Anodic migration of actin and increased levels of a cathodic fibronectin among the cytoskeletal changes that correlate with increased cell adherence in liver epitheloid tumor cells

Liver epitheloid tumor cells exposed to iododeoxyuridine revealed increased resistance to detachment from their growth substratum when exposed to low levels of EDTA. Two-dimensional analysis of the Triton-X-100 insoluble cytoskeleton from cells grown with iododeoxyuridine revealed an increased level of cathodic fibronectin and a more anodic migration of actin-like components concurrent with the reduced expression of an anodic 50K component and of a cathodic 60K component.

Transformed cells exhibit altered response to db cycle amp-mediated modulation of protein phosphorylation and different endogenous phosphoprotein acceptors

Endogenous protein phosphorylation has been studied in extracts from rat cells transformed by temperature-sensitive derivatives of Rous sarcoma virus which can reversibly express a transformed behavior at 33 degrees C and reacquire "normal" properties at 39 degrees C. The expression of transformation appeared associated with marked alterations in the type of phosphoprotein acceptors and with an increased protein kinase activity, particularly in detergent solubilized fractions. A comparison of the effect of dibutyryl cyclic AMP on protein phosphorylation revealed a transformation-dependent response, as well as a different effect of the cycle nucleotide in cytoplasmic and detergent solubilized fractions. Our studies suggest that the processes leading to malignant transformation are accompanied by altered response of the phosphorylating system to cyclic nucleotide-mediated modulation and by marked alteration in phosphoprotein acceptors.

Growth inhibition of mouse mammary tumor cells by dexamethasone concurrent with enhanced endogenous protein phosphorylation: effects of retinoic acid

Exposure of Mm 5mt mouse mammary tumor cells to either dexamethasone, retinoic acid or both drugs, results in growth inhibition of the cultures, as compared with controls. Endogenous protein phosphorylation using gamma-32P ATP revealed prominent labelling mainly in the 58K region in extracts from retinoic acid-treated and control cultures. Extracts from dexamethasone-treated cultures showed phosphorylation in the 58K, 53K, 47K and 27K regions. Exposure to both drugs gave extracts showing labelling in the 60K and 65K regions in addition to the bands phosphorylated in extracts exposed only to the steroid, concurrent with an even more marked inhibition of growth.

Effect of malignant transformation and arginine limitation on fibronectin and other cell surface macromolecules of liver epithelial cultures

Surface labeling of "normal" nontumorigenic rat liver epithel cells permitted the detection of a 140,000-dalton species and of another 230,000-dalton molecule that comigrated with fibronectin, an external transformation-sensitive protein of fibroblasts. Reaction of surface-labeled normal liver epithelial cells with anti-fibronectin serum led to the selective recognition of the 230,000-dalton component, which revealed a peptide composition similar to that of the homologous fibroblasts fibronection. Similar experimental conditions with the tumorigenic liver epithelial cell counterpart revealed decreased labeling in the fibronectin region and preferential labeling in the 140,000- and 60,000-dalton regions. Arginine limitation was found to produce growth arrest in both normal and malignant liver epithelial cells, concurrent with a marked decrease in the labeling of the surface-associated fibronectin and different surface macromolecular alterations in normal and transformed cells. Mild proteolysis combined with brief neuraminidase treatment did not produce marked alterations in tumorigenic cell surface labeling but did lead to a decrease in the fibronectin of normal cells and to the increased expression of other transformation-associated changes in surface macromolecules different from fibronectin. Our results show the involvement of an arginine-regulated fibronectin and other cell surface macromolecules among the changes that occur during the conversion of normal liver epithelial cells to a malignant state.

Differential susceptibility of fibroblastic and non-fibroblastic surface fibronectins to periodate-borohydride labelling and enzymic treatment

Surface labelling of liver epithelioid cells permits the detection of a 230,000 dalton component reactive with antifibronectin serum, when tritiated borohydride labelling is preceded by oxidation of sugar residues with galactose oxidase but not with sodium periodate. Similar experiments with liver fibroblasts lead to the labelling of a similar 230,000 dalton component both when sugar oxidation is carried out with galactose oxidase or periodate. Neuraminidase treatment prior to surface labelling lead to an increased labelling in both cell types, although a decreased labelling in the fibronectin region was apparent in the epithelioid cells.

