Hyun-Kyung Choi

Sungkyunkwan University, Seoul, Seoul, South Korea

Are you Hyun-Kyung Choi?

Claim your profile

Publications (7)23.9 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The promyogenic cell surface molecule Cdo is required for activation of extracellular signal-regulated kinase (ERK) and nuclear factor of activated T cells c3 (NFATc3) induced by netrin-2 in myogenic differentiation. However, the molecular mechanism leading to NFATc3 activation is unknown. Stromal interaction molecule 1 (Stim1), an internal calcium sensor of the endoplasmic reticulum store, promotes myogenesis via activation of NFATc3. In this study we investigated the functional interaction between Cdo and Stim1 in myogenic differentiation. Overexpression and depletion of Stim1 enhanced or decreased myotube formation, respectively. Of interest, Stim1 protein levels were decreased in Cdo-deficient perinatal hindlimb muscles or primary myoblasts; this correlates with defective NFATc3 activation in Cdo(-/-) myoblasts upon differentiation. Forced activation of NFATc3 by overexpression of calcineurin restored differentiation of Cdo-depleted C2C12 myoblasts. Furthermore, Cdo and Stim1 formed a complex in 293T cells or in differentiating C2C12 myoblasts. The netrin-2-mediated NFATc3 activation was coincident with robust interactions between Cdo and Stim1 in myoblasts and the ERK-mediated Stim1 phosphorylation at serine 575. The serine 575 phosphorylation was enhanced in C2C12 cells upon differentiation, and the alanine substitution of serine 575 failed to restore differentiation of Stim1-depleted myoblasts. Taken together, the results indicate that cell adhesion signaling triggered by netrin-2/Cdo induces Stim1 phosphorylation at serine 575 by ERK, which promotes myoblast differentiation.
    Molecular biology of the cell 02/2012; 23(7):1376-87. · 5.98 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Esco2 is an acetyltransferase that is required for the establishment of sister chromatid cohesion. Roberts-SC phocomelia (RBS) syndrome caused by the mutations of Esco2 gene, is an autosomal recessive development disorder characterized by growth retardation, limb reduction and craniofacial abnormalities including cleft lip and palate. Here, we show that Esco2 protein co-immunoprecipitates with Notch but not with CBF1. Esco2 represses the transactivational activity of Notch protein in an acetyltransferase-independent manner. Chromatin immunoprecipitation experiments suggest that Esco2 might regulate the activity of NICD-CBF1 via attenuating NICD binding to CBF1 on the promoter of Hes1, the downstream target gene of Notch. Furthermore, we demonstrate that the overexpression of Esco2 promotes the neuronal differentiation of P19 embryonic carcinoma cells and C17.2 neural progenitor cells and the knockdown of Esco2 by siRNA blocks the differentiation. The inhibitory effects of Notch protein on neuronal differentiation of P19 cells was suppressed by Esco2 overexpression. Taken together, our study suggests that Esco2 may play an important role in neurogenesis by attenuating Notch signaling to promote neuronal differentiation.
    Cellular Signalling 11/2011; 23(11):1876-84. · 4.47 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: M-type (KCNQ) potassium channels play an important role in regulating the action potential firing in neurons. Here, we investigated the effect of cholesterol on M current in superior cervical ganglion (SCG) sympathetic neurons, using the patch clamp technique. M current was inhibited in a dose-dependent manner by cholesterol loading with a methyl-beta-cyclodextrin-cholesterol complex. This effect was prevented when membrane cholesterol level was restored by including empty methyl-beta-cyclodextrin in the pipette solution. Dialysis of cells with AMP-PNP instead of ATP prevented cholesterol action on M currents. Protein kinase C (PKC) inhibitor, calphostin C, abolished cholesterol-induced inhibition whereas the PKC activator, PDBu, mimicked the inhibition of M currents by cholesterol. The in vitro kinase assay showed that KCNQ2 subunits of M channel can be phosphorylated by PKC. A KCNQ2 mutant that is defective in phosphorylation by PKC failed to show current inhibition not only by PDBu but also by cholesterol. These results indicate that cholesterol-induced inhibition of M currents is mediated by PKC phosphorylation. The inhibition of M currents by PDBu and cholesterol was completely blocked by PIP(2) loading, indicating that the decrease in PIP(2)-channel interaction underlies M channel inhibition by PKC-mediated phosphorylation. We conclude that cholesterol specifically regulates M currents in SCG neurons via PKC activation.
