Human NRD convertase: a highly conserved metalloendopeptidase expressed at specific sites during development and in adult tissues

Loss of Nardilysin, a Mitochondrial Co-chaperone for α-Ketoglutarate Dehydrogenase, Promotes mTORC1 Activation and Neurodegeneration

We previously identified mutations in Nardilysin (dNrd1) in a forward genetic screen designed to isolate genes whose loss causes neurodegeneration in Drosophila photoreceptor neurons. Here we show that NRD1 is localized to mitochondria, where it recruits mitochondrial chaperones and assists in the folding of α-ketoglutarate dehydrogenase (OGDH), a rate-limiting enzyme in the Krebs cycle. Loss of Nrd1 or Ogdh leads to an increase in α-ketoglutarate, a substrate for OGDH, which in turn leads to mTORC1 activation and a subsequent reduction in autophagy. Inhibition of mTOR activity by rapamycin or partially restoring autophagy delays neurodegeneration in dNrd1 mutant flies. In summary, this study reveals a novel role for NRD1 as a mitochondrial co-chaperone for OGDH and provides a mechanistic link between mitochondrial metabolic dysfunction, mTORC1 signaling, and impaired autophagy in neurodegeneration.

Heparin-binding EGF-like growth factor and enteric neural stem cell transplantation in the prevention of experimental necrotizing enterocolitis in mice

BACKGROUND

Necrotizing enterocolitis (NEC) is associated with loss of neurons and glial cells in the enteric nervous system (ENS). Our goal was to determine whether enteric neural stem cell (NSC) transplantation, in conjunction with heparin-binding epidermal growth factor-like growth factor (HB-EGF), could protect against experimental NEC.

METHODS

In vitro, HB-EGF on NSC proliferation and migration, and the effects of receptors utilized by HB-EGF to exert these effects, were determined. In vivo, mouse pups were exposed to experimental NEC and treated with NSC alone, HB-EGF alone, NSC+HB-EGF, or HB-EGF overexpressing NSC. NSC engraftment and differentiation into neurons in the ENS, intestinal injury, intestinal permeability, and intestinal motility were determined.

RESULTS

HB-EGF promoted NSC proliferation via ErbB-1 receptors and enhanced NSC migration via ErbB-1, ErbB-4, and Nardilysin receptors. HB-EGF significantly enhanced the engraftment of transplanted NSC into the ENS during NEC. NSC transplantation significantly reduced NEC incidence and improved gut barrier function and intestinal motility, and these effects were augmented by simultaneous administration of HB-EGF or by transplantation of HB-EGF overexpressing NSC.

CONCLUSION

HB-EGF promotes NSC proliferation and migration. HB-EGF and NSC reduce intestinal injury and improve gut barrier function and intestinal motility in experimental NEC. Combined HB-EGF and NSC transplantation may represent a potential future therapy to prevent NEC.

Genome-wide association discoveries of alcohol dependence

OBJECTIVE

To report the genome-wide significant and/or replicable risk variants for alcohol dependence and explore their potential biological functions.

METHODS

We searched in PubMed for all genome-wide association studies (GWASs) of alcohol dependence. The following three types of the results were extracted: genome-wide significant associations in an individual sample, the combined samples, or the meta-analysis (p < 5 × 10(-8) ); top-ranked associations in an individual sample (p < 10(-5) ) that were nominally replicated in other samples (p < .05); and nominally replicable associations across at least three independent GWAS samples (p < .05). These results were meta-analyzed. cis-eQTLs in human, RNA expression in rat and mouse brains and bioinformatics properties of all of these risk variants were analyzed.

RESULTS

The variants located within the alcohol dehydrogenase (ADH) cluster were significantly associated with alcohol dependence at the genome-wide level (p < 5 × 10(-8) ) in at least one sample. Some associations with the ADH cluster were replicable across six independent GWAS samples. The variants located within or near SERINC2, KIAA0040, MREG-PECR or PKNOX2 were significantly associated with alcohol dependence at the genome-wide level (p < 5 × 10(-8) ) in meta-analysis or combined samples, and these associations were replicable across at least one sample. The associations with the variants within NRD1, GPD1L-CMTM8 or MAP3K9-PCNX were suggestive (5 × 10(-8)  < p < 10(-5) ) in some samples, and nominally replicable in other samples. The associations with the variants at HTR7 and OPA3 were nominally replicable across at least three independent GWAS samples (10(-5)  < p < .05). Some risk variants at the ADH cluster, SERINC2, KIAA0040, NRD1, and HTR7 had potential biological functions.

