Identification of cDNAs encoding two novel rat pancreatic serine proteases

Purification and Biological Function of Caldecrin

Blood calcium homeostasis is critical for biological function. Caldecrin, or chymotrypsin-like elastase, was originally identified in the pancreas as a serum calcium-decreasing factor. The serum calcium-decreasing activity of caldecrin requires the trypsin-mediated activation of the protein. Protease activity-deficient mature caldecrin can also reduce serum calcium concentration, indicating that structural processing is necessary for serum calcium-decreasing activity. Caldecrin suppresses the differentiation of bone-resorbing osteoclasts from bone marrow macrophages (BMMs) by inhibiting receptor activator of NF-κB ligand (RANKL)-induced nuclear factor of activated T-cell cytoplasmic 1 expression via the Syk-PLCγ-Ca2+ oscillation-calcineurin signaling pathway. It also suppresses mature osteoclastic bone resorption by RANKL-stimulated TRAF6-c-Src-Syk-calcium entry and actin ring formation. Caldecrin inhibits lipopolysaccharide (LPS)-induced osteoclast formation in RANKL-primed BMMs by inducing the NF-κB negative regulator A20. In addition, caldecrin suppresses LPS-mediated M1 macrophage polarization through the immunoreceptor triggering receptor expressed on myeloid cells (TREM) 2, suggesting that caldecrin may function as an anti-osteoclastogenic and anti-inflammatory factor via TREM2. The ectopic intramuscular expression of caldecrin cDNA prevents bone resorption in ovariectomized mice, and the administration of caldecrin protein also prevents skeletal muscle destruction in dystrophic mice. In vivo and in vitro studies have indicated that caldecrin is a unique multifunctional protease and a possible therapeutic target for skeletal and inflammatory diseases.

Caldecrin: A pancreas-derived hypocalcemic factor, regulates osteoclast formation and function

Caldecrin was originally isolated from the pancreas as a factor that reduced serum calcium levels. This secreted serine protease has chymotrypsin-like activity and is also known as chymotrypsin C; it belongs to the elastase family. Although intravenous administration of caldecrin decreases the serum calcium concentration even when its protease activity is blocked, this effect does require cleavage of caldecrin’s pro-peptide by trypsin, converting it to the mature enzyme. Ectopic intramuscular expression of caldecrin prevented bone resorption in ovariectomized mice. Caldecrin inhibited parathyroid hormone-stimulated calcium release from fetal mouse long bone organ cultures. Furthermore, caldecrin suppressed the formation of osteoclasts from bone marrow cells by inhibiting the receptor activator of nuclear factor-κ B ligand (RANKL)-stimulated phospholipase Cγ-calcium oscillation-calcineurin-nuclear factor of activated T-cells, cytoplasmic 1 pathway. Caldecrin also suppressed the bone resorption activity of mature osteoclasts by preventing RANKL-stimulated Src activation, calcium entry, and actin ring formation. In vivo and in vitro studies have indicated that caldecrin is a unique multifunctional protease with anti-osteoclastogenic activities that are distinct from its protease activity. Caldecrin might be a potential therapeutic target for the treatment of osteolytic diseases such as osteoporosis and osteoarthritis. This mini-review describes caldecrin’s historical background and its mechanisms of action.

Identification of trypsin I as a candidate for influenza A virus and Sendai virus envelope glycoprotein processing protease in rat brain

Extracellular cleavage of virus envelope fusion glycoprotein hemagglutinin (HA0) by host trypsin-like proteases is a prerequisite for the infectivity and pathogenicity of human influenza A viruses and Sendai virus. The common epidemic influenza A viruses are pneumotropic, but occasionally cause encephalopathy or encephalitis, although the HA0 processing enzyme in the brain has not been identified. In searching for the brain processing proteases, we identified a processing enzyme in rat brain that was inducible by infection with these viruses. The purified enzyme exhibited an apparent molecular mass of approximately 22 kDa on SDS-PAGE and the N-terminal amino acid sequence was consistent with that of rat pancreatic trypsin I. Its substrate specificities and inhibition profiles were the same as those of pancreatic trypsin I. In situ hybridization and immunohistochemical studies on trypsin I distribution revealed heavy deposits in the brain capillaries, particularly in the allocortex, as well as in clustered neuronal cells of the hippocampus. The purified enzyme efficiently processed the HA0 of human influenza A virus and the fusion glycoprotein precursor of Sendai virus. Our results suggest that trypsin I in the brain potentiates virus multiplication in the pathogenesis and progression of influenza-associated encephalopathy or encephalitis.

