Biomedical subjects

Jung Hwa Kim

Publications and source records attributed to Jung Hwa Kim.

14 recordsLinked to original sources

PubMed2006

Roles of sumoylation of a reptin chromatin-remodelling complex in cancer metastasis.

Defining the functional modules within transcriptional regulatory factors that govern switching between repression and activation events is a central issue in biology. Recently, we have reported the dynamic role of a beta-catenin-reptin chromatin remodelling complex in regulating a metastasis suppressor gene KAI1 (ref.1), which is capable of inhibiting the progression of tumour metastasis. Here, we identify signalling factors that confer repressive function on reptin and hence repress the expression of KAI1. Biochemical purification of a reptin-containing complex has revealed the presence of specific desumoylating enzymes that reverse the sumoylation of reptin that underlies its function as a repressor. Desumoylation of reptin alters the repressive function of reptin and its association with HDAC1. Furthermore, the sumoylation status of reptin modulates the invasive activity of cancer cells with metastatic potential. These data clearly define a functional model and provide a novel link for SUMO modification in cancer metastasis.

ATPases Associated with Diverse Cellular Activitie↗

PubMed2006

Transient ischemia-induced expression and changes of tyrosine kinase A in the hippocampal dentate gyrus of the gerbil.

The present study examined ischemia-related changes in tyrosine kinase A (trkA) immunoreactivity and its protein content in the dentate gyrus after 5 min of transient forebrain ischemia in gerbils. One day after ischemic insult, cresyl violet-positive polymorphic cells showed ischemic degeneration. The ischemia-induced changes in trkA immunoreactivity were found in the polymorphic layer (PL) and granule cell layer (GCL) of the dentate gyrus. In the sham-operated group, trkA immunoreactivity in the dentate gyrus was very weak. From 30 min after ischemia, trkA immunoreactivity was increased in the dentate gyrus and peaked in the dentate gyrus at 12 h after ischemia-reperfusion. Thereafter, trkA immunoreactivity was decreased time-dependently after ischemia-reperfusion. Four days after ischemic insult, trkA immunoreactivity was similar to that of the sham-operated group. In addition, it was found that ischemia-related changes in trkA protein content were similar to the immunohistochemical changes. These results suggest that the chronological changes of trkA in the dentate gyrus after transient forebrain ischemia may be associated with ischemic damage in polymorphic cells of the dentate gyrus.

Analysis of Variance↗

PubMed2006

Inactivation of the fibronectin-binding adhesin gene bbk32 significantly attenuates the infectivity potential of Borrelia burgdorferi.

Borrelia burgdorferi, the aetiological agent of Lyme disease, utilizes multiple adhesins to interact with both the arthropod vector and mammalian hosts it colonizes. One such adhesive molecule is a surface-exposed fibronectin-binding lipoprotein, designated BBK32. Previous characterization of BBK32-mediated fibronectin binding has been limited to biochemical analyses due to the difficulty in mutagenizing infectious isolates of B. burgdorferi. Here we report an alternative method to inactivate bbk32 via allelic exchange through use of a low-passage variant of B. burgdorferi strain B31 that is more readily transformed. The resulting mutant does not synthesize BBK32, exhibits reduced fibronectin binding in solid phase assays and manifests decreased interactions with mouse fibroblast cells relative to both the infectious parent and genetic complement. Furthermore, the bbk32 knockout was significantly attenuated in the murine model of Lyme disease, whereas a genetically complemented control was not, indicating that BBK32 is necessary for maximal B. burgdorferi infection in the mouse. To our knowledge this is the first mutational analysis of a surface exposed, functional borrelial lipoprotein adhesin whose activity is associated with the mammalian host environment. By analogy with other pathogens that utilize fibronectin binding as an important virulence determinant, the borrelial fibronectin-BBK32 interaction is likely to be important in B. burgdorferi-specific pathogenic mechanisms, particularly in the context of dissemination, secondary colonization and/or persistence.

Adhesins, Bacterial↗

PubMed2005

Multicomponent Lyme vaccine: three is not a crowd.

