scholarly journals Characterization of the Aalpha and Abeta subunit isoforms of protein phosphatase 2A: differences in expression, subunit interaction, and evolution

2003 ◽  
Vol 369 (2) ◽  
pp. 387-398 ◽  
Author(s):  
Jin ZHOU ◽  
Huong T. PHAM ◽  
Ralf RUEDIGER ◽  
Gernot WALTER
Keyword(s):  
Cell Cycle ◽  
Cell Lines ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Expression Patterns ◽  
Simian Virus 40 ◽  
Polyoma Virus ◽  
Tumour Antigen ◽  
Small Tumour ◽  
Phosphatase 2A

Protein phosphatase 2A (PP2A) is very versatile owing to a large number of regulatory subunits and its ability to interact with numerous other proteins. The regulatory A subunit exists as two closely related isoforms designated Aα and Aβ. Mutations have been found in both isoforms in a variety of human cancers. Although Aα has been intensely studied, little is known about Aβ. We generated Aβ-specific antibodies and determined the cell cycle expression, subcellular distribution, and metabolic stability of Aβ in comparison with Aα. Both forms were expressed at constant levels throughout the cell cycle, but Aα was expressed at a much higher level than Aβ. Both forms were found predominantly in the cytoplasm, and both had a half-life of approx. 10h. However, Aα and Aβ differed substantially in their expression patterns in normal tissues and in tumour cell lines. Whereas Aα was expressed at similarly high levels in all tissues and cell lines, Aβ expression varied greatly. In addition, in vivo studies with epitope-tagged Aα and Aβ subunits demonstrated that Aβ is a markedly weaker binder of regulatory B and catalytic C subunits than Aα. Construction of phylogenetic trees revealed that the conservation of Aα during the evolution of mammals is extraordinarily high in comparison with both Aβ and cytochrome c, suggesting that Aα is involved in more protein—protein interactions than Aβ. We also measured the binding of polyoma virus middle tumour antigen and simian virus 40 (SV40) small tumour antigen to Aα and Aβ. Whereas both isoforms bound polyoma virus middle tumour antigen equally well, only Aα bound SV40 small tumour 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 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

Identification of a protein phosphatase 2A family member that regulates cell cycle progression in Trypanosoma brucei

2014 ◽  
Vol 194 (1-2) ◽  
pp. 48-52 ◽  
Author(s):  
Karen G. Rothberg ◽  
Neal Jetton ◽  
James G. Hubbard ◽  
Daniel A. Powell ◽  
Vidya Pandarinath ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Family Member ◽  
Trypanosoma Brucei ◽  
Protein Phosphatase ◽  
Cell Cycle Progression ◽  
Protein Phosphatase 2A ◽  
Cycle Progression ◽  
Phosphatase 2A

scholarly journals Molecular genetic analysis of Rts1p, a B' regulatory subunit of Saccharomyces cerevisiae protein phosphatase 2A.

1997 ◽  
Vol 17 (6) ◽  
pp. 3242-3253 ◽  
Author(s):  
Y Shu ◽  
H Yang ◽  
E Hallberg ◽  
R Hallberg
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
High Temperatures ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Molecular Genetic Analysis ◽  
Regulatory Subunit ◽  
Temperature Sensitive ◽  
Checkpoint Control ◽  
Phosphatase 2A

The Saccharomyces cerevisiae gene RTS1 encodes a protein homologous to a variable B-type regulatory subunit of the mammalian heterotrimeric serine/threonine protein phosphatase 2A (PP2A). We present evidence showing that Rts1p assembles into similar heterotrimeric complexes in yeast. Strains in which RTS1 has been disrupted are temperature sensitive (ts) for growth, are hypersensitive to ethanol, are unable to grow with glycerol as their only carbon source, and accumulate at nonpermissive temperatures predominantly as large-budded cells with a 2N DNA content and a nondivided nucleus. This cell cycle arrest can be overcome and partial suppression of the ts phenotype of rts1-null cells occurs if the gene CLB2, encoding a Cdc28 kinase-associated B-type cyclin, is expressed on a high-copy-number plasmid. However, CLB2 overexpression has no suppressive effects on other aspects of the rts1-null phenotype. Expression of truncated forms of Rts1p can also partially suppress the ts phenotype and can fully suppress the inability of cells to grow on glycerol and the hypersensitivity of cells to ethanol. By contrast, the truncated forms do not suppress the accumulation of large-budded cells at high temperatures. Coexpression of truncated Rts1p and high levels of Clb2p fully suppresses the ts phenotype, indicating that the inhibition of growth of rts1-null cells at high temperatures is due to both stress-related and cell cycle-related defects. Genetic analyses show that the role played by Rts1p in PP2A regulation is distinctly different from that played by the other known variable B regulatory subunit, Cdc55p, a protein recently implicated in checkpoint control regulation.

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.

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