Functional characterization of Cystatin C in orange-spotted grouper, Epinephelus coioides

Molecular characterization, expression and immune functional analysis of cystatin 10 in turbot

BACKGROUND

Cystatin is a protease inhibitor that also regulates genes expression linked to inflammation and plays a role in defense and regulation.

METHODS AND RESULTS

Cystatin 10 (Smcys10) was cloned from Scophthalmus maximus and encodes a 145 amino acid polypeptide. The results of qRT-PCR showed that Smcys10 exhibited tissue-specific expression patterns, and its expression was significantly higher in the skin than in other tissues. The expression level of Smcys10 was significantly different in the skin, gill, head kidney, spleen and macrophages after Vibrio anguillarum infection, indicating that Smcys10 may play an important role in resistance to V. anguillarum infection. The recombinant Smcys10 protein showed binding and agglutinating activity in a Ca2+-dependent manner against bacteria. rSmcys10 treatment upregulated the expression of IL-10, TNF-α and TGF-β in macrophages of turbot and hindered the release of lactate dehydrogenase (LDH) from macrophages after V. anguillarum infection, which confirmed that rSmcys10 reduced the damage to macrophages by V. anguillarum. The NF-κB pathway was suppressed by Smcys10, as demonstrated by dual-luciferase analysis.

CONCLUSIONS

These results indicated that Smcys10 is involved in the host antibacterial immune response.

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.

Functional analysis of the Cystatin F gene response to SGIV infection in orange-spotted grouper, Epinephelus coioides

Cystatin F (CyF), an inhibitor of cysteine protease, was widely studied in immune defense and cancer therapy. However, the function of CyF and its latent molecular mechanism during virus infection in fish remain vacant. In our research, we cloned the open reading frame (ORF) of CyF homology from orange-spotted grouper (Ec-CyF) consisting of 342 nucleotides and encoding a 114-amino acid protein. Ec-CyF included two cystatins family sequences containing one KXVXG sequence without the signal peptide, and a hairpin ring containing proline and tryptophan (PW). Tissue distribution analysis indicated that Ec-CyF was highly expressed in spleen and head kidney. Besides, further analysis showed that the expression of Ec-CyF increased during SGIV infection in grouper spleen (GS) cells. Subcellular localization assay demonstrated that Ec-CyF was mainly distributed in cytoplasm in GS cells. Overexpressed Ec-CyF demoted the mRNA level of viral genes MCP, VP19 and LITAF. Meanwhile, SGIV-induced apoptosis in fat head minnow (FHM) cells was impeded, as well as the restraint of caspase 3/7 and caspase 8. In addition, Ec-CyF overexpression up-regulated the expression of IFN related molecules including ISG15, IFN, IFP35, IRF3, IRF7, MYD88 and down-regulated proinflammatory factors such as IL-1β, IL-8 and TNF-α. At the same time, Ec-CyF-overexpressing increased the activity of IFN3 and ISRE promoter, but impeded NF-κB promoter activity by luciferase reporter gene assay. In summary, our findings suggested that Ec-CyF was involved in innate immunity response and played a key role in DNA virus infection.

Functional analysis of the cystatin A gene response to SGIV infection in orange-spotted grouper, Epinephelus coioides

Cystatin A (CyA), an inhibitor of cysteine protease, was widely studied in immune defense and cancer therapy. However, the function of CyA and its potential molecular mechanism during virus infection in fish remain unknown. In our study, we cloned the open reading frame (ORF) of CyA homology from orange-spotted grouper (Ec-CyA) consisting of 303 nucleotides and encoding a 101-amino acid protein. Ec-CyA included two conserved sequences containing one N-terminal glycine fragment and one QXVXG sequence (48aa-52aa) without the signal peptide. Tissue distribution analysis showed that Ec-CyA was highly expressed in spleen and head kidney. Moreover, further analysis indicated that the expression of Ec-CyA increased during SGIV simulation in grouper spleen (GS) cells. Subcellular localization assay demonstrated that Ec-CyA was mainly distributed in cytoplasm in GS cells. Overexpressed Ec-CyA promoted the mRNA level of viral genes MCP, VP19 and LITAF. Meanwhile, SGIV-induced apoptosis in fat head minnow (FHM) cells was facilitated, as well as the activation of caspase-3/7, caspase-9. In addition, Ec-CyA overexpression down-regulated the expression of interferon (IFN) related molecules including ISG15, IFN, IRF3, MAVS, MyD88, TRAF6 and up-regulated proinflammatory factors such as IL-1β, IL-8 and TNF-α. At the same time, Ec-CyA-overexpressing inhibited the activity of IFN and ISRE promoter, but induced NF-κB promoter activity by luciferase reporter gene assay. In summary, our findings suggested that Ec-CyA was involved in innate immune response and played a key role in DNA virus infection.

