Novel peptide inhibitor (SPAI) of Na+, K+-ATPase from porcine intestine

Immunogenic cell death inducer peptides: A new approach for cancer therapy, current status and future perspectives

Immunogenic Cell Death (ICD) is a type of cell death that kills tumor cells by stimulating the adaptive immune response against other tumor cells. ICD depends on the endoplasmic reticulum (ER) stress and the secretion of Damage-Associated Molecular Patterns (DAMP) by the dying tumor cell. DAMPs recruit innate immune cells such as Dendritic Cells (DC), triggering a cancer-specific immune response such as cytotoxic T lymphocytes (CTLs) to eliminate remaining cancer cells. ICD is accompanied by several hallmarks in dying cells, such as surface translocation of ER chaperones, calreticulin (CALR), and extracellular secretion of DAMPs such as high mobility group protein B1 (HMGB1) and adenosine triphosphate (ATP). Therapeutic peptides can kill bacteria and tumor cells thus affecting the immune system. They have high specificity and affinity for their targets, small size, appropriate cell membrane penetration, short half-life, and simple production processes. Peptides are interesting agents for immunomodulation since they may overcome the limitations of other therapeutics. Thus, the development of peptides affecting the TME and active antitumoral immunity has been actively pursued. On the other hand, several peptides have been recently identified to trigger ICD and anti-cancer responses. In the present review, we review previous studies on peptide-induced ICD, their mechanism, their targets, and markers. They include anti-microbial peptides (AMPs), cationic or mitochondrial targeting, checkpoint inhibitors, antiapoptotic inhibitors, and "don't eat me" inhibitor peptides. Also, peptides will be investigated potentially inducing ICD that is divided into ER stressors, ATPase inhibitors, and anti-microbial peptides.

Proteo-Transcriptomic Characterization of Sirex nitobei (Hymenoptera: Siricidae) Venom

The wood-boring woodwasp Sirex nitobei is a native pest in Asia, infecting and weakening the host trees in numerous ecological and commercial coniferous forest plantations. In China, hosts of S. nitobei are diverse, so the pest has spread to several provinces of China, resulting in considerable economic and ecological damage. During female oviposition, S. nitobei venom along with arthrospores of the symbiotic fungus Amylostereum areolatum or A. chaetica is injected into host trees, and the combination of these two biological factors causes the death of xylem host trees. The presence of venom alone causes only the yellowing and wilting of needles. In this study, we constructed the venom gland transcriptome of S. nitobei for the first time and a total of 15,036 unigenes were acquired. From the unigenes, 11,560 ORFs were identified and 537 encoding protein sequences with signal peptides at the N-terminus. Then, we used the venomics approach to characterize the venom composition of female S. nitobei and predicted 1095 proteins by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. We focused on seven proteins that were both highly expressed in the venom gland transcriptome and predicted in the crude venom proteome. These seven proteins are laccase-2, laccase-3, a protein belonging to the Kazal family, chitooligosaccharidolytic β-N-acetylglucosaminidase, beta-galactosidase, icarapin-like protein, and waprin-Thr1-like protein. Using quantitative real-time PCR (qRT-PCR), we also proved that the genes related to these seven proteins are specifically expressed in the venom glands. Finally, we revealed the functional role of S. nitobei venom in the physiological response of host trees. It can not only promote the colonization of symbiotic fungus but contribute to the development of eggs and larvae. This study provides a deeper understanding of the molecular mechanism of the woodwasp–pine interaction.

A single WAP domain (SWD)-containing protein with antiviral activity from Pacific white shrimp Litopenaeus vannamei

The single whey acidic protein (WAP) domain (SWD)-containing proteins, also called type III crustins, are a group of antimicrobial peptides (AMPs) in crustaceans. At present, a number of SWDs have been identified in shrimp, which showed essential antibacterial activities. However, the roles of SWDs in antiviral immune responses have not been reported up to now. In this study, a novel SWD (LvSWD3) was identified from Pacific white shrimp, Litopenaeus vannamei, which contained a typical single WAP domain homologous to those of other crustacean SWDs. Although lacking the pro and arg-rich region between the signal peptide and the WAP domain, LvSWD3 was closely clustered with other shrimp SWDs in the phylogenetic tree. Similar to many shrimp SWDs, the highest expression of LvSWD3 was detected in hemocytes. The LvSWD3 expression exhibited only limited changes after challenges with Vibrio parahaemolyticus, Poly (I:C) and lipopolysaccharide, but was significantly up-regulated after white spot syndrome virus (WSSV) infection. Silencing of LvSWDs significantly accelerated the death of the WSSV-infected but not the V. parahaemolyticus-infected shrimp. The recombinant LvSWD3 protein did not show proteinase inhibitory and antibacterial activities but could significantly postpone the death of WSSV-infected shrimp and reduce the viral load in tissues. These suggested that LvSWD3 was a novel SWD with antiviral activity.

