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Biomedical subjects

H M Chang

Publications and source records attributed to H M Chang.

At least 73 records · Page 4Linked to original sources
PubMed1996

The cutRS signal transduction system of Streptomyces lividans represses the biosynthesis of the polyketide antibiotic actinorhodin.

The nucleotide sequence of a two-component signal transduction operon (cutRS) of Streptomyces lividans TK64 was elucidated. Transcription of the operon was detected during the transition and stationary phases of growth, initiating at a single site upstream of cutR. This promoter region also possessed promoter activity directed away from cutRS, which appears to be responsible for the previously observed suppression of the translational deficiency of a melC1 mutation. Mutations in cutR and cutS were generated by gene replacement. The resulting mutants exhibited accelerated and increased production of the polyketide antibiotic, actinorhodin, which could be reversed by introduction of cutR on a plasmid. cutRS was also shown to repress actinorhodin production in the closely related species, Streptomyces coelicolor A3(2). The cutRS operon is the second two-component system found in Streptomyces that negatively regulates secondary metabolism.

Amino Acid Sequence↗
PubMed1996

Establishment and characterization of two cell lines derived from a single hepatocellular carcinoma containing multiploid DNA distribution.

Previous studies showed that patients with resectable multiploid hepatocellular carcinoma (HCC) had lower overall survival rate and higher recurrent rate than did those with diploid or single aneuploid tumors after hepatic resection. We describe in this study the establishment and characterization of cell lines derived from a single HCC nodule containing multiploid DNA distribution. Two human HCC cell lines, designated HAGS 2.1 and HAGS 2.2, were established by primary culture and single cell cloning methods from a patient with a multiploid HCC tumor. Both cell lines expressed bile canalicular domain-specific antigen of human hepatocyte. The HAGS 2.1 cells were spindle-shaped without prominent intracellular vesicles and had a doubling time of 38 h with DNA ploidy of 4.4 N; cells of HAGS 2.2 were polygonal with many intracellular vesicles and had a doubling time of around 42 h with DNA ploidy of 5.1 N. Hepatitis B surface antigen was detectable in HAGS 2.2 but negative in HAGS 2.1 cells. Both HAGS 2.1 and HAGS 2.2 expressed major histocompatibility complex (MHC) class I antigen, but the former expressed more MHC class II antigen than did the latter. Polymerase chain reaction and subsequent single strain conformation polymorphism analysis disclosed the presence of preS and S regions and the absence of C and X regions of HBV genome in cells of both HAGS 2.1 and HAGS 2.2. We conclude that the establishment of cell lines derived from a single HCC tumor containing multiploid DNA distribution might provide a good in vitro model to study the carcinogenesis and the recurrence mechanism of human hepatocellular carcinoma.

Antigens, Neoplasm↗
PubMed1995

Attenuation of channel kinetics and conductance by cholesterol: an interpretation using structural stress as a unifying concept.

The ubiquity of cholesterol in cell membranes and changes in its concentration during development, aging and in various diseases suggest that it plays an important role in modulating cell function. We examined this possibility by monitoring the effects of cholesterol on the activity of the calcium-activated potassium (BK) channel reconstituted into lipid bilayers from rat brain homogenates. Increasing the cholesterol concentration to 11% of total lipid weight resulted in a 70% reduction in channel mean open time and a reduction of the open probability of the channel by 80%. Channel conductance was reduced by 7%. Cholesterol is known to change the order state and the modulus of compressibility of bilayers. These physico-chemical changes may be translated into an overall increase in the structural stress in the bilayer, and this force may be transmitted to proteins residing therein. By examining the characteristics of the BK channel as a function of temperature, in the presence and absence of cholesterol, we were able to estimate the activation energy based on Arrhenius plots of channel kinetics. Cholesterol reduced the activation energy of the BK channel by 50% for the open to closed transition. This result is consistent with an increased stress energy in the bilayer and favors the channel moving into the closed state. Taken together, these data are consistent with a model in which cholesterol induces structural stress which enhances the transition from the open to the closed state of the channel. We suggest that this is an important mechanism for regulating the activity of membrane-integral proteins and therefore membrane function, and that the concept of structural stress may be relevant to understanding the modulation of ion channel activity in cell membranes.

