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T H Chang

Publications and source records attributed to T H Chang.

At least 19 recordsLinked to original sources
PubMed1997

Requirement of the DEAD-Box protein ded1p for messenger RNA translation.

The DED1 gene, which encodes a putative RNA helicase, has been implicated in nuclear pre-messenger RNA splicing in the yeast Saccharomyces cerevisiae. It is shown here by genetic and biochemical analysis that translation, rather than splicing, is severely impaired in two newly isolated ded1 conditional mutants. Preliminary evidence suggests that the protein Ded1p may be required for the initiation step of translation, as is the distinct DEAD-box protein, eukaryotic initiation factor 4A (eIF4A). The DED1 gene could be functionally replaced by a mouse homolog, PL10, which suggests that the function of Ded1p in translation is evolutionarily conserved.

Animals↗
PubMed1997

Dbp3p, a putative RNA helicase in Saccharomyces cerevisiae, is required for efficient pre-rRNA processing predominantly at site A3.

In Saccharomyces cerevisiae, ribosomal biogenesis takes place primarily in the nucleolus, in which a single 35S precursor rRNA (pre-rRNA) is first transcribed and sequentially processed into 25S, 5.8S, and 18S mature rRNAs, leading to the formation of the 40S and 60S ribosomal subunits. Although many components involved in this process have been identified, our understanding of this important cellular process remains limited. Here we report that one of the evolutionarily conserved DEAD-box protein genes in yeast, DBP3, is required for optimal ribosomal biogenesis. DBP3 encodes a putative RNA helicase, Dbp3p, of 523 amino acids in length, which bears a highly charged amino terminus consisting of 10 tandem lysine-lysine-X repeats ([KKX] repeats). Disruption of DBP3 is not lethal but yields a slow-growth phenotype. This genetic depletion of Dbp3p results in a deficiency of 60S ribosomal subunits and a delayed synthesis of the mature 25S rRNA, which is caused by a prominent kinetic delay in pre-rRNA processing at site A3 and to a lesser extent at sites A2 and A0. These data suggest that Dbp3p may directly or indirectly facilitate RNase MRP cleavage at site A3. The direct involvement of Dbp3p in ribosomal biogenesis is supported by the finding that Dbp3p is localized predominantly in the nucleolus. In addition, we show that the [KKX] repeats are dispensable for Dbp3p's function in ribosomal biogenesis but are required for its proper localization. The [KKX] repeats thus represent a novel signaling motif for nuclear localization and/or retention.

Amino Acid Sequence↗
PubMed1996

Purification and characterization of a naturally processed hepatitis B virus peptide recognized by CD8+ cytotoxic T lymphocytes.

In vitro studies in patients with hepatitis B virus (HBV) infection have suggested that hepatocytolysis induced by CD8+ cytotoxic T lymphocytes (CTLs) is the most important effector pathway in eliminating infected cells. The recognition is implicated in the endogenously processed HBV antigens in the context of HLA class I molecules presented on the liver cell membrane. However, the naturally occurring HBV peptide antigens have not yet been demonstrated. We report here that a naturally processed peptide antigen P2 was isolated from HLA class I molecules of HBV-infected liver cell membrane. The P2 peptide exhibited the activity of sensitizing target cells for lysis by CD8+ CTLs. The P2 sequence (YVNVNMGLK) purified from liver tissue was in concordance with that encoded by the viral genome for the HBV nucleocapsid antigen or HBcAg 88-96. P2 peptide could also be isolated from the EBV-transformed B cells that were transfected by HBcAg-expressing vector. The P2 epitope, sharing the HLA-A11 binding motifs, was recognized by HLA-A11-restricted CD8+ CTLs. The data provided direct evidence that, in hepatitis B patients, antigenic peptides of HBV were processed by hepatocytes, presented with the class I MHC molecules, and recognized by CD8+ CTLs.

Adult↗
PubMed1996

Induction of cyclin A gene expression by homocysteine in vascular smooth muscle cells.

