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Biomedical subjects

J Park

Publications and source records attributed to J Park.

At least 253 records · Page 14Linked to original sources
PubMed1998

Heterogeneity of guanylyl cyclase C expressed by human colorectal cancer cell lines in vitro.

In humans, guanylyl cyclase C (GCC) is expressed by mucosal cells lining the intestine, from the duodenum to the rectum, but not by extraintestinal tissues. Expression of GCC persists after mucosal cells undergo neoplastic transformation, and this protein has been identified in all primary and metastatic colorectal tumors examined to date, suggesting that GCC may be a highly specific biomarker for colorectal cancer. The utility of GCC as a diagnostic biomarker and therapeutic target is predicated, in part, on defining the variability of its expression in colorectal cancer cells. Similarly, the utility of this biomarker to define tumor burden in diagnosing, staging, and postoperative surveillance of patients is predicated on quantifying GCC expression in cancer cells in tissues and blood. The present studies examined the heterogeneity of GCC expression in eight human colorectal carcinoma cell lines in vitro representing the full spectrum of cytological differentiation. Quantification of GCC expression by ligand binding and stimulation of cGMP accumulation demonstrated that functional GCC expression is heterogeneous in different colorectal cancer cell lines. Qualitative reverse transcription (RT)-PCR demonstrated that all colorectal cancer cells examined expressed GCC mRNA. However, GCC expression varied 100-fold in different colorectal cancer cell lines, determined by a novel quantitative RT-PCR assay. Functional and molecular expressions of GCC were unrelated to the differentiation state of cancer cells. These studies suggest that GCC is heterogeneously expressed by colorectal cancer cells in vitro and suggest a role for quantitative RT-PCR analysis in the development of diagnostic tests using GCC as a biomarker for metastatic colorectal cancer.

Biomarkers, Tumor↗
PubMed1998

The role of oxygen in the antiviral activity of hypericin and hypocrellin.

The light-induced antiviral activity of hypericin and hypocrellin in the presence and absence of oxygen was examined under experimental conditions where the effect of oxygen depletion could be quantified. There was a significant reduction of light-induced antiviral activity of hypericin and hypocrellin under hypoxic conditions. Interestingly, antiviral activity of hypocrellin was not observed at low oxygen levels at which hypericin retained measurable virucidal activity. This suggests that additional pathways, such as the generation of protons from excited states of hypericin, may enhance the biological activity of activated oxygen species.

Adenosine Triphosphate↗
PubMed1997

Integrin-mediated activation of mitogen-activated protein kinase is independent of the activation of protein kinase C epsilon during the spreading of HeLa cells on a gelatin substratum.

Spreading of HeLa cells on a gelatin substratum is initiated by the activation of protein kinase C epsilon (PKC epsilon) upon contact of the cells with the matrix. In this study, we examined the functional role of PKC epsilon in the activation of mitogen-activated protein kinase (MAP kinase) and its relationship to cell spreading. MAP kinase isoforms, Erk-1 and -2, are activated upon attachment of HeLa cells to gelatin. Inhibition of PKC with calphostin C blocked cell spreading without any effect on MAP kinase activation. In contrast, inhibition of MAP kinase kinase blocked adhesion-induced MAP kinase activation, but showed no effect on either translocation of PKC epsilon or cell spreading. Thus, activation of PKC epsilon that occurs upon HeLa cell attachment to gelatin is related to cell spreading but not to the activation of MAP kinase, and MAP kinase is activated upon HeLa cell attachment in the absence of cell spreading.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1997

Intermediate sequences increase the detection of homology between sequences.

Two homologous sequences, which have diverged beyond the point where their homology can be recognised by a simple direct comparison, can be related through a third sequence that is suitably intermediate between the two. High scores, for a sequence match between the first and third sequences and between the second and the third sequences, imply that the first and second sequences are related even though their own match score is low. We have tested the usefulness of this idea using a database that contains the sequences of 971 protein domains whose structures are known and whose residue identities with each other are some 40% or less (PDB40D). On the basis of sequence and structural information, 2143 pairs of these sequences are known to have an evolutionary relationship. FASTA, in an all-against-all comparison of the sequences in the database, detected 320 (15%) of these relationships as well as three false positive (i.e. 1% error rate). Using intermediate sequences found by FASTA matches of PDB40D sequences to those in the large non-redundant OWL database we could detect 550 evolutionary relationships with an error rate of 1%. This means the intermediate sequence procedure increases the ability to recognise the evolutionary relationships amongst the PDB40D sequences by 70%.