Identification and functional characterization of Cystatin B in orange-spotted grouper, Epinephelus coioides

Cystatin B is a cysteine protease inhibitor that plays a crucial role in immune response. Nevertheless, the molecular mechanism of fish Cystatin B in virus replication remains obscure. In this study, we identified and characterized Cystatin B (Ec-CysB) in the orange-spotted grouper (Epinephelus coioides). The Ec-CysB encoded a 100-amino acid protein with the conserved QXVXG motif, PC motif and cysteine protease inhibitory motif, which shared high identities with reported Cystatin B. The abundant transcriptional level of Ec-CysB was found in gill, intestine and head kidney. And the Ec-CysB expression was significantly up-regulated in spleen after infection with Singapore grouper iridovirus (SGIV) in vitro. Subcellular localization analysis revealed that Ec-CysB was distributed mainly in the cytoplasm and nucleus. Further studies showed that overexpression of Ec-CysB in vitro significantly increased SGIV replication and virus-induced cell apoptosis, but replication of SGIV was inhibited by knockdown or mutant of Ec-CysB. Moreover, overexpression of Ec-CysB significantly inhibited the interferon (IFN), interferon-stimulated response element (ISRE) promoter activities, and enhanced apoptosis-related transcription factors p53 promoter activities. Collectively, our results suggest that Ec-CysB affect viral replication and virus-induced cell apoptosis, which will help us to explore its potential functions during SGIV infection.

Molecular characterization, expression, and functional analysis of cystatin B in the big-belly seahorse (Hippocampus abdominalis)

Cystatins are a diverse group of cysteine protease inhibitors widely present among various organisms. Beyond their protease inhibitor function, cystatins play a crucial role in diverse pathophysiological conditions in animals, including neurodegenerative disorders, tumor progression, inflammatory diseases, and immune response. However, the role of cystatins in immunity against viral and bacterial infections in fish remains to be elucidated. In this study, the cystatin B from big-belly seahorse, Hippocampus abdominalis, designated as HaCSTB, was identified and characterized. HaCSTB shared the highest homology with type 1 cystatin family members of teleosts and had three cystatin catalytic domains with no signal peptides or disulfide bonds. HaCSTB transcripts were mainly expressed in peripheral blood cells (PBCs), followed by the testis and pouch of healthy big-belly seahorses. Immune challenge with lipopolysaccharides (LPS), polyinosinic:polycytidylic acid (Poly I:C), and Streptococcus iniae induced upregulation of relative HaCSTB mRNA expression in PBCs. Subcellular localization analysis revealed the distribution of HaCSTB in the cytosol, mitochondria, and nuclei of fathead minnow cells (FHM). Recombinant HaCSTB (rHaCSTB) exhibited potent in vitro inhibitory activity against papain, a cysteine protease, in a concentration-, pH-, and temperature-dependent manner. Overexpression of HaCSTB in viral hemorrhagic septicemia virus (VHSV)-susceptible FHM cells increased cell viability and reduced VHSV-induced apoptosis. Collectively, these results suggest that HaCSTB might engage in the teleostean immune protection against bacteria and viruses.

Identification and molecular profiling of a novel homolog of cystatin C from rock bream (Oplegnathus fasciatus) evidencing its transcriptional sensitivity to pathogen infections

Cystatins are reversible inhibitors of cysteine proteases which show an omnipresent distribution in the life on earth. Although, cystatins with mammalian origin were well characterized and their roles in physiology were reported in details, those from teleostean origin are still underrepresented in literature. However, role of cystatins in fish physiology and immune defense is highlighted in few recent reports. In this study, a cystatin C holmologue from rock bream (Oplegnathus fasciatus); termed RbCytC was identified and molecularly characterized. The complete coding sequence of RbCytC was 387 bp in length, which codes for a polypeptide with 129 amino acids, including a signal peptide of 19 amino acids. The consensus cystatin family signatures including a G residue, turning up towards the N-terminus region, QVVAG motif, locating at the middle of the sequence and the PW motif at the c terminal region was found to be well conserved in RbCytC. Phylogenetic analysis using different cystatin counterparts affirmed the close evolutionary relationship of RbCytC with its teleostan homologs which belong to family 2 cystatins. The predicted molecular model of RbCytC resembled most of the structural features of empirically elucidated tertiary structures for chicken egg white cystatin. According to the qPCR assays, RbCytC showed detectable expression in all fish tissues used in the experiment, with markedly pronounced expression level in liver. Moreover, its basal mRNA expression was up-regulated in liver and spleen tissues by experimental rock bream iridovirus infection, whereas down regulated in the same tissues, post live Edwardsiella tarda injection. Collectively, outcomes of our study validate the structural homology of RbCytC with known cystatin C similitudes, especially those of teleosts and suggest its potential roles in proteolytic processes of rock bream physiology as well as in host immune defense mechanisms.