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 cr itical host responses during infection, we have used high-density DNA micro arrays, consisting of 1,506 human cDNA clones, to monitor gene expression i n the A549 lung pneumocyte cell line during exposure to P. aeruginosa. We h ave 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 gen es involved in various cellular functions was identified, and we selected t he gene encoding the transcription factor interferon regulatory factor 1 (I RF-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 increa se of IRF-1 mRNA was observed in A549 cells exposed to wild-type P. aerugin osa when compared to an isogenic, nonpiliated strain. However, this differe nce was abolished when serum was present during the incubation of bacteria. Exposure of A549 cells to purified P, aeruginosa lipopolysaccharide did no t result in a significant increase in IRF-1 mRNA. Although the P. aeruginos a-induced increased IRF-1 expression depends on the presence of bacterial a dhesin, our findings do not preclude the possibility that other bacterial p roducts are responsible for IRF-1 activation, which is enhanced by bacteria l adherence to cells. These data show that microarray technology can be an important tool for studying the complex interplay between bacterial pathoge ns and host.