Biomedical subjects

Keun Il Kim

Publications and source records attributed to Keun Il Kim.

At least 19 recordsLinked to original sources

PubMed2006

SUMOylation code in cancer development and metastasis.

Protein modification by small ubiquitin-like modifier (SUMO) controls diverse cellular functions of protein targets including transcription factors and coregulators mainly in the nucleus and participates in maintaining cellular homeostasis. In addition, SUMO system plays important roles in DNA damage repair and maintaining genome integrity. Thus, in some cases, the loss of control on SUMOylation or deSUMOylation processes causes a defect in maintaining homeostasis and hence gives a cue to cancer development. Furthermore, recent study showed that SUMO system is also involved in cancer metastasis. In this review, we will summarize and discuss the possible role of SUMO system in cancer development and metastasis.

Animals↗

PubMed2006

SUMO-specific protease SUSP4 positively regulates p53 by promoting Mdm2 self-ubiquitination.

The p53 tumour suppressor has a key role in the control of cell growth and differentiation, and in the maintenance of genome integrity. p53 is kept labile under normal conditions, but in response to stresses, such as DNA damage, it accumulates in the nucleus for induction of cell-cycle arrest, DNA repair or apoptosis. Mdm2 is an ubiquitin ligase that promotes p53 ubiquitination and degradation. Mdm2 is also self-ubiquitinated and degraded. Here, we identified a novel cascade for the increase in p53 level in response to DNA damage. A new SUMO-specific protease, SUSP4, removed SUMO-1 from Mdm2 and this desumoylation led to promotion of Mdm2 self-ubiquitination, resulting in p53 stabilization. Moreover, SUSP4 competed with p53 for binding to Mdm2, also resulting in p53 stabilization. Overexpression of SUSP4 inhibited cell growth, whereas knockdown of susp4 by RNA interference (RNAi) promoted of cell growth. UV damage induced SUSP4 expression, leading to an increase in p53 levels in parallel with a decrease in Mdm2 levels. These findings establish a new mechanism for the elevation of cellular p53 levels in response to UV damage.

Animals↗

PubMed2006

Tumor necrosis factor-alpha and interleukin-1beta increases CTRP1 expression in adipose tissue.

CTRP1, a member of the CTRP superfamily, consists of an N-terminal signal peptide sequence followed by a variable region, a collagen repeat domain, and a C-terminal globular domain. CTRP1 is expressed at high levels in adipose tissues of LPS-stimulated Sprague-Dawley rats. The LPS-induced increase in CTRP1 gene expression was found to be mediated by TNF-alpha and IL-1beta. Also, a high level of expression of CTRP1 mRNA was observed in adipose tissues of Zucker diabetic fatty (fa/fa) rats, compared to Sprague-Dawley rats in the absence of LPS stimulation. These findings indicate that CTRP1 expression may be associated with a low-grade chronic inflammation status in adipose tissues.

Adipokines↗

PubMed2006

UBP43 is a novel regulator of interferon signaling independent of its ISG15 isopeptidase activity.

Interferons (IFNs) regulate diverse cellular functions through activation of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Lack of Ubp43, an IFN-inducible ISG15 deconjugating enzyme, leads to IFN hypersensitivity in ubp43-/- mice, suggesting an important function of Ubp43 in downregulation of IFN responses. Here, we show that Ubp43 negatively regulates IFN signaling independent of its isopeptidase activity towards ISG15. Ubp43 functions specifically for type I IFN signaling by downregulating the JAK-STAT pathway at the level of the IFN receptor. Using molecular, biochemical, and genetic approaches, we demonstrate that Ubp43 specifically binds to the IFNAR2 receptor subunit and inhibits the activity of receptor-associated JAK1 by blocking the interaction between JAK and the IFN receptor. These data implicate Ubp43 as a novel in vivo inhibitor of signal transduction pathways that are specifically triggered by type I IFN.

Animals↗

PubMed2006

Adiponectin is a negative regulator of NK cell cytotoxicity.

