Induction of MUC2 and MUC5AC Mucins by Factors of the Epidermal Growth Factor (EGF) Family Is Mediated by EGF Receptor/Ras/Raf/Extracellular Signal-regulated Kinase Cascade and Sp1*

Abstract

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 mucoepidermoid NCI-H292 lung cancer cell line. Cell treatment with epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or tumor necrosis factor alpha (TNF-alpha) resulted in a dramatic increase of MUC2 and MUC5AC mRNAs levels, promoter activity, and apomucin 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-alpha-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-alpha-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.