scholarly journals Identification of Structural Elements Involved in the Interaction of Simian Virus 40 Small Tumor Antigen with Protein Phosphatase 2A

1998 ◽  
Vol 273 (52) ◽  
pp. 35339-35346 ◽  
Author(s):  
Scott C. Mateer ◽  
Sergei A. Fedorov ◽  
Marc C. Mumby
Keyword(s):  
Tumor Antigen ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Structural Elements ◽  
Small Tumor ◽  
Phosphatase 2A

scholarly journals Signaling and Transcriptional Changes Critical for Transformation of Human Cells by Simian Virus 40 Small Tumor Antigen or Protein Phosphatase 2A B56γ Knockdown

2004 ◽  
Vol 64 (19) ◽  
pp. 6978-6988 ◽  
Author(s):  
Carlos S. Moreno ◽  
Sumathi Ramachandran ◽  
Danita G. Ashby ◽  
Noelani Laycock ◽  
Courtney A. Plattner ◽  
...  
Keyword(s):  
Tumor Antigen ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Human Cells ◽  
Small Tumor ◽  
Transcriptional Changes ◽  
Phosphatase 2A

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 The Protein Phosphatase 2A regulatory subunit Twins stabilizes Plk4 to induce centriole amplification

2011 ◽  
Vol 195 (2) ◽  
pp. 231-243 ◽  
Author(s):  
Christopher W. Brownlee ◽  
Joey E. Klebba ◽  
Daniel W. Buster ◽  
Gregory C. Rogers
Keyword(s):  
Cell Cycle ◽  
Protein Phosphatase ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Regulatory Subunit ◽  
Unknown Mechanism ◽  
Small Tumor ◽  
Centriole Duplication ◽  
Phosphatase 2A ◽  
Pp2a Inhibitor

Centriole duplication is a tightly regulated process that must occur only once per cell cycle; otherwise, supernumerary centrioles can induce aneuploidy and tumorigenesis. Plk4 (Polo-like kinase 4) activity initiates centriole duplication and is regulated by ubiquitin-mediated proteolysis. Throughout interphase, Plk4 autophosphorylation triggers its degradation, thus preventing centriole amplification. However, Plk4 activity is required during mitosis for proper centriole duplication, but the mechanism stabilizing mitotic Plk4 is unknown. In this paper, we show that PP2A (Protein Phosphatase 2ATwins) counteracts Plk4 autophosphorylation, thus stabilizing Plk4 and promoting centriole duplication. Like Plk4, the protein level of PP2A’s regulatory subunit, Twins (Tws), peaks during mitosis and is required for centriole duplication. However, untimely Tws expression stabilizes Plk4 inappropriately, inducing centriole amplification. Paradoxically, expression of tumor-promoting simian virus 40 small tumor antigen (ST), a reported PP2A inhibitor, promotes centrosome amplification by an unknown mechanism. We demonstrate that ST actually mimics Tws function in stabilizing Plk4 and inducing centriole amplification.

scholarly journals Different oligomeric forms of protein phosphatase 2A activate and inhibit simian virus 40 DNA replication

1994 ◽  
Vol 14 (7) ◽  
pp. 4616-4623
Author(s):  
A Cegielska ◽  
S Shaffer ◽  
R Derua ◽  
J Goris ◽  
D M Virshup
Keyword(s):  
Dna Replication ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Catalytic Subunit ◽  
B Subunit ◽  
Phosphatase 2A ◽  
Sv40 Dna

The ability of simian virus 40 (SV40) large T antigen to catalyze the initiation of viral DNA replication is regulated by its phosphorylation state. Previous studies have identified the free catalytic subunit of protein phosphatase 2A (PP2Ac) as the cellular phosphatase which can remove inhibitory phosphoryl groups from serines 120 and 123. The catalytic C subunit exists in the cell complexed with a 65-kDa A subunit and one of several B subunits. To determine if any of the holoenzymes could activate T antigen, we tested the ability of the heterodimeric AC and two heterotrimeric ABC forms to stimulate T-antigen function in unwinding the origin of SV40 DNA replication. Only free catalytic subunit C and the heterotrimeric form with a 72-kDa B subunit (PP2A-T72) could stimulate T-antigen-dependent origin unwinding. Both the dimeric form (PP2A-D) and the heterotrimer with a 55-kDa B subunit (PP2A-T55) actively inhibited T-antigen function. We found that PP2A-T72 activated T antigen by dephosphorylating serines 120 and 123, while PP2A-D and PP2A-T55 inactivated T antigen by dephosphorylating the p34cdc2 target site, threonine 124. Thus, alterations in the subunit composition of PP2A holoenzymes have significant functional consequences for the initiation of in vitro SV40 DNA replication. The regulatory B subunits of PP2A may play a role in regulating SV40 DNA replication in infected cells as well.

