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Vascular Smooth Muscle Cells Differ from Other Smooth Muscle Cells

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Vascular Smooth Muscle Cells Differ from Other Smooth Muscle Cells Proc. NatL Acad. Sci. USA Vol. 78, No. 1, pp. 298-302, January 1981 Cell Biology Vascular smooth muscle cells differ from other smooth muscle cells: Predominance of vimentin filaments and a specific a-type actin (intermediate filaments/desmin/muscle differentiation/blood vessels/atherosclerosis) GIULIO GABBIANI*, ERIKA SCHMIDt, STEFANIE WINTERt, CHRISTINE CHAPONNIER*, CATHERINE DE CHASTONAY*, JOEL VANDEKERCKHOVEt, KLAus WEBERf, AND WERNER W. FRANKEt *Department of Pathology, University of Geneva, 1211 Geneva 4, Switzerland; t Department of Membrane Biology and Biochemistry, Institute for.Cell and Tumor Biology, German Cancer Research Center, D-6900 Heidelberg, Federal Republic of Germany; and *Max Planck Institute for Biophysical Chemistry, D-3400 Goettingen, Federal Republic of Germany Communicated by Earl P. Benditt, September 2, 1980 ABSTRACT Smooth muscle cells of the digestive, respiratory, It has recently been noted that the actin composition of and urogenital tracts contain desmin as their major, if not exclu- smooth muscle tissue ofbovine aorta is unique in that it shows sive, intermediate-sized filament constituent and also show a pre- dominance of y-type smooth muscle actin. We have now examined a predominance of a smooth muscle a-type actin with the smooth muscle tissue of different blood vessels (e.g., aorta, small amino-terminal sequence Glu-Glu-Glu-Asp-Ser, which is dif- arteries, arterioles, venules, and vena cava) from various mam- ferent in two amino acid positions from the y-type smooth mus- mals (man, cow, pig, rabbit, rat) by one- and two-dimensional gel cle actin predominant in bovine rumen and uterus and in electrophoresis of cell proteins and by immunofluorescence mi- chicken gizzard (27, 28). croscopy using antibodies to different intermediate-sized filament Here we report that vascular smooth muscle cells of various proteins. Intermediate-sized filaments of vascular smooth muscle cells contain abundant amounts of vimentin and little, if any, des- species, humans included, profoundly differ from smooth mus- min. On gel electrophoresis, vascular smooth muscle vimentin cle cells of digestive, respiratory, and urogenital tract by the appears as two isoelectric variants of apparent-pI values of 5.30 presence oflarge amounts ofvimentin filaments and ofa-actin. and 5.29, shows the characteristic series of proteolytic fragments, and is oneof the major cell proteins. Thus vimentin has been dem- onstrated in a smooth muscle cell present in the body. Vascular MATERIALS AND METHODS smooth muscle cells are also distinguished by the predominance Segments ofthe aorta were removed from male or female adult of a smooth muscle-specific e-type actin, whereas y-type smooth rats, cows, pigs, and rabbits, and were directly frozen either at muscle actin is present only as a minor component. It is proposed that the intermediate filament and actin composition of vascular - 150'C (in isopentane) for immunofluorescence microscopy (8, smooth muscle cells reflects a differentiation pathway separate 29) or at -20'C for protein analysis. In some experiments, ly- from that of other smooth muscle cells and may be related to spe- ophilized tissue was used. Alternatively, aortic tissue was di- cial functions and pathological disorders of blood vessels. rectly extracted in the sample buffer used for polyacrylamide gel electrophoresis (see below). Cytoskeletons were prepared Different cell types contain distinct species of contractile and by extraction with high-salt buffers and Triton X-100 as de- cytoskeletal proteins. This is especially evident in the class of scribed for chicken gizzard (2, 22, 30). Pieces ofaorta were dis- the intermediate-sized (7- to 11-nm) filaments (refs. 1-4, for sected and stripped pure media was prepared. Parts of the in- review see ref. 5). Thus, epithelial cells contain intermediate ferior vena cava were removed from rats and processed as filament proteins related to epidermal prekeratin (2, 6-9) and described for aortic tissue. Heart muscle tissue and smooth mesenchymal cells contain filaments of the vimentin type (1, muscle-rich tissues ofuterus, trachea, stomach, small intestine, 2, 4). Vimentin has also been reported to exist in various cul- and colon were removed and processed as described for aorta. tured cells, nonmesenchymal ones included (1, 2, 10, 11), and Human tissues were collected as follows: aorta was obtained in association with Z-disks of striated muscle (ref. 12; see, how- at autopsy from 4 males and 4 females with a mean age of 57 ever, ref. 13). The major protein constituent of intermediate years (47 to 73). The cross section ofthe whole wall was used for filaments of chicken gizzard smooth muscle ["desmin". (14)], immunofluorescent staining. For protein analysis intima and which is similar, if not identical, to the intermediate filament adventitia were stripped offwith a fine pair offorceps and the protein predominant in smooth muscle of mammalian colon integrity ofthe media was