Interactions of human lacrimal and salivary cystatins with adenovirus endopeptidase

Identification, expression profiling, and functional characterization of cystatin C from big-belly seahorse (Hippocampus abdominalis)

Cystatins are natural inhibitors of lysosomal cysteine proteases, including cathepsins B, L, H, and S. Cystatin C (CSTC) is a member of the type 2 cystatin family and is an essential biomarker in the prognosis of several diseases. Emerging evidence suggests the immune regulatory roles of CSTC in antigen presentation, the release of different inflammatory mediators, and apoptosis in various pathophysiologies. In this study, the 390-bp cystatin C (HaCSTC) cDNA from big-belly seahorse (Hippocampus abdominalis) was cloned and characterized by screening the pre-established cDNA library. Based on similarities in sequence, HaCSTC is a homolog of the teleost type 2 cystatin family with putative catalytic cystatin domains, signal peptides, and disulfide bonds. HaCSTC transcripts were ubiquitously expressed in all tested big-belly seahorse tissues, with the highest expression in ovaries. Immune challenge with lipopolysaccharides, polyinosinic:polycytidylic acid, Edwardsiella tarda, and Streptococcus iniae caused significant upregulation in HaCSTC transcript levels. Using a pMAL-c5X expression vector, the 14.29-kDa protein of recombinant HaCSTC (rHaCSTC) was expressed in Escherichia coli BL21 (DE3), and its protease inhibitory activity against papain cysteine protease was determined with the aid of a protease substrate. Papain was competitively blocked by rHaCSTC in a dose-dependent manner. In response to viral hemorrhagic septicemia virus (VHSV) infection, HaCSTC overexpression strongly decreased the expression of VHSV transcripts, pro-inflammatory cytokines, and pro-apoptotic genes; while increasing the expression of anti-apoptotic genes in fathead minnow (FHM) cells. Furthermore, HaCSTC overexpression protected VHSV-infected FHM cells against VHSV-induced apoptosis and increased cell viability. Our findings imply the profound role of HaCSTC against pathogen infections by modulating fish immune responses.

Cystatin C, COVID-19 severity and mortality: a systematic review and meta-analysis

Background

Combined markers of renal dysfunction and inflammation, e.g., cystatin C, might assist with risk stratification and clinical decisions in patients with coronavirus disease 19 (COVID-19). We conducted a systematic review and meta-analysis with meta-regression of serum cystatin C in COVID-19.

Methods

We searched PubMed, Web of Science and Scopus, between January 2020 and February 2021, for studies reporting serum cystatin C concentrations, measures of clinical severity and survival outcomes in hospitalized COVID-19 patients (PROSPERO registration number: CRD42021245295).

Results

Thirteen studies in 2510 COVID-19 patients, 1972 with low severity or survivor status and 538 with high severity or non-survivor status during follow up, were included in the meta-analysis. The pooled results showed that serum cystatin C concentrations were higher in patients with high disease severity or non-survivor status (standard mean deviation, SMD, 1.71, 95% CI 0.95 to 2.46, p < 0.001). Extreme between-study heterogeneity was observed (I² = 97.5%, p < 0.001). Sensitivity analysis, performed by sequentially removing each study and re-assessing the pooled estimates, showed that the magnitude and direction of the effect size was not substantially modified. The Begg’s and Egger’s t tests did not show publication bias. In meta-regression, the SMD of serum cystatin C was not associated with age, proportion of males, C-reactive protein, neutrophils, lymphocytes, aspartate aminotransferase, alanine aminotransferase, albumin, creatinine, creatine kinase-MB, lactate dehydrogenase, and proportion of patients with diabetes or hypertension.

Conclusions

Higher concentrations of serum cystatin C were associated with higher COVID-19 severity and mortality.

Graphic abstract

RP-HPLC-ESI-IT Mass Spectrometry Reveals Significant Variations of the Human Salivary Protein Profile Associated with Predominantly Antibody Deficiencies

PURPOSE

Present study is designed to discover potential salivary biomarkers associated with predominantly antibody deficiencies, which include a large spectrum of disorders sharing failure of antibody production, and B cell defects resulting in recurrent infections, autoimmune and inflammatory manifestations, and tumor susceptibility. Understanding and clinical classification of these syndromes is still challenging.

METHODS

We carried out a study of human saliva based on liquid chromatography-mass spectrometry measurements of intact protein mass values. Salivary protein profiles of patients (n = 23) and healthy controls (n = 30) were compared.

RESULTS

Patients exhibited lower abundance of α-defensins 1-4, cystatins S1 and S2, and higher abundance of glutathionylated cystatin B and cystatin SN than controls. Patients could be clustered in two groups on the basis of different levels of cystatin SN, S1 and S2, suggesting that these proteins may play different roles in the disease.