A double WAP domain-containing protein Es-DWD1 from Eriocheir sinensis exhibits antimicrobial and proteinase inhibitory activities

Whey acidic proteins (WAP) belong to a large gene family of antibacterial peptides, which are critical in the host immune response against microbial invasion. The common feature of these proteins is a single WAP domain maintained by at least one four-disulfide core (4-DSC) structure rich in cysteine residues. In this study, a double WAP domain (DWD)-containing protein, Es-DWD1, was first cloned from the Chinese mitten crab (Eriocheirsinensis). The full-length Es-DWD1cDNA was 1193 bp, including a 411 bp open reading frame (ORF) encoding 136 amino acids with a signal peptide of 22 amino acids in the N-terminus. A comparison with other reported invertebrate and vertebrate sequences revealed the presence of WAP domains characteristic of WAP superfamilies. As determined by quantitative real-time RT-PCR, Es-DWD1 transcripts were ubiquitously expressed in all tissues, but it was up-regulated in hemocytes post-challenge with pathogen-associated molecular patterns (PAMPs). The mature recombinant Es-DWD1 (rEs-DWD1) protein exhibited different binding activities to bacteria and fungus. Moreover, rEs-DWD1 could exert agglutination activities against Bacillus subtilis and Pichiapastoris and demonstrated inhibitory activities against the growth of Staphylococcus aureus, Aeromonas hydrophila and P. pastoris. Furthermore, rEs-DWD1 showed a specific protease inhibitory activity in B. subtilis. Coating of rEs-DWD1 onto agarose beads enhanced encapsulation of the beads by crab hemocytes. Collectively, the results suggest that Es-DWD1 is a double WAP domain containing protein with antimicrobial and proteinase inhibitory activities, which play significant roles in the immunity of crustaceans.

A secretory leukocyte proteinase inhibitor (SLPI)-like protein from Litopenaeus vannamei haemocytes

A partial clone coding for a two-WAP domain protein was isolated from a Litopenaeus vannamei haemocytes cDNA library. The complete sequence was obtained by RACE, and the full-length cDNA sequence is 0.8 Kb long and encodes for a 116-amino acid protein. The domain composition is similar to the mammalian WFDC5 (WAP four disulfide core) and secretory leukocyte proteinase inhibitor (SLPI). Modifications in expression were determined by real-time PCR, after injection of Vibrio alginolyticus, suggesting its participation in the shrimp immune response. Structural and phylogenetic analyses showed close similarity between shrimp and mammalian SLPI, indicating a probable common ancestor. This is the first report of a mammalian SLPI-like protein in an invertebrate.

Antimicrobial activity of omwaprin, a new member of the waprin family of snake venom proteins

We have isolated and characterized omwaprin, a 50-amino-acid cationic protein from the venom of inland taipan (Oxyuranus microlepidotus). It is a new member of the waprin family of snake venom proteins. A synthetic gene was designed and constructed for expressing the recombinant protein in Escherichia coli. Recombinant omwaprin was used for carrying out functional analyses. The protein is non-toxic to Swiss albino mice at doses of up to 10 mg/kg when administered intraperitoneally. However, it shows selective and dose-dependant antibacterial activity against Gram-positive bacteria. The minimum inhibitory doses were in the range 2-10 microg for selected species of bacteria in radial diffusion assays. The antibacterial activity is salt-tolerant up to 350 mM NaCl. However, omwaprin lost its antibacterial activity upon reduction and alkylation of its cysteine residues, or upon deletion of six N-terminal amino acid residues, four of which are positively charged. These observations indicate that the three-dimensional structure constrained by four disulfide bonds and the N-terminal residues are essential for its activity. The mechanism of action is via membrane disruption, as shown by scanning electron microscopy. Importantly, omwaprin lacks haemolytic activity on human erythrocytes. This demonstrates the specificity of omwaprin for bacterial membranes. Unlike other reported WAP (whey acidic protein) domain-containing antibacterial proteins, including elafin, EPPIN (epididymal proteinase inhibitor), SWAM1 and SWAM2 [single WAP (whey acidic protein) motif proteins 1 and 2] and SLPI (secretory leucocyte proteinase inhibitor), omwaprin shows species-specific activity on the Gram-positive bacteria tested.

Novel epididymal protease inhibitors with Kazal or WAP family domain

The epididymal maturation of spermatozoa is regulated by changes in the luminal ion concentration and the processing of the sperm surface membrane by several glycosidases and proteases. In the present study, we identified five novel protease inhibitors that are highly expressed in the mouse epididymis. Four of the proteins were found to belong to the Kazal protease inhibitor family and were named SPINK8, SPINK10, SPINK11, and SPINK12, whereas one of the proteins, WFDC10, contained the WAP four-disulfide core domain structure. The novel genes showed very specific segmental expression patterns. The expression of all the five genes was regulated by testis-derived factors and decreased after gonadectomy. With the exception of Spink11, mRNA levels could be restored by testosterone replacement. We hypothesize that the protease inhibitors discovered represent a group of epididymal genes that contribute to the regulation of sperm maturation by regulating the proteolytic processing of the sperm membrane during epididymal transit.

Perlwapin, an abalone nacre protein with three four-disulfide core (whey acidic protein) domains, inhibits the growth of calcium carbonate crystals

We have isolated a new protein from the nacreous layer of the shell of the sea snail Haliotis laevigata (abalone). Amino acid sequence analysis showed the protein to consist of 134 amino acids and to contain three sequence repeats of approximately 40 amino acids which were very similar to the well-known whey acidic protein domains of other proteins. The new protein was therefore named perlwapin. In addition to the major sequence, we identified several minor variants. Atomic force microscopy was used to explore the interaction of perlwapin with calcite crystals. Monomolecular layers of calcite crystals dissolve very slowly in deionized water and recrystallize in supersaturated calcium carbonate solution. When perlwapin was dissolved in the supersaturated calcium carbonate solution, growth of the crystal was inhibited immediately. Perlwapin molecules bound tightly to distinct step edges, preventing the crystal layers from growing. Using lower concentrations of perlwapin in a saturated calcium carbonate solution, we could distinguish native, active perlwapin molecules from denaturated ones. These observations showed that perlwapin can act as a growth inhibitor for calcium carbonate crystals in saturated calcium carbonate solution. The function of perlwapin in nacre growth may be to inhibit the growth of certain crystallographic planes in the mineral phase of the polymer/mineral composite nacre.