Human mesotrypsin defies natural trypsin inhibitors: from passive resistance to active destruction

More than twenty years ago Rinderknecht et al. identified a minor trypsin isoform resistant to natural trypsin inhibitors in the human pancreatic juice. At the same time, Estell and Laskowski found that an inhibitor-resistant trypsin from the pyloric caeca of the starfish, Dermasterias imbricata rapidly hydrolyzed the reactive-site peptide bonds of trypsin inhibitors. A connection between these two seminal discoveries was made recently, when human mesotrypsin was shown to cleave the reactive-site peptide bond of the Kunitz-type soybean trypsin inhibitor, and degrade the Kazal-type pancreatic secretory trypsin inhibitor. These observations indicate that proteases specialized for the degradation of protease inhibitors are ubiquitous in metazoa, and prompt new investigations into their biological significance. Here we review the history and properties of human mesotrypsin, and discuss its function in the digestive degradation of dietary trypsin inhibitors and possible pathophysiological role in pancreatitis.

Identification of ectopic anionic trypsin I in rat lungs potentiating pneumotropic virus infectivity and increased enzyme level after virus infection

Extracellular cleavage of virus envelope fusion glycoproteins by host cellular proteases is a prerequisite for the infectivity of mammalian and nonpathogenic avian influenza viruses, and Sendai virus. In search of such target processing proteases in the airway, we recently found a new candidate trypsin-like processing protease in rat lungs, which was induced by Sendai virus infection, and identified as ectopic rat anionic trypsin I. On SDS/PAGE under reducing and nonreducing conditions, the purified enzyme gave protein bands corresponding to 29 and 22 kDa, respectively, i.e. at the same positions as rat pancreatic anionic trypsin I. It exhibited an apparent molecular mass of 31 kDa on molecular sieve chromatography and its isoelectric point was pH 4.7. The amino-acid sequences of the N-terminus and proteolytic digest peptides of the purified enzyme were consistent with those of rat pancreatic anionic trypsin I. Its substrate specificities and inhibitor sensitivities were the same as those of the pancreatic enzyme. The purified enzyme efficiently processed the fusion glycoprotein precursor of Sendai virus and hemagglutinin of human influenza A virus, and potentiated the infectivity of Sendai virus in the same dose-dependent manner as the pancreatic one. Immunohistochemical studies revealed that this protease is located in the stromal cells in peri-bronchiolar regions. These results suggest that ectopic anionic trypsin I in rat lungs induced by virus infection may trigger virus spread in rat lungs.

Cold adapted enzymes

The number of reports on enzymes from cold adapted organisms has increased significantly over the past years, and reveals that adaptive strategies for functioning at low temperature varies among enzymes. However, the high catalytic efficiency at low temperature seems, for the majority of cold active enzymes, to be accompanied by a reduced thermal stability. Increased molecular flexibility to compensate for the low working temperature, is therefore still the most dominating theory for cold adaptation, although there also seem to be other adaptive strategies. The number of experimentally determined 3D structures of enzymes possessing cold adaptation features is still limited, and restricts a structural rationalization for cold activity. The present summary of structural characteristics, based on comparative studies on crystal structures (7), homology models (7), and amino acid sequences (24), reveals that there are no common structural feature that can account for the low stability, increased catalytic efficiency, and proposed molecular flexibility. Analysis of structural features that are thought to be important for stability (e.g. intra-molecular hydrogen bonds and ion-pairs, proline-, methionine-, glycine-, or arginine content, surface hydrophilicity, helix stability, core packing), indicates that each cold adapted enzyme or enzyme system use different small selections of structural adjustments for gaining increased molecular flexibility that in turn give rise to increased catalytic efficiency and reduced stability. Nevertheless, there seem to be a clear correlation between cold adaptation and reduced number of interactions between structural domains or subunits. Cold active enzymes also seem, to a large extent, to increase their catalytic activity by optimizing the electrostatics at and around the active site.

Identification of novel serine proteinase gene transcripts in the midguts of two tropical insect pests, Scirpophaga incertulas (Wk.) and Helicoverpa armigera (Hb.)

We have used RT PCR and 3'RACE to identify diverse serine proteinase genes expressed in the midguts of the rice yellow stem borer (Scirpophaga incertulas) and Asian corn borer (Helicoverpa armigera). The RT-PCR primers encoded the conserved regions around the active site histidine57 and serine195 of Drosophila melanogaster alpha trypsin, including aspartate189 of the specificity pocket. These primers amplified three transcripts (SiP1-3) from midguts of S. incertulas, and two transcripts (HaP1-2) from midguts of H. armigera. The five RT PCR products were sequenced to permit design of gene-specific forward primers for use with anchored oligo dT primers in 3'RACE. Sequencing of the 3'RACE products indicated that SiP1, SiP2 and HaP1 encoded trypsin-like serine proteinases, while HaP2 encoded a chymotrypsin-like serine proteinases. The SiP3 transcript proved to be an abundant 960 nt mRNA encoding a trypsin-like protein in which the active site serine195 was replaced by aspartate. The possible functions of this unusual protein are discussed.

