Molecular cloning and tissue distribution of mouse protein C inhibitor (PCI)

The Serpin Superfamily and Their Role in the Regulation and Dysfunction of Serine Protease Activity in COPD and Other Chronic Lung Diseases

Chronic obstructive pulmonary disease (COPD) is a debilitating heterogeneous disease characterised by unregulated proteolytic destruction of lung tissue mediated via a protease-antiprotease imbalance. In COPD, the relationship between the neutrophil serine protease, neutrophil elastase, and its endogenous inhibitor, alpha-1-antitrypsin (AAT) is the best characterised. AAT belongs to a superfamily of serine protease inhibitors known as serpins. Advances in screening technologies have, however, resulted in many members of the serpin superfamily being identified as having differential expression across a multitude of chronic lung diseases compared to healthy individuals. Serpins exhibit a unique suicide-substrate mechanism of inhibition during which they undergo a dramatic conformational change to a more stable form. A limitation is that this also renders them susceptible to disease-causing mutations. Identification of the extent of their physiological/pathological role in the airways would allow further expansion of knowledge regarding the complexity of protease regulation in the lung and may provide wider opportunity for their use as therapeutics to aid the management of COPD and other chronic airways diseases.

Regulation of the Extracellular SERPINA5 (Protein C Inhibitor) Penetration Through Cellular Membranes

It is generally accepted that the phospholipid bilayer of the cell membrane is impermeable for proteins and peptides and that these molecules require special mechanisms for their transport from the extra- to the intracellular space. Recently there is increasing evidence that certain proteins/peptides can also directly cross the phospholipid membrane. SERPINA5 (protein C inhibitor) is a secreted protease inhibitor with broad protease reactivity and wide tissue distribution. It binds glycosaminoglycans and certain phospoholipids, which can modulate its inhibitory activity. SERPINA5 has been shown to be internalized by platelets, granulocytes, HL-60 promyelocytic leukemia cells, and by Jurkat lymphoma cells. Once inside the cell it can translocate to the nucleus. There are several indications that SERPINA5 can directly cross the phospholipid bilayer of the cell membrane. In this review we will describe what is known so far about the conditions, as well as the cellular and molecular requirements for SERPINA5 translocation through the cell membrane and for its penetration of pure phospholipid vesicles.

Host protein C inhibitor inhibits tumor growth, but promotes tumor metastasis, which is closely correlated with hypercoagulability

INTRODUCTION

Protein C inhibitor (PCI), a member of the serine protease inhibitor family, is expressed in various human tissues, including liver and kidneys. In the plasma, PCI physiologically inhibits an anticoagulant serine protease, activated protein C (APC). PCI expressed by cancer cells suppresses tumor invasion by inhibiting urokinase-type plasminogen activator, and inhibits tumor growth and metastasis, which are independent of its protease-inhibitory activity. In the present study, we clarified the effects of host PCI on growth and metastasis of B16 melanoma (B16) cells by comparing between wild-type mice and mice transgenic for human PCI gene (hPCI-TG), which have a tissue distribution of PCI similar to that observed in humans.

MATERIALS AND METHODS

Growth of intracutaneously-injected B16 cells was evaluated by measuring the tumor volume, and metastatic behavior of intravenously-injected B16 cells by counting the number of metastatic lung nodules.

RESULTS

Growth of intracutaneously injected B16 cells was significantly faster in wild-type mice than in hPCI-TG mice; however, hPCI-TG mice developed more metastatic nodules of B16 cells in the lungs. Immunohistochemical analysis using anti-mouse fibrinogen antibody revealed more fibrin deposition in the lung in hPCI-TG mice than in wild-type mice. Furthermore, the more invasive behavior observed in hPCI-TG mice was reduced by rabbit anti-human PCI IgG, APC, or soluble TM administration for 3 consecutive days including the day that B16 cells were injected.

CONCLUSIONS

Our results suggest that like PCI expressed in tumor cells, host PCI also inhibits tumor growth, but host PCI promotes tumor metastasis via its procoagulant properties.

