Zebrafish MARCH8 downregulates fish IFN response by targeting MITA and TBK1 for protein degradation

E3 ubiquitin ligase MARCH5 positively regulates Japanese encephalitis virus infection by catalyzing the K27-linked polyubiquitination of viral E protein and inhibiting MAVS-mediated type I interferon production

Membrane-associated RING-CH-type finger (MARCH) proteins, a class of E3 ubiquitin ligases, have been reported to be involved in the infection of multiple viruses and the regulation of type I interferon (IFN) production. However, the specific role and mechanisms by which MARCH proteins influence Japanese encephalitis virus (JEV) infection remain poorly understood. Here, we systematically investigate the functional relevance of MARCH proteins in JEV replication by examining the effects of siRNA-mediated knockdown of MARCHs on viral infection. We identified MARCH5 as a positive regulator of JEV replication. The knockout of MARCH5 dramatically reduced viral yields, whereas its overexpression significantly enhanced JEV replication. Mechanistically, MARCH5 specifically interacts with the JEV envelope (E) protein and promotes its K27-linked polyubiquitination at the lysine (K) residues 136 and 166. This ubiquitination enhances viral attachment to permissive cells. Substituting these lysine residues with arginine (R) attenuated JEV replication in vitro and reduced viral virulence in vivo. Furthermore, JEV infection upregulated the expression of MARCH5. We also discovered that MARCH5 degrades mitochondrial antiviral-signaling protein (MAVS) through the ubiquitin-proteasome pathway by catalyzing its K48-linked ubiquitination, thereby inhibiting type I IFN production in JEV-infected cells. This suppression of type I IFN further facilitates JEV infection. In conclusion, these findings disclosed a novel role of MARCH5 in positively regulating JEV infection and revealed an important mechanism employed by MARCH5 to regulate the innate immune response.IMPORTANCEJEV is the leading cause of viral encephalitis in many countries of Asia with an estimated 100,000 clinical human cases and causes economic loss to the swine industry. Until now, there is no clinically approved antiviral for the treatment of JEV infection. Although vaccination prophylaxis is widely regarded as the most effective strategy for preventing Japanese encephalitis (JE), the incidence of JE cases continues to rise. Thus, a deeper understanding of virus-host interaction will enrich our knowledge of the mechanisms underlying JEV infection and identify novel targets for the development of next-generation live-attenuated vaccines and antiviral therapies. To the best of our knowledge, this study is the first to identify MARCH5 as a pro-viral host factor that facilitates JEV infection. We elucidated two distinct mechanisms by which MARCH5 promotes JEV infection. First, MARCH5 interacts with viral E protein and mediates the K27-linked ubiquitination of E protein at the K136 and K166 residues to facilitate efficient viral attachment. Furthermore, double mutations of K136R-K166R attenuated JEV infection in vitro and reduced viral virulence in mice. Second, the upregulated expression of MARCH5 induced by JEV infection further suppresses the RIG-I-like receptor (RLR) signaling pathway to benefit viral infection. MARCH5 downregulates type I IFN production by conjugating the K48-linked polyubiquitin at the K286 of MAVS, which leads to MAVS degradation through the ubiquitin-proteasome pathway. In summary, this study provides novel insights into the role played by MARCH proteins in JEV infection and identifies specific ubiquitination sites on JEV E protein that could be targeted for viral attenuation and the development of antiviral therapeutics.

pacsin1 inhibits antiviral immunity by promoting MITA degradation through autophagy in miiuy croaker, Miichthysmiiuy

Pacsin1 is a crucial protein involved in vesicle formation and transport, and its role in neuronal development and cytosolic dynamics has been extensively studied. However, its involvement in immune regulation still needs to be better understood. In this study, we show that pacsin1 exerts a negative regulatory effect on RLR-mediated signaling pathways activated by SCRV or poly(I:C), thereby inhibiting MITA-mediated antiviral responses. Mechanistically, pacsin1 facilitates the degradation of MITA, thus impeding immune signaling. Additionally, overexpression of pacsin1 promotes the conversion of LC3B-I to LC3B-II, while treatment with the autophagy inhibitor ammonium chloride results in the accumulation of LC3B-II and prevents pacsin1-mediated MITA degradation. Our findings suggest that pacsin1 targets MITA for autophagic degradation, thereby suppressing the innate antiviral response in fish.

