Diversity in the Regulatory B-Subunits of Protein Phosphatase 2A: Identification of a Novel Isoform Highly Expressed in Brain

Zołnierowicz, Stanisław; Csortos, Csilla; Bondor, Jeffry; Verin, Alexander D.; Mumby, Marc C.; DePaoli‐Roach, Anna A.

doi:10.1021/bi00205a023

Cited by 115 publications

(108 citation statements)

References 58 publications

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“…In the present report we show, using immunoblots of fractionated cell extracts and indirect immunofluorescence, that the B55-type regulatory subunit is a predominantly cytoplasmic protein in Hs68 fibroblasts. Its cytoplasmic localization is consistent with the absence of a nuclear localization signal in the primary structure of B55 isoforms (Mayer et al, 1991;Zolnierowicz et al, 1994). Moreover, all processes in which B55-containing PP2A holoenzymes have been implicated to date appear to be cytoplasmic (Healy et al, 1991;Mayer-Jaekel et al, 1993, 1994Uemura et al, 1993;Lee et al, 1994;Pitcher et al, 1995;Hansra et al, 1996;Sontag et al, 1996).…”

supporting

confidence: 67%

“…The B55 peptide CTNNLYIFQDKVN (Synthem, Nimes, France), corresponding to the carboxyl-terminal region of B55 ␣, ␤, and ␥ (Mayer et al, 1991;Zolnierowicz et al, 1994) was coupled to thyroglobulin using sulfo-m-maleimidobenzoyl-N-hydroxysulfo-succinimide ester (Pierce, Rockford, IL). Rabbits were immunized using 0.3-1 mg of the peptide-protein conjugate.…”

Section: Subunit-specific Antibodiesmentioning

confidence: 99%

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Vimentin Dephosphorylation by Protein Phosphatase 2A Is Modulated by the Targeting Subunit B55

Turowski

Myles

Hemmings

et al. 1999

MBoC

101

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The intermediate filament protein vimentin is a major phosphoprotein in mammalian fibroblasts, and reversible phosphorylation plays a key role in its dynamic rearrangement. Selective inhibition of type 2A but not type 1 protein phosphatases led to hyperphosphorylation and concomitant disassembly of vimentin, characterized by a collapse into bundles around the nucleus. We have analyzed the potential role of one of the major protein phosphatase 2A (PP2A) regulatory subunits, B55, in vimentin dephosphorylation. In mammalian fibroblasts, B55 protein was distributed ubiquitously throughout the cytoplasm with a fraction associated to vimentin. Specific depletion of B55 in living cells by antisense B55 RNA was accompanied by disassembly and increased phosphorylation of vimentin, as when type 2A phosphatases were inhibited using okadaic acid. The presence of B55 was a prerequisite for PP2A to efficiently dephosphorylate vimentin in vitro or to induce filament reassembly in situ. Both biochemical fractionation and immunofluorescence analysis of detergent-extracted cells revealed that fractions of PP2Ac, PR65, and B55 were tightly associated with vimentin. Furthermore, vimentinassociated PP2A catalytic subunit was displaced in B55-depleted cells. Taken together these data show that, in mammalian fibroblasts, the intermediate filament protein vimentin is dephosphorylated by PP2A, an event targeted by B55. INTRODUCTIONProtein phosphatase 2A (PP2A) is implicated in a significant array of cellular processes, including metabolism, DNA replication, transcription, translation, cell cycle progression, and membrane-to-nuclear signal transduction (for review, see Shenolikar, 1994;Wera and Hemmings, 1995). Regulatory flexibility is conferred by the association of a constant dimeric core of a 36-kDa catalytic (PP2Ac) and a 65-kDa (PR65 or A) subunit with a third, variable B subunit . To date three families of B subunits have been identified, which we will refer to as B55, B56, and B72, according to the predicted molecular weight of their founding member (Mayer et al., 1991;Hendrix et al., 1993a;McCright and Virshup, 1995). At least 10 individual genes code for B-type regulators, with this number being further increased by the additional presence of alternatively spliced forms of certain messages (Hendrix et al., 1993a;Csortos et al., 1996;McCright et al., 1996;Tanabe et al., 1996;Tehrani et al., 1996;Zolnierowicz et al., 1996). By analogy to PP1, in which associated noncatalytic subunits target the catalytic subunit to different subcellular compartments and/or substrates, it was proposed that the B-type regulators act as targeting subunits for PP2A (Hubbard and Cohen, 1993). Indeed, B subunits affect the substrate specificity of PP2A in vitro and in vivo (Agostinis et al., 1987;Cegielska et al., 1994;Kamibayashi et al., 1994;Zhao et al., 1997). Distinct subcellular localization has been reported for some B subunits (McCright et al., 1996;Tehrani et al., 1996). The 55-kDa regulatory subunit B55 (or PR55) was one of the first B-type re...

