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Biomedical subjects

Y Choi

Publications and source records attributed to Y Choi.

At least 253 records · Page 14Linked to original sources
PubMed1996

Identification of a putative G protein-coupled receptor induced during activation-induced apoptosis of T cells.

During development, self-reactive immature thymocytes are clonally deleted in the thymus, a phenomenon which establishes T cell tolerance (negative selection). It has been shown that the deletion of self-reactive immature T cells in the thymus is mediated by apoptosis upon T cell receptor (TCR) engagement. Apoptosis of immature thymocytes mediated by the TCR requires the expression of a new set of genes. To define which genes are required during the TCR-mediated death of immature thymocytes, we sought to identify genes whose expression is increased during TCR-mediated cell death. Using the technique of differential mRNA display, we have identified a novel gene, TDAG8, which encodes a putative G protein-coupled receptor. The expression of TDAG8 is greatly induced upon activation of T cells by anti-TCR antibody or by phorbol 12-myristate 13-acetate plus ionomycin. The treatment of T cells with glucocorticoids also greatly induces the expression of TDAG8. In mice, TDAG8 is predominantly expressed in thymus and spleen. The tissue-specific expression of TDAG8 and the induction of its expression during cell death of T cells mediated by the TCR or glucocorticoids suggest that it may have a role in activation-induced cell death or differentiation of T cells.

Amino Acid Sequence↗
PubMed1996

T cell receptor-dependent cell death of T cell hybridomas mediated by the CD30 cytoplasmic domain in association with tumor necrosis factor receptor-associated factors.

CD30 is a member of the tumor necrosis factor superfamily and a surface marker for Hodgkin's disease. Normal activated T cells and several virally transformed T or B cell lines also show CD30 expression. The interaction of CD30 with its ligand induces cell death or proliferation, depending on the cell type. In this report we characterize the signals mediated by the intracellular domain of CD30 and show that, in combination with signal(s) transduced by the T cell receptor, the multimerization of CD30 cytoplasmic domain induces Fas(CD95)-independent cell death in T cell hybridomas. Deletion analysis shows that the COOH-terminal 66 amino acids of CD30 are required to induce cell death. Using the yeast two-hybrid system, we have identified that the same region of CD30 interacts with tumor necrosis factor receptor-associated factor (TRAF)1 and TRAF2. These results indicate that TRAF1 and/or TRAF2 play an important role in cell death in addition to their previously identified roles in cell proliferation.

Base Sequence↗
PubMed1996

Neuropathic pain in rats is associated with altered nitric oxide synthase activity in neural tissue.

Peripheral nerve injury may lead to a chronic neuropathic pain state that results from an increase in excitability of central neurons. This central sensitization is mediated via an N-methyl-D-aspartic acid (NMDA) receptor and may involve the production of nitric oxide (NO). As NO is suggested to play a role in nociceptive transmission following nerve injury, we examined for altered NO synthase activity at multiple levels of peripheral and spinal neural tissue in a rat model of neuropathic pain. Peripheral neuropathy was induced in rats (N = 12) by ligation of the left L5 and L6 nerve roots. Six other rats had sham surgery. An ipsilateral decrease in paw withdrawal threshold to mechanical stimuli confirmed the presence of a neuropathic pain state. Samples of the lumbar and thoracic spinal cords, L4, L5, and L6 dorsal root ganglia (DRGs), and the sciatic nerves were obtained from the lesioned and contralateral sides at 2 and 4 weeks after neuropathic surgery (N = 6 per group). In the lumbar spinal cord, a bilateral decrease in nitric oxide synthase (NOS) activity was observed 2 and 4 weeks after neuropathic surgery. NOS activity was increased in the ipsilateral L5 and 6 DRGs 2 weeks following neuropathic surgery. An increase in NOS activity in the DRG may be an early mechanism for inducing more central changes. The bilaterally decreased NOS activity in the lumbar spinal cord may be secondary to a negative feedback mechanism resulting from increased NO production in the spinal dorsal root ganglia. Multiple alterations in expression of NOS activity that occur in both peripheral and central processing may play a role in the pain behavior resulting from peripheral nerve injury. (Preliminary results of these studies have been presented in abstract form at the annual meetings of the Society for Neuroscience, 1994, and the American Society of Anesthesiologists, 1994).