Lyme disease is caused by the spirochete Borrelia burgdorferi and it is the most common vector-borne disease in the United States. Disseminated spirochetes can persist in various tissues and can result in a variety of different disease manifestations. Vaccination trials testing various lipoprotein candidates have yielded mixed results despite the generation of robust antibody titers. Data presented in this report demonstrate that a combination vaccine composed of DbpA, BBK32 and OspC is more effective than single or double component formulations and that the ratio of each component dramatically impacts vaccine efficacy when tested in protection experiments against Borrelia following needle inoculation.

Adhesins, Bacterial↗

PubMed2005

Transcriptional regulation of a metastasis suppressor gene by Tip60 and beta-catenin complexes.

Defining the molecular strategies that integrate diverse signalling pathways in the expression of specific gene programmes that are critical in homeostasis and disease remains a central issue in biology. This is particularly pertinent in cancer biology because downregulation of tumour metastasis suppressor genes is a common occurrence, and the underlying molecular mechanisms are not well established. Here we report that the downregulation of a metastasis suppressor gene, KAI1, in prostate cancer cells involves the inhibitory actions of beta-catenin, along with a reptin chromatin remodelling complex. This inhibitory function of beta-catenin-reptin requires both increased beta-catenin expression and recruitment of histone deacetylase activity. The coordinated actions of beta-catenin-reptin components that mediate the repressive state serve to antagonize a Tip60 coactivator complex that is required for activation; the balance of these opposing complexes controls the expression of KAI1 and metastatic potential. The molecular mechanisms underlying the antagonistic regulation of beta-catenin-reptin and the Tip60 coactivator complexes for the metastasis suppressor gene, KAI1, are likely to be prototypic of a selective downregulation strategy for many genes, including a subset of NF-kappaB target genes.

Acetyltransferases↗

PubMed2005

Chronological changes of neurofilament 200 kDa immunoreactivity in the lateral olfactory tract after transient forebrain ischemia in gerbils.

This study was carried out to investigate the transient ischemia-induced changes of neurofilament 200 kDa (NF-200) immunoreactivity and protein content in the gerbil lateral olfactory tract (LOT) after 5 min of transient forebrain ischemia. Weak NF-200 immunoreactivity was detectable in the LOT in the sham-operated group. In this group, a few somata of mitral cells showed weak NF-200 immunoreactivity. One day after transient ischemia, NF-200 immunoreactivity in the LOT was increased significantly. NF-200 immunoreactivity in the LOT by 15 days after ischemia was similar to that in the 1 day post-ischemic group. In this time period, strong NF-200 immunoreactivity was expressed in the mitral cell processes, but the immunoreactivity in the mitral cell somata was significantly decreased. Thereafter, NF-200 immunoreactivity in the LOT was decreased significantly by 30 days after ischemic insult. At this time after ischemia, NF-200 immunoreactivity in the mitral cell dendrites was significantly decreased. The result of Western blot study showed that the pattern of NF-200 expression was similar to that of immunohistochemistry after ischemia-reperfusion. Our result suggests that changes of NF-200 protein in the gerbil LOT may be related to response to ischemic damage and that the axonal transport followed transient ischemia may be disturbed.

Animals↗

PubMed2005

Borrelia burgdorferi binds fibronectin through a tandem beta-zipper, a common mechanism of fibronectin binding in staphylococci, streptococci, and spirochetes.

BBK32 is a fibronectin-binding protein from the Lyme disease-causing spirochete Borrelia burgdorferi. In this study, we show that BBK32 shares sequence similarity with fibronectin module-binding motifs previously identified in proteins from Streptococcus pyogenes and Staphylococcus aureus. Nuclear magnetic resonance spectroscopy and isothermal titration calorimetry are used to confirm the binding sites of BBK32 peptides within the N-terminal domain of fibronectin and to measure the affinities of the interactions. Comparison of chemical shift perturbations in fibronectin F1 modules on binding of peptides from BBK32, FnBPA from S. aureus, and SfbI from S. pyogenes provides further evidence for a shared mechanism of binding. Despite the different locations of the bacterial attachment sites in BBK32 compared with SfbI from S. pyogenes and FnBPA from S. aureus, an antiparallel orientation is observed for binding of the N-terminal domain of fibronectin to each of the pathogens. Thus, these phylogenetically and morphologically distinct bacterial pathogens have similar mechanisms for binding to human fibronectin.

