Comparison of characteristics and anti-MDA5 antibody distribution and effect between clinically amyopathic dermatomyositis and classic dermatomyositis: a retrospective case-control study.

Background: Clinically amyopathic dermatomyositis (CADM) is a distinct subtype of dermatomyositis (DM) characterized by typical DM cutaneous findings but with minimal or no evidence of myositis. It possesses unique features different from classic DM (CDM). Anti-melanoma differentiation-associated gene 5 (MDA5) antibodies were found in CADM and are thought to increase the risk of rapidly progressive interstitial lung disease (RP-ILD) and are present in both CADM and CDM patients, affecting their condition and prognosis. Nevertheless, no large-sample studies have compared all aspects concerning patients with CADM and those with CDM. This study aimed to investigate differences in clinical characteristics and risk factors for mortality between CADM and CDM and to clarify the distribution and impact of anti-MDA5 antibodies in patients with these conditions. Methods: A retrospective case-control study included 330 patients and collected and analyzed their clinical data from The First Affiliated Hospital of Shandong First Medical University and Shandong Provincial Hospital of Traditional Chinese Medicine between January 2015 and July 2022; all patients were followed up to evaluate changes in their condition and prognosis. Several new cohorts were designed around anti-MDA5 antibodies to explore their distribution and impact in CADM and CDM. Results: We found CADM to be associated with higher rates of mortality, 1-year mortality, interstitial lung disease (ILD), and RP-ILD than CDM. In CADM, RP-ILD, anti-MDA5 antibodies, and high ferritin and lactate dehydrogenase (LDH) levels were identified as independent risk factors for death. In CDM, the neutrophil-to-lymphocyte ratio, anti-MDA5 antibodies, and high ferritin levels were shown to be independent risk factors for death, whereas mechanic's hand was considered a protective factor against it. Anti-MDA5 antibody-positive patients did not exhibit any significant difference based on whether they belonged to the CADM or CDM groups. When no anti-MDA5 antibody-positive patients participated, the ferritin levels and rates of RP-ILD and ILD were still higher in CADM than in CDM; however, such differences decreased, whereas the LDH levels, rates of mortality, and 1-year mortality did not differ. Anti-MDA5 antibody-positive patients consistently showed higher LDH and ferritin levels, lower lymphocyte levels, higher probability of RP-ILD and ILD, and worse prognosis than anti-MDA5 antibody-negative patients, irrespective of whether the patients had DM, CADM, or CDM. Conclusion: Patients with CADM exhibit relatively worse symptoms, serological findings, and prognosis than those with CDM. Furthermore, patients with CADM and those with CDM have commonalities and differences in risk factors for death. Moreover, CADM may necessitate earlier and more aggressive treatment strategies than CDM. Anti-MDA5 antibodies occur at a high level in patients with CADM, not only affecting the symptoms and prognosis of DM but also having a non-negligible impact on the differences between CADM and CDM. Hence, screening for anti-MDA5 antibodies in patients with CADM and CDM is extremely essential.

A novel strategy for optimal component formula of anti-PRRSV from natural compounds using tandem mass tag labeled proteomic analyses.