Homocysteine is an important and independent risk factor for arteriosclerosis. We showed previously that homocysteine stimulates vascular smooth muscle cell proliferation, a hallmark of arteriosclerosis. We show here that homocysteine and serum increased DNA synthesis synergistically in both human and rat aortic smooth muscle cells (RASMCs). Treatment of quiescent RASMCs with 1 mM homocysteine or 2% calf serum for 36 h increased cyclin A mRNA levels by 8- and 14-fold, respectively, whereas homocysteine plus serum increased cyclin A mRNA levels by 40-fold, indicating a synergistic induction of cyclin A mRNA. Homocysteine did not increase the half-life of cyclin A mRNA (2.9 h), but it did increase the transcriptional rate of the cyclin A gene in nuclear run-on experiments. The positive effect of homocysteine on cyclin A gene transcription was confirmed by our finding that homocysteine increased cyclin A promoter activity and ATF-binding protein levels in RASMCs. Finally, 1 mM homocysteine increased cyclin A protein levels and cyclin A-associated kinase activity by threefold. This homocysteine-induced expression lesions by promoting proliferation of vascular smooth muscle cells.

Activating Transcription Factors↗
PubMed1996

SV40 T antigen increases the expression and activities of p34cdc2, cyclin A, and cyclin B prior to immortalization of human diploid fibroblasts.

SV40 T antigen induces karyotype instability soon after it is expressed in human diploid fibroblasts and ultimately promotes cell immortalization and tumorigenesis. Protein levels and activities of mitotic cell cycle proteins have been shown to be elevated in several immortal cell lines relative to their normal parental cells, suggesting a possible role for the aberrant regulation of mitosis in karyotype instability. We show here that IMR-90 human diploid lung fibroblasts expressing the SV40 tumor antigens display increased protein levels and associated enzymatic activities of cyclin A, cyclin B, and p34cdc2 long before crisis and immortalization. These elevations cannot be explained by faster cell growth or altered cell cycle distributions. Increased protein levels were not totally accounted for by elevated levels of the corresponding mRNA, indicating that T antigen modulates expression at least partially by posttranscriptional mechanisms. These results indicate that perturbation of mitotic regulatory proteins precedes crisis, and imply that altered mitotic control is a direct consequence of T antigen expression rather than an outcome of secondary events associated with immortalization.

Amino Acid Sequence↗
PubMed1996

Mobile cecum syndrome: a report of two cases.

Mobile cecum syndrome is characterized by chronic right lower quadrant pain with the evidence of neither appendicitis nor other pathological findings at operation. Two cases of mobile cecum syndrome are reported; both had intermittent right lower quadrant cramping pain for months. One had received appendectomy because of chronic right lower quadrant pain at another hospital about nine months before admission here. The symptoms did not improve postoperatively, and the patient underwent laparotomy under impression of partial intestinal obstruction. The other patient underwent laparotomy under impression of chronic appendicitis. At surgery, both were found to have cecum and ascending colon were not attached to the posterior parietal wall, and cecopexy was performed. They have now been symptom free for one year. Cecopexy appears therefore to be an effective method of treatment of mobile cecum syndrome.

Abdominal Pain↗
PubMed1995

Expression of the Epstein-Barr virus DNA polymerase in Escherichia coli for use as antigen for the diagnosis of nasopharyngeal carcinoma.

Epstein-Barr virus (EBV) encoded DNA polymerase (POL) was cloned and over-expressed in Escherichia coli. Western blot analysis confirmed the presence of antibody to this POL protein in sera from nasopharyngeal carcinoma (NPC) patients. By Western blot analysis, moderate to high concentration of IgG POL-specific antibodies were present in 43 of 48 NPC sera and only 4 of 48 healthy, seropositive controls. The POL-specific IgG antibodies appear as early as stage I of NPC, suggesting that the recombinant POL protein can be a useful diagnostic marker for early diagnosis of the disease. It was also found that human sera containing high titer of cytomegalovirus (CMV) antibodies or herpes simplex virus type 1 (HSV-1) antibodies did not cross-react with the recombinant EBV POL, despite the homology shared by DNA polymerase proteins of these viruses.

Amino Acid Sequence↗
PubMed1994

Effects of a pyranocoumarin compound isolated from a Chinese medicinal plant on ischemic myocardial dysfunction in anesthetized dogs.