Adhesins, Bacterial↗

PubMed2005

Ischemia-related changes in galanin expression in the dentate hilar region after transient forebrain ischemia in gerbils.

Although galanin (GAL) protects hippocampal neurons from ischemic damage, no study has examined ischemia-related changes in endogenous GAL in the hippocampal dentate gyrus. We investigated the chronological changes of GAL, well-known as the potassium channel opener, expression in the dentate gyrus at various times after 5 min of transient forebrain ischemia in gerbils. A few GAL-immunoreactive (IR) neurons were found in the polymorphic layer of the sham-operated group. Three hours after ischemia-reperfusion, the pattern of GAL immunoreactivity was similar to that of the sham-operated group and the number of GAL-IR neurons and immunoreactivity were highest 12 h after ischemic insult. At this time, GAL-IR neurons in the polymorphic layer showed strong GAL immunoreactivity. Thereafter, GAL-IR neurons and immunoreactivity significantly decreased in the dentate hilar region. Four days after ischemic insult, GAL-IR neurons were not detectable. In addition, the results of a Western blot study showed a pattern of GAL expression similar to the immunohistochemical changes. GAL protein content also was highest 12 h after ischemia. In conclusion, the increased expression of endogenous GAL in the dentate gyrus after ischemia is related to response to the ischemic damage.

Animals↗

PubMed2004

BBK32, a fibronectin binding MSCRAMM from Borrelia burgdorferi, contains a disordered region that undergoes a conformational change on ligand binding.

BBK32 is a fibronectin-binding lipoprotein on Borrelia burgdorferi, the causative agent of Lyme disease. Analysis using secondary structure prediction programs suggested that BBK32 is composed of two domains, an N-terminal segment lacking well defined secondary structure and a C-terminal segment composed largely of alpha-helices. Analysis of purified recombinant forms of the two domains by circular dichroism spectroscopy, gel permeation chromatography, and intrinsic viscosity determination were consistent with an N-terminal-extended, unstructured segment and a C-terminal globular domain in BBK32. Solid phase binding experiments suggest that the unstructured N-terminal domain binds fibronectin. Analysis of changes in circular dichroism spectra of the N-terminal segment of BBK32 upon binding of the N-terminal domain of fibronectin revealed an increase in beta-sheet content in the complex. Hence, BBK32, which belongs to a different family of proteins and shows no overall sequence similarity with the fibronectin binding MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) of Gram-positive bacteria, binds fibronectin by a mechanism that is reminiscent of the "tandem beta-zipper" previously demonstrated for the fibronectin binding of streptococcal adhesins.

Adhesins, Bacterial↗

PubMed2004

High affinity streptococcal binding to human fibronectin requires specific recognition of sequential F1 modules.

Fibronectin (Fn) binding by the Streptococcus pyogenes protein SfbI has been shown to trigger integrin-dependent internalization of this pathogen by human epithelial and endothelial cells. Here, using nuclear magnetic resonance spectroscopy and isothermal titration calorimetry in a dissection approach, the basis for the specificity and high affinity of the interaction between the N-terminal domain of Fn and SfbI is revealed. Each of the five Fn type 1 modules is directly involved in the interaction and is recognized by short consecutive motifs within the repeat region of SfbI. Crucially, these motifs must be combined in the correct order to form a high affinity ligand for the N-terminal domain of Fn.

Amino Acid Motifs↗

PubMed2003

Pathogenic bacteria attach to human fibronectin through a tandem beta-zipper.