Animals↗
PubMed1995

Lipid-ion channel interactions: increasing phospholipid headgroup size but not ordering acyl chains alters reconstituted channel behavior.

We have recently shown (Chang et al., 1995) that lipid-channel interactions, exemplified by the effects of cholesterol on the calcium-activated potassium (BK) channel, profoundly affect channel properties. The present study further explores such interactions by monitoring changes in BK channel behavior after reconstitution into bilayers where the size of phospholipid (PL) headgroups is increased and where the freedom of motion (inverse order) of fatty acid chains is incremented. Increasing the PL headgroup cross-sectional area, from that of N-meth-DOPE to that of DOPC (an increase from ca. 60 to 70 A2), is associated with a doubling of the channel mean opentime. Channel conductance, however, was unaffected. Increasing the order of the fatty acid chains, from that of DOPE to POPE and to that of DEPE, had no significant effect on channel properties (at 22 degrees C). We interpret the changes reported here to reflect lipid-protein interactions through the induction of structural stress related to the headgroup structures of phospholipids.

Fatty Acids↗
PubMed1995

HLA DQA1 genotypes and its interaction with HLA DQB1 in Chinese IDDM living in Taiwan.

To study the role of the HLA DQA1 gene and its interaction with DQB1 in the susceptibility of IDDM, subjects with insulin-dependent (type 1) diabetes mellitus and non-diabetic unrelated controls were recruited from a Chinese population living in northern Taiwan. HLA DQA1 exon 2 was enzymatically amplified by polymerase chain reaction. HLA DQA1 alleles were diagnosed by dot blotting and hybridization with 11 sequence-specific oligonucleotide probes. Among all the DQA1 alleles, DQA1*0301 and DQA1*0501 were more frequent while DQA1*0102, DQA1*0103 and DQA1*0601 were less frequent in Chinese with IDDM than in controls. Among the DQA1 genotypes, only DQA1*0301/0301 and DQA1*0301/0501 were associated with increased risk to IDDM while DQA1*0301/0601 and DQA1*0102/0103 were protective against IDDM in our population. As the cell surface HLA DQ molecules were formed from each DQA1 and DQB1 alleles either in cis- or trans-position, the numbers of susceptible HLA DQ alpha beta heterodimers were then derived from the genotypes of HLA DQA1/DQB1 in each person. The numbers of the possible diabetogenic DQ alpha beta dimers correlated with the degree of risk to IDDM (r = 0.92) but were not statistically significant (p > 0.05). Subjects with absence of diabetogenic HLA DQ molecules were resistant to developing IDDM while subjects with two or more forms of diabetogenic DQ molecules were associated with increased risk to IDDM. In conclusion, both DQA1 and DQB1 genes, which determine the formation of susceptible DQ alpha beta heterodimers, were significantly associated with IDDM in Chinese subjects living in Taiwan.

Alleles↗
PubMed1994

Glycosyl-phosphatidylinositol anchor synthesis in paroxysmal nocturnal hemoglobinuria: partial or complete defect in an early step.

The defect in the biosynthesis of the glycosyl-phosphatidyl inositol (GPI) anchor in paroxysmal nocturnal hemoglobinuria (PNH) appears to be in the initial steps. In biosynthetic studies using [3H]mannose, abnormal granulocytes of eight patients, and B lymphocytes transformed by Epstein-Barr virus of six different patients synthesized dolichyl phosphoryl mannose, but little or no later mannosylated intermediates. When fused with murine cell lines known to be deficient at different biosynthetic steps of the GPI anchor, the GPI-anchor-deficient granulocytes of 21/21 patients and lymphocytes from 6/6 patients complemented all murine cell lines except those of class A; cells of this class are not able to add N-acetylglucosamine to phosphatidylinositol. These studies indicate that the defect in GPI-anchor synthesis in PNH is early in the pathway, and is the same as that of class A mutants, but may be partial in some patients, resulting in the production of small amounts of mannosylated intermediates.

