Surface T-antigen expression in simian virus 40-transformed mouse cells: correlation with cell growth rate

1985 ◽  
Vol 5 (5) ◽  
pp. 1051-1057
Author(s):  
M Santos ◽  
J S Butel
Keyword(s):  
Growth Rate ◽  
Cell Growth ◽  
Growth Control ◽  
Simian Virus 40 ◽  
Antigen Expression ◽  
Simian Virus ◽  
T Antigen ◽  
Transformed Cells ◽  
Seeding Density ◽  
Cell Growth Rate

Cell growth control appears to be drastically altered as a consequence of transformation. Because the cell surface appears to have a role in modulating cell growth and simian virus 40 (SV40)-transformed cells express large T antigen (T-Ag) in the plasma membrane, we investigated whether surface T-Ag expression varies according to cell growth rate. Different growth states were obtained by various combinations of seeding density, serum concentration, and temperature, and cell cycle distributions were determined by flow microcytofluorometry. Actively dividing SV40-transformed mouse cell cultures were consistently found to express higher levels of surface T-Ag and T-Ag/p53 complex than cultures in which cells were mostly resting. In addition, the T-Ag/p53 complex disappeared from the surface of tsA7-transformed cells cultured under restrictive conditions known to induce complete growth arrest (39.5 degrees C), although the surface complex did not disappear from other tsA transformants able to keep cycling at 39.5 degrees C. These results suggest that surface SV40 T-Ag or surface T-Ag/p53 complex, or both, are involved in determining the growth characteristics of SV40-transformed cells.

scholarly journals Surface T-antigen expression in simian virus 40-transformed mouse cells: correlation with cell growth rate.

1985 ◽  
Vol 5 (5) ◽  
pp. 1051-1057 ◽  
Author(s):  
M Santos ◽  
J S Butel
Keyword(s):  
Growth Rate ◽  
Cell Growth ◽  
Growth Control ◽  
Simian Virus 40 ◽  
Antigen Expression ◽  
Simian Virus ◽  
T Antigen ◽  
Transformed Cells ◽  
Seeding Density ◽  
Cell Growth Rate

Cell growth control appears to be drastically altered as a consequence of transformation. Because the cell surface appears to have a role in modulating cell growth and simian virus 40 (SV40)-transformed cells express large T antigen (T-Ag) in the plasma membrane, we investigated whether surface T-Ag expression varies according to cell growth rate. Different growth states were obtained by various combinations of seeding density, serum concentration, and temperature, and cell cycle distributions were determined by flow microcytofluorometry. Actively dividing SV40-transformed mouse cell cultures were consistently found to express higher levels of surface T-Ag and T-Ag/p53 complex than cultures in which cells were mostly resting. In addition, the T-Ag/p53 complex disappeared from the surface of tsA7-transformed cells cultured under restrictive conditions known to induce complete growth arrest (39.5 degrees C), although the surface complex did not disappear from other tsA transformants able to keep cycling at 39.5 degrees C. These results suggest that surface SV40 T-Ag or surface T-Ag/p53 complex, or both, are involved in determining the growth characteristics of SV40-transformed cells.

Characterization of an SV40-transformed 3T3 cell line expressing an unusual phenotype

1975 ◽  
Vol 18 (3) ◽  
pp. 427-440
Author(s):  
J.E. Thompson ◽  
J.D. Elligsen ◽  
H.E. Frey
Keyword(s):  
Plasma Membranes ◽  
Polyacrylamide Gel Electrophoresis ◽  
Growth Control ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Transformed Cells ◽  
Con A ◽  
Normal Cells ◽  
Unusual Phenotype

A transformed variant derived as a clone from normal 3T3 cells infected with simian virus 40 (SV40) has been found to possess a phenotype intermediate between that of normal cells and that characteristic of the transformed state, yet cells of the variant still test positively for the SV40-specific nuclear T-antigen. The variant exercises growth control, although not as stringently as do normal cells. Its cell size more closely resembles that of normal cells than of transformed cells. The variant also exhibits levels of spontaneous agglutination that are in line with those characteristic of the normal cells from which it was derived, and far higher than corresponding values for cells exhibiting the fully transformed phenotype. Plasma membranes of variant cells more closely resemble those of transformed cells than of normal cells as estimated by polyacrylamide gel electrophoresis. Perhaps the most distinguishing characteristic of the transformed variant is its complete immunity to agglutination by concanavalin A (Con A), even at concentrations of the lectin as high as 500 mug/ml. Moreover, trypsinization does not render variant cells as agglutinable in the presence of Con A as are untreated fully transformed cells. By contrast the variant displays a low tolerance of Con A toxicity, as monitored by ability to grow after treatment with the lectin, and on this count resembles transformed cells. Moreover a survey of several normal cell lines has revealed that even they do not consistently show resistance to Con A toxicity. These observations indicate that Con A-mediated agglutination and inability to grow after treatment with Con A are quite independent and do not bear a cause and effect relationship.

scholarly journals C/EBPα Inhibits Cell Growth via Direct Repression of E2F-DP-Mediated Transcription

