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Biomedical subjects

H Lee

Publications and source records attributed to H Lee.

At least 235 records · Page 13Linked to original sources
PubMed2000

Homodimerization via a leucine zipper motif is required for enzymatic activity of quiescent cell proline dipeptidase.

Quiescent cell proline dipeptidase (QPP) is an intracellular serine protease that is also secreted upon cellular activation. This enzyme cleaves N-terminal Xaa-Pro dipeptides from proteins, an unusual substrate specificity shared with dipeptidyl peptidase IV (CD26/DPPIV). QPP is a 58-kDa protein that elutes as a 120-130-kDa species from gel filtration, indicating that it forms a homodimer. We analyzed this dimerization with in vivo co-immunoprecipitation assays. The amino acid sequence of QPP revealed a putative leucine zipper motif, and mutational analyses indicated that this leucine zipper is required for homodimerization. The leucine zipper mutants showed a complete lack of enzymatic activity, suggesting that homodimerization is important for QPP function. On the other hand, an enzyme active site mutant retained its ability to homodimerize. These data are the first to demonstrate a role for a leucine zipper motif in a proteolytic enzyme and suggest that leucine zipper motifs play a role in mediating dimerization of a diverse array of proteins.

Amino Acid Motifs↗
PubMed2000

Transduction effect of antisense K-ras on malignant phenotypes in gastric cancer cells.

The antitumoral effects of antisense RNA to K-ras were investigated in gastric cancer cell lines by examining the level of K-ras expression and the tumorigenicity in vitro and in vivo. Polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), DNA sequencing, and immunoblotting analysis revealed that YCC-1 gastric cancer cells overexpressed wild type K-ras, whereas YCC-2 cells had a homozygous mutation in codon 12 from GGT (glycine) to AGT (serine), while SNU-1 cells had a heterozygous mutation to GAT (asparagine) in the identical position. Both YCC-1 and YCC-2 cells were transduced by LNC-AS/K-ras containing the antisense 2.2 kb genomic K-ras DNA fragment covering exon 2 and exon 3 specific for K-ras. The application of antisense K-ras significantly downregulated the expression of K-ras and had no influence on the expression of either H-ras or N-ras. The antisense-transduced YCC-2 cells grew considerably slower than the control group transduced by LNCX, whereas the growth inhibition of antisense-transduced YCC-1 cells was less prominent than that of transduced YCC-2 cells. In addition, the tumorigenicity of YCC-2 cells transduced by LNC-AS/K-ras was totally lost. Therefore, our results imply that the specific inhibition of K-ras p21 protein can be accomplished by introducing the antisense covering the K-ras- specific region to gastric cancer cells with aberrant K-ras expression, resulting in a reduction of the growth rate and suppression of tumorigenicity.

Animals↗
PubMed2000

Activation of thiol-dependent antioxidant activity of human serum albumin by alkaline pH is due to the B-like conformational change.

Antioxidant activity of human serum albumin (HSA) increased steeply as the reaction mixture was shifted from neutral to alkaline pH. The antioxidant activity was also remarkably increased by Ca(2+) or a cationic detergent (cetyltrimethylammonium chloride). Carboxyl group modification of HSA resulted in about 40-fold increase of the antioxidant activity. The chemical modification study indicated that in addition to functional cysteine(s), cationic amino acid residues such as histidine, arginine and lysine appeared to involve in the antioxidant reaction. HSA also exhibited alkaline-pH dependent peroxidase activity to remove fatty acid hydroperoxide. At neutral pH, only two thiols of Cys-289 and free Cys-34 of HSA were modified by a thiol-specific modification reagent, 5-((((2-iodoacetyl)amino)ethy)amino)naphthalene-1-sulfonic acid (I14), regardless of the presence or absence of dithiothreitol (DTT), and the resultant antioxidant activity was not decreased, suggesting that Cys-289 and Cys-34 did not participate in the antioxidant reaction. At alkaline pH, I14 modified several additional HSA thiols in the presence, but did not in the absence of DTT. The antioxidant activity of the modified HSA was remarkably decreased to as much as 30% of the antioxidant activity given by the unmodified HSA in the absence of DTT. The HPLC pattern for tryptic peptides containing modified cysteine(s) derived from the I14-treated c-HSA (carboxyl group-modified HSA) at pH 7.0 with DTT was very similar to that of the I14-modified HSA at pH 8.0 with DTT. Taken together, these results suggest that activation of thiol-dependent antioxidant activity of HSA at alkaline pH is due to the conformational change favorable for the functional cysteine(s)-mediated catalysis.

