• Archives of Pharmacal Research
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• v.27 no.1
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• pp.68-76
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• 2004

Mistletoe lectin has been reported to induce apoptosis in different cancer cell lines in vitro and to show antitumor activity against a variety of tumors in animal models. We previously demonstrated the Korean mistletoe lectin (Viscum album var. coloratum, VCA)-induced apoptosis by down-regulation of Bcl-2 and telomerase activity and by up-regulation of Bax through p53- and p21-independent pathway in hepatoma cells. In the present study, we observed the induction of apoptotic cell death through activation of caspase-3 and the inhibition of telomerase activity through transcriptional down-regulation of hTERT in the VCA-treated A253 cells. We also observed the inhibition of telomerase activity and induction of apoptosis resulted from dephosphorylation of Akt in the survival signaling pathways. In addition, combining VCA with the inhibitors of phosphatidylinositol 3-kinase (PI3-kinase) upstream of Akt, wortmannin and LY294002 showed an additive inhibitory effect of telomerase activity. In contrast, the inhibitor of protein phosphatase 2A (PP2A), okadaic acid inhibited VCA-induced dephosphorylation of Akt and inhibition of telomerase activity. Taken together, VCA induces apoptotic cell death through Akt signaling pathway in correlated with the inhibition of telomerase activity and the activation of caspase-3. From these results, together with our previous studies, we suggest that VCA triggers molecular changes that resulting in the inhibition of cell growth and the induction of apoptotic cell death of cancer cells, which suggest that VCA may be useful as chemotherapeutic agent for cancer cells.

• Molecules and Cells
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• v.42 no.8
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• pp.604-616
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• 2019

Phosphoserine phosphatase (PSPH) is one of the key enzymes of the L-serine synthesis pathway. PSPH is reported to affect the progression and survival of several cancers in an L-serine synthesis-independent manner, but the mechanism remains elusive. We demonstrate that PSPH promotes lung cancer progression through a noncanonical L-serine-independent pathway. PSPH was significantly associated with the prognosis of lung cancer patients and regulated the invasion and colony formation of lung cancer cells. Interestingly, L-serine had no effect on the altered invasion and colony formation by PSPH. Upon measuring the phosphatase activity of PSPH on a serine-phosphorylated peptide, we found that PSPH dephosphorylated phospho-serine in peptide sequences. To identify the target proteins of PSPH, we analyzed the protein phosphorylation profile and the PSPH-interacting protein profile using proteomic analyses and found one putative target protein, IRS-1. Immunoprecipitation and immunoblot assays validated a specific interaction between PSPH and IRS-1 and the dephosphorylation of phospho-IRS-1 by PSPH in lung cancer cells. We suggest that the specific interaction and dephosphorylation activity of PSPH have novel therapeutic potential for lung cancer treatment, while the metabolic activity of PSPH, as a therapeutic target, is controversial.

• Proceedings of the Zoological Society Korea Conference
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• 2001.10a
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• pp.211.1-211
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• 2001

No Abstract, See Full Text

• Proceedings of the Zoological Society Korea Conference
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• 1998.04a
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• pp.57.1-57
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• 1998

No Abstract, See Full Text

• Proceedings of the PSK Conference
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• 2001.10a
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• pp.287.1-287.1
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• 2001

• BMB Reports
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• v.47 no.10
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• pp.593-598
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• 2014

RNA polymerase II carboxyl-terminal domain (RNAPII CTD) phosphatases are responsible for the dephosphorylation of the C-terminal domain of the small subunit of RNAPII in eukaryotes. Recently, we demonstrated the identification of several interacting partners with human small CTD phosphatase1 (hSCP1) and the substrate specificity to delineate an appearance of the dephosphorylation catalyzed by SCP1. In this study, using the established cells for inducibly expressing hSCP1 proteins, we monitored the modification of ${\beta}$-O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAcylation is one of the most common post-translational modifications (PTMs). To gain insight into the PTM of hSCP1, we used the Western blot, immunoprecipitation, succinylayed wheat germ agglutinin-precipitation, liquid chromatography-mass spectrometry analyses, and site-directed mutagenesis and identified the $Ser^{41}$ residue of hSCP1 as the O-GlcNAc modification site. These results suggest that hSCP1 may be an O-GlcNAcylated protein in vivo, and its N-terminus may function a possible role in the PTM, providing a scaffold for binding the protein(s).

