Persistent inflammation plays a pivotal role in the initiation and progression of renal fibrosis. Activation of the pattern recognition receptor retinoic acid-inducible gene-I (RIG-I) is implicated in the initiation of inflammation. This study aimed to investigate the upstream mechanisms that regulates the activation of RIG-I and its downstream signaling pathway. Eight-week-old male C57BL/6 mice were used to establish unilateral ureteral obstruction (UUO)-induced renal fibrosis model, and the renal tissue samples were collected 14 days later for analysis. Transforming growth factor-β (TGF-β)-treated mouse renal tubular epithelial cells were used in in vitro studies. The results demonstrated that, compared to the control group, UUO kidney exhibited significant fibrosis, which was accompanied by the increases of RIG-I, p-NF-κB p65 and inflammatory cytokines, such as TNF-α and IL-1β. Additionally, the protein level of the E3 ubiquitin ligase RNF125 was significantly downregulated and predominantly localized in the renal tubular epithelial cells. Similarly, the treatment of tubular cells with TGF-β induced the increases in RIG-I, p-NF-κB p65 and inflammatory cytokines while decreasing RNF125. Co-immunoprecipitation (Co-IP) assays confirmed that RNF125 was able to interact with RIG-I. Overexpression of RNF125 promoted the ubiquitination of RIG-I, and accelerated its degradation via the ubiquitin-proteasome pathway. Overexpression of RNF125 in UUO kidneys and in vitro tubular cells effectively mitigated the inflammatory response and renal fibrosis. In summary, our results demonstrated that the decrease in RNF125 under pathological conditions led to reduction in RIG-I ubiquitination and degradation, activation of the downstream NF-κB signaling pathway and increase in inflammatory cytokine production, which promoted the progression of renal fibrosis.
Animals ; Fibrosis ; Male ; Ubiquitination ; Mice ; Mice, Inbred C57BL ; DEAD Box Protein 58 ; Ubiquitin-Protein Ligases/physiology* ; Inflammation/metabolism* ; Ureteral Obstruction/complications* ; Kidney/pathology* ; Signal Transduction ; Transforming Growth Factor beta/pharmacology*

We knocked out the retinoic acid-inducible gene I (RIG-I) in HEK293 cells via CRISPR/Cas9 to reveal the effects of RIG-I knockout on the key factors in the type I interferon signaling pathway. Three single guide RNAs (sgRNAs) targeting RIG-I were designed, and the recombination vectors were constructed on the basis of the pX459 vector and used to transfect HEK293 cells, which were screened by puromycin subsequently. Furthermore, a mimic of virus, poly I: C, was used to transfect the cells screened out. RIG-I knockout was checked by sequencing, real-time quantitative PCR, Western blotting, and immunofluorescence assay. Meanwhile, the expression levels of key factors of type I interferon signaling pathway such as melanoma differentiation-associated gene 5 (MDA5), interferonβ1 (IFNβ1), and nuclear factor-kappa B p65 [NF-κB(p65)], as well as cell viability, were determined. The results showed that two HEK293 cell lines (S1 and S3) with RIG-I knockout were obtained, which exhibited lower mRNA and protein levels of RIG-I than the wild type HEK293 cells (P < 0.05). The mRNA levels of MDA5 and IFNβ1 in S1 and S3 cells and the protein level of NF-κB(p65) in S3 cells were lower than those in the wild type (P < 0.05). More extranuclear NF-κB(p65) protein was detected in S1 cells than in the wild type after transfection with poly I: C. Plus, the wild-type and S1 cells transfected with poly I: C for 48 h showcased reduced viability (P < 0.05), while S3 cells did not display the reduction in cell viability. In summary, the present study obtained two HEK293 cell lines with RIG-I knockout via CRISPR/Cas9, which provided a stable cell model for exploring the mechanism of type I interferon signaling pathway.
Humans ; HEK293 Cells ; CRISPR-Cas Systems ; DEAD Box Protein 58/metabolism* ; Signal Transduction ; Receptors, Immunologic/metabolism* ; Gene Knockout Techniques ; Transfection ; DEAD-box RNA Helicases/metabolism* ; RNA, Guide, CRISPR-Cas Systems/genetics* ; Interferon-Induced Helicase, IFIH1/metabolism* ; Transcription Factor RelA/metabolism* ; Interferon-beta/metabolism*

