Membrane Associated Mucins in Oral Epithelia

Objectives: Membrane associated mucins (MAMs) of epithelial cells in non-oral systems function to monitor the extracellular environment and as sensor mechanisms to modulate cell signaling in response to epithelial invasion or damage. We therefore explored the expression of MAMs in human buccal (non-keratinized) and hard palate (keratinized) epithelia. Methods: Tissue samples obtained from human cadavers were screened by RT-PCR to determined expressed transcripts, followed by immunohistochemistry to delineate mucin glycoprotein expression and cellular localization. Buccal and hard palate tissues (frozen or paraformaldehyde-fixed) were probed with antibodies against unique peptide domains of each MAM, with detection using Alexa 568-Red labeled secondary antibodies. Non-immune IgGs served as negative controls. Results: RT-PCR detected transcripts for MUC 1, MUC 3, MUC 4, MUC 9, MUC 12, MUC 15, MUC 16, MUC 18, MUC 20 and MUC 21. MUC1 was localized to basal cells and early maturing prickle cells of hard palate, whereas MUC4 was undetected. Muc 9 was detected only in the keratinized layer of hard palate and the superficial layer of buccal tissue. MUC15 was poorly detected in basal cells of both tissues, but was apparent in all other epithelial layers. MUC16 was readily detected in the keratinized, granular and upper prickle cell layers of hard palate, with limited staining of the basal and lower prickle cell layers. All cell layers of buccal epithelium express MUC16. MUC18 was found in the granular and prickle cell layers of hard palate, but with an opposite staining pattern in buccal tissue. Conclusion: Oral epithelia express multiple MAMs, with variable expression between keratinized and non-keratinized epithelium and between the different cell layers. MAMs may likely contribute to innate immunity in the oral cavity.