Molecular cloning, expression analysis and enzymatic characterization of cathepsin K from olive flounder (Paralichthys olivaceus)

Whole genome identification of olive flounder (Paralichthys olivaceus) cathepsin genes: Provides insights into its regulation on biotic and abiotic stresses response

Cathepsins are major lysosomal enzymes involved in essential physiological processes, including protein degradation, tissue differentiation, and innate or adaptive responses. Several kinds of cathepsins have been reported in teleost fishes, but no characterization have been performed for the inflammatory response of cathepsin family in olive flounder until now. In our current study, a total of 17 cathepsins in olive flounder were systematically identified and characterized. Phylogenetic analysis clearly indicated that the cathepsin genes was highly conserved. Analysis of structure and motifs exhibited high sequence similarity of cathepsin genes in olive flounder. Expression profiles of cathepsin genes in different tissues and developmental stages showed that cathepsins were temporally and spatially specific. RNA-seq analysis of bacteria and temperature stresses revealed that members of cathepsin were involved in inflammatory responses. Collectively, our findings would provide a further reference for understanding the molecular mechanisms of cathepsins in olive flounder.

Genome-Wide Identification, Evolutionary Analysis, and Expression Patterns of Cathepsin Superfamily in Black Rockfish (Sebastes schlegelii) following Aeromonas salmonicida Infection

Cathepsins are lysosomal cysteine proteases belonging to the papain family and play crucial roles in intracellular protein degradation/turnover, hormone maturation, antigen processing, and immune responses. In the present study, 18 cathepsins were systematically identified from the fish S. schlegelii genome. Phylogenetic analysis indicated that cathepsin superfamilies are categorized into eleven major clusters. Synteny and genome organization analysis revealed that whole-genome duplication led to the expansion of S. schlegelii cathepsins. Evolutionary rate analyses indicated that the lowest Ka/Ks ratios were observed in CTSBa (0.13) and CTSBb (0.14), and the highest Ka/Ks ratios were observed in CTSZa (1.97) and CTSZb (1.75). In addition, cathepsins were ubiquitously expressed in all examined tissues, with high expression levels observed in the gill, intestine, head kidney, and spleen. Additionally, most cathepsins were differentially expressed in the head kidney, gill, spleen, and liver following Aeromonas salmonicida infection, and their expression signatures showed tissue-specific and time-dependent patterns. Finally, protein–protein interaction network (PPI) analyses revealed that cathepsins are closely related to a few immune-related genes, such as interleukins, chemokines, and TLR genes. These results are expected to be valuable for comparative immunological studies and provide insights for further functional characterization of cathepsins in fish species.

Exploring the role of cathepsin in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease which is marked by leukocytes infiltration inside synovial tissue, joints and also inside synovial fluid which causes progressive destruction of joint cartilage. There are numerous genetical and lifestyle factors, responsible for rheumatoid arthritis. One such factor can be cysteine cathepsins, which act as proteolytic enzymes. These proteolytic enzyme gets activated at acidic pH and are found in lysosomes and are also termed as cysteine proteases. These proteases belong to papain family and have their elucidated role in musculoskeletal disorders. Numerous cathepsins have their targeted role in rheumatoid arthritis. These proteases are secreted through various cell types which includes matrix metalloproteases and papain like cysteine proteases. These proteases can potentially lead to bone and cartilage destruction which causes an immune response in case of inflammatory arthritis.

Identification and characterization of a cathepsin K homologue that interacts with pathogen bacteria in black rockfish, Sebastes schlegelii