Heterogeneity in cell-associated transformation-sensitive proteins antigenically related to fibronectin

Antiserum to purified fibronectin has been used to investigate transformation-associated heterogeneity in surface components antigenically related to fibronectin. Examination of extracts from surface-labeled rat cells by gradient gel electrophoresis revealed in "normal" cells the presence of two species with approximate molecular weights of 250,000 and 230,000, which were decreased in wild-type transformed cells. Reaction with antifibronectin serum revealed the selective precipitation of the two transformation-sensitive surface components. A similar experiment with ts-NT3-KR that expresses a normal phenotype at 37 degrees and a transformed morphology at 33 degrees did not reveal a markedly altered surface labeling pattern at both temperatures. However, reaction with antifibronectin serum did show a weak but detectable recognition of a 230,000-dalton doublet in the cells grown at 37 degrees, and immune precipitation of components in the 100,000- and 60,000-dalton region in cells grown at 33 degrees. Experiments with normal mouse cells revealed a different ratio of two fibronectin-related external proteins with similar molecular weights to those seen in normal rat cells.

Antiserum to murine leukemia virus recognizes novel cell surface molecules associated with growth control and transformation

Antiserum directed against murine leukemia virus also reacts with several external proteins present in rat cells transformed by a temperature-sensitive Rous sarcoma virus. Reaction of iodinated cell extracts with anti-MLV (murine leukemia virus) serum revealed the presence of a 200,000 dalton iodinated component detectable also by metabolic labelling with glucosamine only in serum-starved cultures restricted in the expression of transformation. A similar assay with iodinated cells that express the transformed phenotype revealed the preferential recognition of two components with an approximate molecular weight of 100,00 daltons as well as an additional 65,000-dalton external component. Growth of the transformed non-producer NT3-KR cells in the presence of inducers of C-type viruses leads to an increased synthesis of a 100,000-dalton glycoprotein (gp100) recognized by the anti-MLV serum which is also recognized by the antiserum in NRK-MSV-MLV transformed producer cells, in addition to a virus-like glycoprotein of 71,000 dalton (gp71). Absorption of the anti-MLV serum with monolayers of NT3-KR cells eliminated the ability of the serum to recognize the gp100 but not the gp71 from NRK-MSV-MLV-transformed producer cells. The mediation of post-translational changes in growth control is suggested by the transformation-dependent alteration in the molecular weight of the non-virion surface proteins recognized by anti-MLV serum in the rat cells used in this study.

Dibutyryladenosine 3':5'-cyclic monophosphate-mediated changes in rat cells involve macromolecular alterations in vinblastine-precipitable proteins

ts-NT3-KR rat cell cultures show the loss of three components in the molecular-weight region 200,000--250,000 when exposed to dibutyryl cyclic AMP, under conditions of both restriction and expression of the transformed phenotype. Vinblastine is able to precipitate preferentially from control cultures the species that are decreased by exposure to the cyclic nucleotide. Serum-starved cultures exposed to dibutyryl cyclic AMP reveal differences in their vinblastine precipitates, depending on whether the expression of the transformation phenotype is restricted or not.

Demonstration of different glycosylated antigens in C-type virus-transformed and infected rat cells by antiserum to murine leukemia virus

[3H]Glucosamine labeling of untransformed cells, C-type virus-transformed cells, and virus-infected cells and subsequent analysis by polyacrylamide gel electrophoresis and fluorography permitted the detection of a Pronase-sensitive macromolecular labeling that appeared in about eight regions of radioactivity in every case. Reactions of cell extracts with antiserum to Tween-ether-disrupted purified murine leukemia virus revealed, in most transformed cells, two components with a mobility of about 100,000 daltons, whereas C-type virus-infected cells revealed their radioactivity mainly in a region nearer to that of the major viral glycoprotein at about 69,000 daltons. No comparable components were apparent from the reaction of transformed or infected extracts with preimmune serum or from the reaction of untransformed uninfected cells and immune serum.

Continued presence of similar transformation-associated antigens related to murine oncornavirus proteins in -ransformed cells, morphological revertants, and cells restricted in the expression of transformation

The possible alteration of transformation-related antigens in cells that revert to a normal phenotype but that continue to retain the viral genome, has been investigated in [3H]glucosamine-labeled extracts of rat cells exhibiting a reversible temperature-dependent restriction in the expression of transformation and in a comparison of a morphologically altered mouse cell transformed by the Kirsten sarcoma virus with a flat revertant mouse cell derived from the morphologically transformed cells. With the use of normal goat serum in the presence of dibutyryl cyclic 3':5'-adenosine monophosphate, some differences became obvious in the rat cells restricted in the expression of transformation. However, use of specific antiserum to murine leukemia virus revealed in every case the presence of major components that exhibited an electrophoretic mobility corresponding to about 100,000 daltons both in the parent and revertant mouse cells and in the rat cells exhibiting either untransformed or transformed growth properties. The glycoprotein components detected only by the immune serum may represent a cellular macromolecule antigenically related to an interspecies C-type viral species whose concentration is increased in transformed cells.