CONCLUSIONS

Quantitative variations of these pro-inflammatory and antimicrobial peptides/proteins may be related to immunodeficiency and infectious condition of the patients. The high incidence of tumors in the group with the highest level of cystatin SN, which is recognized as tumoral marker, appeared an intriguing result deserving of future investigations. Data are available via ProteomeXchange with identifier PXD012688.

RP-HPLC-ESI-IT Mass Spectrometry Reveals Significant Variations of the Human Salivary Protein Profile Associated with Predominantly Antibody Deficiencies

PURPOSE

Present study is designed to discover potential salivary biomarkers associated with predominantly antibody deficiencies, which include a large spectrum of disorders sharing failure of antibody production, and B cell defects resulting in recurrent infections, autoimmune and inflammatory manifestations, and tumor susceptibility. Understanding and clinical classification of these syndromes is still challenging.

METHODS

We carried out a study of human saliva based on liquid chromatography-mass spectrometry measurements of intact protein mass values. Salivary protein profiles of patients (n = 23) and healthy controls (n = 30) were compared.

RESULTS

Patients exhibited lower abundance of α-defensins 1-4, cystatins S1 and S2, and higher abundance of glutathionylated cystatin B and cystatin SN than controls. Patients could be clustered in two groups on the basis of different levels of cystatin SN, S1 and S2, suggesting that these proteins may play different roles in the disease.

CONCLUSIONS

Quantitative variations of these pro-inflammatory and antimicrobial peptides/proteins may be related to immunodeficiency and infectious condition of the patients. The high incidence of tumors in the group with the highest level of cystatin SN, which is recognized as tumoral marker, appeared an intriguing result deserving of future investigations. Data are available via ProteomeXchange with identifier PXD012688.

Involvement of cystatin C in immunity and apoptosis

As an abundantly expressed cysteine protease inhibitor widely distributed in the organisms, cystatin C is involved in various physiological processes. Due to its relatively small molecular weight and easy detection, cystatin C is commonly used as a measure for glomerular filtration rate. In pathological conditions, however, growing evidences suggest that cystatin C is associated with various immune responses against either exogenous or endogenous antigens, which ultimately result in inflammatory autoimmune diseases or tumor development if not properly controlled. Thus the fluctuation of cystatin C levels might have more clinical implications than a reflection of kidney functions. Here, we summarize the latest development of studies on the pathophysiological functions of cystatin C, with focus on its immune regulatory roles at both cellular and molecular levels including antigen presentation, secretion of cytokines, synthesis of nitric oxide, as well as apoptosis. Finally, we discuss the clinical implications and therapeutic potentials of what this predominantly expressed protease inhibitor can bring to us.

Journey of cystatins from being mere thiol protease inhibitors to at heart of many pathological conditions

Cystatins are thiol proteinase inhibitors (TPI), present ubiquitously in animals, plants and micro-organisms. These are not merely inhibitors rather they are at heart of many pathological conditions ranging from diabetes to renal failure. These are essential for maintenance of protein balance of the cell; once this balance gets disturbed, it may lead to cell death. Thus, cystatins cannot be merely regarded as TPI's as these have been found to play a pivotal role in tumorigenesis and neurodegenerative diseases. Many studies have reported the variation in cystatin level in incidences of different types of cancer; highlighting an important role played by these inhibitors in cancer development and progression. Cystatin C is increasingly replacing creatinine as a biomarker of glomerular filtration rate (GFR) thereby highlighting the importance of this important inhibitor. Some recent studies have also reported the interaction pattern of various anti-cancer drugs with cystatins in a bid to find how these drugs affect this important inhibitors and whether these drugs have any side effect on cystatins. Thus, in this growing disease era it can be said that cystatins are no more just inhibitors blocking the activity of thiol proteases rather they play a pivotal role in variety of pathological conditions.