Antioxidants↗
PubMed2000

The lipopolysaccharide-activated toll-like receptor (TLR)-4 induces synthesis of the closely related receptor TLR-2 in adipocytes.

The central regulatory role of the adipocyte in whole body energy homeostasis is well established. However, recent findings suggest that preadipocytes and adipocytes may play an important physiological role in the regulation of both the innate and adaptive immune response. To systematically characterize the molecular machinery of the adipocyte that mediates the recognition of pathogens, we have focused our analysis on the recently identified Toll-like receptors (TLRs). These receptors have been implicated as mediators of the cellular response to bacterial lipopolysacharides (LPSs). Here, we report the cloning and functional characterization of mouse TLR-2 from 3T3-L1 adipocytes. TLR-2 synthesis is strongly induced in the adipocyte by LPS, TNFalpha, and the yeast cell wall extract zymosan. TLR-2 undergoes a lengthy intracellular maturation process with a half-life of exit from the ER of approximately 3 h. Furthermore, LPS treatment of adipocytes results in dramatic changes at the level of gene expression, including the synthesis of a distinct set of secretory proteins such as interleukin-6. Our studies demonstrate the presence of a fully intact pathway of innate immunity in the adipocyte that can be activated by LPS binding to the cell surface and results in the secretion of immunomodulatory molecules.

3T3 Cells↗
PubMed2000

Lack of obvious 50 kilobase pair DNA fragments in DNA fragmentation factor 45-deficient thymocytes upon activation of apoptosis.

The DNA fragmentation factor 45 (DFF45/ICAD) is a key subunit of a heterodimeric DNase complex critical for the induction of DNA fragmentation during apoptosis in vivo. To further assess the importance of DFF45 in chromosomal DNA degradation, we induced apoptosis in wild-type control and DFF45 deficient thymocytes and compared the cleavage of chromosomal DNA to 50 kilobase pair size fragments. We found that there is a lack of obvious large chromosomal DNA fragments upon treatments by various apoptotic agents in DFF45 deficient thymocytes. The major organ systems in the DFF45 mutant mice either two months or fifteen months of age appear normal. These results suggest that functional DFF45 is required for cleavage of DNA into both large size and oligonucleosomal size fragments in thymocytes during apoptosis. However, deficiency in DFF45 apparently does not significantly affect normal mouse development and tissue homeostasis.

Age Factors↗
PubMed2000

Improved outcome secondary to concurrent chemoradiotherapy for advanced carcinoma of the nasopharynx: preliminary corroboration of the intergroup experience.

PURPOSE: The recent Intergroup 0099 trial of concurrent chemoradiotherapy for advanced nasopharyngeal carcinomas, demonstrated improved survival for chemoradiotherapy as compared to radiation therapy alone. Following closure of this study, we adopted the chemoradiotherapy regimen used in 0099 as our standard of practice. We herein report our recent institutional results, representing a relatively large uniformly treated cohort. METHODS AND MATERIALS: Between 1995 and 1997, 35 consecutive patients, who had clinically nondisseminated Stage III or IV nasopharyngeal cancer, were treated by chemoradiotherapy. The prescribed radiation regimen was 7000 cGy delivered in 35 fractions over 7 weeks to all macroscopic disease and 5000 cGy to areas considered at risk of harboring microscopic disease. Chemotherapy was designed to deliver cisplatin (100 mg/m(2) i.v.) on Days 1, 22, and 43 of radiation therapy and cisplatin (80 mg/m(2) i.v.) on Days 71, 99, and 127 plus flurouracil (5-FU; 1 g/m(2)/day by 96-h infusion) on Days 71-74, 99-102, and 127-130. RESULTS: All patients had at least a partial response (PR) to treatment, including an 85% complete response (CR) rate. The actuarial 3-year overall survival rate was 93% and the disease-free survival rate was 65%. Both represent substantial improvements over our institutional historical controls treated by radiation therapy alone and both are similar to the rates observed in the Intergroup trial. CONCLUSION: Our data support the conclusion that concurrent chemoradiotherapy followed by adjuvant chemotherapy (as was used in Intergroup 0099) should be considered the current standard of care for patients who have advanced cancers of the nasopharynx.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

Identification of a new active site for autocatalytic processing of penicillin acylase precursor in Escherichia coli ATCC11105.

