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T W Lee

Publications and source records attributed to T W Lee.

At least 19 recordsLinked to original sources
PubMed1998

Different effects of Gsalpha splice variants on beta2-adrenoreceptor-mediated signaling. The beta2-adrenoreceptor coupled to the long splice variant of Gsalpha has properties of a constitutively active receptor.

The beta2-adrenoreceptor (beta2AR) couples to the G-protein Gs to mediate adenylyl cyclase activation. The splice variants of Gsalpha differ by a 15-amino acid insert between the Ras-like domain and the alpha-helical domain. The long splice variant of Gsalpha (GsalphaL) binds GDP with lower affinity than the short splice variant (GsalphaS), but the impact of this difference on the interaction of Gsalpha with the beta2AR is not known. We studied the beta2AR/Gsalpha interaction using receptor/G-protein fusion proteins (beta2ARGsalphaS and beta2ARGsalphaL) expressed in Sf9 cells. Fusion of the beta2AR to Gsalpha promotes efficient coupling as shown by high-affinity agonist binding and GTPase and adenylyl cyclase activation and ensures fixed stoichiometry between receptor and G-protein. Importantly, fusion does not change the fundamental properties of the beta2AR or Gsalpha. The beta2AR in beta2ARGsalphaL showed hallmarks of constitutive activity (increased potency and intrinsic activity of partial agonists, increased efficacy of inverse agonists, and increased basal GTPase activity) compared with the beta2AR in beta2ARGsalphaS. The apparent constitutive activity of the beta2AR in beta2ARGsalphaL may be due to the lower GDP affinity of GsalphaL compared with GsalphaS, i.e. GsalphaL is more often nucleotide-free than GsalphaS and, therefore, more frequently available to stabilize the beta2AR in the active (R*) state. This study demonstrates that subtle structural differences between closely related G-protein alpha-subunits can have important consequences for the functional properties of a G-protein-coupled receptor.

Adenylyl Cyclases↗
PubMed1998

Spatially independent activity patterns in functional MRI data during the stroop color-naming task.

A method is given for determining the time course and spatial extent of consistently and transiently task-related activations from other physiological and artifactual components that contribute to functional MRI (fMRI) recordings. Independent component analysis (ICA) was used to analyze two fMRI data sets from a subject performing 6-min trials composed of alternating 40-sec Stroop color-naming and control task blocks. Each component consisted of a fixed three-dimensional spatial distribution of brain voxel values (a "map") and an associated time course of activation. For each trial, the algorithm detected, without a priori knowledge of their spatial or temporal structure, one consistently task-related component activated during each Stroop task block, plus several transiently task-related components activated at the onset of one or two of the Stroop task blocks only. Activation patterns occurring during only part of the fMRI trial are not observed with other techniques, because their time courses cannot easily be known in advance. Other ICA components were related to physiological pulsations, head movements, or machine noise. By using higher-order statistics to specify stricter criteria for spatial independence between component maps, ICA produced improved estimates of the temporal and spatial extent of task-related activation in our data compared with principal component analysis (PCA). ICA appears to be a promising tool for exploratory analysis of fMRI data, particularly when the time courses of activation are not known in advance.

Algorithms↗
PubMed1998

Role of mononuclear cells of IgA nephropathy on ICAM-1 expression in mesangial cells.

OBJECTIVES: To investigate the possible role of mononuclear cells and their products in the pathogenesis of IgA nephropathy, in vitro expression of ICAM-1 on cultured mouse mesangial cell (MC) was examined after stimulation with mononuclear cell culture supernatant from patients with IgA nephropathy. METHODS: Peripheral blood mononuclear cells (PBMC) were isolated and cultured from 18 patients with primary IgA nephropathy, 8 normal controls and 5 patients with non-IgA nephropathy (FSGS 1, MGN 3, MPGN 1). ICAM-1 expression on cultured mouse MC by TNF-alpha, IL-1 beta and culture supernants of PBMC were analyzed using a cell ELISA method. The concentration of IL-1 beta and TNF-alpha in culture supernatants was measured by using a commercially available radioimmunoassay kit. RESULTS: Addition of human recombinant TNF-alpha induced an increased ICAM-1 expression in a dose-dependent manner. The expression of ICAM-1 was further increased after co-stimulation with TNF-alpha and IL-1 beta. Addition of PBMC culture supernatants into mouse MC induced significantly higher expression of ICAM-1 by supernatants from the patients with IgA nephropathy compared with that from normal controls. The concentration of TNF-alpha and IL-1 beta in supernatants from the patients with IgA nephropathy was significantly higher than that from those with non-IgA nephropathy. CONCLUSION: TNF-alpha and IL-1 released from mononuclear cells induced the up-regulation of ICAM-1 expression and this may be related to the immune pathogenesis of IgA nephropathy.

