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The organization of intermediate filaments in cultured epithelial cells was rapidly and radically affected by intracellularly injected monoclonal antikeratin filament antibodies. Different antibodies had different effects, ranging from an apparent splaying apart of keratin filament bundles to the complete disruption of the keratin filament network. Antibodies were detectable within cells for more than four days after injection. The antibody-induced disruption of keratin filament organization had no light-microscopically discernible effect on microfilament or microtubule organization, cellular morphology, mitosis, the integrity of epithelial sheets, mitotic rate, or cellular reintegration after mitosis. Cell-to-cell adhesion junctions survived keratin filament disruption. However, antibody injected into a keratinocyte-derived cell line, rich in desmosomes, brought on a superfasciculation of keratin filament bundles, which appeared to pull desmosomal junctions together, suggesting that desmosomes can move in the plane of the plasma membrane and may only be 'fixed' by their anchoring to the cytoplasmic filament network. Our observations suggest that keratin filaments are not involved in the establishment or maintenance of cell shape in cultured cells.Intermediate filaments are a prominent component of the cytoskeleton in many eucaryotic cells (for reviews see references 2, 35, and 54). The intricate patterns they form have led some investigators to surmise that they are actively involved in determining cellular morphology and behavior. However, a number of observational and experimental results, most notably the reported absence of intermediate filaments in the early mouse embryo (9, 28, 42), their remarkably variable organization in cultured ceils (33), and the absence of effect when the intermediate filaments of fibroblasts were collapsed by intracellularly injected antibodies (21, 30, 39), suggest that intermediate filaments are not directly involved in the determination of cellular morphology.The keratin filaments of epithelial cells are by far the most complex class of intermediate filaments (for reviews see references 17 and 35). They are the first intermediate filaments to appear during development in the mouse (9,28,29,42). Desmosomal (macula adherentes) (15) intercellular junctions form first and keratin filaments subsequently integrate into them (12,28,41). Linked through these junctions into a supra-494 cellular network, 8-12-nm thick, keratin filaments course throughout the cell, forming an intricate system of anastomosing filament bundles which also anchor the epithelial sheet, through hemi-desmosomes, to the underlying basal lamina. The keratin filament proteins are a complex and distinct group, although they do share ultrastructural features (50) and some antigenic determinants (11, 43) with other intermediate filament subunit types. The subunit composition of keratin filaments varies depending on the particular tissue in which they occur (17, and references therein), and such differences ca...

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In the course of immunohistochemical studies it has become apparent that there is a distinct phenotype of keratin expression that is shared by basal epithelial cells in a variety of different tissues. A basal cell can be defined as a cell in contact with a basal lamina but with no free luminal surface; this distinguishes it from a simple epithelial cell, which has a free luminal surface as well as basal lamina contact, and from stratifying suprabasal keratinocytes, which have neither basal lamina contact nor free luminal surface. All basal cells, whether they are in glandular ductal or secretory epithelia, or in stratified squamous epithelia, express the keratin pair K5 and K14. In this paper we describe monoclonal and polyclonal antibodies that are monospecific for both keratins 14 and 5 or are specific for denaturation-sensitive epitopes unique to basal cells, including five new monoclonal antibodies: LL001 and LL002 (to keratin 14), 2.1.D7 (to keratins 5, 6 and 8), and LH6 and LH8 (conformation-specific basal cell markers). These antibodies have been used to monitor the distribution of the basal cell phenotype and to demonstrate the expression of keratins 5 and 14 in this cell type, in both stratified epithelia and mixed epithelial glands. The consistent association of this keratin pair with basal cells suggests a possible specific function for these keratin in reinforcing epithelia under physical stress, whilst expression of these keratins may conflict with the differentiated functions of most simple epithelial cells.