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Biomedical subjects

S W Lee

Publications and source records attributed to S W Lee.

At least 19 recordsLinked to original sources
PubMed1997

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) delays and induces escape from senescence in human dermal microvascular endothelial cells.

Like most other normal cells, human endothelial cells possess a limited replicative life span, and, after multiple passages in vitro, develop an arrest in cell division referred to as replicative senescence. For many cell types senescence can be delayed by oncogenes or tumor suppressor genes or prevented altogether by malignant transformation; however, once developed, senescence has been regarded as irreversible. We now report that a cytokine, vascular permeability factor/vascular endothelial growth factor (VPF/VEGF), significantly delays senescence in human dermal microvascular endothelial cells (HDMEC). Typically, VPF/VEGF-treated HDMEC could be cultured for at least 15-20 more population doublings (PD) than control cells. Protection from senescence was reversible in that subsequent withdrawal of VPF/VEGF returned cells to the senescent phenotype. Expression of several cell cycle-related genes (p21, p16 and p27) was significantly reduced in VPF/VEGF-treated cells but p53 expression was not significantly altered. Of particular importance, VPF/VEGF was able to rescue senescent HDMEC, restoring them to proliferation, to a more normal morphology, and to reduced expression of a senescence marker, neutral beta-galactosidase. Taken together, VPF/VEGF delayed the onset of senescence and also reversed senescence in microvascular endothelial cells without inducing cell transformation.

Brain-Derived Neurotrophic Factor↗
PubMed1997

Instantaneous center of rotation and instability of the cervical spine. A clinical study.

STUDY DESIGN: This study was designed to investigate flexion and extension of the cervical spine in patients with "instability" of the cervical spine. OBJECTIVES: To establish a new method of calculating the instantaneous center of rotation (ICR) of the skull relative to the thorax and to compare the differences in the ICR between normal volunteers and patients. SUMMARY OF BACKGROUND DATA: "Instability" of the cervical spine commonly is investigated using functional radiographs, which is an unreliable method. Although the ICR was suggested as an objective parameter in measuring spinal "instability," the ICR of the skull relative to the thorax has not been studied before. METHOD: Three groups of subjects (27 normal volunteers, 28 patients with chronic cervical spondylosis, and 17 patients undergoing fusion for cervical disc degeneration) were measured with a CA-6000 system (OSI, CA). The ICR then were calculated and compared at various angles of flexion and extension. RESULTS: The horizontal component of the ICR in the preoperative group was found to have shifted anteriorly from 5 degrees to 25 degrees of flexion (P < 0.05) and at 5 degrees of extension (P < 0.05), compared with that of the healthy subjects. There also was a significant difference in the vertical component of the ICR at 15 degrees of flexion (P < 0.05). However, there were no significant differences in the horizontal and the vertical components of the ICR between the normal and nonoperative groups. CONCLUSION: The ICR in patients with "instability" of the cervical spine was found to have shifted anteriorly; the method described in this study might be useful for identifying patients who suffer from this condition.

Aged↗
PubMed1997

Downregulation of DNA topoisomerase I in old versus young human diploid fibroblasts.

DNA topoisomerase I (Topo I) is an enzyme that alters the superhelicity of DNA. It has been implicated in such critical cellular functions as transcription, DNA replication, and recombination. Roles for Topo I in DNA repair following DNA damage have also been studied extensively. In the present investigation, we examined the regulation of Topo I expression and activity during cellular replicative senescence. We found that the capacity of Topo I to relax supercoiled DNA molecules is significantly decreased in senescent diploid fibroblasts when compared to young (early passage) fibroblasts. We also found that the steady-state expression level of Topo I mRNA is correlated with enzyme activity, i.e., decreased in early vs. late passage cells. We also treated early and late passage cells with agents that may modulate the process of cellular senescence: UV light, retinoic acid, and interleukin-1 beta. We found that all three agents decreased the activity of Topo I in young fibroblasts and increased the activity of Topo I in senescent fibroblasts. This effect was most striking following exposure of the cells to retinoic acid, so to analyze this effect, we postulated an age-dependent kinetics of Topo I mRNA induction in response to retinoic acid. Consistent with this postulate, we found that whereas exposure of early passage cells to retinoic acid results, in a matter of hours, in a decrease in the expression of Topo I mRNA, exposure of the senescent cells to retinoic acid results in an increased expression. These observations suggest that processes that are altered in senescent fibroblasts, such as DNA replication and repair, may be due, in part, to alteration in the expression and activity of DNA Topo I.

