The Catalog of Human Cytokeratins: Patterns of Expression in Normal Epithelia, Tumors and Cultured Cells

Roland Mall, Werner W. Franke and Dorothea L. Schiller Division of Membrane Biology and Biochemistry institute of Cell and Tumor Biology German Cancer Research Center D-6900 Heidelberg, Federal Republic of Germany Benjamin Geiger Department of Chemical Immunology The Weizmann Institute of Science Rehovot, Israel Reinhard Krepler Department of Pathology University of Vienna School of Medicine A-l 090 Vienna, Austria Introduction A large proportion of the cytoplasm of vertebrate cells, normal or transformed, is represented by components of the cytoskeleton, including actin-containing micro- filaments, tubulin-containing microtubules and fila- ments of intermediate size, with diameters of 7-l 1 nm. Although such structures have a widespread oc- currence in diverse cell types, examples have been reported in which they are formed in different cell types from different proteins of a multigene family of proteins, or from different subunit polypeptides of a class of related proteins. For example, differentiation specificity of expression of different actins has been described in different cell types of mammals (Vande- kerckhove and Weber, 1979). By far the most striking differentiation specificity of composition has been ob- served for the intermediate-sized filaments. Although all filaments of this category are morphologically iden- tical in different cell types, are insoluble in solutions of a broad range of low or high salt concentrations and non-ionic detergents and seem to share some common assembly properties (Steinert et al., 1981 b) and antigenic determinants (Pruss et al., 1981) im- munological and biochemical criteria allow us to dis- tinguish at least five different types of intermediate filaments (Bennett et al., 1978; Franke et al., 1978a, 1981f; Hynes and Destree, 1978; Lazarides, 1980; Anderton, 1981 ; Holtzer et al., 1981; Osborn et al., 1981). First, filaments containing keratin-like proteins (“cytokeratins”) are characteristic of epithelial cells. Second, vimentin filaments occur in mesenchymally derived cells, in astrocytes, in Sertoli cells, in vascular smooth muscle cells and in many cultured cell lines. Third, desmin filaments are typical of most types of myogenic cells. Fourth, neurofilaments are typical of neuronal cells. Fifth, glial filaments are typical of as- trocytes. During cell transformation and tumor devel- opment this cell type specificity of intermediate fila- ments is largely conserved’ (Franke et al., 1978a, 1978b, 1979a; Hynes and Destree, 1978; Sun and Green, 1978a; Sun et al., 1979; Bannasch et al., 1980; Battifora et al., 1980; Schlegel et al., 1980a; Altmannsberger et al., 1981; Gabbiani et al., 1981; Denk et al., 1982) and classification of tumors by their specific type of intermediate filaments has re- cently become very valuable in clinical histodiagnosis (see, for example, Schlegel et al., 1980a; Gabbiani et al., 1981; Ramaekers et al., 1981). The intermediate filaments of the vimentin, desmin or glial types all consist usually of only one type of subunit protein (desmin and vimentin can occur in the same filament in BHK cells and vascular smooth mus- cle cells; Steinert et al., 1981 a; Quinlan and Franke, 1982). In contrast with these, the cytokeratin fila- ments, which are composed of proteins related to, but not identical with, epidermal (Y keratins, are a complex family of many different polypeptides. These cytoker- atins, which show biochemical and immunological re- lationships of various degrees, are expressed, in dif- ferent epithelia, in different combinations polypep- tides ranging in their isoelectric pH values from 5 to 8 and in their apparent molecular weights from 40,000 to 68,000 (Doran et al., 1980; Winter et al., 1980; Fuchs and Green, 1980, 1981; Franke et al., 1981 a, 1981 b, 1981 c; Milstone and McGuire, 1981; Wu and Rheinwald, 1981). A given epithelium or epithelial cell can therefore be characterized by the specific pattern of its cytokeratin components. Human Cytokeratin Polypeptides and Their Tissue Distribution Cytoskeletal preparations from epithelial tissues ex- tracted in high salt buffer and Triton X-l 00 are highly enriched in intermediate-sized filaments containing proteins that react specifically with antibodies to au- thentic epidermal [Y keratin (see, for example, Sun and Green, 1977; Fuchs and 1978, 1980, 1981; Franke et al., 1978b, 1980, 1981a, 1981 b, 1981~; Wu and Rheinwald, 1981) and that are recovered in filaments reconstituted in vitro from denatured mono- mers (Tezuka and Freedberg, 1972; Lee and Baden, 1976; Steinert et al., 1976, 1981 a; Sun and Green, 1978b; Gipson and Anderson, 1980; Milstone, 1981; Franke et al., 1981 b, 1981~; Renner et al., 1981). When such preparations are made from different hu- man tissues and examined by two-dimensional gel electrophoresis, with the aid of isoelectric focusing as well as nonequilibrium pH gradient electrophoresis for better resolution of basic polypeptides, complex pat- terns of cytokeratin polypeptides are found. The dis- tinct cytokeratin polypeptides that we have so far identified in various human tissues are schematically summarized and arranged according to their specific coordinates on two-dimensional gel electrophoresis in Figure 1, and the corresponding tissue distribution is shown in Table 1 A. Typically, the cytokeratin polypep- tides appear in series of isoelectric variants; all but the most basic spot usually represent phosphorylated