Expression of Specific Keratin Rabbit Corneal, Conjunctival, during Vitamin A Deficiency Markers by and Esophageal Epithelia

Using an in vivo rabbit model system, we have studied the morphological and biochemical changes in corneal, conjunctival, and esophageal epithelia during vitamin A deficiency. Light and electron microscopy showed that the three epithelia undergo different degrees of morphological keratinization. Corneal and conjunctival epithelia became heavily keratinized, forming multiple layers of superficial, anucleated cornified cells. In contrast, esophageal epithelium underwent only minor morphological changes. To correlate morphological alterations with the expression of specific keratin molecules, we have analyzed the keratins from these epithelia by the immunoblot technique using the subfamily-specific AE1 and AE3 monodonal antikeratin antibodies. The results indicate that during vitamin A deficiency, all three epithelia express an AEl-reactive, acidic 56.5-kd keratin and an AE3-reactive, basic 65-67-kd keratin. Furthermore, the expression of these two keratins correlates roughly with the degree of morphological keratinization. AE2 antibody (specific for the 56.5and 6567-kd keratins) stained keratinized corneal epithelial sections suprabasally, as in the epidermis, suggesting that these two keratins are expressed mainly during advanced stages of keratinization. These two keratins have previously been suggested to represent markers for epidermal keratinization. Our present data indicate that they can also be expressed by other stratified epithelia during vitamin A deficiency-induced keratinization, and suggest the possibility that they may play a role in the formation of the densely packed tonofilament bundles in cornified cells of keratinized tissues. It has been well established that vitamin A plays an important role in regulating epithelial growth and differentiation (for reviews, see 8, 12, 32, 63, 67, 69). Fell and co-workers (14) have shown that vitamin A excess can induce mucous metaplasia in organ-cultured embryonic chick epidermis. Conversely, Moil (37), and Wolbach and Howe (66) have shown that vitamin A deficiency can cause squamous metaplasia and keratinization in a wide variety of nonkeratinized and secretory epithelia. Since metaplastic changes similar to those seen in vitamin A deficiency also occur in certain epithelia as an intermediate stage of carcinogenesis, and since vitamin A possesses anti-carcinogenic effects in some experimental animals (3, 25, 45), there has been a surge of interest in studying the mechanisms of vitamin A deficiency-induced squamous metaplasia and abnormal epithelial keratinization. Normal epidermis is a keratinized tissue consisting of basal, spinous, granular and (anucleated) eornified layers (21, 27, 33, 36, 41). Recent studies have shown that the expression of keratins--the protein subunits of tonofilaments (16, 17, 53, 54)--changes during epidermal keratinization (19). The basal cells express an acidic 50and a basic 58-kd keratin, whereas the suprabasal cells express in addition an acidic 56.5and a THE JOURNAL OF CELL BIOLOGY • VOLUME 99 DECEMBER 1984 2279-2286 ©The Rockefeller University Press . 0021-952518411212279108 $1.0