NK cells are a key component of innate immune systems, and their activity is regulated by cytokines and hormones. Adiponectin, which is secreted from white adipose tissues, plays important roles in various diseases, including hypertension, cardiovascular diseases, inflammatory disorders, and cancer. In this study the effect of adiponectin on NK cell activity was investigated. Adiponectin was found to suppress the IL-2-enhanced cytotoxic activity of NK cells without affecting basal NK cell cytotoxicity and to inhibit IL-2-induced NF-kappaB activation via activation of the AMP-activated protein kinase, indicating that it suppresses IL-2-enhanced NK cell cytotoxicity through the AMP-activated protein kinase-mediated inhibition of NF-kappaB activation. IFN-gamma enhances NK cell cytotoxicity by causing an increase in the levels of expression of TRAIL and Fas ligand. The production of IFN-gamma, one of the NF-kappaB target genes in NK cells, was also found to be suppressed by adiponectin, accompanied by the subsequent down-regulation of IFN-gamma-inducible TRAIL and Fas ligand expression. These results clearly demonstrate that adiponectin is a potent negative regulator of IL-2-induced NK cell activation and thus may act as an in vivo regulator of anti-inflammatory functions.

Adiponectin↗

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

Ube1L and protein ISGylation are not essential for alpha/beta interferon signaling.

The expression of ubiquitin-like modifier ISG15 and its conjugation to target proteins are highly induced by interferon (IFN) stimulation and during viral and bacterial infections. However, the biological significance of this modification has not been clearly understood. To investigate the function of protein modification by ISG15, we generated a mouse model deficient in UBE1L, an ISG15-activating enzyme. Ube1L-/- mice did not produce ISG15 conjugates but expressed free ISG15 normally. ISGylation has been implicated in the reproduction and innate immunity. However, Ube1L-/- mice were fertile and exhibited normal antiviral responses against vesicular stomatitis virus and lymphocytic choriomeningitis virus infection. Our results indicate that UBE1L and protein ISGylation are not critical for IFN-alpha/beta signaling via JAK/STAT activation. Moreover, using Ube1L/Ubp43 double-deficient mice, we showed that lack of UBP43, but not the increase of protein ISGylation, is related to the increased IFN signaling in Ubp43-deficient mice.

Animals↗

PubMed2005

ISG15 modification of ubiquitin E2 Ubc13 disrupts its ability to form thioester bond with ubiquitin.

ISG15 was the first ubiquitin-like modifier to be identified. However, the function of ISG15 modification has been an enigma for many years. At present, no data are available about the function of ISGylation for any target. In this paper, we report the identification of Ubc13, which forms a unique ubiquitin-conjugating enzyme (Ubc) complex with ubiquitin enzyme variant Mms2 and generates atypical Lys63-linked ubiquitin conjugates, as one of the targets of ISG15 modification. Furthermore, we identify Lys92 as the only ISG15 modification site in Ubc13, which is the first report about the ISG15 modification site. Using the "covalent affinity" purification assay, we found that unmodified Ubc13 can bind to the ubiquitin-agarose, whereas ISGylated Ubc13 cannot. This result indicates that ISGylation of Ubc13 disrupts its ability to form thioester bond with ubiquitin.

Amino Acid Sequence↗

PubMed2005

Enhanced antibacterial potential in UBP43-deficient mice against Salmonella typhimurium infection by up-regulating type I IFN signaling.

ISG15 is an IFN-inducible ubiquitin-like protein and its expression and conjugation to target proteins are dramatically induced upon viral or bacterial infection. We have generated a UBP43 knockout mouse model that is lacking an ISG15-specific isopeptidase to study the biological role of the protein ISGylation system. We report that UBP43-deficient mice are hypersensitive to LPS-induced lethality and that TIR domain-containing adapter inducing IFN-beta --> IFN regulatory factor 3 --> type I IFN is the major axis to induce protein ISGylation and UBP43 expression in macrophages upon LPS treatment. In ubp43(-/-) macrophages, upon LPS treatment we detected increased expression of IFN-stimulated genes, including genes for several cytokines and chemokines involved in the innate immune response. The ubp43(-/-) mice were able to restrict the growth of Salmonella typhimurium more efficiently than wild-type mice. These results clearly demonstrate two aspects of IFN-signaling, a beneficial effect against pathogens but a detriment to the body without strict control.

Adaptor Proteins, Vesicular Transport↗

PubMed2005

UBP43, an ISG15-specific deconjugating enzyme: expression, purification, and enzymatic assays.

UBP43 is the only deconjugating enzyme for the protein ISGylation system thus far identified. UBP43 activity is not critical for precursor processing, as UBP43-deficent cells can generate ISG15 conjugates upon type I interferon treatment. However, UBP43 deficiency caused a defect in the negative regulation of type I interferon signaling, resulting in enhanced and prolonged activation of Jak/Stat upon type I interferon treatment. This chapter describes the expression, purification, and enzymatic assays for UBP43.

Animals↗

PubMed2004

Role of ISG15 protease UBP43 (USP18) in innate immunity to viral infection.