Antigens, CD↗
PubMed1994

Biosynthesis and processing of the glycosylphosphatidylinositol anchor in mammalian cells.

Many T cell surface proteins are attached to the cell membrane by glycosylphosphatidylinositol (GPI) anchors, which may be involved in cell signaling, protein targeting or protein release. Proteins destined to be GPI-anchored have both N- and C-terminal signal peptides, which permit the nascent polypeptides to transverse the endoplasmic reticulum and to be transferred to preformed GPI anchors in a transamidase reaction. The biosynthetic pathway of the GPI anchor in mammalian cells has been elucidated using a panel of T cell mutants that cannot express GPI-anchored proteins on their cell surfaces. The first step in anchor biosynthesis is the transfer of N-acetylglucosamine (GlcNAc) to a phosphoinositol (PI) acceptor to form GlcNAc-PI, which is then deacetylated to form GlcN-PI. Subsequently, a fatty acid is added to the inositol ring and three mannose residues are transferred to the elongating GPI core. Finally, ethanolamine phosphates are transferred to the mannose residues. Three human cDNAs encoding for GPI synthases (Classes A, F and H) have been identified using expression cloning technique. Mutation in the X-linked class A gene was shown to be the cause of paroxysmal nocturnal hemoglobinuria, an acquired disease affecting hematopoietic stem cells in which the abnormal cells are deficient in GlcNAc-PI formation. The potential involvement of GPI-anchored proteins or GPIs in T cell activation is also discussed.

Acylation↗
PubMed1993

Correction of the class H defect in glycosylphosphatidylinositol anchor biosynthesis in Ltk- cells by a human cDNA clone.

Previous attempts to express glycosylphosphatidylinositol-anchored proteins in Ltk- cells have not been successful because Ltk- cells cannot synthesize N-acetylglucosamine-phosphatidylinositol, the first intermediate in anchor biosynthesis. Using complementation cloning, we have identified a human cDNA that corrects the defect in anchor biosynthesis and allows the expression of glycosylphosphatidylinositol-anchored proteins in Ltk- cells. The nucleotide sequence predicts a novel cytosolic protein of 188 amino acids.

Amino Acid Sequence↗
PubMed1993

Lithospermic acid B as an antioxidant-based protector of cultured ventricular myocytes and aortic endothelial cells of rabbits.

Lithospermic acid B, an active principle found in a Chinese herbal medicine for treating various heart ailments, was recently isolated, purified and demonstrated by us to salvage the postischemic rabbit heart from reperfusion injury. In this work, we further report that lithospermate B is able to protect each of two types of rabbit cardiocytes, namely ventricular myocytes and aortic endothelial cells against necrosis inflicted by oxyradicals generated pharmacologically with xanthine oxidase and hypoxanthine. Biochemically, the lithospermate B also inhibits the reduction of cytochrome c by superoxide radical anion. Thus, our in vitro data here are in concord with our earlier in vivo finding that lithospermic acid B is most likely an effective antioxidant-based myocardial protector.

Animals↗
PubMed1993

Comparison of antitumor activity of vitamins K1, K2 and K3 on human tumor cells by two (MTT and SRB) cell viability assays.

Vitamin K (VK) congeners (VK1, VK2, and VK3) have been used as antihemorrhagic agents, while VK3 has also been found to inhibit growth in various rodent and human tumor cells. We have compared the antitumor activities of vitamin K1, K2, and K3 against a panel of human cancer cell lines. For each test agent, a dose-response profile was generated by using an MTT (3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) and an SRB (sulforhodamine B) assay. Both assays yielded similar results. The respective ID50 values of VK3 in five hepatoma cell lines, HA59T, HA22T, PLC, HepG2, and Hep3B, of increasing differentiation state, were 42, 36, 28, 27, and 20 microM. For nasopharyngeal carcinoma (CG1), leukemia (U937), oral epidermoid carcinoma (KB), and breast carcinoma (BC-M1) cells, the ID50 values of VK3 were 26, 15, 25, and 33 microM, respectively. For all the above cells, the ID50 values of VK1 ranged from 6 to 9 mM, and the ID50 values of VK2 ranged from 1 to 2 mM. Thus, the relative potencies of antitumor activity of VK3 compared to VK2 and to VK1 are about 60- and 300-fold, respectively. These results support the preference for use of VK3 over VK1 and VK2 in cancer therapy.