Identification, evolution, and regulation of expression of Guinea pig trappin with an unusually long transglutaminase substrate domain

Trappins are found in human, bovine, hippopotamus, and members of the pig family, but not in rat and mouse. To clarify the evolution of the trappin genes and the functional significance of their products, we isolated the trappin gene in guinea pig, a species belonging to a rodent family distinct from rat and mouse. Guinea pig trappin was confirmed to encode the same domain structure as trappin, consisting of a signal sequence, an extra large transglutaminase substrate domain, and a whey acidic protein motif. Northern blot analysis and in situ hybridization histochemistry as well as immunohistochemistry demonstrated that guinea pig trappin is expressed solely in the secretory epithelium of the seminal vesicle and that its expression is androgen-dependent. We confirmed that guinea pig trappin is cross-linked by prostate transglutaminase and that the whey acidic protein motif derived from guinea pig trappin has an inhibitory activity against leukocyte elastase. Genome sequence analysis showed that guinea pig trappin belongs to the family of REST (rapidly evolving seminal vesicle transcribed) genes.

Structural and functional differences of Litopenaeus vannamei crustins

Penaeid crustins were described in Litopenaeus vannamei and L. setiferus as proteins belonging to an antibacterial peptide family with similar sequences but different sizes. Six crustin-coding clones were isolated from a cDNA library from L. vannamei hemocytes, sequenced and compared. Two different isoforms (named I and P) were found, based on two nucleotide differences that produce one change in amino acid sequence (Ile/Pro). Other single differences in nucleotide sequences were also noted, but they did not change the translated product. The mRNA steady state levels of crustin I, but not of crustin P, were down regulated by Vibrio alginolyticus inoculation. Thus, the differences among penaeid crustins seem to be associated with one amino acid substitution, which affects their expression after bacterial inoculation. By structural similarity, shrimp crustins seem to belong to an antibacterial WAP-domain containing protein family.

Antimicrobial Activity of Human EPPIN, an Androgen-Regulated, Sperm-Bound Protein with a Whey Acidic Protein Motif1

The role of epididymal sperm-binding proteins in reproductive tract immunity is now well recognized in addition to their role in sperm maturation. Spermatozoa acquire forward motility and fertilizing ability during their passage through the epididymis, where they acquire a wide variety of proteins belonging to different classes. Previously, we demonstrated that EPPIN (epididymal protease inhibitor), an androgen-regulated, sperm-binding protein containing protease-inhibitory motifs, is expressed specifically in the testis and epididymis. In the present study, we investigated the antibacterial activity of EPPIN against Escherichia coli and the mechanism of antimicrobial action. EPPIN exhibited dose- and time-dependent antibacterial activity that was relatively insensitive to salt. However, EPPIN lost its antibacterial activity completely on reduction and alkylation of its cysteines, indicating the importance of disulfide bonds for its activity. EPPIN permeabilized the outer and inner membranes of E. coli, which is consistent with its ability to induce striking morphological alterations of E. coli membranes as shown by scanning electron microscopy. EPPIN did not cause disruption of eukaryotic membranes in the rat erythrocyte hemolytic assay. The present results indicate that EPPIN has a role in the innate immune system of human epididymis.

A blood plasma inhibitor is responsible for circadian changes in rat renal Na,K-ATPase activity

Rhythmic changes in activity following a circadian schedule have been described for several enzymes. The possibility of circadian changes in Na,K-ATPase activity was studied in homogenates of rat kidney cortex cells. Male Sprague-Dawley rats were kept on a schedule of 12h light (06:00-18:00 h) and 12 h darkness (18:00-06:00 h) for 2 weeks. At the end of the conditioning period, one rat was killed every 2 h, until completion of a 24 h cycle. Outermost kidney cortex slices were prepared, homogenized and assayed for Na,K-ATPase activity. The whole procedure was repeated six times. Na,K-ATPase activity shows an important oscillation (2 cycles/24 h). Peak activities were detected at 09:00 and 21:00 h, whereas the lowest activities were detected at 15:00 and 01:00-03:00 h. The highest activity was 40+/-3 nmoles Pi mg protein(-1)min(-1) (09:00 h), and the lowest was 79+/-3 nmoles Pi mg protein(-1)min(-1) (15:00 h). The amount of the Na+-stimulated phosphorylated intermediate is the same for the 09:00 h and 15:00 h homogenates. Preincubation of 09:00 h kidney cortex homogenates with blood plasma drawn from rats at either 03:00 h or 15:00 h, significantly inhibited their Na,K-ATPase activity. This inhibition was not seen when the preincubation was carried out with either 09:00 h or 21:00 h blood plasma. The striking oscillation (2 cycles/24 h) of the Na,K-ATPase activity of rat kidney cortex cells is ascribed to the presence of an endogenous inhibitor in blood plasma.

A single WAP domain-containing protein from Litopenaeus vannamei hemocytes

A cDNA clone coding for a single WAP domain (SWD) protein was isolated from a hemocyte cDNA library of Litopenaeus vannamei. The full-length cDNA sequence is 0.4kb long and encodes a 93-amino acid protein. Using this sequence as a probe a similar clone coding for a 92-amino acids protein was found in a cDNA library from Penaeus monodon hemocytes. The mRNA size was confirmed by Northern blot as well as that gene is expressed in hemocytes, but not in hepatopancreas. mRNA levels of the shrimp SWD protein were modified after injection of Vibrio alginolyticus, indicating the probable role of this protein in the immune response. Although amino acid sequence seems to be similar to those of other WAP domain-containing proteins, shrimp SWD protein does not have any other functional domain, similar to a mouse single WAP motif (SWAM) protein reported in mouse; however, the phylogenetic analysis shows that shrimp SWD is more related to other WAP proteins than to mouse SWAM.