Staphylococcus aureus and Streptococcus pyogenes, two important human pathogens, target host fibronectin (Fn) in their adhesion to and invasion of host cells. Fibronectin-binding proteins (FnBPs), anchored in the bacterial cell wall, have multiple Fn-binding repeats in an unfolded region of the protein. The bacterium-binding site in the amino-terminal domain (1-5F1) of Fn contains five sequential Fn type 1 (F1) modules. Here we show the structure of a streptococcal (S. dysgalactiae) FnBP peptide (B3) in complex with the module pair 1F12F1. This identifies 1F1- and 2F1-binding motifs in B3 that form additional antiparallel beta-strands on sequential F1 modules-the first example of a tandem beta-zipper. Sequence analyses of larger regions of FnBPs from S. pyogenes and S. aureus reveal a repeating pattern of F1-binding motifs that match the pattern of F1 modules in 1-5F1 of Fn. In the process of Fn-mediated invasion of host cells, therefore, the bacterial proteins seem to exploit the modular structure of Fn by forming extended tandem beta-zippers. This work is a vital step forward in explaining the full mechanism of the integrin-dependent FnBP-mediated invasion of host cells.

Amino Acid Motifs↗

PubMed2003

Deubiquitinating enzymes as cellular regulators.

Modification of proteins by the covalent attachment of ubiquitin is a key regulatory mechanism of many cellular processes including protein degradation by the 26S proteasome. Deubiquitination, reversal of this modification, must also regulate the fate and function of ubiquitin-conjugated proteins. Deubiquitinating enzymes catalyze the removal of ubiquitin from ubiquitin-conjugated substrate proteins as well as from its precursor proteins. Deubiquitinating enzymes occupy the largest family of enzymes in the ubiquitin system, implying their diverse function in regulation of the ubiquitin-mediated pathways. Here we explore the diversity of deubiquitinating enzymes and their emerging roles as cellular regulators.

Animals↗

PubMed2002

Antagonistic regulation of myogenesis by two deubiquitinating enzymes, UBP45 and UBP69.

Protein modification by ubiquitin is a dynamic and reversible process that is involved in the regulation of a variety of cellular processes. Here, we show that myogenic differentiation of embryonic muscle cells is antagonistically regulated by two deubiquitinating enzymes, UBP45 and UBP69, that are generated by alternative splicing. Both enzymes cleaved off ubiquitin from polyubiquitinated protein conjugates in vivo as well as from linear ubiquitin-protein fusions in vitro. In cultured myoblasts, the level of UBP69 mRNA markedly but transiently increased before membrane fusion, whereas that of UBP45 mRNA increased as the cells fused to form myotubes. Both myoblast fusion and accumulation of myosin heavy chain were dramatically stimulated by the stable expression of UBP69 but strongly attenuated by that of the catalytically inactive form of the protease, suggesting that the mutant enzyme acts dominant negatively on the function of the wild-type protease. In contrast, stable expression of UBP45 completely blocked both of the myogenic processes but that of inactive enzyme did not, indicating that the catalytic activity of the enzyme is essential for its inhibitory effects. These results indicate that differential expression of UBP45 and UBP69 is involved in the regulation of muscle cell differentiation.

Animals↗

PubMed2002

Involvement of protein phosphatase-1-mediated MARCKS translocation in myogenic differentiation of embryonic muscle cells.

Myristoylated alanine-rich C kinase substrate (MARCKS) translocates from the cytosol to the plasma membrane while mononucleated myoblasts fuse to form multinucleated myotubes. Here, we show that protein phosphatase-1-mediated dephosphorylation of MARCKS largely influences its subcellular localization and the fusion process. Treatment with okadaic acid or tautomycin, which are potent inhibitors of protein phosphatases and cell fusion, was found to reversibly block the MARCKS translocation. Moreover, the dephosphorylating activity against MARCKS markedly increased during myogenesis, and this increase was closely correlated with the membrane fusion of the cells. In addition, protein phosphatase-1 was identified as a major enzyme that is responsible for dephosphorylation of MARCKS. Furthermore, a mutation preventing MARCKS phosphorylation and thus facilitating MARCKS translocation resulted in promotion of the cell fusion. In contrast, overexpression of MARCKS carrying a mutation that blocks myristoylation and thus prevents the MARCKS translocation impaired the myoblast fusion. Together with the fact that MARCKS regulates the cytoskeleton dynamics by crosslinking the actin filaments in the plasma membrane and that myoblast fusion accompanies massive cytoskeleton reorganization, these results suggest that protein phosphatase-1-mediated MARCKS localization at the membrane is required for the fusion of embryonic muscle cells.

Amino Acid Sequence↗