NLRC3 Attenuates Antiviral Innate Immune Response by Targeting IRF7 in Grass Carp (Ctenopharyngodon idelus)

NLRC3 belongs to the NOD-like receptor family and is recognized as a modulator of innate immune mechanisms. In this study, we firstly report that Ctenopharyngodon idelus NLRC3 (CiNLRC3) acts as a negative regulator in the antiviral immune response. Cinlrc3 is ubiquitously expressed across tested tissues, displaying particularly high expression in the intestine, spleen, gill and kidney. Notably, Cinlrc3 expression is markedly upregulated following grass carp reovirus (GCRV) infection both in vivo and in vitro. Functional assays reveal that the overexpression of CiNLRC3 hampers cellular antiviral responses, thereby facilitating viral replication. Conversely, the silencing of CiNLRC3 through siRNA transfection enhances these antiviral activities. Additionally, CiNLRC3 substantially diminishes the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR)-mediated interferon (IFN) response in fish. Subsequent molecular investigations indicates that CiNLRC3 interacts with the RLR molecule node, IRF7 but not IRF3, by degrading the IRF7 protein in a proteasome-dependent manner. Furthermore, CiNLRC3 co-localizes with CiIRF7 in the cytoplasm and impedes the IRF7-induced IFN response, resulting in impairing IRF7-mediated antiviral immunity. Summarily, these findings underscore the critical inhibitory role of teleost NLRC3 in innate immunity, offering new perspectives on its regulatory functions and potential as a target for resistant breeding in fish.

Molecular depiction and functional delineation of E3 ubiquitin ligase MARCH5 in yellowtail clownfish (Amphiprion clarkii)

Membrane-associated Ring-CH 5 (MARCH5) is a mitochondrial E3 ubiquitin ligase playing a key role in the regulation of mitochondrial dynamics. In mammals, MARCH5 negatively regulates mitochondrial antiviral signaling (MAVS) protein aggregation during viral infection and hampers downstream type I interferon signaling to prevent excessive immune activation. However, its precise functional role in the teleost immune system remains unclear. This study investigated the molecular characteristics and immune response of the MARCH5 ortholog in Amphiprion clarkii (A. clarkii; AcMARCH5). The predicted AcMARCH5 protein sequence consists of 287 amino acids with a molecular weight of 32.02 kDa and a theoretical isoelectric point of 9.11. It contains four C-terminal transmembrane (TM) domains and an N-terminal RING cysteine-histidine (CH) domain, which directly regulates ubiquitin transfer. Multiple sequence alignment revealed a high level of conservation between AcMARCH5 and its orthologs in other vertebrate species. Under normal physiological conditions, AcMARCH5 showed the highest mRNA expression in the muscle, brain, and kidney tissues of A. clarkii. Upon stimulation with polyinosinic:polycytidylic acid (Poly I:C), lipopolysaccharide (LPS), and Vibrio harveyi, AcMARCH5 expression was drastically modulated. Functional assays showed that overexpression of AcMARCH5 in fathead minnow (FHM) cells downregulated antiviral gene expression, accompanied by enhanced viral hemorrhagic septicemia virus (VHSV) replication. In murine macrophages, AcMARCH5 overexpression markedly reduced the production of pro-inflammatory cytokines in response to poly I:C treatment. Additionally, AcMARCH5 exhibited an anti-apoptotic effect in H2O2-treated FHM cells. Collectively, these results suggest that AcMARCH5 may play a role in maintaining cellular homeostasis under disease and stress conditions in A. clarkii.

Biochemical profiling of the protein encoded by grass carp reovirus genotype II

In this study, we obtained the whole genome sequence of GCRV-DY197 and investigated the localization, post-translational modifications, and host interactions of the 11 viral proteins encoded by GCRV-DY197 in grass carp ovary (GCO) cells. The whole genome sequence is 24,704 kb and contains 11 segments (S1-S11). Subcellular localization showed that the VP1, VP2, VP3, VP5, VP56, and VP35 proteins were localized in both cytoplasm and nucleus, whereas the NS79, VP4, VP41, VP6, and NS38 proteins were localized in the cytoplasm. The NS79 and NS38 proteins were phosphorylated, and the ubiquitination modification sites were identified in VP41 and NS38. An interaction network containing 9 viral proteins and 140 host proteins was also constructed. These results offer a theoretical basis for an in-depth understanding of the biochemical characteristics and pathogenic mechanism of GCRV-II.