Reverse biochemistry: use of macromolecular protease inhibitors to dissect complex biological processes and identify a membrane-type serine protease in epithelial cancer and normal tissue

Serine proteases of the chymotrypsin fold are of great interest because they provide detailed understanding of their enzymatic properties and their proposed role in a number of physiological and pathological processes. We have been developing the macromolecular inhibitor ecotin to be a "fold-specific" inhibitor that is selective for members of the chymotrypsin-fold class of proteases. Inhibition of protease activity through the use of wild-type and engineered ecotins results in inhibition of rat prostate differentiation and retardation of the growth of human PC-3 prostatic cancer tumors. In an effort to identify the proteases that may be involved in these processes, reverse transcription-PCR with PC-3 poly(A)+ mRNA was performed by using degenerate oligonucleotide primers. These primers were designed by using conserved protein sequences unique to chymotrypsin-fold serine proteases. Five proteases were identified: urokinase-type plasminogen activator, factor XII, protein C, trypsinogen IV, and a protease that we refer to as membrane-type serine protease 1 (MT-SP1). The cloning and characterization of the MT-SP1 cDNA shows that it encodes a mosaic protein that contains a transmembrane signal anchor, two CUB domains, four LDLR repeats, and a serine protease domain. Northern blotting shows broad expression of MT-SP1 in a variety of epithelial tissues with high levels of expression in the human gastrointestinal tract and the prostate. A His-tagged fusion of the MT-SP1 protease domain was expressed in Escherichia coli, purified, and autoactivated. Ecotin and variant ecotins are subnanomolar inhibitors of the MT-SP1 activated protease domain, suggesting a possible role for MT-SP1 in prostate differentiation and the growth of prostatic carcinomas.

Production of trypsins by human gastric cancer cells correlates with their malignant phenotype

Proteolytic degradation of extracellular matrix is a critical step in tumour invasion and metastasis. To examine the role of trypsin in tumour dissemination, we cloned two variants (S4 and R3 cells) from STKM-1, a trypsinogen 1-producing diffuse gastric cancer cell line. Western blot analysis with antitrypsin antibody showed that 26 and 24 kDa proteins were highly detected in S4 conditioned medium (CM) in comparison to R3 CM. In addition to the 26 and 24 kDa proteins, 25 and 23 kDa bands, which correspond to enterokinase-activated trypsin, were found only in S4 CM. When the CMs of the two clones were treated with enterokinase, the 25 and 23 kDa trypsin activities in S4 CM were effectively increased as compared with R3 CM. When the two clones were inoculated intraperitoneally (i.p.) into nude mice, S4 cells strongly invaded the liver, pancreas and peritoneum and killed the hosts more rapidly than R3 cells: the 50% survival time was 50 days for S4 and 82 days for R3 cells. These results suggest that trypsin production is associated with the invasive growth of STKM-1 gastric cancer cells.

Zyme, a novel and potentially amyloidogenic enzyme cDNA isolated from Alzheimer's disease brain

The deposition of the beta amyloid peptide in neuritic plaques and cerebral blood vessels is a hallmark of Alzheimer's disease (AD) pathology. The major component of the amyloid deposit is a 4.2-kDa polypeptide termed amyloid beta-protein of 39-43 residues, which is derived from processing of a larger amyloid precursor protein (APP). It is hypothesized that a chymotrypsin-like enzyme is involved in the processing of APP. We have discovered a new serine protease from the AD brain by polymerase chain reaction amplification of DNA sequences representing active site homologous regions of chymotrypsin-like enzymes. A cDNA clone was identified as one out of one million that encodes Zyme, a serine protease. Messenger RNA encoding Zyme can be detected in some mammalian species but not in mice, rats, or hamster. Zyme is expressed predominantly in brain, kidney, and salivary gland. Zyme mRNA cannot be detected in fetal brain but is seen in adult brain. The Zyme gene maps to chromosome 19q13.3, a region which shows genetic linkage with late onset familial Alzheimer's disease. When Zyme cDNA is co-expressed with the APP cDNA in 293 (human embryonic kidney) cells, amyloidogenic fragments are detected using C-terminal antibody to APP. These co-transfected cells release an abundance of truncated amyloid beta-protein peptide and shows a reduction of residues 17-42 of Abeta (P3) peptide. Zyme is immunolocalized to perivascular cells in monkey cortex and the AD brain. In addition, Zyme is localized to microglial cells in our AD brain sample. The amyloidogenic potential and localization in brain may indicate a role for this protease in amyloid precursor processing and AD.