Amino Acid Sequence↗
PubMed1997

Differential transcriptional regulation of the two vascular endothelial growth factor receptor genes. Flt-1, but not Flk-1/KDR, is up-regulated by hypoxia.

Vascular endothelial growth factor (VEGF) and its two endothelial cell-specific receptor tyrosine kinases, Flk-1/KDR and Flt-1, play a key role in physiological and pathological angiogenesis. Hypoxia has been shown to be a major mechanism for up-regulation of VEGF and its receptors in vivo. When we exposed human umbilical vein endothelial cells to hypoxic conditions in vitro, we observed increased levels of Flt-1 expression. In contrast, Flk-1/KDR mRNA levels were unchanged or slightly repressed. These findings suggest a differential transcriptional regulation of the two receptors by hypoxia. To identify regulatory elements involved in the hypoxic response, promoter regions of the mouse Flt-1 and Flk-1/KDR genes were isolated and tested in conjunction with luciferase reporter gene. In transient transfection assays, hypoxia led to strong transcriptional activation of the Flt-1 promoter, whereas Flk-1/KDR transcription was essentially unchanged. Promoter deletion analysis demonstrated a 430-bp region of the Flt-1 promoter to be required for transcriptional activation in response to hypoxia. This region includes a heptamer sequence matching the hypoxia-inducible factor-1 (HIF) consensus binding site previously found in other hypoxia-inducible genes such as the VEGF gene and erythropoietin gene. We further narrowed down the element mediating the hypoxia response to a 40-base pair sequence including the putative HIF binding site. We show that this element acts like an enhancer, since it activated transcription irrespective of its location or orientation in the construct. Furthermore, mutations within the putative HIF consensus binding site lead to impaired transcriptional activation by hypoxia. These findings indicate that, unlike the KDR/Flk-1 gene, the Flt-1 receptor gene is directly up-regulated by hypoxia via a hypoxia-inducible enhancer element located at positions -976 to -937 of the Flt-1 promoter.

Amino Acid Sequence↗
PubMed1997

Differential modulation of short and long latency sensory responses in the SI cortex by IL-6.

The effects of topical application of interleukin-6 (IL-6) on the short and long latency evoked unit responses of the neurones in the primary somatosensory (SI) cortex were determined quantitatively in anaesthetized rats. IL-6 (0.01, 0.1, 1.0 units) significantly suppressed (-15.13 +/- 3.4%) short latency afferent sensory responses, while it induced profound facilitation (+464.74 +/- 132.7%) of long latency responses in a dose-dependent manner. IL-6-induced afferent modulations fully recovered by 60 min after drug administration. In control experiments, saline solution containing 0.2% bovine serum albumin, used as a vehicle, did not affect afferent sensory transmission. Implications of these results are discussed with reference to the different somatosensory functions of short and long latency response components in the SI cortex.

Administration, Topical↗
PubMed1997

Identification of YH439 and its metabolites in rat urine by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry.

YH439 is a potential drug candidate for the treatment of various hepatic disorders. YH439 and its three metabolites have been identified in rat urine by liquid chromatography-mass spectrometry (LC-MS) and by gas chromatography (GC)-MS. Identification of YH439 and its metabolites was established by comparing their GC retention times and mass spectra with those of the synthesized authentic standards. Both electron impact- and positive chemical ionization MS have been evaluated. The metabolism study was performed in the rat using oral administration of the drug. A major metabolite (YH438) was identified as the N-dealkylation product of YH439. Other identified metabolites were caused by the loss of the methyl thiazolyl amine group (metabolite II) from YH439, the isopropyl hydrogen malonate group (metabolite IV) and the decarboxylated product (metabolite III) of metabolite II.

Administration, Oral↗
PubMed1997

Activation of c-Jun N-terminal kinase antagonizes an anti-apoptotic action of Bcl-2.

Bcl-2 is an intracellular membrane-associated protein that prevents cell death induced by a variety of apoptotic stimuli. A mechanism by which Bcl-2 exerts an anti-cell death effect is, however, not fully understood. In the present study, Bcl-2 suppressed cell death of N18TG neuroglioma cells caused by various apoptotic stresses, including etoposide, staurosporine, anisomycin, and ultraviolet irradiation. Concomitantly, Bcl-2 disrupted a signaling cascade to the c-Jun N-terminal kinase activation induced by the apoptotic stresses. Bcl-2 also prevented the etoposide-induced stimulation of MEKK1. Furthermore, overexpression of c-Jun N-terminal kinase antagonized the death-protective function of Bcl-2. These data suggest that suppression of the c-Jun N-terminal kinase signaling pathway may be critical for Bcl-2 action.