Innate immune responses provide the host with an early protection barrier against infectious agents, including viruses, and help shape the nature and quality of the subsequent adaptive immune responses of the host. Expression of ISG15 (UCRP), a ubiquitin-like protein, and protein ISGylation are highly increased upon viral infection. We have identified UBP43 (USP18) as an ISG15 deconjugating protease. Protein ISGylation is enhanced in cells deficient in UBP43 (ref. 6). Here we have examined the role of UBP43, encoded by the gene Usp18, in innate immunity to virus infection. Usp18(-/-) mice were resistant to the fatal lymphocytic choriomeningitis and myeloencephalitis that developed in wild-type mice after intracerebral inoculation with lymphocytic choriomeningitis virus (LCMV) or vesicular stomatitis virus (VSV), respectively. Survival of Usp18(-/-) mice after intracerebral LCMV infection correlated with a severe inhibition of LCMV RNA replication and antigen expression in the brain and increased levels of protein ISGylation. Consistent with these findings, mouse embryonic fibroblasts (MEF) and bone marrow-derived macrophages from Usp18(-/-) mice showed restricted LCMV replication. Moreover, MEF from Usp18(-/-) mice showed enhanced interferon-mediated resistance to the cytopathic effect caused by VSV and Sindbis virus (SNV). This report provides the first direct evidence that the ISG15 protease UBP43 and possibly protein ISGylation have a role in innate immunity against viral infection.

Animals↗

PubMed2004

Interferon-inducible ubiquitin E2, Ubc8, is a conjugating enzyme for protein ISGylation.

Protein ISGylation is unique among ubiquitin-like conjugation systems in that the expression and conjugation processes are induced by specific stimuli, mainly via the alpha/beta interferon signaling pathway. It has been suggested that protein ISGylation plays a special role in the immune response, because of its interferon-signal dependency and its appearance only in higher eukaryotic organisms. Here, we report the identification of an ISG15-conjugating enzyme, Ubc8. Like other components of the protein ISGylation system (ISG15, UBE1L, and UBP43), Ubc8 is an interferon-inducible protein. Ubc8 clearly mediates protein ISGylation in transfection assays. The reduction of Ubc8 expression by small interfering RNA causes a decrease in protein ISGylation in HeLa cells upon interferon treatment. Neither UbcH7/UbcM4, the closest homologue of Ubc8 among known ubiquitin E2s, nor the small ubiquitin-like modifier E2 Ubc9 supports protein ISGylation. These findings strongly suggest that Ubc8 is a major ISG15-conjugating enzyme responsible for protein ISGylation upon interferon stimulation. Furthermore, we established an assay system to detect ISGylated target proteins by cotransfection of ISG15, UBE1L, and Ubc8 together with a target protein to be analyzed. This method provides an easy and effective way to identify new targets for the ISGylation system and will facilitate related studies.

Animals↗

PubMed2003

ISG15, not just another ubiquitin-like protein.

ISG15 is a ubiquitin-like protein containing two ubiquitin homology domains and becomes conjugated to a variety of proteins when cells are treated with type I interferon or lipopolysaccharide. Although ISG15 shares several common properties with those of other ubiquitin-like molecules, it is a unique member, whose expression and conjugation to target proteins are tightly regulated by specific signaling pathways, indicating it may be associated with specialized functions in innate immune system. Loss of UBP43 (USP18), a protease that specifically removes ISG15 from ISG15-modified proteins, in mice leads to decreased life span, brain cell injury, and hypersensitivity to interferon stimulation. In UBP43 deficient cells, interferon induces a prolonged Stat1 tyrosine phosphorylation and DNA binding, which result in a prolonged and enhanced activation of interferon-stimulated genes.

Amino Acid Sequence↗

PubMed2003

Protein ISGylation modulates the JAK-STAT signaling pathway.

ISG15 is one of the most strongly induced genes upon viral infection, type I interferon (IFN) stimulation, and lipopolysaccharide (LPS) stimulation. Here we report that mice lacking UBP43, a protease that removes ISG15 from ISGylated proteins, are hypersensitive to type I IFN. Most importantly, in UBP43-deficient cells, IFN-beta induces a prolonged Stat1 tyrosine phosphorylation, DNA binding, and IFN-mediated gene activation. Furthermore, restoration of ISG15 conjugation in protein ISGylation-defective K562 cells increases IFN-stimulated promoter activity. These findings identify UBP43 as a novel negative regulator of IFN signaling and suggest the involvement of protein ISGylation in the regulation of the JAK-STAT pathway.