Evolutionary silencing of the human elastase I gene (ELA1)

The human pancreatic elastase I gene is transcriptionally silent, despite the apparent integrity of the structural gene. The transcriptional regulatory sequences necessary and sufficient for transcription of the active rat homologue are localized within 205 base pairs (bp) of the transcriptional start and comprise a pancreas-specific transcriptional enhancer of 134 bp immediately upstream of a 71 bp non-specific promoter. The human gene has 58 nucleotide differences within this region, 13 of which are in the three functional elements (A, B and C) that constitute the enhancer. Through cell transfection analyses with a pancreatic acinar tumor cell line, we show that the nucleotide differences in the human 5' flanking gene sequences have inactivated both the enhancer and the promoter. The changes in the three elements of the human enhancer alone are sufficient to inactivate the enhancer; conversely, restoring these to the rat configuration partially restores the activity of the human enhancer. The two mutations in the A element and the four mutations in the B element abolish the binding of the transcription factors previously shown to mediate the activity of these elements. Replacing the active 71 bp rat promoter with the human promoter also prevents expression. Therefore, the evolutionary silencing of the human elastase I gene appears due to mutations that inactivate crucial enhancer and promoter elements.

Dietary modulation of the mRNA stability of trypsin isozymes and the two forms of secretory trypsin inhibitor in the rat pancreas

The stability of the mRNAs encoding pancreatic trypsin isozymes, namely the cationic form and the two anionic forms I and II, as well as that of the secretory trypsin inhibitors I and II, were studied in rats fed on either a high-protein diet, or a protein-free diet compared with a standard diet for a 10-day period. Either immediately or 3 h and 6 h after injecting the transcription inhibitor, actinomycin D, the mRNA levels were quantified by performing dot-blot hybridization with specific oligonucleotide probes. Under high-protein dietary conditions, the stability of the mRNAs coding for anionic trypsin II and cationic trypsin showed no change, whereas that of anionic trypsin I and the two forms of secretory trypsin inhibitor were affected. The mRNA half-life of anionic trypsin I and trypsin inhibitor II increased, in sharp contrast with that of trypsin inhibitor I, which decreased. When rats were fed on a protein-free diet, the stabilities of both anionic trypsin forms and trypsin inhibitor I increased, whereas that of trypsin inhibitor II decreased and that of cationic trypsin remained unchanged. The present results show the existence of differences in the mechanisms whereby gene expression of trypsin isozymes and secretory trypsin inhibitors is regulated, although they are synthesized in parallel in the pancreatic acinar cell and stored in zymogen granules before being secreted into the intestinal lumen.

Molecular cloning and expression of human caldecrin

Earlier we reported the primary structure of serum calcium-decreasing factor (caldecrin) from rat pancreas, a protein which is considered to be a member of the elastase family. In this report, we describe the isolation of the two homologous cDNA clones encoding caldecrin from human pancreas, the structures of which are identical except for one base and the corresponding amino acid residue. These human caldecrin isoforms are composed of a signal peptide of 16 amino acids, a propeptide of 13 amino acids, and a mature form of 239 amino acids. Both recombinant caldecrins showed the same chymotrypsin-type protease activity and hypocalcemic activity. The hypocalcemic activity of both remained intact even after treatment with PMSF to abolish their protease activity. These results suggest that human caldecrin possesses hypocalcemic activity that has no connection with its protease activity.

Isolation and characterization of two cDNAs from Atlantic cod encoding two distinct psychrophilic elastases

The cDNAs encoding two different Atlantic cod elastases have been isolated and sequenced. The predicted amino acid sequences revealed two preproelastases, consisting of a signal peptide, an activation peptide and a mature enzyme of 242 and 239 amino acids. Amino acid sequence identity between the two cod elastases was 60.1% and identity with mammalian elastases ranged from 50-64%. The two cod elastases contain all the major structural features common to serine proteases, such as the catalytic triad His57, Asp102 and Ser195. Both cod elastases have a high content of methionine, consistent with previous findings in psychrophilic fish enzymes.

