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

Diagnostic and therapeutic value of human serpin family proteins

SERPIN (serine proteinase inhibitors) is an acronym for the superfamily of structurally similar proteins found in animals, plants, bacteria, viruses, and archaea. Over 1500 SERPINs are known in nature, while only 37 SERPINs are found in humans, which participate in inflammation, coagulation, angiogenesis, cell viability, and other pathophysiological processes. Both qualitative or quantitative deficiencies or overexpression and/or abnormal accumulation of SERPIN can lead to diseases commonly referred to as "serpinopathies". Hence, strategies involving SERPIN supplementation, elimination, or correction are utilized and/or under consideration. In this review, we discuss relationships between certain SERPINs and diseases as well as putative strategies for the clinical explorations of SERPINs.

Establishment and characterization of an immortalized bovine intestinal epithelial cell line

Primary bovine intestinal epithelial cells (PBIECs) are an important model for studying the molecular and pathogenic mechanisms of diseases affecting the bovine intestine. It is difficult to obtain and grow PBIECs stably, and their short lifespan greatly limits their application. Therefore, the purpose of this study was to create a cell line for exploring the mechanisms of pathogen infection in bovine intestinal epithelial cells in vitro. We isolated and cultured PBIECs and established an immortalized BIEC line by transfecting PBIECs with the pCI-neo-hTERT (human telomerase reverse transcriptase) recombinant plasmid. The immortalized cell line (BIECs-21) retained structure and function similar to that of the PBIECs. The marker proteins characteristic of epithelial cells, cytokeratin 18, occludin, zonula occludens protein 1 (ZO-1), E-cadherin and enterokinase, were all positive in the immortalized cell line, and the cell structure, growth rate, karyotype, serum dependence and contact inhibition were normal. The hTERT gene was successfully transferred into BIECs-21 where it remained stable and was highly expressed. The transport of short-chain fatty acids and glucose uptake by the BIECs-21 was consistent with PBIECs, and we showed that they could be infected with the intestinal parasite, Neospora caninum. The immortalized BIECs-21, which have exceeded 80 passages, were structurally and functionally similar to the primary BIECs and thus provide a valuable research tool for investigating the mechanism of pathogen infection of the bovine intestinal epithelium in vitro.

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.

Novel Compound Heterozygous TMPRSS15 Gene Variants Cause Enterokinase Deficiency

Background

Enterokinase deficiency (EKD) is a rare autosomal recessively inherited disorder mainly characterized by diarrhea, hypoproteinemia and failure to thrive in infancy. Loss-of-function variants in the TMPRSS15 gene cause EKD.

Methods

We report the clinical manifestations and molecular basis of EKD in a Chinese child. We investigated in vitro two TMPRSS15 variants: the c.1921G > A as a possible splicing variant by minigene assay; the c.2396T > A(p.Val799Asp) as a missense change by protein expression analysis, enterokinase activity and effect on cellular localization.

Results

The proband presented with intractable diarrhea accompanied by vomiting, failure to thrive and hypoproteinemia in his second year. Genetic analysis showed that the patient was compound heterozygous for two variants in the TMPRSS15 gene: c.[1921G > A];[2396T > A]. The c.1921 G > A variant may change the glutamic acid 641 into lysine; this change is predicted to be benign by bioinformatics analysis. However, it was predicted to disrupt the splicing donor site. Our minigene assay revealed that c.1921G > A caused the skipping of exon 16. The c.2396T > A(p.Val799Asp) change in the serine protease domain predicted to be deleterious hitting an evolutionary conserved amino acid. Functional studies in vitro revealed that the p.Val799Asp variant decreased the total expression level of TMPRSS15 by 29%, and the enterokinase activity of p.Val799Asp mutants was decreased by 37%, compared with that of wild type.

Conclusion

We reported an EKD patient with novel compound heterozygous variants in the TMPRSS15 gene, expanding the genotypic and phenotypic spectrum of EKD. The functional characterization in vitro demonstrated that the c.1921G > A variant alters pre-mRNA splicing and the p.Val799Asp variant leads to a decrease in protein expression and enzyme activity.

Quantitative proteomic analysis of pancreatic cyst fluid proteins associated with malignancy in intraductal papillary mucinous neoplasms

Background

The application of advanced imaging technologies for identifying pancreatic cysts has become widespread. However, accurately differentiating between low-grade dysplasia (LGD), high-grade dysplasia (HGD), and invasive intraductal papillary mucinous neoplasms (IPMNs) remains a diagnostic challenge with current biomarkers, necessitating the development of novel biomarkers that can distinguish IPMN malignancy.

Methods

Cyst fluid samples were collected from nine IPMN patients (3 LGD, 3 HGD, and 3 invasive IPMN) during their pancreatectomies. An integrated proteomics approach that combines filter-aided sample preparation, stage tip-based high-pH fractionation, and high-resolution MS was applied to acquire in-depth proteomic data of pancreatic cyst fluid and discover marker candidates for IPMN malignancy. Biological processes of differentially expressed proteins that are related to pancreatic cysts and aggressive malignancy were analyzed using bioinformatics tools such as gene ontology analysis and Ingenuity pathway analysis. In order to confirm the validity of the marker candidates, 19 cyst fluid samples were analyzed by western blot.

Results

A dataset of 2992 proteins was constructed from pancreatic cyst fluid samples. A subsequent analysis found 2963 identified proteins in individual samples, 2837 of which were quantifiable. Differentially expressed proteins between histological grades of IPMN were associated with pancreatic diseases and malignancy according to ingenuity pathway analysis. Eighteen biomarker candidates that were differentially expressed across IPMN histological grades were discovered—7 DEPs that were upregulated and 11 that were downregulated in more malignant grades. HOOK1 and PTPN6 were validated by western blot in an independent cohort, the results of which were consistent with our proteomic data.

