Temperature-dependent surface changes in cells infected or transformed by a thermosensitive mutant of polyoma virus

P-glycoprotein-mediated multidrug resistance phenotype of L1210/VCR cells is associated with decreases of oligo- and/or polysaccharide contents

Multidrug resistance of murine leukaemic cell line L1210/VCR (obtained by adaptation of parental drug-sensitive L1210 cells to vincristine) is associated with overexpression of mdr1 gene product P-glycoprotein (Pgp)-the ATP-dependent drug efflux pump. 31P-NMR spectra of L1210 and L1210/VCR cells (the latter in the presence of vincristine) revealed, besides the decrease of ATP level, a considerable lower level of UDP-saccharides in L1210/VCR cells. Histochemical staining of negatively charged cell surface binding sites (mostly sialic acid) by ruthenium red (RR) revealed a compact layer of RR bound to the external coat of sensitive cells. In resistant cells cultivated in the absence or presence of vincristine, the RR layer is either reduced or absent. Consistently, resistant cells were found to be less sensitive to Concanavalin A (ConA). Moreover, differences in the amount and spectrum of glycoproteins interacting with ConA-Sepharose were demonstrated between sensitive and resistant cells. Finally, the content of glycogen in resistant cells is lower than in sensitive cells. All the above facts indicate that multidrug resistance of L1210/VCR cells mediated predominantly by drug efflux activity of Pgp is accompanied by a considerable depression of oligo- and/or polysaccharides biosynthesis.

Phosphorylation of polyomavirus large T antigen: effects of viral mutations and cell growth state

Phosphorylation is responsible for the shift in electrophoretic mobility of polyomavirus large T antigen observed in pulse-chase or continuous-labeling experiments. Phosphorylated forms migrated more slowly than newly synthesized [35S]methionine large T antigen, and alkaline phosphatase treatment reversed the mobility shift. Analysis of phosphopeptides with Staphylococcus aureus V8 protease showed that large T antigen forms of intermediate mobility were enriched in peptides 1 to 4, 8, and 9, while the slower migrating species had all nine phosphopeptides, including peptides 5 and 7. The phosphorylations represented by phosphopeptides 5 and 7 were of particular interest. These phosphopeptides were entirely lacking in large T antigen from tsa mutants such as ts616 labeled at the nonpermissive temperature. Also, the phosphorylation of peptides 5 and 7 depends on the growth state of the cell. Early in infection of quiescent cells intermediate mobility forms of large T antigen with little or no phosphorylation, particularly of peptides 5 and 7, were seen, whereas peptides 5 and 7 were well represented at the same time in patterns from growing cells. Later in infection of growth-arrested cells, these phosphorylations were observed, suggesting that infection stimulates the relevant kinase. Because large T antigen of hrt mutants, which lack middle and small T antigens, showed phosphorylation of peptides 5 and 7, large T antigen was apparently responsible for the stimulation. Because some differences in the distribution of phosphopeptides were noted between hrt mutants and the wild type, middle T antigen, small T antigen, or both may play a modulating role in large T antigen phosphorylation.

Studies on a Factor in Sweet Potato Root Which Agglutinates Spores of Ceratocystis fimbriata, Black Rot Fungus