Cells, Cultured↗
PubMed1997

Simple bone cyst of the axis.

A 12-year-old girl presented with a 1-month history of posterior neck pain and a large cyst in the second cervical vertebra. She underwent complete curettage of the cyst wall without any kind of bone graft, and the surgical result was good. Microscopic findings in the cyst wall were consistent with simple bone cyst, which is very rare in the spine.

Adolescent↗
PubMed1997

Isolation of a nuclease-resistant decoy RNA that can protect human acetylcholine receptors from myasthenic antibodies.

The muscular weakness and fatigability associated with myasthenia gravis are engendered by autoantibodies directed against acetylcholine receptors on muscle cells at neuromuscular junctions. The pathogenic consequences of this immune response can potentially be modulated by molecules that bind such autoantibodies and block their interaction with these receptors. We report the isolation of a small nuclease-resistant RNA molecule that binds both a rat monoclonal antibody that recognizes the main immunogenic region on the acetylcholine receptor, and autoantibodies from patients with myasthenia gravis. Moreover, this RNA can act as a decoy and protect acetylcholine receptors on human cells from the effects of these antibodies.

Animals↗
PubMed1997

Genetic variations at four tetrameric tandem repeat loci in Korean population.

Allele and genotype frequencies for four tetrameric short tandem repeat (STR) loci, HumFES/FPS, HumFOLP23, HumGABRB15, and HumCYAR04, have been determined by polymerase chain reaction (PCR) amplification and subsequent polyacrylamide gel electrophoresis from approximately 200 genetically unrelated Koreans. This method allows a single base pair resolution and rapid typing with silver staining. The allele and genotype distributions satisfy Hardy-Weinberg expectation. Also, these STR loci have proven to be useful for forensic analyses and paternity tests in which the variable number of tandem repeat (VNTR) loci have some limitations.

Alleles↗
PubMed1997

Molecular interactions of aging and cancer.

The increased incidence of cancer as a function of age has long been interpreted to suggest that multiple genetic changes are required for tumorigenesis. Cancer cells differ from normal cells in many characteristics, including loss of differentiation, increased invasiveness, and decreased drug sensitivity. Although recent molecular advances have helped to clarify the possible relationships between carcinogenesis and aging, it remains unclear whether genetic markers may be common to all cancer types or which markers may be associated with increased age of cancer patients. Fundamental aspects of cancer development for older people are not well understood. Further insight into the genetic factors that may be responsible for the initiation and progression of cancer and their connections to the aging process may be gained in part by studying in vitro cellular or replicative senescence.

Age Distribution↗
PubMed1997

Comparison of muscle activity and occlusal contacts during maximal and habitual clenching in varied chair positions.

The activity of anterior temporal muscle, the number of tooth contacts, and total duration of closure during maximal and habitual clenching were studied in varied chair positions. Fifteen subjects were evaluated. The means for the muscle activity of anterior temporal muscle during habitual clenching were 63.5-73.5% of maximum muscle activity. The number of tooth contacts and total duration of closure were significantly increased as biting pressure was increased from habitual to maximal clenching. No significant differences were detected in all variables among varied chair positions. The above results also suggested that occlusal instability was very common. Further research is required to explain the relationship, if any, of these variables to craniomandibular disorders.

Adult↗
PubMed1996

Differences in turnover rates of vinculin and talin caused by viral transformation and cell density.

