Protein phosphatase 4 – from obscurity to vital functions

Cohen, Patricia T.W.; Philp, Amanda; Vázquez-Martin, Cristina

doi:10.1016/j.febslet.2005.04.070

Cited by 141 publications

(148 citation statements)

References 52 publications

(75 reference statements)

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“…The decrease in dS6K phosphorylation may contribute to the 20% decrease in cell growth previously observed in S2 cells depleted of dPP4 [31]. PP4 has been implicated in a variety of regulatory processes [24], but has not been extensively studied in Drosophila. Reduction in dPP4 levels results in a semi-lethal phenotype in Drosophila early embryos and defects in microtubule assembly [44].…”

Section: Discussionmentioning

confidence: 99%

“…PP2A, PP4, and PP6 comprise the type 2A subfamily within the serine/threonine phosphatase gene family. These enzymes play vital roles in multiple aspects of cellular signal transduction [24]. The term PP2A refers to a diverse group of phosphatases composed of a common catalytic subunit that forms oligomeric complexes with a variety of regulatory proteins.…”

Section: Introductionmentioning

confidence: 99%

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Functional analysis of the PP2A subfamily of protein phosphatases in regulating Drosophila S6 kinase

Bielinski¹,

Mumby²

2007

Experimental Cell Research

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Phosphorylation and activation of ribosomal S6 protein kinase is an important link in the regulation of cell size by the target of rapamycin (TOR) protein kinase. A combination of selective inhibition and RNA interference were used to test the roles of members of the PP2A subfamily of protein phosphatases in dephosphorylation of Drosophila S6 kinase (dS6K). Treatment of Drosophila Schneider 2 cells with calyculin A, a selective inhibitor of PP2A-like phosphatases, resulted in a 7-fold increase in the basal level of dS6K phosphorylation at the TOR phosphorylation site (Thr398) and blocked dephosphorylation following inactivation of TOR by amino acid starvation or rapamycin treatment. Knockdown of the PP2A catalytic subunit increased basal dS6K phosphorylation and inhibited dephosphorylation induced by amino acid withdrawal. In contrast, depletion of the catalytic subunits of the other two members of the subfamily did not enhance dS6K phosphorylation. Knockdown of PP4 caused a 20% decrease in dS6K phosphorylation and knockdown of PP6 had no effect. Knockdown of the Drosophila B56-2 subunit resulted in enhanced dephosphorylation of dS6K following removal of amino acids. In contrast, knockdown of the homologs of the other PP2A regulatory subunits had no effects. Knockdown of the Drosophila homolog of the PP2A/PP4/PP6 interaction protein α4/Tap42 did not affect S6K phosphorylation, but did induce apoptosis. These results indicate that PP2A, but not other members of this subfamily, is likely to be a major S6K phosphatase in intact cells and is consistent with an important role for this phosphatase in the TOR pathway.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Functional analysis of the PP2A subfamily of protein phosphatases in regulating Drosophila S6 kinase

Bielinski¹,

Mumby²

2007

Experimental Cell Research

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“…The F-Box/WD-40 protein ( fbxw7 gene) has a role in targeted degradation of cyclin E, c-Myc, c-Jun, and Notch, thereby acting as a tumor suppressor (15). Protein phosphatase 4 regulatory subunit 2 modulates DNA repair and acts on microtubule assembly at the centrosome (16). Phosphatase and tensin homolog is a tumor suppressor acting through negative regulation of phosphatidylinositol 3-kinase signaling (17).…”

Section: Discussionmentioning

confidence: 99%

RNA expression in a cartilaginous fish cell line reveals ancient 3′ noncoding regions highly conserved in vertebrates

Forest

Nishikawa

Kobayashi

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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We have established a cartilaginous fish cell line [Squalus acanthias embryo cell line (SAE)], a mesenchymal stem cell line derived from the embryo of an elasmobranch, the spiny dogfish shark S. acanthias. Elasmobranchs (sharks and rays) first appeared >400 million years ago, and existing species provide useful models for comparative vertebrate cell biology, physiology, and genomics. Comparative vertebrate genomics among evolutionarily distant organisms can provide sequence conservation information that facilitates identification of critical coding and noncoding regions. Although these genomic analyses are informative, experimental verification of functions of genomic sequences depends heavily on cell culture approaches. Using ESTs defining mRNAs derived from the SAE cell line, we identified lengthy and highly conserved gene-specific nucleotide sequences in the noncoding 3 UTRs of eight genes involved in the regulation of cell growth and proliferation. Conserved noncoding 3 mRNA regions detected by using the shark nucleotide sequences as a starting point were found in a range of other vertebrate orders, including bony fish, birds, amphibians, and mammals. Nucleotide identity of shark and human in these regions was remarkably well conserved. Our results indicate that highly conserved gene sequences dating from the appearance of jawed vertebrates and representing potential cis-regulatory elements can be identified through the use of cartilaginous fish as a baseline. Because the expression of genes in the SAE cell line was prerequisite for their identification, this cartilaginous fish culture system also provides a physiologically valid tool to test functional hypotheses on the role of these ancient conserved sequences in comparative cell biology.noncoding sequence ͉ sequence conservation ͉ Squalus acanthias E fforts toward a comprehensive compilation of cell biological, physiological, and genomic information from a variety of vertebrate species are providing a rich source of comparative data representing critical points in evolutionary divergence (1). Although available information is rapidly expanding for teleosts (bony fishes; ref.2), few cell biological or genomic data are available for the most primitive jawed vertebrates, the cartilaginous fish, class Chondrichthyes, largely represented by the order Elasmobranchii (3, 4). This information would extend comparative data through Ͼ450 million years of evolution. We have derived an embryonic mesenchymal stem cell line [Squalus acanthias embryo cell line (SAE)] from the elasmobranch S. acanthias, the spiny dogfish shark (5). This cell line from a cartilaginous fish provides a means to study the cell biology, physiology, and genomics of Chondrichthyes. Recently, the National Human Genome Research Institute targeted for comprehensive genomic sequencing Leucoraja erinacia, an elasmobranch of the superorder Squaliformes, related to S. acanthias, underscoring the value of Chondrichthyes for comparative biology (6) In efforts to explore the cell biology and genomics of c...

