Stimulator of interferon genes (STING, also known as MITA and ERIS) is critical in protecting the host against DNA pathogen invasion. However, the molecular mechanism underlying the regulation of STING remains unclear. Here, we show that PPM1A negatively regulates antiviral signaling by targeting STING in its phosphatase activity-dependent manner, and in a line with this, PPM1A catalytically dephosphorylates STING and TBK1 in vitro. Importantly, we provide evidence that whereas TBK1 promotes STING aggregation in a phosphorylation-dependent manner, PPM1A antagonizes STING aggregation by dephosphorylating both STING and TBK1, emphasizing that phosphorylation is crucial for the efficient activation of STING. Our findings demonstrate a novel regulatory circuit in which STING and TBK1 reciprocally regulate each other to enable efficient antiviral signaling activation, and PPM1A dephosphorylates STING and TBK1, thereby balancing this antiviral signal transduction.

Retinoic acid-inducible gene I (RIG-I) plays important roles in pathogen recognition and antiviral signalling transduction. Here we show that syndecan-4 (SDC4) is a RIG-I-interacting partner identified in a yeast two-hybrid screen. We find that SDC4 negatively regulates the RIG-I-mediated antiviral signalling in a feedback-loop control manner. The genetic evidence obtained by using knockout mice further emphasizes this biological role of SDC4 in antiviral signalling. Mechanistically, we show that SDC4 interacts with both RIG-I and deubiquitinase CYLD via its carboxyl-terminal intracellular region. SDC4 likely promotes redistribution of RIG-I and CYLD in a perinuclear pattern post viral infection, and thus enhances the RIG-I–CYLD interaction and potentiates the K63-linked deubiquitination of RIG-I. Collectively, our findings uncover a mechanism by which SDC4 antagonizes the activation of RIG-I in a CYLD-mediated deubiquitination-dependent process, thereby balancing antiviral signalling to avoid deleterious effects on host cells.

MAVS is a critical adaptor required for activating an innate antiviral immune response against viral infection. The activation of MAVS requires modification of the Lys63-linked ubiquitination and formation of prion-like aggregates. However, the molecular mechanisms regulating MAVS activity remain largely obscured. In this study, we identified a deubiquitinase YOD1, also known as a member of the ovarian tumor family, as a negative regulator of MAVS activation in both human and murine cells. YOD1 was recruited to mitochondria to interact with MAVS through its UBX and Znf domains after viral infection. Subsequently, YOD1 cleaved the K63-linked ubiquitination and abrogated the formation of prion-like aggregates of MAVS, which led to attenuation of IRF3, P65 activation, and IFN-β production. Knockdown of YOD1 potentiated IRF3 and P65 activation, IFN-β production, and antiviral innate immune response to RNA virus. Our findings thus provided, to our knowledge, novel insights into the regulatory cascade of the cellular antiviral response through YOD1-mediated K63-linked deubiquitination and aggregation of MAVS.

Transcriptional status determines the HIV replicative state in infected patients. However, the transcriptional mechanisms for proviral replication control remain unclear. In this study, we show that, apart from its function in HIV integration, LEDGF/p75 differentially regulates HIV transcription in latency and proviral reactivation. During latency, LEDGF/p75 suppresses proviral transcription via promoter-proximal pausing of RNA polymerase II (Pol II) by recruiting PAF1 complex to the provirus. Following latency reversal, MLL1 complex competitively displaces PAF1 from the provirus through casein kinase II (CKII)–dependent association with LEDGF/p75. Depleting or pharmacologically inhibiting CKII prevents PAF1 dissociation and abrogates the recruitment of both MLL1 and Super Elongation Complex (SEC) to the provirus, thereby impairing transcriptional reactivation for latency reversal. These findings, therefore, provide a mechanistic understanding of how LEDGF/p75 coordinates its distinct regulatory functions at different stages of the post-integrated HIV life cycles. Targeting these mechanisms may have a therapeutic potential to eradicate HIV infection.