Analysis of Variance↗
PubMed1996

Isolated lymphadenopathy on chest radiographs of HIV-infected patients.

AIM: To determine the aetiology of isolated intrathoracic lymphadenopathy on chest radiographs of HIV-infected patients. PATIENTS AND METHODS: Over a 40 month span in 1990-1993, 18 HIV-infected patients (13 men, 5 women) from our New York City adult HIV outpatient clinic development isolated intrathoracic lymphadenopathy (defined as intrathoracic nodal enlargement without other persistent abnormalities on chest radiographs). Serial chest radiographs (n = 18), CT scans when available (n = 7), and clinical charts (n = 18) were reviewed retrospectively. RESULTS: Median patient age was 34 (range 25-49) years. The diagnoses associated with adenopathy were Mycobacterium tuberculosis (Mtb) in eight (44%), Mycobacterium avium intracellulare complex (MAC) in four (22%), and Mtb and MAC co-infection in three (17%). Cryptococcal infection, thymic hyperplasia, and spontaneous resolution without diagnosis or treatment occurred in one patient each. In 16 (89%) of the 18 patients, lymphadenopathy was present in more than one nodal station. Enlarged nodes were found in the following sites: paratracheal/tracheobronchial (n = 14), aortopulmonary window (n = 9), hilar (n = 7), anterior mediastinum (n = 3), subcarinal (n = 2), and left paraesophageal (n = 2). CONCLUSION: Mycobacterial infection was the aetiology of isolated intrathoracic lymphadenopathy in 15 of 18 (83%) HIV-infected patients. When an inner city HIV-infected patient presents with isolated intrathoracic lymphadenopathy, we recommend an aggressive work-up for mycobacterial disease.

AIDS-Related Complex↗
PubMed1996

A novel gene product that couples TCR signaling to Fas(CD95) expression in activation-induced cell death.

Cross-linking the TCR in T cell hybridomas induces cell apoptosis following activation. This activation-induced apoptosis has been used as a model for clonal deletion of thymocytes or peripheral T cells. Anti-TCR-induced apoptosis of T cell hybridomas requires de novo macromolecular synthesis, including up-regulation of Fas and FasL. The Fas-FasL interaction then activates the apoptosis program. To study apoptosis-specific signaling processes, we generated a mutant T cell hybridoma line defective in induction of apoptosis, but competent to induce activation, upon TCR triggering. Subsequently, we cloned the gene TDAG51, which restored activation-induced apoptosis when transfected into the mutant cell line, and showed that TDAG51 expression was required for Fas expression. Thus, TDAG51 plays an essential role in induction of apoptosis by coupling TCR stimulation to Fas expression.

Amino Acid Sequence↗
PubMed1996

Suppression of TRH-stimulated TSH secretion by glucose-induced hypothalamic somatostatin release.

To determine whether the combined glucose-thyrotropin-releasing hormone (TRH) test can be a useful method for the evaluation of the hypothalamic somatostatinergic activity, we investigated whether TRH-induced thyroid stimulating hormone (TSH) secretion can be suppressed by the oral glucose administration that stimulates the hypothalamic somatostatin (SRIH) secretion. Six tests were performed in ten healthy young men. Test 1: 1 ml of normal saline was intravenously administered at 0 min. Test 2: TRH was administered intravenously at 0 min. Test 3: Glucose, 75 g, was administered orally at -60 min. Test 4: Glucose and TRH were administered as above. Test 5: Pyridostigmine (PST), 120 mg, was given orally at -90 min followed by the administration of GH and TRH as above. Basal TSH levels were suppressed slightly, but significantly. In Test 3 compared to those observed in Test 1. The oral glucose administration also significantly suppressed TRH-stimulated TSH response by 27-35% between 40 min and 80 min in Test 4. In contrast, the pretreatment with PST completely reverted the suppressive effect of glucose on TRH-stimulated TSH response in Test 5. These data suggest that the increased hypothalamic SRIH secretion induced by oral glucose administration can suppress TRH-stimulated TSH response in normal men, and the combined glucose-TRH test can be a useful method to evaluate the hypothalamic somatostatinergic activity.