Conclusions

This study demonstrates that novel biomarker candidates for IPMN malignancy can be discovered through proteomic analysis of pancreatic cyst fluid.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9193-1) contains supplementary material, which is available to authorized users.

Targeting the membrane-anchored serine protease testisin with a novel engineered anthrax toxin prodrug to kill tumor cells and reduce tumor burden

The membrane-anchored serine proteases are a unique group of trypsin-like serine proteases that are tethered to the cell surface via transmembrane domains or glycosyl-phosphatidylinositol-anchors. Overexpressed in tumors, with pro-tumorigenic properties, they are attractive targets for protease-activated prodrug-like anti-tumor therapies. Here, we sought to engineer anthrax toxin protective antigen (PrAg), which is proteolytically activated on the cell surface by the proprotein convertase furin to instead be activated by tumor cell-expressed membrane-anchored serine proteases to function as a tumoricidal agent. PrAg's native activation sequence was mutated to a sequence derived from protein C inhibitor (PCI) that can be cleaved by membrane-anchored serine proteases, to generate the mutant protein PrAg-PCIS. PrAg-PCIS was resistant to furin cleavage in vitro, yet cytotoxic to multiple human tumor cell lines when combined with FP59, a chimeric anthrax toxin lethal factor-Pseudomonas exotoxin fusion protein. Molecular analyses showed that PrAg-PCIS can be cleaved in vitro by several serine proteases including the membrane-anchored serine protease testisin, and mediates increased killing of testisin-expressing tumor cells. Treatment with PrAg-PCIS also potently attenuated the growth of testisin-expressing xenograft tumors in mice. The data indicates PrAg can be engineered to target tumor cell-expressed membrane-anchored serine proteases to function as a potent tumoricidal agent.

Antithrombin controls tumor migration, invasion and angiogenesis by inhibition of enteropeptidase

Antithrombin is a key inhibitor of the coagulation cascade, but it may also function as an anti-inflammatory, anti-angiogenic, anti-viral and anti-apoptotic protein. Here, we report a novel function of antithrombin as a modulator of tumor cell migration and invasion. Antithrombin inhibited enteropeptidase on the membrane surface of HT-29, A549 and U-87 MG cells. The inhibitory process required the activation of antithrombin by heparin, and the reactive center loop and the heparin binding domain were essential. Surprisingly, antithrombin non-covalently inhibited enteropeptidase, revealing a novel mechanism of inhibition for this serpin. Moreover, as a consequence of this inhibition, antithrombin was cleaved, resulting in a molecule with anti-angiogenic properties that reduced vessel-like formation of endothelial cells. The addition of antithrombin and heparin to U-87 MG and A549 cells reduced motility in wound healing assays, inhibited the invasion in transwell assays and the degradation of a gelatin matrix mediated by invadopodia. These processes were controlled by enteropeptidase, as demonstrated by RNA interference experiments. Carcinoma cell xenografts in nude mice showed in vivo co-localization of enteropeptidase and antithrombin. Finally, treatment with heparin reduced experimental metastasis induced by HT29 cells in vivo. In conclusion, the inhibition of enteropeptidase by antithrombin may have a double anti-tumor effect through inhibiting a protease involved in metastasis and generating an anti-angiogenic molecule.

Permanent proteins in the urine of healthy humans during the Mars-500 experiment

Urinary proteins serve as indicators of various conditions in human normal physiology and disease pathology. Using mass spectrometry proteome analysis, the permanent constituent of the urine was examined in the Mars-500 experiment (520 days isolation of healthy volunteers in a terrestrial complex with an autonomous life support system). Seven permanent proteins with predominant distribution in the liver and blood plasma as well as extracellular localization were identified. Analysis of the overrepresentation of the molecular functions and biological processes based on Gene Ontology revealed that the functional association among these proteins was low. The results showed that the identified proteins may be independent markers of the various conditions and processes in healthy humans and that they can be used as standards in determination of the concentration of other proteins in the urine.

A+-helix of protein C inhibitor (PCI) is a cell-penetrating peptide that mediates cell membrane permeation of PCI

Protein C inhibitor (PCI) is a serpin with broad protease reactivity. It binds glycosaminoglycans and certain phospholipids that can modulate its inhibitory activity. PCI can penetrate through cellular membranes via binding to phosphatidylethanolamine. The exact mechanism of PCI internalization and the intracellular role of the serpin are not well understood. Here we showed that testisin, a glycosylphosphatidylinositol-anchored serine protease, cleaved human PCI and mouse PCI (mPCI) at their reactive sites as well as at sites close to their N terminus. This cleavage was observed not only with testisin in solution but also with cell membrane-anchored testisin on U937 cells. The cleavage close to the N terminus released peptides rich in basic amino acids. Synthetic peptides corresponding to the released peptides of human PCI (His¹–Arg¹¹) and mPCI (Arg¹–Ala¹⁸) functioned as cell-penetrating peptides. Because intact mPCI but not testisin-cleaved mPCI was internalized by Jurkat T cells, a truncated mPCI mimicking testisin-cleaved mPCI was created. The truncated mPCI lacking 18 amino acids at the N terminus was not taken up by Jurkat T cells. Therefore our model suggests that testisin or other proteases could regulate the internalization of PCI by removing its N terminus. This may represent one of the mechanisms regulating the intracellular functions of PCI.