Vinculin and talin are two major components of focal contacts which interact with each other. In order to understand how the relative levels of these proteins are maintained under various conditions, the synthesis rates and half-lives of vinculin and talin in chick embryonic fibroblasts were determined by autoradiography combined with immunoblotting. High cell density and transformation by Rous sarcoma virus decreased the vinculin synthesis rate by 40%. Upon viral transformation, the synthesis rate of talin decreased by 30%. In contrast to vinculin, the synthesis rate of talin was not affected by cell density. The effect of cell density on the synthesis rate of vinculin was retained after viral transformation, suggesting that cell density and viral transformation affect vinculin synthesis by two independent mechanisms. The synthesis rate of vinculin was approximately two to three times greater than that of talin under all conditions tested. The half-lives of vinculin and talin remained constant at different cell densities in untransformed cells (t1/2 = 18-21 h), but transformation slightly decreased half-lives of both proteins (t1/2 = 16-18 h). These results suggest that the decreased expression of vinculin and talin in transformed chick fibroblasts can be attributed mainly to changes in their biosynthesis rates rather than degradation. This may contribute to a decrease in the number of focal contacts in transformed cells.

Animals↗
PubMed1996

Isolation of a nuclease-resistant decoy RNA that selectively blocks autoantibody binding to insulin receptors on human lymphocytes.

An RNA containing 2'-amino pyrimidines has been isolated using in vitro selection techniques that specifically and avidly (apparent Kd approximately 30 nM) binds a mouse monoclonal antibody called MA20. This 2'-amino-derivatized RNA is at least 10,000-fold more stable than unmodified RNA in serum, and can act as a decoy and block MA20 binding to its natural antigen, the human insulin receptor, on lymphocytes. Furthermore, this RNA decoy can inhibit MA20-mediated downmodulation of insulin receptor expression on human lymphocytes in culture by up to 90%. Surprisingly, the decoy RNA cross-reacts with autoantibodies from patients with extreme insulin resistance and can inhibit these antiinsulin receptor antibodies from downmodulating insulin receptor expression by up to 80% without impeding insulin binding to its receptor. These results suggest that in vitro-selected decoy RNAs may be able to specifically and selectively block oligoclonal autoimmune responses to self-antigens in patients with autoimmune diseases.

Animals↗
PubMed1996

Iterative optimization of high-affinity proteases inhibitors using phage display. 1. Plasmin.

We generated a series of libraries having variants of the first Kunitz domain of human lipoprotein-associated coagulation inhibitor (LACI-D1, also known as tissue-factor pathway inhibitor-I) displayed on bacteriophage M13 as pIII-fusions. We varied LACI-DI iteratively in two regions: the P1 region (positions 10-21) and the "second loop", (positions 31-39), which together form one end of the domain. Display-phage library Lib#1 allows 31 200 amino-acid sequences in P1 region (residues 13, 16-19). Preliminary, we screened Lib#1 against human plasmin (PLA, EC 3.4.21.7) immobolized on agarose to enrich for phage displaying variants with PLA affinity. We introduced a 1600-fold increase in second-loop diversity (residues 31, 32, 34, 39) into the population of selectants from Lib#1, yielding Lib#2. Lib#2 (allowing approximately 50 million amino-acid sequences) was screened against PLA-agarose to isolate highest affinity binders. Protein EPI-P211, derived from the best isolate of Lib#2, inhibits PLA with Ki = 2 nM (at least 500-fold better than LACI-D1) and with high specificity. We used amino-acid sequences of PLA-binding selectants to design a PLA-biased library (Lib#3) which we screened against PLA. The protein EPI-P302 (derived from the best binder obtained from Lib#3) has Ki for PLA inhibition of 87 pM, which is 25-fold better than the first-round best binder and > or = 12 500-fold better than LACI-D1. EPI-P302 also shows very high specificity for PLA vs other human proteases and is resistant to inactivation by oxidants and extremes of temperature or pH. Thus, one can use selectants from one library to design target-tailored combinatorial libraries and obtain quite stable, highly specific, very high-affinity binding molecules while maintaining an essentially human framework.

