Extracellular serpins such as antithrombin and alpha1-antitrypsin are the quintessential regulators of proteolytic pathways. In contrast, the biological functions of the intracellular serpins remain obscure. We now report that the C. elegans intracellular serpin, SRP-6, exhibits a prosurvival function by blocking necrosis. Minutes after hypotonic shock, srp-6 null animals underwent a catastrophic series of events culminating in lysosomal disruption, cytoplasmic proteolysis, and death. This newly defined hypo-osmotic stress lethal (Osl) phenotype was dependent upon calpains and lysosomal cysteine peptidases, two in vitro targets of SRP-6. By protecting against both the induction of and the lethal effects from lysosomal injury, SRP-6 also blocked death induced by heat shock, oxidative stress, hypoxia, and cation channel hyperactivity. These findings suggest that multiple noxious stimuli converge upon a peptidase-driven, core stress response pathway that, in the absence of serpin regulation, triggers a lysosomal-dependent necrotic cell death routine.

Human umbilical cord blood is an excellent primitive source of noncontroversial stem cells for treatment of hematologic disorders; meanwhile, new stem cell candidates in the umbilical cord (UC) tissue could provide therapeutic cells for nonhematologic disorders. We show novel in situ characterization to identify and localize a panel of some markers expressed by mesenchymal stromal cells (MSCs; CD44, CD105, CD73, CD90) and CD146 in the UC. We describe enzymatic isolation and purification methods of different UC cell populations that do not require manual separation of the vessels and stroma of the coiled, helical-like UC tissue. Unique quantitation of in situ cell frequency and stromal cell counts upon harvest illustrate the potential to obtain high numerical yields with these methods. UC stromal cells can differentiate to the osteogenic and chondrogenic lineages and, under specific culturing conditions, they exhibit high expandability with unique long-term stability of their phenotype. The remarkable stability of the phenotype represents a novel finding for human MSCs, from any source, and supports the use of these cells as highly accessible stromal cells for both basic studies and potentially therapeutic applications such as allogeneic clinical use for musculoskeletal disorders.

SQN-5 is a mouse serpin that is highly similar to the human serpins SCCA1 (SERPINB3) and SCCA2 (SERPINB4). Previous studies characterizing the biochemical activity of SQN-5 showed that this serpin, like SCCA2, inhibited the chymotrypsin-like enzymes mast cell chymase and cathepsin G. Using an expanded panel of papain-like cysteine proteinases, we now show that SQN-5, like SCCA1, inhibited cathepsins K, L, S, and V but not cathepsin B or H. These interactions were characterized by stoichiometries of inhibition that were nearly 1:1 and second-order rate constants of >10(4) M(-1) s(-1). Reactive site loop (RSL) cleavage analysis showed that SQN-5 employed different reactive centers to neutralize the serine and cysteine proteinases. To our knowledge, this is the first serpin that serves as a dual inhibitor of both chymotrypsin-like serine and the papain-like cysteine proteinases by employing an RSL-dependent inhibitory mechanism. The ability of serpins to inhibit both serine and/or papain-like cysteine proteinases may not be a recent event in mammalian evolution. Phylogenetic studies suggested that the SCCA and SQN genes evolved from a common ancestor approximately 250-280 million years ago. When the fact that mammals and birds diverged approximately 310 million years ago is considered, an ancestral SCCA/SQN-like serpin with dual inhibitory activity may be present in many mammalian genomes.