USP46 promotes the interferon antiviral signaling in black carp by deubiquitinating TBK1

Ubiquitin-specific peptidase 46 (USP46) functions as a deubiquitinating enzyme, facilitating the removal of ubiquitin molecules attached to substrate proteins and playing a critical role in cancer and neurodegenerative diseases. However, its function in innate antiviral immunity is unknown. In this study we cloned and identified bcUSP46, a homolog of USP46 from black carp. We discovered that overexpression of bcUSP46 enhanced the transcription of interferon (IFN) promoters and increased the expression of IFN, PKR, and Mx1. In addition, bcUSP46 knockdown significantly inhibited the expression of ISG genes, as well as the antiviral activity of the host cells. Interestingly, when bcUSP46 was co-expressed with the RLR factors, it significantly enhanced the activity of the IFN promoter mediated by these factors, especially TANK-binding kinase 1 (TBK1). The subsequent co-immunoprecipitation (co-IP) and immunofluorescence (IF) assay confirmed the association between bcUSP46 and bcTBK1. Noteworthily, co-expression of bcUSP46 with bcTBK1 led to an elevation of bcTBK1 protein level. Further analysis revealed that bcUSP46 stabilized bcTBK1 by eliminating the K48-linked ubiquitination of bcTBK1. Overall, our findings highlight the unique role of USP46 in modulating TBK1/IFN signaling and enrich our knowledge of the function of deubiquitination in regulating innate immunity in vertebrates.

RING finger protein 122-like (RNF122L) negatively regulates antiviral immune response by targeting STING in common carp (Cyprinus carpio L.)

Stimulator of interferon genes (STING), as an imperative adaptor protein in innate immune, responds to nucleic acid from invading pathogens to build antiviral responses in host cells. Aberrant activation of STING may trigger tissue damage and autoimmune diseases. Given the decisive role in initiating innate immune response, the activity of STING is intricately governed by several posttranslational modifications, including phosphorylation and ubiquitination. Here, we cloned and characterized a novel RNF122 homolog from common carp (named CcRNF122L). Expression analysis disclosed that the expression of CcRNF122L is up-regulated under spring viremia of carp virus (SVCV) stimulation in vivo and in vitro. Overexpression of CcRNF122L hampers SVCV- or poly(I:C)-mediated the expression of IFN-1 and ISGs in a dose-dependent way. Mechanistically, CcRNF122L interacts with STING and promotes the polyubiquitylation of STING. This polyubiquitylation event inhibits the aggregation of STING and the subsequent recruitment of TBK1 and IRF3 to the signaling complex. Additionally, the deletion of the TM domain abolishes the negative regulatory function of CcRNF122L. Collectively, our discoveries unveil a mechanism that governs the STING function and the precise adjustment of the innate immune response in teleost.

Autophagy mediated degradation of MITA/TBK1/IRF3 by a hnRNP family member attenuates interferon production in fish

HnRNP A/B belongs to the heterogeneous nuclear ribonucleoprotein (hnRNP) family and plays an important role in regulating viral protein translation and genome replication. Here, we found that overexpression of hnRNP A/B promoted spring viremia of carp virus (SVCV) and cyprinid herpesvirus 3 (CyHV3) replication. Further, hnRNP A/B was shown to act as a negative regulator of type I interferon (IFN) response. Mechanistically, hnRNP A/B interacted with MITA, TBK1 and IRF3 to initiate their degradation. In addition, hnRNP A/B bound to the kinase domain of TBK1, the C terminal domain of MITA and IAD domain of IRF3, and the RRM1 domain of hnRNP A/B bound to TBK1, RRM2 domain bound to IRF3 and MITA. Our study provides novel insights into the functions of hnRNP A/B in regulating host antiviral response.

USP14 negatively regulates IFN signaling by dampening K63-linked ubiquitination of TBK1 in black carp