Identification of a novel family of proteins in snake venoms. Purification and structural characterization of nawaprin from Naja nigricollis snake venom

The three-dimensional structure of nawaprin has been determined by nuclear magnetic resonance spectroscopy. This 51-amino acid residue peptide was isolated from the venom of the spitting cobra, Naja nigricollis, and is the first member of a new family of snake venom proteins referred to as waprins. Nawaprin is relatively flat and disc-like in shape, characterized by a spiral backbone configuration that forms outer and inner circular segments. The two circular segments are held together by four disulfide bonds, three of which are clustered at the base of the molecule. The inner segment contains a short antiparallel beta-sheet, whereas the outer segment is devoid of secondary structures except for a small turn or 310 helix. The structure of nawaprin is very similar to elafin, a human leukocyte elastase-specific inhibitor. Although substantial parts of the nawaprin molecule are well defined, the tips of the outer and inner circular segments, which are hypothesized to be critical for binding interactions, are apparently disordered, similar to that found in elafin. The amino acid residues in these important regions in nawaprin are different from those in elafin, suggesting that nawaprin is not an elastase-specific inhibitor and therefore has a different function in the snake venom.

A locus on human chromosome 20 contains several genes expressing protease inhibitor domains with homology to whey acidic protein

A locus containing 14 genes, encoding protein domains that have homology with whey acidic protein (WAP), has been identified in a region of 678 kb on human chromosome 20q12-13.1. Among them are genes of the known or postulated protease inhibitors elafin, secretory leucocyte protease inhibitor, human epididymis gene product 4, eppin, and huWAP2. Nucleotide sequences of full-length transcripts were obtained from cDNA fragments generated by rapid amplification of cDNA ends. Characteristic features of the genes are that the upstream promoter regions are devoid of TATA-boxes and that the coding nucleotides are divided into distinct exons for the signal peptide and for each WAP domain. In most cases, there is also a separate exon encompassing a few terminal codons and the 3' untranslated nucleotides. There are also examples of mixed type inhibitors, that encode inhibitor domains of both WAP and Kunitz types. Several of the genes appear to be expressed ubiquitously, but, in most cases, the highest transcript levels are found in epididymis followed by testis and trachea. Some of the genes also display high transcript levels in neural tissues. Potential biological roles of protein products could be in host defence against invading micro-organisms or in the regulation of endogenous proteolytic enzymes, of which those originating from the kallikrein gene locus on chromosome 19 are of particular interest.

Identification of a novel protease inhibitor gene that is highly expressed in the prostate

A novel gene was identified 52 kb upstream of the gene encoding the protease inhibitor elafin (PI3) on human chromosome 20q12-13.1. The transcript of the new gene, denoted huWAP2, was characterized by rapid amplification of cDNA ends and DNA sequencing. The size is 774 bp and it gives rise to a polypeptide of 111 amino acid residues that is homologous to elafin and similar WAP-type protease inhibitors. By RT-PCR it was shown that the gene is highly expressed in prostate, skin, lung, and esophagus.

Selection of peptidic mimics of digoxin from phage-displayed peptide libraries by anti-digoxin antibodies

Since the initial report of the development of methodology to generate high-affinity digitalis-specific (digoxin) antibodies, these antibodies have proven extremely useful tools to monitor digoxin levels in digitalized patients and, as Fab fragments, to reverse toxic digoxin effects in life-threatening digoxin overdoses. These antibodies (both digoxin-specific and ouabain-specific) have been used extensively by investigators for the identification and characterization of putative endogenous digitalis-like factors. In this study, we used two well-characterized mouse anti-digoxin monoclonal antibodies (mAbs), designated 26-10 and 45-20, as binding templates with which to select short bacteriophage-displayed (pIII protein inserted) peptides that are capable of binding to these mAbs and mimicking the conformational structure of digoxin. Selective enrichment from two phage-displayed random peptide libraries enabled us to isolate and identify distinct 15 and 26 amino acid residue peptide inserts that bind with high avidity and idiotypic specificity to the selecting mAbs. Among these displayed inserts a subset was identified whose mAb binding is inhibited by digoxin and whose corresponding synthetic peptides inhibit phage binding. They, therefore, appear to bind at the mAbs digoxin-binding sites. These data provide the first clear evidence that short polypeptides can serve as surrogates for the low molecular mass hapten digoxin.

A 75-kDa Na+,K+-ATPase competitive inhibitor protein isolated from rat brain cytosol binds to a site different from the ouabain-binding site

A Na+,K+-ATPase inhibitor protein has been purified to homogeneity from rat brain cytosol by ammonium sulphate precipitation, DEAE anion-exchange chromatography and hydroxyapatite adsorption column chromatography. The purified protein migrates as a single polypeptide band of 75 kDa on 7.5% SDS/PAGE. Amino acid composition data shows the presence of a high number of acidic amino acids in the molecule in relation to the pI value of 4.6. The inhibitor binds Na+,K+-ATPase reversibly and blocks ATP binding sites at micromolar concentrations with an I50 of approximately 700 nm. As a result, formation of the phosphorylated intermediate of Na+,K+-ATPase is hindered in the presence of the inhibitor. It does not affect p-nitrophenylphosphatase activity. Tryptophan fluorescence studies and CD analysis suggest conformational changes of Na+,K+-ATPase on binding to the inhibitor.

