scholarly journals A novel pool of protein phosphatase 2A is associated with microtubules and is regulated during the cell cycle.

1995 ◽  
Vol 128 (6) ◽  
pp. 1131-1144 ◽  
Author(s):  
E Sontag ◽  
V Nunbhakdi-Craig ◽  
G S Bloom ◽  
M C Mumby
Keyword(s):  
Cell Cycle ◽  
Enzymatic Activity ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
S Phase ◽  
Phosphatase 2A ◽  
Spindle Microtubules ◽  
Cycle Dependent ◽  
Cycle Regulation

Immunofluorescence microscopy revealed the presence of protein phosphatase 2A (PP2A) on microtubules in neuronal and nonneuronal cells. Interphase and mitotic spindle microtubules, as well as centrosomes, were all labeled with antibodies against individual PP2A subunits, showing that the AB alpha C holoenzyme is associated with microtubules. Biochemical analysis showed that PP2A could be reversibly bound to microtubules in vitro and that approximately 75% of the PP2A in cytosolic extracts could interact with microtubules. The activity of microtubule-associated PP2A was differentially regulated during the cell cycle. Enzymatic activity was high during S phase and intermediate during G1, while the activity in G2 and M was 20-fold lower than during S phase. The amount of microtubule-bound PP2A remained constant throughout the cell cycle, implying that cell cycle regulation of its enzymatic activity involves factors other than microtubules. These results raise the possibility that PP2A regulates cell cycle-dependent microtubule functions, such as karyokinesis and membrane transport.

Identification of rat epidermal profilaggrin phosphatase as a member of the protein phosphatase 2A family

1993 ◽  
Vol 106 (1) ◽  
pp. 219-226 ◽  
Author(s):  
E. Kam ◽  
K.A. Resing ◽  
S.K. Lim ◽  
B.A. Dale
Keyword(s):  
Enzymatic Activity ◽  
Intermediate Filaments ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Gel Filtration ◽  
Phosphatase Inhibitors ◽  
Rate Analysis ◽  
Phosphatase 2A

The aggregation of cellular intermediate filaments is an important step in the terminal differentiation of keratinocytes. It has been shown that epidermal filaggrin can cause intermediate filaments to aggregate in vitro and may also have the same function in vivo. Filaggrin is derived via dephosphorylation and proteolysis from a highly phosphorylated precursor, profilaggrin, which is found in the granular layer of the epidermis. Using casein kinase II phosphorylated filaggrin as substrate, a profilaggrin phosphatase has been partially purified from rat epidermal homogenate by three chromatographic steps (DE52, hydroxylapatite and S200 gel filtration). Profilaggrin phosphatase activity eluted from the last column has a Km of 0.12 mM and a Vmax of 8 nmol/mg/min with respect to phosphofilaggrin. Results obtained by initial rate analysis showed that the enzymatic activity is not affected by phospho-tyrosyl phosphatase inhibitors and the active fractions preferentially dephosphorylate the alpha subunit of phosphorylase kinase which has been phosphorylated by cAMP-dependent kinase. These results suggest that epidermal profilaggrin phosphatase is not a phospho-tyrosyl phosphatase or a type 1 phospho-seryl/phospho-threonyl phosphatase. Dephosphorylation is not affected by EDTA, calcium or magnesium, but is very sensitive to okadaic acid inhibition (IC50 = 80 pM), suggesting that the enzymatic activity is related to that of the protein phosphatase 2A (PP2A).(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Cell Cycle Dependent Association of EBP50 with Protein Phosphatase 2A in Endothelial Cells

PLoS ONE ◽  
2012 ◽  
Vol 7 (4) ◽  
pp. e35595 ◽  
Author(s):  
Anita Boratkó ◽  
Pál Gergely ◽  
Csilla Csortos
Keyword(s):  
Cell Cycle ◽  
Endothelial Cells ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Phosphatase 2A ◽  
Cycle Dependent

scholarly journals Regulation of the Cell Cycle by Protein Phosphatase 2A in Saccharomyces cerevisiae

2006 ◽  
Vol 70 (2) ◽  
pp. 440-449 ◽  
Author(s):  
Yu Jiang
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Protein Phosphatase ◽  
Cell Cycle Progression ◽  
Protein Phosphatase 2A ◽  
Cyclin Dependent Kinase ◽  
Cycle Progression ◽  
Phosphatase 2A ◽  
Direct Target ◽  
Cycle Regulation

