Human transcriptome analysis reveals a potential role for active transport in the metabolism of Pseudomonas aeruginosa autoinducers

The opportunistic pathogen Pseudomonas aeruginosa employs acyl homoserine lactones (AHL) as signaling compounds to regulate virulence gene expression via quorum sensing. The AHL N-3-oxo-dodecanoyl-l-homoserine lactone (3OC12-HSL) also induces mammalian cell responses, including apoptosis and immune modulation. In certain cell types the apoptotic effects of 3OC12-HSL are mediated via a calcium-dependent signaling pathway, while some pro-inflammatory effects involve intracellular transcriptional regulators. However, the mechanisms by which mammalian cells perceive and respond to 3OC12-HSL are still not completely understood. Here we used microarray analysis to investigate the transcriptional response of human lung epithelial cells after exposure to 3OC12-HSL. These data revealed that mRNA levels for several genes involved in xenobiotic sensing and drug transport were increased in cells exposed to 3OC12-HSL, which led us to examine the intracellular fate of 3OC12-HSL. Using radiolabeled autoinducer uptake assays, we discovered that intracellular 3OC12-HSL levels increased after exposure and achieved maximal levels after 20-30 min. Intracellular 3OC12-HSL decreased to background levels over the next 90 min and this process was blocked by pre-treatment with an inhibitor of the ABC transporter ABCA1. Taken together, these data suggest that mammalian cells detect 3OC12-HSL and activate protective mechanisms to expel it from the cell.