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“…Serine/threonine-protein Phosphatase 4 regulatory Subunit 2 is localized to the centrosome and its complex with the protein phosphatase catalytic subunit is known to be essential for maturation of the centrosome, though the regulation mechanism is not known (39). So, further study on the phosphorylation of the subunit in Xenopus eggs may provide some clues elucidating the mechanism.…”

Section: Validation Of Phosphorylation Sitesmentioning

confidence: 99%

Exploring the phosphoproteome profiles duringXenopusegg activation by calcium stimulation using a fully automated phosphopeptide purification system

Kanno

Horigome

2015

J Biochem

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To explore the phosphoproteome profiles during Xenopus egg activation by Ca 2+ -stimulation, an automated phosphopeptide purification system involving a titania column was improved by introducing 4-step elution with phosphate buffers. The number of detected phosphopeptides in the tryptic digest of a Xenopus egg cytosol fraction on mass spectrometry (MS) was increased 1.5-fold and the percentage of multiply phosphorylated peptides increased from 17 to 24% with introduction of the 4-step elution method. Phosphopeptides were purified by the improved method from tryptic digests of cytosol fractions of Xenopus eggs without and with a Ca 2+ -stimulus, and then, analysed by MS. One thousand three hundred and seventy-five and 994 phosphopeptides were reproducibly detected on duplicate MS, respectively. They included 818 and 437 phosphopeptides specific to each digest, respectively. A method involving isobaric tags for relative and absolute quantitation (iTRAQ) was also applied to compare the phosphorylation levels in Xenopus eggs without and with a Ca 2+ -stimulus, the ratios for 112 phosphopeptides in tryptic digests of these egg cytosol fractions being obtained. It was suggested from all the results that the phosphorylation sites and levels change during Xenopus egg activation for many known and unknown sites on structural proteins, signalling related proteins, cell cyclerelated proteins and others.Keywords: egg/phosphoproteome/proteome/titania/ Xenopus.Abbreviations: 4EBP, eukaryotic translation initiation factor 4E binding protein; iTRAQ, isobaric tags for relative and absolute quantitation; LC MS/MS, nano-flow liquid chromatography-linear ion trap/ Orbitrap tandem mass spectrometry; MAPK, mitogen-activated protein kinase; MS, mass spectrometry; mTOR, mammalian target of rapamycin; m/z, massto-charge ratio; ODS, octadecylsilica; TFA, trifluoroacetic acid.Xenopus eggs have been used in studies on egg maturation, egg activation and other mechanisms, which facilitated the progress of developmental biology (1, 2). It has been shown that signalling pathways including protein phosphorylation and dephosphorylation participate greatly in these regulation mechanisms (1, 3, 4). To clarify the complicated regulation mechanism of egg activation, comprehensive analysis of protein phosphorylation during egg activation is a powerful means. The cell cycle of Xenopus eggs is arrested at the second meiotic metaphase. So, Xenopus eggs without Ca 2+ -stimulation show meiotic metaphase properties. When eggs are activated by Ca 2+ -stimulation to mimic fertilization, they show synthetic phase properties. So, we can analyse the changes of protein phosphorylation during activation of Xenopus eggs by comparison of the phosphorylation in Ca 2+ -unstimulated and Ca 2+ -stimulated eggs (5). In this study, therefore, we obtained phosphoproteome profiles of Xenopus egg cytosol fractions without and with Ca 2+ -stimulation as a basis for understanding the egg activation mechanism.To obtain high quality phosphoproteome data, i) determination of a ...

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Protein phosphatase 4 – from obscurity to vital functions

Cited by 141 publications

References 52 publications

Functional analysis of the PP2A subfamily of protein phosphatases in regulating Drosophila S6 kinase

Functional analysis of the PP2A subfamily of protein phosphatases in regulating Drosophila S6 kinase

RNA expression in a cartilaginous fish cell line reveals ancient 3′ noncoding regions highly conserved in vertebrates

Exploring the phosphoproteome profiles duringXenopusegg activation by calcium stimulation using a fully automated phosphopeptide purification system

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