The cGAS-STING signaling axis can be activated by cytosolic DNA, including both non-self DNA and self DNA. This axis is used by the innate immune system to monitor invading pathogens and/or damage. ...Increasing evidence has suggested that the cGAS-STING pathway not only facilitates inflammatory responses and the production of type I interferons (IFN), but also activates other cellular processes, such as apoptosis. Recently, many studies have focused on analyzing the mechanisms of apoptosis induced by the cGAS-STING pathway and their consequences. This review gives a detailed account of the interplay between the cGAS-STING pathway and apoptosis. The cGAS-STING pathway can induce apoptosis through ER stress, NLRP3, NF-κB, IRF3, and IFN signals. Conversely, apoptosis can feed back to regulate the cGAS-STING pathway, suppressing it via the activation of caspases or promoting it via mitochondrial DNA (mtDNA) release. Apoptosis mediated by the cGAS-STING pathway plays crucial roles in balancing innate immune responses, resisting infections, and limiting tumor growth.
The cGAS-STING pathway is a key component of the innate immune system and exerts crucial roles in the detection of cytosolic DNA and invading pathogens. Accumulating evidence suggests that the ...intrinsic cGAS-STING pathway not only facilitates the production of type I interferons (IFN-I) and inflammatory responses but also triggers autophagy. Autophagy is a homeostatic process that exerts multiple effects on innate immunity. However, systematic evidence linking the cGAS-STING pathway and autophagy is still lacking. Therefore, one goal of this review is to summarize the known mechanisms of autophagy induced by the cGAS-STING pathway and their consequences. The cGAS-STING pathway can trigger canonical autophagy through liquid-phase separation of the cGAS-DNA complex, interaction of cGAS and Beclin-1, and STING-triggered ER stress-mTOR signaling. Furthermore, both cGAS and STING can induce non-canonical autophagy via LC3-interacting regions and binding with LC3. Subsequently, autophagy induced by the cGAS-STING pathway plays crucial roles in balancing innate immune responses, maintaining intracellular environmental homeostasis, alleviating liver injury, and limiting tumor growth and transformation.
African swine fever virus (ASFV) encodes more than 150 proteins, which establish complex interactions with the host for the benefit of the virus in order to evade the host’s defenses. However, ...currently, there is still a lack of information regarding the roles of the viral proteins in host cells. Here, our data demonstrated that ASFV structural protein p17 exerts a negative regulatory effect on cGAS-STING signaling pathway and the STING signaling dependent anti-HSV1 and anti-VSV functions. Further, the results indicated that ASFV p17 was located in ER and Golgi apparatus, and interacted with STING. ASFV p17 could interfere the STING to recruit TBK1 and IKKϵ through its interaction with STING. It was also suggested that the transmembrane domain (amino acids 39–59) of p17 is required for interacting with STING and inhibiting cGAS-STING pathway. Additionally, with the p17 specific siRNA, the ASFV induced IFN-β, ISG15, ISG56, IL-6 and IL-8 gene transcriptions were upregulated in ASFV infected primary porcine alveolar macrophages (PAMs). Taken together, ASFV p17 can inhibit the cGAS-STING pathway through its interaction with STING and interference of the recruitment of TBK1 and IKKϵ. Our work establishes the role of p17 in the immune evasion and thus provides insights on ASFV pathogenesis.
African swine fever virus (ASFV) is a highly pathogenic large DNA virus that causes African swine fever (ASF) in domestic pigs and wild boars. The p17 protein, encoded by the D117L gene, is a major ...transmembrane protein of the capsid and the inner lipid envelope. The aim of this study was to investigate the effects of p17 on cell proliferation and the underlying mechanisms of action. The effects of p17 on cell proliferation, cell cycle, apoptosis, oxidative stress, and endoplasmic reticulum (ER) stress have been examined in 293T, PK15, and PAM cells, respectively. The results showed that p17 reduced cell proliferation by causing cell cycle arrest at G2/M phase. Further, p17-induced oxidative stress and increased the level of intracellular reactive oxygen species (ROS). Decreasing the level of ROS partially reversed the cell cycle arrest and prevented the decrease of cell proliferation induced by p17 protein. In addition, p17-induced ER stress, and alleviating ER stress decreased the production of ROS and prevented the decrease of cell proliferation induced by p17. Taken together, this study suggests that p17 can inhibit cell proliferation through ER stress and ROS-mediated cell cycle arrest, which might implicate the involvement of p17 in ASF pathogenesis.
