Vitamin A: a key nutrient for the maintenance of epithelial differentiation.

Vitamin A deficiency or benzo(a)pyrene instillation into tracheas of Syrian golden hamsters causes squamous metaplasia of tracheobronchial epithelium, normally a mucous secretory tissue. In the present studies, we have employed a tracheal organ culture system and have reproduced the in vivo phenomenon of squamous metaplasia during culturing under vitamin A free conditions as well as after carcinogen treatment. The squamous metaplasia induced by vitamin A deficiency, both in vivo and in vitro, was accompanied by an overall increase in keratin synthesis. Vitamin A deficient tracheas were shown to contain keratins of 50, 48, 46.5 Kd detected with the antibody AE1, and 58, 56 and 52 Kd detected with AE3. These proteins were either absent or present in much less quantity in control tracheas. In deficient tracheas 60 kd keratin was found to be located specifically in squamous suprabasal cells, and 55 and 50 Kd keratin proteins were found in a greatly expanded basal cell compartment. Following carcinogen exposure, the appearance of 60 kd keratin and the enhanced expression of 50 and 55 Kd keratins preceded the squamoid metaplastic response as detected morphologically. Both the keratin changes and the morphological changes were prevented by retinoid treatment.