BACKGROUND: Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most important porcine viral diseases which have been threatening the pig industry in China. At present, most commercial vaccines fail to provide complete protection because of highly genetic diversity of PRRSV strains. This study aimed to optimize a component formula from traditional Chinese medicine(TCM)compounds with defined chemical characteristics and clear mechanism of action against PRRSV. METHODS: A total of 13 natural compounds were screened for the anti-PRRSV activity using porcine alveolar macrophages (PAMs). Three compounds with strong anti-PRRSV activity were selected to identify their potential protein targets by proteomic analysis. The optimal compound formula was determined by orthogonal design based on the results of proteomics. MTT assay was used to determine the maximum non-cytotoxic concentration (MNTC) of each compound using PAMs. QPCR and western blot were used to investigate the PRRSV N gene and protein expression, respectively. The Tandem Mass Tag (TMT) technique of relative quantitative proteomics was used to detect the differential protein expression of PAMs treated with PRRSV, matrine (MT), glycyrrhizic acid (GA) and tea saponin (TS), respectively. The three concentrations of these compounds with anti-PRRSV activity were used for orthogonal design. Four formulas with high safety were screened by MTT assay and their anti-PRRSV effects were evaluated. RESULTS: MT, GA and TS inhibited PRRSV replication in a dose-dependent manner. CCL8, IFIT3, IFIH1 and ISG15 were the top four proteins in expression level change in cells treated with MT, GA or TS. The relative expression of IFIT3, IFIH1, ISG15 and IFN-ß mRNAs were consistent with the results of proteomics. The component formula (0.4 mg/mL MT + 0.25 mg/mL GA + 1.95 µg/mL TS) showed synergistic anti-PRRSV effect. CONCLUSIONS: The component formula possessed anti-PRRSV activity in vitro, in which the optimal dosage on PAMs was 0.4 mg/mL MT + 0.25 mg/mL GA + 1.95 µg/mL TS. Compatibility of the formula was superposition of the same target with GA and TS, while different targets of MT. IFN-ß may be one of the targets of the component formula possessed anti-PRRSV activity.

Gender-specific development of experimental autoimmune cholangitis induced by double-stranded RNA.

Here we investigated the gender difference in murine cholangitis resembling human primary biliary cholangitis (PBC) caused by synthetic double-stranded RNA, and underlying hepatic innate immune responses. Female C57Bl/6 mice given repeated injections of polyinosinic-polycytidylic acid (poly I:C) for 24 weeks developed overt cholangitis with positive serum anti-mitochondria-M2 antibody, whereas male mice showed minimal pathological changes without induction in autoantibody. Poly I:C induced hepatic inflammatory cytokines and type-I interferons predominantly in females. Hepatic expression levels of toll-like receptor (TLR) 3 and melanoma differentiation-associated protein (MDA) 5 were equivalent in both genders; however, both mRNA and protein levels of retinoic acid-inducible gene (RIG)-I were nearly doubled in female livers. Following 4-week injections of poly I:C, not only hepatic RIG-I, but also TLR3 and MDA5 showed female-predominance. Moreover, hepatic RIG-I levels were 25% lower in ovariectomized mice, whereas supplementation of 17 ß-estradiol enhanced hepatic RIG-I expression, as well as cytokine induction. These results clearly indicate that hepatic RIG-I expression is potentiated by estrogen, and triggers gender-dependent hepatic innate immune response against double-stranded RNA, which most likely play a pivotal role in the pathogenesis of autoimmune cholangiopathies including PBC.

Dietary Supplementation with Biobran/MGN-3 Increases Innate Resistance and Reduces the Incidence of Influenza-like Illnesses in Elderly Subjects: A Randomized, Double-Blind, Placebo-Controlled Pilot Clinical Trial.