SUMMARY Protein phosphatase 2A (PP2A) has long been implicated in cell cycle regulation in many different organisms. In the yeast Saccharomyces cerevisiae, PP2A controls cell cycle progression mainly through modulation of cyclin-dependent kinase (CDK) at the G2/M transition. However, CDK does not appear to be a direct target of PP2A. PP2A affects CDK activity through its roles in checkpoint controls. Inactivation of PP2A downregulates CDK by activating the morphogenesis checkpoint and, consequently, delays mitotic entry. Defects in PP2A also compromise the spindle checkpoint and predispose the cell to an error-prone mitotic exit. In addition, PP2A is involved in controlling the G1/S transition and cytokinesis. These findings suggest that PP2A functions in many stages of the cell cycle and its effect on cell cycle progression is pleiotropic.

scholarly journals Cyclin G2 Associates with Protein Phosphatase 2A Catalytic and Regulatory B′ Subunits in Active Complexes and Induces Nuclear Aberrations and a G1/S Phase Cell Cycle Arrest

2002 ◽  
Vol 277 (30) ◽  
pp. 27449-27467 ◽  
Author(s):  
David A. Bennin ◽  
Aruni S. Arachchige Don ◽  
Tiffany Brake ◽  
Jennifer L. McKenzie ◽  
Heidi Rosenbaum ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Arrest ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
S Phase ◽  
Phase Cell ◽  
Cycle Arrest ◽  
Phosphatase 2A ◽  
Cyclin G2 ◽  
B Subunits

scholarly journals Inhibition of Protein Phosphatase 2A Sensitizes Mucoepidermoid Carcinoma to Chemotherapy via the PI3K-AKT Pathway in Response to Insulin Stimulus

2018 ◽  
Vol 50 (1) ◽  
pp. 317-331 ◽  
Author(s):  
Limin Liu ◽  
Herui Wang ◽  
Jing Cui ◽  
Qi Zhang ◽  
Wei Zhang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Phosphatase ◽  
Mucoepidermoid Carcinoma ◽  
Protein Phosphatase 2A ◽  
Locally Advanced ◽  
Carcinoma Cells ◽  
Akt Pathway ◽  
Phosphatase 2A

Background/Aims: Protein phosphatase 2A (PP2A) is a ubiquitous serine/threonine phosphatase that mediates cell cycle regulation and metabolism. Mounting evidence has indicated that PP2A inhibition exhibits considerable anticancer potency in multiple types of human cancers. However, the efficacy of PP2A inhibition remains unexplored in mucoepidermoid carcinoma (MEC), especially in locally advanced and metastatic cases with limited systemic treatment. In this study, we demonstrated the therapeutic potency of LB100 in mucoepidermoid carcinoma. Methods: In this study, the expression of PP2A was evaluated using immunohistochemical (IHC) staining. The effects associated with LB100 alone and in combination with cisplatin for the treatment of mucoepidermoid carcinoma were investigated both in vitro, regarding metabolism, proliferation, and migration, and in vivo in a mucoepidermoid carcinoma xenograft model. In addition, with LB100 treatment and in response to an insulin stimulus, the expression levels and phosphorylation levels of targets in the PI3K-AKT pathway were determined using western blot analysis and immunoblotting. Results: The expression of protein phosphatase 2A was significantly upregulated in the clinical specimens of high-grade MECs compared with those of low-/medium-grade MECs and normal controls. In this article, we report that a small molecule PP2A inhibitor, LB100, decreased cellular viability and glycolytic activity and induced G2/M cell cycle arrest. Importantly, LB100 enhanced the efficacy of cisplatin in mucoepidermoid carcinoma cells both in vitro and in vivo. PP2A inhibition by LB100 increased the phosphorylation of insulin receptor substrate 1(IRS-1) on serine residues, downregulated the expression of phosphatidylinositol 3-kinase (PI3K) p110 alpha subunit and dephosphorylated AKT at Ser473 and Thr308 in mucoepidermoid carcinoma cells in response to insulin stimulus. Conclusion: These results highlight the translational potential of PP2A inhibition to synergize with cisplatin in mucoepidermoid carcinoma treatment.