Animals↗

PubMed2003

High-throughput immunoblotting. Ubiquitiin-like protein ISG15 modifies key regulators of signal transduction.

ISG15 is a ubiquitin-like protein that conjugates to numerous proteins in cells treated with interferon or lipopolysaccharide. Dysregulation of protein ISG15 modification (ISGylation) in mice leads to decreased life expectancy, brain cell injury, and hypersensitivity to interferon. Although ISG15 was identified more than two decades ago, the exact biochemical and physiological functions of ISG15-modification remain unknown, and the proteins targeted by ISG15 have not been identified. The major purpose of this work was to identify ISG15 targets among well characterized proteins that could be used as models for biological studies. We purified ISGylated proteins from human thymus by immunoaffinity chromatography and analyzed ISG15 conjugates by a high-throughput Western blot screen (PowerBlot). We found that three key regulators of signal transduction, phospholipase Cgamma1, Jak1, and ERK1 are modified by ISG15. In addition to that, we demonstrate that transcription factor Stat1, an immediate substrate of Jak1 kinase, is also ISGylated. Using whole cell protein extracts and phospholipase Cgamma1 as an example we demonstrate that ISG15 conjugates are not accumulated in cells treated with specific inhibitors of proteasomes. Our work suggests a role for ISG15 in the regulation of multiple signal transduction pathways and offers attractive models to further elucidate the biochemical function of ISGylation.

Child↗

PubMed2003

Pleuropulmonary blastoma in a young adult presenting as a ruptured cystic teratoma in radiology.

Pleuropulmonary blastoma (PPB) is a rare malignant dysontogenetic neoplasm primarily affecting children and is characterized histologically by a variably mixed blastematous and sarcomatous patterns. We herein report a very exceptional adult case of PPB. A 21-yr-old male patient presented with a left chest pain of two weeks' duration. A computed tomography scan revealed a large, multicystic tumor occupying the left lower hemithorax, leading to the impression of a ruptured mediastinal cystic teratoma. A thoracotomy for resection of the tumor was performed. On histologic examination, the tumor consisted of cystic walls and associated solid lesions which showed undifferentiated blastemal tissues with focal fibrosarcomatous and rhabdoid features. Immunohistochemically the tumor cells only showed diffuse strong positivity for vimentin. The histologic findings corresponded to a type II PPB. The authors suggest that PPB, especially of type I or II, should be included in the radiologic differential diagnosis of mediastinal cystic neoplasms in a young adult.

Adult↗

PubMed2002

UBP43 (USP18) specifically removes ISG15 from conjugated proteins.

UBP43 shows significant homology to well characterized ubiquitin-specific proteases and previously was shown to hydrolyze ubiquitin-beta-galactosidase fusions in Escherichia coli. In our assays, the activity of UBP43 toward Ub fusions was undetectable in vitro directing us to investigate the possibility of Ub-like proteins such as SUMO, Nedd8, and ISG15 as probable substrates. We consequently demonstrate that UBP43 can efficiently cleave only ISG15 fusions including native ISG15 conjugates linked via isopeptide bonds. In addition to commonly used methods we introduce a new experimental design featuring ISG15-UBP43 fusion self-processing. Deletion of the UBP43 gene in mouse leads to a massive increase of ISG15 conjugates in tissues indicating that UBP43 is a major ISG15-specific protease. UBP43 is the first bona fide ISG15-specific protease reported. Both ISG15 and UBP43 genes are known to be strongly induced by interferon, genotoxic stress, and viral infection. We postulate that UBP43 is necessary to maintain a critical cellular balance of ISG15-conjugated proteins in both healthy and stressed organisms.

Animals↗

PubMed2002

Versatile protein tag, SUMO: its enzymology and biological function.

Small ubiquitin-related modifier (SUMO) is a member of a ubiquitin-like protein family that regulates cellular function of a variety of target proteins. SUMO and ubiquitin are synthesized as precursors that need to be processed prior to conjugation to target proteins, and their mature forms have a similar tertiary structure. The mechanism for SUMO conjugation is also analogous to that of the ubiquitin system, such as the utilization of E1, E2, and E3 cascade enzymes. However, the biological consequence of SUMO modification is quite different from that of the ubiquitin system. Whereas ubiquitination of most proteins is for the degradative pathway, SUMO modification of target proteins is involved in nuclear protein targeting, formation of subnuclear structures, regulation of transcriptional activities or DNA binding abilities of transcription factors, and control of protein stability. This review will summarize the recent progress made in the enzymology of SUMO and its biological significance.

Amino Acid Sequence↗