Mechanism of activation of simian virus 40 DNA replication by protein phosphatase 2A

1992 ◽  
Vol 12 (11) ◽  
pp. 4883-4895
Author(s):  
D M Virshup ◽  
A A Russo ◽  
T J Kelly
Keyword(s):  
Dna Replication ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Insertion Mutation ◽  
Wild Type ◽  
Phosphatase 2A ◽  
Half Site

The catalytic subunit of protein phosphatase 2A (PP2Ac) stimulates the initiation of replication of simian virus 40 DNA in vitro by dephosphorylating T antigen at specific phosphoserine residues (K. H. Scheidtmann, D. M. Virshup, and T. J. Kelly, J. Virol. 65:2098-2101, 1991). To better define the biochemical mechanism responsible for this stimulation, we investigated the effect of PP2Ac on the interaction of T antigen with wild-type and mutant origins of replication. Analysis of the binding of T antigen to the wild-type origin as a function of protein concentration revealed that binding occurs in two relatively discrete steps: the assembly of a T-antigen hexamer on one half-site of the origin, followed by the assembly of the second hexamer on the other half-site. The major effect of PP2Ac was to stimulate binding of the second hexamer, so that the binding reaction became much more cooperative. This observation suggests that dephosphorylation of T antigen by PP2Ac primarily affects interactions between the two hexamers bound to the origin. Pretreatment with PP2Ac increased the ability of the bound T antigen to unwind the origin of replication but had no effect on the intrinsic helicase activity of the protein. Thus, dephosphorylation of PP2Ac appears to increase the efficiency of the initial opening of the origin by T antigen. An insertion mutation at the dyad axis in the simian virus 40 origin, which altered the structural relationship of the two halves of the origin, abolished the effect of the phosphatase on the cooperativity of binding and completely prevented origin unwinding. These findings suggest that the ability of T antigen to open the viral origin of DNA replication is critically dependent on the appropriate functional interactions between T-antigen hexamers and that these interactions are regulated by the phosphorylation state of the viral initiator protein.

scholarly journals The interaction of SV40 small tumor antigen with protein phosphatase 2A stimulates the map kinase pathway and induces cell proliferation

Cell ◽  
1993 ◽  
Vol 75 (5) ◽  
pp. 887-897 ◽  
Author(s):  
Estelle Sontag ◽  
Sergei Fedorov ◽  
Craig Kamibayashi ◽  
David Robbins ◽  
Melanie Cobb ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Map Kinase ◽  
Tumor Antigen ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Small Tumor ◽  
Phosphatase 2A ◽  
Map Kinase Pathway ◽  
Kinase Pathway

scholarly journals Simian Virus 40 Small t Antigen Mediates Conformation-Dependent Transfer of Protein Phosphatase 2A onto the Androgen Receptor

2005 ◽  
Vol 25 (4) ◽  
pp. 1298-1308 ◽  
Author(s):  
Chun-Song Yang ◽  
Michael J. Vitto ◽  
Scott A. Busby ◽  
Benjamin A. Garcia ◽  
Cristina T. Kesler ◽  
...  
Keyword(s):  
Androgen Receptor ◽  
Protein Phosphatase ◽  
Tumor Antigens ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Phosphatase 2A ◽  
A Subunit ◽  
Small T Antigen

ABSTRACT The tumor antigens simian virus 40 small t antigen (ST) and polyomavirus small and medium T antigens mediate cell transformation in part by binding to the structural A subunit of protein phosphatase 2A (PP2A). The replacement of B subunits by tumor antigens inhibits PP2A activity and prolongs phosphorylation-dependent signaling. Here we show that ST mediates PP2A A/C heterodimer transfer onto the ligand-activated androgen receptor (AR). Transfer by ST is strictly dependent on the agonist-activated conformation of AR, occurs within minutes of the addition of androgen to cells, and can occur in either the cytoplasm or the nucleus. The binding of ST changes the conformation of the A subunit, and ST rapidly dissociates from the complex upon PP2A A/C heterodimer binding to AR. PP2A is transferred onto the carboxyl-terminal half of AR, and the phosphatase activity is directed to five phosphoserines in the amino-terminal activation function region 1, with a corresponding reduction in transactivation. Thus, ST functions as a transfer factor to specify PP2A targeting in the cell and modulates the transcriptional activity of AR.

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