CONCLUSION

The most robust risk locus was the ADH cluster. SERINC2, KIAA0040, NRD1, and HTR7 were also likely to play important roles in alcohol dependence. PKNOX2, MREG, PECR, GPD1L, CMTM8, MAP3K9, PCNX, and OPA3 might play less important roles in risk for alcohol dependence based on the function analysis. This conclusion will significantly contribute to the post-GWAS follow-up studies on alcohol dependence.

NRD1, which encodes nardilysin protein, promotes esophageal cancer cell invasion through induction of MMP2 and MMP3 expression

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignancies worldwide. In the present study, to identify novel prognostic markers or therapeutic targets for ESCC, we reviewed a list of genes with upregulated expression in ESCC compared with normal esophagus, as identified by our serial analysis of gene expression (SAGE) analysis. We focused on the NRD1 gene, which encodes the nardilysin protein. Quantitative reverse transcription–polymerase chain reaction (qRT-PCR) in 34 ESCC tissue samples revealed that mRNA expression of NRD1 was upregulated in 56% of ESCC tissue samples. Immunohistochemical analysis of nardilysin in 109 ESCC tissue samples demonstrated that 43 (39%) ESCC cases were positive for nardilysin. Nardilysin-positive ESCC cases were more advanced in terms of T classification (P = 0.0007), N classification (P = 0.0164), and tumor stage (P < 0.0001) than nardilysin-negative ESCC cases. Furthermore, nardilysin expression was significantly associated with poorer prognosis (P = 0.0258). Univariate and multivariate analyses revealed that nardilysin expression is an independent prognostic classifier of patients with ESCC. The invasiveness of NRD1-knockdown TE1 and TE5 esophageal cancer cell lines was less than that of the negative control siRNA-transfected cell lines. Expression of MMP2 and MMP3 mRNA was significantly lower in NRD1-knockdown TE5 cells than in negative control siRNA-transfected cells. These results suggest that nardilysin is involved in tumor progression, and is an independent prognostic classifier in patients with ESCC.

Nardilysin in human brain diseases: both friend and foe

Nardilysin is a metalloprotease that cleaves peptides, such as dynorphin-A, α-neoendorphin, and glucagon, at the N-terminus of arginine and lysine residues in dibasic moieties. It has various functionally important molecular interaction partners (heparin-binding epidermal growth factor-like growth factor, tumour necrosis factor-α-converting enzyme, neuregulin 1, beta-secretase 1, malate dehydrogenase, P42(IP4)/centaurin-α1, the histone H3 dimethyl Lys4, and others) and is involved in a plethora of normal brain functions. Less is known about possible implications of nardilysin for brain diseases. This review, which includes some of our own recent findings, attempts to summarize the current knowledge on possible roles of nardilysin in Alzheimer disease, Down syndrome, schizophrenia, mood disorders, alcohol abuse, heroin addiction, and cancer. We herein show that nardilysin is a Janus-faced enzyme with regard to brain pathology, being probably neuropathogenic in some diseases, but neuroprotective in others.

Decreased expression of nardilysin in SH-SY5Y cells under ethanol stress and reduced density of nardilysin-expressing neurons in brains of alcoholics

There is evidence for a genetic link between the metalloendopeptidase nardilysin and alcohol dependence, but the functional implication of the enzyme in alcoholism is unknown. Interestingly, some of the enzyme's substrates and interaction partners are altered in neural and non-neural tissues under the influence of ethanol consumption. To learn more about putative roles of nardilysin in alcohol dependence we studied the expression of the enzyme protein in human neuroblastoma cells under chronic ethanol exposure as well as in four brain regions of alcoholics and matched controls. Cultured SH-SY5Y cells were exposed for 96 h to two different concentrations of ethanol (50 and 200 mM). Nardilysin expression was determined using Western blotting with densitometric analysis. Furthermore, we morphometrically studied the cellular expression of nardilysin in postmortem brains of eight chronic alcoholics and nine controls by counting the number of nardilysin-immunopositive neurons in left frontal limbic area, Nuc. basalis of Meynert, paraventricular and supraoptic hypothalamic nuclei and calculating numerical cell densities. Nardilysin expression was significantly reduced after 96 h of SH-SY5Y cells exposure to 200 mM ethanol. In human brains nardilysin protein was localized to multiple neurons. In heavy drinkers there was a significantly reduced density of nardilysin immunoreactive neurons in Nuc. basalis of Meynert, paraventricular, and supraoptic nuclei. The alcohol-dependent reduction of nardilysin in cell culture and nervous tissue points to an implication of the enzyme in the pathophysiology of alcoholism.

