Divergence of Apoptosis-Inducing and Preventing Signals in Bacteria-Faced Macrophages Through Myeloid Differentiation Factor 88 and IL-1 Receptor-Associated Kinase Members

Abstract

The induction of apoptosis in host cells is a common strategy by which pathogenic bacteria interfere with the host immune response. The Yersinia enterocolitica outer protein P (YopP) inhibits activation of transcription factor NF-κB in macrophages, which suppresses NF-κB-dependent antiapoptotic activities. The simultaneous initiation of proapoptotic signaling by yersiniae infection or LPS treatment results in macrophage apoptosis. In this study, we used YopP as a tool to dissect survival- and death-inducing pathways in bacteria-faced macrophages. We cotransfected J774A.1 macrophages with expression plasmids for YopP and dominant-negative mutants of signal transmitters of the NF-κB cascade downstream from the LPS receptor complex. Dominant-negative myeloid differentiation factor 88 (MyD88) or IL-1R-associated kinase (IRAK) 2 diminished LPS-induced apoptosis in YopP-transfected macrophages, suggesting implication of MyD88 and IRAK2 in signaling cell death. In contrast, dominant-negative IRAK1 and TNFR-associated factor 6 (TRAF6) did not provide protection, but augmented LPS-mediated apoptosis in the absence of YopP, which indicates roles of IRAK1 and TRAF6 in the antiapoptotic signal relay of the NF-κB cascade. The distinct functions of IRAK members in macrophage survival were reflected by opposing effects of dominant-negative IRAK1 and IRAK2 on Y. enterocolitica-mediated apoptosis. Yersiniae- and LPS-dependent cell death were substantially attenuated by a specific caspase-8 inhibitory peptide or by dominant negative Fas-associated death domain protein (FADD). This suggests, that Yersinia-induced apoptosis involves a proapoptotic signal relay through MyD88 and IRAK2, which potentially targets the Fas-associated death domain protein/caspase-8 apoptotic pathway, whereas IRAK1 and TRAF6 counteract the bacteria-induced cytotoxic response by signaling macrophage survival.

CC chemokine receptor 2 regulates leukocyte recruitment and IL‐10 production during acute polymicrobial sepsis

“…Thus, even in case of reduced chemotactic activity in peritoneal cavities of MyD88-deficient mice attenuation of leukocyte apoptosis might compensate for diminished cell recruitment. Accordingly, TLR-and MyD88-mediated signals are well known to trigger apoptosis of leukocytes and other cell types [45][46][47][48][49][50]. Moreover, our previous work [51] has shown that attenuation of TLR responsiveness through induction of in vivo LPS tolerance results in diminished neutrophil apoptosis and enhanced peritoneal neutrophil accumulation during septic peritonitis.…”

A Dominant Role of Toll-Like Receptor 4 in the Signaling of Apoptosis in Bacteria-Faced Macrophages

“…TLR2-dependent apoptotic signaling is coupled to the cell death machinery through activation of MyD88 and FADD (47), a cytotoxic pathway that is potentially also involved in Yersinia-mediated apoptosis (48,62). MyD88 binds to the TLR2 intracellular signaling domain and recruits FADD through death domain-death domain interaction (47).…”

“…None of the overexpressed constructs induced substantial cell death in the absence of MG-132 (Ref. 48; data not shown).…”

“…Because of a lower transfection efficiency in J774A.1 macrophages, expression of the proteins in J774A.1 cells was checked by immunofluorescence microscopy at the single cell level using the Abs that recognized the respective overexpressed constructs in HEK293 cells (Ref. 48; data not shown). For analysis of NF-B activation, J774A.1 cells were cotransfected with the NF-B-dependent ELAM-luciferase reporter plasmid and luciferase activities were monitored 5 h after LPS stimulation (Fig.…”

Prolongation of islet allograft survival following ex vivo transduction with adenovirus encoding a soluble type 1 TNF receptor–Ig fusion decoy

“…[33][34][35]64 Nevertheless, the highest levels of apoptosis are achieved by combination cytokine provision, 7,44,63 suggesting that TNFa could sensitize cells to the effects of IL-1b or could prime these cells for IRAK-mediated signaling. 21,22,[65][66][67][68][69] Although TNFR-Ig confers protection to human islets from TNFa effects, it was not effective in completely preventing apoptosis activation in culture, as measured by Annexin V staining in FACS analysis. This is not unexpected in the light of the preceding discussion.…”