USP14 regulates the immune related pathways by deubiquitinating the signaling molecules in mammals. In teleost, USP14 is also reported to inhibit the antiviral immune response through TBK1, but its regulatory mechanism remains obscure. To elucidate the role of USP14 in the RLR/IFN antiviral pathway in teleost, the homolog USP14 (bcUSP14) of black carp (Mylopharyngodon piceus) has been cloned and characterize in this paper. bcUSP14 contains 490 amino acids (aa), and the sequence is well conserved among in vertebrates. Over-expression of bcUSP14 in EPC cells attenuated SVCV-induced transcription activity of IFN promoters and enhanced SVCV replication. Knockdown of bcUSP14 in MPK cells led to the increased transcription of IFNs and decreased SVCV replication, suggesting the improved antiviral activity of the host cells. The interaction between bcUSP14 and bcTBK1 was identified by both co-immunoprecipitation and immunofluorescent staining. Co-expressed bcUSP14 obviously inhibited bcTBK1-induced IFN production and antiviral activity in EPC cells. K63-linked polyubiquitination of bcTBK1 was dampened by co-expressed bcUSP14, and bcTBK1-mediated phosphorylation and nuclear translocation of IRF3 were also inhibited by this deubiquitinase. Thus, all the data demonstrated that USP14 interacts with and inhibits TBK1 through deubiquitinating TBK1 in black carp.

USP13 Cooperates with MARCH8 to Inhibit Antiviral Signaling by Targeting MAVS for Autophagic Degradation in Teleost

Mitochondrial antiviral signaling protein (MAVS), as a central adapter protein in retinoic acid-inducible gene I-like receptor signaling, is indispensable for innate antiviral immunity. Yet, the molecular mechanisms modulating the stability of MAVS are not fully understood in low vertebrates. In this study, we report that the deubiquitinase ubiquitin-specific protease 13 (USP13) acts as a negative regulator of antiviral immunity by targeting MAVS for selective autophagic degradation in teleost fish. USP13 is induced by RNA virus or polyinosinic:polycytidylic acid stimulation and acts as a negative regulator to potentiate viral replication in fish cells. Mechanistically, USP13 functions as a scaffold to enhance the interaction between MAVS and the E3 ubiquitin ligase MARCH8, thus promoting MARCH8 to catalyze MAVS through K27-linked polyubiquitination for selective autophagic degradation. Taken together, to our knowledge, our study demonstrates a novel mechanism by which viruses evade host antiviral immunity via USP13 in fish and provides a new idea for mammalian innate antiviral immunity.

A zebrafish NLRX1 isoform downregulates fish IFN responses by targeting the adaptor STING

In mammals, NLRX1 is a unique member of the nucleotide-binding domain and leucine-rich repeat (NLR) family showing an ability to negatively regulate IFN antiviral immunity. Intron-containing genes, including NLRX1, have more than one transcript due to alternative splicing; however, little is known about the function of its splicing variants. Here, we identified a transcript variant of NLRX1 in zebrafish (Danio rerio), termed NLRX1-tv4, as a negative regulator of fish IFN response. Zebrafish NLRX1-tv4 was slightly induced by viral infection, with an expression pattern similar to the full-length NLRX1. Despite the lack of an N-terminal domain that exists in the full-length NLRX1, overexpression of NLRX1-tv4 still impaired fish IFN antiviral response and promoted viral replication in fish cells, similar to the full-length NLRX1. Mechanistically, NLRX1-tv4 targeted STING for proteasome-dependent protein degradation by recruiting an E3 ubiquitin ligase RNF5 to drive the K48-linked ubiquitination, eventually downregulating the IFN antiviral response. Mapping of NLRX1-tv4 domains showed that its N-terminal and C-terminal regions exhibited a similar potential to inhibit STING-mediated IFN antiviral response. Our findings reveal that like the full-length NLRX1, zebrafish NLRX-tv4 functions as an inhibitor to shape fish IFN antiviral response.IMPORTANCEIn this study, we demonstrate that a transcript variant of zebrafish NLRX1, termed NLRX1-tv4, downregulates fish IFN response and promotes virus replication by targeting STING for protein degradation and impairing the interaction of STING and TBK1 and that its N- and C-terminus exhibit a similar inhibitory potential. Our results are helpful in clarifying the current contradictory understanding of structure and function of vertebrate NLRX1s.

TBK1 upregulates the interferon response against virus by the TBK1-IRF3/7 axis in yellow catfish (Pelteobagrus fulvidraco)