African swine fever (ASF) is mainly an acute hemorrhagic disease which is highly contagious and lethal to domestic pigs and wild boars. The global pig industry has suffered significant economic ...losses due to the lack of an effective vaccine and treatment. The African swine fever virus (ASFV) has a large genome of 170-190 kb, encoding more than 150 proteins. During infection, ASFV evades host innate immunity via multiple viral proteins. A528R is a very important member of the polygene family of ASFV, which was shown to inhibit IFN-β production by targeting NF-κB, but its mechanism is not clear. This study has shown that A528R can suppress the TLR8-NF-κB signaling pathway, including the inhibition of downstream promoter activity, NF-κB p65 phosphorylation and nuclear translocation, and the antiviral and antibacterial activity. Further, we found the cellular co-localization and interaction between A528R and p65, and ANK repeat domains of A528R and RHD of p65 are involved in their interaction and the inhibition of p65 activity. Therefore, we conclude that A528R inhibits TLR8-NF-κB signaling by targeting p65 activation and nuclear translocation.
The innate immune DNA sensing cGAS-STING signaling pathway has been widely recognized for inducing interferons (IFNs) and subsequent antiviral state. In addition to IFN, the cGAS-STING pathway also ...elicits other cell autonomous immunity events including autophagy and apoptosis. However, the downstream signaling events of this DNA sensing pathway in livestock have not been well defined. Here, we systematically analyzed the porcine STING (pSTING) induced IFN, autophagy and apoptosis, revealed the distinct dynamics of three STING downstream events, and established the IFN independent inductions of autophagy and apoptosis. Further, we investigated the regulation of autophagy on pSTING induced IFN and apoptosis. Following TBK1-IRF3-IFN activation, STING induced Atg5/Atg16L1 dependent autophagy through LIR motifs. In turn, the autophagy likely promoted the pSTING degradation, inhibited both IFN production and apoptosis, and thus restored the cell homeostasis. Therefore, this study sheds lights on the molecular mechanisms of innate immunity in pigs.
African swine fever virus (ASFV) is a large double-stranded DNA virus that is highly infectious and seriously affects domestic pigs and wild boars. African swine fever (ASF) has caused huge economic ...losses to endemic countries and regions. At present, there is still a lack of effective vaccines and therapeutics. Therefore, rapid and accurate detection is essential for the prevention and control of ASF. The portable DNA endonuclease (Cas12a)-mediated lateral flow strip detection method (Cas12a-LFS) combined with recombinant polymerase amplification (RPA) has been gradually recognized as effective for virus detection including ASFV. In this study, based on the ASFV structural protein p17 gene (D117L), an RPA-Cas12a-LFS detection method was established. The detection method exhibits a sensitivity of up to two gene copies and has no cross-reaction with nine other swine viruses. Thus, the method is highly sensitive and specific. In 68 clinical samples, the coincidence rate of the p17 strip was 100%, compared to the traditional quantitative PCR (qPCR). In conclusion, we have developed a simple, rapid, sensitive, and specific ASFV visual detection method and demonstrated the potential of on-site detection of ASFV.
It has been recently recognized that the DNA sensing innate immune cGAS-STING pathway exerts an IFN-independent antiviral function; however, whether and how chicken STING (chSTING) exerts such an ...IFN-independent antiviral activity is still unknown. Here, we showed that chSTING exerts an antiviral activity in HEK293 cells and chicken cells, independent of IFN production. chSTING was able to trigger cell apoptosis and autophagy independently of IFN, and the apoptosis inhibitors, rather than autophagy inhibitors, could antagonize the antiviral function of chSTING, suggesting the involvement of apoptosis in IFN-independent antiviral function. In addition, chSTING lost its antiviral function in IRF7-knockout chicken macrophages, indicating that IRF7 is not only essential for the production of IFN, but also participates in the other activities of chSTING, such as the apoptosis. Collectively, our results showed that chSTING exerts an antiviral function independent of IFN, likely via apoptosis.