Antineoplastic Agents↗
PubMed1993

Can determination of the proliferative capacity of the nontumor portion predict the risk of tumor recurrence in the liver remnant after resection of human hepatocellular carcinoma?

To test the hypothesis that increased proliferative capacity of cells in a liver remnant is a risk factor for tumor recurrence in patients who have undergone liver resection for hepatocellular carcinoma, DNA flow-cytometric measurement and cell-cycle analysis of the nontumor parts of resected hepatocellular carcinomas (tumor size < 5 cm) were performed. The disease-free survival rates 1, 2, 3 and 4 yr after surgery were 64%, 58%, 43%, and 36%, respectively. Proliferative capacity (fractions of synthetic, postsynthetic and mitotic phases) of the nontumor parts, irrespective of liver pathology, was higher than that of normal liver and statistically lower than that of tumor parts from resected hepatocellular carcinoma specimens. Livers with chronic active hepatitis (+) and with hepatocyte dysplasia (-) had significantly lower proliferative activity than did those with chronic active hepatitis (-) and with hepatocyte dysplasia (+), respectively [corrected]. We saw no significant difference in proliferative capacity between patients with and without cirrhosis. Disease-free-survival analysis showed that the presence of liver pathology (hepatitis B infection, cirrhosis, chronic active hepatitis and hepatocyte dysplasia) was not the factor linked to tumor recurrence in the liver remnant and that a marked increase in proliferative capacity (> or = 18%), regardless of liver pathology, was the risk factor linked to tumor recurrence after liver resection. We conclude that there is some degree of increased proliferative capacity in the nontumor parts of resected hepatocellular carcinomas and that a marked increase in the proliferative capacity (> or = 18%) of the nontumor part is a significant risk factor in predicting tumor recurrence in the liver remnant after liver resection.

Aged↗
PubMed1992

Identification of a missing link in glycosylphosphatidylinositol anchor biosynthesis in mammalian cells.

A large number of mammalian proteins are anchored to the cell membrane by a glycosylphosphatidylinositol (GPI) anchor. Biosynthetic intermediates of the GPI anchor have been identified in mammalian cells. The early GPI precursors are sensitive to phosphatidylinositol (PI)-specific phospholipase C (PLC). However, all of the later GPI precursors, which contain 1 or more mannose residues, are PI-PLC-resistant, suggesting that there is another unidentified precursor. Here, we report the identification of this missing link. This GPI precursor can only be labeled with glucosamine and inositol, and is resistant to PI-PLC but sensitive to GPI-phospholipase D. It accumulates in large quantity only in mutants which are defective in the addition of the first mannose residue to the elongating GPI core. Thus, fatty acylation of glucosaminylphosphatidylinositol, to render it PI-PLC-resistant, is an obligatory step in the biosynthesis of mammalian GPI anchor precursors.

Animals↗
PubMed1992

Defective glycosylphosphatidylinositol anchor synthesis in paroxysmal nocturnal hemoglobinuria granulocytes.

To investigate the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor in the granulocytes of paroxysmal nocturnal hemoglobinuria (PNH), the glycolipids of granulocytes from PNH patients and normal volunteers were biosynthetically labeled with [3H]mannose in the presence of tunicamycin. Extracted glycolipids were examined by thin-layer chromatography and compared with known biosynthetic intermediates. Normal granulocytes consistently showed [3H]mannose incorporation into the complete GPI core, several GPI biosynthetic intermediates, and dolichol phosphate mannose (DPM). The granulocytes of 10 patients with PNH that had no expression of CD55 and CD59 on greater than 95% of the cells were able to incorporate [3H]mannose into DPM, but were not able to incorporate detectable amounts into the complete GPI core. THus, PNH granulocytes do not synthesize detectable amounts of the complete GPI core and this defect likely accounts for the absence of GPI-linked membrane proteins on hematopoietic cells in this syndrome.

