E1A induces phosphorylation of the retinoblastoma protein independently of direct physical association between the E1A and retinoblastoma products

1991 ◽  
Vol 11 (8) ◽  
pp. 4253-4265
Author(s):  
H G Wang ◽  
G Draetta ◽  
E Moran
Keyword(s):  
Cell Cycle ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Binding Activity ◽  
T Antigen ◽  
Physical Interaction ◽  
Resting Cells ◽  
Wild Type ◽  
Quiescent Cells ◽  
Kinase Expression

We have studied the initial effects of adenovirus E1A expression on the retinoblastoma (RB) gene product in normal quiescent cells. Although binding of the E1A products to pRB could, in theory, make pRB phosphorylation unnecessary for cell cycle progression, we have found that the 12S wild-type E1A product is capable of inducing phosphorylation of pRB in normal quiescent cells. The induction of pRB phosphorylation correlates with E1A-mediated induction of p34cdc2 expression and kinase activity, consistent with the possibility that p34cdc2 is a pRB kinase. Expression of simian virus 40 T antigen induces similar effects. Induction of pRB phosphorylation is independent of the pRB binding activity of the E1A products; E1A domain 2 mutants do not bind detectable levels of pRB but remain competent to induce pRB phosphorylation and to activate cdc2 protein kinase expression and activity. Although the kinetics of induction are slower, domain 2 mutants induce wild-type levels of pRB phosphorylation and host cell DNA synthesis and yet fail to induce cell proliferation. These results imply that direct physical interaction between the RB and E1A products does not play a required role in the early stages of E1A-mediated cell cycle induction and that pRB phosphorylation is not, of itself, sufficient to allow quiescent cells to divide. These results suggest that the E1A products do not need to bind pRB in order to stimulate resting cells to enter the cell cycle. Indeed, a more important role of the RB binding activity of the E1A products may be to prevent dividing cells from returning to G0.

scholarly journals E1A induces phosphorylation of the retinoblastoma protein independently of direct physical association between the E1A and retinoblastoma products.

1991 ◽  
Vol 11 (8) ◽  
pp. 4253-4265 ◽  
Author(s):  
H G Wang ◽  
G Draetta ◽  
E Moran
Keyword(s):  
Cell Cycle ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Binding Activity ◽  
T Antigen ◽  
Physical Interaction ◽  
Resting Cells ◽  
Wild Type ◽  
Quiescent Cells ◽  
Kinase Expression

We have studied the initial effects of adenovirus E1A expression on the retinoblastoma (RB) gene product in normal quiescent cells. Although binding of the E1A products to pRB could, in theory, make pRB phosphorylation unnecessary for cell cycle progression, we have found that the 12S wild-type E1A product is capable of inducing phosphorylation of pRB in normal quiescent cells. The induction of pRB phosphorylation correlates with E1A-mediated induction of p34cdc2 expression and kinase activity, consistent with the possibility that p34cdc2 is a pRB kinase. Expression of simian virus 40 T antigen induces similar effects. Induction of pRB phosphorylation is independent of the pRB binding activity of the E1A products; E1A domain 2 mutants do not bind detectable levels of pRB but remain competent to induce pRB phosphorylation and to activate cdc2 protein kinase expression and activity. Although the kinetics of induction are slower, domain 2 mutants induce wild-type levels of pRB phosphorylation and host cell DNA synthesis and yet fail to induce cell proliferation. These results imply that direct physical interaction between the RB and E1A products does not play a required role in the early stages of E1A-mediated cell cycle induction and that pRB phosphorylation is not, of itself, sufficient to allow quiescent cells to divide. These results suggest that the E1A products do not need to bind pRB in order to stimulate resting cells to enter the cell cycle. Indeed, a more important role of the RB binding activity of the E1A products may be to prevent dividing cells from returning to G0.

scholarly journals Induction of cellular DNA synthesis by a simian virus 40 mutant defective in nuclear transport of T antigen.

