Defectively N-glycosylated and non-O-glycosylated aminopeptidase N (CD13) is normally expressed at the cell surface and has full enzymatic activity

Specific Blood Plasma Circulating miRs Are Associated with the Physiological Impact of Total Fish Meal Replacement with Soybean Meal in Diets for Rainbow Trout (Oncorhynchus mykiss)

High dietary SBM content is known to induce important physiological alterations, hampering its use as a major FM alternative. Rainbow trout (Oncorhynchus mykiss) juveniles were fed two experimental diets during 9 weeks: (i) a FM diet containing 12% FM; and (ii) a vegetable meal (VM) diet totally devoid of FM and based on SBM (26%). Fish fed the VM diet did not show reduced growth performance when compared with fish fed the FM diet. Nevertheless, fish fed the VM diet had an increased viscerosomatic index, lower apparent fat digestibility, higher aminopeptidase enzyme activity and number of villi fusions, and lower α-amylase enzyme activity and brush border integrity. Small RNA-Seq analysis identified six miRs (omy-miR-730a-5p, omy-miR-135c-5p, omy-miR-93a-3p, omy-miR-152-5p, omy-miR-133a-5p, and omy-miR-196a-3p) with higher expression in blood plasma from fish fed the VM diet. Bioinformatic prediction of target mRNAs identified several overrepresented biological processes known to be associated with high dietary SBM content (e.g., lipid metabolism, epithelial integrity disruption, and bile acid status). The present research work increases our understanding of how SBM dietary content has a physiological impact in farmed fish and suggests circulating miRs might be suitable, integrative, and less invasive biomarkers in fish.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Molecular Imaging of Aminopeptidase N in Cancer and Angiogenesis

This review focuses on recent advances in the molecular imaging of aminopeptidase N (APN, also known as CD13), a zinc metalloenzyme that cleaves N-terminal neutral amino acids. It is overexpressed in multiple cancer types and also on the surface of vasculature undergoing angiogenesis, making it a promising target for molecular imaging and targeted therapy. Molecular imaging probes for APN are divided into two large subgroups: reactive and nonreactive. The structures of the reactive probes (substrates) contain a reporter group that is cleaved and released by the APN enzyme. The nonreactive probes are not cleaved by the enzyme and contain an antibody, peptide, or nonpeptide for targeting the enzyme exterior or active site. Multivalent homotopic probes utilize multiple copies of the same targeting unit, whereas multivalent heterotopic molecular probes are equipped with different targeting units for different receptors. Several recent preclinical cancer imaging studies have shown that multivalent APN probes exhibit enhanced tumor specificity and accumulation compared to monovalent analogues. The few studies that have evaluated APN-specific probes for imaging angiogenesis have focused on cardiac regeneration. These promising results suggest that APN imaging can be expanded to detect and monitor other diseases that are associated with angiogenesis.

Identification of placental leucine aminopeptidase and triton-slowed aminopeptidase N in serum of pregnant women

BACKGROUND

Previously, we found characteristic triton-slowed bands of aminopeptidase N (APN) in cholestatic serum by triton-polyacrylamide gel electrophoresis (triton-PAGE) [Makoto Kawai, Yukichi Hara, Triton-polyacrylamide gel electrophoresis and leucine aminopeptidase activity staining detect Triton-slowed bands including high-molecular-mass aminopeptidase N (CD13) isoform in cholestatic patient sera. Clin Chim Acta 2006; 364:188-195].

METHODS

Sera from 14 normal pregnant women were electrophoresed on polyacrylamide gel containing 0.02 l/l triton (triton-PAGE) or a 0-0.02 l/l horizontal gradient of triton (gradient-triton-PAGE), and stained with leucine-beta-naphthylamide. Some samples were pretreated with a monoclonal APN antibody or rabbit anti-placental leucine aminopeptidase (PLAP) serum. The stained bands were eluted from the gel, treated with N- and O-glycosidase, and analyzed by Western blotting with rabbit anti-APN or anti-PLAP serum.

RESULTS

Triton-PAGE clearly differentiated 5 LAP activity bands (1-5 from the front). Gradient-triton-PAGE revealed that bands 4-5 were slowed by triton (triton-slowed bands) much more than bands 1-3. Triton-PAGE of antibody-treated serum showed that bands 1, 2, 4, and 5 are mainly APN and that band 3 is PLAP. The molecular mass of PLAP was about 130-140 kDa before treatment with glycosidases but 100 kDa after. Triton-PAGE detected PLAP in 13 and triton-slowed APN in 4 of the 14 women.

CONCLUSIONS

Triton-PAGE differentiates PLAP from APN. Triton-slowed APN as well as PLAP is present in the serum of pregnant women.

