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Biomedical subjects

J G Park

Publications and source records attributed to J G Park.

At least 19 recordsLinked to original sources
PubMed2004

Analysis of insulin signalling by RNAi-based gene silencing.

Using siRNA-mediated gene silencing in cultured adipocytes, we have dissected the insulin-signalling pathway leading to translocation of GLUT4 glucose transporters to the plasma membrane. RNAi (RNA interference)-based depletion of components in the putative TC10 pathway (CAP, CrkII and c-Cbl plus Cbl-b) or the phospholipase Cgamma pathway failed to diminish insulin signalling to GLUT4. Within the phosphoinositide 3-kinase pathway, loss of the 5'-phosphatidylinositol 3,4,5-trisphosphate phosphatase SHIP2 was also without effect, whereas depletion of the 3'-phosphatase PTEN significantly enhanced insulin action. Downstream of phosphatidylinositol 3,4,5-trisphosphate and PDK1, silencing the genes encoding the protein kinases Akt1/PKBalpha, or CISK(SGK3) or protein kinases Clambda/zeta had little or no effect, but loss of Akt2/PKBbeta significantly attenuated GLUT4 regulation by insulin. These results show that Akt2/PKBbeta is the key downstream intermediate within the phosphoinositide 3-kinase pathway linked to insulin action on GLUT4 in cultured adipocytes, whereas PTEN is a potent negative regulator of this pathway.

Adipocytes↗
PubMed2001

PTEN gene mutations in colorectal cancers displaying microsatellite instability.

To determine the relationship between the mutation of the PTEN gene and genomic instability in human colorectal cancer, we screened the PTEN gene in 32 colorectal cancers (eight cell lines and 24 tissues) displaying microsatellite instability (MSI) and 32 colorectal cancers (six cell lines and 26 tissues) displaying microsatellite stability (MSS). Of 64 samples, six frameshift mutations were identified in six MSI colorectal cancers (two cell lines and four tumor tissues) but not in MSS colorectal cancers. Of the six MSI colorectal cancers containing PTEN mutation, two case (one cell line and one tumor tissue) showed biallelic mutation of PTEN. Furthermore, to compare the frequency of PTEN mutation with that of other MSI target genes, the mononucleotide repeat sequences of TGF-betaRII, BAX, IGFIIR, hMSH6 and hMSH3 were analyzed. The frequencies of frameshift mutation were revealed 78% in TGF-betaRII, 56% in BAX, 46.9% in hMSH3, 37.5% in hMSH6, 21.9% in IGFIIR, and 18.8% in PTEN. These results suggest that the PTEN gene is a target of genomic instability in MSI colorectal tumorigenesis.

Colorectal Neoplasms↗
PubMed2001

PYK2 as a mediator of endothelin-1/G alpha 11 signaling to GLUT4 glucose transporters.

Endothelin-1 (ET-1) signaling through G alpha(q/11) stimulates translocation of intracellular GLUT4 glucose transporters to the plasma membrane of 3T3-L1 adipocytes by an unknown mechanism that requires protein tyrosine phosphorylation and ADP-ribosylation factor 6 (ARF6) but is independent of phosphatidylinositol 3 (PI3)-kinase. In contrast, insulin action on this process requires PI3-kinase but not ARF6. Here we report the identification of two proteins selectively tyrosine-phosphorylated in response to ET-1 but not insulin: the Ca(2+)-activated tyrosine kinase PYK2 and its physiological substrate, the adhesion scaffold protein paxillin. Endogenous paxillin as well as expressed Myc-tagged PYK2 or a Myc-tagged kinase-deficient PYK2 protein were acutely directed to F-actin-rich adhesion sites from the adipocyte cytoplasm in response to ET-1 but not insulin. CADTK-related non-kinase (CRNK) is a dominant negative form of PYK2 containing the C-terminal portion of the protein, which binds paxillin but lacks the PYK2 autophosphorylation site (Tyr(402)). CRNK expression in 3T3-L1 adipocytes inhibited ET-1-mediated F-actin polymerization and translocation of Myc-tagged GLUT4-enhanced green fluorescent protein (EGFP) to the plasma membrane without disrupting insulin action on these processes. These data reveal the tyrosine kinase PYK2 as a required signaling element in the regulation of GLUT4 recycling in 3T3-L1 adipocytes by ET-1, whereas insulin signaling is directed through a different pathway.

3T3 Cells↗
PubMed2001

Signaling complexes of the FERM domain-containing protein GRSP1 bound to ARF exchange factor GRP1.