Penicillin acylase (PA) from Escherichia coli ATCC11105 is a periplasmic heterodimer consisting of a 24 kDa small subunit and a 65 kDa large subunit. It is synthesized as a single 96 kDa precursor and then matures to functional PA via a posttranslational processing pathway. The GST-PA fusion protein expression system was established for monitoring the precursor PA processing in vitro. The purified PA precursor was processed into mature PA the same way as in vivo, but pH dependently. From the primary sequence analysis, we identified a putative conserved lysine residue (K299) responsible for the pH dependent processing. The substitution of K299 residue by site-directed mutagenesis affected both the enzyme activity and the precursor PA processing in vivo. Furthermore, it was shown that the processing rates of wild-type and mutant precursor PAs depended on the pKa values of their side chain R group. These results demonstrated that the lysine residue (K299) was involved in the precursor processing of PA together with N-terminal serine residue (S290) of the large subunit.

Amino Acid Sequence↗
PubMed2000

MDM2 mRNA expression is a favorable prognostic factor in non-small-cell lung cancer.

MDM2 is one of the downstream target genes for transcriptional activation by the product of the p53 tumor-suppressor gene. Transactivation of MDM2 gene expression is represented by the presence of a functional p53 protein. We hypothesized that MDM2 mRNA expression may be a more suitable prognostic factor than p53 or MDM2 protein expression and p53 gene mutations. In this study, expression of MDM2 mRNA, p53 protein, and MDM2 protein and mutations of the p53 gene were assessed in 81 lung tumor tissue specimens using RT-PCR, immunohistochemistry, and direct sequencing among exons 5-8, respectively. By immunohistochemistry, 33 and 42 of 81 patients with p53 (40.7%) and MDM2 (51.5%) protein expression were found in lung tumor specimens, respectively. The p53 direct sequencing data indicated that 13 of 81 patients (16.0%) had p53 mutations. However, Kaplan-Meier analysis showed that p53 protein and MDM2 protein expression and p53 mutation were not useful as prognostic factors. Interestingly, the survival of patients with MDM2 mRNA expression was longer than that of patients without MDM2 mRNA expression, though MDM2 mRNA expression was not associated with clinicopathological parameters, including tumor grade, tumor stage, tumor type, and TNM values. Moreover, Cox regression analysis showed that MDM2 mRNA expression was a significantly independent favorable prognostic factor in non-small-cell lung cancer (NSCLC) patients. Thus, measuring MDM2 mRNA expression using RT-PCR may be a simple, useful approach for predicting the survival of NSCLC patients.

Adenocarcinoma↗
PubMed2000

Gelsolin binding and cellular presentation of lysophosphatidic acid.

Lysophosphatidic acid (LPA) in biological fluids binds to serum albumin and other proteins that enhance its effects on cellular functions. The actin-severing protein gelsolin binds LPA with an affinity (K(d) = 6 nm) similar to that of the G protein-coupled LPA receptors encoded by endothelial differentiation genes 2, 4, and 7 (Edg-2, -4, and -7 receptors) and greater than that of serum albumin (K(d) = 360 nm). At concentrations of 10% or less of that in plasma, which are observed in fluids of injured tissues, purified and recombinant gelsolin augment LPA stimulation of nuclear signals and protein synthesis in rat cardiac myocytes (RCMs) that express Edg-2 and -4 receptors. At concentrations of 20% or more of that in plasma, gelsolin suppresses LPA stimulation of RCMs. The lack of effect of gelsolin on RCM responses to monoclonal anti-Edg-4 receptor antibody plus a phorbol ester without LPA attests to its specificity for LPA delivery and the absence of post-receptor effects. Inhibition of gelsolin binding and cellular delivery of LPA by l-alpha-phosphatidylinositol-4,5-bisphosphate (PIP2) and peptides constituting the two PIP2 binding domains of gelsolin suggests competition between LPA and PIP2 for the same sites. Thus, delivery of LPA to RCMs is affinity-coupled to Edg receptors by gelsolin in a PIP2-regulated process.

Amino Acid Sequence↗
PubMed2000

A homochiral metal-organic porous material for enantioselective separation and catalysis

Inorganic zeolites are used for many practical applications that exploit the microporosity intrinsic to their crystal structures. Organic analogues, which are assembled from modular organic building blocks linked through non-covalent interactions, are of interest for similar applications. These range from catalysis, separation and sensor technology to optoelectronics, with enantioselective separation and catalysis being especially important for the chemical and pharmaceutical industries. The modular construction of these analogues allows flexible and rational design, as both the architecture and chemical functionality of the micropores can, in principle, be precisely controlled. Porous organic solids with large voids and high framework stability have been produced, and investigations into the range of accessible pore functionalities have been initiated. For example, catalytically active organic zeolite analogues are known, as are chiral metal-organic open-framework materials. However, the latter are only available as racemic mixtures, or lack the degree of framework stability or void space that is required for practical applications. Here we report the synthesis of a homochiral metal-organic porous material that allows the enantioselective inclusion of metal complexes in its pores and catalyses a transesterification reaction in an enantioselective manner. Our synthesis strategy, which uses enantiopure metal-organic clusters as secondary building blocks, should be readily applicable to chemically modified cluster components and thus provide access to a wide range of porous organic materials suitable for enantioselective separation and catalysis.

