The 50- and 58-kdalton keratin classes as molecular markers for stratified squamous epithelia: cell culture studies.

Abstract

The keratins are a highly heterogeneous group of proteins that form intermediate filaments in a wide variety of epithelial cells. These proteins can be divided into at least 7 major classes according to their MW and their immunological reactivity with monoclonal antibodies. Tissue-distribution studies revealed a correlation between the expression of specific keratin classes and different morphological features of in vivo epithelial differentiation (simple vs., stratified; keratinized vs. nonkeratinized). Specifically, 50,000- and a 58,000-dalton keratin class were found in all stratified epithelia but not in simple epithelia, and a 56,500- and a 65-67,000-dalton keratin class were found only in keratinized epidermis. To determine whether these keratin classes can serve as markers for identifying epithelial cells in culture, cytoskeletal proteins from various cultured human cells were analyzed by the immunoblot technique using AE1 and AE3 monoclonal antikeratin antibodies. The 56,500- and 65-67,000-dalton keratins were not expressed in any cultured epithelial cells examined so far, reflecting the fact that none of them underwent morphological keratinization. The 50,000- and 58,000-dalton keratin classes were detected in all cultured cells that originated from stratified squamous epithelia, but not in cells that originated from simple epithelia. Human epidermal cells growing as a monolayer in low Ca medium continued to express the 50,000- and 58,000-dalton keratin classes. The 50,000 and 58,000-dalton keratin classes may be regarded as permanent markers for stratified squamous epithelial cells (keratinocytes) and the expression of these keratin markers does not depend on the process of cellular stratification. The selective expression of the 50,000- and 58,000-dalton keratin classes, which are synthesized in large quantities on a per cell basis, may explain the high keratin content of cultured keratinocytes.