The salivary proteome profile in patients affected by SAPHO syndrome characterized by a top-down RP-HPLC-ESI-MS platform

SAPHO syndrome is a rare and often unrecognized disease with prominent inflammatory cutaneous and articular symptoms characterized by musculoskeletal manifestations (synovitis, hyperostosis, osteomyelitis) associated with dermatological conditions (severe acne and pustulosis). The acidic soluble fraction of whole saliva from 10 adult women affected by SAPHO syndrome and from a group of 28 healthy women was analysed by RP-HPLC-ESI-MS with the aim of discovering salivary biomarkers of the disorder. The levels of the oral proteins and peptides were correlated with clinical data. The following proteins showed a significant decreased concentration in saliva of SAPHO subjects with respect to controls: cystatin S1 and SN, histatins, the major acidic PRPs, P-C and P-B peptides. The cystatin SN abundance lowered according to the disease duration and histatins showed positive correlations with the C reactive protein. Statistical analysis performed excluding one patient with a different pattern of salivary proteins/peptides highlighted a positive relationship between cystatin S1, histatins 3, histatin 5, and the neutrophil count. Moreover, histatin 3 correlated positively with the total white cell count and negatively with the erythrocyte sedimentation rate. Levels and frequency of S100A12 protein showed a trend to increase in SAPHO patients. The high expression of this pro-inflammatory protein is probably related to the inflammatory response and to the altered neutrophil responses to functional stimuli that characterize SAPHO syndrome suggesting a possible application as a salivary biomarker.

Cystatins in immune system

Cystatins comprise a large superfamily of related proteins with diverse biological activities. They were initially characterised as inhibitors of lysosomal cysteine proteases, however, in recent years some alternative functions for cystatins have been proposed. Cystatins possessing inhibitory function are members of three families, family I (stefins), family II (cystatins) and family III (kininogens). Stefin A is often linked to neoplastic changes in epithelium while another family I cystatin, stefin B is supposed to have a specific role in neuredegenerative diseases. Cystatin C, a typical type II cystatin, is expressed in a variety of human tissues and cells. On the other hand, expression of other type II cystatins is more specific. Cystatin F is an endo/lysosome targeted protease inhibitor, selectively expressed in immune cells, suggesting its role in processes related to immune response. Our recent work points on its role in regulation of dendritic cell maturation and in natural killer cells functional inactivation that may enhance tumor survival. Cystatin E/M expression is mainly restricted to the epithelia of the skin which emphasizes its prominent role in cutaneous biology. Here, we review the current knowledge on type I (stefins A and B) and type II cystatins (cystatins C, F and E/M) in pathologies, with particular emphasis on their suppressive vs. promotional function in the tumorigenesis and metastasis. We proposed that an imbalance between cathepsins and cystatins may attenuate immune cell functions and facilitate tumor cell invasion.

Modelling family 2 cystatins and their interaction with papain

Cystatins are extensively studied cysteine protease inhibitors, found in wide range of organisms with highly conserved structural folds. S-type of cystatins is well known for their abundance in saliva, high selectivity and poorer activity towards host cysteine proteases in comparison to their immediate ancestor cystatin C. Despite more than 90% sequence similarity, the members of this group show highly dissimilar binding affinity towards papain. Cystatin M/E is a potent inhibitor of legumain and papain like cysteine proteases and recognized for its involvement in skin barrier formation and potential role as a tumor suppressor gene. However, the structures of these proteins and their complexes with papain or legumain are still unknown. In the present study, we have employed computational methods to get insight into the interactions between papain and cystatins. Three-dimensional structures of the cystatins are generated by homology modelling, refined with molecular dynamics simulation, validated through numerous web servers and finally complexed with papain using ZDOCK algorithm in Discovery Studio. A high degree of shape complementarity is observed within the complexes, stabilized by numerous hydrogen bonds (HB) and hydrophobic interactions. Using interaction energy, HB and solvent accessible surface area analyses, we have identified a series of key residues that may be involved in papain-cystatin interaction. Differential approaches of cystatins towards papain are also noticed which are possibly responsible for diverse inhibitory activity within the group. These findings will improve our understanding of fundamental inhibitory mechanisms of cystatin and provide clues for further research.

Scientific frontiers: emerging technologies for salivary diagnostics

Saliva, a biofluid historically well-studied biochemically and physiologically, has entered the post-genomic 'omics' era, where its proteomic, genomic, and microbiome constituents have been comprehensively deciphered. The translational path of these salivary constituents has begun toward a variety of personalized individual medical applications, including early detection of cancer. Salivary diagnostics is a late-comer, but it is catching up where dedicated resources, like the Salivaomics Knowledge Base (SKB), now have taken center stage in the dissemination of the diagnostic potentials of salivary biomarkers and other translational and clinical utilities.

