The 11p15 mucin genes (MUC2, MUC5AC, MUC5B and MUC6) possess a cell-specific pattern of expression in normal lung that is altered during carcinogenesis. Growth factors of the epidermal growth factor family are known to target key genes that in turn may affect the homeostasis of lung mucosae. Our aim was to study the regulation of the 11p15 mucin genes both at the promoter and protein levels to assess whether their altered expression may represent a key event during lung carcinogenesis. Studies were performed in the mucoepi-dermoid NCI-H292 lung cancer cell line. Cell treatment with epidermal growth factor (EGF), transforming growth factor ␣ (TGF-␣), or tumor necrosis factor ␣ (TNF-␣) resulted in a dramatic increase of MUC2 and MUC5AC mRNAs levels, promoter activity, and apomu-cin expression, whereas those of MUC5B and MUC6 were unchanged. pGL3 deletion mutants of MUC2, MUC5AC, and MUC5B promoters were constructed and used in transient transfection assays to characterize EGF-and TGF-␣-responsive regulatory regions within the promoters. They were located in the ؊2627/؊2097 and ؊202/؊1 regions of MUC2 and MUC5AC promoters, respectively. Finally, we demonstrate that transcription factor Sp1 not only binds and activates MUC2 and MUC5AC promoters but also participates to their EGF-and TGF-␣-mediated up-regulation. We also show that Sp3 is a strong inhibitor of 11p15 mucin gene transcription. In conclusion, MUC2 and MUC5AC are two target genes of EGFR ligands in lung cancer cells, and up-regulation of these two genes goes through concomitant activation of the EGFR/Ras/Raf/Extracellular Signal-regulated Kinase-signaling pathway and Sp1 binding to their promoters. Mucins have been postulated to be important molecules in maintaining epithelium homeostasis in inflammatory diseases and cancer in that they are large O-glycoproteins expressed either at the cell surface or as secreted molecules to form a protective gel. Mucin genes MUC2, MUC5AC, MUC5B, and MUC6 are clustered on the p15 arm of chromosome 11 (1) and encode large secreted O-glycoproteins that participate in mucus formation and epithelium protection (2, 3). However, their precise biological role as key genes during sequential steps of lung carcinogenesis has yet to be proven. In the surface epithelium of the respiratory tract, MUC5AC is exclusively expressed in mucus-secreting goblet cells, whereas MUC1 and MUC4 are expressed in all epithelial cells. MUC5B is prominent in the mucous cells of the submucosal glands, and MUC2 is weakly expressed in both cell types (4-6). In epithelial lung diseases this pattern of expression is altered and has been correlated to poor prognosis of the tumor (inva-siveness, metastasis) (7). For example, aberrant expression of MUC6 in bronchiopulmonary adenocarcinoma, loss of expression of MUC5AC and MUC5B in epidermoid carcinoma, and a strong expression of the four 11p15 mucin genes in bronchioal-veolar carcinoma was recently described (5). Growth factors are thought to be involved in goblet cell production because hypersecretory diseases are associated with abnormal epithelial cell growth and differentiation, and epithelium wounding leads to repair and remodeling processes (8). More recently, Nadel and co-workers (9, 10) focused on MUC5AC regulation by epidermal growth factor (EGF) 1 in the lung. They showed that MUC5AC mRNA expression was increased after ligand binding to the EGFR and activation of the mitogen-activated protein kinase cascade. Positive correlation between EGFR and MUC5AC expression and localization in goblet cells of human bronchi is also in favor of the activation of a series of events involving EGFR followed by activation of MUC5AC expression in lung cells (11). However, these studies only focused on MUC5AC, whereas it has been shown by our laboratory that the expression of the other 11p15 mucin genes is also impaired in lung diseases (5, 6). Moreover, despite these promising studies, no data regarding the molecular mechanisms responsible for mucin gene regulation at the promoter level are available. Their identification remains a big challenge but is mandatory if one wants to demonstrate whether mucins are indeed key molecules in carcinogenesis. At this time, promoter structures of MUC2 (12, 13),