Influenza-like illness (ILI) remains a major cause of severe mortality and morbidity in the elderly. Aging is associated with a decreased ability to sense pathogens and mount effective innate and adaptive immune responses, thus mandating the development of protective nutraceuticals. Biobran/MGN-3, an arabinoxylan from rice bran, has potent anti-aging and immunomodulatory effects, suggesting that it may be effective against ILI. The objective of the current study was to investigate the effect of Biobran/MGN-3 on ILI incidence, natural killer (NK) cell activity, and the expressions of RIG-1 (retinoic acid-inducible gene 1), MDA5 (melanoma differentiation-associated protein 5), and their downstream signaling genes ISG-15 (interferon-stimulated genes 15) and MX1 (myxovirus (influenza) resistance 1, interferon-inducible). A double-blind, placebo-controlled clinical trial included eighty healthy older adults over 55 years old, 40 males and 40 females, who received either a placebo or Biobran/MGN-3 (500 mg/day) for 3 months during known ILI seasonality (peak incidence) in Egypt. The incidence of ILI was confirmed clinically according to the WHO case definition criteria. Hematological, hepatic, and renal parameters were assessed in all subjects, while the activity of NK and NKT (natural killer T) cells was assessed in six randomly chosen subjects in each group by the degranulation assay. The effect of Biobran/MGN-3 on RIG-1 and MDA5, as well as downstream ISG15 and MX1, was assessed in BEAS-2B pulmonary epithelial cells using flow cytometry. The incidence rate and incidence density of ILI in the Biobran/MGN-3 group were 5.0% and 0.57 cases per 1000 person-days, respectively, compared to 22.5% and 2.95 cases per 1000 person-days in the placebo group. Furthermore, Biobran/MGN-3 ingestion significantly enhanced NK activity compared to the basal levels and to the placebo group. In addition, Biobran/MGN-3 significantly upregulated the expression levels of RIG-1, MDA5, ISG15, and MX1 in the human pulmonary epithelial BEAS-2B cell lines. No side effects were observed. Taken together, Biobran/MGN-3 supplementation enhanced the innate immune response of elderly subjects by upregulating the NK activity associated with reduction of ILI incidence. It also upregulated the intracellular RIG-1, MDA5, ISG15, and MX1 expression in pulmonary epithelial tissue cultures. Biobran/MGN-3 could be a novel agent with prophylactic effects against a wide spectrum of respiratory viral infections that warrants further investigation.

Interstitial Lung Disease in Anti-MDA5 Positive Dermatomyositis.

Anti-melanoma differentiation-associated gene 5-positive dermatomyositis (MDA5+ DM) is a rare autoimmune disease predominantly reported in East Asia. MDA5+ DM is an intractable disease with impressively high mortality due to rapid-progressive interstitial lung disease (RPILD). Other typical clinical manifestations comprise DM-specific rash (Gottron's papules, heliotrope rash) and amyopathic/hypomyopathic muscle involvement. Multiple prognostic factors have been identified. Baseline forced vital capacity (FVC) %-based staging could serve as a simplified risk stratification system. Serum biomarkers including MDA5 Ab titers, ferritin, KL-6 levels, and CD4+CXCR4+ T cell percentage could provide additional surrogate value of ILD severity and treatment response, as well as potential predictive value for survival. Spontaneous pneumomediastinum (PNM), ground-glass opacity (GGO), and consolidation were demonstrated to be the most significant features in pulmonary high-resolution computed tomography (HRCT) findings of MDA5+ DM-ILD. The semi-quantitative assessment of lesions in HRCT has also been demonstrated relevant to the outcome. The current treatment of this disease is still largely empirical. Immunosuppressive treatments, i.e., "triple therapy" (combination of high-dose glucocorticoids, tacrolimus, and intravenous cyclophosphamide) and JAK inhibitor-based therapy, are the mainstream regimens for MDA5+ DM-ILD, supported by the recently published trials. However, more efficacious regimen with favorable safety profile and high-level evidence is still urgently demanded for patients with MDA5+ DM-ILD, especially those at advanced-stage. We will summarize the terminology, etiology and pathogenesis, clinical features and outcome, prognostic factors, and treatment of MDA5+ DM-ILD in this review.

Different types of effective fractions from Radix Isatidis revealed a multiple-target synergy effect against respiratory syncytial virus through RIG-I and MDA5 signaling pathways, a pilot study to testify the theory of superposition of traditional Chinese Medicine efficacy.