High molecular weight serpins are members of a large superfamily of structurally conserved proteins that inactivate target proteinases by a suicide substrate-like mechanism. In vertebrates, different clades of serpins distribute predominantly to either the intracellular or extracellular space. Although much is known about the function, structure, and inhibitory mechanism of circulating serpins such as ␣ 1 -antitrypsin (SERPINA1) and antithrombin III (SERPINC1), relatively little is known about the function of the vertebrate intracellular (clade B) serpins. To gain a better understanding of the biology of the intracellular serpins, we initiated a comparative genomics study using Caenorhabditis elegans as a model system. A screen of the C. elegans genomic and cDNA databases revealed nine serpin genes, tandemly arrayed on chromosome V. Although the C. elegans serpins represent a unique clade (L), they share significant functional homology with members of the clade B group of intracellular serpins, since they lack typical N-terminal signal peptides and reside intracellularly. To determine whether nematode serpins function as proteinase inhibitors, one family member, srp-2, was chosen for further characterization. Biochemical analysis of recombinant SRP-2 protein revealed SRP-2 to be a dual cross-class inhibitor of the apoptosis-related serine proteinase, granzyme B, and the lysosomal cysteine proteinases, cathepsins K, L, S, and V. Analysis of temporal and spatial expression indicated that SRP-2 was present during early embryonic development and highly expressed in the intestine and hypoderm of larval and adult worms. Transgenic animals engineered to overexpress SRP-2 were slow growing and/or arrested at the first, second, or third larval stages. These data suggest that perturbations of serpin-proteinase balance are critical for correct postembryonic development in C. elegans.Serpins are a unique class of proteinase inhibitors that irreversibly neutralize target proteinases by a mechanism involving the conformational distortion of the proteinase. Serpins have been identified in animals, plants, insects, and certain viruses (1, 2). More recently, serpins have been detected in prokaryotes (3). A search of genome data bases provides evidence for Ͼ500 serpins that are grouped into 17 clades (plus Ͼ10 unclassified orphans) based upon phylogenetic relationships (4). In humans, ϳ35 serpins have been identified. These serpins are distributed among nine clades (A-I), and most are secreted and function in the circulation or extracellular spaces. These serpins regulate proteinases involved in blood coagulation, fibrinolysis, complement activation, inflammation, and extracellular matrix remodeling. In contrast, serpins belonging to clade B reside predominantly intracellularly and have been implicated in regulating apoptosis, tumor progression, and metastasis (5). However, their biological functions in terms of an intact organism have not been well defined. To date, no naturally occurring mutations with an identifiable phenotype...

Members of the human serpin family regulate a diverse array of serine and cysteine proteinases associated with essential biological processes such as fibrinolysis, coagulation, inflammation, cell mobility, cellular differentiation, and apoptosis. Most serpins are secreted and attain physiologic concentrations in the blood and extracellular fluids. However, a subset of the serpin superfamily, the ov-serpins, also resides intracellularly. Using high throughput genomic sequence, we identified a novel member of the human ov-serpin gene family, SERPINB12. The gene mapped to the ov-serpin cluster at 18q21 and resided between SERPINB5 (maspin) and SERPINB13 (headpin). The presence of SERPINB12 in silico was confirmed by cDNA cloning. Expression studies showed that SERPINB12 was expressed in many tissues, including brain, bone marrow, lymph node, heart, lung, liver, pancreas, testis, ovary, and intestines. Based on the presence of Arg and Ser at the reactive center of the RSL, SERPINB12 appeared to be an inhibitor of trypsin-like serine proteinases. This hypothesis was confirmed because recombinant SERPINB12 inhibited human trypsin and plasmin but not thrombin, coagulation factor Xa, or urokinase-type plasminogen activator. The second-order rate constants for the inhibitory reactions were 2.5 ؎ 1.6 ؋ 10 5 and 1.6 ؎ 0.2 ؋ 10 4 M ؊1 s ؊1 , respectively. These data show that SERPINB12 encodes for a new functional member of the human ov-serpin family.The serpin 1 superfamily contains over 500 members and has representatives in the genomes of most metazoa, plants, and certain viruses (reviewed in Ref. 1). Family members are easily identified by amino acid sequence alignments due to their high degree of structural conservation. The serpin tertiary structure consists of three ␤-sheets, approximately nine ␣-helices, and several loops that are arranged into a metastable conformation. Serpins employ a unique suicide-substrate-like inhibitory mechanism to neutralize their target proteinases. The mobile reactive site loop (RSL), which is perched on the surface of the molecule, serves as the pseudo-substrate and binds to the active site of the proteinase. Upon RSL cleavage, the serpin undergoes a major conformational rearrangement that traps the proteinase in a covalent acyl-enzyme intermediate (2). Serpins utilize this inhibitory mechanism to regulate proteinase cascades involved in blood clotting, fibrinolysis, complement activation, cell motility, inflammation, and cell death (1, 3, 4). In 1993, Remold-O'Donnell (5) reported on a subset of serpins with a high degree of sequence similarity to chicken ovalbumin. Unlike the canonical serpin ␣1-antitrypsin (SER-PINA1), members of the ov-serpin subfamily lack both classic N-terminal signal peptides and long N-and C-terminal extensions. The ov-serpins also contain a variable length loop between helices C and D that may confer functional motifs involved in, for example, nuclear localization (6) or transglutamination (7). Also, most of the ov-serpins appear to reside intracellularly with...

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Tryptase ⑀ is a member of the chromosome 16p13.3 family of human serine proteases that is preferentially expressed by epithelial cells. Recombinant protryptase ⑀ was generated to understand how the exocytosed zymogen might be activated outside of the epithelial cell, as well as to address its possible role in normal and diseased states.

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