Interaction of protein C inhibitor with the type II transmembrane serine protease enteropeptidase

The serine protease inhibitor protein C inhibitor (PCI) is expressed in many human tissues and exhibits broad protease reactivity. PCI binds glycosaminoglycans and certain phospholipids, which modulate its inhibitory activity. Enteropeptidase (EP) is a type II transmembrane serine protease mainly found on the brush border membrane of epithelial cells in the duodenum, where it activates trypsinogen to initiate the digestion of food proteins. Some active EP is also present in duodenal fluid and has been made responsible for causing pancreatitis in case of duodeno-pancreatic reflux. Together with its substrate trypsinogen, EP is furthermore present in the epidermis and in some cancer cells. In this report, we show that PCI inhibited EP with an apparent 2nd order rate constant of 4.48 × 10(4) M(-1) s(-1). Low molecular weight (LMWH) and unfractionated heparin (UFH) slightly reduced the inhibitory effect of PCI. The SI (stoichiometry of inhibition) value for the inhibition of EP by PCI was 10.8 in the absence and 17.9 in the presence of UFH (10 U/ml). By inhibiting trypsin, chymotrypsin, and additionally EP, PCI might play a role in the protection of the pancreas from autodigestion. Furthermore the interaction of PCI with EP may influence the regulation of epithelial differentiation.

Immunolocalization of protein C inhibitor in differentiation of human epidermal keratinocytes

Keratinocytes propagated in low calcium (0.05 mM) serum-free medium grow as monolayers and exhibit morphological and biosynthetic phenotypes similar to the keratinocytes of the basal layer in normal epidermis. When the calcium in the medium is increased to 1.5 mM, the keratinocytes start to stratify and differentiate. Such differentiation is important in the formation of an epidermal barrier. Proteolysis plays a crucial role in the process. The functions of most of the plasminogen activator cascade components in human skin have been studied, but little was known about the expression and role of protein C inhibitor in the differentiation of human epidermal keratinocytes. In the present study, we used immunohistochemistry and immunocytochemistry to examine the immunolocalization of protein C inhibitor in normal human skin and in cultured keratinocytes in serum-free medium with low and high calcium, respectively. The results indicated that protein C inhibitor is mainly localized in superficial and more differentiated keratinocytes in normal human epidermis. Keratinocytes positive for protein C inhibitor were detected in cultures containing both low and high calcium media, and the level of protein C inhibitor was increased in high calcium medium. This increase was accompanied by an altered intracellular distribution, from the perinuclear cytoplasm in undifferentiated keratinocytes to the whole cytoplasm in differentiated keratinocytes. Further study revealed that protein C inhibitor was incorporated into the cornified envelope in normal skin keratinocytes and cultured differentiated keratinocytes. Our results suggest that protein C inhibitor may be involved in the differentiation of keratinocytes.

Protein C inhibitor inhibits breast cancer cell growth, metastasis and angiogenesis independently of its protease inhibitory activity

Protein C inhibitor (PCI) regulates the anticoagulant protein C pathway and also inhibits urinary plasminogen activator (uPA), a mediator of tumor cell invasion. In the present study, we evaluated the effect of human PCI and its inactive derivatives on tumor growth and metastasis of human breast cancer (MDA-231) cells, and on angiogenesis in vivo. The invasiveness of MDA-231 cells was inhibited by recombinant intact PCI, but not by reactive site-modified PCI (R354APCI) or by the N-terminal fragment of protease-cleaved PCI (NTPCI). The in vitro invasiveness of MDA-231 cells expressing intact PCI (MDA-PCI) was significantly decreased as compared to MDA-231 cells expressing R354APCI (MDA-R354APCI) or NTPCI (MDA-NTPCI). Further, in vivo growth and metastatic potential of MDA-PCI, MDA-R354APCI and MDA-NTPCI cells in severe combined immunodeficient (SCID) mice were significantly decreased as compared to MDA-Mock cells. Angiogenesis was also significantly decreased in Matrigel implant containing MDA-PCI, MDA-R354APCI or MDA-NTPCI cells as compared to that containing MDA-Mock cells. In vivo angiogenesis in rat cornea and in vitro tube formation were also inhibited by recombinant intact PCI, R354APCI and NTPCI. Furthermore, the anti-angiogenic activity of PCI was strong as cleaved antithrombin (AT), and slightly stronger than that of plasminogen activator inhibitor (PAI)-1 and pigment epithelium-derived factor (PEDF). Overall, this study showed that, in addition to a reactive site-dependent mechanism, PCI may also regulate tumor growth and metastasis independently of its protease inhibitory activity by inhibiting angiogenesis.