GRP1 is a member of a family of proteins that contain a coiled-coil region, a Sec7 homology domain with guanosine nucleotide exchange activity for the ARF GTP-binding proteins, and a pleckstrin homology domain at the C terminus. The pleckstrin homology domain of GRP1 binds phosphatidylinositol (3,4,5) trisphosphate and mediates the translocation of GRP1 to the plasma membrane upon agonist stimulation of PI 3-kinase activity. Using a (32)P-labeled GRP1 probe to screen a mouse brain cDNA expression library, we isolated a cDNA clone encoding a GRP1-binding partner (GRSP1) that exists as two different splice variants in brain and lung. The GRSP1 protein contains a FERM protein interaction domain as well as two coiled coil domains and may therefore function as a scaffolding protein. Mapping experiments revealed that the interaction of GRP1 and GRSP1 occurs through the coiled coil domains in the two proteins. Immunodepletion experiments indicate that virtually all of the endogenous GRSP1 protein exists as a complex with GRP1 in lung. When co-expressed in Chinese hamster ovary cells expressing the human insulin receptor, both proteins display a diffuse, cytoplasmic localization. Acute translocation and co-localization of GRSP1 and GRP1 to ruffles in the plasma membrane was evident after insulin stimulation. These results identify GRSP1 as a novel member of GRP1 signaling complexes that are acutely recruited to plasma membrane ruffles in response to insulin receptor signaling.

ADP-Ribosylation Factors↗
PubMed2001

Mutations in fibroblast growth factor receptor 2 and fibroblast growth factor receptor 3 genes associated with human gastric and colorectal cancers.

Autosomal dominant disorders of skeletal and cranial development have been linked to fibroblast growth factor receptor (FGFR) 2 and FGFR3. Here we report two identical mutations in FGFR2 that cause craniosynostosis syndromes, Crouzon, Apert, and Pfeiffer in gastric carcinoma. A missense mutation (Ser267Pro) in exon IIIa and a splice site mutation (940-2A-->G) in exon IIIc were detected in gastric cancer patients. Interestingly, these heterozygous somatic mutations are identical to the germinal activating mutations in FGFR2 reported previously in craniosynostosis syndromes. In addition, the two novel mutations of FGFR3 in colorectal carcinomas were identified. All identified mutations occurred at highly conserved sequences, not only in the FGFR family of molecules, but also throughout evolution and clustered in the immunoglobulin-like loop-III domain, highlighting the functional importance of this domain. Our results indicate that FGFR2 and FGFR3, in addition to their potential role in skeletal dysplasias, play an important role in tumorigenesis.

Amino Acid Sequence↗
PubMed2001

Synthesis and muscarinic activity of 1,2,3,4-tetrahydropyrimidine derivatives.

3-Methyl-1,2,3,4-tetrahydropyrimidine-5-carbaldehyde O-substituted oximes 4 and 1-(3-methyl-1,2,3,4-tetrahydropyrimidin-5-yl)ethanone O-substituted oximes 9 have been prepared as bioisosteric congeners of arecoline which is a muscarinic agonist for treatment of Alzheimer's disease. Starting from pyrimidine-5-carbaldehyde 1, formation of the 3-methylpyrimidinium salt and subsequent reduction afforded 1,2,3,4-tetrahydropyrimidine derivatives which were converted into oxalate salts in the interest of purity and stability. Binding affinities of prepared compounds for the cloned human muscarinic M1 receptor (h-M1) were determined by radioligand binding assay using [3H]-N-methylscopolamine (NMS).

Animals↗
PubMed2001

Identification of four novel RB1 germline mutations in Korean retinoblastoma patients.

To elucidate RB1 germline mutations in Korean retinoblastoma patients, DNA samples from 14 children with bilateral (including three familial cases) and 19 children with unilateral retinoblastoma were analyzed. We found germline mutations in three out of 14 bilateral cases and one out of 19 unilateral cases. There were no germline mutations in the three familial cases. PCR-SSCP from each exon showed bandshifts in four patients which, upon sequencing, were shown to be K616E in exon 19 (c.1846A>G), an AA insertion in exon 7 (c.684-685insAA), R500G in exon 16 (c.1498A>G), and an A insertion in exon 23 (c.2391-2392insA), respectively. Hum Mutat 18:252, 2001.

Chromosomes, Human, Pair 13↗
PubMed2001

Detection and typing of human papillomavirus in anal epidermoid carcinomas: sequence variation in the E7 gene of human papillomavirus Type 16.