Journal Article↗
PubMed2000

Enteritis necroticans (pigbel) in a diabetic child.

BACKGROUND AND METHODS: Enteritis necroticans (pigbel), an often fatal illness characterized by hemorrhagic, inflammatory, or ischemic necrosis of the jejunum, occurs in developing countries but is rare in developed countries, where its occurrence is confined to adults with chronic illnesses. The causative organism of enteritis necroticans is Clostridium perfringens type C, an anaerobic gram-positive bacillus. In December 1998, enteritis necroticans developed in a 12-year-old boy with poorly controlled diabetes mellitus after he consumed pig intestines (chitterlings). He presented with hematemesis, abdominal distention, and severe diabetic ketoacidosis with hypotension. At laparotomy, extensive jejunal necrosis required bowel resection, jejunostomy, and ileostomy. Samples were obtained for histopathological examination. Polymerase-chain-reaction (PCR) assay was performed on paraffin-embedded bowel tissue with primers specific for the cpa and cpb genes, which code for the alpha and beta toxins produced by C. perfringens. RESULTS: Histologic examination of resected bowel tissue showed extensive mucosal necrosis, the formation of pseudomembrane, pneumatosis, and areas of epithelial regeneration that alternated with necrotic segments--findings consistent with a diagnosis of enteritis necroticans. Gram's staining showed large gram-positive bacilli whose features were consistent with those of clostridium species. Through PCR amplification, we detected products of the cpa and cpb genes, which indicated the presence of C. perfringens type C. Assay of ileal tissue obtained during surgery to restore the continuity of the patient's bowel was negative for C. perfringens. CONCLUSIONS: The preparation or consumption of chitterlings by diabetic patients and other chronically ill persons can result in potentially life-threatening infectious complications.

Animals↗
PubMed2000

Disruption of interkringle disulfide bond of plasminogen kringle 1-3 changes the lysine binding capability of kringle 2, but not its antiangiogenic activity.

Kringle 1-3 of human plasminogen is a potent inhibitor of endothelial cell proliferation. To understand a possible role for the unique cystine bridge between kringle 2 and kringle 3, we disrupted the interkringle disulfide bond by mutating Cys(169) and Cys(297) to serine residues. The yield of the mutant during the refolding process was decreased significantly. Anti-endothelial cell proliferative activity of the mutant was similar to that of the wild type. There was no significant difference in in vivo antiangiogenic activity between the wild type and the mutant in chorioallantoic membrane assay. However, in the mutant, the weak lysine binding capability of kringle 2 was not detected and its mobility in nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis is different from that of the wild type. These results support the notion that the overall antiangiogenic function of angiostatin is mediated by individual kringles, and suggest that the lysine binding capability of kringle 2 is likely not important for the antiangiogenic activity of kringle 1-3.

Amino Acid Substitution↗
PubMed2000

Nuclear matrix of calreticulin in hepatocellular carcinoma.

Nuclear matrix protein profiles of malignant cells vary from their normal counterparts. By two-dimensional gel electrophoresis, we analyzed nuclear matrix proteins in 11 hepatocellular carcinomas and compared them with corresponding non-neoplastic liver tissue. Although the compositions were mostly similar, several peptides were noted predominantly in the former. The most prominent one was an acidic protein of apparent Mr 62,000, which was identified to be calreticulin upon NH2-terminal amino acid sequencing. By immunoblotting, calreticulin was confirmed to be present abundantly in the nuclear matrix fraction of carcinomas but not in that of the nonmalignant liver tissue. Interestingly, the total content of calreticulin was similar between them. By immunofluorescence microscopy, evident nuclear immunostaining was detected in carcinomas. Calreticulin was also found to be in the nuclear matrices of various carcinoma cell lines. We conclude that calreticulin is a component of the nuclear matrix. The formation and/or expansion of the calreticulin-nuclear matrix may be related to the activated cell growth.

Adult↗
PubMed2000

The Dwarf Irregular Galaxy UGC 7636 Exposed: Stripping at Work in the Virgo Cluster.