ETHNOPHARMACOLOGICAL RELEVANCE: Radix Isatidis, a commonly used traditional Chinese medicine, is also documented in "Dictionary of Chinese Ethnic Medicine" being as an ethnic herb clinically utilized by different nations in China such as Mongol, Uygur, and Dong et al. It has been reported to have a very strong efficacy on respiratory viruses, but to date the mechanism remains unknown. Similarly, it is unclear how different types of effective fractions of Radix Isatidis interact to exert antiviral effects. AIM OF STUDY: To reveal the underlying mechanisms for the inhibitory effects of three active fractions from Radix Isatidis, i.e. total alkaloids, lignans and organic acids, on respiratory syncytial virus when used alone or in combination. In addition, we investigated whether these three parts worked synergistically in vivo and in vitro. MATERIALS AND METHODS: A mouse model of RSV infection was constructed by intranasal infection, and the pathological changes of lung tissues in different parts were observed. The level changes of IFNß and inflammatory cytokines in the mouse alveolar lavage fluid were detected by enzyme-linked immunosorbent assay (ELISA). The anti-RSV effects of different effective fractions were evaluated by the plaque reduction test. The mRNA and protein expressions of RIG-I, MDA-5, MAVS and IRF3 in RAW264.7 cells were detected by RT-PCR and Western blot respectively. RESULTS: HE staining showed that Radix Isatidis extracts alone or in combination relieved virus-induced mouse lung lesions. Compared with individual drugs, the lung lesions were alleviated more significantly after treatment with the three fractions in combination. ELISA demonstrated that the expression levels of IFNß and inflammatory cytokines were maintained balanced between antiviral and proinflammatory effects. The plaque reduction test indicated that the antiviral effect of combination treatment was much stronger than those of individual drugs. RT-qPCR and Western blot suggested that the mRNA and protein expression levels of key signaling molecules in the RIG-I and MDA5 pathways in mouse macrophages were down-regulated by different effective parts alone or in combination. CONCLUSIONS: The three effective fractions of Radix Isatidis have remarkable synergistic anti-RSV effects in vitro and in vivo, and total alkaloids and lignans show multi-target synergistic effects via the RIG-I and MDA5 signaling pathways.

Targeting Cytosolic Nucleic Acid-Sensing Pathways for Cancer Immunotherapies.

The innate immune system provides the first line of defense against pathogen infection though also influences pathways involved in cancer immunosurveillance. The innate immune system relies on a limited set of germ line-encoded sensors termed pattern recognition receptors (PRRs), signaling proteins and immune response factors. Cytosolic receptors mediate recognition of danger damage-associated molecular patterns (DAMPs) signals. Once activated, these sensors trigger multiple signaling cascades, converging on the production of type I interferons and proinflammatory cytokines. Recent studies revealed that PRRs respond to nucleic acids (NA) released by dying, damaged, cancer cells, as danger DAMPs signals, and presence of signaling proteins across cancer types suggests that these signaling mechanisms may be involved in cancer biology. DAMPs play important roles in shaping adaptive immune responses through the activation of innate immune cells and immunological response to danger DAMPs signals is crucial for the host response to cancer and tumor rejection. Furthermore, PRRs mediate the response to NA in several vaccination strategies, including DNA immunization. As route of double-strand DNA intracellular entry, DNA immunization leads to expression of key components of cytosolic NA-sensing pathways. The involvement of NA-sensing mechanisms in the antitumor response makes these pathways attractive drug targets. Natural and synthetic agonists of NA-sensing pathways can trigger cell death in malignant cells, recruit immune cells, such as DCs, CD8+ T cells, and NK cells, into the tumor microenvironment and are being explored as promising adjuvants in cancer immunotherapies. In this minireview, we discuss how cGAS-STING and RIG-I-MAVS pathways have been targeted for cancer treatment in preclinical translational researches. In addition, we present a targeted selection of recent clinical trials employing agonists of cytosolic NA-sensing pathways showing how these pathways are currently being targeted for clinical application in oncology.

An origin of the immunogenicity of in vitro transcribed RNA.