Identification and characterization of nardilysin as a novel dimethyl H3K4-binding protein involved in transcriptional regulation

Histone methylation on lysine residues is believed to function primarily as docking sites to recruit specific proteins termed as histone code "readers" or "effectors." Each lysine residue can be mono-, di, and tri-methylated and different methylation states can have different effect on chromatin function. While an increasing number of proteins have been identified and characterized as specific effectors for methylated histones, very few of the proteins are known to recognize a particular state of methylation. In this study, we identified nardilysin (NRDc), a member of M16 family metalloendopeptidases, as a novel dimethyl-H3K4 (H3K4me2)-binding protein. Among three methylated states, NRDc binds preferentially H3K4me2 both in vitro and in vivo. Biochemical purification demonstrated that NRDc interacts with the NCoR/SMRT corepressor complex. We identified target genes repressed by NRDc through microarray. We showed that NRDc is physically associated with and recruits the NCoR complex to some of the repressed genes and this association correlates with binding of H3K4me2. Thus, our study has identified a novel H3K4me2-binding protein and revealed a role of NRDc in transcriptional regulation.

A meta-analysis of two genome-wide association studies identifies 3 new loci for alcohol dependence

Family, twin and adoption studies have clearly demonstrated that genetic factors are important in modulating the vulnerability to alcohol dependence. Several genome-wide association (GWA) studies of alcohol dependence have been conducted; however, few loci have been replicated. A meta-analysis was performed on two GWA studies of 1283 cases of alcohol dependence and 1416 controls in Caucasian populations. Through meta-analysis we identified 131 SNPs associated with alcohol dependence with p<10(-4). The best novel signal was rs6701037 (p=1.86 × 10(-7)) at 1q24-q25 within KIAA0040 gene while the second best novel hit was rs1869324 (p=4.71 × 10(-7)) at 2q22.1 within THSD7B. The third novel locus was NRD1 at 1p32.2 (the top SNP was rs2842576 with p=7.90 × 10(-6)). We confirmed the association of PKNOX2 at 11q24.4 with alcohol dependence. The top hit of PKNOX2 (rs750338 with p=1.47 × 10(-6)) in the meta-analysis was replicated with the Australian Twin-Family Study of 778 families (p=1.39 × 10(-2)) Furthermore, several flanking SNPs of the top hits in the meta-analysis demonstrated borderline associations with alcohol dependence in the family sample (top SNPs were rs2269655, rs856613, and rs10496768 with p=4.58 × 10(-3), 2.1 × 10(-4), and 2.86 × 10(-3) for KIAA0040, NRD1 and THSD7B, respectively). In addition, ALK, CASC4, and SEMA5A were strongly associated with alcohol dependence (p<2 × 10(-5)) in the meta-analysis. In conclusion, we identified three new loci (KIAA0040, THSD7B and NRD1) and confirmed the previous association of PKNOX2 with alcohol dependence. These findings offer the potential for new insights into the pathogenesis of alcohol dependence.

Tubulin potentiates the interaction of the metalloendopeptidase nardilysin with the neuronal scaffold protein p42IP4/centaurin-α1 (ADAP1)

We found colocalization of the neuronal protein p42(IP4) (centaurin-α1; ArfGAP with dual pleckstrin homology domain [ADAP1]), the metalloendopeptidase nardilysin (NRD; involved in axonal maturation and myelination) and tubulin in the cytosol and at the plasma membrane of SH-SY5Y neuroblastoma cells. To examine the importance of tubulin for the interaction of NRD with p42(IP4), we treated cells with nocodazole, which interferes with tubulin polymerization. Nocodazole did not affect the colocalization of p42(IP4) and tubulin but caused a clear redistribution of the proteins in cells, so that the colocalization of p42(IP4), tubulin and NRD was visible exclusively in multiple foci. To reveal the mechanism of the interaction between NRD, p42(IP4) and tubulin observed in neuronal cells, we performed Far-Western blotting, a technique that directly detects protein-protein interactions on Western blots. This technique demonstrated that tubulin enhanced the binding of NRD to functionally renatured p42(IP4). The mutation of a highly conserved cysteine residue in NRD to alanine abolished the potentiation by tubulin. NRD lacking the characteristic acidic domain was able to bind p42(IP4) but addition of tubulin did not significantly potentiate the binding of this deletion mutant to p42(IP4). A function-abolishing mutation of the Zn(2+)-binding motif of NRD did not affect the potentiation by tubulin. Thus, the capacity of tubulin to enhance the interaction between p42(IP4) and NRD together with the known interaction of p42(IP4) with F-actin support the novel notion that p42(IP4) plays a possible role as a linker between the two networks, actin and tubulin, in neural cells.