Yellow catfish (Pelteobagrus fulvidraco) is an important economic species of freshwater fish, widely distributed in China. Recently, viral diseases of yellow catfish have been identified in Chian (Hubei province), arising more attention to the viral immunity in P. fulvidraco. Tumor necrosis factor (TNF) receptor-associated factor NF-κB activator (TANK)-binding kinase 1 (TBK1) plays an essential role in IFN production and innate antiviral immunity. In the present study, we characterized the P. fulvidraco TBK1 (PfTBK1) and reported its function in interferon response. The full-length open reading frame (ORF) is 2184 bp encoding a protein with 727 amino acids, which is composed of four conserved domains, including KD, ULD, CCD1, and CCD2, similar to TBK1 in other species. Pftbk1 was widely expressed in all detected tissues by qPCR and was not inducible by the spring viremia of carp virus (SVCV), a single-strand RNA virus. In addition, the cellular distribution indicated that PfTBK1 was only located in the cytoplasm. Moreover, PfTBK1 induced strong IFN promoter activities through the Jak-stat pathway, and PfTBK1 interacted with and significantly phosphorylated IFN regulatory factor 3/7 (IRF3/7) in P. fulvidraco, promoting the nuclear translocation of pfIRF3 and PfIRF7, and PfTBK1 upregulated IFN response by PfTBK1-PfIRF3/7 axis. Above all, PfTBK1 triggered IFN response and strongly inhibited the replication of SVCV in EPC cells through induction of IFN downstream IFN-stimulated genes (ISGs). Summarily, this work reveals that PfTBK1 plays a positive regulatory role in IFN induction through the TBK1-IRF3/7 axis, laying a foundation for further exploring the molecular mechanism of the antiviral process in P. fulvidraco.

The emerging roles of MARCH8 in viral infections: A double-edged Sword

The host cell membrane-associated RING-CH 8 protein (MARCH8), a member of the E3 ubiquitin ligase family, regulates intracellular turnover of many transmembrane proteins and shows potent antiviral activities. Generally, 2 antiviral modes are performed by MARCH8. On the one hand, MARCH8 catalyzes viral envelope glycoproteins (VEGs) ubiquitination and thus leads to their intracellular degradation, which is the cytoplasmic tail (CT)-dependent (CTD) mode. On the other hand, MARCH8 traps VEGs at some intracellular compartments (such as the trans-Golgi network, TGN) but without inducing their degradation, which is the cytoplasmic tail-independent (CTI) mode, by which MARCH8 hijacks furin, a cellular proprotein convertase, to block VEGs cleavage. In addition, the MARCH8 C-terminal tyrosine-based motif (TBM) 222YxxL225 also plays a key role in its CTI antiviral effects. In contrast to its antiviral potency, MARCH8 is occasionally hijacked by some viruses and bacteria to enhance their invasion, indicating a duplex role of MARCH8 in host pathogenic infections. This review summarizes MARCH8's antiviral roles and how viruses evade its restriction, shedding light on novel antiviral therapeutic avenues.

march2 negatively regulates antiviral immune response by targeting tbk1 in grass carp (Ctenopharyngodon idella)

Grass carp is one of the most economically important fish species. Hemorrhagic diseases caused by grass carp reovirus (GCRV) can seriously damage the economic yield of grass carp. Therefore, antiviral research on grass carp is urgently needed. Membrane-associated RING-CH2 (MARCH2) negatively regulates the innate immune response in mice. However, little is known about the role of march2 in the antiviral innate immune response in teleost fish. Our present study showed that march2 has high homology in grass carp, its orthologs, and mammals, and has the same amino acid sequence in grass carp and crucian carp. Overexpression of Cimarch2 (Ctenopharyngodon idella march2) significantly inhibited interferon (IFN) activation induced by Polyinosinic-polycytidylic acid (poly I: C), spring viremia of carp virus (SVCV), and GCRV. However, knocking down Cimarch2 enhanced the activation of IFN induced by poly I: C, SVCV, and GCRV. Overexpression of Cimarch2 can promotes viral replication. Mechanistically, Cimarch2 tightly bound to TANK-binding kinase 1 (tbk1) and downregulated tbk1 through the proteasome pathway. Our results demonstrated the potential role of Cimarch2 in the antiviral breeding of grass carp.

