PPX, a novel protein serine/threonine phosphatase localized to centrosomes.

Brewis, Neil; Street, Alasdair J.; Prescott, Alan R.; Cohen, Philip

doi:10.1002/j.1460-2075.1993.tb05739.x

Cited by 217 publications

(197 citation statements)

References 63 publications

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“…First, the inhibition of type 2A protein phosphatases by OA in Hs68 fibroblasts induced marked hyperphosphorylation and reorganization of vimentin, in accordance with other reports (Yatsunami et al, 1991;Eriksson et al, 1992;Lee et al, 1992;Lai et al, 1993). OA is a very potent inhibitor of PP2A but appears to be equally potent in inhibiting other PP2A-related phosphatases (Brewis et al, 1993;Chen et al, 1994). However, the abundance of phosphovimentin would rather imply PP2A as major vimentin protein phosphatase and discount a role of less-abundant PP2A-related phosphatases.…”

supporting

confidence: 89%

“…Cells were injected as described (Lamb and Fernandez, 1997). Before injection the plasmid, pECE-B55as, was diluted to 0.1 mg/ml with PBS containing 1 mg/ml mouse, rabbit, 1 OA and related toxins have been shown to exhibit a similar inhibitory potential toward certain PP1-and PP2A-related minor phosphatases than toward PP1 and PP2A themselves (Brewis et al, 1993;Chen et al, 1994). In this report we use the terms "type 1" for PP1 and PP1-related and "type 2A" for PP2A and PP2A-related enzymes.…”

Section: Microinjection and Immunofluorescence Analysismentioning

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: 89%

Section: Microinjection and Immunofluorescence Analysismentioning

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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“…In eukaryotes, dephosphorylation at the serine/ threonine sites is largely executed by four major protein phosphatases: phosphatase-1 (PP-1), phosphatase-2A (PP-2A), phosphatase-2B (PP-2B) and phosphatase-2C (PP-2C) (Cohen, 1989;Mumby and Walter, 1993), although other protein phosphatases, including phosphatase-4 (PP-4), phosphatase-5 (PP-5), phosphatase-6 (PP-6) and phosphatase-7 (PP-7), also contribute to this process (Brewis et al, 1993;Bastians and Ponstingl, 1994;Chen et al, 1994;Chinkers, 1994;Huang and Honkananen, 1998). The majority of intracellular protein phosphatase activity has been attributed to PP-1 and PP-2A (Cohen, 1989).…”

Section: Introductionmentioning

confidence: 99%

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

et al. 2006

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We have previously demonstrated that the serine/threonine protein phosphatase-1 (PP-1) plays an important role in promoting cell survival. However, the molecular mechanisms by which PP-1 promotes survival remain largely unknown. In the present study, we provide evidence to show that PP-1 can directly dephosphorylate a master regulator of apoptosis, p53, to negatively modulate its transcriptional and apoptotic activities, and thus to promote cell survival. As a transcriptional factor, the function of p53 can be greatly regulated by phosphorylation and dephosphorylation. While the kinases responsible for phosphorylation of the 17 serine/threonine sites have been identified, the dephosphorylation of these sites remains largely unknown. In the present study, we demonstrate that PP-1 can dephosphorylate p53 at Ser-15 and Ser-37 through co-immunoprecipitation, in vitro and in vivo dephosphorylation assays, overexpression and silence of the gene encoding the catalytic subunit for PP-1. We further show that mutations mimicking constitutive dephosphorylation or phosphorylation of p53 at these sites attenuate or enhance its transcriptional activity, respectively. As a result of the changed p53 activity, expression of the downstream apoptosis-related genes such as bcl-2 and bax is accordingly altered and the apoptotic events are either largely abrogated or enhanced. Thus, our results demonstrate that PP-1 directly dephosphorylates p53, and dephosphorylation of p53 has as important impact on its functions as phosphorylation does. In addition, our results reveal that one of the molecular mechanisms by which PP-1 promotes cell survival is to dephosphorylate p53, and thus negatively regulate p53-dependent death pathway.

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“…The catalytic subunit of protein phosphatase 4 (PP4 C ) is 65% identical to PP2A C at the amino acid level (18) and has been placed in the type 2A family of phosphatases. PP4 C has been highly conserved between species sharing 91% amino acid identity between human and Drosophila (19).…”

mentioning

confidence: 99%

Purification and Identification of a Novel Subunit of Protein Serine/Threonine Phosphatase 4

Kloeker¹,

Wadzinski

1999

Journal of Biological Chemistry

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The catalytic subunit of protein serine/threonine phosphatase 4 (PP4 C ) has greater than 65% amino acid identity to the catalytic subunit of protein phosphatase 2A (PP2A C ). Despite this high homology, PP4 does not appear to associate with known PP2A regulatory subunits. As a first step toward characterization of PP4 holoenzymes and identification of putative PP4 regulatory subunits, PP4 was purified from bovine testis soluble extracts. PP4 existed in two complexes of approximately 270 -300 and 400 -450 kDa as determined by gel filtration chromatography. The smaller PP4 complex was purified by sequential phenyl-Sepharose, Source 15Q, DEAE2, and Superdex 200 gel filtration chromatographies. The final product contained two major proteins: the PP4 catalytic subunit plus a protein that migrated as a doublet of 120 -125 kDa on SDS-polyacrylamide gel electrophoresis. The associated protein, termed PP4 R1 , and PP4 C also bound to microcystinSepharose. Mass spectrometry analysis of the purified complex revealed two major peaks, at 35 (PP4 C ) and 105 kDa (PP4 R1 ). Amino acid sequence information of several peptides derived from the 105 kDa protein was utilized to isolate a human cDNA clone. Analysis of the predicted amino acid sequence revealed 13 nonidentical repeats similar to repeats found in the A subunit of PP2A (PP2A A ). The PP4 R1 cDNA clone engineered with an N-terminal Myc tag was expressed in COS M6 cells and PP4 C co-immunoprecipitated with Myc-tagged PP4 R1 . These data indicate that one form of PP4 is similar to the core complex of PP2A in that it consists of a catalytic subunit and a "PP2A A -like" structural subunit.

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PPX, a novel protein serine/threonine phosphatase localized to centrosomes.

Cited by 217 publications

References 63 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 serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

Purification and Identification of a Novel Subunit of Protein Serine/Threonine Phosphatase 4

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