BACKGROUND: The hepatitis B virus (HBV) vaccine has been efficiently used for decades. However, hepatocellular carcinoma caused by HBV is still prevalent globally. We previously reported that interferon (IFN)-induced tripartite motif-containing 25 (TRIM25) inhibited HBV replication by increasing the IFN expression, and this study aimed to further clarify the anti-HBV mechanism of TRIM25. METHODS: The TRIM25-mediated degradation of hepatitis B virus X (HBx) protein was determined by detecting the expression of HBx in TRIM25-overexpressed or knocked-out HepG2 or HepG2-NTCP cells via Western blotting. Co-immunoprecipitation was performed to confirm the interaction between TRIM25 and HBx, and colocalization of TRIM25 and HBx was identified via immunofluorescence; HBV e-antigen and HBV surface antigen were qualified by using an enzyme-linked immunosorbent assay (ELISA) kit from Kehua Biotech. TRIM25 mRNA, pregenomic RNA (pgRNA), and HBV DNA were detected by quantitative real-time polymerase chain reaction. The retinoic acid-inducible gene I (RIG-I) and pgRNA interaction was verified by RNA-binding protein immunoprecipitation assay. RESULTS: We found that TRIM25 promoted HBx degradation, and confirmed that TRIM25 could enhance the K90-site ubiquitination of HBx as well as promote HBx degradation by the proteasome pathway. Interestingly, apart from the Really Interesting New Gene (RING) domain, the SPRY domain of TRIM25 was also indispensable for HBx degradation. In addition, we found that the expression of TRIM25 increased the recognition of HBV pgRNA by interacting with RIG-I, which further increased the IFN production, and SPRY, but not the RING domain is critical in this process. CONCLUSIONS The study found that TRIM25 interacted with HBx and promoted HBx-K90-site ubiquitination, which led to HBx degradation. On the other hand, TRIM25 may function as an adaptor, which enhanced the recognition of pgRNA by RIG-I, thereby further promoting IFN production. Our study can contribute to a better understanding of host-virus interaction.
Humans ; Hepatitis B virus ; DEAD Box Protein 58/metabolism* ; RNA ; Liver Neoplasms ; Virus Replication ; Tripartite Motif Proteins/genetics* ; Transcription Factors ; Ubiquitin-Protein Ligases/genetics*

RNA helicases, the largest family of proteins that participate in RNA metabolism, stabilize the intracellular environment through various processes, such as translation and pre-RNA splicing. These proteins are also involved in some diseases, such as cancers and viral diseases. Autophagy, a self-digestive and cytoprotective trafficking process in which superfluous organelles and cellular garbage are degraded to stabilize the internal environment or maintain basic cellular survival, is associated with human diseases. Interestingly, similar to autophagy, RNA helicases play important roles in maintaining cellular homeostasis and are related to many types of diseases. According to recent studies, RNA helicases are closely related to autophagy, participate in regulating autophagy, or serve as a bridge between autophagy and other cellular activities that widely regulate some pathophysiological processes or the development and progression of diseases. Here, we summarize the most recent studies to understand how RNA helicases function as regulatory proteins and determine their association with autophagy in various diseases.
Animals ; Antiviral Agents/pharmacology* ; Autophagy ; Beclin-1/metabolism* ; Carcinogenesis ; Cell Survival ; DEAD Box Protein 58/metabolism* ; Disease Progression ; Gene Expression Regulation ; Homeostasis ; Humans ; Immune System/physiology* ; Neoplasms/metabolism* ; RNA Helicases/metabolism* ; RNA Splicing ; Receptors, Immunologic/metabolism*

It was widely known that retinoic acid inducible gene I (RIG-I) functions as a cytosolic pattern recognition receptor that initiates innate antiviral immunity by detecting exogenous viral RNAs. However, recent studies showed that RIG-I participates in other various cellular activities by sensing endogenous RNAs under different circumstances. For example, RIG-I facilitates the therapy resistance and expansion of breast cancer cells and promotes T cell-independent B cell activation through interferon signaling activation by recognizing non-coding RNAs and endogenous retroviruses in certain situations. While in hepatocellular carcinoma and acute myeloid leukemia, RIG-I acts as a tumor suppressor through either augmenting STAT1 activation by competitively binding STAT1 against its negative regulator SHP1 or inhibiting AKT-mTOR signaling pathway by directly interacting with Src respectively. These new findings suggest that RIG-I plays more diverse roles in various cellular life activities, such as cell proliferation and differentiation, than previously known. Taken together, the function of RIG-I exceeds far beyond that of a pattern recognition receptor.
Animals ; DEAD Box Protein 58 ; genetics ; metabolism ; Mice ; RNA, Viral ; genetics ; metabolism ; STAT1 Transcription Factor ; genetics ; metabolism ; Signal Transduction ; genetics ; physiology