We present the results of optical spectroscopy of a newly discovered H ii region residing in the H i gas cloud located between the dwarf irregular galaxy UGC 7636 and the giant elliptical galaxy NGC 4472 in the Virgo Cluster. By comparing UGC 7636 with dwarf irregular galaxies in the field, we show that the H i cloud must have originated from UGC 7636 because (1) the oxygen abundance of the cloud agrees with that expected for a galaxy with the blue luminosity of UGC 7636 and (2) MHi&solm0;LB for UGC 7636 becomes consistent with the measured oxygen abundance of the cloud if the H i mass of the cloud is added back into UGC 7636. It is likely that tides from NGC 4472 first loosened the H i gas, after which ram pressure stripping removed the gas from UGC 7636.

Journal Article↗
PubMed2000

Quantum-critical conductivity scaling for a metal-insulator transition

Temperature (T)- and frequency (omega)-dependent conductivity measurements are reported here in amorphous niobium-silicon alloys with compositions (x) near the zero-temperature metal-insulator transition. There is a one-to-one correspondence between the frequency- and temperature-dependent conductivity on both sides of the critical concentration, thus establishing the quantum-critical nature of the transition. The analysis of the conductivity leads to a universal scaling function and establishes the critical exponents. This scaling can be described by an x-, T-, and omega-dependent characteristic length, the form of which is derived by experiment.

Journal Article↗
PubMed2000

Control of GluR1 AMPA receptor function by cAMP-dependent protein kinase.

Modulation of postsynaptic AMPA receptors in the brain by phosphorylation may play a role in the expression of synaptic plasticity at central excitatory synapses. It is known from biochemical studies that GluR1 AMPA receptor subunits can be phosphorylated within their C terminal by cAMP-dependent protein kinase A (PKA), which is colocalized with the phosphatase calcineurin (i.e., phosphatase 2B). We have examined the effect of PKA and calcineurin on the time course, peak open probability (P(O, PEAK)), and single-channel properties of glutamateevoked responses for neuronal AMPA receptors and homomeric GluR1(flip) receptors recorded in outside-out patches. Inclusion of purified catalytic subunit Calpha-PKA in the pipette solution increased neuronal AMPA receptor P(O,PEAK) (0.92) compared with recordings made with calcineurin included in the pipette (P(O,PEAK) 0.39). Similarly, Calpha-PKA increased P(O,PEAK) for recombinant GluR1 receptors (0. 78) compared with patches excised from cells cotransfected with a cDNA encoding the PKA peptide inhibitor PKI (P(O,PEAK) 0.50) or patches with calcineurin included in the pipette (P(O,PEAK) 0.42). Neither PKA nor calcineurin altered the amplitude of single-channel subconductance levels, weighted mean unitary current, mean channel open period, burst length, or macroscopic response waveform for recombinant GluR1 receptors. Substitution of an amino acid at the PKA phosphorylation site (S845A) on GluR1 eliminated the PKA-induced increase in P(O,PEAK), whereas the mutation of a Ca(2+), calmodulin-dependent kinase II and PKC phosphorylation site (S831A) was without effect. These results suggest that AMPA receptor peak response open probability can be increased by PKA through phosphorylation of GluR1 Ser845.

Animals↗
PubMed2000

Can migraine damage the inner ear?

BACKGROUND: Auditory and vestibular symptoms and signs are common in patients with migraine, yet little is known about the pathogenesis of these symptoms and signs. OBJECTIVE: To perform clinicopathological correlation in a patient with migraine, sudden deafness, and delayed endolymphatic hydrops. METHODS: A patient with long-standing migraine with aura developed sudden hearing loss in the left ear at the age of 50 years and Ménière disease on the right side at age 73. At age 76, he had a flurry of sudden drop attacks typical of otolithic crisis. He died of unrelated causes at age 81. The brain and temporal bones were removed approximately 24 hours after death. The cochlea and vestibular end organs were dissected after the surrounding bone was carefully removed. RESULTS: The brain and cerebrovasculature were normal. The left cochlea showed prominent fibrosis consistent with an old infarction. The right inner ear showed hydrops, with relatively good preservation of the hair cells in the cochlea, saccular macule, and cristae of the semicircular canals. However, the utricular macule was denuded of hair cells. CONCLUSIONS: The sudden left-sided deafness likely resulted from ischemia, possibly due to migraine-associated vasospasm. Presumably, the right ear suffered only minimal damage when the patient was 50 years old, but this damage later led to the development of delayed endolymphatic hydrops on the right. Otolithic crises are thought to result from pressure changes across the utricular macule. We speculate that loss of hair cells in the utricular macule resulted from a collapse of the utricular membrane onto the macule.

Aged↗