Run-down of the GABAA response under experimental ischaemia in acutely dissociated CA1 pyramidal neurones of the rat

1. The effect of experimental ischaemia on the response to gamma-aminobutyric acid (GABA) was assessed in acutely dissociated CA1 pyramidal neurones of rats, using the patch-clamp technique. 2. Rapid application of 3 x 10(-5) M GABA induced a bicuculline-sensitive inward Cl- current (IGABA) at a holding potential (Vh) of -44 mV. The peak amplitude of IGABA showed a time-dependent decrease (run-down) when it was recorded with the conventional whole-cell mode without internal ATP. The run-down was not observed when the intracellular ATP concentration ([ATP]i) was maintained by the nystatin-perforated recording with an intracellular Na+ concentration ([Na+]i) of 0 mM. 3. When [Na+]i was increased to more than 30 mM, the IGABA run-down was observed even with the nystatin-perforated recording. 4. The IGABA run-down observed at 60 mM [Na+]i with the nystatin method was further enhanced under experimental ischaemia without changes in the reversal potential of IGABA. The enhanced run-down was suppressed by application of the Na+,K(+)-ATPase inhibitors, ouabain and SPAI-1. 5. IGABA run-down during ischaemia was also accompanied by an outward holding current and a concomitant increase in intracellular free Ca2+ concentration ([Ca2+]i) in 48.5% of the neurones. The outward current was a Ca(2+)-activated K+ current, which was blocked by 3 x 10(-7) M charybdotoxin. 6. In the inside-out mode of the single-channel analysis, GABA activated three subconductance states with conductances of 33.4, 22.7 and 15.2 pS. Reduction of ATP concentration from 2 to 0 mM on the intracellular side suppressed the channel activities, while an increase in Ca2+ concentration from 0.7 x 10(-9) to 1.1 x 10(-6) M had no effect. 7. These results suggest that ischaemia induces the run-down of the postsynaptic GABA response at the GABAA receptor level, and that this run-down is triggered by a decrease in [ATP]i.

Purification and functional characterization of a low-molecular-mass Na+, K+-ATPase inhibitor protein from rat brain cytosol

A number of low-molecular mass (12-13 kDa) Na+, K+-ATPase inhibitor proteins have been purified from rat brain cytosol by gel filtration followed by FPLC fractionation on a Mono Q anion-exchange column. Eight peaks were obtained using 0.1 M NaCl eluent of which one peak was found to be the most potent inhibitor of Na+, K+-ATPase. The molcular mass of the inhibitor was about 13 kDa on 16.5% SDS/PAGE. The concentration at which 50% inhibition (I50) was found was in the nanomolar range. The inhibitor seems to bind to Na+, K+-ATPase at a site distal from the ATP-binding site. The binding to the ATPase is non-competitive. The CD analysis suggests an unordered secondary structural element. It also inhibits p-nitrophenyl phosphatase activity from rat brain with comparable I50 value to that for Na+, K+-ATPase. The protein does not contain any Trp as evident from Trp fluorescence and amino acid analysis. Amino acid analysis shows that glycine and serine, derivatives of tyrosine and phenylalanine are the predominant amino acids. The data suggests that it is a negatively charged protein in which the contribution of the hydrophobic part is 27%.

Cryptic origin of SPAI, a plasma protein with a transglutaminase substrate domain and the WAP motif, revealed by in situ hybridization and immunohistochemistry

SPAI, originally isolated as a sodium/potassium-ATPase inhibitor and now considered to be a proteinase inhibitor of unknown specificity based on its similarity to elafin (an elastase inhibitor), is a new type of plasma protein that has a transglutaminase substrate domain, which serves as an anchoring sequence to be covalently cross-linked at target sites. To determine the source of SPAI, we carried out in situ hybridization and immunohistochemistry using an antisense cRNA probe and an antiserum against recombinant SPAI, respectively. Since previous RNase protection analysis had indicated that SPAI mRNA is almost exclusively expressed in the porcine small intestine, we used its frozen sections for the staining. The lower crypt was decorated with both the cRNA probe and antiserum, indicating that SPAI is synthesized and secreted by the enteroendocrine cells located near the crypt base. The native form of SPAI was also characterized by Western blotting. This result together with the previous biochemical and molecular biological characterizations may set the stage for identifying the physiological roles of the conceptually very interesting protein SPAI.

A galanin-mastoparan chimeric peptide activates the Na+,K(+)-ATPase and reverses its inhibition by ouabain

The effect of the neuropeptide galanin, the wasp venom toxin amphiphilic peptide toxin mastoparan and the chimeric peptide, galparan, consisting of N-terminal 13 amino acids of neuropeptide galanin linked at C-terminus to mastoparan amide (and its inactive analog Mas17) on the activity of Na+,K(+)-ATPase has been studied. Mastoparan inhibits the activity of the Na+,K(+)-ATPase with IC50 = 7.5 microM and also reduces the cooperativity for Na+ and K+, respectively, while galanin has no effect on the Na+,K(+)-ATPase activity. The chimeric peptide, galanin(1-13)-mastoparan amide (galparan), exhibits biphasic interaction with Na+,K(+)-ATPase, it activates the enzyme at maximal stimulating concentration of 4 microM followed by inhibition of the enzyme with IC50 of 100 microM. At maximum stimulating concentration (4 microM), galparan partly reduces the cooperativity only for Na+ and it also counteracts the inhibitory effect of oubain on Na+,K(+)-ATPase. Galparan's stimulatory effect was influenced by ATP. The chimeric peptide [19Lys,26Leu]-galparan, containing the inactive analog of mastoparan (Mas17), has no effects on rat brain Na+,K(+)-ATPase activity. Both chimeric peptides galparan and [19Lys,26Leu]-galparan are high-affinity galanin receptor ligands with IC50 of 6.4 nM and 0.71 nM, respectively, while galanin (1-13) and mastoparan alone have significantly lower affinity for the galanin receptor, IC50 of 125 nM and 1 microM, respectively. The ability of chimeric peptides to bind to galanin receptors does not correlate with their effects on the Na+,K(+)-ATPase.

