Acute effect of cigarette smoke on TNF-α release by macrophages mediated through the erk1/2 pathway

Pulmonary emphysema is a major cause of mortality and morbidity in chronic obstructive pulmonary disease (COPD). Cigarette smoking is a major risk factor in the development of pulmonary emphysema. In this study, we investigated the acute effect of cigarette smoke in vitro on the production of tumour necrosis factor-α (TNF-α) using differentiated U937 cells, a macrophage model system. We found that stimulation of the macrophages with cigarette smoke media (CSM) leads to a rapid activation of extracellular-regulated kinases 1 and 2 (erk1/2), p90RSK and a transient decrease in phosphorylation of PKB/akt. The CSM also caused the subsequent induction of TNF-α release. Our studies revealed that U0126, an inhibitor of the erk1/2 pathway, markedly suppressed CSM-induced TNF-α release. Consistent with this finding, U0126 blocked CSM-stimulated erk1/2 phosphorylation, as well as phosphorylation of the downstream kinase, p90RSK. On the other hand, the PI3-K inhibitor, LY294002, and epidermal growth factor receptor (EGFR)-specific inhibitor, AG1478, did not suppress the release of TNF-α. Thus, CSM induction of TNF-α production by differentiated macrophages is regulated primarily via the erk1/2 pathway.