NF-κB- and C/EBPβ-driven Interleukin-1β Gene Expression and PAK1-mediated Caspase-1 Activation Play Essential Roles in Interleukin-1β Release from Helicobacter pylori Lipopolysaccharide-stimulated Macrophages

Department of Chemistry, Bose Institute, 93/1 Acharya Prafulla Chandra Road, Kolkata 700009, India.
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2005; 280(6):4279-88. DOI: 10.1074/jbc.M412820200
Source: PubMed


Helicobacter pylori is a Gram-negative microaerophilic bacterium that causes chronic gastritis, peptic ulcer, and gastric carcinoma. Interleukin-1beta (IL-1beta) is one of the potent proinflammatory cytokines elicited by H. pylori infection. We have evaluated the role of H. pylori lipopolysaccharide (LPS) as one of the mediators of IL-1beta release and dissected the signaling pathways leading to LPS-induced IL-1beta secretion. We demonstrate that both the NF-kappaB and the C/EBPbeta-binding elements of the IL-1beta promoter drive LPS-induced IL-1beta gene expression. NF-kappaB activation requires the classical TLR4-initiated signaling cascade leading to IkappaB phosphorylation as well as PI-3K/Rac1/p21-activated kinase (PAK) 1 signaling, whereas C/EBPbeta activation requires PI-3K/Akt/p38 mitogen-activated protein (MAP) kinase signaling. We observed a direct interaction between activated p38 MAP kinase and C/EBPbeta, suggesting that p38 MAPK is the immediate upstream kinase responsible for activating C/EBPbeta. Most important, we observed a role of Rac1/PAK1 signaling in activation of caspase-1, which is necessary for maturation of pro-IL-1beta. H. pylori LPS induced direct interaction between PAK1 and caspase-1, which was inhibited in cells transfected with dominant-negative Rac1. PAK1 immunoprecipitated from lysates of H. pylori LPS-challenged cells was able to phosphorylate recombinant caspase-1, but not its S376A mutant. LPS-induced caspase-1 activation was abrogated in cells transfected with caspase-1(S376A). Taken together, these results suggested a role of PAK1-induced phosphorylation of caspase-1 at Ser376 in activation of caspase-1. To the best of our knowledge our studies show for the first time that LPS-induced Rac1/PAK1 signaling leading to caspase-1 phosphorylation is crucial for caspase-1 activation. These studies also provide detailed insight into the regulation of IL-1beta gene expression by H. pylori LPS and are particularly important in the light of the observations that IL-1beta gene polymorphisms are associated with increased risk of H. pylori-associated gastric cancer.

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    • "Serum lipopolyaccharides originate from the gastrointestinal tract and their levels increase after eating a meal rich of lipids. H. pylori gastritis and its role in mucosal activation of innate immunity and upregulation of IL-1β is also suggested in the pathogenesis of IR (25). H.pylori gastritis and its effects on ghrelin may also affect appetite and insulin sensitivity (26). "
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    • "ti - vate both signals , increase the level of the precursor IL - 1b protein , and activate the IPAF inflammasome , leading to the maturation of IL - 1b in primary rat astrocytes . The regulation of proeIL - 1b expression by transcription factor , nuclear factor kappa - light - chain - enhancer of activated B cells ( NFkB ) , is well established ( Basak et al . , 2005 ) , and NFkB is known to be activated by fatty acids , such as PA or a high - fat diet ( Wang et al . , 2012 ) . In support of this , we observed that NFkB expression in the astrocytes is increased on PA treatment ( Supplementary Fig . 6 ) and inhibiting NFkB significantly reduced the mRNA level of proeIL - 1b ( Supplementary Fig . 7 ) "
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    • "Moreover, the Rac1 interaction partner LIM kinase has been proposed to signal to caspase-1 [53]. Also, an interaction between the Rac1 effector “p21 activated kinase 1” and caspase-1 has been suggested [56]. Further studies examining the links between Rac1 and inflammasomes are required to fully understand their interaction in bacterial infections. "
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