The emergence of RNA-based therapeutics demands robust and economical methods to produce RNA with few byproducts from aberrant activity. While in vitro transcription using the bacteriophage T7 RNA polymerase is one such popular method, its transcripts are known to display an immune-stimulatory activity that is often undesirable and uncontrollable. We here showed that the immune-stimulatory activity of T7 transcript is contributed by its aberrant activity to initiate transcription from a promoter-less DNA end. This activity results in the production of an antisense RNA that is fully complementary to the intended sense RNA product, and consequently a long double-stranded RNA (dsRNA) that can robustly stimulate a cytosolic pattern recognition receptor, MDA5. This promoter-independent transcriptional activity of the T7 RNA polymerase was observed for a wide range of DNA sequences and lengths, but can be suppressed by altering the transcription reaction with modified nucleotides or by reducing the Mg2+ concentration. The current work thus not only offers a previously unappreciated mechanism by which T7 transcripts stimulate the innate immune system, but also shows that the immune-stimulatory activity can be readily regulated.

MDA5 complements TLR3 in suppression of neuroblastoma.

Toll-like receptor3 (TLR3) has been confirmed to be differentially expressed in neuroblastoma (NB), and predicts a favorable prognosis with a high expression in tumor tissues. Treatment with TLR3 agonist--polyinosinic-polycytidylic acid [poly(I:C)] could induce significant but limited apoptosis in TLR3-expressing NB cells, suggesting that other viral RNA sensors, including melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I) in the cytosolic compartment might also be implicated in poly(I:C)-induced NB cell death. MDA5 and RIG-I were induced by poly(I:C) to express in two of six NB cell lines, SK-N-AS (AS) and SK-N-FI, which were associated with up-regulation of caspase9 and active caspase3. While knockdown of either MDA5 or RIG-I alone is ineffective to decrease caspase9 and active caspase3, simultaneously targeting MDA5 and TLR3 showed the best effect to rescue poly(I:C) induced up-regulation of mitochondrial antiviral signaling protein (MAVS), caspase9, active caspase3, and apoptosis in AS cells. Over-expression of MDA5 in FaDu cells resulted in significantly less colony formation and more poly(I:C)-induced cell death. Further studies in human NB tissue samples revealed that MDA5 expression in NB tissues predicted a favorable prognosis synergistically with TLR3. Our findings indicate that MDA5 may serve as a complementary role in the TLR3 activated suppression of NB.

Paramyxovirus V protein interaction with the antiviral sensor LGP2 disrupts MDA5 signaling enhancement but is not relevant to LGP2-mediated RLR signaling inhibition.

The interferon antiviral system is a primary barrier to virus replication triggered upon recognition of nonself RNAs by the cytoplasmic sensors encoded by retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated gene 5 (MDA5), and laboratory of genetics and physiology gene 2 (LGP2). Paramyxovirus V proteins are interferon antagonists that can selectively interact with MDA5 and LGP2 through contact with a discrete helicase domain region. Interaction with MDA5, an activator of antiviral signaling, disrupts interferon gene expression and antiviral responses. LGP2 has more diverse reported roles as both a coactivator of MDA5 and a negative regulator of both RIG-I and MDA5. This functional dichotomy, along with the concurrent interference with both cellular targets, has made it difficult to assess the unique consequences of V protein interaction with LGP2. To directly evaluate the impact of LGP2 interference, MDA5 and LGP2 variants unable to be recognized by measles virus and parainfluenza virus 5 (PIV5) V proteins were tested in signaling assays. Results indicate that interaction with LGP2 specifically prevents coactivation of MDA5 signaling and that LGP2's negative regulatory capacity was not affected. V proteins only partially antagonize RIG-I at high concentrations, and their expression had no additive effects on LGP2-mediated negative regulation. However, conversion of RIG-I to a direct V protein target was accomplished by only two amino acid substitutions that allowed both V protein interaction and efficient interference. These results clarify the unique consequences of MDA5 and LGP2 interference by paramyxovirus V proteins and help resolve the distinct roles of LGP2 in both activation and inhibition of antiviral signal transduction. Importance: Paramyxovirus V proteins interact with two innate immune receptors, MDA5 and LGP2, but not RIG-I. V proteins prevent MDA5 from signaling to the beta interferon promoter, but the consequences of LGP2 targeting are poorly understood. As the V protein targets MDA5 and LGP2 simultaneously, and LGP2 is both a positive and negative regulator of both MDA5 and RIG-I, it has been difficult to evaluate the specific advantages conferred by LGP2 targeting. Experiments with V-insensitive proteins revealed that the primary outcome of LGP2 interference is suppression of its ability to synergize with MDA5. LGP2's negative regulation of MDA5 and RIG-I remains intact irrespective of V protein interaction. Complementary experiments demonstrate that RIG-I can be converted to V protein sensitivity by two amino acid substitutions. These findings clarify the functions of LGP2 as a positive regulator of MDA5 signaling, demonstrate the basis for V-mediated LGP2 targeting, and broaden our understanding of paramyxovirus-host interactions.