Animals↗
PubMed1997

Up-regulation of the levels of expression and function of a constitutively active mutant of the hamster alpha1B-adrenoceptor by ligands that act as inverse agonists.

The alpha1-adrenergic agonist phenylephrine stimulated phospholipase D (PLD) activity in Rat 1 fibroblasts transfected to express either the wild-type hamster alpha1B-adrenoceptor or a constitutively active mutant (CAM) form of this receptor. The EC50 for agonist stimulation of PLD activity was substantially lower at the CAM receptor than at the wild-type receptor as previously noted for phenylephrine stimulation of phosphoinositidase C activity. Sustained treatment of cells expressing the CAM alpha1B-adrenoceptor with phentolamine resulted in a marked up-regulation in levels of this receptor with half-maximal effects produced within 24 h and with an EC50 of approx. 40 nM. Such an up-regulation could be produced with a range of other ligands generally viewed as alpha1-adrenoceptor antagonists but equivalent treatment of cells expressing the wild-type alpha1B-adrenoceptor was unable to mimic these effects. After sustained treatment of the CAM alpha1B-adrenoceptor expressing cells with phentolamine, basal PLD activity was increased and phenylephrine was now able to stimulate PLD activity to greater levels than in vehicle-treated CAM alpha1B-adrenoceptor-expressing cells. The EC50 for phenylephrine stimulation of PLD activity was not altered, however, by phentolamine pretreatment and the associated up-regulation of the receptor. After phentolamine-induced up-regulation of basal PLD activity, a range of alpha1-antagonists were shown to possess the characteristics of inverse agonists of the CAM alpha1B-adrenoceptor as they were able to substantially decrease the elevated basal PLD activity.

Adrenergic alpha-1 Receptor Agonists↗
PubMed1997

Circulating factors in sera or peripheral blood mononuclear cells in patients with membranous nephropathy or diabetic nephropathy.

In order to investigate the status of some circulating factors in nephrotic syndrome, we examined the secretion of monocyte chemotactic peptide (MCP)-1, tumor necrosis factor (TNF) alpha or fibronectin in sera or by peripheral blood mononuclear cells (PBMC) from patients with membranous nephropathy (MN), diabetic nephropathy (DN) or minimal change disease (MCD). Also the effects of PBMC or sera on human mesangial cells (MC) were evaluated. Serum TNF alpha levels were higher in patients with MN than in controls, but PBMC exhibited no differences in TNF alpha production between patients and controls. Serum fibronectin levels were higher in patients with MN than in controls. PBMC from diabetic patients with or without nephropathy produced more MCP-1 than cells from controls. When MC were cultured with PBMC supernatants from patients, TNF alpha levels in PBMC supernatants correlated with production of MCP-1 or fibronectin by MC. PBMC supernatants obtained from patients with MCD and MN decreased MCP-1 production by MC, but did not affect thymidine incorporation or fibronectin production by MC. Sera obtained from patients with DN and MCD reduced thymidine incorporation in MC. In summary, serum TNF alpha or fibronectin levels were increased in patients with MN that is known to progress to renal failure. MCP-1 Production was increased by PBMC obtained from diabetic patients with or without nephropathy. Also TNF alpha production by PBMC in individual patients may affect the pathophysiology of their MC.

Adult↗
PubMed1996

A constitutively active mutant of the alpha 1B-adrenergic receptor can cause greater agonist-dependent down-regulation of the G-proteins G9 alpha and G11 alpha than the wild-type receptor.

