N-(3-Oxo-acyl)homoserine Lactones Signal Cell Activation through a Mechanism distinct from the Canonical Pathogen-associated Molecular Pattern Recognition Receptor Pathways

Abstract

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas doublestranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2␣ (eIF2␣). Here we have shown that p38 and eIF2␣ phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gramnegative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

Future research trends in the major chemical language of bacteria

“…It has been established that the 3-oxo-C12-HSL produced by P. aeruginosa impairs the ability of mammalian cells to respond to the invading bacterial pathogen via the innate immune system (Kravchenko et al, 2008;Kravchenko et al, 2006;Shiner et al, 2006). One of the key steps in this response immediately after receptor-recognition of the pathogen is the activation of the nuclear transcription factor NF-B and consequential expression of genes encoding pro-inflammatory cytokines.…”

Pseudomonas aeruginosa Homoserine Lactone Activates Store-operated cAMP and Cystic Fibrosis Transmembrane Regulator-dependent Cl− Secretion by Human Airway Epithelia

“…When CF patients become colonized with P. aeruginosa, the bacteria secrete quorum-sensing molecules, including N-(3-oxo-dodecanoyl)-S-homoserine lactone (3O-C12) and butyryl homoserine lactone, to signal each other and to regulate their own gene expression, including genes involved in formation of biofilms (1)(2)(3)(4)(5)(6). Concentrations of 3O-C12 in CF sputum are thought to be in the nanomolar range (7) but reach 5 M in P. aeruginosa supernatants and may reach Ͼ100 M in regions adjacent to biofilms (8,9).…”

“…3O-C12 operates through TLR-and Nod/Ipaf/caterpillarindependent signaling to activate multiple proinflammatory genes that are associated with NF-B signaling, including IL8, Cox2, and MUC5AC in both epithelial and other cell types (7)(8)(9)(10)(11)(12). Some of these proinflammatory effects may be mediated through activation of MAPKs (8,9) or Ca 2ϩ (7,13) or inhibition of peroxisome proliferator-activated receptor ␥ (14). However, 3O-C12 also inhibits NF-B signaling and expression of proinflammatory cytokines in macrophages and primary human bronchial airway epithelial cells (9) when cells are treated with both 3O-C12 and another agonist like LPS or TNF␣ that activates NF-B on its own.…”

“…Some of these proinflammatory effects may be mediated through activation of MAPKs (8,9) or Ca 2ϩ (7,13) or inhibition of peroxisome proliferator-activated receptor ␥ (14). However, 3O-C12 also inhibits NF-B signaling and expression of proinflammatory cytokines in macrophages and primary human bronchial airway epithelial cells (9) when cells are treated with both 3O-C12 and another agonist like LPS or TNF␣ that activates NF-B on its own. Thus, 3O-C12 appears to stimulate proinflammatory responses on its own but inhibit responses when present with other proinflammatory agonists.…”

The quorum quenching antibody RS2-1G9 protects macrophages from the cytotoxic effects of the Pseudomonas aeruginosa quorum sensing signalling molecule N-3-oxo-dodecanoyl-homoserine lactone

“…Several studies have reported on the biochemical effects of AHLs on mammalian cells (Kravchenko et al, 2006;Ritchie et al, 2003;Smith et al, 2002a;Smith et al, 2002b;Telford et al, 1998). Notably, 3-oxo-C 12 -HSL specifically promotes induction of apoptosis in macrophages and neutrophils (Tateda et al, 2003).…”