily takes place in amphisomes rather than in lysosomes. Lactate dehydrogenase (LDH) was similarly degraded primarily in amphisomes by leupeptin-sensitive proteolysis, but some additional leupeptin-resistant LDH degradation in lysosomes was also indicated. The autophagic sequestration of BHMT appeared to be nonselective, as the accumulation of p10 (in the presence of leupeptin) or of its precursors (in the additional presence of AJN-230) proceeded at approximately the same rate as the model autophagic cargo, LDH. The complete lack of a cytosolic background makes p10 suitable for use in a "fragment assay" of autophagic activity in whole cells. Incubation of hepatocytes with ammonium chloride, which neutralizes amphisomes as well as lysosomes, caused rapid, irreversible inhibition of legumain activity and stopped all p10 formation. The availability of several methods for selective targeting of legumain in intact cells may facilitate functional studies of this enigmatic enzyme, and perhaps suggest novel ways to reduce its contribution to cancer cell metastasis or autoimmune disease.

Cystatin E/M suppresses legumain activity and invasion of human melanoma

Background

High activity of cysteine proteases such as legumain and the cathepsins have been shown to facilitate growth and invasion of a variety of tumor types. In breast cancer, several recent studies have indicated that loss of the cysteine protease inhibitor cystatin E/M leads to increased growth and metastasis. Although cystatin E/M is normally expressed in the skin, its role in cysteine protease regulation and progression of malignant melanoma has not been studied.

Methods

A panel of various non-melanoma and melanoma cell lines was used. Cystatin E/M and C were analyzed in cell media by immunoblotting and ELISA. Legumain, cathepsin B and L were analyzed in cell lysates by immunoblotting and their enzymatic activities were analyzed by peptide substrates. Two melanoma cell lines lacking detectable secretion of cystatin E/M were transfected with a cystatin E/M expression plasmid (pCST6), and migration and invasiveness were studied by a Matrigel invasion assay.

Results

Cystatin E/M was undetectable in media from all established melanoma cell lines examined, whereas strong immunobands were detected in two of five primary melanoma lines and in two of six lines derived from patients with metastatic disease. Among the four melanoma lines secreting cystatin E/M, the glycosylated form (17 kD) was predominant compared to the non-glycosylated form (14 kD). Legumain, cathepsin B and L were expressed and active in most of the cell lines, although at low levels in the melanomas expressing cystatin E/M. In the melanoma lines where cystatin E/M was secreted, cystatin C was generally absent or expressed at a very low level. When melanoma cells lacking secretion of cystatin E/M were transfected with pCST6, their intracellular legumain activity was significantly inhibited. In contrast, cathepsin B activity was not affected. Furthermore, invasion was suppressed in cystatin E/M over-expressing melanoma cell lines as measured by the transwell Matrigel assay.

Conclusions

These results suggest that the level of cystatin E/M regulates legumain activity and hence the invasive potential of human melanoma cells.

HlLgm2, a member of asparaginyl endopeptidases/legumains in the midgut of the ixodid tick Haemaphysalis longicornis, is involved in blood-meal digestion

Here we describe a cDNA encoding the second asparaginyl endopeptidase/legumain (HlLgm2) from the midgut of the ixodid tick Haemaphysalis longicornis. Endogenous HlLgm2 was expressed in all the developmental stages of the tick, localized mainly in the midgut epithelium and was up-regulated by the host blood-feeding process, as demonstrated by immunoblotting and immunohistochemistry. RT-PCR and real-time PCR showed that the HlLgm2 gene was expressed at a lower level during all phases of blood-feeding than our previously characterized legumain (HlLgm) gene from the same tick. More strikingly, there was no expression of HlLgm2 mRNA beyond 96 h of blood-feeding, while HlLgm mRNA expression continued until full engorgement. Escherichia coli-expressed recombinant HlLgm2 (rHlLgm2) efficiently hydrolysed the legumain-specific synthetic substrate. rHlLgm2 activity was inhibited by iodoacetamide and N-ethylmaleimide and also by Fe(2+), Cu(2+), Co(2+) and Ni(2+). rHlLgm2 digested bovine haemoglobin and exhibited strict specificity for the asparaginyl bonds on the carboxy-terminal side of a peptide, as demonstrated by internal amino acid sequence analysis of the cleaved bovine serum albumin products. Our results suggest that HlLgm2, together with HlLgm, plays a pivotal role in host blood-meal digestion process.

Characterization of asparaginyl endopeptidase, legumain induced by blood feeding in the ixodid tick Haemaphysalis longicornis

We characterize here a cDNA from the ixodid tick Haemaphysalis longicornis, which encodes an asparaginyl endopeptidase, legumain (HlLgm), that was present as a functional molecule in the midgut of this tick. Endogenous HlLgm was detected as a 38-kDa antigen in H. longicornis extracts and was seen throughout all developmental stages. Endogenous HlLgm was mainly localized in the midgut epithelium by immunohistochemistry, and was shown to be up-regulated by the host blood-feeding process. Recombinant HlLgm (rHlLgm) produced in Escherichia coli was shown to hydrolyze the synthetic substrate Z-Ala-Ala-Asn-MCA at the rate of 6.42x10(-4)mumol/min/mg protein. Its activity was inhibited by the thiol blocking reagents iodoacetamide and N-ethylmaleimide. The enzyme was shown to possess a unique feature of having an autocatalyzed cleavage at asparagines(364-365) at the C-terminus of both endogenous HlLgm and rHlLgm. rHlLgm degraded bovine hemoglobin and bovine serum albumin (BSA) showing its strict specificity for hydrolysis of the peptide on the carboxyl side of the asparagines, as demonstrated by internal amino acid sequence analysis of proteolytic product of BSA cleavage. These results suggest that HlLgm plays an important role in host blood-meal digestion and may be critical for the final process of digestion of blood components.