Cathepsin K belongs to the family of cysteine cathepsins. It is well known that the cysteine cathepsins participate in various physiological processes and host immune defense in mammals. However, in teleost fish, the function of cathepsin K is very limited. In the present study, a cathepsin K homologue (SsCTSK) from the teleost black rockfish (Sebastes schlegelii) was identified and examined at expression and functional levels. In silico analysis showed that three domains, including signal peptide, cathepsin propeptide inhibitor I29 domain, and functional domain Pept_C1, are existed in SsCTSK. SsCTSK also possesses a peptidase domain with three catalytically essential residues (Cys25, His162 and Asn183). Phylogenetic profiling indicated that SsCTSK was evolutionally close to the cathepsin K of other teleost fish. Expression of SsCTSK occurred in multiple tissues and was induced by bacterial infection. Purified recombinant SsCTSK (rSsCTSK) exhibited apparent maximal peptidase activity at 45 °C, and its enzymatic activity was remarkably declined in the presence of the cathepsin inhibitor E-64. Moreover, rSsCTSK possesses the ability to bind with PAMPs and bacteria. Finally, knockdown of SsCTSK expression facilitated bacterial invasion in black rockfish. Collectively, these results indicated that SsCTSK functions as a cysteine protease and may serves as a target for pathogen manipulation of host defense system.

Characterization and initial functional analysis of cathepsin K in turbot (Scophthalmus maximus L.)

Cathepsins are the best-known group of proteases in lysosomes, playing a significant role in immune responses. Cathepsin K (CTSK) is abundantly and selectively expressed in osteoclasts, dendritic cells and monocyte-derived macrophages, where it is involved in ECM degradation and bone remodeling. A growing body of evidences have indicated the vital roles of cathepsin K in innate immune responses. Here, one CTSK gene was captured in turbot (SmCTSK) with a 993 bp open reading frame (ORF). The genomic structure analysis showed that SmCTSK had 7 exons similar to other vertebrate species. The syntenic analysis revealed that CTSK had the same neighboring genes across all the selected species, which suggested the synteny encompassing CTSK region was conserved during vertebrate evolution. Subsequently, SmCTSK was widely expressed in all the examined tissues, with the highest expression level in spleen and the lowest expression level in liver. In addition, SmCTSK was significantly down-regulated in intestine following Gram-negative bacteria Vibrio anguillarum immersion challenge, but up-regulated in three tissues (gill, skin and intestine) following Gram-positive bacteria Streptococcus iniae immersion challenge. Finally, the rSmCTSK showed strong binding ability to all the examined microbial ligands. Taken together, our results suggested SmCTSK played vital roles in fish innate immune responses against infection. However, the knowledge of SmCTSK is still limited in teleost species, further studies should be carried out to better characterize its comprehensive roles in teleost mucosal immunity.

MITF Regulates Downstream Genes in Response to Vibrio parahaemolyticus Infection in the Clam Meretrix Petechialis

The microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix-leucine zipper protein that plays a key role in cell proliferation, survival and immune defense through the direct transcriptional control of downstream genes. We have found that MITF participates in the immune response to Vibrio parahaemolyticus infection in the clam Meretrix petechialis. In this study, we focused on how MITF functions in immunity. First, PO, CTSK, and BCL-2 were identified as the target genes of MpMITF in the clam by RNAi. EMSAs showed direct binding between the MpMITF protein and the E-box of the MpPO, MpCTSK, and MpBCL-2 promoters. Yeast one-hybrid assays also suggested that MpMITF could activate the expression of these three downstream genes. These results demonstrated that the transcriptional expression of MpPO, MpCTSK, and MpBCL-2 is directly regulated by MpMITF. Second, we analyzed the roles of MpPO, MpCTSK, and MpBCL-2 in clam immunity. The mRNA expression of MpPO, MpCTSK, and MpBCL-2 increased significantly after V. parahaemolyticus challenge, which implied that these genes might take part in the immune defense against V. parahaemolyticus challenge in clams. The purified recombinant proteins, MpPO and MpCTSK, inhibited the growth of V. parahaemolyticus. Additionally, the apoptosis rate of clam haemocytes rose significantly when the activity of MpBCL-2 was suppressed. These results revealed that MpPO, MpCTSK, and MpBCL-2 are involved in the immune defense against V. parahaemolyticus. This study supports the idea that the MpMITF pathway plays a key role in immune defense through the direct regulation of the downstream genes MpPO, MpCTSK, and MpBCL-2 in the clam, M. petechialis.