The innate immune response is the first line of host defense to eliminate viral infection. Pattern recognition receptors in the cytosol, such as RIG-I-like receptors (RLR) and Nod-like receptors (NLR), and membrane bound Toll like receptors (TLR) detect viral infection and initiate transcription of a cohort of antiviral genes, including interferon (IFN) and interferon stimulated genes (ISGs), which ultimately block viral replication. Another mechanism to reduce viral spread is through RIPA, the RLR-induced IRF3-mediated pathway of apoptosis, which causes infected cells to undergo premature death. The transcription factor IRF3 can mediate cellular antiviral responses by both inducing antiviral genes and triggering apoptosis through the activation of RIPA. The mechanism of IRF3 activation in RIPA is distinct from that of transcriptional activation; it requires linear polyubiquitination of specific lysine residues of IRF3. Using RIPA-active, but transcriptionally inactive, IRF3 mutants, it was shown that RIPA can prevent viral replication and pathogenesis in mice.
Animals ; Apoptosis ; DEAD Box Protein 58 ; genetics ; immunology ; metabolism ; Humans ; Immunity, Innate ; Interferon Regulatory Factor-3 ; genetics ; immunology ; metabolism ; Mice ; Virus Diseases ; genetics ; immunology ; metabolism

Cytosolic retinoic acid-inducible gene I (RIG-I) is an important innate immune RNA sensor and can induce antiviral cytokines, e.g., interferon-β (IFN-β). Innate immune response to hepatitis B virus (HBV) plays a pivotal role in viral clearance and persistence. However, knowledge of the role that RIG-I plays in HBV infection is limited. The woodchuck is a valuable model for studying HBV infection. To characterize the molecular basis of woodchuck RIG-I (wRIG-I), we analyzed the complete coding sequences (CDSs) of wRIG-I, containing 2778 base pairs that encode 925 amino acids. The deduced wRIG-I protein was 106.847 kD with a theoretical isoelectric point (pI) of 6.07, and contained three important functional structures [caspase activation and recruitment domains (CARDs), DExD/H-box helicases, and a repressor domain (RD)]. In woodchuck fibroblastoma cell line (WH12/6), wRIG-I-targeted small interfering RNA (siRNA) down-regulated RIG-I and its downstrean effector-IFN-β transcripts under RIG-I' ligand, 5'-ppp double stranded RNA (dsRNA) stimulation. We also measured mRNA levels of wRIG-I in different tissues from healthy woodchucks and in the livers from woodchuck hepatitis virus (WHV)-infected woodchucks. The basal expression levels of wRIG-I were abundant in the kidney and liver. Importantly, wRIG-I was significantly up-regulated in acutely infected woodchuck livers, suggesting that RIG-I might be involved in WHV infection. These results may characterize RIG-I in the woodchuck model, providing a strong basis for further study on RIG-I-mediated innate immunity in HBV infection.
Animals ; Cell Line, Tumor ; Cloning, Molecular ; DEAD Box Protein 58 ; antagonists & inhibitors ; genetics ; immunology ; Fibroblasts ; immunology ; pathology ; Gene Expression ; Hepatitis B ; genetics ; immunology ; pathology ; veterinary ; Hepatitis B Virus, Woodchuck ; Immunity, Innate ; Interferon-beta ; genetics ; immunology ; Isoelectric Point ; Kidney ; immunology ; pathology ; virology ; Liver ; immunology ; pathology ; virology ; Marmota ; genetics ; immunology ; virology ; Open Reading Frames ; Protein Domains ; RNA, Double-Stranded ; RNA, Small Interfering ; genetics ; metabolism ; Rodent Diseases ; genetics ; immunology ; pathology ; virology

OBJECTIVETo observe the anti-virus effects of andrographolide (AD) on the retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) signaling pathway when immunological cells were infected with H1N1.

METHODSLeukomonocyte was obtained from umbilical cord blood by Ficoll density gradient centrifugation, and immunological cells were harvested after cytokines stimulation. Virus infected cell model was established by H1N1 co-cultured with normal human bronchial epithelial cell line (16HBE). The optimal concentration of AD was defined by methyl-thiazolyl-tetrazolium (MTT) assay. After the virus infected cell model was established, AD was added into the medium as a treatment intervention. After 24-h co-culture, cell supernatant was collected for interferon gamma (IFN-γ) and interleukin-4 (IL-4) enzyme-linked immunosorbent assay (ELISA) detection while immunological cells for real-time polymerase chain reaction (RT-PCR).