A factor which agglutinated the spores of Ceratocystis fimbriata in the presence of Ca(2+) was purified from sweet potato (Ipomea batatas Lam cv. Norin[1]) root. Element composition of the purified factor was as follows; analysis found: C (29.8%), H (3.97%), O (65.34%), N (0.81%): calculated for C(43)H(69)O(70)N(1): C (30.02%), H (4.01%), O (65.15%), N (0.81%). The factor was mainly composed of galacturonic acid (53% of dry weight) and contained arabinose, fucose, and unidentified component as minor components. The factor also agglutinated A-, B-, AB-, and O types of human erythrocytes to almost the same degree in the presence of Ca(2+). The differential spore-agglutinating activity of the factor depended on the pH of the assay medium; it agglutinated similarly the germinated spores of sweet potato and coffee strains at pH 7.5 and 5.5, whereas it displayed a distinct differential agglutinating activity at pH 6.5. The factor was assayed for spore-agglutinating activity at pH 6.5, using the germinated and ungerminated spores of seven strains of C. fimbriata; sweet potato, coffee, prune, cacao, oak, taro, and almond strains. The factor agglutinated ungerminated spores of all seven strains similarly, although small differences were observed among strains. On the other hand, a clear differential agglutination was observed among the germinated spores of various strains; sweet potato and almond strains were highly insensitive in comparison with other strains. The growth of the agglutinated spores of C. fimbriata was inhibited. These results are discussed in relation to host-parasite specificity.

Transforming genes and gene products of polyoma and SV40

The small DNA-containing viruses, SV40 and polyoma, transform cells in vitro and induce tumors in vivo. For both viruses two genes required for transformation have been found. The genes required for transformation are also involved in productive infection. Although the two viruses are similar in their effects on cells, the organization of the transforming genes and gene products is different. The purpose of this review is to compare what is known about the biology and the biochemistry of the early regions of the two viruses. The genetic and biochemical studies defining the sequences important for transformation will be reviewed. Then, the products of the transforming genes, called T antigens, will be discussed in detail. There is a substantial body of descriptive information on those products, and studies on the function of the T antigens have also begun.

Fluorescein-concanavalin A conjugates distinguish between normal and malignant human cells: a preliminary report

A method is described for using a fluorescein isothiocyanate concanavalin A conjugate to stain human cell membranes in formalin fixed paraffin embedded tissue. 57 neoplastic and normal tissue sites were examined. In 54 malignant tumours, bright green fluorescence was confined to the cell membranes while in 23 benign tumours and normal tissue sites, the membranes were unstained or showed a diminished level of fluorescence. The distinction between malignant and hyperplastic or normal cells was clear cut and definite.

Polyoma T (tumor) antigen species in abortively and stably transformed cells

Stable neoplastic transformation of cells by polyoma virus requires the particpation of two viral genes, designated ts-a and hr-t. The effects of mutations in these two genes on the patterns of T-antigen synthesis during productive infection have been previously described: ts-a mutants are affected in the "large" (100K) nuclear T antigen, and hr-t mutants are affected in the "middle" (36K, 56K, 63K) and "small" (22K) T antigens. The latter are associated predominantly with the plasma membrane (56K) and cytosol fractions, respectively. Here we examine the expression of the various forms of polyoma T antigen in nonproductive infection (abortive transformation) as well as in stably transformed cell lines of different species. The results on abortive transformation are essentially the same as those described above for productive infection. In stably transformed cells, the middle and small T antigens are seen to various extents. The large T antigen, however, is often absent or present below the level of detection. Clones lacking the large T antigen are found most often among mouse transformants, but are also seen among rat transformants. Retention of the 100K species in transformed cells therefore appears to be, at least in part, an inverse function of the level of permissivity of the host toward productive viral infection. These findings indicate that the induction of the transformed phenotype in both abortively and stably transformed cells generally does not require the large T antigen, but rather the products of the hr-t gene.

Role of the simian virus 40 gene A product in regulation of DNA synthesis in transformed cells

Cells transformed by tsA mutants of simian virus 40 (SV40) are temperature sensitive for the maintenance of the transformed phenotype. The kinetics of induction of DNA synthesis were determined for hamster cell transformants shifted to the permissive temperature after a 48-h serum arrest at the nonpermissive temperature. DNAsynthesis was initiated in the tsA transformants by 8 h after shiftdown was maximal by 12 h. The presence or absence of fetal bovine serum at the time of temperature shift had no effect on the kinetics of initiation of DNA synthesis. Analysis of TTP in tsA transformants revealed similar levels of incorporation of [3H]thymidine into TTP at both permissive and nonpermissive temperatures. Autoradiography revealed that by 12 h after a shift to the permissive temperature, approximately 50% of the cells exhibited labeled nuclei after a 60-min pulse with [3H]thymidine, indicating that a majority of the cells were actively synthesizing DNA. By 8 to 12 h after a shiftup of confluent tsA transformants to the nonpermissive temperature, the number of labeled nuclei was reduced to approximately 16%, regardless of serum concentration. These data indicate that the SV40 gene A product, either directly or indirectly, regulates cellular DNA synthesis in transformed cells.