Serpins in thrombosis, hemostasis and fibrinolysis

Hemostasis and fibrinolysis, the biological processes that maintain proper blood flow, are the consequence of a complex series of cascading enzymatic reactions. Serine proteases involved in these processes are regulated by feedback loops, local cofactor molecules, and serine protease inhibitors (serpins). The delicate balance between proteolytic and inhibitory reactions in hemostasis and fibrinolysis, described by the coagulation, protein C and fibrinolytic pathways, can be disrupted, resulting in the pathological conditions of thrombosis or abnormal bleeding. Medicine capitalizes on the importance of serpins, using therapeutics to manipulate the serpin-protease reactions for the treatment and prevention of thrombosis and hemorrhage. Therefore, investigation of serpins, their cofactors, and their structure-function relationships is imperative for the development of state-of-the-art pharmaceuticals for the selective fine-tuning of hemostasis and fibrinolysis. This review describes key serpins important in the regulation of these pathways: antithrombin, heparin cofactor II, protein Z-dependent protease inhibitor, alpha(1)-protease inhibitor, protein C inhibitor, alpha(2)-antiplasmin and plasminogen activator inhibitor-1. We focus on the biological function, the important structural elements, their known non-hemostatic roles, the pathologies related to deficiencies or dysfunction, and the therapeutic roles of specific serpins.

Protective role of protein C inhibitor in monocrotaline-induced pulmonary hypertension

BACKGROUND

Protein C inhibitor (PCI) plays a role in multiple biological processes including fertilization, coagulation, fibrinolysis and kinin systems.

OBJECTIVES

We hypothesized that PCI participates in the pathogenesis of pulmonary hypertension. To demonstrate this, we compared the development of pulmonary hypertension in mice overexpressing PCI in the lung with wild-type (WT) mice. Pulmonary hypertension was induced by s.c. injection of 600 mg kg-1 of monocrotaline weekly for 8 weeks.

RESULTS

Right ventricular arterial pressure was significantly increased in monocrotaline-treated WT mice compared with that in monocrotaline-treated transgenic mice. Bronchoalveolar lavage fluid (BALF) levels of thrombin-antithrombin complex, monocyte chemoattractant protein-1 and platelet-derived growth factor, and the plasma level of tumor necrosis factor-alpha were significantly increased in monocrotaline-treated WT mice as compared with monocrotaline-treated PCI transgenic mice. Increased level of PCI-thrombin complex was detected in BALF from monocrotaline-treated PCI transgenic mice as compared with saline-treated PCI transgenic mice.

CONCLUSIONS

This study showed that increased expression of PCI in the lung is protective against monocrotaline-induced pulmonary hypertension, suggesting a potential beneficial effect of PCI for the therapy of this disease.

Characterization of a novel human protein C inhibitor (PCI) gene transgenic mouse useful for studying the role of PCI in physiological and pathological conditions

In humans, protein C inhibitor (PCI) is expressed in various tissues and present in many body fluids including plasma and seminal fluid. In rodents, PCI is expressed in reproductive organs only and is absent in plasma. In this study, we characterized the tissue expression and physiological role of PCI in novel human PCI gene transgenic (TG) mice. Northern blot and immunohistochemical analyses demonstrated that human PCI is expressed in liver hepatocytes, renal epithelial cells as well as heart, brain and reproductive organs of the TG mice. This PCI tissue distribution is similar to that found in humans. PCI in plasma of TG mice showed the same immunological and functional properties as human plasma PCI. Next, we evaluated the effect of PCI on coagulation, inflammation and tissue damage in lipopolysaccharide-treated TG mice. The results suggested that PCI efficiently inhibits not only the anticoagulant and anti-inflammatory activities of exogenously injected human activated protein C (APC) but also that of endogenously produced APC in mice with endotoxemia. These findings suggest that PCI exerts a procoagulant and proinflammatory effect by inhibiting APC. We believe our results also show how useful these TG mice may be for assessing the therapeutic effect of human APC in vivo and for evaluating the role of PCI in human physiological and pathological conditions.

Role of each Asn-linked glycan in the anticoagulant activity of human protein C inhibitor

The N-glycosylation site mutants of human protein C inhibitor (PCI; N230S, N243Q, N319Q, N230S/N243Q, and N230S/N319Q) were prepared by amino acid replacement of the asparagine residue with a serine or glutamine residue using site-directed mutagenesis and expressed in the baculovirus/insect cell expression system. To examine the importance of each Asn-linked glycan in the activity of PCI, we compared wtPCI with the mutants of N-glycosylation site(s) in terms of the procoagulant protease-inhibitory and anticoagulant activities. The inhibitory activities of N230S, N319Q, and N230S/N319Q toward human thrombin and plasma kallikrein were significantly increased compared with wtPCI, but those of N243Q and N230S/N243Q were reduced. The inhibitory activity of N230S toward human plasma coagulation was significantly increased compared with wtPCI, and that of N230S/N319Q was also significantly increased compared with N319Q. Furthermore, the procoagulant protease-inhibitory and anticoagulant activities of N230S/N319Q (glycosylated on Asn243 only) compared favorably with those of N230S, and both of the mutants possessed highest activities in the purified mutants. These results suggest that the Asn243-linked glycan in PCI molecule possesses critical roles for its anticoagulant activity in the circulation, and the Asn230-linked glycan down-regulates the activity of PCI.