INTRODUCTION: Human papillomavirus, particularly Type 16, plays a central role in the development of anogenital squamous-cell carcinomas. A common sequence variation of human papillomavirus Type 16 in cervical cancer cell lines and in cervical cancer tissues from Korean patients was recently reported. The present study was performed to determine the integration type of human papillomavirus DNA in anal epidermoid carcinoma and to identify the common sequence variations in the human papillomavirus Type 16 E7 gene that had been previously reported. METHODS: Twenty-one formalin-fixed, paraffin-embedded specimens collected from 29 patients with anal epidermoid carcinomas treated at the Seoul National University Hospital over a ten-year period (1989-1998) were investigated. Genomic DNA from the 21 specimens was extracted and analyzed using the polymerase chain reaction with a general primer and a type-specific primer for human papillomavirus Types 16 and 18. Direct sequencing was performed. As a control, 13 normal anal epithelia available from these patients were microdissected. As another control, 21 hemorrhoidal squamous epithelia obtained from a demographically adjusted group were also analyzed. RESULTS: Human papillomavirus Type 16 DNA was present in all 21 anal epidermoid carcinomas. All controls were negative for human papillomavirus DNA. Sequence analysis revealed that 57 percent (12/21) specimens showed two types of sequence variation in the E7 gene. One variant with a single nucleotide change at position 647 (amino acid 29, AAT-->AGT, asparagine to serine) was found in 38 percent (8/21) of the samples. This variant has been detected in cervical cancers from Korean patients: 19 (39 percent) of 49 cervical cancer tissues and 6 (50 percent) of 12 cervical cancer cell lines. Another single nucleotide change at position 645 (amino acid 28, TTA-->TTC, leucine to phenylalanine) was found in 19 percent (4/21) of the samples. These two variants exhibit a change of amino acid affecting the critical sites for Rb binding. CONCLUSION: Human papillomavirus Type 16 was found to be present in all 21 anal epidermoid carcinomas. Furthermore, in the Korean population, the most common sequence variant found in cervical

Anus Neoplasms↗
PubMed2001

A novel tumor-associated mucin of gastrointestinal carcinoma.

PURPOSE: To identify a new tumor-associated antigen, a monoclonal antibody, SC142, was produced by immunizing mice with a stomach cancer cell line. The tumor specificity of mAb SC142 was studied by immunohistochemical staining, and the biochemical characteristics of this new gastrointestinal tumor-associated antigen were also studied. METHODS: The expression of SC142-reactive antigen was investigated in various cancers by immunohistochemical staining. The SC142-reactive antigen was characterized by immunoblotting, sodium metaperiodate treatment assay, O-glycanase digestion assay, and lectin binding assay. RESULTS: The SC142-reactive antigen was highly expressed in 78% of gastric cancers (29/37) and 87% of colon cancers (27/31). No normal colon or stomach tissues remote from the tumor were positive for the antigen. The antibody also reacted with other tumors of epithelial origin such as lung squamous cell cancer (2/4), breast ductal cancer (2/20), bladder transitional cell carcinoma (4/6), and uterine cancer (3/16). Western blot analysis of the antigen revealed glycoprotein(s) which migrated as a smear ranging from the origin of the gel to about the 80 kDa region. The reactivity of this antigen with SC142 was reduced by sodium metaperiodate treatment or O-glycanase digestion, but not by N-glycanase, suggesting that the epitope is an O-glycan. In lectin-binding assay, this antigen reacted only with wheat germ agglutinin but not with Ricinus communis agglutinin, Datura stramonium agglutinin, and Sambucus nigra agglutinin. CONCLUSIONS: Our findings indicate that the antigen defined by SC142 is a tumor-associated antigen that could differentiate the gastrointestinal cancer cells from the normal cells. Therefore, SC142 may become a valuable tool for the immunohistochemical diagnosis and tumor immunoscintigraphy of the gastrointestinal cancer patients.

Animals↗
PubMed2001

Phosphorylation of purified recombinant hepatitis B virus-X protein by mitogen-activated protein kinase and protein kinase C in vitro.

The recombinant human hepatitis B virus-X protein (rhHBx) has been expressed as inclusion bodies in Escherichia coli and purified. By sequential dialysis of urea, rhHBx was folded into the native structure, which was demonstrated by both the efficacy of its transcriptional activation of the adenovirus major late promoter, fluorescence and circular dichroism (CD) analysis. The increase in CD values at 220 nm and a corresponding blue shift of the intrinsic fluorescence emission confirmed the ability of HBx to refold in lower concentrations of urea to produce the active protein. After purification and renaturation, the rhHBx protein was found to be phosphorylated by protein kinase C (PKC) and mitogen-activated protein kinase (MAPK). In vivo phosphorylation of HBx was also demonstrated. Although PKC and MAPK enhance the HBx phosphorylation in vitro, neither protein kinase A nor caseine kinase II (CKII) phosphorylate HBx protein, though there are possible substrate residues of both kinases in HBx protein. Phosphoamino acid analysis of the total acid hydrolyzed HBx showed that serine residues can be phosphorylated by PKC or MAPK.

