PKACs attenuate innate antiviral response by phosphorylating VISA and priming it for MARCH5-mediated degradation.

Sensing of viral RNA by RIG-I-like receptors initiates innate antiviral response, which is mediated by the central adaptor VISA. How the RIG-I-VISA-mediated antiviral response is terminated at the late phase of infection is enigmatic. Here we identified the protein kinase A catalytic (PKAC) subunits α and ß as negative regulators of RNA virus-triggered signaling in a redundant manner. Viral infection up-regulated cellular cAMP levels and activated PKACs, which then phosphorylated VISA at T54. This phosphorylation abrogated virus-induced aggregation of VISA and primed it for K48-linked polyubiquitination and degradation by the E3 ligase MARCH5, leading to attenuation of virus-triggered induction of downstream antiviral genes. PKACs-deficiency or inactivation by the inhibitor H89 potentiated innate immunity to RNA viruses in cells and mice. Our findings reveal a critical mechanism of attenuating innate immune response to avoid host damage at the late phase of viral infection by the house-keeping PKA kinase.

Ablation of the Cß2 subunit of PKA in immune cells leads to increased susceptibility to systemic inflammation in mice.

Protein kinase A (PKA) is a holoenzyme composed of a regulatory subunit dimer and two catalytic subunits and regulates numerous cellular functions including immune cell activity. There are two major catalytic subunit genes, PRKACA and PRKACB encoding the catalytic subunits Cα and Cß. The PRKACB gene encodes several splice variants including Cß2, which is enriched in T-, B- and natural killer cells. Cß2 is significantly larger (46 kDa) than any other C splice variant. In this study we characterized mice ablated for the Cß2 protein demonstrating a significantly reduced cAMP-induced catalytic activity of PKA in the spleenocytes, lymphocytes and thymocytes. We also observed a significantly increased number of CD62L-expressing CD4+ and CD8+ T cells in LNs, accompanied by increased susceptibility to systemic inflammation by the Cß2 ablated mice. The latter was reflected in an elevated sensitivity to collagen-induced arthritis (CIA), as well as higher concentration of TNF-α and lower concentration of IL-10 in response to LPS challenges. We suggest a role of Cß2 in regulating innate as well as adaptive immune sensitivity in vivo.