A pyranocoumarin compound, 3'-angeloyloxy-4'-acetoxy-3',4'-dihydroseselin (Pd-Ia), isolated from Bai-Hua Qian-Hu, a Chinese medicine, is known to possess a Ca2+ channel antagonist action. We examined the effect of Pd-Ia on cardiohemodynamics and regional myocardial dysfunction after transient ischemia in anesthetized open-chest dogs. I.v. injections of Pd-Ia (0.1-3.0 mg/kg, n = 7) significantly and dose dependently increased coronary blood flow and decreased mean aortic pressure, maximal rate of rise in left ventricular pressure, rate pressure product and systemic vascular resistance, together with a slight increase in heart rate. Diltiazem (0.03-1.00 mg/kg, n = 6) showed effects on the cardiohemodynamics similar to those of Pd-Ia, except for a marked decrease in heart rate. The effects of Pd-Ia on mean aortic pressure and rate pressure product were approximately 10 times less potent than those of diltiazem. In the second experiment, the effect of a 30-min infusion of Pd-Ia (0.15 mg/kg/min) or vehicle on regional myocardial dysfunction was examined in 16 anesthetized dogs subjected to a 15-min occlusion of the left anterior descending coronary artery followed by a 3-h reperfusion. Infusion of Pd-Ia was started 15 min before coronary occlusion. The vehicle caused a decrease in percent segment shortening throughout the reperfusion period (n = 8). However, Pd-Ia at the dose that produced no significant changes in cardiohemodynamics resulted in a marked improvement in percent segment shortening of the ischemic and reperfused myocardium (n = 8, P < 0.05 vs. control group).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Immune response to a hepatitis C virus nonstructural protein in chronic hepatitis C virus infection.

The immune responses to a hepatitis C virus nonstructural protein (T3Ag) overlapping with the C100-3 antigen were examined in three groups of patients with chronic non-A, non-B hepatitis. Group I included 20 cases positive for both anti-C100-3 and the second-generation anti-HCV test (anti-HCV-II): Group II, five cases with anti-C100-3(-)/anti-HCV-II(+); and Group III, seven cases negative for both tests. HCV RNA was detectable in 20 (100%), 4 (80%) and 0 (0%) patients in each group, respectively. Proliferative responses of peripheral blood mononuclear cells to T3Ag were present in 16 (80%), 3 (60%) and 0 (0%) cases in each group, respectively (p < 0.05). Removal of CD8+ T cells from peripheral blood mononuclear cells resulted in a conversion of unresponsiveness to significant proliferation to T3Ag in the remaining cases in groups I and II, but not in group III. This change paralleled the antigen-induced production of interferon-gamma and interleukin-2, but not interleukin-4. The removal also enhanced the T3Ag-stimulated anti-C100-3 antibody production from cultured peripheral blood mononuclear cells in group II patients. These results indicate that the T3Ag-specific type 1 T helper cells play an important role in regulating anti-C100-3 antibody secretion in hepatitis C patients.

Adult↗
PubMed1994

Presence of hepatitis B surface antigen (HBsAg)-specific cytotoxic T cells in asymptomatic HBsAg carriers.

To investigate whether there is any evidence of an immune stimulation against hepatitis B virus surface antigen (HBsAg) in asymptomatic HBsAg carriers, proliferative and cytotoxic responses to HBsAg were measured in their peripheral blood lymphocytes. Although the majority of asymptomatic carriers had no proliferative response to HBsAg, 3 (25%) of 12 carriers showed significant T cell proliferation against HBsAg. In addition, using HBsAg-expressing autologous lymphoblastoid cell line (LCL) as target cells, HBsAg-specific cytotoxic activity was found in 2 of 3 asymptomatic HBsAg carriers who had a proliferative response against HBsAg. Furthermore, 6 cytotoxic T lymphocyte (CTL) clones were isolated from 1 asymptomatic carrier. The epitope recognized by 2 CTL clones was mapped to the major HBsAg residues 158-172. These CTL clones were able to produce interferon-gamma, tumor necrosis factor-alpha, or granulocyte-macrophage colony-stimulating factor. These findings demonstrate the presence of HBsAg-specific, major histocompatibility complex class I-restricted CTL in asymptomatic HBsAg carriers.