The dissociation of the surface architecture described by enhanced lectin agglutinability and the transformed phenotype expressed as anchorage independence

Using a series of cold-sensitive variants of chemically transformed BHK-21 cells, revertants to the normal phenotype derived from a dimethyl-nitrosamine transformed clone of BHK-21 as well as revertants to the normal phenotype derived from polyoma transformed BHK-21 cells we have demonstrated that the surface phenotype described by enhanced agglutinability with Con A and WGA can be dissociated from the transformed phenotype described by anchorage independence (growth in semisolid medium). Specifically we have demonstrated that the surface characteristic of enhanced agglutinability may be found in a variety of cell lines which fail to display to grow in agar. Our work clearly shows that the two phenotypes described are not concomitantly controlled and tends to suggest that the phenotype of enhanced lectin agglutinability may be dissociated from the transformed phenotype.

Deficiency in histone acetylation in nontransforming host range mutants of polyoma virus

Histones H3 and H4 derived from transforming wild-type polyoma and simian virus 40 particles show extensive acetylation compared to the histones of the host cells. The same histone fractions derived from nontransforming host range mutants of polyoma virus fail to show this high degree of acetylation.

A consideration of the role of cell surface macromolecules in the process of viral transformation

There is extensive physiological evidence implicating the cell surface as the key organelle which mediates the cell:cell interactions which underlie both normal and neoplastic growth. This information has now been supplemented with biochemical and biophysical data which indicates that surface macromolecules, in particular the heteroglycans of transformed cells, differ from those which lie at the periphery of normal cells. In the case of cells neoplastically transformed by most tumour viruses it is clear that the small virus genome (2-5 x 10(6) daltons) cannot carry the total genetic information to accomodate these various biochemical modifications, if indeed they are encoded in separate genes (1). To examine the part played in transformation by cellular genes coding for surface heteroglycan formation, we have turned to a study of SV-3T3 cells (ts H6-15) which are temperature-sensitive for expression of the transformed cell phenotype (2). The data show that cells grown under conditions permissive and non-permissive for such expression exhibit the same pattern of formation of glycolipids, and the majority of the polypeptides of the plasma membrane. There are, however, significant differences in the synthesis of some glycopeptides. A large molecular weight, trypsin-labile glycopeptide, present at the surface of untransformed fibroblasts but barely measurable in some of their virus-transformed derivatives (3), was detected, essentially at the same level, at the surface of ts H6-15 cells grown at the permissive and non-permissive temperatures. The signficance of these observations is discussed.

Temperature-dependent properties of cells transformed by a thermosensitive mutant (TS-121) of polyoma virus. II. Characterization of 121-6 cells

The properties of 121-6 cells were characterized. This cell line is transformed by ts-121, a temperature-sensitive mutant of polyoma virus. Both the morphology and saturation density of the 121-6 cells were affected by temperature; i.e. at 39 degrees C, the cells grew to monolayer sheets and remained contact inhibitied for a long time (at least 25 days), while at 35 degrees C, they grew beyond the monolayer density, like cells transformed by wild-type polyoma virus. These phenotypic changes were reversible, but increased agglutinability by Concanavalin A, which was another phenotype of these transformed cells, was not temperature-sensitive, and even at high temperature, 121-6 cells, like transformed cells, showed high agglutinability.