Molecular cloning and expression of serum calcium-decreasing factor (caldecrin)

We previously reported on the purification of a serum calcium-decreasing factor, referred to as caldecrin, from porcine pancreas, that is thought to be a serine protease (Tomomura, A., Fukushige, T., Noda, T., Noikura, T., and Saheki, T. (1992) FEBS Lett. 301, 277-281). In the present study, we purified caldecrin from rat pancreas and determined its primary structure by cDNA cloning. The predicted caldecrin protein is presumed to be synthesized as a preproenzyme of 268 amino acids with a signal peptide of 16 amino acids and an activation peptide of 13 amino acids, and is, with the exception of a central region, almost identical to the reported rat pancreatic elastase IV sequence. The caldecrin gene is selectively expressed in the pancreas, as judged by Northern blot analysis. After expression in BMT-10 cells, immunoreactive caldecrin was found in the culture supernatant, and it inhibited the parathyroid hormone-stimulated 45Ca release from cultured fetal long bones. Catalytic site mutants were synthesized in a baculovirus system, and recombinant mutants also decreased the serum calcium level of mice. These data implicate caldecrin, a protease closely related to elastase IV, in the regulation of blood calcium levels.

Trypsinogen expression in human ovarian carcinomas

Increased secretion of matrix metalloproteinases and serine proteinases is well known to be associated with cancer invasion and metastasis. We aimed to elucidate the implication of trypsin, a serine proteinase and a representative digestive enzyme in invasion and metastasis of human carcinomas. Northern blot, RT-PCR and Western blot analyses and immunohistochemical studies were performed to detect and analyze trypsinogen expression in 5 ovarian carcinoma cell lines and 10 human ovarian carcinoma tissues using a DNA probe for trypsinogen I, and monoclonal and polyclonal antibodies to human trypsin I. Among the 5 ovarian carcinoma cell lines, only the MCAS (mucinous cystadenocarcinoma) cell line showed a high level of trypsinogen production and mRNA expression by Western and Northern blot analyses, respectively. However, Southern blot analysis of RT-PCR products could detect considerable levels of trypsinogen mRNA in all ovarian cancer cell lines. In Northern analysis of ovarian cancer tissues, all advanced cancer samples showed trypsinogen gene expression. Serous cystadenocarcinomas exhibited particularly high levels of gene expression. Immunohistochemical staining also detected trypsin in ovarian carcinoma tissues. In contrast, normal ovaries and tumors with low malignant potential did not show trypsinogen expression. Our results demonstrate the extra-pancreatic production and distribution of trypsinogen in human ovarian carcinomas.

Identification of one- and two-chain forms of trypsinogen 1 produced by a human gastric adenocarcinoma cell line

It has previously been reported that two kinds of human gastric adenocarcinoma cell lines (STKM-1 and MKN28) secrete a trypsin-like enzyme. In this study, four molecular forms of the enzyme (26, 25, 24 and 23 kDa on non-reducing SDS/PAGE) were purified from the serum-free conditioned medium of STKM-1 cells. Analysis of N-terminal amino acid sequences showed that the 26 kDa protein was a two-chain form of trypsinogen 1 which had been produced by proteolytic cleavage of the Arg107-Val108 bond of trypsinogen 1, and the 24 kDa protein was the one-chain form of trypsinogen 1. The 25 and 23 kDa proteins were the activated forms of the two-chain and one-chain trypsinogen 1 respectively. Isoelectric focusing gave pI values of 6.3 and 6.6 for the 26 kDa two-chain form and the 24 kDa one-chain form of trypsinogen 1 respectively. Comparison of the proteolytic activities indicated that the one-chain trypsin 1 had amidolytic activity about four times higher than that of the two-chain enzyme.

Cloning of the cDNA encoding human brain trypsinogen and characterization of its product

We designed degenerated oligodeoxyribonucleotide primers derived from amino acid (aa) sequences of the highly conserved active sites of mammalian serine proteases (SPs). These primers were used to selectively amplify, in polymerase chain reactions (PCRs), cDNA fragments coding for a SP. We used poly(A)+RNA from human brain to obtain cDNA fragments and amplified one cDNA encoding a novel SP. The full-length nucleotide (nt) sequence was identified by PCR and screening a genomic library in order to obtain the 5'-region. The deduced as sequence shows a high degree of homology to trypsinogens, except for the first exon. In addition to this brain-specific trypsinogen, there exists a variant of the cDNA in pancreas, differing only in the nt sequence of the first exon. An active form of the trypsin was synthesized in vitro and purified by affinity chromatography using soybean trypsin inhibitor (STI) agarose to demonstrate the trypsin-specific interaction with a naturally occurring inhibitor of trypsins.