The omega-3 (ω3) fatty acid docosahexaenoic acid (DHA) can suppress inflammation, specifically IL-1β production through poorly understood molecular mechanisms. Here, we show that DHA reduces macrophage IL-1β production by limiting inflammasome activation. Exposure to DHA reduced IL-1β production by ligands that stimulate the NLRP3, AIM2, and NAIP5/NLRC4 inflammasomes. The inhibition required Free Fatty Acid Receptor (FFAR) 4 (also known as GPR120), a G-protein coupled receptor (GPR) known to bind DHA. The exposure of cells to DHA recruited the adapter protein β-arrestin1/2 to FFAR4, but not to a related lipid receptor. DHA treatment reduced the initial inflammasome priming step by suppressing the nuclear translocation of NF-κB. DHA also reduced IL-1β levels by enhancing autophagy in the cells. As a consequence macrophages derived from mice lacking the essential autophagy protein ATG7 were partially resistant to suppressive effects of DHA. Thus, DHA suppresses inflammasome activation by two distinct mechanisms, inhibiting the initial priming step and by augmenting autophagy, which limits inflammasome activity.

Autophagy is an essential eukaryotic pathway requiring tight regulation to maintain homeostasis and preclude disease. Using yeast and mammalian cells, we report a conserved mechanism of autophagy regulation by RNA helicase RCK family members in association with the decapping enzyme Dcp2. Under nutrient-replete conditions, Dcp2 undergoes TOR-dependent phosphorylation and associates with RCK members to form a complex with autophagy-related (ATG) mRNA transcripts, leading to decapping, degradation and autophagy suppression. Simultaneous with the induction of ATG mRNA synthesis, starvation reverses the process, facilitating ATG mRNA accumulation and autophagy induction. This conserved post-transcriptional mechanism modulates fungal virulence and the mammalian inflammasome, the latter providing mechanistic insight into autoimmunity reported in a patient with a PIK3CD/p110δ gain-of-function mutation. We propose a dynamic model wherein RCK family members, in conjunction with Dcp2, function in controlling ATG mRNA stability to govern autophagy, which in turn modulates vital cellular processes affecting inflammation and microbial pathogenesis.

G-protein signaling modulators (GPSM) play diverse functional roles through their interaction with G-protein subunits. AGS3 (GPSM1) contains four G-protein regulatory motifs (GPR) that directly bind G␣ i free of G␤␥ providing an unusual scaffold for the "G-switch" and signaling complexes, but the mechanism by which signals track into this scaffold are not well understood. We report the regulation of the AGS3⅐ G␣ i signaling module by a cell surface, seven-transmembrane receptor. AGS3 and G␣ i1 tagged with Renilla luciferase or yellow fluorescent protein expressed in mammalian cells exhibited saturable, specific bioluminescence resonance energy transfer indicating complex formation in the cell. Activation of ␣ 2 -adrenergic receptors or -opioid receptors reduced AGS3-RLuc⅐G␣ i1 -YFP energy transfer by over 30%. The agonist-mediated effects were inhibited by pertussis toxin and co-expression of RGS4, but were not altered by G␤␥ sequestration with the carboxyl terminus of GRK2. G␣ i -dependent and agonist-sensitive bioluminescence resonance energy transfer was also observed between AGS3 and cell-surface receptors typically coupled to G␣ i and/or G␣ o indicating that AGS3 is part of a larger signaling complex. Upon receptor activation, AGS3 reversibly dissociates from this complex at the cell cortex. Receptor coupling to both G␣␤␥ and GPR-G␣ i offer additional flexibility for systems to respond and adapt to challenges and orchestrate complex behaviors.