Retinoic acid-induced upregulation of the metalloendopeptidase nardilysin is accelerated by co-expression of the brain-specific protein p42(IP4) (centaurin α 1; ADAP1) in neuroblastoma cells

The mainly neuronally expressed protein p42(IP4) (centaurin α1; ADAP1), which interacts with the metalloendopeptidase nardilysin (NRD) was found to be localized in neuritic plaques in Alzheimer disease (AD) brains. NRD was shown to enhance the cleavage of the amyloid precursor protein (APP) by α-secretases, thereby increasing the release of neuroprotective sAPPα. We here investigated in vitro the biochemical interaction of p42(IP4) and NRD and studied the physiological interaction in SH-SY5Y cells. NRD is a member of the M16 family of metalloendopeptidases. Some members of this M16 family act bi-functionally, as protease and as non-enzymatic scaffold protein. Here, we show that p42(IP4) enhances the enzymatic activity of NRD 3-4 times. However, p42(IP4) is not a substrate for NRD. Furthermore, we report that differentiation of SH-SY5Y cells by stimulation with 10μM retinoic acid (RA) results in upregulation of NRD protein levels, with a 6-fold rise after 15 days. NRD is expressed in the neurites of RA-stimulated SH-SY5Y cells, and localized in vesicular structures. Since p42(IP4) is not expressed in untreated SH-SY5Y cells, we could use this cell system as a model to find out, whether there is a functional interaction. Interestingly, SH-SY5Y cells, which we stably transfected with GFP-tagged-p42(IP4) showed an enhanced NRD protein expression already at an earlier time point after RA stimulation.

The genome of the leaf-cutting ant Acromyrmex echinatior suggests key adaptations to advanced social life and fungus farming

We present a high-quality (>100× depth) Illumina genome sequence of the leaf-cutting ant Acromyrmex echinatior, a model species for symbiosis and reproductive conflict studies. We compare this genome with three previously sequenced genomes of ants from different subfamilies and focus our analyses on aspects of the genome likely to be associated with known evolutionary changes. The first is the specialized fungal diet of A. echinatior, where we find gene loss in the ant's arginine synthesis pathway, loss of detoxification genes, and expansion of a group of peptidase proteins. One of these is a unique ant-derived contribution to the fecal fluid, which otherwise consists of "garden manuring" fungal enzymes that are unaffected by ant digestion. The second is multiple mating of queens and ejaculate competition, which may be associated with a greatly expanded nardilysin-like peptidase gene family. The third is sex determination, where we could identify only a single homolog of the feminizer gene. As other ants and the honeybee have duplications of this gene, we hypothesize that this may partly explain the frequent production of diploid male larvae in A. echinatior. The fourth is the evolution of eusociality, where we find a highly conserved ant-specific profile of neuropeptide genes that may be related to caste determination. These first analyses of the A. echinatior genome indicate that considerable genetic changes are likely to have accompanied the transition from hunter-gathering to agricultural food production 50 million years ago, and the transition from single to multiple queen mating 10 million years ago.

Antigen processing by nardilysin and thimet oligopeptidase generates cytotoxic T cell epitopes

Cytotoxic T lymphocytes (CTLs) recognize peptides presented by HLA class I molecules on the cell surface. The C terminus of these CTL epitopes is considered to be produced by the proteasome. Here we demonstrate that the cytosolic endopeptidases nardilysin and thimet oligopeptidase (TOP) complemented proteasome activity. Nardilysin and TOP were required, either together or alone, for the generation of a tumor-specific CTL epitope from PRAME, an immunodominant CTL epitope from Epstein-Barr virus protein EBNA3C, and a clinically important epitope from the melanoma protein MART-1. TOP functioned as C-terminal trimming peptidase in antigen processing, and nardilysin contributed to both the C-terminal and N-terminal generation of CTL epitopes. By broadening the antigenic peptide repertoire, nardilysin and TOP strengthen the immune defense against intracellular pathogens and cancer.

Expression of type II chorionic gonadotropin genes supports a role in the male reproductive system

Human chorionic gonadotropin (hCG) is a glycoprotein hormone essential to pregnancy. hCG is heterodimeric and functionally defined by its β subunit. hCGβ evolved from the β subunit of luteinizing hormone in two phases. In the first phase, type I genes (hCGβ3, -5, -7, and -8) acquired changes affecting gene expression and extending the proteins' C terminus. In the second phase, type II genes (hCGβ1 and -2) were formed by the insertion of a DNA element into the type I 5' end. The insertion includes the small noncoding RNA gene snaR-G and has been predicted to drastically change the protein products encoded. We trace the insertion to the common ancestor of the African great apes and show that it contains transcription signals, including snaR-G. Type II transcripts are predominantly expressed in testis. Contrary to predictions, the product of the major mRNA splice form is hCGβ. A novel peptide is encoded by alternatively spliced transcripts. These findings support the view that type II genes evolved in African great apes to function in the male reproductive system.

