Oral mucosal epithelial cells express the membrane anchored mucin MUC1.

OBJECTIVE: The presence of a stable salivary pellicle (SP) is essential to provide a wet surface for the oral mucosal epithelia. The oral mucosa is covered by the SP which is suggested to be a mixed film of both salivary and epithelial components. Our aim was to analyse the presence of membrane-anchored mucin MUC1 in the oral mucosal epithelia.

DESING: The presence of MUC1 was studied by immunohistochemical and immunoelectron microscopical methods in 19 buccal mucosal specimens. The localization and intensity of the epithelial expression were analyzed.

RESULTS: Strong staining of MUC1 was found in the epithelial cells of intermediate and superficial layers. Some basal cells were shown faint expression. In the intermediate and superficial layers, the MUC1 expression was seen mainly on the upper cell surface. Furthermore, the expression of MUC1 was noted in the cytoplasm near the nucleus and in the rough granules. By electron microscopy, extracellular domain of membrane-anchored molecules extruded about 15-30nm above the cell surface in the apical cells of the oral epithelium. Immunoelectron microscopic examination shows that MUC1 is mainly localized in the plasma membrane of epithelial cells and also in small vesicles (75-100nm) just below the plasma membrane.

CONCLUSION: The membrane-anchored MUC1 is expressed in the superficial layer of the oral mucosal epithelium, especially on the upper surface of epithelial cells. MUCI may be the anchoring protein of the salivary pellicle stabilization.