Ubiquitin-specific Protease Family Research Articles

Genome-wide identification and characterization of UBP gene family in wheat (Triticum aestivum L.).

Ubiquitination is essential for plant growth and development. Deubiquitination cooperates with ubiquitination to regulate the ubiquitination levels of target proteins. The ubiquitin-specific protease (UBP) family is the largest group of deubiquitinases (DUBs), which perform extensive and significant roles in eukaryotic organisms. However, the UBP genes in wheat (TaUBPs) are not identified, and the functions of TaUBPs are unknown. The present study identified 97 UBP genes in the whole genome of T. aestivum. These genes were divided into 15 groups and non-randomly distributed on chromosomes of T. aestivum. Analyses of evolutionary patterns revealed that TaUBPs mainly underwent purification selection. The studies of cis-acting regulatory elements indicated that they might be involved in response to hormones. Quantitative real-time PCR (qRT-PCR) results showed that TaUBPs were differentially expressed in different tissues. Besides, several TaUBPs were significantly up-regulated when plants were treated with salicylic acid (SA), implying that these DUBs may play a role in abiotic stress responses in plants and few TaUBPs displayed differential expression after viral infection. Furthermore, TaUBP1A.1 (TraesCS1A02G432600.1) silenced by virus-induced gene silencing (VIGS) facilitates Chinese wheat mosaic virus (CWMV) infection in wheat, indicating that TaUBP1A.1 may be involved in a defense mechanism against viruses. This study comprehensively analyzed the UBP gene family in wheat and provided a basis for further research of TaUBPs functions in wheat plant response to viral infection.

USP48 Is Upregulated by Mettl14 to Attenuate Hepatocellular Carcinoma via Regulating SIRT6 Stabilization.

Exploiting cancer metabolism for the clinical benefit of patients with hepatocellular carcinoma (HCC) is a topic under active investigation. Ubiquitin-specific peptidase 48 (USP48), a member of the ubiquitin-specific protease family, is involved in tumor growth, inflammation, and genome stability. However, the role of USP48 in HCC tumorigenesis remains unknown. In this study, we report that expression of USP48 is downregulated in diethylnitrosamine-induced liver tumorigenesis in mice as well as in human HCC. USP48 physically bound and stabilized SIRT6 by K48-linked deubiquitination at the K33 and K128 sites of SIRT6, which impeded metabolic reprogramming to hamper HCC tumorigenesis. Moreover, methyltransferase-like 14 (Mettl14)-induced m6A modification participated in the regulation of USP48 in HCC by maintaining USP48 mRNA stability. Our work uncovers the tumor-suppressive function of the Mettl14-USP48-SIRT6 axis via modulation of glycolysis, providing new insights into the critical roles of metabolic activities in HCC and identifying an attractive target for future treatment studies. SIGNIFICANCE: These findings demonstrate that USP48 is regulated by Mettl14-induced m6A modification and stabilizes SIRT6 to attenuate HCC glycolysis and malignancy.

USP15: a review of its implication in immune and inflammatory processes and tumor progression.

The covalent post-translational modification of proteins by ubiquitination not only influences protein stability and half-life, but also several aspects of protein function including enzymatic activity, sub-cellular localization, and interactions with binding partners. Protein ubiquitination status is determined by the action of large families of ubiquitin ligases and deubiquitinases, whose combined activities regulate many physiological and cellular pathways. The Ubiquitin Specific Protease (USP) family is one of 8 subfamilies of deubiquitinating enzymes composed of more than 50 members. Recent studies have shown that USP15 plays a critical role in regulating many aspects of immune and inflammatory function of leukocytes in response to a broad range of infectious and autoimmune insults and following tissue damage. USP15 regulated pathways reviewed herein include TLR signaling, RIG-I signaling, NF-kB, and IRF3/IRF7-dependent transcription for production of pro-inflammatory cytokines and type I interferons. In addition, USP15 has been found to regulate pathways implicated in tumor onset and progression such as p53, and TGF-β signaling, but also influences the leukocytes-determined immune and inflammatory microenvironment of tumors to affect progression and outcome. Hereby reviewed are recent studies of USP15 in model cell lines in vitro, and in mutant mice in vivo with reference to available human clinical datasets.