Disruption of the protein C inhibitor gene results in impaired spermatogenesis and male infertility

Protein C inhibitor (PCI) is a nonspecific, heparin-binding serpin (serine protease inhibitor) that inactivates many plasmatic and extravascular serine proteases by forming stable 1:1 complexes. Proteases inhibited by PCI include the anticoagulant activated protein C, the plasminogen activator urokinase, and the sperm protease acrosin. In humans PCI circulates as a plasma protein but is also present at high concentrations in organs of the male reproductive tract. The biological role of PCI has not been defined so far. However, the colocalization of high concentrations of PCI together with several of its target proteases in the male reproductive tract suggests a role of PCI in reproduction. We generated mice lacking PCI by homologous recombination. Here we show that PCI(-/-) mice are apparently healthy but that males of this genotype are infertile. Infertility was apparently caused by abnormal spermatogenesis due to destruction of the Sertoli cell barrier, perhaps due to unopposed proteolytic activity. The resulting sperm are malformed and are morphologically similar to abnormal sperm seen in some cases of human male infertility. This animal model might therefore be useful for analyzing the molecular bases of these human conditions.

Molecular cloning, tissue distribution and androgen regulation of rat protein C inhibitor

Protein C inhibitor (PCI) is the plasma serine protease inhibitor of activated protein C, the active enzyme of the anticoagulant protein C pathway. Recently, PCI was also detected in human seminal plasma and reproductive organs (testis, seminal vesicle and prostate) suggesting that PCI may also play an important role in the reproductive system. In this study, we cloned the full length of rat PCI cDNA, and determined its amino acid sequence and tissue distribution. We also evaluated the effect of androgen on PCI mRNA expression in seminal vesicles and testes. The isolated 2074-bp rat PCI cDNA was composed of a 47-bp 5'-non-coding region, a 1218-bp coding region of a 406-amino acid precursor protein, a stop codon and a 806-bp 3'-non-coding region. The deduced amino acid sequence of rat PCI showed 85.7%, 64.1% and 62.2% homology with that of mouse, rhesus monkey and human PCIs, respectively. Northern blot analysis showed that the rat PCI mRNA is expressed strongly in the seminal vesicle, moderately in the testis, but not in the liver. PCI mRNA expression in seminal vesicles and testes was found to increase during the process of development, suggesting that it is under androgen control. Subsequently, we examined the effect of castration and/or treatment with 17beta-estradiol or testosterone on PCI mRNA expression in the mature rat seminal vesicles. The PCI mRNA expression in seminal vesicles was significantly decreased after castration or 17beta-estradiol treatment. Testosterone itself did not affect PCI mRNA expression, but treatment in castrated rats significantly enhanced its mRNA expression. These findings suggest that the PCI gene expression in rat seminal vesicles is regulated by androgen.

Protein C inhibitor (PCI)

PCI is a non-specific serpin that inhibits several proteases of the coagulation and fibrinolytic systems as well as plasma- and tissue kallikreins and the sperm protease acrosin. The precise physiological role of PCI has not been defined yet. Heparin stimulates most PCI/protease reactions, but interferes with the tissue kallikrein/PCI-interaction. Thereby heparin not only regulates PCI-activity but also its specificity in systems containing two or more of its target proteases. This effect is not restricted to heparin, but is also seen with other glycosaminoglycans (GAGs) and large, negatively charged molecules. PCI also binds to GAGs present on the surface of epithelial kidney cells, and GAGs isolated from these cells have a similar effect on PCI activity as heparin. Studies analyzing the role of PCI as an acrosin inhibitor revealed that endogenous PCI is immunocytochemically localized to disrupted acrosomal membranes of morphologically abnormal sperms, while intact sperms are negative for PCI-antigen. In a mouse in vitro fertilization model human PCI inhibited sperm/egg binding and decreased the fertilization rate. Northern blotting of human and mouse mRNA using human and mouse PCI-cDNA probes revealed that in the mouse PCI is exclusively synthesized in the genital tract (testis, seminal vesicle, ovary), while in humans PCI is additionally synthesized in many other organs (e.g., liver, pancreas, heart). Therefore PCI might regulate enzymes involved in fertilization (e.g. acrosin) in both species. Other proteases (e.g., tissue kallikrein) are possibly regulated in a species specific manner by different inhibitors.