AMP-activated Kinase (AMPK) Promotes Innate Immunity and Antiviral Defense through Modulation of Stimulator of Interferon Genes (STING) Signaling

Abstract

Edited by Luke O'NeillThe host protein Stimulator of Interferon Genes (STING) has been shown to be essential for recognition of both viral and intracellular bacterial pathogens, but its regulation remains unclear. Previously, we reported that mitochondrial membrane potential regulates STING-dependent IFN-␤ induction independently of ATP synthesis. Because mitochondrial membrane potential controls calcium homeostasis, and AMP-activated protein kinase (AMPK) is regulated, in part, by intracellular calcium, we postulated that AMPK participates in STING activation; however, its role has yet to be been defined. Addition of an intracellular calcium chelator or an AMPK inhibitor to either mouse macrophages or mouse embryonic fibroblasts (MEFs) suppressed IFN-␤ and TNF-␣ induction following stimulation with the STING-dependent ligand 5,6-dimethyl xanthnone-4-acetic acid (DMXAA). These pharmacological findings were corroborated by showing that MEFs lacking AMPK activity also failed to up-regulate IFN-␤ and TNF-␣ after treatment with DMXAA or the natural STING ligand cyclic GMP-AMP (cGAMP). As a result, AMPK-deficient MEFs exhibit impaired control of vesicular stomatitis virus (VSV), a virus sensed by STING that can cause an influenza-like illness in humans. This impairment could be overcome by pretreatment of AMPK-deficient MEFs with type I IFN, illustrating that de novo production of IFN-␤ in response to VSV plays a key role in antiviral defense during infection. Loss of AMPK also led to dephosphorylation at Ser-555 of the known STING regulator, UNC-51-like kinase 1 (ULK1). However, ULK1-deficient cells responded normally to DMXAA, indicating that AMPK promotes STING-dependent signaling independent of ULK1 in mouse cells.Pathogen sensing by innate immune cells is essential for host defense in response to invading microorganisms. Recognition by pattern recognition receptors typically activates signal transduction pathways, leading to up-regulation of cytokines like TNF-␣ and IFN-␤. Although IFN-␤ has a well established role in defense against viral infection, intracellular bacterial infections also induce this cytokine. In the past decade, our understanding of the molecular basis for these signaling pathways has expanded greatly and it has been discovered that there is some overlap between proteins responsible for recognition of bacteria and virus alike. One particular example is the mitochondrial and endoplasmic reticulum resident protein stimulator of interferon genes (STING) 2 (1-3). STING has been shown to be crucial for recognition of both DNA viruses (4 -6) and intracellular bacterial pathogens (7-12). STING senses DNA viruses indirectly, requiring the host enzyme cyclic GMP-AMP synthase (cGAS) to convert the viral double stranded DNA into the compound cGAMP (13-15). This metazoan second messenger, in turn, binds with high affinity to STING dimers, changing the protein conformation (16), such that it leads to activation of the kinase TBK1 and subsequent phosphorylation of the transcription factor IRF3, which is piv...

DENV up-regulates the HMG-CoA reductase activity through the impairment of AMPK phosphorylation: A potential antiviral target

“…More recently, it has been described that AMPK promotes innate immunity and antiviral defense through modulation of Stimulator of Interferon Genes (STING) Signaling [79]. It is well known that STING is a crucial adaptor in immune cells after infection with DENV and it is the target for cleavage and degradation by the viral protein NS2B-NS3 to inhibit innate immune responses [80].…”

Antiviral activity of double‐stranded RNA‐binding protein PACT against influenza A virus mediated via suppression of viral RNA polymerase

“…When IFNs prevail, IAV replication is inhibited and finally cleared. It is known that some cellular proteins, such as DPF2 (48) and AMPK (49), as well as small-molecule compounds, such as FA-613 (50), exert their antiviral activity against IAV by boosting the IFN response. Enhancing the antiviral response to a level that cannot be inhibited by IAV might be critical to the anti-IAV effect of these factors.…”

Kinetic Deuterium Isotope Effects in Cytochrome P450 Reactions

“…Thus, the absolute rate of a P450 reaction does not appear to provide any insight into how rate-limiting the C-H bond-breaking step is. In more recent studies we have used site-directed mutagenesis to make a series of naturally-occurring P450 21A2 variants identified in the clinic (Wang et al, 2017). Some of these have only 1/10 6 the catalytic activities of the wild-type enzyme but the high KIEs were seen with all.…”