• KSBB Journal
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• v.7 no.4
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• pp.302-307
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• 1992

Protein phosphatase 2A was obtained from a cytosolic fraction of bovine brain homogenate. The phosphatase activity using phosphorylated histone Hl as substrate was suppressed in the presence of liposomes composed of dipalmitoylphosphatidylcholine(DPPC) or the mixture of phosphatidylserine and DPPC. The binding of protein phosphatase to liposome was indicated by the facts that the phosphatase activity of the supernatant of protein phosphatase/multilayer vesicle mixture was decreased with increasing amount of liposome, and that [$^{125}I$]-labeled protein phosphatase was coeluted with liposome. However, the affinity of the protein for phospholipid membrane was not so high. On the other hand, okadaic acid and liposome reduced the phosphatase activity synergistically, which means that okadaic acid binds neither to lipid membrane nor to the membrane-associated phosphatase, The inhibitory effect of liposome was, therefore, ascribed to association of the protein phosphatase 2A with the lipid bilayer membrane.

• Journal of Life Science
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• v.21 no.1
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• pp.31-35
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• 2011

Dual-specificity protein phosphatases (DUSPs) constitute a family of protein phosphatase characterized by the ability to dephosphorylate phospho-tyrosyl and phospho-seryl/threonyl residues. Most DUSPs are involved in regulation of cell survival and differentiation. In this study, a human dual-specificity protein phosphatase, DUSP28, was isolated from a human kidney cDNA. The recombinant protein was successfully produed in E.coli and showed sufficient phosphatase activity toward DiFMUP (6,8-difluoro-4-methylumbelliferyl phosphate). Various phosphatase inhibitors and divalent metals were tested for their effects on the DUSP28 phosphatase activity. As a result, $Zn^{2+}$ was found to strongly inhibit DUSP28 phosphatase activity, suggesting DUSP28 is involved in Zn-related signal transduction pathway. Furthermore, the DUSP28 protein preferred phospho-tyrosyl residues to phospho-threonyl residues, implying its physiological roles in the cellular process.

• Molecules and Cells
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• v.42 no.7
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• pp.546-556
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• 2019

Protein phosphatase 4 (PP4) is a crucial protein complex that plays an important role in DNA damage response (DDR), including DNA repair, cell cycle arrest and apoptosis. Despite the significance of PP4, the mechanism by which PP4 is regulated remains to be elucidated. Here, we identified a novel PP4 inhibitor, protein phosphatase 4 inhibitory protein (PP4IP) and elucidated its cellular functions. PP4IP-knockout cells were generated using the CRISPR/Cas9 system, and the phosphorylation status of PP4 substrates (H2AX, KAP1, and RPA2) was analyzed. Then we investigated that how PP4IP affects the cellular functions of PP4 by immunoprecipitation, immunofluorescence, and DNA double-strand break (DSB) repair assays. PP4IP interacts with PP4 complex, which is affected by DNA damage and cell cycle progression and decreases the dephosphorylational activity of PP4. Both overexpression and depletion of PP4IP impairs DSB repairs and sensitizes cells to genotoxic stress, suggesting timely inhibition of PP4 to be indispensable for cells in responding to DNA damage. Our results identify a novel inhibitor of PP4 that inhibits PP4-mediated cellular functions and establish the physiological importance of this regulation. In addition, PP4IP might be developed as potential therapeutic reagents for targeting tumors particularly with high level of PP4C expression.

• BMB Reports
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• v.56 no.11
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• pp.618-623
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• 2023

Most cancer cells utilize glucose at a high rate to produce energy and precursors for the biosynthesis of macromolecules such as lipids, proteins, and nucleic acids. This phenomenon is called the Warburg effect or aerobic glycolysis- this distinct characteristic is an attractive target for developing anticancer drugs. Here, we found that Phosphofructokinase-1 (PFK-1) is a substrate of the Protein Phosphatase 4 catalytic subunit (PP4C)/PP4 regulatory subunit 1 (PP4R1) complex by using immunoprecipitation and in vitro assay. While manipulation of PP4C/PP4R1 does not have a critical impact on PFK-1 expression, the absence of the PP4C/PP4R1 complex increases PFK-1 activity. Although PP4C depletion or overexpression does not cause a dramatic change in the overall glycolytic rate, PP4R1 depletion induces a considerable increase in both basal and compensatory glycolytic rates, as well as the oxygen consumption rate, indicating oxidative phosphorylation. Collectively, the PP4C/PP4R1 complex regulates PFK-1 activity by reversing its phosphorylation and is a promising candidate for treating glycolytic disorders and cancers. Targeting PP4R1 could be a more efficient and safer strategy to avoid pleiotropic effects than targeting PP4C directly.