Animals↗
PubMed1997

Adjuvant and salvage irradiation following radical prostatectomy for prostate cancer.

PURPOSE: We performed a retrospective analysis to assess the durability of benefit derived from irradiation after prostatectomy for pT3N0 disease, and the possibility of cure. METHODS AND MATERIALS: We studied 88 patients who were irradiated after prostatectomy and had available prostate specific antigen (PSA) data, no known nodal or metastatic disease, no hormonal treatment, and follow-up of at least 12 months from surgery. Forty patients received adjuvant therapy for a high risk of local failure with undetectable PSA. Forty-eight patients received salvage therapy for elevated PSA levels. Mean follow up was 44 months from date of surgery and 31 months from irradiation. Biochemical failure was strictly defined as a confirmed rise in PSA of >10%, or as the ability to detect a previously undetectable PSA value. RESULTS: After salvage irradiation, 69% of patients attained an undetectable PSA. Eighty-eight percent of adjuvant patients were biochemically and clinically free of disease (bNED) at 3 years from prostatectomy. Sixty-eight percent of those receiving salvage irradiation were bNED 3 years after surgery. On univariate analysis, treatment group (adjuvant or salvage), pre-operative PSA, and the status of seminal vesicles were significant prognostic factors. The extent of PSA elevation in the salvage group was also significant. We did not demonstrate a significant difference between those salvage patients referred for persistently elevated PSA as compared to those with a late rise in PSA. On multivariate analysis, the only significant predictor of outcome was treatment group, with adjuvant irradiation having better outcome than salvage. CONCLUSION: More than two-thirds of this group of patients remain biochemically disease free at 3 years following irradiation, attesting to a number of potential cures. For patients with stage pT3N0 prostate cancer following radical prostatectomy, our data support the use of either routine postoperative adjuvant irradiation or close PSA follow-up with early salvage treatment.

Aged↗
PubMed1997

Prospective evaluation of dietary and other predictors of fatal stroke in Shanghai, China.

BACKGROUND: Although a number of risk factors for fatal stroke are well established in Western populations, this is less true for Asian countries, many of which have stroke mortality rates that are historically high. In a prospective study in Shanghai, China, we determined whether the same factors predict risk for fatal stroke as in the West. We also studied a number of potential dietary associations, particularly those with dietary antioxidants because these have been suggested to reduce atherogenesis. METHODS AND RESULTS: Between 1986 and 1989, 18 244 men aged 45 to 64 years living in four geographically defined areas of Shanghai, China were recruited to participate in a prospective study of diet and cancer. All participants completed an in-person, structured interview and provided blood and urine samples. As of March 1994, fatal stroke accounted for 245 of the 980 observed deaths. The most important risk factor for stroke mortality was a history of hypertension (multivariate relative risk, 4.5; 95% confidence interval, 3.3, 6.2). Cigarette smoking was not strongly associated with risk, and alcohol consumption increased risk only in the extreme categories of lifetime consumption. Educational level was strongly, inversely associated with fatal stroke, and this could not be explained by adjustment for any other risk factors. No macronutrient was associated with risk, including total energy, fat consumption, or any component of fat. There also were no significant inverse associations for stroke mortality with several micronutrients of interest, including vitamin C, carotene, vitamin E, riboflavin, or calcium. CONCLUSIONS: Our data demonstrate that hypertension is by far the most important contributor to stroke mortality in Shanghai and that among dietary factors, only alcohol consumption shows any evidence whatsoever of being a risk factor.

Alcohol Drinking↗
PubMed1997

Post-translational processing and renal expression of mouse Indian hedgehog.

