Adenovirus E4orf4 protein interacts with both Bα and B′ subunits of protein phosphatase 2A, but E4orf4-induced apoptosis is mediated only by the interaction with Bα

Shtrichman, Ronit; Sharf, Rakefet; Kleinberger, Tamar

doi:10.1038/sj.onc.1203705

Cited by 66 publications

(89 citation statements)

References 46 publications

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“…It also relies on the finding that E4orf4-induced cell death requires an interaction between E4orf4 and an active PP2A, containing both catalytic and regulatory subunits (22,23). The mutants selected by this protocol may be deficient in their ability to bind either E4orf4 or the PP2A-AC heterodimer.…”

Section: Selection For Cdc55 Mutants That Cannot Mediate E4orf4mentioning

confidence: 99%

“…We have previously shown that E4orf4 interacts with the PP2A holoenzyme through a direct association with the B␣/B55 subunit (17), and can also bind PP2A complexes containing BЈ/B56 (23). We, and others, have recently shown that the interaction with PP2A complexes that include the B␣/B55, but not the BЈ/B56 subunit, is required for induction of apoptosis by E4orf4 (22)(23)(24).…”

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confidence: 99%

“…We, and others, have recently shown that the interaction with PP2A complexes that include the B␣/B55, but not the BЈ/B56 subunit, is required for induction of apoptosis by E4orf4 (22)(23)(24). Binding the B subunit alone is not sufficient for induction of apoptosis, because an E4orf4 mutant, A3 (S95P), could bind the B subunit, whereas the A and C subunits were excluded from the complex, causing A3 to act as a dominant negative mutant (23). The presence of an active PP2A also contributes to other functions performed by the E4orf4 protein, including down-regulation of transcription (17,25,26) and alternative splicing (18).…”

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confidence: 99%

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The Scaffolding A/Tpd3 Subunit and High Phosphatase Activity Are Dispensable for Cdc55 Function in the Saccharomyces cerevisiae Spindle Checkpoint and in Cytokinesis

Koren¹,

Rainis²,

Kleinberger

2004

Journal of Biological Chemistry

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Protein serine/threonine phosphatase 2A (PP2A) is a multifunctional enzyme whose trimeric form consists of a scaffolding A subunit, a catalytic C subunit, and one of several regulatory B subunits (B, B , and B؆). The adenovirus E4orf4 protein associates with PP2A by directly binding the B or B subunits. An interaction with an active PP2A containing the B subunit, or its homologue in yeast, Cdc55, is required for E4orf4-induced apoptosis in mammalian cells and for induction of growth arrest in Saccharomyces cerevisiae. In this work, Cdc55 was randomly mutagenized by low-fidelity PCR amplification, and Cdc55 mutants that lost the ability to transduce the E4orf4 toxic signal in yeast were selected. The mutations obtained by this protocol inhibited the association of Cdc55 with E4orf4, or with the PP2A-AC subunits, or both. Functional analysis revealed that a mutant that does not bind Tpd3, the yeast A subunit, as well as wild type Cdc55 in a tpd3⌬ background, can form a heterodimer with the catalytic subunit. This association requires C subunit carboxyl methylation. The residual phosphatase activity associated with Cdc55 in the absence of Tpd3 is sufficient to maintain a partially active spindle checkpoint and to prevent cytokinesis defects.PP2A 1 is one of the major protein serine/threonine phosphatases in the cell, which plays a role in several cellular processes, including metabolism, transcription, RNA splicing, translation, cell cycle progression, morphogenesis, signal transduction, development, and transformation (1, 2).Several reports indicate that the predominant form of PP2A in cells is a heterotrimer consisting of three subunits. Two of them, the 36-kDa catalytic C subunit and the 63-kDa scaffolding A subunit (PR65), form the core enzyme, and the regulatory B subunit binds the core enzyme to form the holoenzyme. The A and C subunits both exist as two isoforms (␣ and ␤), which are closely related, whereas the B subunit is variable, and its multiple isoforms belong to at least three unrelated gene families, B/B55/PR55 (␣-␦ isoforms), BЈ/B56/PR61 (␣-⑀ isoforms), and BЉ/PR72/PR130/PR59/PR48 (3). The core PP2A enzyme has also been shown to bind other cellular proteins, including striatin and SG2NA (4). Viral proteins, such as the SV40 small t antigen and the polyomavirus small and middle T antigens, can replace the cellular B subunits (5). The various cellular PP2A B subunits target the PP2A holoenzyme to different substrates and dictate its subcellular localization (reviewed in Ref.3).In Saccharomyces cerevisiae, two closely related genes, PPH21 and PPH22, redundantly encode the major PP2A catalytic subunit (6). TPD3 encodes the only A subunit, and two distinct B subunits, encoded by CDC55 and RTS1, are highly homologous to mammalian B and BЈ, respectively (7-9). Mutations of CDC55 are viable, but yield defects in cytokinesis and in the spindle checkpoint and result in abnormal cell morphology. Methylation of the C-terminal leucine residue of the PP2A catalytic subunit by a specific methyltransferase increase...