Amino Acid Sequence↗
PubMed1996

Transient protection of human T-cells from human immunodeficiency virus type 1 infection by transduction with adeno-associated viral vectors which express RNA decoys.

RNA decoys are oligonucleotides corresponding to the TAR and RRE sequences of HIV which inhibit the HIV-encoded regulatory proteins Tat and Rev, respectively. Adeno-associated viral vectors encoding RNA decoys stably transduced into the human T-cell line CEM-SS expressed transactivating region (TAR) and Rev-responsive element (RRE) RNA decoys from tRNA polIII promoters at high levels, without any apparent deleterious effects on cell growth or expression of CD4. DNA blot analysis indicated that RNA decoy-encoding vectors were not rearranged and were integrated into the genomic DNA of selected cell lines. Vector DNA with the appropriate TAR and RRE sequences was isolated from transduced cell lines after prolonged growth in culture, further confirming that the vector DNA was present in a stable form through multiple cell cycles. Cell lines expressing TAR and RRE decoys transiently inhibited HIV gene expression and replication by 70-99% as determined by measurement of intracellular and extracellular HIV p24 production. Adeno-associated vectors encoding RNA decoys may be useful for gene therapy of HIV infection.

Cell Line↗
PubMed1996

No subacute thrombosis and femoral bleeding complications under full anticoagulation in 150 consecutive patients receiving non-heparin-coated intracoronary Palmaz-Schatz stents.

Intracoronary stenting has been shown to have better immediate and long-term clinical outcomes and less restenosis than standard balloon angioplasty. However, the benefit was achieved at the cost of higher rates of coronary thrombosis, bleeding complications, the need for anticoagulation, and longer hospital stay. For the latter reasons there is a tendency to replace the anticoagulants by antiplatelet agents alone after stenting. However, we prospectively monitored 150 consecutive patients (133 men, 17 women, mean age 58.5 years) from two centers since February 1993. They all had coronary artery disease and underwent percutaneous implantation of non-heparin-coated Palmaz-Schatz coronary stents under a full but lower dose of anticoagulation. The femoral approach was used in all patients except one. In the 150 patients, 200 stents were implanted in 165 target arteries with 172 lesions. Stenting was performed without the guidance of intravascular ultrasonography; high-pressure poststenting inflation was used in only 17.3% of patients with less than optimal angiographic results. Coronary angiography was performed at baseline, immediately after the procedure, and after 6 months (mean 207 +/- 53.6 days SD) of stenting. The mean (+/-SD) coronary minimum luminal diameter increased from 0.52 0.31 mm to 3.13 +/- 0.42 mm immediately after stenting was performed and was 2.12 +/- 0.91 mm at 6 months. There was a 0% subacute thrombosis rate and a 0% femoral bleeding complication rate in the whole series. Only three (2%) major events occurred: one Q-wave myocardial infarction from closure of an angioplasty site distal to the stent on a very long lesion, one cerebrovascular accident, and one noncoronary-related death. The only patient who underwent the brachial approach had hematoma; otherwise no other minor event occurred. The mean hospital stay was 4.5 days in one of the two study centers. The long-term clinical follow-up rate was 97.3%. The mean (+/- SD) clinical follow-up period was 589 +/- 363 days. Clinical symptoms improved; the percentage of patients who had angina according to the Canadian Cardiovascular Society functional class II, III, and IV was 31.3%, 44.7%, and 4%, respectively, before stenting was performed and was reduced to 4.7%, 3.7%, and 0%, respectively at 6-month follow-up after stenting was performed. The 6-month angiographic restudy rate was 90.6%, and the restenosis rate was 18.3%. In contrast to other reported series, these results support the idea that with careful puncture technique and meticulous postoperative wound care, intracoronary stenting can be successfully performed with the patient under full anticoagulation without major risks of bleeding and femoral vascular complications. Furthermore with a full but comparatively lower dose of anticoagulation, subacute thrombotic complications can be reduced to 0% even with non-heparin-coated stents without the use of intravascular ultrasound guidance and without the use of adjunctive high-pressure poststenting inflation in most patients. The restenosis rate and long-term clinical outcomes remained very favorable.