Properties of cells transformed by DNA tumor viruses

Transformation by the papovaviruses, SV40 and polyoma, is reviewed briefly, including factors that affect the frequency of transformation. Virus markers useful in the determination of the etiology of virus-free tumors are described, including viral DNA, viral mRNA, virus-induced antigens, and the rescue of infectious virus. Finally, the evidence that viral genes are involved in the maintenance of transformation is presented.

Malignant hemangioendotheliomas produced by subcutaneous inoculation of Balb/3T3 cells attached to glass beads

The Balb/3T3 mouse embryo cell line has been frequently used in cancer research as representative of nontumorigenic cells with the characteristic in vitro properties of postconfluence inhibition of cell division, low saturation density, and anchorage dependence. On the reasoning that anchorage dependence might also apply in vivo, each of nine mice were subcutaneously inoculated with an average of 15,400 Balb/3T3 cells attached to two glass beads 3 millimeters in diameter. After 8 weeks, all the mice had developed large bloody tumors that microscopically proved to be hemangioendotheliomas. Ther inoculation of Balb/3T3 cells alone or beads alone produced no tumors. Transplants of each tumor into normal mice grew to kill the animal within 6 weeks. Tumor cells from collagenase-disaggregated tumor tissue had a plating efficiency of 21.2 percent compared to that of normal adult subcutaneous fibroblasts of less than 0.1 percent. The tumor cells in vitro closely resembled Balb/3T3 cells in appearance and were tumorigenic at a dose of 10-4 cells. A second, repeat experiment produced the same type of tumors grossly and microscopically in 17 of 25 mice between 99 and 211 days after inoculation of the Balb/3T3 cells attached to glass beads. These findings require a reassessment of the postulate that low saturation density, postconfluence of cell division, and anchorage dependence are characteristic in vitro properties only of nonneoplastic cells.

Role of simian virus 40 gene A function in maintenance of transformation

Mouse, hamster, and human cells were transformed at the permissive temperature by mutants from simian virus 40 (SV40) complementation group A in order to ascertain the role of the gene A function in transformation. The following parameters of transformation were monitored with the transformed cells under permissive and nonpermissive conditions: morphology; saturation density; colony formation on plastic, on cell monolayers, and in soft agar; uptake of hexose; and the expression of SV40 tumor (T) and surface (S) antigens. Cells transformed by the temperature-sensitive (ts) mutants exhibited the phenotype of transformed cells at the nonrestrictive temperature for all of the parameters studied. However, when grown at the restrictive temperature, they were phenotypically similar to normal, untransformed cells. Growth curves showed that the (ts) A mutant-transformed cells exhibited the growth characteristics of wild-type virus-transformed cells at the permissive temperature and resembled normal cells when placed under restrictive conditions. There were 3-to 51-fold reductions in the levels of saturation density, colony formation, and uptake of hexose when the mutant-transformed cells were the elevated temperature as compared to when they were grown at the permissive temperature. Mutant-transformed cells from the nonpermissive temperature were able to produce transformed foci when shifted down to permissive conditions, indicating that the phenotypically reverted cells were still viable and that the reversion was a reversible event. SV40 T antigen was present in the cells at both temperatures, but S antigen was not detected in cells maintained at the nonpremissive temperature. All of the wild-type virus-transformed cells exhbited a transformed cells exhibited a transformed phenotype when grown under either restrictive or nonrestrictive conditions. Thers results indicate that the SV40 group A mutant-transformed cells are temperature sensitive for the maintenance of growth properties characteristics of transformation. Virus rescued from the mutant-transformed cells by the transfection method was ts, suggesting that the SV40 gene A function, rather than a cellular one, is responsible for the ts behavior of the cells.