Histochemical evidence for wide expression of the metalloendopeptidase nardilysin in human brain neurons

Nardilysin is a metalloendopeptidase that in vitro cleaves peptides such as dynorphin-A, somatostatin-28, alpha-neoendorphin and glucagon at the N-terminus of arginine and lysine residues in dibasic moieties. The enzyme is highly expressed in many endocrine tissues. Nardilysin has also been found in the brain. Previously, we have detected that nardilysin interacts with brain-specific proteins, i.e. p42(IP4)/centaurin-alpha1 [Stricker R, Chow KM, Walther D, Hanck T, Hersh LB, Reiser G (2006) Interaction of the brain specific protein p42(IP4)/centaurin-alpha1 with the peptidase nardilysin is regulated by the cognate ligands of p42(IP4), PtdIns(3,4,5)P(3) and Ins(1,3,4,5)P(4), with stereospecificity. J Neurochem 98:343-354]. However, very little is known about the distribution of nardilysin in the brain. The aim of the present study was to reveal its regional distribution and cellular localization in developing and adult human brain. Using immunohistochemistry and Western blot analysis we demonstrate that the enzyme is widely, but unevenly, expressed in the human brain. We found high staining intensity in the hypothalamus, neocortex and brain stem nuclei. The cellular localization is almost exclusively confined to neurons. In pre- and perinatal human brain cortex, most neurons express the enzyme. In cortical neurons nardilysin protein was found to be partially co-localized with parvalbumin but not calretinin. No co-expression was seen with somatostatin-28 immunoreactivity. A considerable overlap was revealed between p42(IP4) and nardilysin. Our data support the hypothesis that nardilysin might possibly play a role in brain development, whereas its putative function in brain peptide metabolism remains to be clarified further.

Skeletal muscle stem cells express anti-apoptotic ErbB receptors during activation from quiescence

To be effective for tissue repair, satellite cells (the stem cells of adult muscle) must survive the initial activation from quiescence. Using an in vitro model of satellite cell activation, we show that erbB1, erbB2 and erbB3, members of the EGF receptor tyrosine kinase family, appear on satellite cells within 6 h of activation. We show that signalling via erbB2 provides an anti-apoptotic survival mechanism for satellite cells during the first 24 h, as they progress to a proliferative state. Inhibition of erbB2 signalling with AG825 reduced satellite cell numbers, concomitant with elevated caspase-8 activation and TUNEL labelling of apoptotic satellite cells. In serum-free conditions, satellite cell apoptosis could be largely prevented by a mixture of erbB1, erbB3 and erbB4 ligand growth factors, but not by neuregulin alone (erbB3/erbB4 ligand). Furthermore, using inhibitors specific to discrete intracellular signalling pathways, we identify MEK as a pro-apoptotic mediator, and the erbB-regulated factor STAT3 as an anti-apoptotic mediator during satellite cell activation. These results implicate erbB2 signalling in the preservation of a full compliment of satellite cells as they activate in the context of a damaged muscle.

Nardilysin enhances ectodomain shedding of heparin-binding epidermal growth factor-like growth factor through activation of tumor necrosis factor-alpha-converting enzyme

Like other members of the epidermal growth factor family, heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized as a transmembrane protein that can be shed enzymatically to release a soluble growth factor. Ectodomain shedding is essential to the biological functions of HB-EGF and is strictly regulated. However, the mechanism that induces the shedding remains unclear. We have recently identified nardilysin (N-arginine dibasic convertase (NRDc)), a metalloendopeptidase of the M16 family, as a protein that specifically binds HB-EGF (Nishi, E., Prat, A., Hospital, V., Elenius, K., and Klagsbrun, M. (2001) EMBO J. 20, 3342-3350). Here, we show that NRDc enhances ectodomain shedding of HB-EGF. When expressed in cells, NRDc enhanced the shedding in cooperation with tumor necrosis factor-alpha-converting enzyme (TACE; ADAM17). NRDc formed a complex with TACE, a process promoted by phorbol esters, general activators of ectodomain shedding. NRDc enhanced TACE-induced HB-EGF cleavage in a peptide cleavage assay, indicating that the interaction with NRDc potentiates the catalytic activity of TACE. The metalloendopeptidase activity of NRDc was not required for the enhancement of HB-EGF shedding. Notably, a reduction in the expression of NRDc caused by RNA interference was accompanied by a decrease in ectodomain shedding of HB-EGF. These results indicate the essential role of NRDc in HB-EGF ectodomain shedding and reveal how the shedding is regulated by the modulation of sheddase activity.