scholarly journals IMMU-47. PROTEIN PHOSPHATASE 2A INHIBITION IN NK CELL THERAPY FOR TREATMENT OF MEDULLOBLASTOMA

2020 ◽  
Vol 22 (Supplement_2) ◽  
pp. ii115-ii115
Author(s):  
Rongze Olivia Lu ◽  
Winson Ho ◽  
Brandon Chiou
Keyword(s):  
Nk Cells ◽  
Cell Line ◽  
Protein Phosphatase ◽  
Nk Cell ◽  
Protein Phosphatase 2A ◽  
T Cell Response ◽  
Intrinsic Activity ◽  
Cd107a Expression ◽  
Phosphatase 2A

Abstract Checkpoint immunotherapy (ICB) thus far has shown limited efficacy against brain tumors, such as medulloblastoma (MB). Its low mutational burden is thought to result in a paucity of neoantigen to trigger an effective T-cell response. Natural killer (NK) cells, can recognize tumor cells independently of neoantigens, making them appealing against MBs. Modulation of NK cells to enhance cytotoxicity against MBs could be a novel treatment strategy. Protein Phosphatase 2A (PP2A), a ubiquitous serine/threonine phosphatase, has been shown to inhibit IFNg and Granzyme B production by NK cells. We hypothesize that NK92, a transformed human NK cell line, has intrinsic activity against human MB cells and that inhibiting PP2A pharmacologically can enhance cytotoxicity of NK92 cells. We performed NK cytotoxicity assay and granulation assay against human MB cell line D425. We also used a small molecular inhibitor, LB100, to modulate PP2A activity in NK92. NK92 cells were co-cultured with D425, in increasing E:T (Effector:Target) ratio for 4 hours. D425 cells were pre-labeled with CellTrace Violet dye. The percentage of D425 (Violet+) cells in apoptosis (Cas3/7+) or necrosis (AAD+) were compared with different ET ratios to quantify NK mediated cell cytotoxicity. We also measured CD107a expression in NK92 to assess granulation with LB100 treatment. D425 cells were sensitive to NK92 killing. Percentage of D425 cells either apoptotic or necrotic increased with increasing ET ratio, suggesting that there was NK92 mediated cytotoxicity. Percentage of killed D425 cells ranged from 18% at baseline (without NK92) to 80% at ET ratio of 20. Inhibition of PP2A using LB100, enhanced NK92 degranulation. CD107a+ NK92 cells increased from 19% to 28% with 8uM of LB100. NK92 cells are cytotoxic against MB cells in vitro and inhibition of PP2A in NK cells can enhance their activity against MB cells.

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.

The Xenopus protein kinase pEg2 associates with the centrosome in a cell cycle-dependent manner, binds to the spindle microtubules and is involved in bipolar mitotic spindle assembly

1998 ◽  
Vol 111 (5) ◽  
pp. 557-572 ◽  
Author(s):  
C. Roghi ◽  
R. Giet ◽  
R. Uzbekov ◽  
N. Morin ◽  
I. Chartrain ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Kinase ◽  
Mitotic Spindle ◽  
Cultured Cells ◽  
Dependent Manner ◽  
Egg Extracts ◽  
Pericentriolar Material ◽  
Spindle Microtubules ◽  
Cycle Dependent

By differential screening of a Xenopus laevis egg cDNA library, we have isolated a 2,111 bp cDNA which corresponds to a maternal mRNA specifically deadenylated after fertilisation. This cDNA, called Eg2, encodes a 407 amino acid protein kinase. The pEg2 sequence shows significant identity with members of a new protein kinase sub-family which includes Aurora from Drosophila and Ipl1 (increase in ploidy-1) from budding yeast, enzymes involved in centrosome migration and chromosome segregation, respectively. A single 46 kDa polypeptide, which corresponds to the deduced molecular mass of pEg2, is immunodetected in Xenopus oocyte and egg extracts, as well as in lysates of Xenopus XL2 cultured cells. In XL2 cells, pEg2 is immunodetected only in S, G2 and M phases of the cell cycle, where it always localises to the centrosomal region of the cell. In addition, pEg2 ‘invades’ the microtubules at the poles of the mitotic spindle in metaphase and anaphase. Immunoelectron microscopy experiments show that pEg2 is located precisely around the pericentriolar material in prophase and on the spindle microtubules in anaphase. We also demonstrate that pEg2 binds directly to taxol stabilised microtubules in vitro. In addition, we show that the presence of microtubules during mitosis is not necessary for an association between pEg2 and the centrosome. Finally we show that a catalytically inactive pEg2 kinase stops the assembly of bipolar mitotic spindles in Xenopus egg extracts.

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