Expression characterization, genomic structure and function analysis of fish ubiquitin-specific protease 18 (USP18) genes

Rainbow trout USP4 downregulates LPS-induced inflammation by removing the K63-linked ubiquitin chain on TAK1

Ubiquitin-specific protease 4 (USP4) is pivotal in negatively regulating the Toll-like receptor (TLR) signaling-mediated innate immune response. Although USP4 has been well studied in mammals, its role in TLR signaling pathways in fish remains largely unknown. In this study, we investigated the role of USP4 (OmUSP4) in regulating TLR response in rainbow trout Oncorhynchus mykiss. OmUSP4 contained the characteristic domains conserved in other USP4s: domain in USP (DUSP), ubiquitin-like (UBL), and the bi-part catalytic domain known as USP. OmUSP4 expression was increased in RTH-149 cells by stimulation with fish-pathogenic bacteria and bacterial ligands. Gain- and loss-of-function experiments revealed that OmUSP4 mitigated the activation of MAPKs and NF-κB, as well as the expression of pro-inflammatory cytokines in LPS-stimulated cells. OmUSP4 interacted with TAK1, a critical mediator in TLR-mediated NF-κB signaling pathways. LPS stimulation increased the K63-linked polyubiquitination of TAK1, which was significantly suppressed when OmUSP4 was compelled to be overexpressed. These results imply that OmUSP4 might function like mammals to downregulate LPS-induced inflammation in rainbow trout by removing the K63-linked ubiquitin chain on TAK1.

Grouper USP12 exerts antiviral activity against nodavirus infection

The ubiquitin-specific proteases (USPs) have attracted particular attention due to their multiple functions in different biological processes. USP12, a member of the USP family, has been demonstrated to exert critical roles in diverse cellular processes, including cell death, cancer and antiviral immunity. Here, we cloned a USP12 homolog from orange spotted grouper (Epinephelus coioides, E. coioides), and its roles in fish RNA virus replication were investigated. EcUSP12 contained a 1119-bp open reading frame (ORF) encoding a 372-amino acid polypeptide, which shared 100.00% and 91.32% identity with USP12 homolog of Etheostoma cragini and Homo sapiens, respectively. Sequence analysis indicated that EcUSP12 contained a conserved peptidase-C19G domain (aa 40-369). qPCR analysis showed that EcUSP12 transcript was most abundant in head kidney and spleen of grouper E. coioides. The expression of EcUSP12 was significantly upregulated in grouper spleen (GS) cells in response to red-spotted grouper nervous necrosis virus (RGNNV) infection. Subcellular localization analysis showed that EcUSP12 was evenly distributed throughout the cytoplasm, and mainly co-localized with endoplasmic reticulum (ER). Interestingly, during RGNNV infection, the endogenous distribution of EcUSP12 was obviously altered, and mostly overlapped with viral coat protein (CP). Co-Immunoprecipitation (Co-IP) assay indicated that EcUSP12 interacted with viral CP. In addition, overexpression of EcUSP12 significantly inhibited the replication of RGNNV in vitro, as evidenced by the decrease in viral gene transcription and protein synthesis during infection. Consistently, knockdown of EcUSP12 by small interfering RNA (siRNA) promoted the replication of RGNNV. Furthermore, EcUSP12 overexpression also increased the transcription level of inflammatory factors and interferon-related genes, including tumor necrosis factor α (TNF-α), interleukin (IL)-1β, IL-6, IL-8, interferon regulatory factor 3 (IRF3), and IRF7. Taken together, our results demonstrated that EcUSP12, as a positive regulator of IFN signaling, interacted with viral CP to inhibit virus infection.

Expression pattern, antiviral role and regulation analysis of interferon-stimulated gene 15 in black seabream, Acanthopagrus schlegelii

Interferon stimulated gene 15 (ISG15) is an IFN inducible ubiquitin-like protein and plays a critical role in immune response against viral infection. In this study, an ISG15 gene (AsISG15) was cloned and characterized from the marine fish black seabream, Acanthopagrus schlegelii. The full-length cDNA of AsISG15 was 1302 bp and encoded 155 amino acids containing two ubiquitin-like motifs and a LRGG conjugation domain. Multiple alignment and phylogenetic tree showed that AsISG15 shared 31-70% amino acid identity with other known ISG15s and had a closer evolutionary relationship with teleost ISG15s. In vitro, AsISG15 expression was inducible by poly I:C, LPS and red spotted nervous necrosis virus (RGNNV) in cultured black seabream brain cells. In vivo, AsISG15 was ubiquitously expressed in all examined tissues with higher expression levels in eye and gill, and the expression was significantly up-regulated in most tissues post RGNNV infection, especially in liver, spleen and kidney. The testing of antiviral activity showed that silencing AsISG15 significantly increased RGNNV replication in RGNNV infected AsS cells, and the LRGG domain was crucial for the anti-RGNNV activity of AsISG15. By promoter-driven luciferase reporter assay, we demonstrated that two IFN-stimulated response elements within the promoter region of AsISG15 and the promoter-proximal intron were essential for AsISG15 expression. Furthermore, our results showed that the gamma-IFN activation sequence located in the intron was required for the intron mediated enhancement for AsISG15 expression. Our results would provide insights for understanding the underlying regulation mechanism of ISG15 in teleost.