Adult↗
PubMed1996

Staphylococcal food poisoning caused by imported canned mushrooms.

From February through April 1989, four outbreaks of staphylococcal food poisoning in the United States were associated with eating mushrooms canned in the People's Republic of China (PRC). In the four outbreaks, 99 persons who ate at a suspect facility developed gastrointestinal symptoms within 24 h, including 18 who were hospitalized. Illness was associated with eating mushrooms at a university cafeteria (relative risk [RR] = 53.0), a hospital cafeteria (RR = 13.8), a pizzeria (odds ratio [OR] = infinity), and a restaurant (OR = infinity) (all P < .0001). Staphylococcal enterotoxin A was found by ELISA in mushrooms at the sites of two outbreaks and in unopened cans from the three plants thought to have produced mushrooms implicated in outbreaks. These investigations led to multistate recalls and a US Food and Drug Administration order to restrict entry into the United States of all mushrooms produced in the PRC; until this action, the United States imported approximately 50 million pounds yearly.

Adult↗
PubMed1996

Diagnosis of Yersinia pseudotuberculosis infection by polymerase chain reaction.

BACKGROUND: The diagnosis of Yersinia pseudotuberculosis infection is usually based on serologic and/or bacteriologic tests. However, successfully culturing Y. pseudotuberculosis is difficult, and serologic tests in many cases require at least two serial sera obtained during 1-week intervals to confirm rising agglutination antibody titers. METHODS: We applied a nested polymerase chain reaction method for rapid diagnosis of Y. pseudotuberculosis infection. The DNAs extracted from the peripheral blood and urine of patients and from mountain water, a suspected source of infection, were used as templates for the polymerase chain reaction with consequent amplification of a fragment of the inv gene in the chromosomal DNA of Y. pseudotuberculosis. RESULTS: The overall rate of diagnosis with the polymerase chain reaction, which was based on a positive result with a single blood sample or one or more positive results with serial samples, was 93.3%. The polymerase chain reaction was also positive in two mountain water samples that were thought to be a source of infection. CONCLUSION: Based on our results the nested polymerase chain reaction method can be used clinically for rapid and precise diagnosis of Y. pseudotuberculosis infection.

Base Sequence↗
PubMed1996

A novel extensin gene encoding a hydroxyproline-rich glycoprotein requires sucrose for its wound-inducible expression in transgenic plants.

A novel hydroxyproline-rich glycoprotein (SbHRGP3) that consists of two different domains is encoded by an extensin gene from soybean. The first domain (domain 1) located at the N terminus is composed of 11 repeats of Ser-Pro4-Lys-His-Ser-Pro4-Tyr3-His, whereas the second domain (domain 2) at the C terminus contains five repeats of Ser-Pro4-Val-Tyr-Lys-Tyr-Lys-Ser-Pro4-Tyr-Lys-Tyr-Pro-Ser-Pro5-Tyr-Lys-T yr- Pro-Ser-Pro4-Val-Tyr-Lys-Tyr-Lys. These two repeat motifs are organized in an extremely well-ordered pattern in each domain, which suggests that SbHRGP3 belongs to a new group of proteins having the repeat motifs of two distinct groups of dicot extensins. The expression of the SbHRGP3 gene increased with seedling maturation, and its expression was relatively high in the mature regions of the hypocotyl and in the root of soybean seedlings. An SbHRGP3-beta-glucuronidase (SbHRGP3-GUS) chimeric gene was constructed and expressed in transgenic tobacco plants. The expression of the SbHRGP3-GUS gene was not induced by wounding alone in transgenic tobacco plants; sucrose was also required. Expression was specific to phloem tissues and cambium cells of leaves and stems. In transgenic tobacco seedlings, SbHRGP3-GUS gene expression was activated by the maturation of the primary root and then inactivated; however, reactivation was specifically at the epidermis of the zone from which the lateral root was to be initiated. Its reactivation occurred just before the lateral root initiation. These results indicate that the SbHRGP3 gene in different tissues responds to different signals.