Rhodiola inhibits dengue virus multiplication by inducing innate immune response genes RIG-I, MDA5 and ISG in human monocytes.

Recognition of virus infection by retinoic acid-inducible gene (RIG) I and melanoma differentiation-associated protein (MDA) 5, which are RNA helicases, and interferon-stimulated gene (ISG) 15 activates cascades of signal transduction pathways leading to production of type I interferons and proinflammatory cytokines that orchestrate the elimination of the viruses. However, it has been demonstrated that RNA-helicase-mediated innate immunity plays an essential role in defending the host from infection. In our efforts to identify plant-derived antivirals that selectively enhance ISG- and RNA-helicase-mediated antiviral immune responses, we identified a plant, rhodiola, that significantly promoted ISG, RIG-I and MDA 5 gene expression and an antiviral immune response against dengue virus (DENV) infection. Rhodiola induced interferon (IFN) ß and other cytokines, including IL-1ß, TNF-α, IL-6 and IL-8, in infected cells. It was also found that rhodiola upregulated phosphorylated eIF-2α, PKR and NF-kB in infected cells. In addition, the number of NK cells was also increased by rhodiola treatment in dengue-virus-infected human PBMCs. Treatment with a crude extract of rhodiola (RAE) resulted in effects in the 20 % range, which is similar to the magnitude of the same effects observed in DENV infections. Taken together, our results imply that rhodiola induces pharmacological modulation of RIG-I, MDA 5 and ISG signal transduction pathways in favor of the induction of a beneficial antiviral immune response against dengue virus, which can be a novel therapeutic strategy for management of infection.

Poly(I:C) exhibits an anti-cancer effect in human gastric adenocarcinoma cells which is dependent on RLRs.

Poly(I:C), an agonist of TLR3 and RLRs, has been used as an immune adjuvant in clinical trials for many years. Although it has been found to trigger apoptosis in a variety of cancers, its mechanisms in human gastric adenocarcinoma is unclear. The purpose of this study was to assess the effect of poly(I:C) on human gastric adenocarcinoma cells. Our observations showed that intracellular delivery of poly(I:C) by liposomes had a pro-apoptotic effect in vitro, and significantly inhibited xenograft growth of human gastric adenocarcinoma in nude mice. Further investigations indicated that RLRs, as intrinsic RNA sensors, contributed to the poly(I:C)-triggered apoptotic effect through upregulation of RIG-I, MDA-5, and most significantly, LGP2, accompanied by increased expression of Bcl-2 family members. Conversely, this apoptotic effect was greatly reduced by silencing RIG-I, MDA-5, or LGP2. Although LGP2 is considered an innate immune negative regulator of RIG-I and MDA-5, it exhibited a positive regulatory effect on poly(I:C)-induced apoptosis in human gastric adenocarcinoma cells. These findings suggested that poly(I:C) may be a promising chemotherapeutic agent against human gastric adenocarcinoma.

Dose dependent activation of retinoic acid-inducible gene-I promotes both proliferation and apoptosis signals in human head and neck squamous cell carcinoma.

