Cell, Vol. 31, 1 l-24, November 1982, Copyright 0 1982 by MIT The Catalog of Human Cytokeratins: Review Patterns of Expression in Normal Epithelia, Tumors and Cultured Cells Roland Mall, Werner W. Franke and 1980; Battifora et al., 1980; Schlegel et al., 1980a; Dorothea L. Schiller Altmannsberger et al., 1981; Gabbiani et al., 1981; Division of Membrane Biology and Biochemistry Denk et al., 1982) and classification of tumors by institute of Cell and Tumor Biology their specific type of intermediate filaments has re- German Cancer Research Center cently become very valuable in clinical histodiagnosis D-6900 Heidelberg, Federal Republic of Germany (see, for example, Schlegel et al., 1980a; Gabbiani et Benjamin Geiger al., 1981; Ramaekers et al., 1981). Department of Chemical Immunology The intermediate filaments of the vimentin, desmin The Weizmann Institute of Science or glial types all consist usually of only one type of Rehovot, Israel subunit protein (desmin and vimentin can occur in the Reinhard Krepler same filament in BHK cells and vascular smooth mus- Department of Pathology cle cells; Steinert et al., 1981 a; Quinlan and Franke, University of Vienna School of Medicine 1982). In contrast with these, the cytokeratin fila- A-l 090 Vienna, Austria 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- Introduction atins, which show biochemical and immunological re- lationships of various degrees, are expressed, in dif- A large proportion of the cytoplasm of vertebrate cells, ferent epithelia, in different combinations of polypep- normal or transformed, is represented by components tides ranging in their isoelectric pH values from 5 to 8 of the cytoskeleton, including actin-containing micro- and in their apparent molecular weights from 40,000 filaments, tubulin-containing microtubules and fila- to 68,000 (Doran et al., 1980; Winter et al., 1980; ments of intermediate size, with diameters of 7-l 1 Fuchs and Green, 1980, 1981; Franke et al., 1981 a, nm. Although such structures have a widespread oc- 1981 b, 1981 c; Milstone and McGuire, 1981; Wu and currence in diverse cell types, examples have been Rheinwald, 1981). A given epithelium or epithelial cell reported in which they are formed in different cell can therefore be characterized by the specific pattern types from different proteins of a multigene family of of its cytokeratin components. proteins, or from different subunit polypeptides of a class of related proteins. For example, differentiation Human Cytokeratin Polypeptides and Their Tissue specificity of expression of different actins has been Distribution described in different cell types of mammals (Vande- kerckhove and Weber, 1979). By far the most striking Cytoskeletal preparations from epithelial tissues ex- differentiation specificity of composition has been ob- tracted in high salt buffer and Triton X-l 00 are highly served for the intermediate-sized filaments. Although enriched in intermediate-sized filaments containing all filaments of this category are morphologically iden- proteins that react specifically with antibodies to au- tical in different cell types, are insoluble in solutions thentic epidermal [Y keratin (see, for example, Sun and of a broad range of low or high salt concentrations Green, 1977; Fuchs and Green, 1978, 1980, 1981; and non-ionic detergents and seem to share some Franke et al., 1978b, 1980, 1981a, 1981 b, 1981~; common assembly properties (Steinert et al., 1981 b) Wu and Rheinwald, 1981) and that are recovered in and antigenic determinants (Pruss et al., 1981) im- filaments reconstituted in vitro from denatured mono- munological and biochemical criteria allow us to dis- mers (Tezuka and Freedberg, 1972; Lee and Baden, tinguish at least five different types of intermediate 1976; Steinert et al., 1976, 1981 a; Sun and Green, filaments (Bennett et al., 1978; Franke et al., 1978a, 1978b; Gipson and Anderson, 1980; Milstone, 1981; 1981f; Hynes and Destree, 1978; Lazarides, 1980; Franke et al., 1981 b, 1981~; Renner et al., 1981). Anderton, 1981 ; Holtzer et al., 1981; Osborn et al., When such preparations are made from different hu- 1981). First, filaments containing keratin-like proteins man tissues and examined by two-dimensional gel (“cytokeratins”) are characteristic of epithelial cells. electrophoresis, with the aid of isoelectric focusing as Second, vimentin filaments occur in mesenchymally well as nonequilibrium pH gradient electrophoresis for derived cells, in astrocytes, in Sertoli cells, in vascular better resolution of basic polypeptides, complex pat- smooth muscle cells and in many cultured cell lines. terns of cytokeratin polypeptides are found. The dis- Third, desmin filaments are typical of most types of tinct