The full-length mouse Indian hedgehog (Ihh) cDNA was cloned from an embryonic 17.5-day kidney library and was used to study the post-translational processing of the peptide and temporal and spatial expression of the transcript. Sequence analysis predicted two putative translation initiation sites. Ihh translation was initiated at both initiation sites when expressed in an in vitro transcription/translation system. Expression of an Ihh mutant demonstrated that the internal translation initiation site was sufficient to produce the mature forms of Ihh. Ihh post-translational processing proceeded in a fashion similar to Sonic and Drosophila hedgehog; the unprocessed form underwent signal peptide cleavage as well as internal proteolytic processing to form a 19-kDa amino-terminal peptide and a 26-kDa carboxyl-terminal peptide. This processing required His313 present in a conserved serine protease motif. Ihh transcript was detected by in situ RNA hybridization as early as 10 days postcoitum (dpc) in developing gut, as early as 14.5 dpc in the cartilage primordium, and in the developing urogenital sinus. In semiquantitative reverse transcription-polymerase chain reaction experiments, Indian hedgehog transcript was first detected in the mouse metanephros at 14.5 dpc; transcript abundance increased with gestational age, becoming maximal in adulthood. In adult kidney, Ihh transcript was detected only in the proximal convoluted tubule and proximal straight tubule.

Amino Acid Sequence↗
PubMed1997

Urinary polyamine evaluation for effective diagnosis of various cancers.

With a newly modified analytical method, the concentrations of free and acetylated urinary polyamines were simultaneously determined in a control group (32 cases) and patients with various types of cancers (104 cases, 20 males and 84 females) by gas chromatography-nitrogen-phosphorus detection. Significant concentration differences between normal subjects and various cancer patients were found. The various types of cancers (advanced gastric carcinoma, ovarian cancer, acute myelocyte leukemia, non-Hodgkin's lymphoma) gave unique patterns of urinary polyamine profile as well as significant differences of concentration. To indirectly evaluate the possible involvement of enzymes, precursor-to-product concentration ratios were compared between controls and patients with various types of cancers.

Adult↗
PubMed1997

Multidrug-resistant transport proteins in yeast: complete inventory and phylogenetic characterization of yeast open reading frames with the major facilitator superfamily.

Screening of the complete genome sequence from the yeast Saccharomyces cerevisiae reveals that 28 open reading frames (ORFs) are homologous to each other and to established bacterial members of the drug-resistant subfamily of the major facilitator superfamily. The phylogenesis of these protein sequences shows that they fall into three major clusters. Cluster I contains 12 ORFs, cluster II contains ten ORFs and cluster III contains six ORFs. Hydropathy analyses indicate that in cluster II and III ORFs, 14 transmembrane spans are predicted whereas only 12 transmembrane spans are predicted in cluster I ORFs. Three ORFs that have known functions as multidrug-resistance pumps in other yeast species such as Schizosaccharomyces pombe (CAR1), Candida albicans (BMRP) or C. maltosa (CYHR), also fall into cluster I. Two S. cerevisiae ORFs of known multidrug-resistance function (ATR1, SGE1) fall into cluster II. Cluster III consists exclusively of ORFs of unknown function but binary sequence comparisons show homology to ORFs from cluster II. Analysis of the multiple alignment for these proteins leads to the identification of characteristic signature sequences for each of the three clusters.

Amino Acid Sequence↗
PubMed1997

Uncoordinated regulation of mRNA expression of the three isoforms of transforming growth factor-beta in the mouse skin carcinogenesis model.

The mRNA expression and autoregulation of expression of the three isoforms of transforming growth factor-beta (TGFbeta) were examined in the mouse skin carcinogenesis model by northern analyses. We found that TGFbeta3 mRNA levels followed a pattern similar to those of TGFbeta1 during carcinogenesis: the levels were somewhat low in normal skin but became highly overexpressed in late-stage papillomas and squamous cell carcinomas (15- to 20-fold higher than in normal skin). On the other hand, the TGFbeta2 mRNA levels remained relatively low in all benign and malignant tumors, even though the levels were higher than the nearly undetectable levels in normal skin. In a squamous cell carcinoma cell line (CH72), stable transfection and expression of a mutated simian TGFbeta1 cDNA producing bioactive TGFbeta1 significantly downregulated (mean greater than ten-fold) TGFbeta2 mRNA levels and modestly downregulated (about twofold) murine TGFbeta1 expression but had no effect on TGFbeta3 mRNA. In contrast, treatment of all CH72 clones with exogenous TGFbeta1, TGFbeta2, or TGFbeta3 either had no effect or slightly downregulated TGFbeta1 mRNA, upregulated TGFbeta2 mRNA expression an average of twofold to threefold, and strongly upregulated (mean 13- to 27-fold) TGFbeta3 mRNA levels. TGFbeta treatment of primary cultures of mouse skin keratinocytes upregulated all three TGFbeta mRNA levels slightly to moderately (1.3- to 5-fold). Thus, although TGFbeta1 and TGFbeta3 mRNA expressions were apparently coordinately upregulated during mouse skin carcinogenesis, the three TGFbeta mRNAs were differentially regulated by stable transfection of active TGFbeta1 versus exogenous TGFbeta treatment in CH72 cells and by TGFbeta treatments of normal keratinocytes versus carcinoma CH72 cells.

