Molecular cloning, expression and functional characterization of interferon-γ-inducible lysosomal thiol reductase (GILT) gene from mandarin fish (Siniperca chuatsi)

Functional of tongue sole (Cynoglossus semilaevis) gamma-interferon-inducible lysosomal thiol reductase with implications in innate immune reponse depend on CXXC active site

The enzyme gamma-interferon-inducible lysosomal thiol reductase (GILT) plays an important role in promoting the processing and presentation of major histocompatibility complex (MHC) class II-restricted antigens. It is also involved in MHC I-restricted antigens catalyzing disulfide bond reduction in fishes' adaptive immunity. The open reading frame of tongue sole (Cynoglossus semilaevis) GILT (tsGILT) gene is 771 bp long, encoding 257 amino acids, with a calculated molecular weight of 28.465 kDa and isoelectric point (pI) of 5.35. After induction with lipopolysaccharide, the expression of tsGILT mRNA was upregulated in spleen and kidney and recombinant tsGILT protein transferred to late endosomes and lysosomes in HeLa cells. The refolded tsGILT was capable of catalyzing the reduction of the interchain disulfide bonds against an IgG substrate depend on the active site CXXC motif at residues 75-78. The process of immune response to bacteria challenge needs GILT to catalyze the reduction of disulfide bond and unfolding native protein antigens, promoting their hydrolysis by proteases. Whether a single mutation or a double mutation of active site CXXC at residues75-78, the 3D structure of tsGILT protein has undergone major changes and lost its activity of catalyzing the reduction of the interchain disulfide bonds.

Antigen Presentation and Autophagy in Teleost Adaptive Immunity

Infectious diseases are a burden for aquaculture. Antigen processing and presentation (APP) to the immune effector cells that fight pathogens is key in the adaptive immune response. At the core of the adaptive immunity that appeared in lower vertebrates during evolution are the variable genes encoding the major histocompatibility complex (MHC). MHC class I molecules mainly present peptides processed in the cytosol by the proteasome and transported to the cell surface of all cells through secretory compartments. Professional antigen-presenting cells (pAPC) also express MHC class II molecules, which normally present peptides processed from exogenous antigens through lysosomal pathways. Autophagy is an intracellular self-degradation process that is conserved in all eukaryotes and is induced by starvation to contribute to cellular homeostasis. Self-digestion during autophagy mainly occurs by the fusion of autophagosomes, which engulf portions of cytosol and fuse with lysosomes (macroautophagy) or assisted by chaperones (chaperone-mediated autophagy, CMA) that deliver proteins to lysosomes. Thus, during self-degradation, antigens can be processed to be presented by the MHC to immune effector cells, thus, linking autophagy to APP. This review is focused on the essential components of the APP that are conserved in teleost fish and the increasing evidence related to the modulation of APP and autophagy during pathogen infection.

Immune Response of Senegalese Sole against Betanodavirus Mutants with Modified Virulence

Nervous necrosis virus (NNV), genus Betanodavirus, the etiological agent of the viral encephalopathy and retinopathy (VER), presents a genome with two positive-sense single-stranded RNA segments. Striped jack nervous necrosis virus (SJNNV) and red-spotted grouper nervous necrosis virus (RGNNV), together with reassortants RGNNV/SJNNV, are the betanodaviruses predominantly isolated in Southern Europe. An RGNNV/SJNNV reassortant isolated from Senegalese sole (wt160) causes high mortalities in this fish species. This virus presents differences in the sequence of the 3’ non-coding region (NCR) of both segments compared to RGNNV and SJNNV reference strains. Previously, it has been reported that the reversion of two of these differences (nucleotides 1408 and 1412) in the RNA2 3’NCR to the SJNNV-type (recombinant r1408-1412) resulted in a decrease in sole mortality. In the present study, we have applied an OpenArray^® to analyse the involvement of sole immune response in the virulence of several recombinants: the r1408-1412 and two recombinants, developed in the present study, harbouring mutations at positions 3073 and 3093 of RNA1 3’NCR to revert them to RGNNV-type. According to the correlation values and to the number of expressed genes, the infection with the RNA2-mutant provoked the most different immune response compared to the immune response triggered after the infection with the rest of the viruses, and the exclusive and high upregulation of genes related to the complement system. The infection with the RNA1-mutants also provoked a decrease in mortality and their replication was delayed at least 24 h compared to the wt160 replication, which could provoke the lag observed in the immune response. Furthermore, the infection with the RNA1-mutants provoked the exclusive expression of pkr and the downregulation of il17rc.