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.

Comparison of natural and recombinant clitocypins, the fungal cysteine protease inhibitors

A member of the cysteine protease inhibitor clitocypin gene family from basidiomycete Clitocybe nebularis was expressed in Escherichia coli. Following careful optimization of the expression procedure the active inhibitor was purified from inclusion bodies and its properties examined and compared to those of the natural clitocypin. The CD spectrum of recombinant clitocypin was similar to that of natural clitocypin, indicating that protein was properly refolded during purification. In spite of some differences in primary structure, structural, functional and immunological equivalence was established. Kinetic analyses of the natural and recombinant clitocypins were performed. Both clitocypins inhibited a range of cysteine proteases to a similar extent, and demonstrated an unusually broad inhibitory spectrum, including distantly related proteases, such as papain and legumain, belonging to different protease families. The homogenous, biologically active recombinant clitocypin is obtained at levels adequate for further structure-function studies.

Proteinases participating in the processing and activation of prolegumain in primary cultured rat macrophages

The mammalian legumain is a recently identified lysosomal cysteine proteinase belonging to the clan CD and homologous to plant legumain. This enzyme has the characteristic of specifically hydrolyzing peptide bonds after asparagine residues. As in the case of papain-type cysteine proteinases, legumain is synthesized as an inactive zymogen, and processed into a mature form localized in lysosomes. However, the mechanism of its activation remains unclear. In this study, we analyze which types of proteinases may participate in the processing of legumain in rat primary cultured macrophages using various proteinase inhibitors after 24 h treatment with Bafilomycin A1, a vacuolar ATPase inhibitor. The processing of legumain in macrophages was accomplished by papain-type cysteine proteinases other than cathepsin B.

Fusion of lamellar body with plasma membrane is driven by the dual action of annexin II tetramer and arachidonic acid

Annexin II has been implicated in membrane fusion during the exocytosis of lamellar bodies from alveolar epithelial type II cells. Most previous studies were based on the fusion assays by using model membranes. In the present study, we investigated annexin II-mediated membrane fusion by using isolated lamellar bodies and plasma membrane as determined by the relief of octadecyl rhodamine B (R18) self-quenching. Immunodepletion of annexin II from type II cell cytosol reduced its fusion activity. Purified annexin II tetramer (AIIt) induced the fusion of lamellar bodies with the plasma membrane in a dose-dependent manner. This fusion is Ca2+-dependent and is highly specific to AIIt because other annexins (I and II monomer, III, IV, V, and VI) were unable to induce the fusion. Modification of the different functional residues of AIIt by N-ethylmaleimide, nitric oxide, or peroxynitrite abolished AIIt-mediated fusion. Arachidonic acid enhanced AIIt-mediated fusion and reduced its Ca2+ requirement to an intracellularly achievable level. This effect is due to membrane-bound arachidonic acid, not free arachidonic acid. Other fatty acids including linolenic acid, palmitoleic acid, myristoleic acid, stearic acid, palmitic acid, and myristic acid had little effect. AIIt-mediated fusion was suppressed by the removal of arachidonic acid from lamellar body and plasma membrane using bovine serum albumin. The addition of arachidonic acid back to the arachidonic acid-depleted membranes restored its fusion activity. Our results suggest that the fusion between lamellar bodies with the plasma membrane is driven by the synergistic action of AIIt and arachidonic acid.

Biosynthetic processing of cathepsins and lysosomal degradation are abolished in asparaginyl endopeptidase-deficient mice

Asparaginyl endopeptidase (AEP)/legumain, an asparagine-specific cysteine proteinase in animals, is an ortholog of plant vacuolar processing enzyme (VPE), which processes the exposed asparagine residues of various vacuolar proteins. In search for its physiological role in mammals, here we generated and characterized AEP-deficient mice. Although their body weights were significantly reduced, they were normally born and fertile. In the wild-type kidney where the expression of AEP was exceedingly high among various organs, the localization of AEP was mainly found in the lamp-2-positive late endosomes in the apical region of the proximal tubule cells. In these cells of AEP-deficient mice, the lamp-2-positive membrane structures were found to be greatly enlarged. These aberrant lysosomes, merged with the late endosomes, accumulated electron-dense and membranous materials. Furthermore, the processing of the lysosomal proteases, cathepsins B, H, and L, from the single-chain forms into the two-chain forms was completely defected in the deficient mice. Thus, the AEP deficiency caused the accumulation of macromolecules in the lysosomes, highlighting a pivotal role of AEP in the endosomal/lysosomal degradation system.