2000 ◽  
Vol 20 (16) ◽  
pp. 5986-5997 ◽  
Author(s):  
Beatrix A. Slomiany ◽  
Kenneth L. D'Arigo ◽  
Margaret M. Kelly ◽  
David T. Kurtz
Keyword(s):  
Cell Growth ◽  
Ectopic Expression ◽  
Simian Virus 40 ◽  
Normal Liver ◽  
Simian Virus ◽  
Binding Activity ◽  
T Antigen ◽  
S Phase ◽  
3T3 Cells ◽  
L Cells

ABSTRACT Using an inducible transcription system which allows the regulated expression of C/EBP isoforms in tissue culture cells, we have found that the ectopic expression of C/EBPα, at a level comparable to that found in normal liver tissue, has a pronounced antimitogenic effect in mouse L cells and NIH 3T3 cells. The inhibition of cell division by C/EBPα in mouse cells cannot be reversed by simian virus 40 T antigen, by oncogenic ras, or by adenovirus E1a protein. When expressed in thymidine kinase-deficient L cells or 3T3 cells, C/EBPα is detected in a protein complex which binds to the E2F binding sites found in the promoters of the genes for E2F-1 and dihydrofolate reductase (DHFR). Bacterially expressed C/EBPα has no affinity for these E2F sites, but when recombinant C/EBPα is added to nuclear extracts from mouse fibroblasts, a new E2F binding activity appears, which contains the C/EBPα protein. Using an E2F-DP1-responsive promoter linked to a reporter gene, it can be shown that C/EBPα directly inhibits the induction of this promoter by E2F-DP1 in transient-transfection assays. Furthermore, C/EBPα can be shown to inhibit the S-phase induction of the E2F and DHFR promoters in permanent cell lines. These findings delineate a straightforward mechanism for C/EBPα-mediated cell growth arrest through repression of E2F-DP-mediated S-phase transcription.

Functional simian virus 40 T antigen is expressed in hybrid cells having finite proliferative potential

1987 ◽  
Vol 7 (4) ◽  
pp. 1541-1544
Author(s):  
O M Pereira-Smith ◽  
J R Smith
Keyword(s):  
Dna Synthesis ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Transformed Cells ◽  
Proliferative Potential ◽  
Hybrid Cells ◽  
Ras Oncogenes ◽  
Immortal Cells ◽  
Cellular Dna

Simian virus 40-transformed human cells fused with other independently derived simian virus 40-transformed cells and tumor-derived cells containing activated H-ras and N-ras oncogenes yielded hybrids capable of indefinite division. Fusions with various other immortal cells yielded hybrids that had limited division potential. T antigen expressed in limited-division hybrids was functional for the induction of cellular DNA synthesis.

scholarly journals Downregulation of Protein Disulfide Isomerase Inhibits Infection by the Mouse Polyomavirus

2006 ◽  
Vol 80 (21) ◽  
pp. 10868-10870 ◽  
Author(s):  
Joanna Gilbert ◽  
Wu Ou ◽  
Jonathan Silver ◽  
Thomas Benjamin
Keyword(s):  
Protein Disulfide Isomerase ◽  
Current Knowledge ◽  
Simian Virus 40 ◽  
Antigen Expression ◽  
Simian Virus ◽  
T Antigen ◽  
Disulfide Isomerase ◽  
Cellular Markers ◽  
Interfering Rna ◽  
Protein Disulfide

ABSTRACT Early stages of infection by the mouse polyomavirus have been studied using HeLa cells stably expressing small interfering RNA to protein disulfide isomerase (PDI). Infectibility measured by nuclear T antigen expression was reduced commensurately with the degree of PDI downregulation. Infectibility was restored by transfection with a plasmid expressing PDI but not with a control expressing catalytically inactive enzyme. Deconvolution microscopy using fluorescently labeled virus and cellular markers showed that virus reaches the endoplasmic reticulum (ER) normally in cells with reduced PDI but subsequently fails to exit the ER. Simian virus 40 infection was not inhibited in PDI-downregulated cells. The results are discussed in terms of structural differences between the two viruses and current knowledge of virus disassembly in the ER.

scholarly journals Activation of a retinoblastoma-protein-dependent pathway by sphingosine

1995 ◽  
Vol 310 (2) ◽  
pp. 453-459 ◽  
Author(s):  
G S Dbaibo ◽  
R A Wolff ◽  
L M Obeid ◽  
Y A Hannun
Keyword(s):  
Cell Growth ◽  
Retinoblastoma Protein ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Lung Epithelial Cells ◽  
Breakdown Product ◽  
Sequence Element ◽  
Specific Effects ◽  
Leukaemic Cells