verified by light microscopy. Uterus ["skeletin" (15, 16)], has been shown to occur in differentiated was obtained from a 40-year-old female hysterectomized for a smooth muscle cells of the digestive and urogenital tracts of uterine myoma. The endometrium was carefully eliminated and chicken (1, 4, 14, 17-20) and mammals (20-22), in cultured car- normal myometrium was used for immunofluorescence and diac myocytes (18, 23), in filaments of skeletal myotubes (13, protein analysis. Human trachea and cardiac tissue were ob- 18, 24), in Z-lines of mature skeletal and cardiac muscle of birds tained at autopsy from two females aged 76 and 50, respectively, and mammals (3, 13, 14, 17-19, 22, 24), and in intercalated disks without macroscopically and microscopically visible respiratory of heart muscle (14, 22). or cardiac pathology, with the exception of thickening ofcoro- To date, vimentin-has not been carefully demonstrated in nary intima. smooth muscle (refs. 14-17, 19, 20, and 25; for culturedsmooth The preparation ofguinea pig antisera and monospecific an- muscle cells see, however, ref. 18), though antibodies to vi- tibodies against murine and human vimentin (2, 11), desmin mentin have been shown to react strongly with the wall of small from chicken gizzard (22, 30), and bovineprekeratin (2, 6, 22) as arteries (2, 26). well as procedures used for-immunofluorescence microscopy on frozen sections (22, 29) were as previously described. The publication costs ofthis article were defrayed in part by page charge One-dimensional gel electrophoresis was essentially accord- payment. This article must therefore be hereby marked "advertise- ing to Laemmli (31). In two-dimensional gel electrophoresis (32) ment" in accordance with 18 U. S. C. §1734 solely to indicate this fact. the modification of Kelly and Cotman (33) was used in some ex- 298 Downloaded by guest on September 25, 2021 Cell Biology: Gabbiani et aL Proc. Natl. Acad. Sci. USA 78 (1981) 299 periments in order to minimize proteolytic degradation of vi- - dIEF L V mentin in the 9.5 M urea buffer used for isoelectric focusing A m I Mr .. (12, 34). v _m Actins were purified and used for isoelectric focusing analysis n T-i and characterization oftheir amino-terminal tryptic peptides as b T described (27, 28). -LI n A A mn RESULTS Gel Electrophoresis. Smooth muscle-rich tissue and cyto- a skeletal fractions from stomach, small intestine, colon, and D V - m ! a prominent desmin band and comparatively '. uterus all showed D fv . _ .'r little protein in the position ofvimentin (e.g., Fig. 1, lane a) as rn shown by one-dimensional gel electrophoresis of total tissue proteins and cytoskeletal fractions. At the same time, in all spe- A u cies examined, aortic and venous tissues showed a prominent polypeptide band comigrating with purified mammalian vimen- d e tin (2, 11). In order to minimize the problem of contamination with vimentin-containing cells of non-smooth-muscle origin, FIG. 2. Two-dimensional gel electrophoresis (orientation is indi- we also analyzed stripped aortic media, because this tissue con- cated in a: IEF, isoelectric focusing; Mr, second electrophoresis in the tains only smooth muscle cells (35). Fig. 1, lane b shows an ex- presence of NaDodSO4 for estimation of Mr values) of proteins of stripped media of human aorta (a-c) and human uterus tissue (d and ample of protein from stripped aortic media. A faint band of e). Brackets indicate the positions ofactin (A; a-, f-, and -t-type actins electrophoretic mobility slightly higher than that of vimentin are separated in c; see also Fig. 3b), tropomyosin (T), vimentin (V), and was noted only in some preparations ofaortic tissue; comparison desmin (D in d and e). Proteolytic fragments ofvimentin (some are de- and coelectrophoresis with desmin showed that this polypep- noted by arrows in b and e) are conspicuous in samples directly lysed in tide band had significantly higher mobility than authentic mam- 9.5 M urea lysis buffer (32) but are reduced in samples denatured prior malian desmin (2, 22). to isoelectric focusing (c; ref. 33). Note absence of detectable amounts ofdesmin in aortic media (a-c). A large part, ifnot all, ofthe vimentin Two-dimensional gel electrophoresis ofaortic tissue or cyto- found in uterine tissue (d and e) is from blood vessels and connective skeletons showed the presence ofrelatively large proportions of tissue cells such as fibroblasts (see text). vimentin (Figs. 2 a-c and 3 present examples for man and rat, respectively). Characteristically, vascular vimentin appeared in the form of two isoelectric variants (apparent pI values of 5.30 and 5.29), one ofwhich probably represents phosphorylated vi- mentin (for comparison see studies in cultured cells in refs. 25 and 37). In all vascular tissues vimentin was a major protein, next to the three actin components separated on these gels 1j1 - Mr 94,000 (Figs. 2-4) and the tropomyosins. The identity of the vimentin was demonstrated by its enrichment in high-salt-extracted cy- toskeletons, by coelectrophoresis with vimentin from purified _--- M 68,000 cytoskeletons of cultured cells of murine, bovine, and human --- Vimentin origin (refs.
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