Cell surface changes and Rous sarcoma virus gene expression in synchronized cells

We have investigated whether cell surface changes associated with growth control and malignant transformation are linked to the cell cycle. Chicken embryo cells synchronized by double thymidine block were examined for cell-cycle-dependent alterations in membrane function (measured by transport of 2-deoxyglucose, uridine, thymidine, and mannitol), in cell surface morphology (examined by scanning electron microscopy), and in the ability of tumor virus gene expression to induce a transformation-specific change in membrane function. We reach the following conclusions: (a) The high rate of 2-deoxyglucose transport seen in transformed cells and the low rates of 2-deoxyglucose and uridine transport characteristic of density-inhibited cells do not occur in normal growing cells as they traverse the cell cycle. (b) Although there are cell cycle-dependent changes in surface morphology, they are not reflected in corresponding changes in membrane function. (c) Tumor virus gene expression can alter cell membrane function at any stage in the cell cycle and without progression through the cell cycle.

The characteristics of succinylated con A induced growth inhibition of 3T3 cells in tissue culture

The growth of untransformed 3T3 fibroblasts can be inhibited by dimeric, non-agglutinating concanavalin A prepared by succinylation (Suc-CON A). This growth inhibition is non-toxic, reversible, and specific for Suc-Con A binding; the cell density at which growth terminates is dependent upon the final cell number and independent of the initial (i.e., plating) density. The part of the cell cycle during which Suc-Con A can exert its growth inhibitory effect appears to be restricted to mitosis and/or early G-1 phase.

Cyclic AMP mediates the concanavalin A agglutinability of mouse fibroblasts

We have devised a quantitative way to measure the agglutination of cells which utilizes the size discrimination feature of an automatic particle counter. With this method we have studied the agglutinability by concanavalin A of 3T3 cells, a mutant of 3T3 cells (3T3cAMP(tcs)) in which cyclic AMP levels fall when the cells are subjected to temperature change or fresh serum, and L929 cells. We find with 3T3cAMP(tcs) cells that low levels of cyclic AMP correlate with increased agglutinability and that high levels of cyclic AMP correlate with decreased agglutinability. Prior treatment of these cells with a cyclic AMP phosphodiesterase inhibitor or Bt(2)cAMP blocks the increase in agglutinability induced by temperature change. When 3T3 cells are treated with fresh serum, their agglutinability also increases although to a much smaller extent than with 3T3cAMP(tcs) cells. Cells change their agglutinability very rapidly. Treatment of L929 cells for 15 min with 1-methyl-3-isobutyl xanthine at 1 mM decreases their agglutinability to the level of normal 3T3 cells. We conclude that in normal and transformed cells the level of cyclic AMP regulates agglutinability.

Mutant of polyoma virus with impaired adsorption to BHK cells

A mutant of polyoma virus PY235 has an impaired adsorption to guinea pig red blood cells and BHK-21 hamster cells. Adsorption to 3T3 mouse cells is much less inhibited. These altered adsorption properties are responsible for the apparent inability of PY235 to cause cell transformation or hemagglutination.

Cyclic changes in the cell surface. I. Change in thymidine transport and its inhibition by cytochalasin B in Chinese hamster ovary cells

Cytochalasin B (CB) shows a marked concentration-dependent inhibition of the incorporation of [(3)H]thymidine into Chinese hamster ovary cells. This inhibition was shown to result from an inhibition of thymidine uptake, not from an inhibition of DNA synthesis. Cells normally acquire the capacity to transport thymidine as they move from the G1 stage of the cell cycle into the S phase. If CB is added to cells while they are in G1, they do not acquire the ability to transport thymidine as they enter S. However, the addition of CB to cells that are already in S has no effect on their ability to transport thymidine. These results are discussed in terms of a model in which elements involved in thymidine transport enter the cell surface membrane as the cells move from G1 to S. It is proposed that CB prevents this structural transition by binding to the cell surface.