• Journal of Applied Biological Chemistry
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• v.50 no.4
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• pp.301-303
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• 2007

• YAKHAK HOEJI
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• v.36 no.2
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• pp.129-136
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• 1992

The effects of ginseng saponins, gypsophila saponin, sodium dodecyl sulfate(SDS), and Triton X-100 on membrane $K^+-dependent$ phosphatase activity which is lipid dependent and represents dephosphorylation step of the complete Na+, $K^+-ATPase$ reaction were investigated in this study to elucidate whether the effects of ginseng saponins are due to the detergent action, using sarcolemma enriched preparation isolated from dog ventricle. $Na^+$, $K^+-ATPase$ and $K^+-dependent$ phosphatase activities of cardiac sarcolemma were about $143\;{\mu}mol$ Pi/mg protein/hr and $34\;{\mu}mol$ p-nitrophenol/mg protein/hr, respectively. While ginseng saponins (triol>total>diol) inhibited $K^+-dependent$ phosphatase activity, gypsophila saponin, and low dose of SDS($0.4\;{\mu}g/{\mu}g$ protein), and Triton X-100 ($0.6\;{\mu}g/{\mu}g$ protein) increased the enzyme activity, indicating disruptive effect of detergents on membrane barriers. The activating effect of low doses of Triton X-100 on membrane $K^+-dependent$ phosphatase appeared at concentration decreasing light scattering. However, the inhibitory effect of ginseng saponin appeared before a decrease in light scattering. These results suggest that low concentrations of ginseng saponins inhibit the membrane $K^+-dependent$ phosphatase by interacting directly with enzyme before membrane disruption.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1275-1277
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• 2013

• BMB Reports
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• v.53 no.4
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• pp.181-190
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• 2020

Protein phosphatase 4 (PP4), one of serine/threonine phosphatases, is involved in many critical cellular pathways, including DNA damage response (DNA repair, cell cycle regulation, and apoptosis), tumorigenesis, cell migration, immune response, stem cell development, glucose metabolism, and diabetes. PP4 has been steadily studied over the past decade about wide spectrum of physiological activities in cells. Given the many vital functions in cells, PP4 has great potential to develop into the finding of key working mechanisms and effective treatments for related diseases such as cancer and diabetes. In this review, we provide an overview of the cellular and molecular mechanisms by which PP4 impacts and also discuss the functional significance of it in cell health.

• Parasites, Hosts and Diseases
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• v.31 no.4
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• pp.353-362
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• 1993

The present study was carried out to investigate the localization and isozyme patterns of acid phosphatase and alkaline phosphatase in metacercariae and in adults of F. seoulensis by enzyme-histochemistry method and electrophoresis. Acidphosphatase showed a strong activity at pH 5 in the intestinal caecum of adults, but showed no reactions in the nonsubstrate control and in the inhibitor-treated control. Alkaline phosphatase showed a strong activity at pH 8 in the intestinal caecum and the tribocytic organ of adults, and in the intestinal caecum and in the genital anlagen of metacercariae. In non-denature PAGE, ten bands of protein fraction from the extracts of metacercariae and twenty-two bands from adults were detected. In denature PAGE, two protein bands having molecular weights of 192 kDa and 123 kDa were detected in the metacercariae, but absent from adult stage. In adults, protein fractions of 27.5 kDa, 24.5 kDa, 21.4 kDa, 18 kDa, 16 kDa and 15 kDa were detected. In non-denature PAGE, isozymes of acid phosphatase showed the most strong activity at pH 5, whereas no activity was shown at pH 2 and pH 7. One isozyme 85 kDa, 73 kDa and 62 kDa) in adults.

• Journal of Marine Bioscience and Biotechnology
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• v.2 no.4
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• pp.230-233
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• 2007

Protein tyrosine phosphatase 1B (PTP1B) acts as a negative regulator of insulin signaling, and selective inhibition of PTP1B has served as a potential drug target for the treatment of type 2 diabetes. As part of our searching for PTP1B inhibitors from natural products, the extracts of marine microorganisms were screened for the inhibitory effects on the activity of protein tyrosine phosphatase 1B (PTP1B). Among the tested 304 extracts, 29 extracts exhibited inhibition rate ranging 40.1 - 83.6 % against PTP1B at the concentration level of $30{\mu}g/mL$.