Accelerated evolution in inhibitor domains of porcine elafin family members

Through the analysis of the porcine gene encoding the elastase inhibitor elafin, we demonstrated that there are at least three closely related members of the elafin family, and their genes have arisen by accelerated evolution. A porcine genomic DNA library was screened with a previously cloned human elafin cDNA probe, and several positive clones were obtained that can be distinguished by a combination of restriction enzymes. Sequence analysis of these clones revealed the presence of three homologous members whose genes, all consisting of three exons and two introns, are almost identical except the exon 2 sequences encoding the inhibitor domain called "WAP motif"; the intron sequences are related to each other with sequence similarities of 93-98%, whereas the exon 2 sequences exhibited only 60-77% similarities among the three members. The extreme divergence in the exon 2 sequences compared to the highly conserved intron sequences may be generated by accelerated mutations confined in a short stretch of the genes following recent duplication events of a single ancestral gene. An RNase protection assay indicated that the messages of the elafin family members are abundantly expressed in the trachea and intestine, suggesting that the most likely selective forces for the accelerated evolution are extrinsic proteinases produced by invasive microorganisms.

Cloning, characterization, and tissue distribution of porcine SPAI, a protein with a transglutaminase substrate domain and the WAP motif

The primary and gene structures and tissue distribution of porcine SPAI-2, a protein that belongs to the WAP protein superfamily and has a sodium-potassium ATPase inhibitory activity, were determined by molecular cloning and Northern analysis. A full-length cDNA clone was isolated from a porcine duodenum cDNA library. The cDNA insert encoded a polypeptide of 187 amino acids, which is composed of three domains: a hydrophobic presequence of 21 amino acids, a prosegment of 105 amino acids ending with Asp126, and the mature SPAI-2 sequence of 61 amino acids beginning with Pro127. The prosegment contained 16 repeats of a hexapeptide that is highly homologous to the repetitive sequence found in the transglutaminase domain of the human elafin, an elastase-specific inhibitor that also belongs to the WAP superfamily. The repetitive sequence was demonstrated to be a good substrate of transglutaminase using a recombinant preparation produced in Escherichia coli. A porcine genomic library was then screened for the SPAI gene. Characterization and sequencing of positive clones indicated that the gene is similar to the elafin gene, having 3 exons encoding the 5'-untranslated region and signal sequence, proSPAI, and 3'-untranslated region, respectively. Northern blot analysis revealed intestine-specific expression of SPAI mRNA; the message was especially abundant in the small intestine. ProSPAI was also found in the circulation. The similarity of proSPAI to elafin in the domain structure, the acid-labile nature of the cleavage site (Asp126-Pro127), and the fact that the major form of SPAI in the plasma is proSPAI strongly suggest that proSPAI is not the precursor but rather it is the native form of SPAI. Like elafin, therefore, SPAI appears to be a new type of biologically active substance with a transglutaminase substrate domain that acts as an anchoring sequence.

Activation of Na,K-ATPase by an endogenous peptide, PEC-60

Several peptidic and non-peptidic factors can modulate Na,K-ATPase activity, among them mainly inhibitors of this enzyme, ouabain being the most effective. In a very few cases only, activation of Na,K-ATPase by endogenous factors has been recorded. We have investigated the effect on Na,K-ATPase of a novel regulatory peptide, PEC-60, recently isolated from porcine intestine. Various biological effects have been described for PEC-60 in different tissues, including brain. We have found that PEC-60 caused a dose-dependent activation of Na,K-ATPase from rat brain frontal cortex, whereas the carboxymethylated form of PEC-60 or other hormonal peptides had no effect. The maximal value of activity reaches up to 125% at close to micromolar concentrations of PEC-60 and the dependence can be described with a bell-shaped curve, indicating a complex mechanism for the interaction. The activation of the enzyme by PEC-60 is apparently related to Na(+)-dependent steps of the Na,K-ATPase system. The kinetic parameters for K(+)-phosphatase were unaffected. Moreover, the activating effect was enhanced by preincubation at low concentrations of ATP that transform the enzyme into the Na(+)-form. Due to the crucial physiological role of Na,K-ATPase, its activity has to be finely controlled and thus PEC-60 may be one of the endogenous factors that regulate this enzyme.

An Na+/K(+)-ATPase inhibitor protein from rat brain cytosol

A protein isolated from rat brain cytosol is found to inhibit Na+/K(+)-ATPase in rat brain and kidney and H+/K(+)-ATPase from toad gastric mucosa, but has no effect on Ca2+,Mg(2+)-ATPase and Ca(2+)-ATPase isolated either from rat testis or goat spermatozoa. The inhibitor has been partially purified by ammonium sulphate precipitation followed by gel-filtration through Sephadex G-100. The inhibitor seems to bind at or close to the ATP binding site of Na+/K(+)-ATPase, such that the binding of the inhibitor to ATPase is reversible and competitive in nature with respect to the substrate. Optimum inhibition is observed at around the phase transition temperature of brain Na+/K(+)-ATPase and the inhibitory activity is only partially dependent on -SH or -NH2 group(s) of the inhibitor protein.

