We focused on the regulation of inflammatory mediator expression by adenovirus E1A in lung epithelial cells and the role of this viral protein in the pathogenesis of chronic obstructive pulmonary disease (COPD). We previously reported that E1A, a well-known regulator of host genes, increased intercellular adhesion molecule-1 (ICAM-1) expression in human bronchial epithelial (HBE) and A549 cells in response to lipopolysaccharide (LPS) stimulation. In this report, we clarified the mechanism of this regulation. We found NF-B translocation to the nucleus after LPS stimulation in both E1A positive and negative HBE cells. ICAM-1 promoter reporter constructs revealed that a mutation in the proximal NF-B binding site completely inhibited increased transcription while the mutation in a distal site did not. We analyzed E1A's participation in transcriptional complex formation at this promoter using chromatin immunoprecipitation. In E1A positive HBE and A549 cells, LPS stimulation increased ICAM-1 promoter immunoprecipitation by NF-B p65 and p300 but not activator protein-1 antibodies with a concomitant increase by the E1A antibody. No increase was found in E1A negative cells, except in HBE cells with p65 antibody. E1A's association with the increased promoter immunoprecipitation with p300 was also observed after tumor necrosis factor- stimulation of A549 cells. These results suggest that adenovirus E1A regulates the ICAM-1 promoter through its proximal NF-B binding site, most likely by interacting with the transcriptional complex which forms at this site. E1A regulation of the LPS response may play a role in acute exacerbations as a consequence of bacterial infections in COPD.