Suppression of LPS-Induced TNF-α Production in Macrophages by cAMP Is Mediated by PKA-AKAP95-p105

Abstract

The activation of macrophages through Toll-like receptor (TLR) pathways leads to the production of a broad array of cytokines and mediators that coordinate the immune response. The inflammatory potential of this response can be reduced by compounds, such as prostaglandin E 2 , that induce the production of cyclic adenosine monophosphate (cAMP). Through experiments with cAMP analogs and multigene RNA interference (RNAi), we showed that key anti-inflammatory effects of cAMP were mediated specifically by cAMP-dependent protein kinase (PKA). Selective inhibitors of PKA anchoring, time-lapse microscopy, and RNAi screening suggested that differential mechanisms of PKA action existed. We showed a specific role for A kinase-anchoring protein 95 in suppressing the expression of the gene encoding tumor necrosis factor-α, which involved phosphorylation of p105 (also known as Nfkb1) by PKA at a site adjacent to the region targeted by inhibitor of nuclear factor κB kinases. These data suggest that crosstalk between the TLR4 and cAMP pathways in macrophages can be coordinated through PKA-dependent scaffolds that localize specific pools of the kinase to distinct substrates.

PGE2 induced in and released by dying cells functions as an inhibitory DAMP

“…That PGE2 can suppress LPS-induced inflammatory cytokine and type I IFN secretion is known, however the mechanism of these suppressive effects has been controversial (12,14). One study showed suppression of the NF-κB pathway by cAMP, a downstream effecter molecule of PGE2 signaling, whereas another argued that the NF-κB pathway is unaffected by cAMP signaling (15,16). We found no evidence that the NF-κB pathway is affected by PGE2 signaling (Fig.…”

“…The observations showing that dead cell-derived PGE2 inhibits the LPS-mediated induction of Tnf and Ifnb1 mRNA also prompted us to study the underlying mechanism, which has been poorly understood (12,(14)(15)(16). Because the induction of TNF-α by LPS requires activation of NF-κB and MAPK pathways (3, 4), we next examined the effect of PGE2 on the LPS-mediated activation of canonical NF-κB and MAPK in RAW 264.7 cells.…”

“…PGE2 is the main product of two cyclooxygenases, COX-1 and COX-2, of which COX-1 is constitutively expressed and COX-2 is induced by various stimuli such as cytokines and various PAMPs (12,13). PGE2 is the most abundant eicosanoid lipid in the inflammatory environment, and its receptors EP2 and EP4 and their downstream signaling to cAMP are proposed for the suppression of inflammation, although the precise mechanism is unclear (10,12,(14)(15)(16). COX-2 is also overexpressed in various forms of cancer, and PGE2 produced by COX-2 has been implicated in the exacerbation of cancer (11,13).…”

Targeting the adenosine 2A receptor enhances chimeric antigen receptor T cell efficacy

“…Our studies also revealed that A 2A R-deficient CAR T cells exhibited increased secretion of TNF-α within the tumor microenvironment. The reasons for this remain to be elucidated but could be related to the observation that the cAMP/PKA pathway (the predominant signaling pathway for the A 2A R) potently inhibits TNF-α production in macrophages (52). Although our results indicate that increased IFN-γ production is critical for the efficacy of dual PD-1/A 2A R targeting, this does not preclude a role for TNF-α in this effect given that TNF-α may act in part to increase IFN-γ production.…”

Transforming Growth Factor (TGF)-β-activated Kinase 1 (TAK1) Activation Requires Phosphorylation of Serine 412 by Protein Kinase A Catalytic Subunit α (PKACα) and X-linked Protein Kinase (PRKX)

“…They are activated by an elevated cellular concentration of the second messenger cAMP (20), although their activation independent of cAMP has also been reported (21,22). Many studies have shown that the cAMP-PKA module is involved in the regulation of NF-B signaling through the phosphorylation of p65 or p105 in a positive or negative manner, depending on cell type (16,(23)(24)(25)(26). Determination of whether PKA also targets other components in NF-B signaling pathways requires more study.…”