Negative regulation of the RLR-mediated IFN signaling pathway by duck ubiquitin-specific protease 18 (USP18)

Ubiquitin-specific protease 18 (USP18) plays an important role in regulating type I interferon (IFN) signaling in innate immunity, and has a crucial impact on the IFN therapeutic effect. Although significant progress has been made in elucidating USP18 function in mammals, the role of USP18 in ducks (duUSP18) remains poorly understood. In this study, we cloned the USP18 gene from white crested ducks by reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of complementary DNA (cDNA) ends. We determined that duUSP18 cDNA contains a 52-bp 5'UTR, a 1,131-bp open reading frame and a 356-bp 3'UTR, and encodes a 376-amino acid protein. Multiple sequence alignments showed that duUSP18 shares high similarity with USP18 from other vertebrates. Overexpression of duUSP18 inhibited nuclear factor-κB (NF-κB) and interferon regulatory factor 1 (IRF1) activity, and reduced IFN-β production following 5' triphosphate double-stranded RNA (5'ppp dsRNA) or lipopolysaccharide (LPS) stimulation. duUSP18 knockdown significantly activated 5'ppp dsRNA-induced and LPS-induced NF-κB and IRF1 activation, and induced IFN-β expression in duck embryo fibroblasts. Furthermore, Quantitative real-time PCR (qRT-PCR) revealed that overexpression or knockdown of duUSP18 could alter the expression of genes related to the RLR-mediated IFN signaling pathway following the treatment with 5'ppp dsRNA. In addition, site-directed mutation analysis revealed that cysteine 66 (C66), histidine 313 (H313), and histidine 321 (H321) of duUSP18 were critical for inhibiting IFN-β activity. Taken together, these results suggest that duck USP18 plays an important role in innate immune responses against double-stranded RNA viruses in the RLR-mediated IFN signaling pathway, and that further studies are warranted to elucidate its underlying mechanisms, which could provide molecular insights into the effect of the treatment of duck diseases.

Distinct herpesvirus resistances and immune responses of three gynogenetic clones of gibel carp revealed by comprehensive transcriptomes

Background

Gibel carp is an important aquaculture species in China, and a herpesvirus, called as Carassius auratus herpesvirus (CaHV), has hampered the aquaculture development. Diverse gynogenetic clones of gibel carp have been identified or created, and some of them have been used as aquaculture varieties, but their resistances to herpesvirus and the underlying mechanism remain unknown.

Results

To reveal their susceptibility differences, we firstly performed herpesvirus challenge experiments in three gynogenetic clones of gibel carp, including the leading variety clone A⁺, candidate variety clone F and wild clone H. Three clones showed distinct resistances to CaHV. Moreover, 8772, 8679 and 10,982 differentially expressed unigenes (DEUs) were identified from comparative transcriptomes between diseased individuals and control individuals of clone A⁺, F and H, respectively. Comprehensive analysis of the shared DEUs in all three clones displayed common defense pathways to the herpesvirus infection, activating IFN system and suppressing complements. KEGG pathway analysis of specifically changed DEUs in respective clones revealed distinct immune responses to the herpesvirus infection. The DEU numbers identified from clone H in KEGG immune-related pathways, such as “chemokine signaling pathway”, “Toll-like receptor signaling pathway” and others, were remarkably much more than those from clone A⁺ and F. Several IFN-related genes, including Mx1, viperin, PKR and others, showed higher increases in the resistant clone H than that in the others. IFNphi3, IFI44-like and Gig2 displayed the highest expression in clone F and IRF1 uniquely increased in susceptible clone A⁺. In contrast to strong immune defense in resistant clone H, susceptible clone A⁺ showed remarkable up-regulation of genes related to apoptosis or death, indicating that clone A⁺ failed to resist virus offensive and evidently induced apoptosis or death.

Conclusions

Our study is the first attempt to screen distinct resistances and immune responses of three gynogenetic gibel carp clones to herpesvirus infection by comprehensive transcriptomes. These differential DEUs, immune-related pathways and IFN system genes identified from susceptible and resistant clones will be beneficial to marker-assisted selection (MAS) breeding or molecular module-based resistance breeding in gibel carp.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3945-6) contains supplementary material, which is available to authorized users.

The evolution and functional diversification of the deubiquitinating enzyme superfamily

Ubiquitin and ubiquitin-like molecules are attached to and removed from cellular proteins in a dynamic and highly regulated manner. Deubiquitinating enzymes are critical to this process, and the genetic catalogue of deubiquitinating enzymes expanded greatly over the course of evolution. Extensive functional redundancy has been noted among the 93 members of the human deubiquitinating enzyme (DUB) superfamily. This is especially true of genes that were generated by duplication (termed paralogs) as they often retain considerable sequence similarity. Because complete redundancy in systems should be eliminated by selective pressure, we theorized that many overlapping DUBs must have significant and unique spatiotemporal roles that can be evaluated in an evolutionary context. We have determined the evolutionary history of the entire class of deubiquitinating enzymes, including the sequence and means of duplication for all paralogous pairs. To establish their uniqueness, we have investigated cell-type specificity in developmental and adult contexts, and have investigated the coemergence of substrates from the same duplication events. Our analysis has revealed examples of DUB gene subfunctionalization, neofunctionalization, and nonfunctionalization.