Isolation of an endogenous Na-pump specific inhibitor from normal pig urine: characterization and comparison with the inhibitor purified from bovine adrenal glands

An endogenous Na-pump specific inhibitor has been purified to homogeneity from normal pig urine using Amberlite XAD-2 adsorption chromatography followed by five steps of reverse phase HPLC. Although most of the dose response curves for this purified Na-pump inhibitor, designated uroxin, in the various assay systems paralleled those of authentic ouabain and the specific Na-pump inhibitor previously purified from bovine adrenal glands (designated adrexin C), the cross-reactivity curve with anti-ouabain antibodies did not. The retention times of uroxin on various types of reverse phase HPLC columns were also different from those of plant-derived cardiotonic steroids and adrexin C. The cross-reaction curve of adrexin C was superimposable with that of ouabain, and adrexin C coeluted with ouabain from all of the HPLC columns tested. The results from physical and chemical characterization of both purified inhibitors suggest that uroxin is a novel Na-pump inhibitor which is structurally different from any of the known cardiotonic steroids or other substances previously reported to exhibit Na-pump inhibitory activity. The results also indicate that adrexin C is indistinguishable from ouabain. These results suggest that there are at least two different types of endogenous Na+,K(+)-ATPase inhibitors in the mammalian body.

Characterization and gene sequence of the precursor of elafin, an elastase-specific inhibitor in bronchial secretions

Human bronchial mucous secretions have been shown to contain inhibitors of serine proteinases secreted by neutrophils. The role of these inhibitors is probably to control the enzymes secreted in the airways and in the lung interstitium. Three of these inhibitors have been identified and characterized: alpha 1-proteinase inhibitor, mucus proteinase inhibitor, and elafin. The elafin molecule, a 6.0 kD inhibitor of serine proteinases shows homology with mucus proteinase inhibitor. We recently isolated both molecules in bronchial secretions. In this report, we present evidence for the existence of a precursor of the elafin molecule. We have cloned and sequenced the gene for this precursor and show that it is composed of three exons. The coding information for a 117 amino acid precursor protein of elafin (inclusive of the signal peptide) is contained in the first two exons. This was confirmed at the mRNA and protein levels. By Northern Blot analysis we detected a 800 bp long product, and by immunoaffinity we detected in sputum and in cultured epithelial cell supernatant (NCI-H322 cell line) a 12 kD protein species cross-reacting with anti-elafin IgG. The finding of possible cross-linking function for the precursor in addition to its antiproteinase activity indicates a possible role for this molecule as a cross-linker agent in the extracellular matrix.

In search of synaptosomal Na+, K+-ATPase regulators

The arrival of the nerve impulse to the nerve endings leads to a series of events involving the entry of sodium and the exit of potassium. Restoration of ionic equilibria of sodium and potassium through the membrane is carried out by the sodium/potassium pump, that is the enzyme Na+,K(+)-ATPase. This is a particle-bound enzyme that concentrates in the nerve ending or synaptosomal membranes. The activity of Na+,K(+)-ATPase is essential for the maintenance of numerous reactions, as demonstrated in the isolated synaptosomes. This lends interest to the knowledge of the possible regulatory mechanisms of Na+,K(+)-ATPase activity in the synaptic region. The aim of this review is to summarize the results obtained in the author's laboratory, that refer to the effect of neurotransmitters and endogenous substances on Na+,K(+)-ATPase activity. Mention is also made of results in the field obtained in other laboratories. Evidence showing that brain Na+,K(+)-ATPase activity may be modified by certain neurotransmitters and insulin have been presented. The type of change produced by noradrenaline, dopamine, and serotonin on synaptosomal membrane Na+,K(+)-ATPase was found to depend on the presence or absence of a soluble brain fraction. The soluble brain fraction itself was able to stimulate or inhibit the enzyme, an effect that was dependent in turn on the time elapsed between preparation and use of the fraction. The filtration of soluble brain fraction through Sephadex G-50 allowed the separation of two active subfractions: peaks I and II. Peak I increased Na+,K(+)- and Mg(2+)-ATPases, and peak II inhibited Na+,K(+)-ATPase. Other membrane enzymes such as acetylcholinesterase and 5'-nucleotidase were unchanged by peaks I or II. In normotensive anesthetized rats, water and sodium excretion were not modified by peak I but were increased by peak II, thus resembling ouabain effects. 3H-ouabain binding was unchanged by peak I but decreased by peak II in some areas of the CNS assayed by quantitative autoradiography and in synaptosomal membranes assayed by a filtration technique. The effects of peak I and II on Na+,K(+)-ATPase were reversed by catecholamines. The extent of Na+,K(+)-ATPase inhibition by peak II was dependent on K+ concentration, thus suggesting an interference with the K+ site of the enzyme. Peak II was able to induce the release of neurotransmitter stored in the synaptic vesicles in a way similar to ouabain. Taking into account that peak II inhibits only Na+,N(+)-ATPase, increases diuresis and natriuresis, blocks high affinity 3H-ouabain binding, and induces neurotransmitter release, it is suggested that it contains an ouabain-like substance.

The Na,K-ATPase

The energy dependent exchange of cytoplasmic Na+ for extracellular K+ in mammalian cells is due to a membrane bound enzyme system, the Na,K-ATPase. The exchange sustains a gradient for Na+ into and for K+ out of the cell, and this is used as an energy source for creation of the membrane potential, for its de- and repolarisation, for regulation of cytoplasmic ionic composition and for transepithelial transport. The Na,K-ATPase consists of two membrane spanning polypeptides, an alpha-subunit of 112-kD and a beta-subunit, which is a glycoprotein of 35-kD. The catalytic properties are associated with the alpha-subunit, which has the binding domain for ATP and the cations. In the review, attention will be given to the biochemical characterization of the reaction mechanism underlying the coupling between hydrolysis of the substate ATP and transport of Na+ and K+.