RESULTSThe optimal concentration of AD for anti-virus effect was 250 μg/mL. IL-4 and IFN-γ in the supernatant and mRNA levels in RLRs pathway increased when cells was infected by virus, RIG-I, IFN-β promoter stimulator-1 (IPS-1), interferon regulatory factor (IRF)-7, IRF-3 and nuclear transcription factor κB (NF-κB) mRNA levels increased significantly (P<0.05). When AD was added into co-culture medium, the levels of IL-4 and IFN-γ were lower than those in the non-interference groups and the mRNA expression levels decreased, RIG-I, IPS-1, IRF-7, IRF-3 and NF-κB decreased significantly in each group with significant statistic differences (P<0.05).

CONCLUSIONSThe RLRs mediated viral recognition provided a potential molecular target for acute viral infections and andrographolide could ameliorate H1N1 virus-induced cell mortality. And the antiviral effects might be related to its inhibition of viral-induced activation of the RLRs signaling pathway.

Adaptor Proteins, Signal Transducing ; genetics ; metabolism ; Antiviral Agents ; pharmacology ; Cells, Cultured ; Coculture Techniques ; DEAD Box Protein 58 ; DEAD-box RNA Helicases ; genetics ; metabolism ; Dendritic Cells ; drug effects ; immunology ; virology ; Diterpenes ; pharmacology ; Fetal Blood ; cytology ; Humans ; Influenza A Virus, H1N1 Subtype ; drug effects ; immunology ; Influenza, Human ; drug therapy ; immunology ; virology ; Interferon-beta ; genetics ; metabolism ; Interferon-gamma ; metabolism ; Interleukin-4 ; metabolism ; Leukocytes, Mononuclear ; drug effects ; immunology ; virology ; Macrophages ; drug effects ; virology ; NF-kappa B ; genetics ; metabolism ; Promoter Regions, Genetic ; drug effects ; immunology ; RNA, Messenger ; metabolism ; Signal Transduction ; drug effects ; genetics ; immunology

Retinoic acid-inducible gene I (RIG-I) is an important pattern recognition receptor that detects viral RNA and triggers the production of type-I interferons through the downstream adaptor MAVS (also called IPS-1, CARDIF, or VISA). A series of structural studies have elaborated some of the mechanisms of dsRNA recognition and activation of RIG-I. Recent studies have proposed that K63-linked ubiquitination of, or unanchored K63-linked polyubiquitin binding to RIG-I positively regulates MAVS-mediated antiviral signaling. Conversely phosphorylation of RIG-I appears to play an inhibitory role in controlling RIG-I antiviral signal transduction. Here we performed a combined structural and biochemical study to further define the regulatory features of RIG-I signaling. ATP and dsRNA binding triggered dimerization of RIG-I with conformational rearrangements of the tandem CARD domains. Full length RIG-I appeared to form a complex with dsRNA in a 2:2 molar ratio. Compared with the previously reported crystal structures of RIG-I in inactive state, our electron microscopic structure of full length RIG-I in complex with blunt-ended dsRNA, for the first time, revealed an exposed active conformation of the CARD domains. Moreover, we found that purified recombinant RIG-I proteins could bind to the CARD domain of MAVS independently of dsRNA, while S8E and T170E phosphorylation-mimicking mutants of RIG-I were defective in binding E3 ligase TRIM25, unanchored K63-linked polyubiquitin, and MAVS regardless of dsRNA. These findings suggested that phosphorylation of RIG inhibited downstream signaling by impairing RIG-I binding with polyubiquitin and its interaction with MAVS.
Adaptor Proteins, Signal Transducing ; metabolism ; Adenosine Triphosphate ; metabolism ; DEAD Box Protein 58 ; DEAD-box RNA Helicases ; chemistry ; genetics ; metabolism ; Dimerization ; Humans ; Mutagenesis, Site-Directed ; Phosphorylation ; Polyubiquitin ; metabolism ; Protein Binding ; Protein Structure, Tertiary ; RNA, Double-Stranded ; metabolism ; Recombinant Proteins ; biosynthesis ; chemistry ; genetics ; Signal Transduction ; Transcription Factors ; metabolism ; Tripartite Motif Proteins ; Ubiquitin-Protein Ligases ; metabolism ; Ubiquitination

Hepatitis B virus (HBV) infection disrupt the innate immunity response, which may play an important role in the chronic mechanism, while retinoic acid-induced gene I (RIG-I) mediated signaling pathway is one of the most important channel in the innate immunity. HBx and HBV polymerase may disrupt RIG-I mediated signaling pathway. The recent advances about HBV and RIG-I are reviewed in this article.
DEAD Box Protein 58 ; DEAD-box RNA Helicases ; metabolism ; Gene Products, pol ; metabolism ; Hepatitis B ; immunology ; Humans ; Immunity, Innate ; immunology ; Signal Transduction ; Trans-Activators ; metabolism