Adult↗
PubMed1994

Effects of 3'-angeloyloxy-4'-acetoxy-3',4'-dihydroseselin on cardiohemodynamics in anesthetized dogs.

Cardiohemodynamic effects of 3'-angeloyloxy-4'-acetoxy-3',4'-dihydroseselin (Pd-Ia) isolated from the Chinese medicinal plant Peucedanum praeruptorum Dunn were compared with those of diltiazem (Dil) in anesthetized open-chest dogs. Pd-Ia 3 mg.kg-1 increased coronary blood flow from 25 +/- 11 to 58 +/- 16 ml.min-1 (n = 7, P < 0.01) and decreased mean aortic pressure (MAP) from 13 +/- 2 to 8 +/- 1 kPa (P < 0.01), rate pressure product (RPP) from 1.9 +/- 0.5 to 1.3 +/- 0.3 MPa.bpm (P < 0.05), +dp/dtmax from 246 +/- 56 to 160 +/- 36 kPa.s-1 (P < 0.01) and systemic vascular resistance from 19 +/- 4 to 12 +/- 7 Pa.ml-1.min-1 (P < 0.05), together with an increase in HR. Dil showed effects similar to those of Pd-Ia except for a marked decrease in HR. The effects of Pd-Ia on MAP and RPP were approximately one-tenth as potent as those of Dil. The results demonstrated that Pd-Ia was a Ca2+ channel blocker.

Animals↗
PubMed1994

Effect of dl-praeruptorin A on calcium current in ventricular cells of guinea pig.

With patch clamp technic (whole cell recording), the effect of dl-praeruptorin A (Pra), an ingredient of Peucedanum praeruptorum Dunn on calcium current (ICa) in the single ventricular cells of guinea pig was studied. Results showed that under Cs/Cs condition, when the holding potential was -40 mV and in the presence of Pra (1, 10, 100 mumol.L-1), ICa was decreased dose-dependently from 2.02 +/- 0.24, 2.00 +/- 0.12, 2.12 +/- 0.33 nA (control) to 1.60 +/- 0.24, 1.32 +/- 0.08, 1.16 +/- 0.43 nA, respectively, and their inhibitory rates were 21%, 33.5%, 45%, respectively. The current-voltage relation curve showed that the reversal potential of ICa was +60 mV; the potential producing peak value of ICa was about 0 mV. The results indicated that Pra had a Ca2+ channel blocking effect.

Animals↗
PubMed1994

Effects of 3'-angeloyloxy-4'-acetoxy-3',4'-dihydroseselin on myocardial dysfunction after a brief ischemia in anesthetized dogs.

The effect of a 30-min infusion of 3'-angeloyloxy-4'-acetoxy-3', 4'-dihydroseselin (Pd-Ia), a coumarin isolated from Peucedanum praeruptorum Dunn 0.15 mg.kg-1.min-1 on regional myocardial dysfunction was examined in 16 anesthetized open-chest dogs subjected to a 15-min occlusion of the left anterior descending coronary artery followed by a 3-h reperfusion. Segment lengths of left ventricular wall were measured with an ultrasonic micrometer. The control caused a decrease in the % of segment shortening (SS%) throughout the reperfusion period (n = 8), while Pd-Ia ameliorated segment function immediately after reperfusion and restored the SS% to 41 +/- 51% of the baseline value (n = 8, P < 0.05 vs control) 5 min after reperfusion without any significant changes in cardiohemodynamics. The improvement of myocardial function induced by Pd-Ia was maintained at least 3 h after reperfusion. These findings revealed that Pd-Ia had a cardioprotective action in stunned myocardium.

Animals↗
PubMed1993

Four yeast spliceosomal proteins (PRP5, PRP9, PRP11, and PRP21) interact to promote U2 snRNP binding to pre-mRNA.