Amino Acid Sequence↗
PubMed1996

Complement 4 locus II gene deletion and DQA1*0301 gene: genetic risk factors for IgA nephropathy and Henoch-Schönlein nephritis.

There have been several reports suggesting that the deficiency of complement 4 (C4) and/or deletion of C4 genes are the genetic risk factors in patients with IgA nephropathy (IgAN) and Henoch-Schönlein nephritis (HSN). In the current study, we tried to clarify the genetic structure of deleted C4 genes as well as the isotype deficiency of the patients. Also, we investigated the DQB and DRB genes which are located near the C4 genes to identify a possible linkage and to find the associated allele. Our results showed that locus II deletion of C4, not the C4B sequence loss, is a risk factor for these diseases and the deleted gene can be either C4A or C4B. There was no specific isotype deficiency or specific allotype which was significantly increased or decreased in the patients. But, there was an increased frequency of DQA1*0301 gene in the patient group (corrected p = 0.04), which suggests that DQA1*0301 as well as C4 gene deletion could be genetic risk factors for these diseases.

Adult↗
PubMed1996

Characteristics of gsp-positive growth hormone-secreting pituitary tumors in Korean acromegalic patients.

A subset of human growth hormone (GH)-secreting pituitary tumors contains the gsp oncogene that encodes an activation mutation of the alpha-subunit of the stimulatory GTP-binding protein (G(S) alpha). This study was undertaken to investigate the frequency of the gsp oncogene in GH-secreting pituitary tumors in Korean acromegalic patients and to elucidate the clinical characteristics of these patients to endocrine testing. Direct polymerase chain reaction sequencing revealed the gsp oncogene mutation in 9 out of 21 tumors (43%) at amino acid 201 of the G(S) alpha protein. A single nucleotide mutation in the tumors carrying the gsp oncogene was observed, which replaced an arginine (CGT) in the normal protein with cysteine (TGT) in eight tumors and serine (AGT) in one tumor. The patients with the gsp oncogene mutation (group 1) were older (54 +/- 10 vs 41 +/- 11 years, p = 0.0085) than those without the mutation (group 2). Sex, tumor size and grade, basal GH and prolactin levels, the GH response to oral glucose loading, the GH fluctuation and the paradoxical response to thyrotropin-releasing hormone or gonadotropin-releasing hormone did not differ between the groups. The gsp oncogene was found mostly in somatotroph adenomas. The octreotide-induced GH suppression was significantly higher in group 1 than in group 2 (95 +/- 5% vs 81 +/- 17%, p = 0.0335). The GH response to bromocriptine did not differ between the groups. These results suggest that the G(S) alpha mutations of GH-secreting tumor are observed in Korean acromegalic patients with similar frequency to those of western countries. The patients with gsp oncogene are likely to be older than those without the oncogene, and show excellent response of GH suppression to octreotide.

Acromegaly↗
PubMed1995

Solution assembly of a soluble, heteromeric, high affinity interleukin-2 receptor complex.

In this study, we report the use of coiled-coil (leucine zipper) molecular recognition for the solution assembly of stable, high affinity, heteromeric interleukin-2 receptor complexes. Co-expression of interleukin-2 receptor alpha and beta extracellular domains (ectodomains), each fused to seven coiled-coil heptad repeats, resulted in the formation of heteromeric complexes that bound interleukin-2 in a cooperative fashion and with much higher affinity than similar homomeric complexes. The dissociation constants for these solution complexes are within the range of values reported for the comparable cell surface "pseudo high affinity" interleukin-2 receptor. Ligand-induced cross-linking of homomeric or heteromeric receptor subunits is the common signal transmission mechanism employed by hematopoietin receptors. Individual receptor ectodomains, however, often do not bind ligand with measurable affinity. This is the first study to demonstrate the feasibility of coiled-coil mediated preassembly of cytokine receptor complexes.

Allosteric Regulation↗