Growth control in simian virus 40-transformed rat cells: temperature-independent expression of the transformed phenotype in tsA transformants derived by agar selection.

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.

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

Journal of Cell Science ◽

10.1242/jcs.18.3.427 ◽

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.

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Cul7/p185/p193 Binding to Simian Virus 40 Large T Antigen Has a Role in Cellular Transformation

Journal of Virology ◽

10.1128/jvi.78.6.2749-2757.2004 ◽

2004 ◽

Vol 78 (6) ◽

pp. 2749-2757 ◽

Cited By ~ 56

Author(s):

Syed Hamid Ali ◽

Jocelyn S. Kasper ◽

Takehiro Arai ◽

James A. DeCaprio

Keyword(s):

Growth Control ◽

Simian Virus 40 ◽

Cellular Transformation ◽

Soft Agar ◽

Simian Virus ◽

T Antigen ◽

Large T Antigen ◽

Independent Manner ◽

Viral Oncoprotein ◽

Primary Mouse

ABSTRACT Simian virus 40 large T antigen (TAg) is a viral oncoprotein that can promote cellular transformation. TAg's transforming activity results in part by binding and inactivating key tumor suppressors, including p53 and the retinoblastoma protein (pRb). We have identified a TAg-associated 185-kDa protein that has significant homology to the cullin family of E3 ubiquitin ligases. TAg binds to an SCF-like complex that contains p185/Cul7, Rbx1, and the F box protein Fbw6. This SCF-like complex binds to an N-terminal region of TAg. Several p185/Cul7-binding-deficient mutants of TAg were generated that retained binding to pRb and p53 and were capable of overcoming Rb-mediated repression of E2F transcription. Despite binding to pRb and p53, these p185/Cul7-binding-defective mutants of TAg were unable to transform primary mouse embryo fibroblasts. Cells expressing p185/Cul7-binding-defective mutants of TAg were unable to grow to high density or grow in an anchorage-independent manner as determined by growth in soft agar. Considering the significance of other TAg-interacting proteins in regulation of the cell cycle, p185/Cul7 may also regulate an important growth control pathway.

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

Molecular and Cellular Biology ◽

10.1128/mcb.5.5.1051 ◽

1985 ◽

Vol 5 (5) ◽

pp. 1051-1057 ◽

Cited By ~ 9

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.

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