The cyclic GMP–AMP synthase and stimulator of interferon (IFN) genes (cGAS–STING) pathway serves as a crucial component of innate immune defense and exerts immense antiviral activity by inducing the ...expression of type I IFNs. Currently, STING-activated production of type I IFNs has been thought to be mediated only by TANK-binding kinase 1 (TBK1). Here, we identified that porcine IKKε (pIKKε) is also directly involved in STING-induced type I IFN expression and antiviral response by using IKKε−/− porcine macrophages. Similar to pTBK1, pIKKε interacts directly with pSTING on the C-terminal tail. Furthermore, the TBK1-binding motif of pSTING C-terminal tail is essential for its interaction with pIKKε, and within the TBK1-binding motif, the leucine (L) 373 is also critical for the interaction. On the other hand, both kinase domain and scaffold dimerization domain of pIKKε participate in the interactions with pSTING. Consistently, the reconstitution of pIKKε and its mutants in IKKε−/− porcine macrophages corroborated that IKKε and its kinase domain and scaffold dimerization domain are all involved in the STING signaling and antiviral function. Thus, our findings deepen the understanding of porcine cGAS–STING pathway, which lays a foundation for effective antiviral therapeutics against porcine viral diseases.
The innate immune DNA-sensing cyclic GMP-AMP synthase (cGAS)-stimulator of interferon (IFN) gene (STING) pathway exerts strong antiviral activity through downstream IFN production; however, it has ...been recently recognized that an IFN-independent activity of STING also plays an important role in antiviral functions. Nevertheless, the IFN-independent antiviral activity of STING is not fully understood. Here, we showed that porcine STING (pSTING) played a critical role against herpes simplex virus 1 (HSV-1) and vesicular stomatitis virus (VSV) infections, and IFN-defective mutants, including pSTING pLxIS sub, S365A, and △CTT, all exhibited similar antiviral functions, compared to wild-type (WT) pSTING. Furthermore, all of these IFN-defective pSTING mutants possessed comparable autophagy activity, relative to WT pSTING, as expected. From pSTING WT, S365A, and △CTT, the residues responsible for autophagy, including L333A/R334A, Y167A/L170A, and Y245A/L248A, were mutated. Surprisingly, all of these autophagy-defective pSTING mutants still resisted the two viral infections, demonstrating that the pSTING antiviral function is independent of IFN as well as autophagy. On the other hand, all of the autophagy-defective pSTING mutants triggered cell apoptosis, which was associated with and participated in the antiviral functions. Additionally, pSTING lost its antiviral activity in TANK-binding kinase 1 (TBK1)
and IFN regulatory factor 3 (IRF3)
porcine macrophages, indicating the involvement of TBK1 and IRF3 in other STING activities such as apoptosis. Collectively, our results revealed that STING exerts both IFN- and autophagy-independent antiviral activity, and they also suggested that STING-triggered cell apoptosis resists viral infections.
The IFN-independent antiviral function of the cGAS-STING pathway has attracted great attention in recent years; however, the nature of this IFN-independent antiviral function is unknown, although STING-induced autophagy has been shown to mediate the STING antiviral activity. First, we analyzed the antiviral activity through the porcine cGAS-pSTING pathway and established that pSTING signaling exerts an IFN-independent antiviral function. Second, we found that pSTING-induced IFN-independent autophagy and the antiviral activity of pSTING are independent of both IFN and autophagy. Finally, pSTING signaling activates cell apoptosis independently of IFN and autophagy, and the apoptosis is associated with antiviral activity. Our results suggest that pSTING-activated apoptosis at least partially mediates the antiviral activity or multiple pSTING-activated signals, including IFN production, nuclear factor κ light chain enhancer of activated B cells (NF-κB) expression, autophagy, and apoptosis, exert a redundant antiviral role. Thus, the work reveals a new layer of complexity in STING antiviral activity.
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