Zebrafish MARCH7 negatively regulates IFN antiviral response by degrading TBK1

Membrane-associated RING-CH-type finger (MARCH) proteins have been reported to regulate type I IFN production during host antiviral innate immunity. The present study reported the zebrafish MARCH family member, MARCH7, as a negative regulator in virus-triggered type I IFN induction via targeting TANK-binding kinase 1 (TBK1) for degradation. As an IFN-stimulated gene (ISG), we discovered that MARCH7 was significantly induced by spring viremia of carp virus (SVCV) or poly(I:C) stimulation. Ectopic expression of MARCH7 reduced the activity of IFN promoter and dampened the cellular antiviral responses triggered by SVCV and grass carp reovirus (GCRV), which concomitantly accelerated the viral replication. Accordingly, the knockdown of MARCH7 by siRNA transfection significantly promoted the transcription of ISG genes and inhibited SVCV replication. Mechanistically, we found that MARCH7 interacted with TBK1 and degraded it via K48-linked ubiquitination. Further characterization of truncated mutants of MARCH7 and TBK1 confirmed that the C-terminal RING of MARCH7 is essential in the MARCH7-mediated degradation of TBK1 and the negative regulation of IFN antiviral response. This study reveals a molecular mechanism by which zebrafish MARCH7 negatively regulates the IFN response by targeting TBK1 for protein degradation, providing new insights into the essential role of MARCH7 in antiviral innate immunity.

Yellow catfish RIO kinases (RIOKs) negatively regulate fish interferon-mediated antiviral response

In mammals, right open reading frame kinases (RIOKs) are initially reported to participate in cancer cell proliferation, apoptosis, migration and invasion, and recently they have been related to host immune response. Little is known about the homologs of RIOKs in fish. In the current study, we cloned three homologous genes of RIOK family in yellow catfish (Pelteobagrus fulvidraco), termed Pfriok1, Pfriok2 and Pfriok3. Pfriok1, Pfriok2 and Pfriok3 were constitutively expressed at relatively high levels in yellow catfish tissues, and their mRNA levels were not changed under viral infection. Individual overexpression of PfRIOK1, PfRIOK2 and PfRIOK3 attenuated fish interferon (IFN) response, thereby promoting viral replication in fish cells. Mechanistically, yellow catfish RIOK proteins downregulated fish IFN response through attenuating TBK1 protein levels in cytoplasm. Our findings suggest that yellow catfish RIOK1, RIOK2 and RIOK3 are involved in downregulating fish IFN antiviral response.

Identification of multifunctionality of grass carp (Ctenopharyngodon idella) TBK1 during bacterial infection

TBK1 is an atypical IκB kinase family member with a set of functions. It is involved in congenital immunization and autophagy in mammals. In this study, we reported that grass carp TBK1 gene expression could be upregulated by bacterial infection. Overexpression of TBK1 could decrease the number of adhesive bacteria in CIK cells. TBK1 could promote cellular migration, proliferation, vitality, and anti-apoptosis ability. Furthermore, the expression of TBK1 could activate the NF-κB signaling pathway by inducing inflammatory cytokines. In addition, we found that the grass carp TBK1 could cause the autophagy level of CIK cells within the decreasing level of p62 protein. Our finding indicated that TBK1 participated in grass carp innate immune progress and autophagy. This study provides evidence of the positive regulation of TBK1 in teleost innate immunity with its multiple functions. It thus may provide important information about the defense and immune mechanisms used by teleost against pathogens.

Expression profile, subcellular localization of MARCH4 and transcriptome analysis of its potential regulatory signaling pathway in large yellow croaker (Larimichthys crocea)

Membrane-associated RING-CH (MARCH) family, as Ring-type E3 ligases, have attracted extensive attention to their immune functions. MARCH4 plays an essential role in regulating immune response in mammal. In the present study, it is the first to report on MARCH4 characteristics and signal pathway in fish. MARCH4 in large yellow croaker Larimichthys crocea (named as LcMARCH4) encodes a RING-CH domain and two TM domains, as well as other function domains, including an N-terminal proline rich domain, an AxxxG-motif in TM1, a tyrosine-based YXXØ motif, and a C-terminal PDZ-binding domain. LcMARCH4 is a tissue-specific protein with highly significant expression in brain. The mRNA transcripts of LcMARCH4 were significantly induced in the main organs (skin, gill, spleen, and head-kidney) by C. irritans infection. Consistently, significant increase was observed in spleen and head-kidney after LPS, Poly I:C stimulation and V. parahaemolyticus infection. Subcellular localization analysis showed that LcMARCH4 was localized in the cytoplasm and membrane. Moreover, we found 46 DEGs in a comparative transcriptome analysis between the LcMARCH4 overexpression group and control vector group. The analysis showed that HSPA6, HSPA1B and DNAJB1 might play important regulatory roles to MARCH4 in fish. Notably, two noncoding RNA, both RN7SL1 and RN7SL2, the expression levels went up in MARCH4 overexpression cells. Taken together, this study will provide new insights into finfish MARCH4 and its potential regulatory signaling pathway as well.