The retinoblastoma protein (Rb) is a tumour suppressor that is activated by dephosphorylation the function of which appears to be mediated, at least partly, through the inhibition of several transcription factors, such as E2F. We have recently described sphingosine, a sphingolipid-breakdown product, as a potent and specific inducer of Rb dephosphorylation resulting in inhibition of cell growth and a specific arrest in the G0/G1 phase of the cell cycle. Here we examine the role of Rb and its interaction with E2F in mediating the effects of sphingosine on cell growth. Sphingosine potently inhibited growth of lymphoblastic leukaemic cells, Molt-4, at submicromolar concentrations but showed a 10-fold reduced potency in inhibiting growth of retinoblastoma cells, WERI-Rb-1, which lack functional Rb. In addition, sphingosine's ability to inhibit growth of mink lung epithelial cells was significantly attenuated in cells overexpressing simian virus 40 large T antigen which binds Rb and related proteins. Sphingosine treatment of Molt-4 cells, but not WERI-Rb-1 cells, resulted in the loss of the specific E2F bands produced by the interaction of E2F and its specific DNA sequence element on gel-shift assays. The concentration (submicromolar) and kinetics (4 h) of sphingosine treatment were identical with those required to induce Rb dephosphorylation. In addition, at similar concentrations, sphingosine caused c-myc down-regulation in Molt-4 cells starting at 6 h after treatment. These results demonstrate that activation of Rb by sphingosine leads to sequestration of E2F by the active (hypophosphorylated) form of Rb with the resultant loss of its DNA-binding and genetranscribing abilities. A functional Rb is required to mediate the specific effects of sphingosine on growth arrest.

scholarly journals Establishment of rat pancreatic endocrine cell lines by infection with simian virus 40

1979 ◽  
Vol 178 (3) ◽  
pp. 559-568 ◽  
Author(s):  
E J Niesor ◽  
C B Wollheim ◽  
D H Mintz ◽  
B Blondel ◽  
A E Renold ◽  
...  
Keyword(s):  
Simian Virus 40 ◽  
Simian Virus ◽  
Culture Conditions ◽  
T Antigen ◽  
Insulin Biosynthesis ◽  
Transformed Cells ◽  
Immunoreactive Insulin ◽  
Gel Chromatography ◽  
Pancreatic Cells

The feasibility of infection and transformation by SV40 (simian virus 40) of primary cell cultures derived from newborn-rat pancreas was investigated. As judged by the presence of intranuclear SV40 T-antigen, exposure to the virus resulted specifically in infection and transformation of epithelioid (predominantly endocrine) cells. The transformed cells were subcultured (more than 64 passages) and cloned. Culture medium and acid/ethanol extracts of the cells did not contain detectable amounts of immunoreactive insulin after the third subculture. However, inoculation of such SV40-transformed pancreatic cells into immunodeficient rats results in tumours in which insulin production was partially restored through the passage in vivo, since the tumour cells contained and synthesized small amounts of immunoreactive insulin which co-migrated with an insulin marker on gel chromatography. Interestingly, the transformed cells maintained under tissue-culture conditions produced a protein immunologically related to insulin, soluble in aqueous buffer but insoluble in acid/ethanol. This 3000-dalton protein is too large to be a translation product of the rat preproinsulin 9S mRNA. SV40-transformed pancreatic cells might prove useful in the investigation of the factors controlling and maintaining insulin biosynthesis.

scholarly journals Intestinal Dysplasia Induced by Simian Virus 40 T Antigen Is Independent of p53

2005 ◽  
Vol 79 (12) ◽  
pp. 7492-7502 ◽  
Author(s):  
Jennifer A. Markovics ◽  
Patrick A. Carroll ◽  
M. Teresa Sáenz Robles ◽  
Hannah Pope ◽  
Craig M. Coopersmith ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Kinase Inhibitor ◽  
Simian Virus 40 ◽  
Antigen Expression ◽  
Simian Virus ◽  
T Antigen ◽  
Cyclin Dependent Kinase ◽  
Cyclin Dependent Kinase Inhibitor ◽  
Tumor Suppressor Proteins ◽  
Intestinal Hyperplasia

ABSTRACT Transgenic mice expressing simian virus 40 large T antigen in enterocytes develop intestinal hyperplasia that progresses to dysplasia with age. Hyperplasia is dependent on T antigen binding to the retinoblastoma (pRb) family of tumor suppressor proteins. Mice expressing a truncated T antigen that inactivates the pRb-family, but is defective for binding p53, exhibit hyperplasia but do not progress to dysplasia. We hypothesized that the inhibition of the pRb family leads to entry of enterocytes into the cell cycle, resulting in hyperplasia, while inactivation of p53 is required for progression to dysplasia. Therefore, we examined T antigen/p53 complexes from the intestines of transgenic mice. We found that T antigen did not induce p53 stabilization, and we could not detect T antigen/p53 complexes in villus enterocytes. In contrast, T antigen expression led to a large increase in the levels of the cyclin-dependent kinase inhibitor p21. Furthermore, mice in which pRb was inactivated by a truncated T antigen in a p53 null background exhibited intestinal hyperplasia but no progression to dysplasia. These data indicate that loss of p53 function does not play a role in T antigen-induced dysplasia in the intestine. Rather, some unknown function of T antigen is essential for progression beyond hyperplasia.

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