Localization of mitochondria in living cells with rhodamine 123

The laser dye rhodamine 123 is shown to be a specific probe for the localization of mitochondria in living cells. By virtue of its selectivity for mitochondria and its fluorescent properties, the detectability of mitochondria stained with rhodamine 123 is significantly improved over that provided by conventional light microscopic techniques. With the use of rhodamine 123, it is possible to detect alterations in mitochondrial distribution following transformation by Rous sarcoma virus and changes in the shape and organization of mitochondria induced by colchicine treatment.

Malignant behaviour of three adenovirus-2-transformed brain cell lines and their methyl cellulose-selected sub-clones

Three adenovirus-2-transformed rat embryo brain cell lines and their methylcellulose-selected sub-clones were examined for fibronectin expression, anchorage-independent growth, saturation density, T antigen expression and morphology. Tumorigenicity studies were carried out on newborn and ATS immunosuppressed syngeneic rats and congenitally athymic nude mice. With one exception the methylcellulose sub-clones contained significantly fewer fibronectin-positive cells than the parent lines; a number of sub-clones contained no fibronectin-positive cells. Methylcellulose selection did not always alter cell morphology, saturation density or anchorage-independent growth as compared with parent lines. However, the methylcellulose sub-clones were considerably more malignant than the parent cell lines as measured by invasion and metastasis in nude mice. No in vitro characteristic correlated with malignant behaviour.

Possible role of fibronectin in malignancy

Frozen sections of tumors induced by injecting virally transformed cells into animals were stained for fibronectin by immunofluorescence. Many tumor cell lines do not express fibronectin in tumors in situ even though some of them express fibronectin in culture. Cell shape and hormones appear to influence the expression of fibronectin in culture; however, it is unclear how fibronectin expression is regulated in vivo.

Studies on intercellular LETS glycoprotein matrices

Intercellular matrices secreted by chick embryo fibroblasts in culture were studied by scanning electron microscopy. Cell-cell contact is a prerequisite for the expression of such matrices. The smallest fiber detected by transmission electron microscopy is 5--10 nm in diameter. These matrix fibers tend to cluster to form bundles. Immunofluorescence and immunoferritin procedures reveal that LETS protein is one of the components of the matrices. The matrices are isolated from other cellular organelles by detergent treatment. More than 90% of the proteins in cell-free matrices are LETS protein, suggesting that the matrices are probably made of only one component--LETS protein. Since the solubilization of matrices requires beta-mercaptoethanol, LETS protein matrices may be the first known polymer system in nature to use disulfide linkage as an intermolecular polymerization vehicle. Collagen does not appear to be involved in such matrices. The LETS protein matrix supports the morphological conversion of rounded cells into spindle-shaped, and also promotes myoblast fusion. It does not, however, exert an effect upon cell growth, the rate of glucose uptake or protease production.

Control of a cell surface major glycoprotein by epidermal growth factor

When the serum concentration of the culture medium is below 0.7 per-cent, 3T3 mouse cells lose most of their large external transformation sensitive (LETS) protein at the cell surface, Subsequent addition of epidermal growth factor results in the reappearance of massive fibrillar LETS protein networks on the surface of conluent 3T3 cells. Thirteen other hormones tested do not have this effect. It appears that epidermal growth factor can control the expression of LETS protein.

In vitro traits of adenovirus-transformed cell lines and their relevance to tumorigenicity in nude mice

Six independently isolated adenovirus 2-transformed rat cell lines and one adenovirus 5-transformed human cell line have been examined in vitro for serum growth requirements, saturation density, anchorage-independent growth, proteolytic enzyme activity and the presence of LETS glycoprotein and T antigen. This series of adenovirus-transformed cell lines exhibits an oncogeni spectrum ranging from being tumorigenic in immunocompetent rats through to nontumorigenic in adult nude mice. The relevance of the in vitro findings to growth potential in vivo is discussed.

Alteration in cell surface LETS protein during myogenesis

Cell surface alterations during myogenesis have been investigated in Yaffe's myogenic cell line L8, using indirect immunofluorescence with an antibody against the large external transformation-sensitive (LETS) protein. The immunofluorescent technique reveals a susbstantial alteration in the distribution of this surface antigen. With the prefused myoblasts, LETS protein is dispersed all over the cell surface; following myoblast fusion, this pattern is markedly changed. All of the fibril-like surface LETS protein disappears, and in some myotubes, discrete clusters of LETS protein become conspicuous. By use of radioimmunological assay, the total LETS protein is quantitatively reduced upon myoblast fusion.

Binding and internalization of thrombin by normal and transformed chick cells

Thrombin stimulates cell proliferation in cultures of normal chick embryo fibroblasts but not in cells transformed with Rous sarcoma virus. Analysis of medium conditioned by Rous-sarcoma-virus-transformed cultures demonstrates that these cells do not secrete molecules that can inhibit or inactivate thrombin. The interaction of thrombin with these cells was investigated with enzymatically active 125I-thrombin. The amount of cell-associated 125I-thrombin was found to be three times greater with normal cells than with transformed cells. In both types of cell, greater than 50% of the total cell-associated 125I-thrombin was found as a component that was not dissociated from the cells by trypsin treatment, an observation suggesting that a significant portion was not on the cell surface. The amount of the trypsin-insensitive fraction increases with time up to 12 hr, whereas the trypsin-sensitive fraction is saturated after 1-4 hr. Autoradiography of thin sections of 125I-thrombin-treated cells observed by electron microscopy reveals that after 10 hr incubation greater than 70% of the label is localized in the cytoplasm of both normal and transformed cells. Autoradiograms of sodium dodecyl sulfate/polyacrylamide slab gels demonstrate that 40% of the intracellular label is the size of native thrombin with the remainder in two large fragments of 22,000 and 19,500 daltons.