Role of major histocompatibility complex II antigen-presentation pathway genes in orange-spotted grouper infected with Cryptocaryon irritans

Cryptocaryon irritans, a pathogen model for fish mucosal immunity, causes skin mucosal and systematic humoral immune response. Where and how MHC II antigen presentation occurs in fish infected with C. irritans remain unknown. In this study, the full-length cDNA of the grouper cysteine protease CTSS was cloned. The expression distributions of six genes (CTSB, CTSL, CTSS, GILT, MHC IIA and MHC IIB) involved in MHC II antigen presentation pathway were tested. These genes were highly expressed in systematic immune tissues and skin and gill mucosal-associated immune tissues. All six genes were upregulated in skin at most time points. Five genes expected CTSS was upregulated in spleen at most time points. CTSB, CTSL and MHC IIA were upregulated in the gill and head kidney at some time points. These results indicate that the presentation of MHC II antigen intensively occurred in local infected skin and gill. Spleen, not head kidney, had the most extensive systematic antigen presentation. In skin, six genes most likely peaked at day 2, earlier than in spleen (5-7 days), marking an earlier skin antibody peak than any recorded in serum previously. This significant and earlier mucosal antigen presentation indicates that specific immune response occurs in local mucosal tissues.

Identification and functional characterization of interferon-γ-inducible lysosomal thiol reductase (GILT) gene in common Chinese cuttlefish Sepiella japonica

Interferon-γ-inducible lysosomal thiol reductase (GILT) is a pivotal enzyme involved in the histocompatibility complex (MHC) class II-restricted antigen processing whereby it catalyzes the disulfide bond reduction in the endocytic pathway. Here, a novel GILT homologue termed as SjGILT firstly identified from common Chinese cuttlefish Sepiella japonica. SjGILT shared domain topology containing a signal peptide, a signature sequence CQHGX₂ECX₂NX₄C, an activate-site CXXC motif, two potential N-glycosylation sites and six conserved cysteins with its counterparts in other animals. SjGILT transcripts were constitutively expressed in all examined tissues in S. japonica, with the higher expression levels in immune-related tissues such as pancreas, intestines, liver and gills. Upon lipopolysaccharide (LPS) challenge, SjGILT transcripts were significantly induced in liver and gill tissues, and SjGILT protein transferred to late endosomes and lysosomes in HeLa cells. Further study showed that recombinant SjGILT had obvious thiol reductase activity demonstrated by reducing the interchain disulfide bonds of IgG under acidic conditions. Taken together, these results suggested that SjGILT may be involved in the immune response to bacteria challenge, and then might play an important role in the processing of MHC class II-restricted antigens in S. japonica.

Molecular and biological characterization of gamma-interferon-inducible lysosomal thiol reductase in silver carp (Hypophthalmichthys molitrix)

Gamma-interferon-inducible lysosomal thiol reductase (GILT) plays an important role in the processing of major histocompatibility complex (MHC) class II-restricted antigens by catalyzing disulfide bonds reduction. Herein, a GILT homolog (ScGILT) was identified from silver carp. Its open reading frame covers 771 base pairs, encoding a protein of 256 amino acids that possesses GILT signature sequence CQHGX₂ECX₂NX₄C, active-site CXXC motif, and two potential N-linked glycosylation sites. The predicted tertiary structures of ScGILT and other GILTs were quite similar in shape and positional arrangement of the key motifs. ScGILT mRNA was constitutively expressed in all detected tissues, with high-level expression in fish immune organs, spleen and head kidney. After stimulation with lipopolysaccharide, the expression of ScGILT mRNA significantly increased in spleen and head kidney cells, and ScGILT protein translocated to late endosomes and lysosomes in HeLa cells. Recombinant ScGILT fused with a His₆ tag was expressed and purified, and could reduce the interchain disulfide bonds of IgG at pH 4.5. These results suggested that ScGILT was capable of catalyzing disulfide bonds reduction, and then might play an important role in the processing of MHC class II-restricted antigens in silver carp.

