Simian virus 40 small t antigen activates the carboxyl-terminal transforming p53-binding domain of large T antigen.

1996 ◽  
Vol 70 (10) ◽  
pp. 6781-6789 ◽  
Author(s):  
J Zerrahn ◽  
F Tiemann ◽  
W Deppert
Keyword(s):  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Binding Domain ◽  
Large T Antigen ◽  
Carboxyl Terminal ◽  
Small T Antigen

scholarly journals Studies on the origin-specific DNA-binding domain of simian virus 40 large T antigen.

1987 ◽  
Vol 61 (10) ◽  
pp. 3326-3330 ◽  
Author(s):  
M Strauss ◽  
P Argani ◽  
I J Mohr ◽  
Y Gluzman
Keyword(s):  
Dna Binding ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Binding Domain ◽  
Dna Binding Domain ◽  
Large T Antigen

Dephosphorylation of simian virus 40 large-T antigen and p53 protein by protein phosphatase 2A: inhibition by small-t antigen

1991 ◽  
Vol 11 (4) ◽  
pp. 1996-2003 ◽  
Author(s):  
K H Scheidtmann ◽  
M C Mumby ◽  
K Rundell ◽  
G Walter
Keyword(s):  
Protein Phosphatase ◽  
P53 Protein ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
C Subunit ◽  
Phosphatase 2A ◽  
Small T Antigen

Simian virus 40 (SV40) large-T antigen and the cellular protein p53 were phosphorylated in vivo by growing cells in the presence of 32Pi. The large-T/p53 complex was isolated by immunoprecipitation and used as a substrate for protein phosphatase 2A (PP2A) consisting of the catalytic subunit (C) and the two regulatory subunits, A and B. Three different purified forms of PP2A, including free C, the AC form, and the ABC form, could readily dephosphorylate both proteins. With both large-T and p53, the C subunit was most active, followed by the AC form, which was more active than the ABC form. The activity of all three forms of PP2A toward these proteins was strongly stimulated by manganese ions and to a lesser extent by magnesium ions. The presence of complexed p53 did not affect the dephosphorylation of large-T antigen by PP2A. The dephosphorylation of individual phosphorylation sites of large-T and p53 were determined by two-dimensional peptide mapping. Individual sites within large-T and p53 were dephosphorylated at different rates by all three forms of PP2A. The phosphates at Ser-120 and Ser-123 of large-T, which affect binding to the origin of SV40 DNA, were removed most rapidly. Three of the six major phosphopeptides of p53 were readily dephosphorylated, while the remaining three were relatively resistant to PP2A. Dephosphorylation of most of the sites in large-T and p53 by the AC form was inhibited by SV40 small-t antigen. The inhibition was most apparent for those sites which were preferentially dephosphorylated. Inhibition was specific for the AC form; no effect was observed on the dephosphorylation of either protein by the free C subunit or the ABC form. The inhibitory effect of small-t on dephosphorylation by PP2A could explain its role in transformation.

scholarly journals Structure of the origin-binding domain of simian virus 40 large T antigen bound to DNA

2006 ◽  
Vol 25 (24) ◽  
pp. 5961-5969 ◽  
Author(s):  
Elena Bochkareva ◽  
Dariusz Martynowski ◽  
Almagoul Seitova ◽  
Alexey Bochkarev
Keyword(s):  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Binding Domain ◽  
Large T Antigen

scholarly journals The amino-terminal transforming region of simian virus 40 large T and small t antigens functions as a J domain.

1997 ◽  
Vol 17 (8) ◽  
pp. 4761-4773 ◽  
Author(s):  
A Srinivasan ◽  
A J McClellan ◽  
J Vartikar ◽  
I Marks ◽  
P Cantalupo ◽  
...  
Keyword(s):  
Amino Acid ◽  
Atpase Activity ◽  
Mammalian Cells ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
Amino Terminal ◽  
J Domain ◽  
Small T Antigen

Simian virus 40 (SV40) encodes two proteins, large T antigen and small t antigen that contribute to virus-induced tumorigenesis. Both proteins act by targeting key cellular regulatory proteins and altering their function. Known targets of the 708-amino-acid large T antigen include the three members of the retinoblastoma protein family (pRb, p107, and p130), members of the CBP family of transcriptional adapter proteins (cap-binding protein [CBP], p300, and p400), and the tumor suppressor p53. Small t antigen alters the activity of phosphatase pp2A and transactivates the cyclin A promoter. The first 82 amino acids of large T antigen and small t antigen are identical, and genetic experiments suggest that an additional target(s) important for transformation interacts with these sequences. This region contains a motif similar to the J domain, a conserved sequence found in the DnaJ family of molecular chaperones. We show here that mutations within the J domain abrogate the ability of large T antigen to transform mammalian cells. To examine whether a purified 136-amino-acid fragment from the T antigen amino terminus acts as a DnaJ-like chaperone, we investigated whether this fragment stimulates the ATPase activity of two hsc70s and discovered that ATP hydrolysis is stimulated four- to ninefold. In addition, ATPase-defective mutants of full-length T antigen, as well as wild-type small t antigen, stimulated the ATPase activity of hsc70. T antigen derivatives were also able to release an unfolded polypeptide substrate from an hsc70, an activity common to DnaJ chaperones. Because the J domain of T antigen plays essential roles in viral DNA replication, transcriptional control, virion assembly, and tumorigenesis, we conclude that this region may chaperone the rearrangement of multiprotein complexes.