Correlation between tumor induction and the large external transformation sensitive protein on the cell surface

The distribution on the cell surface of the large external LETS protein that is transformation sensitive of normal, transformed and tumorigenic cells was examined by immunofluorescent staining. A correlation was established between the expression of fibril-like LETS protein and the oncogenic capabilities of a series of adenovirus-transformed cell lines. In cells expressing a transformed phenotype in vitro, LETS protein is only detected in cell-cell contact areas, wheras in "untransformed" cells LETS protein is distributed over the cell surface. Transformed cells capable of inducing invasive tumors, and the cells of established tumor lines, have low or undetectable levels of LETS protein, as measured by this method. The results indicate that LETS protein has a role in cell-cell adhesion and that reduced expression of this protein at the cell surface is related to the oncogenic phenotype. This relationship has been established for experimentally induced and spontaneous tumors.

Effects of protease treatment on growth, morphology, adhesion, and cell surface proteins of secondary chick embryo fibroblasts

Several proteolytic enzymes have been studied with regard to their ability to induce DNA synthesis and cell proliferation in resting chick embryo fibroblasts. Of the enzymes examined, thrombin, bromelin, and trypsin exhibit potent mitogenic activity, elastase has significant but less marked activity, whereas thermolysin, papain, and alpha-protease are inactive. The enzymes were also tested for their ability to induce morphological change or to remove two iodinatable proteins of 250,000 and 205,000 daltons. Although the larger protein is removed by some but not all of the proteases examined, every protease tested removed the smaller cell surface proteins; however, loss of the smaller protein does correlate with the reduction of both cytoplasmic spreading and cell-cell interactions observed after protease treatment. A secondary, later event of migration of cells into clumps is observed in those instances when protease treatment did not result in a loss of the 250k protein. Arole for each of these proteins in the processes of cellular adhesion is discussed.

Surface ruffles as markers for studies of cell transformation by Rous sarcoma virus

Confluent chick embryo fibroblasts infected with the Ts68 mutant of Rous sarcoma virus were examined by scanning electron microscopy at the permissive (36 degrees) and nonpermissive (41 degrees) temperatures for transformation. Infected cells shifted from 41 degrees to 36 degrees undergo a change in shape from elongated to rounded. This process is preceded by the appearance of surface ruffles on the cell. These surface ruffles are not observed on cells maintained at 41 degrees, appear as early as 0.5 hr after a shift to 36 degrees, and are common on cells maintained at 36 degrees. By 3.5 hr after the shift from 41 degrees to 36 degrees, cultures appear fully transformed by the criteria of cell roundedness and the presence of surface ruffles. This surface alteration of cells is the earliest event of those so far reported during the transformation process and is not dependent upon protein synthesis and extracellular plasminogen during the period of temperature shift.

Plasminogen-independent fibrinolysis by proteases produced by transformed chick embryo fibroblasts

The fibrinolytic activity of proteases secreted by chick embryo fibroblasts infected with Rous sarcoma virus was studied by use of a procedure in which a fibrin clot was formed with highly purified fibrinogen and thrombin above the cell layer. This procedure results in the formation of fibrin that is apparently a more suitable substrate for studies on fibrinolysis than is fibrin prepared by other methods. Since neither plasminogen nor serum were included in the assay system in the present studies, the fibrinolytic activity observed cannot be ascribed to the conversion of the plasminogen in serum to plasmin by a plasminogen activator produced by transformed cells. Our procedure, therefore, measures proteolytic activities other than those reported by previous investigators. Maintenance of some of the transformed phenotypes of Rous sarcoma virus transformed chick embryo fibroblasts such as morpholigical change and increased rate of glucose uptake apparently does not depend on the presence of plasminogen in the culture medium.

Mitogenic activity of blood components. I. Thrombin and prothrombin

When added to a culture medium of resting confluent chick embryo fibroblasts in the absence of serum, thrombin (EC 3.4.21.5) is able to stimulate DNA synthesis 12 hr later and to cause a substantial increase in cell number over a period of 4 days. As compared to thrombin, prothrombin exhibits low mitogenic activity. However, in the presence of purified Factor Xa (EC 3.4.21.6) and Factor V, prothrombin is converted to thrombin by "thromboplastin activity" supplied by the fibroblasts. Prothrombin, either purified or as a constituent of plasma or serum, may thus be considered to be a reservoir of mitogenic activity in tissue culture unless antithrombin is present in the culture medium in amounts sufficient to neutralize the thrombin formed. By use of a specific inhibitor of proteases, and by separation of prothrombin by absorption on BaSO4, we estimate that the potential mitogenic activity of prothrombin is approximately 30-50% of the total activity that can be obtained by treatment of fibrinogen-free plasma with thromboplastin. In addition to its mitogenic activity, thrombin can also stimulate the migration of cells. These experiments with thrombin illustrate that well-characterized proteases of blood can act as potent mitogens and suggest that they may play a role in the process of wound healing.