Membrane integrity changes upon viral infection activate sphingomyelinase SMPDL3B to restrict cGAS-STING signaling via cGAMP degradation

The cyclic guanosine monophosphate (GMP)-AMP synthase (cGAS)-cyclic GMP-AMP (cGAMP)-stimulator of interferon genes (STING) pathway mediates antiviral innate immunity upon sensing cytosolic DNA. Here, we examined the impact of sphingomyelin phosphodiesterase acid-like 3B (SMPDL3B), a paralog of the LXR lipid metabolism-induced cGAMP-degrading enzyme SMPDL3A, on viral infection. We found that SMPDL3B was induced and stabilized by both viral infection and membrane-disturbing agents, suggesting a role in sensing membrane stress as an early signal of cellular danger. Deletion of SMPDL3B impaired DNA virus infection. Upon induction, SMPDL3B suppressed cGAS-STING signaling and downstream transcriptional pathways, including the interferon response. Mechanistically, SMPDL3B functioned as a cGAMP hydrolase; cGAMP-induced SMPDL3B dimerization enabled its hydrolase activity and a negative feedback loop that dampened STING signaling. SMPDL3B-deficient cells had elevated cGAMP concentrations, and Smpdl3b^-/- mice exhibited enhanced cGAMP accumulation, heightened immune activation, and reduced viral loads upon herpes simplex virus type 1 (HSV-1) infection. Thus, SMPDL3B links membrane stress to modulation of cGAS-STING signaling through cGAMP degradation, with potential implications in the contexts of inflammation or autoimmunity.