We have analyzed the functions of several pre-mRNA processing (PRP) proteins in yeast spliceosome formation. Here, we show that PRP5 (a DEAD box helicase-like protein), PRP9, and PRP11 are each required for the U2 snRNP to bind to the pre-spliceosome during spliceosome assembly in vitro. Genetic analyses of their functions suggest that they and another protein, PRP21, act concertedly and/or interact physically with each other and with the stem-loop IIa of U2 snRNA to bind U2 snRNP to the pre-mRNA. Biochemical complementation experiments also indicate that the PRP9 and PRP11 proteins interact. The PRP9 and PRP11 proteins may be functioning similarly in yeast and mammalian cells. The requirement for ATP and the helicase-like PRP5 protein suggests that these factors might promote a conformational change (involving either the U1 or U2 snRNP) that is required for the association of U2 snRNP with the pre-mRNA.

Adenosine Triphosphate↗
PubMed1993

Whole-cell patch clamp measurements and berberine inhibition of hyperpolarization-activated inward current in rabbit sinoatrial node cells.

Single rabbit sinoatrial node (SAN) cells were isolated by means of an enzymatic dispersion procedure and used for the whole-cell patch clamp experiment. At a holding potential of -40 mV, a time- and voltage-dependent inward current, I(f), was activated at different hyperpolarization potentials from -60 mV to -110 mV. The current-voltage relation curve showed that I(f) was activated at potential more negative than -40 mV. Five min after treatment by CsCl 2 mmol.L-1-containing Tyrode solution, I(f) was almost completely blocked. At a hyperpolarization potential of -110 mV, I(f) was reduced from 1.7 +/- 0.2 nA of the control to 1.2 +/- 0.4 nA after superfusing with Tyrode solution containing berberine (Ber) 1 mumol.L-1 for 5 min. And it was difficult to wash out this action. Ber also had inhibitory effects on other currents to a certain extent. The results indicate that I(f) is a Cs(+)-sensitive current and that the negative chronotropic effect of Ber may be due to the inhibition of I(f) that functions as an important pacemaking modulator for the spontaneous depolarization of SAN tissue.

Action Potentials↗
PubMed1993

Heterogeneous blood pressure response to furosemide and captopril in primary aldosteronism.

The hypertension associated with primary aldosteronism (PA) is often regarded as volume dependent/salt-sensitive. However, not all patients sustain an increase in blood pressure upon sodium loading. In order to examine the sodium sensitivity in PA, 21 patients with aldosteronoma were tested for acute hypotensive response to intravenous furosemide and oral captopril. Ten patients having a decrease in mean blood pressure (MBP) exceeding 5% at the second hour after a 20 mg furosemide injection were defined as diuretic-responders (DR), while the remainder were defined as diuretic-non-responders (DN). The DR group had a higher baseline MBP (135 +/- 6 [mean +/- SE] vs 121 +/- 4 mmHg, p < 0.05) and serum sodium concentration (145.7 +/- 1.4 vs 143.0 +/- 0.7 mmol/L, p < 0.05) than the DN group. The extent of natriuresis induced by furosemide was not different between the two subgroups. Following 100 mg of captopril administered orally, the DR group had a smaller change in MBP (%) than the DN group (3.08 +/- 5.14 vs -7.78 +/- 3.37, p < 0.05). According to the different BP responses to furosemide and captopril, we conclude that PA patients may be further divided into DR and DN. The DR group had a good response to diuretics whereas the DN group responded better to converting enzyme inhibitors. This classification of PA in terms of blood pressure response to furosemide may have therapeutic implications.

Adult↗
PubMed1993

Production and characterization of monoclonal antibodies against alpha and beta spectrin subunits.

Twenty monoclonal antibodies against human erythrocyte spectrin were generated using purified native spectrin as the immunogen. Thirteen out of 20 monoclonal antibodies reacted to the alpha subunit, and the remaining seven monoclonal antibodies reacted to the beta subunit in Western blot analysis. One anti-beta subunit and two anti-alpha subunit monoclonal antibodies cross-reacted with the cell lysate of the non-erythroid T. lymphoma, J. Jhan, cell line. Identification of 20 monoclonal antibodies to the respective tryptic domains was also achieved. The specificity of these antibodies to respective tryptic domains of spectrin confirms the alignments and uniqueness of each of the previously identified five domains in the alpha subunit and four domains in the beta subunit, and establishes the identity of proteolytic daughter peptide fragments.

Animals↗