Reduction of Experimental Human Fibrosarcoma Lung Metastasis in Mice by Adenovirus-Mediated Cystatin C Overexpression in the Host

Tumor cell invasion and metastasis are associated with degradation of components of the extracellular matrix by different proteinases. Among those, papain-like cysteine proteases, such as cathepsin B, seem to play an important role, as they are associated with poor clinical outcome in different cancers. In this study, we tested whether cystatin C, a natural extracellular inhibitor of papain-like cysteine proteases, can inhibit metastasis when overexpressed at the tumor-host interface. Local overexpression of cystatin C in liver and lungs of CD1 nu/nu mice was achieved by gene transfer with a novel adenoviral construct, which also led to the presence of 60 ng/mL of cystatin C in the serum. Three days after gene transfer, these mice were challenged by i.v. inoculation of lacZ-tagged human fibrosarcoma cells (HT1080lacZ-K15), leading to the formation of experimental lung and liver metastases. In this model, formation of experimental metastatic foci correlated with expression of cathepsin B in lungs, whereas there was no correlation with metastasis to the liver. In mice overexpressing cystatin C, the number of lung metastases was significantly reduced by 92%, as compared with mice receiving control adenovirus. The efficacy of extravasation of HT1080lacZ-K15 cells into the liver was not affected, indicating the independence of this process from the activity of cysteine-cathepsins. The present report is the first evidence of successful reduction of metastasis by inhibition of cysteine-cathepsins by cystatin C overexpression in the host microenvironment. Furthermore, organ-specific protease expression during tumor-host cell interactions could affect the success of antiproteolytic intervention against metastasis.

Is the cystatin-like domain of TSL functionally active in external ocular infections and during the normal diurnal cycle?

PURPOSE

To test whether the cystatin-like functional domain in tear specific lipocalin (TSL) is functionally active in tears during the normal diurnal cycle and during external ocular infections.

METHODS

Capillary tube collected reflex (RTF), open (OTF) and closed (CTF) eye tear samples were recovered from six normals and semi-quantitatively western blot assayed for cystatin C and TSL. CTF samples were immunoprecipitated with antibodies raised against TSL, cystatin C and other antiproteases and screened for the co-precipitation of proteases by casein and gelatin zymography. OTF samples recovered from individuals with viral, fungal and bacterial keratitis were similarly screened for TSL-bound proteases. Human tissue was subjected to immunohistochemical study.

RESULTS

Western blot analysis reveals a progressive increase in cystatin C in going from RTF to OTF to CTF samples (approximately 3, 7 and 30 ng microl(-1), respectively). In contrast, the concentration of TSL remains constant (approximately 1500 ng microl(-1)). Immunocytochemistry data show staining of the apical surface of the human conjunctiva and some intra-cellular staining for cystatin C, but not for cystatin A. Zymography confirms earlier data that CTF contains exceptionally high levels of proteases bound to a wide range of specific inhibitors. However, only trace amounts of proteases are complexed with cystatin C and no protease can be detected bound to TSL in either the pathological or CTF samples.

CONCLUSION

Although TSL contains a functional cystatin-like domain, it is not physiologically active during the normal diurnal cycle or during external ocular infections. Reactive proteases in CTF are most likely controlled by the presence of excess levels of more reactive cystatins, especially cystatin C, which accumulates during prolonged eye closure. Immunohistochemical data suggest that the apical conjunctiva may be a contributing source for the accumulating cystatin C.

Adenain, the adenovirus endoprotease (a review)

With the possible exception of very simple viruses, most viruses appear to encode at least one virus specific endopeptidase. In addition to facilitating the orchestrated fragmentation of polyproteins of RNA viruses, these proteolytic enzymes may also be involved in the suppression of host protein synthesis, the regulation of virus assembly, the egress and subsequent uncoating in another cycle of infection of both RNA and DNA viruses. The endopeptidase encoded by adenoviruses (AVP or adenain) appears to be involved in several of these functions. Most of the literature concerns the protease of human adenovirus type 2, but there are good reasons to believe that the proteases of other adenovirus serotypes will be very similar. For a review see Weber [1,2].

Inhibition of adenovirus infection and adenain by green tea catechins

Green tea catechins have been reported to inhibit proteases involved in cancer metastasis and infection by influenza virus and HIV. To date there are no effective anti-adenoviral therapies. Consequently, we studied the effect of green tea catechins, and particularly the predominant component, epigallocatechin-3-gallate (EGCG), on adenovirus infection and the viral protease adenain, in cell culture. Adding EGCG (100 microM) to the medium of infected cells reduced virus yield by two orders of magnitude, giving and IC(50) of 25 microM and a therapeutic index of 22 in Hep2 cells. The agent was the most effective when added to the cells during the transition from the early to the late phase of viral infection suggesting that EGCG inhibits one or more late steps in virus infection. One of these steps appears to be virus assembly because the titer of infectious virus and the production of physical particles was much more affected than the synthesis of virus proteins. Another step might be the maturation cleavages carried out by adenain. Of the four catechins tested on adenain, EGCG was the most inhibitory with an IC(50) of 109 microM, compared with an IC(50) of 714 microM for PCMB, a standard cysteine protease inhibitor. EGCG and different green teas inactivated purified adenovirions with IC(50) of 250 and 245-3095, respectively. We conclude that the anti-adenoviral activity of EGCG manifests itself through several mechanisms, both outside and inside the cell, but at effective drug concentrations well above that reported in the serum of green tea drinkers.