Rat 1 fibroblasts transfected to express either the wild-type hamster alpha 1B-adrenergic receptor or a constitutively active mutant (CAM) form of this receptor resulting from the alteration of amino acid residues 288-294 to encode the equivalent region of the human beta 2-adrenergic receptor were examined. The basal level of inositol phosphate generation in cells expressing the CAM alpha 1B-adrenergic receptor was greater than for the wild-type receptor, The addition of maximally effective concentrations of phenylephrine or noradrenaline resulted in substantially greater levels of inositol phosphate generation by the CAM alpha 1B-adrenergic receptor, although this receptor was expressed at lower steady-state levels than the wild-type receptor. The potency of both phenylephrine and noradrenaline to stimulate inositol phosphate production was approx. 200-fold greater at the CAM alpha 1B-adrenergic receptor than at the wild-type receptor. In contrast, endothelin 1, acting at the endogenously expressed endothelin ETA, receptor, displayed similar potency and maximal effects in the two cell lines. The sustained presence of phenylephrine resulted in down-regulation of the alpha subunits of the phosphoinositidase C-linked, pertussis toxin-insensitive, G-proteins G9 and G11 in cells expressing either the wild-type or the CAM alpha 1B-adrenergic receptor. The degree of down-regulation achieved was substantially greater in cells expressing the CAM alpha 1B-adrenergic receptor at all concentrations of the agonist. However, in this assay phenylephrine displayed only a slightly greater potency at the CAM alpha 1B-adrenergic receptor than at the wild-type receptor. There were no detectable differences in the basal rate of G9 alpha/G11 alpha degradation between cells expressing the wild-type or the CAMalpha 1B-adrenergic receptor. In both cell lines the addition of phenylephrine substantially increased the rate of degradation of these G-proteins, with a greater effect at the CAM alpha 1B-adrenergic receptor. The enhanced capacity of agonist both to stimulate second-messenger production at the CAM alpha 1B-adrenergic receptor and to regulate cellular levels of its associated G-proteins by stimulating their rate of degradation is indicative of an enhanced stoichiometry of coupling of this form of the receptor to G9 and G11.

Adrenergic alpha-1 Receptor Agonists↗
PubMed1996

Conformational change of cyclic AMP receptor protein by the binding of cyclic nucleotide.

The cAMP Receptor Protein (CRP) of Escherichia coli requires a conformational change induced by the binding of cAMP in order to function as a site-specific DNA-binding protein. An intrinsic fluorescence study showed that the tryptophan residues at position 13 and 85 within CRP were located in an internal, nonpolar environment, and the conformational change induced by the binding of cAMP occurred around the tryptophan residue NMR experiment has manifested that the comformational change around the tryptophan residue at position 85 and histidine residue at position 159 of CRP is induced by the binding of cAMP. An extrinsic fluorescence study showed that the distance between the two cysteine 178 residues in the dimer was within about 3.5 A. This distance didn't exhibit a large change upon cAMP binding.

Cyclic AMP↗
PubMed1996

Enterovirus typing by immune electronmicroscopy.

A simple method of typing enteroviruses by immune electronmicroscopy (IEM) is given. Forty-four of 50 picornavirus strains typed by both IEM and neutralisation in cell culture gave identical results. Four strains could not be typed by one or other method. Two rhinovirus isolates were untypable by both methods. There were no discrepant results. The IEM method is convenient and has considerable savings in time and reagents.

Enterovirus↗
PubMed1996

Thoracoscopic management of malignant pleural effusions.

Malignant pleural effusion is a common condition and often presents a challenge for treatment. We report our experience from a single institution with the use of video-assisted thoracoscopic surgery (VATS) in the management of malignant effusions. From September 1992 to April 1995, 69 patients (31 men, 38 women; age range, 38 to 76 years) underwent diagnosis and/or treatment of malignant effusions; these included 46 pleural biopsies, 34 talc insufflations, and 16 limited decortications. There was no mortality and there were no intraoperative complications. Postoperative complications occurred in seven patients (10%). Specific histologic diagnoses were obtained in all but 6 patients (87%). Malignant effusion was confirmed in 25 of 46 cases (54%). Thoracoscopic talc insufflation with or without additional decortication was successful in 32 of 34 cases (94%) in controlling recurrence of effusion after a mean follow-up of 6 months among the survivors (22 patients died during the follow-up period without effusion reaccumulation). We conclude that VATS not only provides an accurate diagnosis but also allows effective therapeutic procedures to be performed for malignant effusions that are associated with an acceptable morbidity.

Adult↗
PubMed1996

Expression of urokinase-type plasminogen activator, its receptor, and its inhibitor in gastric adenocarcinoma tissues.