A general theory of carcinogenesis

A GENERAL HYPOTHESIS OF CARCINOGENESIS IS PROPOSED CONSISTING OF THE FOLLOWING FEATURES: (1) It is suggested that all cells possess multiple structural genes (Tr) capable of coding for transforming factors which can release the cell from its normal constraints on growth. (2) In adult cells they are suppressed by diploid pairs of regulatory genes and some of the transforming genes are tissue specific. (3) The Tr loci are temporarily activated at some stage of embryogenesis and possibly during some stage of the cell cycle in adult cells. (4) Spontaneous tumors, or tumors induced by chemicals or radiation, arise as the result of a double mutation of any set of regulatory genes releasing the suppression of the corresponding Tr genes and leading to transformation of the cell. (5) Autosomal dominant hereditary tumors, such as retinoblastoma, are the result of germ-line inheritance of one inactive regulatory gene. Subsequent somatic mutation of the other regulatory gene leads to tumor formation. (6) The Philadelphia chromosome produces inactivation of one regulatory gene by position effect. A somatic mutation of the other leads to chronic myelogenous leukemia. (7) Oncogenic viruses evolved by the extraction of host Tr genes with their conversion to viral transforming genes. As a result, in addition to the above mechanisms, tumors may also be produced by the reintroduction of these genes into susceptible host cells.

Simian virus 40-host cell interactions. I. Temperature-sensitive regulation of SV40 T antigen in 3T3 mouse cells transformed by the ts*101 temperature-sensitive early mutant of SV40

BALB/3T3 and Swiss/3T3 mouse cells transformed at permissive temperature (33 C) by the early temperature-sensitive mutant of simian virus 40 (SV40), ts(*)101, exhibited a temperature-dependent modulation of SV40 tumor (T) antigen as assayed by immunofluorescence. The percentage of T antigen-positive nuclei in ts(*)101 transformed cells was reduced at restrictive temperature (39 C) when compared to 33 C and to wild-type SV40 transformed cells at either 33 C or 39 C. The percentage of T antigen-positive nuclei in ts(*)101 transformed cells returned to the 33 C control level when the cells were shifted from 39 to 33 C. The ts(*)101 transformed cells could be superinfected with wild-type, but not ts(*)101, virions at 39 C as assayed by an increase in T antigen-positive nuclei.

Antagonism by dibutyryl adenosine cyclic 3',5'-monophosphate and testosterone of cell rounding reactions

In an attempt to understand further the mechanism of the morphological and functional "reverse transformation" of CHO-K1 cells induced by dibutyryl adenosine cyclic 3',5'-monophosphate (cAMP) and testosterone, the kinetics of variation in the susceptibility of cells to rounding after the addition or deletion of dibutyryl cAMP and testosterone have been investigated. Changes in susceptibility to cell rounding upon removal of divalent cations or pulse exposure to concanavalin A were complete within 0.5-1 h after addition or deletion of drug. In comparison, the gross conversion of CHO-K1 cells from epithelial- to fibroblast-like morphology after drug treatment or the converse change after drug removal required 8 or 4 h, respectively. The effects on cell rounding are not caused by an effect of dibutyryl cAMP upon cell growth rate. Inhibitor experiments indicate that the changes investigated do not require continued RNA or protein synthesis and are not prevented by agents which depolymerize microtubules.

The relationship of concanavalin A binding to lectin-initiated cell agglutination

We have investigated the relationship of concanavalin. A binding to the cell surface of normal and transformed cells and the subsequent agglutination of the transformed cells. At room temperature almost no differences could be detected in agglutinin binding between transformed and untransformed cells. At 0 degrees C, however, where endocytosis was negligible, the transformed cells bound three times more agglutinin. However, transformed cells and trypsin-treated normal cells do not agglutinate at 0 degrees C although the amounts of agglutinin bound at 0 degrees C are sufficient to permit agglutination when such cells are shifted up to room temperature. Both transformed and trypsin-treated normal cells show a marked increase in agglutination at 15 degrees C as compared to agglutination at 0 degrees C. From this, as well as the observation that mild glutaraldehyde fixation of the cell surface inhibited agglutination but not agglutinin binding, it was concluded that concanavalin A-mediated cell agglutination requires free movement of the agglutinin receptor sites within the plane of the cell surface.