1985 ◽  
Vol 5 (6) ◽  
pp. 1531-1533 ◽  
Author(s):  
R E Lanford ◽  
J K Hyland ◽  
R Baserga ◽  
J S Butel
Keyword(s):  
Dna Synthesis ◽  
Limit Of Detection ◽  
Nuclear Transport ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Quiescent Cells ◽  
Cellular Dna

The simian virus 40 (SV40) (cT)-3 mutant [SV40(cT)-3], which is defective in nuclear transport of T antigen, was utilized to determine whether cellular DNA synthesis can be stimulated by SV40 in the absence of detectable nuclear T antigen. Cellular DNA synthesis was examined in the temperature-sensitive cell cycle mutants, BHK ts13 and BHK tsAF8, after microinjection of quiescent cells with plasmid DNA containing cloned copies of wild-type SV40 or SV40(cT)-3. The efficiency of induction of cellular DNA synthesis was identical for both wild-type SV40 and SV40(cT)-3 in both cell lines. The results suggest that cell surface-associated T antigen, either alone or possibly in combination with minimal amounts of nuclear T antigen below our limit of detection, is able to stimulate cellular DNA synthesis.

scholarly journals Transduction of Immortalized Human Hepatocytes with p21 to Enhance Differentiated Phenotypes

2002 ◽  
Vol 11 (5) ◽  
pp. 421-428 ◽  
Author(s):  
Takemi Kunieda ◽  
Naoya Kobayashi ◽  
Masakiyo Sakaguchi ◽  
Teru Okitsu ◽  
Toshinori Totsugawa ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Delivery ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
Cmv Promoter ◽  
P21 Protein ◽  
Morphological Alterations ◽  
Human Wild Type

We previously constructed an immortal human hepatocyte line NKNT-3 with a simian virus 40 T antigen (SV40T) to develop cell-based biological therapies. p21 is a molecule that regulates the transition from the G1 phase to the S phase of the cell cycle. Investigators have demonstrated that overexpression of p21 induces differentiation in various cell lines. In the current study we examined the effect of p21 on differentiated phenotypes of SV40T-immortalized NKNT-3 cells. A replication-deficient adenovirus vector expressing a human wild-type p21 cDNA under the control of the CMV promoter (Ad5CMVp21) and a human wild-type p21 protein fused to the protein transduction domain from the human immunodeficiency virus (HIV) TAT protein (TAT/p21) were utilized to achieve efficient delivery of p21 into NKNT-3 cells. Morphological alterations, cell cycle progression, and expression of albumin and p-450 associated enzymes (CYPs) 3A4 and 2C9 were evaluated in NKNT-3 cells treated with Ad5CMVp21 and TAT/p21. Efficient adenovirus-based p21 transfer and TAT-mediated p21 protein delivery were confirmed in NKNT-3 cells in an immuno-fluorescence study and Western blotting analysis. Transduction of NKNT-3 cells with p21 predominantly arrested the cell cycle at the G1 checkpoint, resulting in differentiated hepatic phenotypes in morphology and improvement in protein expression of albumin, CYP 3A4, and CYP C29. We here show that exogenous expression of p21 augments cellular differentiation in immortalized human NKNT-3 cells.

Induction of cellular DNA synthesis by a simian virus 40 mutant defective in nuclear transport of T antigen

1985 ◽  
Vol 5 (6) ◽  
pp. 1531-1533
Author(s):  
R E Lanford ◽  
J K Hyland ◽  
R Baserga ◽  
J S Butel
Keyword(s):  
Dna Synthesis ◽  
Limit Of Detection ◽  
Nuclear Transport ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Temperature Sensitive ◽  
Wild Type ◽  
Quiescent Cells ◽  
Cellular Dna

The simian virus 40 (SV40) (cT)-3 mutant [SV40(cT)-3], which is defective in nuclear transport of T antigen, was utilized to determine whether cellular DNA synthesis can be stimulated by SV40 in the absence of detectable nuclear T antigen. Cellular DNA synthesis was examined in the temperature-sensitive cell cycle mutants, BHK ts13 and BHK tsAF8, after microinjection of quiescent cells with plasmid DNA containing cloned copies of wild-type SV40 or SV40(cT)-3. The efficiency of induction of cellular DNA synthesis was identical for both wild-type SV40 and SV40(cT)-3 in both cell lines. The results suggest that cell surface-associated T antigen, either alone or possibly in combination with minimal amounts of nuclear T antigen below our limit of detection, is able to stimulate cellular DNA synthesis.