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supporting

confidence: 67%

Section: Subunit-specific Antibodiesmentioning

confidence: 99%

Vimentin Dephosphorylation by Protein Phosphatase 2A Is Modulated by the Targeting Subunit B55

Turowski

Myles

Hemmings

et al. 1999

MBoC

101

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“…PP2A is composed of three groups of subunits termed A, B and C subunits and considered to be present as trimeric form in i o (reviewed in [13,14]). PP2A1, previously demonstrated to be a trimeric form [13,[15][16][17][18], includes Bα or Bβ subunit in addition to A and C subunits [14,19,20]. PP2A2 is the dimer of A and C subunits which is regarded as the core structure of PP2A [13,14] ; it is not totally certain whether the AC form is present or absent in i o.…”

Section: Introductionmentioning

confidence: 99%

Protein phosphatase 2A is associated in an inactive state with microtubules through 2A1-specific interaction with tubulin

Hiraga¹,

Tamura

2000

Biochemical Journal

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Protein phosphatase (PP) 2A1, a trimer composed of A-, B-and C-subunits in the PP2A family, has been regarded as a principal form localizing at microtubules (MT), but PP2A2, the dimer of A-and C-subunits, has not. Substantiating the claim, the present work shows that the PP2A1 but not PP2A2, both isolated from bovine extract, largely associated with the purified preparation of MT. Furthermore, PP2A1 was found to bind purified tubulin polymerized by taxol. The presence of MT associated proteins with purified tubulin hardly affected the binding of PP2A1 to the tubulin. In addition, PP2A1 activity towards glycogen phosphorylase, a probably unphysiological but good substrate, was similarly inhibited by MT proteins and purified tubulin, which accounts for 85 % of MT proteins, with their IC &! of about 0n15 mg\ml. In contrast, the inhibition of PP2A2

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“…PP2A exists in cells as 2 abundant forms, core enzyme made up of a 36-kDa catalytic C subunit and 1 65-kDa regulatory A subunit and holoenzyme composed of core enzyme and 1 of several regulatory B subunits. The A and C subunits both exist as 2 isoforms (␣ and ␤ ), whereas the B subunits fall into 3 families designated B, [2][3][4][5] , BЈ (also called B56) 6 -10 and BЉ. [11][12][13][14] A model demonstrating how the A, B and C subunits interact in the holoenzyme is shown in Figure 1.…”

mentioning

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.

show abstract

Diversity in the Regulatory B-Subunits of Protein Phosphatase 2A: Identification of a Novel Isoform Highly Expressed in Brain

Cited by 115 publications

References 58 publications

Vimentin Dephosphorylation by Protein Phosphatase 2A Is Modulated by the Targeting Subunit B55

Vimentin Dephosphorylation by Protein Phosphatase 2A Is Modulated by the Targeting Subunit B55

Protein phosphatase 2A is associated in an inactive state with microtubules through 2A1-specific interaction with tubulin

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

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