Identification and expression of cathepsin B from the freshwater mussel Cristaria plicata

Cathepsin B plays crucial roles in host immune defense against pathogen infection. In present study, a cathepsin B gene from the freshwater mussel, Cristaria plicata (CpCathB) was cloned and characterized. The full-length cDNA of CpCathB was 1825 bp, and contained a 5' untranslated region (UTR) of 36 nucleotides, an open reading frame (ORF) of 1044 bp and a 3' UTR of 745 bp with a poly (A) tail. The deduced CpCathB protein was encoded as a preproenzyme with 347 amino acid residues and predicted molecular weight of 38.55 kDa. Sequence alignment revealed that CpCathB protein shared 56% - 60.7% identity comparison with other species. The predicted tertiary structure of CpCathB protein was highly similar to that of human. The CpCathB mRNA was expressed in hemocytes, hepatopancreas, adductor muscle, gills and mantle tissues of healthy mussels, and the highest expression level was in hepatopancreas. The transcripts of CpCathB were increased in hemocytes and hepatopancreas from mussels after Aeromonas hydrophila challenge. Moreover, the recombinant CpCathB was expressed in the Escherichia coli Rosetta-gami (DE3) strain. The maximum titer of the anti-CpCathB polyclonal antibodies was 1:640,000.The CpCathB protein had a higher expression in hepatopancreas and mantle and a lower level in hemocytes.

Olive flounder (Paralichthys olivaceus) cystatin B: cloning, tissue distribution, expression and inhibitory profile of piscine cystatin B

Among the cystatin superfamily, cystatin B, also known as stefin B, is an intracellular inhibitor that regulates the activities of cysteine proteases, such as papain and cathepsins. In this study, the 536 bp cystatin B cDNA (referred to hereafter as PoCystatin B) was cloned from olive flounder (Paralichthys olivaceus) using a combination of the rapid amplification of cDNA ends (RACE) approach and olive flounder cDNA library screening. To determine the tissue distribution of PoCystatin B mRNA, the expression of PoCystatin B in normal and lipopolysaccharide (LPS)-stimulated flounder tissues were compared with that of the inflammatory cytokines interleukin (IL)-1β, IL-6, and IL-8 by reverse transcription (RT)-polymerase chain reaction (PCR). The results of the RT-PCR analysis revealed ubiquitous PoCystatin B expression in normal and LPS-stimulated tissues. To characterize the enzymatic activity of PoCystatin B protein, recombinant PoCystatin B protein was overexpressed in Escherichia coli BL21(DE3) cells in the pCold™ TF DNA expression vector as a soluble fusion protein of 67-kDa. PoCystatin B inhibited papain cysteine protease, bovine cathepsin B, and fish cathepsins F and X to a greater extent, whereas fish cathepsins L, S, and K were inhibited to a lesser extent. These results indicate that the enzymatic characteristics of the olive flounder cystatin B are similar to those of mammalian cystatin B proteins, and provide a better understanding of the mechanisms of regulation of cathepsins and cystatins in marine organisms.

Cathepsins in the kidney of olive flounder, Paralichthys olivaceus, and their responses to bacterial infection

Cathepsin activities are responsible for mediating various pathways involved in immune response, including the apoptosis pathway, toll-like receptor (TLR) signaling, cytokine induction and activation of granule serine proteases. In the present study, we investigated cathepsin responses in the kidneys of olive flounder infected with Streptococcus parauberis, analyzing cathepsin expression using a label-free, quantitative proteomic approach in conjunction with quantitative real-time polymerase chain reaction (qRT-PCR). In proteomic analyses, we detected cathepsin B, D, L and S proteins, noting significant decreases and increases in cathepsins B and L, respectively, with infection. Taken together with an evaluation of cathepsin B, D, F, K, L, S and X gene expression in normal and infected kidneys by qRT-PCR, our results indicate that cathepsins B, D, L and S are the dominant lysosomal proteases in the immune system of the teleostei, olive flounder. Cathepsins F, K and X were regarded as minor cathepsins.