The plasminogen and plasmin system, which is mainly regulated by urokinase-type plasminogen activator (uPA), its receptor (uPAR) and its inhibitor (PAI-1), is generally believed to play a role in cancer invasion and metastasis. This study was conducted to investigate the role of uPA, uPAR and PAI-1 in the invasion and metastasis of gastric adenocarcinoma. The expression of mRNAs for uPA and PAI-1 was determined by Northern blot analysis in nine primary gastric cancer tissues, nine paired metastatic lymph nodes and normal gastric mucosa. The mRNA of uPA was not or faintly detected in normal mucosa, while the expression was increased in both primary gastric cancer tissues and metastatic lymph nodes to a similar degree. The mRNA expression for PAI-1 in the gastric cancer tissues was not different from that in the paired metastatic lymph nodes and normal mucosae. uPAR was determined by immunohistochemical staining, demonstrating that five (56%) and six (67%) out of nine primary gastric cancer tissues and nine paired metastatic lymph nodes were positive, respectively and the intensity was stronger in metastatic lymph nodes. The results support the concept that most gastric cancer cells may have an innately moderate level of uPA and uPAR, and that increase of uPAR expression can be considered to be closely associated with cancer invasion and metastasis.

Adenocarcinoma↗
PubMed1996

Deletion of Rb1 gene in late osteosarcoma from survivor of unilateral retinoblastoma--a case report.

It has been well known that the survivors of retinoblastoma are prone to have osteosarcoma. But the secondary tumor usually occurs in bilateral, hereditary type of retinoblastoma. We report one case of osteosarcoma in a survivor of unilateral, sporadic retinoblastoma. A fourteen year old male presented with a painfully swollen distal forearm of 2 month duration. He had enucleated his left eye 10 years ago due to retinoblastoma with no other adjuvant therapy. We managed him with our conventional protocol and identified deletion of Rb gene from his pathological specimen by using the PCR-RFLP method. This result is unusual for unilateral nonhereditable retinoblastoma and may suggest gene level change even in sporadic cases. And Rb gene study may be helpful for unilateral, sporadic retinoblastoma patient in detecting the possibility of late osteosarcoma.

Adolescent↗
PubMed1996

Effects of mixed leukocyte reaction, hydrocortisone and cyclosporine on expression of leukocyte adhesion molecules by endothelial and mesangial cells.

We investigated the effects of mixed leukocyte reaction (MLR), hydrocortisone (HC) and cyclosporine A (CsA) on the expression of leukocyte adhesion molecules on the mesangial (MC) and endothelial cells (EnC). Cell surface enzyme immunoassay showed that INFnu, IL-1beta, or TNF alpha stimulated expression of ICAM-1, or VCAM-1 on MC after 24 hours. Flow cytometric analysis demonstrated that MLR supernatant induced a marked increase in mean fluorescence of or % of cells highly expressing intercellular adhesion molecule(ICAM)-1 or vascular cell adhesion molecule (VCAM)-1 on both cells after 24 hours (p<0.001). HC treatment(300 ng/ml) during MLR effectively inhibited MLR-induced upregulation of ICAM-1 and VCAM-1 on both cells (p<0.005). When MLR supernatant with HC was added to adhesion molecule assay, there was no inhibitory effect of HC on VCAM-1. CsA treatment (500 ng/ml) during MLR caused a modest decrease in upregulation of VCAM-1 on EnC (p<0.05), but had no effects on ICAM-1 on both cells. CsA directly decreased expression of VCAM-1 on MC. In conclusion, alloreactive lymphocytes and monocytes upregulate the expression of VCAM-1 and ICAM-1 on target cells probably by the mediation of cytokines. HC effectively prevents MLR-induced upregulation of VCAM-1 and ICAM-1. CsA does not increase the expression of VCAM-1 and ICAM-1.

Cells, Cultured↗
PubMed1996

A case report of a large thymic carcinoid.

Thymic carcinoid is a rare tumour. A case of giant thymic carcinoid with extensive necrosis is reported in a 44-year-old Chinese male. Diagnosis was difficult to make before the operation and even intraoperatively. Subtotal excision was performed followed by adjuvant radiation therapy. The patient remained disease-free at the last follow-up 12 months after surgery. Complete excision remains the mainstay of treatment for this disease.

Carcinoid Tumor↗
PubMed1996

Thoracoscopic talc insufflation versus talc slurry for symptomatic malignant pleural effusion.