• BMB Reports
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• v.47 no.10
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• pp.552-557
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• 2014

The main purpose of this study was to investigate whether type 3 muscarinic acetylcholine receptor (M3R) dysfunction induced vascular hyperpermeability. Transwell system analysis showed that M3R inhibition by selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) and small interfering RNA both increased endothelial permeability. Using coimmunoprecipitation and Western blot assay, we found that M3R inhibition increased VE-cadherin and ${\beta}$-catenin tyrosine phosphorylation without affecting their expression. Using PTP1B siRNA, we found that PTP1B was required for maintaining VE-cadherin and ${\beta}$-catenin protein dephosphorylation. In addition, 4-DAMP suppressed PTP1B activity by reducing cyclic adenosine monophosphate (cAMP), but not protein kinase $C{\alpha}$ ($PKC{\alpha}$). These data indicate that M3R preserves the endothelial barrier function through a mechanism potentially maintaining PTP1B activity, keeping the adherens junction proteins (AJPs) dephosphorylation.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1996.11a
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• pp.135-139
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• 1996

$p70^{s6k}$ lies on a $p21^{ras}$-independent signalling pathway and plays an important role in mitogenesis. Activation is associated with phosphorylation at multiple sites, four of which lie in an autoinhibitory region. The immunosuppressant rapamycin induces $p70^{s6k}$ inactivation through dephosphorylation of a second set of mitogen-induced sites. Here we identify these sites as $T_{229}$, $T_{389}$, and $S_{404}$. $T_{229}$ resides in the "T loop" of the catalytic domain, an essential phosphorylation site in other kinases. However, $p70^{s6k}$ inactivation by rapamycin most closely parallels $T_{389}$ dephosphorylation. Mutation of $T_{389}$ to alanine ablates kinase activity, whereas mutation to glutamic acid confers constitutive kinase activity and rapamycin resistance. indicating an essential role for phosphorylation at this site. $T_{389}$ resides in an unusual hydrophobic motif, not previously noted, between the catalytic and autoinhibitory domains. The importance of this site, and surrounding motif, is emphasized by its conservation in other kinases including homologues of $p70^{s6k}$ derived from such distantly related organisms as yeast and plant.

• Animal cells and systems
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• v.2 no.2
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• pp.223-227
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• 1998

We isolated two soluble forms of glutamate dehydrogenase isoproteins, GDH I and GDH II, from bovine brain. The regulation of GDH I and GDH II by phosphorylation and dephosphorylation has been examined in various conditions. There were dose- and time- dependent activation of the GDH isoproteins when phosphorylated by cAMP-dependent protein kinase. The phosphorylated GDH had 1.1 mol of covalently bound phosphate/mol of subunit and a 2-fold increased specific activity. The phosphorylated amino acid was identified as serine. When treated with alkaline phosphatase, the activities of the phosphorylated GDH isoproteins were reduced in dose and time dependent manner and returned to those of unphosphorylated enzymes. There were no significant differences between GDH I and GDH II in their sensitivities to the action of phosphorylation and dephosphorylation demonstrating that the microenvironmental structures of the phosphorylation site in GDH isoproteins are similar to each other, These results results suggest that the inter-conversion between less active form of brain GDH isoproteins and more active form is regulated by phosphorylation through cAMP-dependent protein kineses.

• Molecules and Cells
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• v.26 no.4
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• pp.329-337
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• 2008

Src-family kinases are critically involved in the control of cytoskeleton organization and in the generation of integrin-dependent signaling responses, inducing tyrosine phosphorylation of many signaling and cytoskeletal proteins. Activity of the Src family of tyrosine kinases is tightly controlled by inhibitory phosphorylation of a carboxy-terminal tyrosine residue, inducing an inactive conformation through binding with its SH2 domain. Dephosphorylation of C-ter tyrosine, as well as its deletion of substitution with phenylalanine in oncogenic Src kinases, leads to autophosphorylation at a tyrosine in the activation loop, thereby leading to enhanced Src activity. Beside this phophorylation/dephosphorylation circuitry, cysteine oxidation has been recently reported as a further mechanism of enzyme activation. Mounting evidence describes Src activation via its redox regulation as a key outcome in several circumstances, including growth factor and cytokines signaling, integrin-mediated cell adhesion and motility, membrane receptor cross-talk as well in cell transformation and tumor progression. Among the plethora of data involving Src kinase in physiological and pathophysiological processes, this review will give emphasis to the redox component of the regulation of this master kinase.