Transcriptional evidence for low contribution of oil droplets to acute toxicity from dispersed oil in first feeding Atlantic cod (Gadus morhua) larvae

We evaluated the potential contribution of oil droplets to the toxicity of dispersed oil to first feeding fish larvae. Atlantic cod larvae were exposed to five concentrations of either artificially weathered (200°C residue) dispersed oil (D1-D5) containing oil droplets [medium size 11-13 μm based on volume] and water-soluble fraction [WSF] or the filtered dispersions containing only the corresponding equilibrium WSFs only (W1-W5). The larvae were exposed for 4 days and harvested for transcriptional analysis at 13 days post hatching. The most significant differently expressed genes were observed in cod larvae exposed to the highest concentration of the dispersed oil (containing 10.41 ± 0.46 μg ∑PAH/L), with CYP1A showing the strongest response. Functional analysis further showed that the top scored network as analyzed with Ingenuity Pathway Analysis was "Drug Metabolism, Endocrine System Development and Function, Lipid Metabolism". Oil exposure also increased the expression of genes involved in bone resorption and decreased the expression of genes related to bone formation. In conclusion, oil exposure affects drug metabolism, endocrine regulation, cell differentiation and proliferation, apoptosis, fatty acid biosynthesis and tissue development in Atlantic cod larvae. The altered gene transcription was dominated by the WSF and the corresponding oil droplet fraction only had a moderate contribution to the observed changes.

Retinoic acid induces two osteocalcin isoforms and inhibits markers of osteoclast activity in Atlantic cod (Gadus morhua) ex vivo cultured craniofacial tissues

Nutritional status including vitamin A could explain some of the developmental deformities observed in cultivated teleosts, including Atlantic cod (Gadus morhua). In the present study we aimed to investigate the transcriptional effect of retinoic acid (RA) on bone related genes using Atlantic cod craniofacial explants tissue cultures. Two different osteoblast specific osteocalcin/bone gla protein isoforms were discovered in cod. Transcription of both isoforms was up-regulated following RA treatment of 65 dph cod lower jaw explants. In contrast, transcripts coding for genes related to bone resorption and osteoclast activity, matrix metalloproteinase 9 and cathepsin K were down-regulated following RA treatment. This could be linked to the decreased transcriptional ratio between receptor activator of nuclear factor kappa-B ligand rankl and osteoprotegerin observed in the same tissue samples. RA treatment of juvenile explants had no effect on runt-related transcription factor 2 and osterix mRNA levels. However, osterix was significantly down-regulated in 25 dph cod head explants following RA treatment. In situ hybridizations revealed differential spatial distribution of the two isoforms and the predominant expression of cathepsin K in bone surrounding tissues. The present study indicates that RA causes a shift in the balance between osteoclast activity and osteoblast activity in favor of the latter.

Cathepsin B differential expression and enzyme processing and activity during Fundulus heteroclitus embryogenesis

The role of lysosomal proteases such as cathepsin B (Ctsb) and one of the paralogs of cathepsin L (Ctsla) during yolk metabolism in fish oocytes is well established. However, the function of Ctsb during embryogenesis, particularly in marine teleosts, has been poorly documented. In this study, the spatio-temporal expression of Ctsb and Ctsla, their enzymatic activities, and the processing of the Ctsb and its cellular localization, was investigated in developing embryos of the killifish (Fundulus heteroclitus). Both fhctsb and fhctsla transcript levels, as well as cathepsin B- and L-like activities, gradually increased in embryos from the 2-4 cell stage up to 7 days post-fertilization. During the morula to gastrula transition an increase of the active FhCtsb single chain form was followed by a rise in cathepsin B activity, which were apparently regulated by post-transcriptional mechanisms. During neurulation, a 8-fold increase in cathepsin B activity was accompanied by a more moderate increase in cathepsin L activity, which was 6-fold enhanced by 7 dpf. These increased catalytic activities were well-correlated to changes in the electrophoretic pattern of yolk proteins and a strong expression of fhctsb and its protein product in the yolk syncytial layer. The increase of cathepsin B activity was further correlated with an increment of the relative amount of the FhCtsb single and double chain forms, both active forms of FhCtsb. These results suggest that FhCtsb may be involved in the mechanisms underlying the onset of gastrulation in F. heteroclitus embryos, and may play complementary roles with FhCtsla during yolk metabolism.