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 seven major classes according to their molecular weight and their immunological reactivity with monoclonal antibodies. Tissue-distribution studies have 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, a 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, we analyzed cytoskeletal proteins from various cultured human cells 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. Furthermore, human epidermal cells growing as a monolayer in low calcium medium continued to express the 50,000-and 58,000-dalton keratin classes. These findings suggest that the 50,000-and 58,000-dalton keratin classes may be regarded as "permanent" markers for stratified squamous epithelial cells (keratinocytes), and that 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.The keratins are a family of water-insoluble proteins that form tonofilaments (a class of intermediate-sized filament), which are present in almost all vertebrate epithelia (13,16,17,59,61,62). Since keratins are usually not detectable in nonepithelial tissues including fibroblasts, muscles, and nerves, immunohistochemical staining of keratins facilitates the detection and identification of epithelial cells, both in tissue section and in culture (1, 2, 7, 8, 24, 35, 37, 46-48, 54, 55, 69).Biochemical data indicate that the polypeptide composition of keratin filaments varies depending on epithelial cell type (12,14,15,18,21,26,39), cellular growth environment (3,12,20,22,23,32,53,60), histological differentiation stage (6, 9, 2 l, 49, 5 l, 56, 66, 67, 70), and embryonic development period (4, 11). It is therefore not surprising that many keratin species have been described in the literature. To study the biological significance of keratin heterogeneity, we have previously prepared three monoclonal antikeratin antibodies (designated A...

The basal keratin network of stratified squamous epithelia: defining K15 function in the absence of K14.

“…K5 and K14 are expressed in the basal layer of all stratified squamous epithelia, and have been considered to be the pair of keratins that typify these tissues (Moll et al, 1982a;Nelson and Sun, 1983). Thus, we anticipated that there might be abnormalities in the architecture of other stratified K14 -/-tissues.…”

Epidermal differentiation: the bare essentials.

“…Basal cells are distinguished by an intracellular cytoskeleton composed of a relatively dispersed, but extensive, network of keratin filaments. These filaments are made of a 1:1 ratio of two distinct keratin prote~ns: K5 (58 kD) and K14 (50 kD) (Nelson and Sun, 1983). Additional hallmarks of basal cells, also common to spinous cells, are desmosomes, which are calcium-activated membrane junctions that interconnect the cells into a three-dimensional lattice (for review, see Franke et al, 1987).…”

Genetic mutations in the K1 and K10 genes of patients with epidermolytic hyperkeratosis. Correlation between location and disease severity.

“…Based on sequence, these proteins fall into two groups, type I and type II (1), which form heteropolymers. K5 (type II) and K14 (type I) are the pair expressed in the mitotically active, basal layer (2). As keratinocytes commit to differentiate, they switch off expression of K5 and K14 and 1.…”