Interaction of the brain-specific protein p42IP4/centaurin-alpha1 with the peptidase nardilysin is regulated by the cognate ligands of p42IP4, PtdIns(3,4,5)P3 and Ins(1,3,4,5)P4, with stereospecificity

The brain-specific protein p42IP4, also called centaurin-alpha1, specifically binds phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. Here, we investigate the interaction of p42IP4/centaurin-alpha1 with nardilysin (NRDc), a member of the M16 family of zinc metalloendopeptidases. Members of this peptidase family exhibit enzymatic activity and also act as receptors for other proteins. We found that p42IP4/centaurin-alpha1 binds specifically to NRDc from rat brain. We further detected that centaurin-alpha2, a protein that is highly homologous to p42IP4/centaurin-alpha1 and expressed ubiquitously, also binds to NRDc. In vivo interaction was demonstrated by co-immunoprecipitation of p42IP4/centaurin-alpha1 with NRDc from rat brain. The acidic domain of NRDc (NRDc-AD), which does not participate in catalysis, is sufficient for the protein interaction with p42IP4. Interestingly, preincubation of p42IP4 with its cognate ligands D-Ins(1,3,4,5)P4 and the lipid diC8PtdIns(3,4,5)P3 negatively modulates the interaction between the two proteins. D-Ins(1,3,4,5)P4 and diC8PtdIns(3,4,5)P3 suppress the interaction with virtually identical concentration dependencies. This inhibition is highly ligand specific. The enantiomer L-Ins(1,3,4,5)P4 is not effective. Similarly, the phosphoinositides diC8PtdIns(3,4)P2, diC8PtdIns(3,5)P2 and diC8PtdIns(4,5)P2 all have no influence on the interaction. Further experiments revealed that endogenous p42IP4 from rat brain binds to glutathione-S-transferase (GST)-NRDc-AD. The proteins dissociate from each other when incubated with D-Ins(1,3,4,5)P4, but not with inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]. In summary, we demonstrate that p42IP4 binds to NRDc via the NRDc-AD, and that this interaction is controlled by the cognate cellular ligands of p42IP4/centaurin-alpha1. Thus, specific ligands of p42IP4 can modulate the recruitment of proteins, which are docked to p42IP4, to specific cellular compartments.

Nardilysin facilitates complex formation between mitochondrial malate dehydrogenase and citrate synthase

Gel filtration chromatography showed that nardilysin activity in a rat testis or rat brain extract exhibited an apparent molecular weight of approximately 300 kDa compared to approximately 187 kDa for the purified enzyme. The addition of purified nardilysin to a rat brain extract, but not to an E. coli extract, produced the higher molecular species. The addition of a GST fusion protein containing the acidic domain of nardilysin eliminated the higher molecular weight nardilysin forms, suggesting that oligomerization involves the acidic domain of nardilysin. Using an immobilized nardilysin column, mitochondrial malate dehydrogenase (mMDH) and citrate synthase (CS) were isolated from a fractionated rat brain extract. Porcine mMDH, but not porcine cytosolic MDH, was shown to form a heterodimer with nardilysin. Mitochondrial MDH increased nardilysin activity about 50%, while nardilysin stabilized mMDH towards heat inactivation. CS was co-immunoprecipitated with mMDH only in the presence of nardilysin showing that nardilysin facilitates complex formation.

Subcellular localization of nardilysin during mouse oocyte maturation

We have previously shown that the peptidase, nardilysin, contains a bipartite nuclear localization signal that permits the enzyme to cycle between the nucleus and cytoplasm. In the present study, we report that nardilysin accumulates in the nucleus of an oocyte as a function of its maturation. Nardilysin is predominantly localized in the cytoplasm of an oocyte when initially placed into culture. The enzyme starts to accumulate in the nucleus within 30 min of in vitro culture. After 3 h, nardilysin is found as a spherical structure surrounded by condensed chromosomal DNA. After 18 h of in vitro culture, it co-localizes with beta-tubulin at the spindle apparatus. Cilostamide, a phosphodiesterase 3A inhibitor that inhibits meiosis, blocks accumulation of nuclear nardilysin. This finding demonstrates that the nuclear entry of nardilysin is tightly controlled in the oocyte. Taken together, these experiments strongly suggest a role for nardilysin in meiosis through its dynamic translocation from cytosol to nucleus, and then to the spindle apparatus.

Heparin-binding EGF-like growth factor shows transient left–right asymmetrical expression in mouse myotome pairs

Heparin-binding EGF-like growth factor (HB-EGF) is a potent mitogen and chemoattractant for diverse cell types including, keratinocytes, fibroblasts and vascular smooth muscle cells. In adult mice, skeletal muscle and endothelial cells prominently express HB-EGF, although analysis of embryonic expression has been limited to studies of heart and kidney development. Here we survey HB-EGF mRNA expression in E7.5-E15 mouse embryos and show that HB-EGF is expressed in branchial arches, limb buds and, transiently, in mature somites between E9.25 and E11. This somitic expression is restricted to the myotomal compartment. Intriguingly, within myotome pairs, the expression of HB-EGF is stronger on the left side of the body, whilst cognate receptors, ErbB1 and ErbB4, are symmetrically expressed in left and right somite pairs. In iv/iv mutant embryos, with inverted left-right body axis, the expression of HB-EGF was also inverted, now being stronger in myotomes on the right side of the body. Thus, the expression of HB-EGF in myotome pairs is regulated by global cues that define the left-right body axis.