Ubiquitin-specific peptidase 8 regulates proliferation and early differentiation of sheep skeletal muscle satellite cells

Ubiquitin-specific protease 8 (USP8), a member of the ubiquitin-specific protease (USP) family, was originally identified as playing a role in the regulation of growth and cell cycle. However, its functional role in myogenesis is unknown. In this study, we investigated the role of USP8 in proliferation and differentiation of sheep skeletal muscle satellite cells. The results showed that the expression level of USP8 was significantly increased on days 2 and 3 following the induction of the differentiation process. Furthermore, knocking down USP8 resulted in a significant increase in myogenin-positive cells, and promoted early differentiation of satellite cells by regulating the expression level of paired box 7 (PAX7). Additionally, knocking down USP8 suppressed muscle satellite cell proliferation, possibly explaining that the relative mRNA level of USP8 was linearly related to muscle fibre density of Hu sheep. Overall, our research demonstrates that USP8 plays a role in proliferation and early differentiation of skeletal muscle satellite cells.

USP47 promotes apoptosis in rat myocardial cells after ischemia/reperfusion injury via NF-κB activation.

An increasing number of studies have associated nuclear factor-κB (NF-κB) activation to the progression of myocardial infarction (MI). Multiple members of the ubiquitin-specific protease (USP) family regulate the NF-κB signaling pathway. This study attempted to investigate the function and underlying mechanism of USP family members in MI. Monocytes were isolated from peripheral blood samples of MI and healthy control, and the expression of several USP family members and NF-κB was examined. After USP47 knockdown or overexpression, cell apoptosis, related protein levels, and NF-κB promoter activity were measured. We found that USP47 and NF-κB expression was significantly increased in MI, and USP47 was positively correlated with NF-κB. In a rat H9c2 myocardial cell ischemia/reperfusion (I/R) injury model, USP47 expression was increased in a time-dependent manner. USP47 knockdown decreased I/R injury-induced apoptosis, with increased survivin and cytoplasmic NF-κB and decreased cleaved caspase-3 and nuclear NF-κB. USP47-induced apoptosis was potently counteracted by the NF-κB inhibitor, and cytoplasmic NF-κB was increased and nuclear NF-κB was decreased. Luciferase reporter showed that USP47 promotes NF-κB promoter activity. These results suggested that USP47 expression may be correlated with MI progression. USP47 knockdown attenuated myocardial cell I/R injury by inhibiting apoptosis.

The USP22 promotes the growth of cancer cells through the DYRK1A in pancreatic ductal adenocarcinoma.

As a member of the ubiquitin-specific protease (USP) family, USP22 could remove ubiquitin moieties from its target proteins to control the function of the target proteins. Accumulating studies show that USP22 essentially participates in diverse types of cancer as an oncogene-like protein. However, the roles of USP22 in human pancreatic ductal adenocarcinoma (PDAC) and the underlying mechanism are unknown. Here we report that USP22 promotes the growth of PDAC cells by promoting the expression of dual-specificity tyrosine regulated kinase 1A (DYRK1A). Our results showed that the expression levels of USP22 were up-regulated in human PDAC tissues and cell lines (BxPC-3, AsPC-1, MIA-PaCa-2, PANC-1, and CAPAN-1). Lentivirus-mediated knockdown of USP22 repressed the rate of proliferation and capacity of colony formation of BxPC3 and CAPAN1 cancer cells and USP22 overexpression promoted the proliferation and capacity of the colony formation of BxPC3 and CAPAN1 cancer cells. The further mechanism study showed that USP22 elevated the expression of the mRNA and protein levels of DYRK1A in PDAC cancer cells. Inhibition of DYRK1A with EHT-5732 or lentivirus-mediated knockdown of DYRK1A blocked the function of USP22 overexpression in the regulation of the proliferation and colony formation of PDAC cells. Taken together, our findings demonstrated that USP22 overexpression in PDAC promoted the growth of the cancer cells partially through upregulating the expression of DYRK1A.

The role of USP34 in the fixation of titanium implants in murine models.

