Activation of RIG-I-mediated antiviral signaling triggers autophagy through the MAVS-TRAF6-Beclin-1 signaling axis

Abstract

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...

Influenza PB1-F2 Inhibits Avian MAVS Signaling

“…RIG-I signaling is tightly regulated in cells through a complex network of positive and negative feedback mechanisms that involve several different de-ubiquitinating enzymes (reviewed in [55]). Indirect and reciprocal negative regulatory mechanisms have also been previously described [56,57], including the induction of autophagy through MAVS [58]. PR8 NS1 was expected to inhibit human TRIM25 mediated ubiquitination [24], however, we observed increased ubiquitination.…”

HIF-1beta Positively Regulates NF-kappaB Activity via Direct Control of TRAF6

“…Conditional knockout models revealed essential roles for TRAF6 in a variety of immune cellular backgrounds but also in epithelial cell types [29][30][31][32], indicating how important this factor is for normal cellular homeostasis. More recently, TRAF6 has been implicated also in cancer signalling, by regulating epithelial to mesenchymal transition (EMT) in colon cancer [33], DNA damage in breast cancer backgrounds [34], and involvement in autophagy responses [35]. Our results demonstrate the importance of TRAF6 in cell survival, following NF-B stimulation, in cancer cells.…”

Focusing on the Unfolded Protein Response and Autophagy Related Pathways to Reposition Common Approved Drugs against COVID-19

“…For instance, the NLRP3 inflammasome could be activated by the RIG-I-like and TLR4 receptors-mediated signaling but is also modulated by the autophagy flux. In turn, the autophagy pathway can be activated either by the canonical ATF4 and DDIT3(CHOP) transcription factors cascade or by the RIG-I-like receptors establishing functional feedback-loops in this signaling network [29][30][31][32][33][34][35][36] . Remarkably, recent publications linked the activation of NLRP3 inflammasome to cytokine storms 37 , which were reported to be involved in severe forms of COVID-19 38 .…”