    Journal of Biological Chemistry 04/2010; 285(14):10939-50. · 4.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Accurate chromosome segregation during cell division requires physical attachment of two sister chromatids from DNA replication until mitosis, a process known as sister chromatid cohesion. Sister chromatid cohesion is mediated by a four-subunit cohesin complex that connects sister chromatids by encircling them as molecular rings. Eco1 is an essential acetyltransferase required for the establishment of sister chromatid cohesion. Eco1 acetylates Smc3 and Mcd1 (Rad21) to establish cohesion during S phase and in response to DNA damage, respectively. Here, we show that Eco1 repress transcription in a dose-dependent manner. Mutations of zinc-finger domain or acetyltransferase domain did not significantly affect the transcriptional repression activity of Eco1. We observed that histone demethylase, Lsd1 interacts with Eco1 and is required for the transcriptional repression activity of Eco1. Chromatin immunoprecipitation (ChIP) experiments show that Eco1 facilitates the demethylation of lysine 4 of histone H3. Taken together, we provide the first evidence that Eco1 represses transcription by interacting with histone demethylase, LSD1 to convert chromatin to inactive state.
    Biochemical and Biophysical Research Communications 03/2010; 394(4):1063-8. · 2.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Accurate chromosome segregation during cell division requires that sister chromatids are kept together by cohesin complex until anaphase, when the chromatids separate and distribute to the two daughter cells. Esco2 is an acetyltransferase that is required for the establishment of sister chromatid cohesion during S phase. Here, we report that Esco2 interacts with several component proteins of the CoREST complex, including a transcription corepressor CoREST, histone demethlyase LSD1, HDAC1, HDAC2, BRAF35, and PHF21A. Esco2 also interacts with various histone methyltransferases Suv39h1, SETDB1 and G9a. Esco2 complex purified from HeLa nuclear extract possesses histone H3 K9 methylation activity and functions as a transcription repressor. Esco2 fused to Gal4 DNA binding domain represses transcription by increasing methylation of histone H3 K9 in the promoter region. These results suggest a novel function of Esco2 in transcription repression through modulation of the chromatin structure.
    Biochemical and Biophysical Research Communications 08/2008; 372(2):298-304. · 2.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Exposure to DNA-damaging agents can activate cell cycle checkpoint and DNA repair processes to ensure genetic integrity. Such exposures also can affect the transcription of many genes required for these processes. In the budding yeast Saccharomyces cerevisiae, changes of global gene expression as a result of a DNA-damaging agent were previously identified by using DNA chip technology. DNA microarray analysis is a powerful tool for identifying genes whose expressions are changed in response to environmental changes. Transcriptional levels, however, do not necessarily reflect cellular protein levels. Green fluorescent protein (GFP) has been widely used as a reporter of gene expression and subcellular protein localization. We have used 4156 yeast strains expressing full-length, chromosome-tagged GFP fusion proteins to monitor changes of protein levels in response to the DNA-damaging agent, methyl methanesulphonate (MMS). Through flow cytometry, we identified 157 proteins whose levels were increased at least three-fold following treatment with MMS. Of 157 responsible genes, transcriptions of 57 were previously not known to be induced by MMS. Immunoblot experiments with tandem affinity-tagged yeast strains under the same experimental conditions confirmed these newly found proteins as inducible. These results suggest, therefore, that the 57 protein expressions are regulated by different mechanisms, such as post-translational modifications, and not by transcriptional regulation.
    Yeast 04/2007; 24(3):145-54. · 1.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Structural maintenance of chromosome 1 (Smc1) is a multifunctional protein, which has been implicated in sister chromatid cohesion, DNA recombination and repair, and the activation of cell cycle checkpoints by ionizing radiation, ultraviolet light, and other genotoxic agents. In order to identify the proteins that interact with Smc1, we conducted the Tandem affinity purification (TAP) technique and analyzed the Smc1-interacting proteins via MALDI-TOF mass spectrometry. We identified minichromosome maintenance 7 (Mcm7), an essential component of the pre-replication complex, as a novel Smc1-interacting protein. Co-immunoprecipitation revealed an interaction occurring between Smc1 and Mcm7, both in vitro and in vivo. Using a GST pull-down assay, we determined that Smc1 interacts physically with Mcm7 via its N-terminal and hinge regions, and Mcm7 interacts with Smc1 via its middle region. Interestingly, we also discovered that Smc1 interacts with other DNA replication proteins, including Mcm6, RFC1, and DNA polymerase alpha. These results suggest that a functional link exists between the cohesin complex and DNA replication proteins.
    Biochemical and Biophysical Research Communications 04/2006; 341(3):770-5. · 2.28 Impact Factor