Ubiquitin-specific protease 34 (USP34), a member of the ubiquitin-specific protease family, regulates osteogenic differentiation of bone marrow mesenchymal stem cells via bone morphogenetic protein signaling. This study aimed to investigate the role of USP34 in fixation of titanium implants in mouse models. Eight-week-old Usp34-knockout (Prx1-Cre;Usp34f/f ) mice and their Usp34 wild-type (Usp34f/f ) control littermates were used. Experimental titanium implants were inserted into the distal ends of femurs and the edentulous area of maxillae. Two and four weeks after surgery, samples of femur and maxilla were obtained, and micro-computed tomography scanning, histomorphometric analyses, and push-in tests were performed on the samples. Compared with controls, Prx1-Cre;Usp34f/f mice showed reduced bone volume for both femurs and maxillae; a decreased femoral bone-implant contact ratio (BIC) at 2wk [mean (standard error of the mean): 62.17% (2.15%) vs. 44.06% (3.45%)] and 4wk [72.46% (1.61%) vs. 64.53% (1.93%)]; decreases in femoral bone volume fraction (BV/TV) and push-in resistance; and lower BIC and BV/TV of the maxillae. Taken together, our data demonstrate that specific deletion of Usp34 in mesenchymal stem cells impairs fixation of titanium implants in mice.

Systematic characterization of the ubiquitin-specific proteases in Magnaporthe oryzae

Ubiquitin-specific protease (UBP) family is the largest group of deubiquitinases, which plays important roles in eukaryotic organisms. Comprehensive analysis of UBP genes has not been conducted in the plant pathogenic fungi. In this study, 11 putative UBP genes were identified and characterized in the rice blast fungus Magnaporthe oryzae. Expression profile analysis showed that UBP3, UBP6, UBP12 and UBP14 were highly expressed in different tissues of M. oryzae. In all ubp mutants, especially Δubp3, Δubp12 and previously reported Δubp14, the ubiquitination levels were evidently elevated, which is consistent with their molecular roles in de-ubiquitination. The Δubp1, Δubp3, Δubp4, Δubp8 and Δubp14 mutants were reduced in colony growth. Most of the ubp mutants were severely reduced in conidia production capacity, indicating important roles of the UBPs in conidia formation. Except for Δubp2 and Δubp16, all of the other mutants were decreased in virulence to host plants and defective in invasive growth. These ubp mutants also induced massive ROS accumulation in host cells. We also found that the UBPs may function as both positive and negative regulators in stress response and nutrient utilization of M. oryzae. Collectively, UBPs are important for development, stress response, nutrient utilization and infection of M. oryzae.

USP32 promotes tumorigenesis and chemoresistance in gastric carcinoma via upregulation of SMAD2.

USP32, a member of the ubiquitin-specific proteases family, has been implicated in the development of breast cancer and small lung cancer. However, its biological functions and clinical significance in gastric cancer (GC) remain unclear. In the present study, we reported that knockdown or depletion of USP32 significantly inhibited GC cell proliferation and migration in vitro and in vivo, indicating that USP32 functions as an oncogene in GC. Importantly, results from immunohistochemical staining in a tissue microarray revealed that USP32 was upregulated in GC tissues compared with paracancerous tissues. Further analyses showed that high expression of USP32 was closely related with high T-staging and poor outcomes of GC patients. Mechanistically, USP32 silencing caused a decrease in the expression of SMAD2, which resulted in the inhibitory effects of GC cells on growth, motility, and chemoresistance to cisplatin. Therefore, our findings strongly suggest the involvement of USP32 in GC progression and provide a potential target for future therapy of GC.

Ubiquitin-Specific Protease 10 Suppresses Cardiac Hypertrophy by Inhibiting Sirt6

Background and Purpose: Cardiac hypertrophy (CH) is a physiological response that compensates for blood pressure overload. Under pathological conditions, hypertrophy can evolve to heart failure as a consequence of the disorganized growth of cardiomyocytes and cardiac tissue. Ubiquitin-specific protease 10 (USP10) is a member of the ubiquitin-specific protease family of cysteine proteases, which are involved in viral infection, oxidative stress, lipid drop formation and heat shock. However, the role of USP10 in CH remains largely unclear. Here, we investigated the roles of USP10 in CH. Experimental Approach: In this study, by utilizing conditional cardiac-specific USP10 knockout (USP10-CKO) mice and USP10- transgenic(USP10-TG) mice, we examined the role of USP10 in hypertrophic hearts. We further examined the specific function of USP10 in cardiomyocytes. Key Results: We show that USP10 expression increased in murine hypertrophic hearts. Mice deficient in USP10 in the heart exhibited an aggravated aortic banding (AB)-induced CH phenotype. However, overexpression of USP10 protected against pressure overload-induced hypertrophy. At the molecular level, the prevention of CH in the absence of USP10 involves elevated Akt pathway components, which are key elements that regulate cell apoptosis and proliferation. Moreover, USP10 physically binds to Sirt6 and inhibits Akt phosphorylation. Conclusion and Implications: These observations demonstrate that USP10 functions as a positive switch in CH. Funding Statement: This work was supported by grants from National Natural Science Foundation of China (81770048;81970242); Cooperative Project of Academy training Foundation of Zhengzhou University(2016-BSTDJJ-13). Declaration of Interests: The authors stated: None. Ethics Approval Statement: All animal use protocols were approved by the Animal Care and Use Committee of The First Affiliated Hospital of Zhengzhou University. The related procedures were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals.