Kinetic studies on aminopeptidase M-mediated degradation of human hemorphin LVV-H7 and its N-terminally truncated products

The human hemorphin LVV-H7 belongs to the class of micro-opiod receptor-binding peptides, which also exhibits significant affinity to insulin-regulated aminopeptidase (IRAP) thereby affecting IRAP inhibition. The inhibitory potency towards IRAP is of pharmaceutical interest for the treatment of Alzheimer's disease. Consecutive N-terminal cleavage of the first two amino acid residues of LVV-H7 affects a drastic increase of the binding affinity (V-H7) but ultimately leads to its complete abolition after cleavage of the next amino acid residue (H7). Therefore, we investigated LVV-H7 truncation by aminopeptidase M (AP-M) identified as a LVV-H7 degrading enzyme potentially regulating hemorphin activity towards IRAP in vivo. Using a selective quantitative multi-component capillary zone electrophoretic method (CZE-UV), we analyzed the AP-M-mediated subsequent proteolysis of the hemorphins LVV-H7 (L32-F41), VV-H7 (V33-F41), and V-H7 (V34-F41) in vitro. Incubations were carried out with synthetic hemorphins applied as single substrates or in combination. Maximum velocities (V(max)), catalytic constants (turnover numbers, kcat), and specific enzyme activities (EA) were calculated. L32 cleavage from LVV-H7 happens more than two-times faster (kcat: 140 min(-1) +/- 9%, EA: 1.0 U/mg +/- 9%) than V33 cleavage from VV-H7 (kcat: 61 min(-1) +/- 10%, EA: 0.43 U/mg +/- 10%) or V32 deletion from V-H7 (kcat: 62 min(-1) +/- 8%, EA: 0.46 U/mg +/- 8%). In contrast, we showed that H7 (Y35-F41) was neither degraded by porcine AP-M nor did it act as an inhibitor for this enzyme. Determined turnover numbers were in the same dimension as those reported for dynorphin degradation. This is the first time that AP-M-mediated truncation of natural underivatized LVV-H7 and its physiological metabolites was analyzed to determine kinetic parameters useful for understanding hemorphin processing and designing hemorphin-derived drug candidates.

A role for galectin-3 in CD13-mediated homotypic aggregation of monocytes

We recently reported that anti-CD13 mAbs induce homotypic aggregation of monocytic cells. This phenomenon is signal transduction dependent and does not require CD13 aminopeptidase activity. Since CD13 is heavily glycosylated and a member of the galectin family (galectin-4) has been shown to associate with CD13 in the intestinal epithelium, we hypothesized that CD13-mediated aggregation might proceed through a carbohydrate-dependent mechanism involving galectin-3, the most highly expressed galectin on monocytes. We report here that lactose and anti-galectin-3 antibodies completely abrogate homotypic aggregation induced by anti-CD13 antibodies. Furthermore, galectin-3 co-immunoprecipitates with CD13 from resting U-937 cells and this association decreases during the aggregation process, a phenomenon that may have functional implications. Together, the results presented here point to a key role for galectin-3 in CD13-mediated homotypic aggregation of monocytic cells.

Discovery of novel human and animal cells infected by the severe acute respiratory syndrome coronavirus by replication-specific multiplex reverse transcription-PCR

The severe acute respiratory syndrome coronavirus (SARS-CoV) is the causative agent of the recent outbreak of severe acute respiratory syndrome. VeroE6 cells, fetal rhesus monkey kidney cells, and human peripheral blood mononuclear cells were the only cells known to be susceptible to SARS-CoV. We developed a multiplex reverse transcription-PCR assay to analyze the susceptibility of cells derived from a variety of tissues and species to SARS-CoV. Additionally, productive infection was determined by titration of cellular supernatants. Cells derived from three species of monkey were susceptible to SARS-CoV. However, the levels of SARS-CoV produced differed by 4 log(10). Mink lung epithelial cells (Mv1Lu) and R-Mix, a mixed monolayer of human lung-derived cells (A549) and mink lung-derived cells (Mv1Lu), are used by diagnostic laboratories to detect respiratory viruses (e.g., influenza virus); they were also infected with SARS-CoV, indicating that the practices of diagnostic laboratories should be examined to ensure appropriate biosafety precautions. Mv1Lu cells produce little SARS-CoV compared to that produced by VeroE6 cells, which indicates that they are a safer alternative for SARS-CoV diagnostics. Evaluation of cells permissive to other coronaviruses indicated that these cell types are not infected by SARS-CoV, providing additional evidence that SARS-CoV binds an alternative receptor. Analysis of human cells derived from lung, kidney, liver, and intestine led to the discovery that human cell lines were productively infected by SARS-CoV. This study identifies new cell lines that may be used for SARS-CoV diagnostics and/or basic research. Our data and other in vivo studies indicate that SARS-CoV has a wide host range, suggesting that the cellular receptor(s) utilized by SARS-CoV is highly conserved and is expressed by a variety of tissues.