scholarly journals Loss of p19ARF Eliminates the Requirement for the pRB-Binding Motif in Simian Virus 40 Large T Antigen-Mediated Transformation

2000 ◽  
Vol 20 (20) ◽  
pp. 7624-7633 ◽  
Author(s):  
Herta H. A. Chao ◽  
Ann M. Buchmann ◽  
James A. DeCaprio
Keyword(s):  
Simian Virus 40 ◽  
Cellular Transformation ◽  
Simian Virus ◽  
T Antigen ◽  
Binding Domain ◽  
Large T Antigen ◽  
Wild Type ◽  
J Domain ◽  
Lxcxe Motif ◽  
Inactivating Mutations

ABSTRACT At least three domains of simian virus 40 large T antigen (TAg) participate in cellular transformation. The LXCXE motif of TAg binds to all members of the retinoblastoma protein (pRB) family of tumor suppressors. The N-terminal 70 residues of TAg have significant homology to the J domain of Hsp40/DnaJ and cooperate with the LXCXE motif to inactivate the pRB family. A bipartite C-terminal domain of TAg binds to p53 and thereby disrupts the ability of p53 to act as a sequence-specific transcription factor. The contribution of these three domains of TAg to cellular transformation was evaluated in cells that contained inactivating mutations in the pRB and p53 pathways. Cells that stably expressed wild-type or selected mutant forms of TAg were generated in mouse embryo fibroblasts (MEFs) containing homozygous deletions in the RB, INK4a, and ARFloci. It was determined that the J domain, the LXCXE motif, and the p53-binding domain of TAg were required for full transformation of wild-type and RB −/− MEFs. In contrast,INK4a −/− MEFs that lacked expression of p16 INK4a and p19 ARF andARF −/− MEFs that lacked p19 ARF but expressed p16 INK4a acquired anchorage-independent growth when expressing wild-type TAg or mutant derivatives that disrupted either the pRB-binding or p53-binding domain. The expression and function of the pRB family members were not overly disrupted inARF −/− MEFs expressing LXCXE mutants of TAg. These results suggest that inactivating mutations of p19 ARF can relieve the requirement for the LXCXE motif in TAg-mediated transformation and that TAg may have additional functions in transformation.

scholarly journals Dephosphorylation of simian virus 40 large-T antigen and p53 protein by protein phosphatase 2A: inhibition by small-t antigen.

1991 ◽  
Vol 11 (4) ◽  
pp. 1996-2003 ◽  
Author(s):  
K H Scheidtmann ◽  
M C Mumby ◽  
K Rundell ◽  
G Walter
Keyword(s):  
Protein Phosphatase ◽  
P53 Protein ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Large T Antigen ◽  
C Subunit ◽  
Phosphatase 2A ◽  
Small T Antigen

Simian virus 40 (SV40) large-T antigen and the cellular protein p53 were phosphorylated in vivo by growing cells in the presence of 32Pi. The large-T/p53 complex was isolated by immunoprecipitation and used as a substrate for protein phosphatase 2A (PP2A) consisting of the catalytic subunit (C) and the two regulatory subunits, A and B. Three different purified forms of PP2A, including free C, the AC form, and the ABC form, could readily dephosphorylate both proteins. With both large-T and p53, the C subunit was most active, followed by the AC form, which was more active than the ABC form. The activity of all three forms of PP2A toward these proteins was strongly stimulated by manganese ions and to a lesser extent by magnesium ions. The presence of complexed p53 did not affect the dephosphorylation of large-T antigen by PP2A. The dephosphorylation of individual phosphorylation sites of large-T and p53 were determined by two-dimensional peptide mapping. Individual sites within large-T and p53 were dephosphorylated at different rates by all three forms of PP2A. The phosphates at Ser-120 and Ser-123 of large-T, which affect binding to the origin of SV40 DNA, were removed most rapidly. Three of the six major phosphopeptides of p53 were readily dephosphorylated, while the remaining three were relatively resistant to PP2A. Dephosphorylation of most of the sites in large-T and p53 by the AC form was inhibited by SV40 small-t antigen. The inhibition was most apparent for those sites which were preferentially dephosphorylated. Inhibition was specific for the AC form; no effect was observed on the dephosphorylation of either protein by the free C subunit or the ABC form. The inhibitory effect of small-t on dephosphorylation by PP2A could explain its role in transformation.

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