Ubiquitin-specific peptidase 46 (USP46) suppresses renal cell carcinoma tumorigenesis through AKT pathway inactivation

USP46, a member of the ubiquitin-specific protease family, plays essential roles in cancer cell proliferation and metastasis and is used as a candidate target for cancer therapeutics. However, the effects of USP46 on renal cell carcinoma (RCC) and its underlying molecular mechanism remain unknown. In this study, the predictive and prognostic relevance of USP46 in RCC, patient-derived primary tissues, and normal liver tissues obtained from the TCGA dataset were analyzed for the USP46 mRNA levels or prognostic relevance. Gain-of-function or loss-of-function assays were used to evaluate the vital roles of USP46 in tumor cell proliferation and cell migration. As a result, the USP46 expression level in RCC is highly decreased compared to normal tissues, and the Kaplan-Meier curve showed that USP46 high expression patients had good prognoses. Functionally, the forced expression of USP46 significantly restrained tumor cell proliferation, colony formation, and cell migration. The shRNA mediated USP46 knockdown cells exhibited the opposite results. We further showed that ectopically expressed USP46 obviously inhibited the AKT signaling pathway in cancer cells, while USP46 depletion caused a dramatic increase in AKT activity reflected by phosphorylation in the serine and threonine residues of AKT or downstream p70S6K1. Importantly, MK2206, a specific AKT inhibitor, completely counteracted the effects on cell proliferation, cell migration, and AKT activity in the USP46 depletion cells. We thus revealed a novel mechanism of USP46 regulation in RCC, and our data indicate that USP46 is a tumor suppressor in RCC via AKT signaling pathway inactivation.

USP21 deubiquitinase promotes pancreas cancer cell stemness via Wnt pathway activation.

The ubiquitin-specific protease (USP) family is the largest group of cysteine proteases. Cancer genomic analysis identified frequent amplification of USP21 (22%) in human pancreatic ductal adenocarcinoma (PDAC). USP21 overexpression correlates with human PDAC progression, and enforced expression of USP21 accelerates murine PDAC tumor growth and drives PanIN to PDAC progression in immortalized human pancreatic ductal cells. Conversely, depletion of USP21 impairs PDAC tumor growth. Mechanistically, USP21 deubiquitinates and stabilizes the TCF/LEF transcription factor TCF7, which promotes cancer cell stemness. Our work identifies and validates USP21 as a PDAC oncogene, providing a potential druggable target for this intractable disease.

USP10 protects against cerebral ischemia injury by suppressing inflammation and apoptosis through the inhibition of TAK1 signaling

Cerebral ischemia is a leading cause of death and long-term disability in the world. Multiple signaling pathways play essential roles in the process. Therefore, identifying the unknown important modulators of these pathways may supply promising therapeutic targets for the treatment of cerebral ischemia. Ubiquitin-specific protease 10 (USP10) is a member of the ubiquitin-specific protease family of cysteine proteases with enzymatic activity to cleave ubiquitin from ubiquitin-conjugated protein substrates, and is involved in multiple pathologies. However, the effects of USP10 in cerebral ischemia-reperfusion (I/R) injury remain unclear. Here, we reported that USP10 expression was markedly decreased in wild type (WT) mice after cerebral I/R injury. USP10 knockout (KO) mice showed significantly elevated infarct size and the neurological deficit score after cerebral I/R operation. USP10 deletion also promoted inflammatory response in ischemic penumbra of cortical regions by further accelerating nuclear factor κB (NF-κB) signaling pathway. In addition, apoptosis was markedly induced in USP10-knockout mice after cerebral I/R injury compared to the WT mice. The c-Jun N-terminal kinase-mitogen-activated protein kinase (JNK-MAPK) signaling induced by cerebral I/R injury was further aggravated in USP10–KO mice. Finally, USP10 was found to display protective effects against cerebral I/R injury through direct interaction with transforming growth factor β-activated kinase 1 (TAK1). Thus, USP10 might be a protective factor in cerebral I/R injury. Modulation of USP10/TAK1 might be a promising strategy to prevent this pathological process.

