cAMP Signaling of Adenylate Cyclase Toxin Blocks the Oxidative Burst of Neutrophils through Epac-Mediated Inhibition of Phospholipase C Activity

Abstract

The adenylate cyclase toxin-hemolysin (CyaA) plays a key role in immune evasion and virulence of the whooping cough agent Bordetella pertussis. CyaA penetrates the complement receptor 3–expressing phagocytes and ablates their bactericidal capacities by catalyzing unregulated conversion of cytosolic ATP to the key second messenger molecule cAMP. We show that signaling of CyaA-generated cAMP blocks the oxidative burst capacity of neutrophils by two converging mechanisms. One involves cAMP/protein kinase A–mediated activation of the Src homology region 2 domain–containing phosphatase-1 (SHP-1) and limits the activation of MAPK ERK and p38 that are required for assembly of the NADPH oxidase complex. In parallel, activation of the exchange protein directly activated by cAMP (Epac) provokes inhibition of the phospholipase C by an as yet unknown mechanism. Indeed, selective activation of Epac by the cell-permeable analog 8-(4-chlorophenylthio)-2′-O-methyladenosine-3′,5′-cyclic monophosphate counteracted the direct activation of phospholipase C by 2,4,6-trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide. Hence, by inhibiting production of the protein kinase C–activating lipid, diacylglycerol, cAMP/Epac signaling blocks the bottleneck step of the converging pathways of oxidative burst triggering. Manipulation of neutrophil membrane composition by CyaA-produced signaling of cAMP thus enables B. pertussis to evade the key innate host defense mechanism of reactive oxygen species–mediated killing of bacteria by neutrophils.

Bordetella pertussis Adenylate Cyclase Toxin Disrupts Functional Integrity of Bronchial Epithelial Layers

“…Moreover, CyaA action caused only a modest inhibition of the IL-17A-induced production of the neutrophil-attracting chemokine IL-8. This must not necessarily be a problem for the infecting bacterium, as cAMP intoxication by the secreted CyaA paralyzes the bactericidal functions of neutrophils very efficiently (18).…”

“…There the AC enzyme is activated by calmodulin and catalyzes the massive and unregulated conversion of ATP into the second messenger molecule, 3=,5=-cyclic AMP (cAMP) (16). cAMP signaling then instantly ablates the bactericidal functions of the myeloid phagocytes, such as the oxidative burst and opsonophagocytic killing of bacteria by neutrophils and macrophages (16)(17)(18)(19)(20). In parallel, the Hly moiety oligomerizes into cation-selective pores and permeabilizes cells for the efflux of cytosolic K ϩ ions, activating mitogen-activated protein kinase signaling (21).…”

Live attenuated pertussis vaccine BPZE1 induces a broad antibody response in humans

“…The mix of subclasses may compete for binding to the bacteria and interfere with uptake and signaling pathways regulating ROS production (67). Another potential explanation for the failure of aPV serum to stimulate ROS may be related to ACT released by B. pertussis, known to inhibit ROS production of neutrophils through cAMP signaling, which is critical for mediating bacterial evasion from immune responses (68). Only the BPZE1 vaccinees had induced robust anti-ACT antibodies, which could potentially have resulted in neutralization of ACT and alleviation of any inhibition of ROS production.…”

Neutrophils to the ROScue: Mechanisms of NADPH Oxidase Activation and Bacterial Resistance

“…Lethal toxin proteolytically cleaves mitogen-activated protein kinase kinases, which are involved in MAP kinase signaling upstream of p47 phox activation (Crawford et al, 2006 ). Edema toxin and CyaA both block oxidative burst in PMNs by catalyzing the unregulated conversion of cytosolic ATP to cAMP (Crawford et al, 2006 ; Cerny et al, 2017 ). Enhanced levels of cAMP, in turn, inhibit oxidative burst through two converging mechanisms.…”

“…Enhanced levels of cAMP, in turn, inhibit oxidative burst through two converging mechanisms. The first involves the aberrant activation of SHP-1, resulting in reduced activation of MAP kinase signaling upstream of p47 phox phosphorylation, and the second involves the activation of Epac (the exchange protein directly activated by cAMP), which promotes inhibition of PLC through an unknown mechanism (Cerny et al, 2017 ). Streptolysin O also blocks oxidative burst in PMNs infected with GAS, as well as in PMNs stimulated with PMA, suggesting that this toxin may interfere with one or more signaling pathways upstream of oxidative burst (Uchiyama et al, 2015 ).…”