cAMP signalling ofBordetellaadenylate cyclase toxin through the SHP‐1 phosphatase activates the BimEL‐Bax pro‐apoptotic cascade in phagocytes

Abstract

The adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) plays a key role in virulence of Bordetella pertussis. CyaA penetrates myeloid cells expressing the complement receptor 3 (αM β2 integrin CD11b/CD18) and subverts bactericidal capacities of neutrophils and macrophages by catalysing unregulated conversion of cytosolic ATP to the key signalling molecule adenosine 3',5'-cyclic monophosphate (cAMP). We show that the signalling of CyaA-produced cAMP hijacks, by an as yet unknown mechanism, the activity of the tyrosine phosphatase SHP-1 and activates the pro-apoptotic BimEL-Bax cascade. Mitochondrial hyperpolarization occurred in human THP-1 macrophages within 10 min of exposure to low CyaA concentrations (e.g. 20 ng ml(-1) ) and was accompanied by accumulation of BimEL and association of the pro-apoptotic factor Bax with mitochondria. BimEL accumulation required cAMP/protein kinase A signalling, depended on SHP-1 activity and was selectively inhibited upon small interfering RNA knockdown of SHP-1 but not of the SHP-2 phosphatase. Moreover, signalling of CyaA-produced cAMP inhibited the AKT/protein kinase B pro-survival cascade, enhancing activity of the FoxO3a transcription factor and inducing Bim transcription. Synergy of FoxO3a activation with SHP-1 hijacking thus enables the toxin to rapidly trigger a persistent accumulation of BimEL, thereby activating the pro-apoptotic programme of macrophages and subverting the innate immunity of the host.

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

“…4C) that the contribution of PKA activation to the inhibition of ROS production in response to fMLF could be indirect and might potentially result from inhibition of MAPK (ERK and p38) signaling toward NADPH complex assembly. This would be in line with our previous reports that activation of PKA signaling by CyaA-generated cAMP activates, by an as yet unknown mechanism, the tyrosine phosphatase SHP-1, which is known to deactivate ERK by dephosphorylation of its Thr 202 and Tyr 204 residues (13,39,54). We have measured fMLF-stimulated phosphorylation of ERK on these two sites and found it to be significantly reduced by incubation with active CyaA toxin (Fig.…”

“…4C, but it remains to be conclusively demonstrated. Intriguingly, we found previously that the CyaA/cAMP-elicited activation of SHP-1 and inhibition of ERK in monocytes was mediated by the cAMP-triggered activity of PKA and not by Epac (13,39,55). The involvement of cAMP-activated PKA signaling in promoting dephosphorylation of ERK and p38 has previously been reported in human neutrophils (56,57 [58] would actually have been Epacspecific if it was modified by a methyl group at the 29 position [63]).…”

“…Previously, we found that signaling of CyaA-produced cAMP through the PKA pathway yields activation of the tyrosine phosphatase Src homology domain 2-containing protein tyrosine phosphatase 1 (SHP-1) that inhibits ERK activity in macrophages (13,39). Therefore, we assessed whether CyaA action on fMLFstimulated neutrophils interferes with the activating phosphorylation of the ERK and p38 kinases that are known to be involved in NADPH oxidase assembly.…”

Exposure to Bordetella pertussis adenylate cyclase toxin affects integrin‐mediated adhesion and mechanics in alveolar epithelial cells

“…In macrophages, inactivation of the GTPase RhoA by CyaA toxin leads to actin cytoskeleton rearrangements including membrane ruffling and alterations of phagocytic functions (Kamanova et al., ). In addition, CyaA can induce apoptosis associated with caspase activation and thus promote the activation of cell death cascade in macrophages cells (Gueirard et al., ; Ahmad et al., ). However, CyaA toxin also invades a broad range of cells that do not express CD11b/CD18, although the functional and patho‐physiological consequences of CyaA cytotoxicity are not fully understood.…”

Bacterial Toxins as Pathogen Weapons Against Phagocytes

“…High levels of cAMP cause a transient inactivation of RhoA inducing massive actin rearrangements that dramatically decrease macropinocytosis, block complement-mediated phagocytosis ( Kamanova et al, 2008 ) and possibly impair the chemotactic properties of primary monocytes. Recently, ACT-induced cAMP synthesis was shown to trigger pro-apoptotic signaling in phagocytes through the activity of tyrosine phosphatase SHP-1, the accumulation of cytosolic BimEL and the consequent activation of Bax, permeabilisation of the outer mitochondrial membrane and activation of programmed cell death ( Ahmad et al, 2015 ; Cerny et al, 2015 ). Besides the immediate action of ACT on the ablation of bactericidal functions of phagocytes, ACT activity was also reported to block the release of TNFα and the production of ROS in human monocytes ( Njamkepo et al, 2000 ), to promote incomplete or aberrant maturation of DCs ( Skinner et al, 2004 ; Boyd et al, 2005 ) and to impair T-cell activation by interfering with immunological synapse signaling ( Paccani et al, 2011 ).…”