cytokeratin polypeptides that we have so far myogenic cells. Fourth, neurofilaments are typical of identified in various human tissues are schematically neuronal cells. Fifth, glial filaments are typical of as- summarized and arranged according to their specific trocytes. During cell transformation and tumor devel- coordinates on two-dimensional gel electrophoresis in opment this cell type specificity of intermediate fila- Figure 1, and the corresponding tissue distribution is ments is largely conserved’ (Franke et al., 1978a, shown in Table 1 A. Typically, the cytokeratin polypep- 1978b, 1979a; Hynes and Destree, 1978; Sun and tides appear in series of isoelectric variants; all but Green, 1978a; Sun et al., 1979; Bannasch et al., the most basic spot usually represent phosphorylated Cell 12 blotting experiments (Franke et al., 1981 c; Moll et al., 1982a, 1982b, 1982c; 0. Gigi, Z. Eshhar, B. Geiger, Ft. Mall, E. Schmid, S. Winter, D. L. Schiller and W. W. Franke, manuscript submitted) and by tryptic pep- tide mapping (see, for example, Schiller et al., 1982) 60 4 Y 5----•fe . can be divided according to their migration on two- i? 6~@0@ 0. :i eo-12 dimensional gel electrophoresis into certain sub- 7 00 00 O-13 6 00 groups: 50- em’ .-E -Relatively large and slightly basic polypeptides are 00, typical of many stratified epithelia. Components 1 and 2 have been described in keratinizing epidermis from various body sites (Baden and Lee, 1978; Fuchs and Green, 1980; Franke et al., 1981 c; Moll et al., 1982b) 7.4 6.4 5.4 and in epithelium of anal canal (Figure 2f) and exo- cervix (Franke et al., 1981 c). Component 3 occurs in Isoelectric pH the cornea of man (Gigi et al., manuscript submitted) Figure 1. Schematic Chart of Human Cytokeratin Polypeptides and shows relationships to components 1, 2 and 5 by Cytoskeletal proteins from various human epithelia, carcinomas and cultured epithelial cells were separated by two-dimensional gel elec- tryptic peptide map (data not shown; for data on trophoresis. Cytokeratin polypeptides detected and identified by an- bovine cornea see Franke et al., 1981~; Schiller et tibody binding in immunoblot experiments, and in most cases also by al., 1982). Components 4-6 are observed, in various peptide mapping, are arranged according to their mobilities in these proportions, in many nonkeratinizing stratified squa- gel electrophoretic systems. Abscissa: isoelectric pH values for mol- mous epithelia of man (for example, tongue mucosa, ecules denatured in 9.5 M urea (data combined from isoelectric focusing and nonequilibrium pH gradient electrophoresis). Ordinate: Figure 2e) as well as in epithelia of trachea and relative molecular weight CM,) as determined by SDS-polyacrylamide apocrine (Figure 2d) and sweat glands of skin and of gel electrophoresis. Cytokeratin polypeptides are designated by Ar- mammary gland (Table 1; see also Moll et al., 1982b, abic numerals. Horizontal series of spots: different isoelectric variants 1982~). Of these, polypeptides 5 and 6 also occur in of the same polypeptide. Large dots: the specific major variant, usually the most basic, nonphosphorylated one. Small dots: minor epidermis and hair follicles (see Figure 2f; Fuchs and variants. Open circles: variants of the specific polypeptide not always Green, 1980; Moll et al., 1982b) and are closely found in analyses from various cell types. PGK: 3-phosphoglycero- related to each other, as judged from peptide maps kinase. BSA: bovine serum albumin. A: rabbit 01 actin. V: human (Schiller et al., 1982). vimentin. -Cytokeratin polypeptides of intermediate size and Two-dimensional gel electrophoresis was performed with nonequili- brium pH gradient electrophoresis (O’Farrell et al., 1977: ampholine electrical charge (components 7 and 8) are found in range, pH 2-1 1; lysis buffer containing 0.25% SDS) or isoelectric diverse simple epithelia, in trachea (Mall et al., focusing (O’Farrell, 1975; ampholine range, pH 4-7) in the first 1982c), in transitional epithelium (urothelium) of blad- dimension. For second dimension electrophoresis on 12% SDS-poly- der (Figure 2c), in several complex glands (Figure 2d; acrylamide gels (Laemmli, 1970), a modified electrode buffer and an Mall et al., 1982~) and in HeLa cells (Franke et al., acrylamide to NJ’-methylene bisacrylamide ratio of 30:0.15 was used (Thomas and Kornberg. 197.5). Gels were stained with Coomas- 1981 c, 1982; Bravo et al., 1982). Cytokeratin 8 is the sie brilliant blue or, mostly for analysis of protein present in micro- only representative of this subgroup in several simple dissected samples, by a silver staining method (Ansorge, 1982). Gels epithelia of man and various animals (“cytokeratin A”; containing 35S-methionine-labeled