Primary structure of the human elafin precursor preproelafin deduced from the nucleotide sequence of its gene and the presence of unique repetitive sequences in the prosegment

The human elafin gene was cloned and its entire nucleotide sequence was determined to deduce the amino acid sequence for the precursor of elafin, an elastase-specific inhibitor. The gene spans approximately 1.7 kb and is divided into 3 exons. The gene product preproelafin consists of 117 amino acids: the initiator Met, a putative 25-amino acid signal peptide, a pro-sequence of about 34 amino acids, and the C-terminal 57 amino acids for mature elafin. Possible covalent clotting of the prosegment and its physiological significance have been pointed out based on a remarkable sequence similarity between the pro-sequence and the guinea pig seminal clotting protein SVP-1.

Expression of the whey acidic protein in transgenic pigs impairs mammary development

The whey acidic protein has been found in milk of mice, rats, rabbits and camels, and its gene is expressed specifically in mammary tissue at late pregnancy and throughout lactation. A characteristic of whey acidic protein is the 'four-disulfide-core' signature which is also present in proteins involved in organ development. We have generated six lines of transgenic pigs which carry a mouse whey acidic protein transgene and express it at high levels in their mammary glands. Transgenic sows from three lines could not produce sufficient quantities of milk to support normal development of healthy offspring. This phenotype appears to be similar, if not identical, to the milchlos phenotype exhibited by mice expressing whey acidic protein transgenes. Mammary tissue from post-partum milchlos sows had an immature histological appearance, which was distinct from that observed during normal development or involution. Expression of the whey acidic protein transgene was found in mammary tissue from sexually immature pigs from milchlos lines, but not in sows from lines that appeared to lactate normally. We suggest that precocious synthesis of whey acidic protein impairs mammary development and function. Impaired mammary development due to inappropriate timing of whey acidic protein expression is consistent with the notion that proteins with the 'four-disulfide-core' signature participate in tissue formation.

Na+,K(+)-ATPase inhibition by an endogenous peptide, SPAI-1, isolated from porcine duodenum

SPAI-1, a peptide isolated from porcine duodenum, has been shown to inhibit Na+,K(+)-ATPase in vitro (Araki et al. (1989) Biochem. Biophys. Res. Commun. 164, 496-502). The characteristics of ATPase inhibition by this novel peptide were examined. SPAI-1 inhibited Na+,K(+)-ATPase preparations isolated from various organs of dog or rat or from sheep kidney with similar potency. Three isoforms of rat Na+,K(+)-ATPase had similar sensitivity to inhibition by SPAI-1 although these isoforms had remarkable differences in their sensitivity to the inhibitory effect of ouabain. Ca(2+)-ATPase isolated from the sarcoplasmic reticulum of rabbit skeletal muscle was insensitive to inhibition by SPAI-1. Ouabain-insensitive Mg(2+)-ATPase activity was unaffected by low concentrations of SPAI-1, but was stimulated at high concentrations. SPAI-1 inhibited H+,K(+)-ATPase from hog stomach in concentrations similar to that required for Na+,K(+)-ATPase inhibition. These results indicate that SPAI-1 is a specific inhibitor for monovalent cation transporting ATPases.

Isolation and identification of hemin as an endogenous Na+/K(+)-ATPase inhibitor from porcine blood cells

A substance which is a potent inhibitor of Na+/K(+)-ATPase activity and competitively displaces [3H]ouabain binding to this enzyme was isolated from porcine blood cells. From its chemical and physiochemical properties, this activity was identified as hemin (chloroprotohemin IX). Hemin showed a dose dependent curve for Na+/K(+)-ATPase inhibitory activity similar to that of ouabain and displaced [3H]ouabain binding as potent as 1/100 of ouabain itself.

The alpha-2 isomer of the sodium pump is inhibited by calcium at physiological levels

The inhibition of the (Na,K)ATPase by calcium was investigated in plasma membrane preparations of rat axolemma, skeletal muscle and kidney outer medulla. Ouabain titration curves demonstrated that physiological calcium (0.08-5 microM) inhibited mainly the high affinity alpha 2 isomer. In axolemma all the (Na,K)ATPase had high ouabain affinity and calcium inhibited 40-50% of the activity with a Ki of 1.9 +/- 0.9 x 10(-7) M. In skeletal muscle high and low ouabain affinity components were present in equal amounts and calcium inhibited only the high affinity component with a Ki of 1.3 +/- 0.3 x 10(-7) M. Kidney enzyme had a low affinity for ouabain and showed very little sensitivity to calcium in the physiological range. It was demonstrated that high calcium levels inhibit the enzyme in a general sense, irrespective of the isomer, with a Ki of 6.5 +/- 6 x 10(-4) M for the kidney and 5.9 +/- 4 x 10(-4) M for the axolemma enzymes. In axolemma, enzyme activity was studied as a function of sodium concentration. Physiological calcium reduced Vmax while not significantly changing K 0.5 for sodium binding.

Four disulfide bonds' allocation of Na+, K(+)-ATPase inhibitor (SPAI)

We have recently reported the primary structures of the three unique peptide inhibitors (SPAI-1, -2, and -3) against Na+, K(+)-ATPase which contained four disulfide bridges in common (Biochem. Biophys. Res. Commun. 164, 496 (1989)). The disulfide connectivities of SPAI were determined by the combination of amino acid analyses with the direct application to a gas-phase sequencer of its proteolytic fragments. The disulfide bond was identified by detection of phenylthiohydantoin derivatives of cystine and its decomposed product dehydroalanine. The four cysteine pairs were disclosed to be Cys20 to Cys49, Cys27 to Cys53, Cys36 to Cys48, and Cys42 to Cys57, all linked by disulfide bridge formation. The allocation pattern of these disulfide bonds was the same as that recently reported for human mucous proteinase inhibitor (EMBO J. 7, 345 (1988], though SPAI showed no proteinase inhibitory activity at all.