FLA, which encodes a homolog of UBP, is required for chlorophyll accumulation and development of lemma and palea in rice.

FLA, the homolog of ubiquitin-specific protease does not have deubiquitination activity, but it is essential for flower and chloroplast development in rice. Ubiquitin-specific proteases (UBPs) are widely distributed and highly conserved proteins and are also members of the most important family of deubiquitination enzymes. Although the functions and phylogenies of UBPs from yeast, mammals and Arabidopsis have been widely reported, the functions and evolutionary relationships of UBPs in rice remain unclear. In this study, we characterized the rice flower and leaf color aberrant mutant (fla), which exhibited a variety of developmental defects, including abnormal floral organs and pollen development, and leaf bleaching. We isolated FLA by positional cloning and found that it encodes a homolog of ubiquitin-specific protease. FLA is a ubiquitously expressed gene with the highest expression in floral organs. Subcellular localization analysis indicated that FLA is a cell membrane protein. Through searches of the rice genome database ( http://rice.plantbiology.msu.edu ), we identified 35 UBP family members in the rice genome. These proteins were grouped into 16 subfamilies based on phylogenetic analysis, and FLA was found to belong to the G8 subfamily. In vitro activity assays revealed that FLA does not have deubiquitination activity. Our data suggest that FLA plays an important role in the development of floral organs and chloroplast in rice, but that this role probably does not involve deubiquitination activity, because FLA does not have an active site and deubiquitination activity.

USP18 - a multifunctional component in the interferon response.

Ubiquitin-specific proteases (USPs) represent the largest family of deubiquitinating enzymes (DUB). These proteases cleave the isopeptide bond between ubiquitin and a lysine residue of a ubiquitin-modified protein. USP18 is a special member of the USP family as it only deconjugates the ubiquitin-like protein ISG15 (interferon-stimulated gene (ISG) 15) from target proteins but is not active towards ubiquitin. Independent of its protease activity, USP18 functions as a major negative regulator of the type I interferon response showing that USP18 is – at least – a bifunctional protein. In this review, we summarise our current knowledge of protease-dependent and -independent functions of USP18 and discuss the structural basis of its dual activity.

Ubiquitin-Specific Peptidase 10 (USP10) Inhibits Hepatic Steatosis, Insulin Resistance, and Inflammation Through Sirt6.

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, insulin resistance and inflammation, and the pathogenic mechanism of NAFLD is poorly understood. Ubiquitin-specific peptidase 10 (USP10), a member of the ubiquitin-specific protease family, is involved in environmental stress responses, tumor growth, inflammation, and cellular metabolism. However, the role of USP10 in hepatic steatosis, insulin resistance, and inflammation remains largely unexplored. USP10 expression was detected in livers of patients with NAFLD, mice with high-fat diet (HFD)-induced obesity, and genetically obese (ob/ob) mice, as well as in palmitate-induced hepatocytes. The function of USP10 in hepatic steatosis, insulin resistance, and inflammation was investigated using hepatocyte-specific USP10 deficiency or overexpression in mice induced by HFD treatment or genetic defect. The molecular mechanisms underlying USP10-regulated hepatic steatosis were further investigated in HFD-treated mice. USP10 expression was significantly decreased in the fatty livers of NAFLD patients and obese mice and in palmitate-treated hepatocytes. USP10 deficiency exacerbated the metabolic dysfunction induced by HFD treatment for 12 weeks. Conversely, USP10 overexpression significantly suppressed metabolic dysfunction in mice after HFD treatment and inhibited the development of NAFLD in ob/ob mice. Further investigation indicated that USP10 regulates hepatic steatosis by interacting with Sirt6 and inhibiting its ubiquitination and degradation. Sirt6 overexpression markedly ameliorated the effects of USP10 deficiency in hepatic steatosis, insulin resistance, and inflammation. Conversely, Sirt6 deficiency decreased the ameliorative effects of USP10 overexpression in response to HFD treatment. Conclusion: USP10 inhibits hepatic steatosis, insulin resistance, and inflammation through Sirt6.

