Cellular FLIP long isoform (cFLIPL)-IKKα interactions inhibit IRF7 activation, representing a new cellular strategy to inhibit IFNα expression

Epigenomic and transcriptomic analyses reveal differences between low-grade inflammation and severe exhaustion in LPS-challenged murine monocytes

Emerging studies suggest that monocytes can be trained by bacterial endotoxin to adopt distinct memory states ranging from low-grade inflammation to immune exhaustion. While low-grade inflammation may contribute to the pathogenesis of chronic diseases, exhausted monocytes with pathogenic and immune-suppressive characteristics may underlie the pathogenesis of polymicrobial sepsis including COVID-19. However, detailed processes by which the dynamic adaption of monocytes occur remain poorly understood. Here we exposed murine bone-marrow derived monocytes to chronic lipopolysaccharide (LPS) stimulation at low-dose or high-dose, as well as a PBS control. The cells were profiled for genome-wide H3K27ac modification and gene expression. The gene expression of TRAM-deficient and IRAK-M-deficient monocytes with LPS exposure was also analyzed. We discover that low-grade inflammation preferentially utilizes the TRAM-dependent pathway of TLR4 signaling, and induces the expression of interferon response genes. In contrast, high dose LPS uniquely upregulates exhaustion signatures with metabolic and proliferative pathways. The extensive differences in the epigenomic landscape between low-dose and high-dose conditions suggest the importance of epigenetic regulations in driving differential responses. Our data provide potential targets for future mechanistic or therapeutic studies.

Role of Alternative Splicing in Regulating Host Response to Viral Infection

The importance of transcriptional regulation of host genes in innate immunity against viral infection has been widely recognized. More recently, post-transcriptional regulatory mechanisms have gained appreciation as an additional and important layer of regulation to fine-tune host immune responses. Here, we review the functional significance of alternative splicing in innate immune responses to viral infection. We describe how several central components of the Type I and III interferon pathways encode spliced isoforms to regulate IFN activation and function. Additionally, the functional roles of splicing factors and modulators in antiviral immunity are discussed. Lastly, we discuss how cell death pathways are regulated by alternative splicing as well as the potential role of this regulation on host immunity and viral infection. Altogether, these studies highlight the importance of RNA splicing in regulating host-virus interactions and suggest a role in downregulating antiviral innate immunity; this may be critical to prevent pathological inflammation.

Cellular FADD-like IL-1β-converting enzyme-inhibitory protein attenuates myocardial ischemia/reperfusion injury via suppressing apoptosis and autophagy simultaneously

BACKGROUND AND AIMS

Myocardial ischemia/reperfusion injury (MI/RI) is a result of coronary revascularization, and often increases cell apoptosis and autophagy. Downregulated cellular FADD-like-IL-1β-converting enzyme-inhibitory protein (cFLIP) was associated with development of several myocardial diseases, whether overexpression of cFLIP can attenuate MI/RI remains unclear. This study aimed to determine the effects of cFLIP on apoptosis and autophagy in MI/RI.

METHODS AND RESULTS

Ischemia/reperfusion (I/R) rat model and hypoxia/reoxygenation (H/R) cardiomyocytes model were established. Both I/R injury and H/R injury down-regulated expression of two cFLIP isoforms (cFLIPL and cFLIPS), and instigated apoptosis and autophagy simultaneously. Overexpression of cFLIPL and/or cFLIPS led to a significant increase in cardiomyocytes viability in vitro, and also reduced the myocardial infarct volume in vivo, these changes were associated with suppressed apoptosis and autophagy. Mechanistically, overexpression of cFLIP significantly downregulated pro-apoptotic molecules (Caspase-3, -8, -9), and pro-autophagic molecules (Beclin-1 and LC3-II). Moreover, cFLIP significantly suppressed activity of NF-κB pathway to upregulate the expression of Bcl-2, which is the molecular of interplay of apoptosis and autophagy.

CONCLUSION

Overexpression of cFLIP significantly attenuated MI/RI both in vivo and vitro via suppression of apoptosis and lethal autophagy. cFLIP can suppress activity of NF-κB pathway, and further upregulated expression of Bcl-2.

Molecular characterisation of ILRUN, a novel inhibitor of proinflammatory and antimicrobial cytokines

Regulation of type-I interferon (IFN) production is essential to the balance between antimicrobial defence and autoimmune disorders. The human protein-coding gene ILRUN (inflammation and lipid regulator with UBA-like and NBR1-like domains, previously C6orf106) was recently characterised as an inhibitor of antiviral and proinflammatory cytokine (interferon-alpha/beta and tumor necrosis factor alpha) transcription. Currently there is a paucity of information about the molecular characteristics of ILRUN, despite it being associated with several diseases including virus infection, coronary artery disease, obesity and cancer. Here, we characterise ILRUN as a highly phylogenetically conserved protein containing UBA-like and a NBR1-like domains that are both essential for inhibition of type-I interferon and tumor necrosis factor alpha) transcription in human cells. We also solved the crystal structure of the NBR1-like domain, providing insights into its potential role in ILRUN function. This study provides critical information for future investigations into the role of ILRUN in health and disease.

C6orf106 is a novel inhibitor of the interferon-regulatory factor 3-dependent innate antiviral response

Host recognition of intracellular viral RNA and subsequent induction of cytokine signaling are tightly regulated at the cellular level and are a target for manipulation by viruses and therapeutics alike. Here, we characterize chromosome 6 ORF 106 (C6orf106) as an evolutionarily conserved inhibitor of the innate antiviral response. C6orf106 suppresses the synthesis of interferon (IFN)-α/β and proinflammatory tumor necrosis factor (TNF) α in response to the dsRNA mimic poly(I:C) and to Sendai virus infection. Unlike canonical inhibitors of antiviral signaling, C6orf106 blocks interferon-regulatory factor 3 (IRF3) and, to a lesser extent, NF-κB activity without modulating their activation, nuclear translocation, cellular expression, or degradation. Instead, C6orf106 interacts with IRF3 and inhibits IRF3 recruitment to type I IFN promoter sequences while also reducing the nuclear levels of the coactivator proteins p300 and CREB-binding protein (CBP). In summary, we have defined C6orf106 as a negative regulator of antiviral immunity that blocks IRF3-dependent cytokine production via a noncanonical and poorly defined mechanism. This work presents intriguing implications for antiviral immunity, autoimmune disorders, and cancer.