scholarly journals The Carboxy Terminus of Simian Virus 40 Large T Antigen Is Required To Disrupt the Yeast Cell Cycle

2002 ◽  
Vol 76 (9) ◽  
pp. 4621-4624 ◽  
Author(s):  
Sheara W. Fewell ◽  
Dena M. Markle ◽  
Jeffrey L. Brodsky
Keyword(s):  
Cell Cycle ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Yeast Cells ◽  
Wild Type ◽  
T Antigens ◽  
Normal Morphology ◽  
Cell Cycle Disruption ◽  
Carboxy Terminal

ABSTRACT Wild-type and J domain mutant simian virus 40 large T antigens alter the cell cycle and bud morphology of Saccharomyces cerevisiae. In contrast, yeast cells expressing mutant T antigen lacking the carboxy-terminal 150 aa exhibit normal morphology, indicating that this region of T antigen is required for cell cycle disruption.

scholarly journals Hyperphosphorylation of the retinoblastoma gene product is determined by domains outside the simian virus 40 large-T-antigen-binding regions.

1990 ◽  
Vol 10 (12) ◽  
pp. 6586-6595 ◽  
Author(s):  
P A Hamel ◽  
B L Cohen ◽  
L M Sorce ◽  
B L Gallie ◽  
R A Phillips
Keyword(s):  
Cell Cycle ◽  
Complex Formation ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Phosphorylation Sites ◽  
Dependent Manner ◽  
Large T Antigen ◽  
T Complex ◽  
Cycle Dependent

With the murine retinoblastoma (RB) cDNA, a series of RB mutants were expressed in COS-1 cells and the pRB products were assessed for their ability (i) to bind to large T antigen (large T), (ii) to become modified by phosphorylation, and (iii) to localize in the nucleus. All point mutations and deletions introduced into regions previously defined as contributing to binding to large T abolished pRB-large T complex formation and prevented hyperphosphorylation of the RB protein. In contrast, a series of deletions 5' to these sites did not interfere with binding to large T. While some of the 5' deletion mutants were clearly phosphorylated in a cell cycle-dependent manner, one, delta Pvu, failed to be phosphorylated depsite binding to large T. pRB with mutations created at three putative p34cdc2 phosphorylation sites in the N-terminal region behaved similarly to wild-type pRB, whereas the construct delta P5-6-7-8, mutated at four serine residues C terminal to the large T-binding site, failed to become hyperphosphorylated despite retaining the ability to bind large T. All of the mutants described were also found to localize in the nucleus. These results demonstrate that the domains in pRB responsible for binding to large T are distinct from those recognized by the relevant pRB-specific kinase(s) and/or those which contain cell cycle-dependent phosphorylation sites. Furthermore, these data are consistent with a model in which cell cycle-dependent phosphorylation of pRB requires complex formation with other cellular proteins.

scholarly journals T Antigens of Simian Virus 40: Molecular Chaperones for Viral Replication and Tumorigenesis

2002 ◽  
Vol 66 (2) ◽  
pp. 179-202 ◽  
Author(s):  
Christopher S. Sullivan ◽  
James M. Pipas
Keyword(s):  
Cell Cycle ◽  
Viral Replication ◽  
Molecular Chaperones ◽  
Tumor Antigens ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
T Antigens ◽  
Sv40 Large T Antigen

SUMMARY Simian virus 40 (SV40) is a small DNA tumor virus that has been extensively characterized due to its relatively simple genetic organization and the ease with which its genome is manipulated. The large and small tumor antigens (T antigens) are the major regulatory proteins encoded by SV40. Large T antigen is responsible for both viral and cellular transcriptional regulation, virion assembly, viral DNA replication, and alteration of the cell cycle. Deciphering how a single protein can perform such numerous and diverse functions has remained elusive. Recently it was established that the SV40 T antigens, including large T antigen, are molecular chaperones, each with a functioning DnaJ domain. The molecular chaperones were originally identified as bacterial genes essential for bacteriophage growth and have since been shown to be conserved in eukaryotes, participating in an array of both viral and cellular processes. This review discusses the mechanisms of DnaJ/Hsc70 interactions and how they are used by T antigen to control viral replication and tumorigenesis. The use of the DnaJ/Hsc70 system by SV40 and other viruses suggests an important role for these molecular chaperones in the regulation of the mammalian cell cycle and sheds light on the enigmatic SV40 T antigen—a most amazing molecule.

