To investigate how respiratory epithelial cells react to an alkylating agent, we exposed human bronchial (BEAS-2B) and alveolar (A549) cells to the nitrogen mustard derivative melphalan. The BEAS-2B cells were highly sensitive to melphalan, as shown by a reduced viability after a 10-min incubation with 300 microM melphalan. The A549 cells were less sensitive and required several hours of exposure to reduce significantly in viability. However, exposure to melphalan also induces activation of intracellular signal transduction pathways, as indicated by phosphorylation of extracellular signal-regulated kinase (ERK1/2) and p38 (proteins belonging to the family of stress-induced mitogen-activated phosphorylated kinases, MAPK) within 5 min, as well as translocation of the transcription factor nuclear factor (NF)-kappaB to the nucleus within 45 min. This early activation was followed by elevated levels of tumor necrosis factor (TNF)-alpha mRNA within 2 h. We also observed increased expression of intercellular adhesion molecule-1 (ICAM-1) on the surface of both cell lines 18 h after exposure to 25 microM melphalan and an increased adhesion of monocytes to the epithelial cells in vitro.In conclusion, we have demonstrated that alkylating compounds not only cause cell death of lung epithelial cells but also activate stress-associated MAPK signal transduction pathways and induce expression of mediators known to participate in the recruitment of inflammatory cells.