Nuclear shuttling of the peptidase nardilysin

The metalloendopeptidase nardilysin contains a putative N-terminal nuclear localization signal. The functionality of this sequence was tested with nardilysin-GFP fusion constructs. Expression in NIH3T3 cells showed approximately 90-95% of nardilysin-GFP as cytoplasmic. However, 3-6% of transfected cells showed both cytosolic and nuclear staining, while 2-4% showed predominantly nuclear staining. A nuclear localization signal mutant and an N-terminally truncated nardilysin-GFP with the nuclear localization signal deleted were completely cytoplasmic. Although endogenous nardilysin was barely detectable in the nucleus, after treatment with leptomycin B, nuclear nardilysin rose to approximately 15% and to over 25% after addition of spermine. The ability of a methionine 49 to act as the sole initiator methionine, as previously proposed, was tested by inserting a c-myc epitope between leucine28 and glycine29. Expression in HEK293 cells showed the presence of the c-myc tag, demonstrating that the enzyme can be translated from the first methionine and contains the nuclear localization signal.

The metalloendopeptidase nardilysin (NRDc) is potently inhibited by heparin-binding epidermal growth factor-like growth factor (HB-EGF)

Nardilysin (N-arginine dibasic convertase, or NRDc) is a cytosolic and cell-surface metalloendopeptidase that, in vitro, cleaves substrates upstream of Arg or Lys in basic pairs. NRDc differs from most of the other members of the M16 family of metalloendopeptidases by a 90 amino acid acidic domain (DAC) inserted close to its active site. At the cell surface, NRDc binds heparin-binding epidermal growth factor-like growth factor (HB-EGF) and enhances HB-EGF-induced cell migration. An active-site mutant of NRDc fulfills this function as well as wild-type NRDc, indicating that the enzyme activity is not required for this process. We now demonstrate that NRDc starts at Met(49). Furthermore, we show that HB-EGF not only binds to NRDc but also potently inhibits its enzymic activity. NRDc-HB-EGF interaction involves the 21 amino acid heparin-binding domain (P21) of the growth factor, the DAC of NRDc and most probably its active site. Only disulphide-bonded P21 dimers are inhibitory. We also show that Ca(2+), via the DAC, regulates both NRDc activity and HB-EGF binding. We conclude that the DAC is thus a key regulatory element for the two distinct functions that NRDc fulfills, i.e. as an HB-EGF modulator and a peptidase.

The use of proteolysis to study the structure of nardilysin

Treatment of a 128 kDa mouse nardilysin with trypsin initially produced an active 105 kDa N-terminally cleaved form. Continued trypsin digestion occurred at the C-terminus, producing inactive core species of approximately 92, 76.5, and 62 kDa. Protease V8 digestion generated a stable approximately 105 kDa form, nardilysin(V8), that was cleaved near the N-terminal trypsin site. The approximately 105 kDa nardilysin(V8) exhibited the same K(m) as did the uncleaved enzyme for substrates of the type Abz-GGFX(1)X(2)X(3)VGQ-EDDnp, where X residues were varied. However, k(cat) for nardilysin(V8) was 5-6 times greater. Both uncleaved nardilysin and nardilysin(V8) are inhibited by NaCl; however, nardilysin(V8) exhibits an IC(50) of approximately 2 mM compared to an IC(50) of approximately 50 mM for uncleaved nardilysin. Nardilysin(V8) is more sensitive to inhibition by phosphate buffer. Treatment of nardilysin(V8) with trypsin generated primarily the 92 kDa form which was inactive. Attempts to express nardilysin as a 105 kDa truncated N-terminal form or as a C-terminally truncated form led to inactive proteins.

N-arginine dibasic convertase is a specific receptor for heparin-binding EGF-like growth factor that mediates cell migration

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a mitogen and chemotactic factor, binds to two receptor tyrosine kinases, erbB1 and erbB4. Now we demonstrate that HB-EGF also binds to a novel 140 kDa receptor on MDA-MB 453 cells. Purification of this receptor showed it to be identical to N-arginine dibasic convertase (NRDc), a metalloendopeptidase of the M16 family. Binding to cell surface NRDc and NRDc in solution was highly specific for HB-EGF among EGF family members. When overexpressed in cells, NRDc enhanced their migration in response to HB-EGF but not to EGF. Conversely, inhibition of endogenous NRDc expression in cells by antisense morpholino oligonucleotides inhibited HB-EGF-induced cell migration. Anti-erbB1 neutralizing antibodies completely abrogated the ability of NRDc to enhance HB-EGF-dependent migration, demonstrating that this NRDc activity was dependent on erbB1 signaling. Although NRDc is a metalloproteinase, enzymatic activity was not required for HB-EGF binding or enhancement of cell migration; neither did NRDc cleave HB-EGF. Together, these results suggest that NRDc is a novel specific receptor for HB-EGF that modulates HB-EGF-induced cell migration via erbB1.