The retinoic-acid-inducible gene (RIG)-like receptor (RLR) family proteins are major pathogen reorganization receptors (PRR) responsible for detection of viral RNA, which initiates antiviral response. Here, we evaluated the functional role of one RLR family member, RIG-I, in human head and neck squamous cell carcinoma (HNSCC). RIG-I is abundantly expressed both in poorly-differentiated primary cancer and lymph node metastasis, but not in normal adjacent tissues. Activation of RIG-I by transfection with low dose of 5'-triphosphate RNA (3p-RNA) induces low levels of interferon and proinflammatory cytokines and promotes NF-κB- and Akt-dependent cell proliferation, migration and invasion. In contrast, activation of RIG-I by a high dose of 3p-RNA induces robust mitochondria-derived apoptosis accompanied by decreased activation of Akt, which is independent of the interferon and TNFα receptor, but can be rescued by over-expression of constitutively active Akt. Furthermore, co-immunoprecipitation experiments indicate that the CARD domain of RIG-I is essential for inducing apoptosis by interacting with caspase-9. Together, our results reveal a dual role of RIG-I in HNSCC through regulating activation of Akt, in which RIG-I activation by low-dose viral dsRNA increases host cell survival, whereas higher level of RIG-I activation leads to apoptosis. These findings highlight the therapeutic potential of dsRNA mediated RIG-I activation in the treatment of HNSCC.

Amino acid requirements for MDA5 and LGP2 recognition by paramyxovirus V proteins: a single arginine distinguishes MDA5 from RIG-I.

Paramyxovirus V proteins bind to MDA5 (melanoma differentiation-associated gene 5) and LGP2 (laboratory of genetics and physiology gene 2) but not RIG-I (retinoic acid-inducible gene I). The results demonstrate MDA5 R806 is essential for inhibition by diverse V proteins. Complementary substitution for the analogous RIG-I L714 confers V protein recognition. The analogous LGP2 R455 is required for recognition by measles V protein, but not other V proteins. These findings indicate that paramyxoviruses use a single amino acid to distinguish MDA5 from RIG-I and have evolved distinct contact sites for LGP2 interference.

Triggering of the dsRNA sensors TLR3, MDA5, and RIG-I induces CD55 expression in synovial fibroblasts.

BACKGROUND: CD55 (decay-accelerating factor) is a complement-regulatory protein highly expressed on fibroblast-like synoviocytes (FLS). CD55 is also a ligand for CD97, an adhesion-type G protein-coupled receptor abundantly present on leukocytes. Little is known regarding the regulation of CD55 expression in FLS. METHODS: FLS isolated from arthritis patients were stimulated with pro-inflammatory cytokines and Toll-like receptor (TLR) ligands. Transfection with polyinosinic-polycytidylic acid (poly(I:C)) and 5'-triphosphate RNA were used to activate the cytoplasmic double-stranded (ds)RNA sensors melanoma differentiation-associated gene 5 (MDA5) and retinoic acid-inducible gene-I (RIG-I). CD55 expression, cell viability, and binding of CD97-loaded beads were quantified by flow cytometry. RESULTS: CD55 was expressed at equal levels on FLS isolated from patients with rheumatoid arthritis (RA), osteoarthritis, psoriatic arthritis and spondyloarthritis. CD55 expression in RA FLS was significantly induced by IL-1ß and especially by the TLR3 ligand poly(I:C). Activation of MDA5 and RIG-I also enhanced CD55 expression. Notably, activation of MDA5 dose-dependently induced cell death, while triggering of TLR3 or RIG-I had a minor effect on viability. Upregulation of CD55 enhanced the binding capacity of FLS to CD97-loaded beads, which could be blocked by antibodies against CD55. CONCLUSIONS: Activation of dsRNA sensors enhances the expression of CD55 in cultured FLS, which increases the binding to CD97. Our findings suggest that dsRNA promotes the interaction between FLS and CD97-expressing leukocytes.

