Interaction of Pseudomonas aeruginosa with epithelial cells:: Identification of differentially regulated genes by expression microarray analysis of human cDNAs

Pseudomonas aeruginosa is an opportunistic pathogen that plays a major role in lung function deterioration in cystic fibrosis patients. To identify critical host responses during infection, we have used high-density DNA microarrays, consisting of 1,506 human cDNA clones, to monitor gene expression in the A549 lung pneumocyte cell line during exposure to P. aeruginosa. We have identified host genes that are differentially expressed upon infection. several of which require interaction with P. aeruginosa and the expression of the major subunit of type IV pill, PilA. Differential expression of genes involved in various cellular functions was identified, and we selected the gene encoding the transcription factor interferon regulatory factor 1 (IRF-1) for further analysis. The levels of the IRF-1 transcript increased 3- to 4-fold in A549 cells after adherence by P. aeruginosa. A similar increase of IRF-1 mRNA was observed in A549 cells exposed to wild-type P. aeruginosa when compared to an isogenic, nonpiliated strain. However, this difference was abolished when serum was present during the incubation of bacteria. Exposure of A549 cells to purified P, aeruginosa lipopolysaccharide did not result in a significant increase in IRF-1 mRNA. Although the P. aeruginosa-induced increased IRF-1 expression depends on the presence of bacterial adhesin, our findings do not preclude the possibility that other bacterial products are responsible for IRF-1 activation, which is enhanced by bacterial adherence to cells. These data show that microarray technology can be an important tool for studying the complex interplay between bacterial pathogens and host.