Acute Disease↗
PubMed1996

Tagging ribozyme reaction sites to follow trans-splicing in mammalian cells.

In mammalian cells, genetic instructions are usually revised by RNA splicing before they are translated to proteins. Here we demonstrate that a trans-splicing group I ribozyme can be employed to intentionally modify the sequence of targeted transcripts in tissue culture cells. By analyzing the ribozyme reaction products, we demonstrate that targeted trans-splicing can proceed in murine fibroblasts with high fidelity, providing direct evidence that ribozymes function as anticipated in a therapeutically relevant setting. Trans-splicing is not very specific however, and the ribozyme reacted with and tagged a variety of cellular transcripts with its 3' exon sequence. RNA tagging provides a unique approach to study RNA catalysis in mammalian cells. Such analysis should facilitate the logical development of safe, therapeutic ribozymes that can repair mutant RNAs associated with a variety of inherited diseases.

3T3 Cells↗
PubMed1996

H-cadherin, a novel cadherin with growth inhibitory functions and diminished expression in human breast cancer.

A newly identified gene, H-cadherin, is reported. H-cadherin encodes a protein related to the cadherin superfamily of cell adhesion molecules, and its expression is shown to be significantly reduced in human breast carcinoma cell lines and breast cancer specimens. H-cadherin was localized to chromosome 16q24 and is highly expressed in the heart. Introduction of H-cadherin cDNA markedly diminished tumor cell growth and resulted in a significant change from invasive morphology to a normal cell-like morphology in the Matrigel outgrowth assay. These studies indicate that downregulation of H-cadherin may be frequent in the breast malignant progression and suggest that it may have prognostic value as a marker for breast cancer development.

Amino Acid Sequence↗
PubMed1996

Endoscopic mucosectomy using an esophageal variceal ligation device for minute gastric cancer.

We present here a modified technique for endoscopic mucosal resection using the technique of esophageal variceal ligation for minute gastric cancer. This method of endoscopic mucosal resection requires only the commonly-used one-channel endoscope, an esophageal variceal ligation device, and some clinical experience with the ligation of esophageal varices and snare polypectomy. It can therefore be considered technically simple and safe. We treated four patients with minute gastric cancer using this endoscopic mucosal resection technique. All tumors were completely resected without major complications. Resected specimens were 1.0-1.5 cm in diameter, sufficient for histopathological evaluation, and curative resection was achieved in all patients.

Adenocarcinoma↗
PubMed1996

Phenotypic expression of Pseudomonas syringae avr genes in E. coli is linked to the activities of the hrp-encoded secretion system.

The specific recognition of elicitors produced by plant pathogenic bacteria carrying avirulence (avr) genes is postulated to initiate cellular defense responses in plants expressing corresponding resistance genes. The biochemical functions of most avr genes, however, are not known. A heterologous system was developed to phenotypically express Pseudomonas syringae avr genes in Escherichia coli cells that required the P. syringae hrp cluster. E. coli MC4100 transformants carrying the plasmic-borne P. syringae pv. syringae Pss61 hrp cluster and p. syringae pv. glycinea avrB expressed from a triple lacUV5 promoter gained the ability to elicit the hypersensitive response in soybean cultivars expressing Rpg1 and in an Arabidopsis thaliana accession expressing RPM1. Inactivation of energy transducing or outer membrane components of the hrp-encoded secretion system blocked phenotypic expression expression of avrB in E. coli, but deletions abolishing harpinPSS production had little effect on the production of the AvrB phenotype by the E. coli transformants. Phenotypic expression of avrA, AvrPto, avrRpm1, avrRpt2, and avrPph3 in E. coli was also shown to require the hrp cluster. The results indicate that generation of the Avr phenotype in P. syringae strains is specifically dependent on the secretion activities of the hrp cluster.

Base Sequence↗