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Section: Selection For Cdc55 Mutants That Cannot Mediate E4orf4mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The Scaffolding A/Tpd3 Subunit and High Phosphatase Activity Are Dispensable for Cdc55 Function in the Saccharomyces cerevisiae Spindle Checkpoint and in Cytokinesis

Koren¹,

Rainis²,

Kleinberger

2004

Journal of Biological Chemistry

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“…15,16 The existence of so many regulatory subunits suggests that the various forms of PP2A have distinct functions. In addition, numerous interactions of PP2A with growth regulatory viral [17][18][19] and cellular 20 proteins have been reported, underscoring its regulatory role.…”

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confidence: 99%

Reduced expression of the A? subunit of protein phosphatase 2A in human gliomas in the absence of mutations in the A? and A? subunit genes

et al. 2001

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Protein phosphatase 2A (PP2A) consists of 3 subunits: the catalytic subunit, C, and the regulatory subunits, A and B. The A and C subunits both exist as 2 isoforms (␣ and ␤) and the B subunit as multiple forms subdivided into 3 families, B, B and B؆. It has been reported that the genes encoding the A␣ and A␤ subunits are mutated in various human cancers, suggesting that they may function as tumor suppressors. We investigated whether A␣ and A␤ mutations occur in human gliomas. Using single strand conformational polymorphism analysis and DNA sequencing, 58 brain tumors were investigated, including 23 glioblastomas, 19 oligodendrogliomas and 16 anaplastic oligodendrogliomas. Only silent mutations were detected in the A␣ gene and no mutations in the A␤ gene. However, in 43% of the tumors, the level of A␣ was reduced at least 10-fold. By comparison, the levels of the B␣ and C␣ subunits were mostly normal. Our data indicate that these tumors contain very low levels of core and holoenzyme and high amounts of unregulated catalytic C subunit.

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“…Another viral protein that interacts with PP2A is adenovirus E4orf4. By binding the B subunit in the holoenzyme, E4orf4 induces p53-independent apoptosis (Kleinberger and Shenk, 1993;Marcellus et al, 2000;Shtrichman et al, 1999Shtrichman et al, , 2000. PP2A also associates with numerous cellular proteins that are involved in growth regulation Virshup, 2000).…”

Section: Introductionmentioning

confidence: 99%

Alterations in protein phosphatase 2A subunit interaction in human carcinomas of the lung and colon with mutations in the Aβ subunit gene

2001

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Protein phosphatase 2A (PP2A) consists of three subunits, A, B and C. The A and B subunits have regulatory functions while C is the catalytic subunit. PP2A core enzyme is composed of subunits A and C, and the holoenzyme of subunits A, B and C. All subunits exist as multiple isoforms or splice variants. The A subunit exists as two isoforms, Aa and Ab. Here we report about the properties of eight Ab mutants, which were found in human lung and colon cancer. These mutants were reconstructed by site-directed mutagenesis and assayed for their ability to bind B and C subunits. Two mutants showed decreased binding of PR72, a member of the B'' family of B subunits, but normal C subunit binding; two mutants exhibited decreased binding of the C subunit and of B''/PR72; and one mutant showed increased binding of both the C subunit and B''/PR72. Of three mutants that behaved like the wildtype Ab subunit, one is a polymorphic variant and another one is altered outside the binding region for B and C subunits. Importantly, we also found that the wildtype Aa and Ab isoforms, although 85% identical, are remarkably di erent in their ability to bind B and C subunits. Our ®ndings may have important implications in regard to the role of PP2A as a tumor suppressor.

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Adenovirus E4orf4 protein interacts with both Bα and B′ subunits of protein phosphatase 2A, but E4orf4-induced apoptosis is mediated only by the interaction with Bα

Cited by 66 publications

References 46 publications

The Scaffolding A/Tpd3 Subunit and High Phosphatase Activity Are Dispensable for Cdc55 Function in the Saccharomyces cerevisiae Spindle Checkpoint and in Cytokinesis

The Scaffolding A/Tpd3 Subunit and High Phosphatase Activity Are Dispensable for Cdc55 Function in the Saccharomyces cerevisiae Spindle Checkpoint and in Cytokinesis

Reduced expression of the A? subunit of protein phosphatase 2A in human gliomas in the absence of mutations in the A? and A? subunit genes

Alterations in protein phosphatase 2A subunit interaction in human carcinomas of the lung and colon with mutations in the Aβ subunit gene

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