Novel, Aberrantly Truncated Isoform of Serum CD13 in a Family with High Serum Aminopeptidase N (CD13) Activity

Background: We previously reported a family in which the propositus and both her father and paternal grandmother had high serum aminopeptidase N (CD13; EC 3.4.11.2) activity (autosomal dominant). The molecular mass of the serum CD13 polypeptide of the propositus was larger than that of normal CD13, suggesting either a mutation in the CD13 gene or an abnormality in posttranslational modification of CD13 polypeptide in this family.

Methods: Reverse transcription-PCR and direct sequencing were performed with leukocyte CD13 mRNA from the propositus. Two-dimensional electrophoresis and N-terminal amino acid sequencing were performed with serum CD13 from the propositus, the father of the propositus, and healthy volunteers.

Results: The sequence of the CD13 cDNA of the propositus was essentially identical with that reported previously. However, the CD13 polypeptide of the propositus and the father of the propositus was truncated, lacking amino acids 1–43 of intact CD13 (43-truncated CD13), whereas CD13 lacking residues 1–58 (58-truncated CD13) and 43-truncated CD13 were detected in serum from healthy volunteers.

Conclusions: In serum from healthy volunteers, we found both 58-truncated CD13, a major isoform reported previously, and 43-truncated CD13, a novel, minor isoform with a larger polypeptide. In serum of the family, 43-truncated CD13 was extremely concentrated, suggesting that proteolytic cleavage of CD13 amino acids 43 and 44 (43-truncation) is abnormally promoted. Because no mutation was found in the CD13 cDNA from the propositus, increased serum CD13 in this family seems to be caused by a mutation in a gene that regulates 43-truncation protease activity.

Structure of the human oxytocinase/insulin-regulated aminopeptidase gene and localization to chromosome 5q21

The human oxytocinase/insulin-regulated aminopeptidase (OTase/IRAP) is a 1024 amino acid type II integral membrane protein that is expressed mainly in fat, muscle and placenta tissues. It has been thought to be involved mainly in the control of onset of labour but recently rat OTase/IRAP was shown to participate in the regulation of glucose transporter isoform 4 vesicle trafficking in adipocytes as well. To approach an understanding of OTase/IRAP gene regulation the organization of the human gene was determined. Accordingly, three overlapping genomic clones were isolated and characterized. The human OTase/IRAP gene (OTASE) was found to span approximately 75 kb containing 18 exons and 17 introns. The gluzincin aminopeptidase motif: GAMEN-(31 amino acids)-HELAH-(18 amino acids)-E associated with Zn2+-binding, substrate binding and catalysis is encoded by exons 6 and 7. A major and a minor transcriptional initiation site in OTASE were identified by primer extension 514 bp and 551 bp, respectively, upstream of the translation start codon. Chloroamphenicol acetyltransferase-reporter assays revealed a functional CpG-rich promoter/enhancer region located between nucleotide -621 and the major transcriptional initiation site. Human OTASE was assigned to chromosome 5 by hybridization to genomic DNA from characterized somatic cell hybrids. Finally, the OTASE and the human aminopeptidase A gene were subchromosomally localized to 5q21 and 4q25, respectively, by in situ hybridization.

The Trypanosoma cruzi mucin family is transcribed from hundreds of genes having hypervariable regions

In previous works we have identified genes in the protozoan parasite Trypanosoma cruzi whose structure resemble those of mammalian mucin genes. Indirect evidence suggested that these genes might encode the core protein of parasite mucins, glycoproteins that were proposed to be involved in the interaction with, and invasion of, mammalian host cells. We now show that the mucin gene family from T. cruzi is much larger and diverse than expected. A minimal number of 484 mucin genes per haploid genome is calculated for a parasite clone. Most, if not all, genes are transcribed, as deduced from cDNA analysis. Comparison of the cDNA sequences showed evidences of a high mutation rate in localized regions of the genes. Sequence conservation among members of the family is much higher in the untranslated (UTR) regions than in the sequences encoding the mature mucin core protein. Transcription units can be classified into two main subfamilies according to the sequence homologies in the 5'-UTR, whereas the 3'-UTR is highly conserved in all clones analyzed. The common origin of members of this gene family as well as their relationships can be defined by sequence comparison of different domains in the transcription units. The regions encoding the N and C termini, supposed to correspond to the leader peptide and membrane-anchoring signal, respectively, (Di Noia, J. M., Sánchez, D. O., and Frasch, A. C. C. (1995) J. Biol. Chem. 270, 24146-24149) are highly conserved. Conversely, the central regions are highly variable. These regions encode the target sites for O-glycosylation and are made of a variable number of repetitive units rich in Thr and Pro residues or are nonrepetitive but still rich in Thr/Ser and Pro residues. The region putatively coding for the N-terminal domain of the mature core protein is hypervariable, being different in most of the transcripts sequenced. Nonrepetitive central domains are unique to each gene. Gene-specific probes show that the relative abundance of different mRNAs varies greatly within the same parasite clone.