scholarly journals Assembly of T-Antigen Double Hexamers on the Simian Virus 40 Core Origin Requires Only a Subset of the Available Binding Sites

1998 ◽  
Vol 18 (5) ◽  
pp. 2677-2687 ◽  
Author(s):  
Woo S. Joo ◽  
Henry Y. Kim ◽  
John D. Purviance ◽  
K. R. Sreekumar ◽  
Peter A. Bullock
Keyword(s):  
Structural Changes ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
The Core ◽  
Structural Distortions ◽  
In The Wild ◽  
Sv40 Dna ◽  
Initial Assembly

ABSTRACT Initiation of simian virus 40 (SV40) DNA replication is dependent upon the assembly of two T-antigen (T-ag) hexamers on the SV40 core origin. To further define the oligomerization mechanism, the pentanucleotide requirements for T-ag assembly were investigated. Here, we demonstrate that individual pentanucleotides support hexamer formation, while particular pairs of pentanucleotides suffice for the assembly of T-ag double hexamers. Related studies demonstrate that T-ag double hexamers formed on “active pairs” of pentanucleotides catalyze a set of previously described structural distortions within the core origin. For the four-pentanucleotide-containing wild-type SV40 core origin, footprinting experiments indicate that T-ag double hexamers prefer to bind to pentanucleotides 1 and 3. Collectively, these experiments demonstrate that only two of the four pentanucleotides in the core origin are necessary for T-ag assembly and the induction of structural changes in the core origin. Since all four pentanucleotides in the wild-type origin are necessary for extensive DNA unwinding, we concluded that the second pair of pentanucleotides is required at a step subsequent to the initial assembly process.

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.

scholarly journals Differential ability of a T-antigen transport-defective mutant of simian virus 40 to transform primary and established rodent cells.

1985 ◽  
Vol 5 (5) ◽  
pp. 1043-1050 ◽  
Author(s):  
R E Lanford ◽  
C Wong ◽  
J S Butel
Keyword(s):  
Cell Lines ◽  
Mouse Embryo ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Wild Type ◽  
Mouse Embryo Fibroblasts ◽  
Established Cell Lines ◽  
Established Cell ◽  
Embryo Fibroblasts

The transforming potential and oncogenicity of a simian virus 40 (SV40) mutant affecting T-antigen (T-ag), SV40(cT)-3, was examined in an effort to dissect T-ag functions in transformation. SV40(cT)-3 has a point mutation at nucleotide 4434 that abolishes the transport of T-ag to the nucleus but does not affect its association with the cell surface. Transfection-transformation assays were performed with primary cells and established cell lines of mouse and rat origin. The efficiency of transformation for established cell lines by SV40(cT)-3 was comparable to that of wild-type SV40, indicating that transformation of established cell lines can occur in the absence of detectable amounts of nuclear T-ag. Transformation of primary mouse embryo fibroblasts by SV40(cT)-3 was markedly influenced by culture conditions; the relative transforming frequency was dramatically reduced in assays involving focus formation in low serum concentrations or anchorage-independent growth. Immunofluorescence tests revealed that the transformed mouse embryo fibroblasts partially transport the mutant cT-ag to the cell nucleus. Transformed cell lines induced by SV40(cT)-3 did not differ in growth properties from wild-type transformants. SV40(cT)-3 was completely defective for the transformation of primary baby rat kidney cells, a primary cell type unable to transport the mutant T-ag to the nucleus. The intracellular localization of cellular protein p53 was found to mimic T-ag distribution in all the transformants analyzed. The mutant virus was weakly oncogenic in vivo: the induction of tumors in newborn hamsters by SV40(cT)-3 was reduced in incidence and delayed in appearance in comparison to wild-type SV40. These observations suggest that cellular transformation is regulated by both nuclear and surface-associated forms of SV40 T-ag.

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