From normal respiratory mucosa to epidermoid carcinoma: expression of human mucin genes

Mucous cells in the respiratory tract contribute to the maintenance of the normal epithelial cell population via mechanisms of cell proliferation and differentiation. Mucous cell hyperplasia often occurs as a basic response to injury in the tracheobronchial epithelium. These cells are also thought to be involved in the histogenesis of epidermoid metaplasia. A typical biochemical feature of these cells is mucus secretion. Aberrant glycosylation or under-glycosylation of mucins is well known in cancer; however, the specific role played by mucin genes is at present unclear. To provide information regarding the expression of these genes in squamous metaplasia and squamous cell carcinoma, we analyzed and compared the expression of MUC1-MUC7 genes by in situ hybridization in control respiratory mucosa and lesions associated with neoplasia (hyperplasia, metaplasia and dysplasia) and squamous cell carcinomas. MUC4 was expressed independently of mucus secretion since it was expressed weakly by basal cells and probably by ciliated cells as well as collecting ducts, epidermoid metaplasia with complete squamous cell differentiation, and most of epidermoid carcinomas even well differentiated and keratinized. In squamous metaplasia and dysplasia, MUC4 gene expression was diffuse and less intense than in normal epithelium. MUC5AC was overexpressed in dysplasia as well as in mucous cell and basal cell hyperplasia and undetectable when squamous differentiation was achieved.