EXPRESSION OF CORNIFIN IN SQUAMOUS DIFFERENTIATING EPITHELIAL TISSUES, INCLUDING PSORIATIC AND RETINOIC ACID-TREATED SKIN

The expression of cornifin, a putative cross-linked envelope precursor , was investigated in several squamous differentiating tissues by in s itu hybridization and immunohistochemical analysis. Cornifin mRNA and protein, which are absent in the normal mucociliary tracheal epitheliu m, are induced in the suprabasal layers of the squamous metaplastic tr acheal epithelium of vitamin A - deficient hamsters. Similar to the in duction of squamous metaplasia in vivo, culture of rabbit tracheal cel ls in the absence of retinoids results in squamous differentiation and expression of cornifin. This induction of cornifin expression is supp ressed by retinoic acid and several of its analogs. Cornifin mRNA and protein are also detected in the suprabasal layers of the squamous epi thelium of rabbit esophagus and tongue. The distribution of cornifin i n human epidermis was compared with that of two other crosslinked enve lope precursor proteins, involucrin and loricrin. The localization of cornifin and involucrin is very similar. Both are induced in the spino us layer and appear at an earlier stage during epidermal differentiati on than loricrin. The expression of cornifin is greatly increased in p soriatic skin. Cornifin mRNA is barely detectable in normal epidermis, whereas it is present at relatively high levels in the suprabasal lay ers of psoriatic epidermis. Topical treatment with RA results in thick ening of the skin and increases the level of cornifin mRNA and protein in the upper spinous layers of mouse skin. Cornifin expression correl ates generally with squamous differentiation in a variety of tissues a nd is abnormally regulated in psoriatic skin and in skin treated topic ally with retinoic acid.