Pseudomonas aeruginosa quorum-sensing molecule homoserine lactone modulates inflammatory signaling through PERK and eI-F2α.

Pseudomonas aeruginosa secrete N-(3-oxododecanoy1)-homoserine lactone (HSL-C12) as a quorum-sensing molecule to regulate bacterial gene expression. Because HSL-C12 is membrane permeant, multiple cell types in P aeruginosa-infected airways may be exposed to HSL-C12, especially adjacent to biofilms where local (HSL-C12) may be high. Previous reports showed that HSL-C12 causes both pro- and anti-inflammatory effects. To characterize HSL-C12's pro- and anti-inflammatory effects in host cells, we measured protein synthesis, NF-KB activation, and KC (mouse IL-8) and IL-6 mRNA and protein secretion in wild-type mouse embryonic fibroblasts (MEF). To test the role of the endoplasmic reticulum stress inducer, PERK we compared these responses in PERK' and PERK-corrected PERK MEF. During 4-h treatments of wild-type MEF, HSL-C12 potentially activated NF-KB p65 by preventing the resynthesis of IKB and increased transcription of KC and IL-6 genes (quantitative PCR). HSL-C12 also inhibited secretion of KC and/or IL-6 into the media (ELISA) both in control conditions and also during stimulation by TNF-a. HSL-C12 also activated PERK (as shown by increased phosphorylation of eI-F2 alpha) and inhibited protein synthesis (as measured by incorporation of [35S]methionine by MEF). Comparisons of PERK' and PERK-corrected MEF showed that HSL-C12's effects were explained in part by activation of PERK Thosphorylation of eI-F2 alpha >inhibition of protein synthesis reduced IKBa production >activation of NF-KB increased transcription of the KC gene but reduced translation and secretion of KC. HSLC12 may be an important modulator of early (up to 4 h) inflammatory signaling in P aeruginosa infections.