Narrowband ultraviolet B inhibits innate cytosolic double-stranded RNA receptors in psoriatic skin and keratinocytes.

BACKGROUND: The mode of action of narrowband ultraviolet B (NB-UVB) therapy in clearing psoriasis is incompletely understood, and in vivo studies at the molecular level in patients undergoing NB-UVB therapy are limited. We previously demonstrated increased expression and activity of double-stranded RNA (dsRNA) receptors in psoriasis lesions, and suggested that this enhanced innate signalling contributed to the maintenance of psoriatic inflammation. OBJECTIVES: We investigated whether NB-UVB affects dsRNA receptor expression and function in vivo as well as in vitro. METHODS: Skin samples of patients with psoriasis undergoing NB-UVB treatment were analysed for epidermal messenger RNA (mRNA) expression of the various dsRNA receptors by microarray and quantitative reverse transcription-polymerase chain reaction. Primary human keratinocytes were irradiated with NB-UVB and stimulated with interferon (IFN)-α or IFN-γ, critical cytokines in psoriasis. The dsRNA analogue polyriboinosinic-polyribocytidylic acid was used to assess the functional responsiveness of the cells to dsRNA. RESULTS: NB-UVB therapy of patients with psoriasis resulted in a significantly reduced mRNA expression of the activating dsRNA receptors MDA5 (IFIH1) and RIG-I (DDX58). On the other hand, expression of LGP2 (DHX58), toll-like receptor 3 (TLR3) and PKR (EIF2AK2) was not affected. In vitro, NB-UVB irradiation completely blocked the upregulation of four of the dsRNA receptors in primary human keratinocytes stimulated with IFN-α or IFN-γ, resulting in an attenuated inflammatory response to dsRNA. CONCLUSIONS: Our results show that NB-UVB irradiation inhibits the local innate inflammatory response to dsRNA, and suggest a novel mechanism of action of NB-UVB phototherapy in psoriasis.

Anticancer function of polyinosinic-polycytidylic acid.

Polyinosinic-polycytidylic acid (polyi:c) is a synthetic analog of double-stranded RNA and an agonist of toll-like receptor (TLR) 3 and retinoic acid inducible gene I (RIG-I)-like receptors (RLRs), including RIG-I and melanoma differentiation-associated gene 5 (MDA5). The effect of polyi:c on tumor immunotherapy has been well explored for several decades. The accumulated evidence suggests that polyi:c could be used as a vaccine adjuvant to enhance innate and adaptive immune responses, and to alter the tumor microenvironment. Recent studies have also shown that activation of TLR3 and RLR signaling by polyi:c can directly trigger apoptosis in some cancer cells. This review focuses on polyi:c-induced signaling pathways and the applications of polyi:c in cancer treatment.

Activation of MDA5 requires higher-order RNA structures generated during virus infection.

Recognition of virus presence via RIG-I (retinoic acid inducible gene I) and/or MDA5 (melanoma differentiation-associated protein 5) initiates a signaling cascade that culminates in transcription of innate response genes such as those encoding the alpha/beta interferon (IFN-alpha/beta) cytokines. It is generally assumed that MDA5 is activated by long molecules of double-stranded RNA (dsRNA) produced by annealing of complementary RNAs generated during viral infection. Here, we used an antibody to dsRNA to show that the presence of immunoreactivity in virus-infected cells does indeed correlate with the ability of RNA extracted from these cells to activate MDA5. Furthermore, RNA from cells infected with encephalomyocarditis virus or with vaccinia virus and precipitated with the anti-dsRNA antibody can bind to MDA5 and induce MDA5-dependent IFN-alpha/beta production upon transfection into indicator cells. However, a prominent band of dsRNA apparent in cells infected with either virus does not stimulate IFN-alpha/beta production. Instead, stimulatory activity resides in higher-order structured RNA that contains single-stranded RNA and dsRNA. These results suggest that MDA5 activation requires an RNA web rather than simply long molecules of dsRNA.