Genomic structure, expression pattern and polymorphisms of GILT in golden pompano Trachinotus ovatus (Linnaeus 1758)

The interferon-g-inducible lysosomal thiol reductase (GILT) plays a significant character in the processing and presentation of MHC class II restricted antigen (Ag) by catalyzing disulfide bond reduction in mammals. To explore the function of GILT in the immune system of fish, we cloned a GILT gene homologue from Trachinotus ovatus, the full-length cDNA of GILT, which consisted of 2, 747 bp with a 771 bp open reading frame, encoding a protein of 256 amino acids. Moreover, similar to other species GILT gene, 7 exons and 6 introns were identified in T. ovatus, the deduced protein also possessed a representative characteristic of known GILT proteins. The result of real-time quantitative PCR showed that GILT mRNA was dramatically expressed in immune-associated tissues, such as spleen (p < 0.01) and kidney (p < 0.05). Bacterial challenge revealed that GILT mRNA level remarkably up-regulation in liver, spleen, kidney and intestine after induction with Photobacterium damsela. Furthermore, based on cloned sequences and genome BLAST, only one SNP site (ToGILT-S1-g.148C>G) was identified, and the allele C was significantly associated with high-susceptibility (HS) group, nevertheless, the allele G was dramatically associated with high-resistance (HR) group, indicating potential application for disease resistant breeding selection in T. ovatus.

Molecular structure and functional characterization of the gamma-interferon-inducible lysosomal thiol reductase (GILT) gene in largemouth bass (Microptenus salmoides)

The enzyme gamma-interferon-inducible lysosomal thiol reductase (GILT) plays a role in facilitating the processing and presentation of major histocompatibility complex (MHC) class II-restricted antigens and is also involved in MHC I-restricted antigens in adaptive immunity catalyzing disulfide bond reduction in mammals. In this study, we cloned a GILT gene homolog from largemouth bass (designated 'lbGILT'), a freshwater fish belonging to Perciformes and known for its nutritive value. We obtained the full-length cDNA of lbGILT by reverse transcription PCR and rapid amplification of cDNA ends. This cDNA is comprised of a 5'-untranslated region (UTR) of 87 bp, a 3'-UTR of 189 bp, and an open reading frame of 771 bp. It encodes a protein of 256 amino acids with a deduced molecular weight of 28.548 kDa and a predicted isoelectric point of 5.62. The deduced protein possesses the typical structural features of known GILTs, including an active site motif, two potential N-linked glycosylation sites, a GILT signature sequence, and six conserved cysteines. Tissue-specific expression of lbGILT was shown by real-time quantitative PCR. The expression of lbGILT mRNA was obviously up regulated in spleen and kidney after induction with lipopolysaccharide. Recombinant lbGILT was produced as an inclusion body with a His6 tag in ArcticExpress (DE3), and the protein was then washed, solubilized, and refolded. The refolded lbGILT showed reduction activity against an IgG substrate. These results suggest that lbGILT plays a role in innate immunity.

Identification of interferon-γ-inducible-lysosomal thiol reductase (GILT) gene in goldfish (Carassius auratus) and its immune response to LPS challenge

The interferon-γ-inducible lysosomal thiol reductase (GILT) has been demonstrated to play an important role in the processing and presentation of MHC class II restricted antigen (Ag) by catalyzing disulfide bond reduction. In this study, we cloned a GILT gene homolog from goldfish (designated gGILT), a kind of precious freshwater fish with high market value. The open reading frame of gGILT consists of 756 bases encoding a protein of 251 amino acids with an estimated molecular mass of 27.8 kDa and a theoretical isoelectric point of 5.24. The deduced protein possesses the typical structural features of known GILT proteins, including an active-site motif, a GILT signature sequence, and 10 conserved cysteines. RT-PCR results showed that gGILT and gIFN-γ (goldfish IFN-γ) mRNA were expressed in a tissue-specific manner and obviously up-regulated in splenocytes and the cells from head kidney after induction with LPS. Recombinant gGILT fused with His6 tag was efficiently expressed in Escherichia coli BL21 (DE3) and purified by Ni-NTA affinity chromatography. Further study revealed that gGILT was capable of catalyzing the reduction of the interchain disulfide bonds from intact IgG. This study shows that gGILT may be involved in the immune response to bacteria challenge and maintain first line of innate immune defense at basal level in goldfish. It also provides the basis for investigating on the role of GILT using goldfish as an animal model.