Permanently proliferating rat vascular smooth muscle cell with maintained expression of smooth muscle characteristics, including actin of the vascular smooth muscle type.

Abstract

Cells of an established clonal line (RVF-SMC) derived from rat vena Cava are described by light and electron microscope methods and biochemical analysis of the major proteins . The cells are flat, and they moderately elongate and form monolayers . They are characterized by prominent cables of microfilament bundles decoratable with antibodies to actin and a-actinin. These bundles contain numerous densely stained bodies and are often flanked by typical rows of surface caveolae and vesicles . The cells are rich in intermediatesized filaments of the vimentin type but do not show detectable amounts of desmin and cytokeratin filaments. Isoelectric focusing and protein chemical studies have revealed actin heterogeneity. In addition to the two cytoplasmic actins, ß and y, common to proliferating cells, two smooth muscle-type actins (an acidic a-like and a -y-like) are found. The major (atype) vascular smooth muscle actin accounts for 28% of the total cellular actin . No skeletal muscle or cardiac muscle actin has been detected . The synthesis of large amounts of actin and vimentin and the presence of at least three actins, including a-like actin, have also been demonstrated by in vitro translation of isolated poly(A) + mRNAs. This is, to our knowledge, the first case of expression of smooth muscle-type actin in a permanently growing cell . We conclude that permanent cell growth and proliferation is compatible with the maintained expression of several characteristic cell features of the differentiated vascular smooth muscle cell, including the formation of smooth muscle-type actin.Studies of biological processes in cells cultured in vitro are often limited by the fact that pronounced changes of cell character occur during culturing. One prominent line of changes observed during culturing involves the loss of certain structures, functions, and chemical compounds that are typical for the differentiated state of the original cell . Another frequently found phenomenon is the expression of structures and chemical compounds in the cultured cell that are not found in the cell in situ. Typical examples include the formation of collagen type I in chondrocytes (24) and of intermediate-sized filaments of the vimentin type in cultured cells from epithelial, neuronal, and muscle origin (e.g., see references 2, 11, and 12).Drastic changes of cell character and composition have also been described in cultures of muscle cells, smooth muscle cells of vascular origin included (e .g ., see references 6-8 and 21 ; for an excellent review, see reference 7) . For example, in vertebrate muscle cells grown in culture, usually the muscle-specific actins and myosins appear to be greatly reduced in amount or even completely lost, concomitant with the expression and increase of the nonmuscle types of actin and myosin; in established cell lines, including those derived from myogenic embryonal tissue, only nonmuscle actins (i.e ., 8-and y-actin) have been found (for myosin, see references 4, 6, and 7; for actin, see references

Proteolysis of vimentin and desmin by the Ca2+-activated proteinase specific for these intermediate filament proteins.

“…This pattern of vimentin-derived peptides is identical to that described in extracts of vascular smooth muscle (9), skeletal muscle (24) and nonmuscle cells grown in vitro (6,8,23), and in cells of the early mammalian embryo (15).…”

Identification and Definition of nucleolus-related fibrillar bodies in micronucleated cells

“…Cells from kidney epithelia of Xenopus laevis (line A6) and rat kangaroo (PtK 2 ) as well as RVF-SMC cells (an established cell line derived from vascular smooth muscle of rat vein) were grown in monolayers as described [5][6][7]. Micronucleation was induced by addition of colchicine (0.2 ~g/ml) to the cultures for 24-48 h [11,16] .…”

Thrombin-stimulated events in cultured vascular smooth-muscle cells

“…These cells were characterized as VSMC on the basis of the following characteristics: growth in typical 'hill-and-valley' pattern, staining ( > 85 % positive at passage 5) with a monoclonal antibody specific for smoothmuscle a-actin (Franke et al, 1980), and presence of high-affinity angiotensin II receptors (Berk et al, 1989). The primary isolates were harvested twice a week with trypsin/EDTA and passaged at a 1:4 ratio in 75 cm2 culture flasks.…”