Salivary (SD-type) cystatins: over one billion years in the making--but to what purpose?

Human saliva contains relatively abundant proteins that are related ancestrally in sequence to the cystatin superfamily. Most, although not all, members of this superfamily are potent inhibitors of cysteine peptidases. Four related genes have been identified, CST1, 2, 4 and 5, encoding cystatins SN, SA, S, and D, respectively. CST1, 4, and probably CST5 are now known to be expressed in a limited number of other tissues in the body, primarily in exocrine epithelia, and the term SD-type cystatin is more appropriate than 'salivary cystatin'. These genes are co-ordinately regulated in the submandibular gland during post-natal development. The organization of these tissue-specifically-expressed genes in the genome, and their phylogeny, indicate that they evolved from an ancestral housekeeping gene encoding the ubiquitously expressed cystatin C, and are members of a larger protein family. Their relationship to rat cystatin S, a developmentally regulated rodent submandibular gland protein, remains to be established. In this review, the evolution of the SD-type cystatins in the cystatin superfamily, their genomics, expression, and structure-function relationships are examined and compared with known cystatin functions, with the goal of providing clues to their biological roles.

The role of the second binding loop of the cysteine protease inhibitor, cystatin A (stefin A), in stabilizing complexes with target proteases is exerted predominantly by Leu73

The aim of this work was to elucidate the roles of individual residues within the flexible second binding loop of human cystatin A in the inhibition of cysteine proteases. Four recombinant variants of the inhibitor, each with a single mutation, L73G, P74G, Q76G or N77G, in the most exposed part of this loop were generated by PCR-based site-directed mutagenesis. The binding of these variants to papain, cathepsin L, and cathepsin B was characterized by equilibrium and kinetic methods. Mutation of Leu73 decreased the affinity for papain, cathepsin L and cathepsin B by approximately 300-fold, >10-fold and approximately 4000-fold, respectively. Mutation of Pro74 decreased the affinity for cathepsin B by approximately 10-fold but minimally affected the affinity for the other two enzymes. Mutation of Gln76 and Asn77 did not alter the affinity of cystatin A for any of the proteases studied. The decreased affinities were caused exclusively by increased dissociation rate constants. These results show that the second binding loop of cystatin A plays a major role in stabilizing the complexes with proteases by retarding their dissociation. In contrast with cystatin B, only one amino-acid residue of the loop, Leu73, is of principal importance for this effect, Pro74 assisting to a minor extent only in the case of cathepsin B binding. The contribution of the second binding loop of cystatin A to protease binding varies with the protease, being largest, approximately 45% of the total binding energy, for inhibition of cathepsin B.

Substrate specificity of adenovirus protease

The adenovirus protease, adenain is functionally required for virion uncoating and virion maturation and release from the infected cell. In addition to hydrolysis of precursor proteins at specific consensus sites, adenain has also been observed to cleave viral proteins at other sites. Here we re-examine the sequences in the consensus sites and also the phenomena of cleavage at other sites on viral proteins II, 100K, V, VI and VII. An examination of the eight residues flanking the scissile bond in 274 consensus sites from 36 different adenovirus serotypes in the DNA sequence databanks provided the following main conclusions: (1) two types of consensus sites, type 1, (M,I,L)XGX-G and type 2, (M,I,L)XGG-X, (2) the variant positions P(3) and P(1) never contained C,P,D,H,W,Y and C,P,G,M amino acids, respectively in type 1, (3) the variant positions P(3) and P(1)' never contained C,D,L,W and C,P,D,Q,H,Y,W amino acids, respectively in type 2, and (4) the thiol forming C residue occurred only twice within the eight residues flanking the scissile bond and that in the P(4)' position. Six unusual serotypes had (M,L,I)XAT-G as the PVII consensus site. Adenain has been proposed to cleave protein VI at an unknown site in the course of virion uncoating. The cleavage of capsid protein VI in the absence of a consensus site is confirmed here in vitro using recombinant adenain. Virion proteins II, V and VII and the nonstructural protein 100K were also digested in vitro into discrete fragments by recombinant adenain. We conclude that adenain preferentially cleaves viral proteins at their consensus sites, but is capable, in vitro of cleavages at other discrete sites which resemble the consensus cleavage sites.