Respiratory syncytial virus (RSV) causes severe acute lower respiratory tract disease. Retinoic acid-inducible gene-I (RIG-I) serves as an innate immune sensor and triggers antiviral responses upon recognizing viral infections including RSV. Since tripartite motif-containing protein 25 (TRIM25)-mediated K63-polyubiquitination is crucial for RIG-I activation, several viruses target initial RIG-I activation through ubiquitination. RSV NS1 and NS2 have been shown to interfere with RIG-I-mediated antiviral signaling. In this study, we explored the possibility that NS1 suppresses RIG-I-mediated antiviral signaling by targeting TRIM25. Ubiquitination of ectopically expressed RIG-I-2Cards domain was decreased by RSV infection, indicating that RSV possesses ability to inhibit TRIM25-mediated RIG-I ubiquitination. Similarly, ectopic expression of NS1 sufficiently suppressed TRIM25-mediated RIG-I ubiquitination. Furthermore, interaction between NS1 and TRIM25 was detected by a co-immunoprecipitation assay. Further biochemical assays showed that the SPRY domain of TRIM25, which is responsible for interaction with RIG-I, interacted sufficiently with NS1. Suppression of RIG-I ubiquitination by NS1 resulted in decreased interaction between RIG-I and its downstream molecule, MAVS. The suppressive effect of NS1 on RIG-I signaling could be abrogated by overexpression of TRIM25. Collectively, this study suggests that RSV NS1 interacts with TRIM25 and interferes with RIG-I ubiquitination to suppress type-I interferon signaling.

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24Autophagy has been implicated in innate immune responses against various intracellular 25 pathogens. Recent studies have reported that autophagy can be triggered by pathogen 26 recognizing sensors, including Toll-like receptors and cyclic guanosine monophosphate-27 adenosine monophosphate synthase, to participate in innate immunity. In the present study, 28 we examined whether the RIG-I signaling pathway, which detects viral infections by 29 recognizing viral RNA, triggers the autophagic process. The introduction of polyI:C into the 30 cytoplasm, or Sendai virus infection, significantly induced autophagy in normal cells but not 31 in RIG-I-deficient cells. PolyI:C transfection or Sendai virus infection induced autophagy in 32 the cells lacking type-I interferon signaling. This demonstrated that the effect was not due to 33 interferon signaling. RIG-I-mediated autophagy diminished by the deficiency of 34 mitochondrial antiviral signaling protein (MAVS) or tumor necrosis factor receptor-35 associated factor (TRAF)6, showing that the RIG-I-MAVS-TRAF6 signaling axis was 36critical for RIG-I-mediated autophagy. We also found that Beclin-1 was translocated to the 37 mitochondria, and it interacted with TRAF6 upon RIG-I activation. Furthermore, Beclin-1 38 underwent K63-polyubiquitination upon RIG-I activation, and the ubiquitination decreased 39 in TRAF6-deficient cells. This suggests that the RIG-I-MAVS-TRAF6 axis induced K63-40 linked polyubiquitination of Beclin-1, which has been implicated in triggering autophagy. 41Collectively, the results of this study show that the recognition of viral infection by RIG-I is 42 capable of inducing autophagy to control viral replication. As deficient autophagy increases 43 3 the type-I interferon response, the induction of autophagy by the RIG-I pathway might also 44 contribute to preventing an excessive interferon response as a negative-feedback mechanism. 45 46 Importance 47 Mammalian cells utilize various innate immune sensors to detect pathogens. Among those 48 sensors, RIG-I recognizes viral RNA to detect intracellular viral replication. Although cells 49 experience diverse physiological changes upon viral infection, studies to understand the role 50 of RIG-I signaling have focused on the induction of type-I interferon. Autophagy is a process 51that sequesters cytosolic regions and degrades the contents to maintain cellular homeostasis. 52Autophagy participates in the immune system, and has been known to be triggered by some 53 innate immune sensors, such as TLR4 and cGAS. We demonstrated that autophagy can be 54 triggered by the activation of RIG-I. In addition, we also proved that MAVS-TRAF6 55 downstream signaling is crucial for the process. Beclin-1, a key molecule in autophagy, is 56 translocated to mitochondria, where it undergoes K63-ubiquitination in a TRAF6-dependent 57 manner upon RIG-I activation. As autophagy negatively regulates RIG-I-mediated signaling, 58 the RIG-I-mediated activation of autophagy may function as a negative-feedback mechanism. 59 60 Intro...

Despite the diverse pharmacological activities of berberine, including anti-cancer and anti-inflammatory effects, the direct proteomic targets of berberine have remained largely unknown. Here, we have identified actin as a direct proteomic target of berberine using an affinity-based chemical probe. In addition, we found that actin assembly was significantly modulated by berberine in vitro at the biochemical level and cellular level.