N-arginine dibasic convertase (nardilysin) isoforms are soluble dibasic-specific metalloendopeptidases that localize in the cytoplasm and at the cell surface

N-arginine (R) dibasic (NRD) convertase (nardilysin; EC 3.4.24.61), a metalloendopeptidase of the M16 family, specifically cleaves peptide substrates at the N-terminus of arginines in dibasic motifs in vitro. In rat testis, the enzyme localizes within the cytoplasm of spermatids and associates with microtubules of the manchette and axoneme. NRD1 and NRD2 convertases, two NRD convertase isoforms, differ by the absence (isoform 1) or presence (isoform 2) of a 68-amino acid insertion close to the active site. In this study, we overexpressed both isoforms, either by vaccinia virus infection of BSC40 cells or transfection of COS-7 cells. The partially purified enzymes exhibit very similar biochemical and enzymic properties. Microsequencing revealed that NRD convertase is N-terminally processed. Results of immunocytofluorescence, immunoelectron microscopy and subcellular fractionation studies argue in favour of a primary cytosolic localization of both peptidases. Although the putative signal peptide did not direct NRD convertase into microsomes in an in vitro translation assay, biotinylation experiments clearly showed the presence of both isoforms at the cell surface. In conclusion, although most known processing events at pairs of basic residues are achieved by proprotein convertases within the secretory pathway, NRD convertase may fulfil a similar function in the cytoplasm and/or at the cell surface.

Cloning, expression, and characterization of human metalloprotease 1: a novel member of the pitrilysin family of metalloendoproteases

A novel cDNA, designated human metalloendoprotease 1 (hMP1), was identified on the basis of homology to known metalloendoproteases of the pitrilysin family. The full-length MP1 codes for a protein with an open reading frame of 1038 amino acids. The N-terminal region contains the HXXEH(X)76E catalytic domain that is conserved in the members of pitrilysin family, namely insulin-degrading enzyme and NRD convertase. The hMP1 mRNA is expressed in a number of cell lines and tissues as a single species of about 3.4 kb. The expression of hMP1 mRNA is higher in muscle and heart than in brain, pancreas, liver, lung, and placenta. The full-length hMP1 was expressed in the baculovirus system and purified to homogeneity using isoelectrofocusing and ion-exchange chromatography. The enzyme exhibited a neutral pH optimum and high sensitivity to thiol reagents. HMP1 was inactivated by 1,10-phenanthroline, a specific inhibitor of Zn(+2)-dependent metalloproteases. The enzyme was not inhibited by agents that inhibit neutral metalloendoproteases of the thermolysin family such as thimet endo-oligopeptidase, enkephalinase, or angiotensin-converting enzyme. HMP1 cleaved a prodynorphin-derived peptide, leumorphin, N-terminal to Arg in the monobasic processing site, as evidenced by MALDI-TOF mass spectrometry. However, the enzyme did not exhibit strict monobasic cleavage specificity, as peptide substrates with amino acid substitutions around the monobasic site was cleaved efficiently by hMP1. Taken together, these results suggest that hMP1 is a novel member of the metalloendoprotease superfamily with ubiquitous distribution that could play a broad role in general cellular regulation.

New fluorogenic substrates for N-arginine dibasic convertase

N-Arginine dibasic (NRD) convertase is a recently described peptidase capable of selectively cleaving peptides between paired basic residues. The characterization of this unique peptidase has been hindered by the fact that no facile assay procedure has been available. Here we report the development of a rapid and sensitive assay for NRD convertase, based on the utilization of two new internally quenched fluorogenic peptides: Abz-GGFLRRVGQ-EDDnp and Abz-GGFLRRIQ-EDDnp. These peptides contain the fluorescent 2-aminobenzoyl moiety that is quenched in the intact peptide by a 2, 4-dinitrophenyl moiety. Cleavage by NRD convertase at the Arg-Arg sequence results in an increase of fluorescence. NRD convertase cleaves these peptides efficiently and with high specificity as observed by both HPLC and fluorescence spectroscopy. The rate of hydrolysis of the fluorogenic substrates is proportional to enzyme concentration, and obeys Michaelis-Menten kinetics. The kinetic parameters for the fluorescent peptides (Km values of approximately 1.0 microM, and Vmax values of approximately 1 microM/(min. mg) are similar to those obtained with peptide hormones as substrates.