BACKGROUND: Talc has been generally accepted to be the most effective sclerosant for chemical pleurodesis, although the optimal route of administration remains unclear. METHODS: We designed a prospective, randomized study to compare video-assisted thoracoscopic talc insufflation with bedside talc slurry in the treatment of malignant pleural effusion. From September 1993 to November 1995, 57 patients were recruited and randomized to either video-assisted thoracoscopic talc insufflation under general anesthesia (n = 28) or talc slurry by the bedside (n = 29). Patients with poor general condition (Karnofsky score less than 30%), poor pulmonary function (forced expiratory volume in 1 second less than 0.5 L), or trapped lungs were excluded from this study. Five grams of purified talc was used for either video-assisted thoracoscopic talc insufflation or talc slurry. RESULTS: There was no statistically significant difference between the two groups of patients with respect to age, sex ratio, chest drainage duration, postprocedural hospital stay, parenteral narcotics requirement, complications, or procedure failure (ie, recurrence). CONCLUSIONS: Video-assisted thoracoscopic talc insufflation has not been shown to be a superior approach compared with talc slurry in our study. Because the former demands more resources, we advocate that talc slurry should be considered as the procedure of choice in the treatment of symptomatic malignant pleural effusion in patients who do not have trapped lungs.

Aged↗
PubMed1995

Comparison of the signalling properties of the long and short isoforms of the rat thyrotropin-releasing-hormone receptor following expression in rat 1 fibroblasts.

cDNA species encoding either the long or the short isoforms of the rat thyrotropin-releasing-hormone (TRH) receptor were expressed stably in Rat 1 fibroblasts, and clones expressing specific binding of [3H]TRH were detected and expanded. Clones expressing each of these receptors at levels up to 1 pmol/mg of membrane protein were selected for analysis. Reverse-transcriptase PCR on RNA isolated from these clones confirmed that each clone expressed only mRNA corresponding to the expected splice variant. Both receptor splice variants bound [3H]TRH with a Kd of some 80 nM when binding assays were performed in the presence of guanosine 5'-[beta gamma-imido]-triphosphate. In the presence of TRH, both receptor subtypes were able to cause stimulation of inositol phosphate generation in a pertussis-toxin-insensitive manner with similar EC50 values and to stimulate the mobilization of intracellular Ca2+, but, despite reports that TRH receptors can also interact with the G-proteins Gs and Gi2, neither receptor splice variant was able to modulate adenylate cyclase activity in either a positive or a negative manner. These data indicate that the long and short isoforms of the rat TRH receptor have similar affinities for TRH and display similar abilities to interact with the Gq-like G-proteins, but show no ability to regulate adenylate cyclase, at least when expressed in this genetic background.

Amino Acid Sequence↗
PubMed1995

Degradation of G11 alpha/Gq alpha is accelerated by agonist occupancy of alpha 1A/D, alpha 1B, and alpha 1C adrenergic receptors.

Cells of clones of rat 1 fibroblasts transfected to express the molecularly defined alpha 1A/D, alpha 1B, or alpha 1C adrenoreceptors and prelabeled with myo-[3H]inositol were each shown to generate high levels of inositol phosphates when exposed to the alpha 1 adrenoreceptor agonist phenylephrine. Maintained exposure of each of these cells to phenylephrine resulted in a large down-regulation of the receptors and also a marked down-regulation of cellular levels of both of the phosphoinositidase C-linked G-proteins Gq alpha and G11 alpha. To examine the mechanism of phenylephrine-induced down-regulation of Gq alpha and G11 alpha, pulse-chase 35S-amino acid labeling experiments were performed with each of the alpha 1A/D, alpha 1B, and alpha 1C adrenoreceptor-expressing cell lines. The rate of degradation of G11 alpha/Gq alpha, which was adequately modeled by a monoexponential with half-life between 33 and 40 h in each of the cell lines in the absence of agonist, was accelerated substantially (some 4-fold) in the presence of phenylephrine. By contrast, the rate of degradation of the G-protein Gi2 alpha, which would not be anticipated to be activated by members of the alpha 1 adrenoreceptor family, was unaltered by the presence of phenylephrine. Levels of mRNA encoding Gq alpha and G11 alpha were not substantially altered by exposure of the cells to phenylephrine in any of the cell lines studied.

Adrenergic alpha-1 Receptor Agonists↗