[Keratin expression in normal and malignant transformed squamous epithelium of the digestive mucosa of the head].

Keratins are alpha-type fibrous polypeptides which basically compose 10 nm thick or intermediate-sized filaments (IF) in almost all epithelial cells and tissues. Their patterns of expression in normal and malignant upper digestive tract squamous epithelium were monitored by high resolution gel electrophoresis, immunoblotting, and immunohistochemical techniques. Uninvolved epithelia, in all instances, were found to express keratins 4, 5, 6 and 13, 14 the members of the high molecular weight basic (type II or Type B) and of the low molecular weight acidic (type I or type A) subfraction, respectively. Cancers of squamous epithelial cell origin retain keratin synthesis. However, their overall patterns of keratin expression appeared aberrant when compared with those of normal epithelia. In particular, these differences result from highly proliferative tumour cells unable in most cases to synthesize keratins 4/13, a type II/type I keratin pair which specifically indicates in squamous primarily non-keratinizing epithelia completely, i.e. terminally differentiated (suprabasal or spinous) cells. The patchwise expression of acidic keratin 13 in related primaries confirms their heterogeneous phenotype, and may be explained, in part, by cancer cells no longer resistant to terminal differentiation as a result perhaps of an altered micro-environment and/or in response to various effects mediated by vitamin A. We discuss some problems pertinent to the biochemical analysis of keratin polypeptides in normal and involved epithelial tissues, and relate to the controversial question whether specific keratin members may actually candidate for markers of malignancy.