Transformation-dependent modifications in released and cell-bound surface proteins detected by antisera to shed antigens

Antiserum against antigens released into the medium by rat cell cultures that express the transformation phenotype has been shown to produce a complement-mediated lysis, not only in the cells that liberate such antigens but to a greater extent in cells that are phenotypically restricted in the expression of transformation properties. Reaction of the antibody with preiodinated surface proteins released into the medium reveals that the expression of transformation leads to a greater degradation of the external proteins shed into the medium.

A cyclic adenosine 3':5'-monophosphate-mediated effect of cholera toxin on high-molecular-weight glycoprotein species of malignant cells

A comparison of the Pronase-sensitive glycosylated species detectable under permissive and nonpermissive conditions by normal rat kidney cells transformed by a temperature-sensitive derivative of Rous sarcoma virus reveals relative decreased labeling of high-molecular-weight glycosylated species under conditions that allow the expression of transformation, in medium supplemented either with 0.5% calf serum or with human alpha2-macroglobulin, 100 mug/ml. Exposure of the cultures to cholera toxin or dibutyryl cyclic adenosine 3':5'-monophosphate leads to a relative increase in the glycosylation of the high-molecular weight species in both wild-type transformed and temperature-sensitive cells exposed to conditions that allow the expression of transformation.

Selective modification of cell surface proteins and thymidine transport in hamster cells exposed to cholera toxin

The increased adherence and morphological response which occurs in Chinese hamster ovary cells as a result of exposure to cholera toxin is paralleled by modification in the relative exposure of outer proteins. Mild proteolysis treatment of the cells prelabeled with [3H] glucosamine reveals a markedly different kinetics of release of external glycopeptides as a result of exposure to cholera toxin. Selective alterations in external tyrosyl-rich proteins can also be detected by lactoperoxidase-catalyzed radioiodination. The above modifications are accompanied by a decrease in the rate of thymidine uptake by toxin-treated cells.

Cholera toxin effects on cell growth accompanied by selective alterations in metabolite uptake and modification of cell surface proteins

Exposure of Chinese hamster ovary cells to cholera toxin at or below mug levels causes a marked morphological changes and increased adhesion and orientation of the cells. Such changes are paralleled by alterations in surface proteins as indicated by the cholera toxin-mediated modifications detectable by lactoperoxidase-catalyzed radioiodination of outer proteins. Mild tryptic treatment of cells prelabeled with [3H]glucosamine revealed a different kinetics of release of external glycoproteins in cells exposed to the toxin. An alteration in a specific glycoprotein species in cholera toxin-treated cells became evident by polyacrylamide gel electrophoresis followed by fluorography of 3H-labeled cellular glycoproteins. The effects of cholera toxin on surface proteins and growth of the cells occurred in the absence of a modification in amino acid uptake or incorporation of precursors into protein. However, thymidine uptake and glucosamine incorporation were inversely affected to toxin treatment. Some of the effects of the toxin appeared to be antagonized by colchicine.

Turnover of high-molecular-weight cell surface proteins during growth and expression of malignant transformation

The turnover of cell surface proteins in normal rat kidney cells transformed by a temperature-sensitive Rous sarcoma virus has been studied by polyacrylamide gel electrophoresis and autoradiography using cell monolayers prelabeled by lactoperoxidase-catalyzed radioiodination. Labeling of serum-starved cells under conditions that are nonpermissive for the expression of transformation reveals most of the radioactivity in the 250,000 molecular weight region. Parallel labeling of cells simultaneously exposed to serum limitation, under conditions that are permissive for the expression of transformation, reveals some radioactivity in the same slow-migrating region, but most of the label appears in the two faster migrating regions. The relative turnover of such external proteins has been investigated by examining the relative alterations in iodinated proteins after addition of normal levels of serum to a medium of serum-starved cells. There is a greater relative turnover of the high-molecular-weight external component under conditions in which ther transformation phenotype is expressed, as compared with conditions that limit the expression of transformation.

An "external" RNA removable from mammalian cells by mild proteolysis

Brief exposure of Chinese hamster ovary cell monolayers prelabeled with [(32)P]phosphate and [(3)H]leucine to 1 mug/ml of trypsin under conditions in which cells remain fully viable causes the release of macromolecular (32)P and (3)H. Whereas ribonuclease treatment was found to affect markedly both the (32)P and (3)H radioactivity, Pronase treatment had little effect on the macromolecular (32)P. Treatment of cells prelabeled with [(3)H]glucosamine and [(32)P]phosphate with insolubilized papain also revealed a parallel release of macromolecular glucosamine together with ribonuclease-susceptible macromolecular phosphate. Lactoperoxidase-mediated radioiodination of surface components in cells prelabeled with [(32)P]phosphate revealed electrophoretic comigration between the (125)I and the (32)P that are removed from the cells by mild proteolysis. Growth of the cells in Bt(2)cAMP-testosterone altered the kinetics of release and nature of the macromolecular (32)P liberated by proteolysis.