Amino Acid Sequence↗
PubMed2001

Genetic changes of hOGG1 and the activity of oh8Gua glycosylase in colon cancer.

oh8Gua glycosylase repairs DNA by removing oh8Gua, a highly mutagenic oxidative DNA adduct. Recently, the gene for human oh8Gua glycosylase (hOGG1) was cloned and several mutational types have been reported. However, the implications of such mutations in human cancer have not been clearly demonstrated. To test the involvement of hOGG1 mutation in colon carcinogenesis, we analysed the genetic changes of hOGG1 and the activity of oh8Gua glycosylase in 15 paired normal and tumorous colon specimens. The activity of antioxidant enzymes (catalase and superoxide dismutase (SOD)) and extent of oxidative cellular damage (oh8Gua and malondialdehyde) were also assessed to compare the oxidative status of normal and tumour tissues. An Arg 154 to His mutation was detected in two tumour samples, but not in the corresponding normal tissues. A Ser 326 to Cys mutation (polymorphism) was found in both the normal and tumour tissues of 3 patients. However, neither the Arg 154 to His mutation nor the polymorphism at codon 326 significantly decreased the oh8Gua glycosylase activity. The mean activity of oh8Gua glycosylase was significantly higher in the tumours than in normal tissues (P=0.022). Antioxidant enzyme activities were decreased (catalase; P=0.004 and SOD; P=0.002), and the extent of oxidative damage correspondingly increased in the tumour tissues (oh8Gua; P=0.007 and malondialdehyde; P=0.046). Although the sample size was limited, these results suggest that the somatic mutation or the polymorphism of hOGG1 is less likely to be involved in colon carcinogenesis. Nevertheless, the greater oxidative DNA damage in the tumour tissues, as a possible result of impaired antioxidant activity, implies an important role for oxygen free-radicals in colon carcinogenesis.

Adult↗
PubMed2001

Microsatellite instability in double primary cancers of the colorectum and stomach.

Little is known about genetic alterations of patients who present multiple primary cancers. We hypothesized that microsatellite instability (MSI) is one of the underlying genetic factors in the development of double primary cancers in colorectal cancer patients. We examined for MSI in 41 colorectal cancer patients who presented with extra-colonic primary cancers consisted of 17 gastric and 24 non-gastric cancers. Coincident MSI+ in tumors of two organs were observed in 3 (17.7%) of 17 patients with colon and stomach cancers and 0 of 24 patients with colon and non-gastric cancers (P =.03). In 17 patients with colon and stomach cancers, 6 (31.6%) of 19 colon cancers and 3 (17.7%) of 17 gastric cancers exhibited MSI+. Among four patients with metachronous colon cancers who were identified within the 41 double primary cancer patients, two patients were associated with the MSI+ phenotype. In summary, the prevalent coincidence of MSI suggests that genetic defect of mismatch repair deficiency may be responsible for a small subset of double primary cancers of the colorectum and stomach.

Aged↗
PubMed2001

G(alpha)11 signaling through ARF6 regulates F-actin mobilization and GLUT4 glucose transporter translocation to the plasma membrane.

The action of insulin to recruit the intracellular GLUT4 glucose transporter to the plasma membrane of 3T3-L1 adipocytes is mimicked by endothelin 1, which signals through trimeric G(alpha)q or G(alpha)11 proteins. Here we report that murine G(alpha)11 is most abundant in fat and that expression of the constitutively active form of G(alpha)11 [G(alpha)11(Q209L)] in 3T3-L1 adipocytes causes recruitment of GLUT4 to the plasma membrane and stimulation of 2-deoxyglucose uptake. In contrast to the action of insulin on GLUT4, the effects of endothelin 1 and G(alpha)11 were not inhibited by the phosphatidylinositol 3-kinase inhibitor wortmannin at 100 nM. Signaling by insulin, endothelin 1, or G(alpha)11(Q209L) also mobilized cortical F-actin in cultured adipocytes. Importantly, GLUT4 translocation caused by all three agents was blocked upon disassembly of F-actin by latrunculin B, suggesting that the F-actin polymerization caused by these agents may be required for their effects on GLUT4. Remarkably, expression of a dominant inhibitory form of the actin-regulatory GTPase ARF6 [ARF6(T27N)] in cultured adipocytes selectively inhibited both F-actin formation and GLUT4 translocation in response to endothelin 1 but not insulin. These data indicate that ARF6 is a required downstream element in endothelin 1 signaling through G(alpha)11 to regulate cortical actin and GLUT4 translocation in cultured adipocytes, while insulin action involves different signaling pathways.

ADP-Ribosylation Factor 6↗
PubMed2001

Classic Kaposi sarcoma presenting as rapidly growing nodules.

Classic Kaposi sarcoma (KS) is a sporadic disease that usually affects persons older than 50 years, with a distinct male predominance. Although classic KS has a protracted, indolent course, there appears to be a rare disseminated fulminant type. This report describes a case of classic KS, presenting as a very rapid enlargement and dissemination of skin lesions, without evidence of human immunodeficiency virus (HIV) infection or involvement of other internal organs.

Antineoplastic Agents, Phytogenic↗