The expression profile of filaggrin-2 in the normal and pathologic human oral mucosa

The epithelial cells of the oral cavity show a remarkable degree of regional variation with respect to their morphology and keratinization status. In the oral cavity, the tongue and palate contain keratinizing stratified epithelia, while the buccal mucosa contains non-keratinizing stratified epithelia. We herein examined the expression of filaggrin-2, a member of the S100 fused-type protein family, in the oral mucosa. Filaggrin-2 was weakly expressed in the normal epithelium of the palate, but not in the buccal mucosa or tongue, although filaggrin protein was observed in the epithelium of the buccal mucosa and the palate. We next examined the expression of filaggrin-2 in the oral mucosa of subjects with hyperkeratotic diseases. The expression of filaggrin-2 was markedly increased in the epithelium of the oral mucosa in patients with lichen planus, leukokeratosis and leukoplakia. Filaggrin-2 positivity was observed in granules, some of which were co-localized with those of filaggrin. These results indicate that filaggrin-2 was expressed in the oral mucosa under certain pathological conditions, demonstrating that an aberrant protein expression, together with filaggrin, indicates the altered differentiation program including hyperkeratosis that occurs in these diseases.