Characterization of the Ubiquitin Specific Protease (USP) family members in the fast and slow muscle fibers from Chinese perch (Siniperca chuatsi)

Skeletal muscle atrophy results from fasting, disuse and other systemic diseases. Muscle atrophy is associated with increased muscle protein degradation via the Ubiquitin proteasome system (UPS). The Ubiquitin Specific Proteases (USPs), also known as deubiquitinating enzymes, regulates a wide variety of cellular processes in skeletal muscle. In our study, among the 41 members of the USP family identified in the skeletal muscle transcriptome of Chinese perch, 24 USPs were differentially expressed between the fast and slow muscle fibers. The expressional profile of 4 muscle-related USPs (USP10, USP14, USP19, USP45) was investigated in the fast and slow muscle in response to fasting at 4 and 7 days. The results showed that the expression of USP10, USP14 and USP19 was significantly increased in the fast muscle after fasting for 4 days and 7 days. But only the USP10 and USP14 had significantly increased at 7 days of fasting in the slow muscle. The expression of MAFbx and MuRF1 up-regulated and major myofibrillar genes down-regulated, indicating that all of these four USPs are involved in the protein degradation of the fast and slow muscle.

The deubiquitinase USP21 stabilizes MEK2 to promote tumor growth

Deubiquitinases (DUBs) play essential roles in normal cell proliferation and tumor growth. However, the molecular mechanisms of DUBs on hepatocellular carcinoma (HCC) remains largely unknown. In this study, based on analysis of several HCC datasets, we found that the USP21 gene, which encodes a member of the ubiquitin-specific protease family, is highly amplified and overexpressed in HCCs, with the extent of this up-regulation significantly correlating with poor clinical outcomes. Inhibition of USP21 in HCC cell lines decreased cell proliferation, anchorage-independent growth, cell cycle progression, and in vivo tumor growth. Conversely, ectopic expression of USP21 transformed the normal human hepatocyte line HL-7702 and increased the tumorigenicity of the HCC cell line MHCC97L. Mechanistically, USP21 stabilized MEK2 by decreasing its polyubiquitination at Lys48, thereby activating the ERK signaling pathway. Importantly, MEK2 partially mediated the optimal expression of USP21-mediated oncogenic phenotypes. These findings indicate that USP21-mediated deubiquitination and stabilization of MEK2 play a critical role in HCC development.

Structure-Guided Development of a Potent and Selective Non-covalent Active-Site Inhibitor of USP7

Deubiquitinating enzymes (DUBs) have garnered significant attention as drug targets in the last 5-10 years. The excitement stems in large part from the powerful ability of DUB inhibitors to promote degradation of oncogenic proteins, especially proteins that are challenging to directly target but which are stabilized by DUB family members. Highly optimized and well-characterized DUB inhibitors have thus become highly sought after tools. Most reported DUB inhibitors, however, are polypharmacological agents possessing weak (micromolar) potency toward their primary target, limiting their utility in target validation and mechanism studies. Due to a lack of high-resolution DUB⋅small-molecule ligand complex structures, no structure-guided optimization efforts have been reported for a mammalian DUB. Here, we report a small-molecule⋅ubiquitin-specific protease (USP) family DUB co-structure and rapid design of potent and selective inhibitors of USP7 guided by the structure. Interestingly, the compounds are non-covalent active-site inhibitors.

Replication of a low-pathogenic avian influenza virus is enhanced by chicken ubiquitin-specific protease 18.

Previous research revealed the induction of chicken USP18 (chUSP18) in the lungs of chickens infected with highly pathogenic avian influenza viruses (HPAIVs). This activity was correlated with the degree of pathogenicity of the viruses to chickens. As mammalian ubiquitin-specific protease (USP18) is known to remove type I interferon (IFN I)-inducible ubiquitin-like molecules from conjugated proteins and block IFN I signalling, we explored the function of the chicken homologue of USP18 during avian influenza virus infection. With this aim, we cloned chUSP18 from cultured chicken cells and revealed that the putative chUSP18 ORF comprises 1137 bp. Comparative analysis of the predicted aa sequence of chUSP18 with those of human and mouse USP18 revealed relatively high sequence similarity among the sequences, including domains specific for the ubiquitin-specific processing protease family. Furthermore, we found that chUSP18 expression was induced by chicken IFN I, as observed for mammalian USP18. Experiments based on chUSP18 over-expression and depletion demonstrated that chUSP18 significantly enhanced the replication of a low-pathogenic avian influenza virus (LPAIV), but not an HPAIV. Our findings suggest that chUSP18, being similar to mammalian USP18, acts as a pro-viral factor during LPAIV replication in vitro.