Antigens, CD↗
PubMed1992

Clinicopathologic comparisons between estrogen receptor-positive and -negative gastric cancers.

We report that a modified dextran-coated charcoal (DCC) assay, including the addition of sodium molybdate and 5% DCC stripping of endogenous hormone, detected higher estrogen receptors (ERs) than those by the conventional assay. ERs in 21 gastric adenocarcinoma were determined by the modified DCC assay; 13 patients had ERs of 2.5 to 520.2 fmol/mg protein with a mean dissociation constant of 1.9 x 10(-10) M. The remaining 8 patients had no detectable amount of the receptor. There were no differences between the ER-positive and ER-negative groups in clinico-pathologic characteristics such as age, sex, tumor size, location, gross appearance, invasive depth, invasion of lymph vessel or vein of stomach wall, nodal involvement, peritoneal dissemination, liver metastasis, and curability. Histological analysis, using Japanese, Lauren's, or Ming's classifications, all revealed no differences between the ER-positive and -negative groups. The survival rate was identical for the 2 study groups. These results suggest that the presence or absence of ERs in gastric adenocarcinoma does not correlate to either biologic or clinicopathologic characteristics of this tumor; the role of ERs in human gastric cancer remains to be elucidated.

Adenocarcinoma↗
PubMed1992

The nontransformed progesterone and estrogen receptors in gastric cancer.

Contents of the progesterone receptors (PgR) and estrogen receptors (ER) in 18 gastric adenocarcinoma tissues were determined using both the dextran-coated charcoal (DCC) assay and enzyme immunoassay (EIA). PgR were found in 15 cancer tissues (range, 1.0-58.8 fmol/mg protein) and 12 normal mucosal tissues (range, 1.4-26.8 fmol/mg protein) by DCC assay, whereas only 6 cancer tissues (ranged, 0.2-3.3 fmol/mg protein) and 7 normal mucosal tissues (range, 0.1-0.8 fmol/mg protein) had measurable PgR by EIA analysis. Similar results were observed for ER. DCC assay found ER in 12 cancer tissues (range, 2.9-112.6 fmol/mg protein) and 12 normal mucosal tissues (range, 1.2-36.6 fmol/mg protein), whereas EIA measured ER in 16 cancer tissues (range, 0.1-3.5 fmol/mg protein) and 15 normal mucosal tissues (range, 0.1-4.8 fmol/mg protein). No significant correlation between DCC and EIA was observed for either PgR or ER. DCC assay and its modified procedures including 5% DCC stripping of cytosol and/or the addition of sodium molybdate in buffer were simultaneously measured in 5 gastric adenocarcinoma tissues and 1 gastritis cystica polyposa tissue (a precancerous lesion). Higher receptor levels were found by the modified procedures than by conventional method. Using the DCC procedure with addition of sodium molybdate in buffer for receptor analysis, PgR and ER were found in gastric tissues in six patients, with significantly increased levels of measurable PgR. The results suggest that PgR and ER may be involved in the physiology of normal and gastric cancer tissues; their clinical implications are worthy of further study.

Aged↗
PubMed1992

Pathophysiology and principles of pain management in rheumatic diseases.

Pain is a major presenting symptom in patients with rheumatic diseases. It is difficult, however, to define pain precisely because there are both objective and subjective components to the experience of pain. Thus, patients with the same degree of tissue inflammation may experience different levels of pain. The variation in individual pain experience often presents us with a diagnostic and therapeutic dilemma. Pain management, therefore, must be based on a solid understanding of the pathophysiology of pain and on a careful review of the risks, benefits, cost, and efficacy of available treatments.

Analgesics↗