Animals↗
PubMed1997

Opposite effect of stable transfection of bioactive transforming growth factor-beta 1 (TGF beta 1) versus exogenous TGF beta 1 treatment on expression of 92-kDa type IV collagenase in mouse skin squamous cell carcinoma CH72 cells.

We have previously shown that transforming growth factor-beta 1 (TGF beta 1) mRNA is consistently overexpressed in squamous cell carcinomas relative to normal mouse skin. Here we show that 92-kDa type IV collagenase (matrix metalloproteinase) (MMP-9) mRNA was likewise progressively overexpressed during mouse skin carcinogenesis. To determine if overexpression of MMP-9 and TGF beta 1 are linked, we stably transfected a bioactive TGF beta 1 into a mouse skin squamous cell carcinoma cell line (CH72), which resulted in about twofold to three-fold higher levels of secreted active TGF beta 1. Active TGF beta 1-transfected cells grew only slightly, but not significantly, more slowly in vitro and in vivo than vector-only transfectants. Two clones overexpressing active TGF beta 1 secreted much reduced levels of MMP-9 activity, as determined by zymogram analyses. However, treatment of these clones with 40 pM exogenous TGF beta 1 for 48 h enhanced secretion of MMP-9 activity. Constitutive mRNA expression of MMP-9 was reduced twofold to 70-fold in five untreated active TGF beta 1-transfected clones relative to the other transfectants. In contrast, treatment with 40 pM exogenous TGF beta 1 induced MMP-9 mRNA expression in a time-dependent fashion, from twofold to fourfold after 4 h to a maximum of 12- to 19-fold after 24-48 h. Induction of MMP-9 mRNA was dose dependent at TGF beta 1 concentrations of 4-400 pM. Thus, stable transfection of bioactive TGF beta 1 downregulated whereas exogenous TGF beta 1 treatment upregulated MMP-9 activity and expression. Treatment of transfectants with a neutralizing TGF beta 1 antibody slightly downregulated constitutive MMP-9 mRNA (20-30%) but completely blocked induction by exogenous TGF beta 1. Thus, the effect of TGF beta 1 transfection was not due to secreted TGF beta 1 but may have been a secondary effect.

Animals↗
PubMed1997

Mercury distribution in sediments and bioaccumulation by fish in two oregon reservoirs: point-source and nonpoint-source impacted systems.

Mercury pollution was compared in two Oregon reservoirs of similar size and age, located within the same ecoregion. Cottage Grove Reservoir was distinguished by a history of mercury mining and processing within its watershed, while Dorena Reservoir was not. Mercury concentrations in sediments of the reservoirs, tributary streams, and three species of fish were measured. Sediment mercury concentrations in the main tributary of Cottage Grove Reservoir, which drains the subbasin where past mercury mining occurred, was tenfold higher than mercury in sediments from other reservoir tributaries. There were no significant differences between sediment mercury concentrations in the tributaries of Dorena Reservoir. The average mercury concentration in the basin sediment of Cottage Grove Reservoir (0.67 +/- 0.05 microg/g dry wt) was higher than for Dorena Reservoir (0.12 +/- 0.01 microg/g dry wt). At Cottage Grove Reservoir, maximum mercury concentrations were near or exceeded 1 microg/g wet wt for largemouth bass (Micropterus salmonides) and bluegill (Lepomis macrochirus) epaxial muscle. Muscle mercury concentrations in largemouth bass and crappie (Pomoxis nigromaculatus) from Cottage Grove Reservoir were significantly higher than from the same species from Dorena Reservoir. Numbers of bluegill of the same age available from both reservoirs were too small for statistical comparisons. Mercury concentrations in largemouth bass muscle fluctuated annually in both reservoirs. Fish ages were consistently positively correlated with muscle mercury concentrations in only the point-source-impacted reservoir. These results indicated that a point source, Black Butte Mine, contributed amounts of mercury greatly in excess of mobilization from natural deposits, atmospheric deposition, and small-scale uses of the metal as an amalgamating agent in gold mining.

Animals↗