Biomedical subjects

H C Chen

Publications and source records attributed to H C Chen.

At least 19 recordsLinked to original sources

PubMed1992

Phosphorylation of CCAAT-enhancer binding protein by protein kinase C attenuates site-selective DNA binding.

Four DNA-recombinant proteins, corresponding to the DNA-binding domain of CCAAT/enhancer binding protein (C/EBP), were phosphorylated in vitro by protein kinase C (PKC). High-performance liquid chromatography-peptide mapping of 32P-labeled C/EBP indicated the presence of three major 32P-labeled peptides: S299 (P)RDK, AKKS277 (P)VDK, and GAAGLPGPGGS248 (P)LK. Phosphorylation of C/EBP by PKC or M-kinase resulted in an attenuation of binding to a 32P-labeled CCAAT oligodeoxynucleotide. Three other truncated forms of C/EBP, C/EBP87, C/EBP87S-C, and C/EBP60, were studied to define the sites of phosphorylation affecting DNA binding. Phosphorylation of the C/EBP87, containing sites Ser299 and Ser277, and C/EBP60, containing only site Ser299, by PKC also resulted in attenuation of DNA binding. In contrast, phosphorylation of C/EBP87S-C, which retained Ser277 but had a Cys in place of Ser299, had no effect on DNA binding. Ser299 could not be phosphorylated by PKC if the protein is already bound to specific DNA. Phosphorylation of intact C/EBP from liver nuclear extract by PKC or M-kinase occurred at Ser299 and Ser277 and at an additional site, as demonstrated by immunoprecipitation and peptide mapping.

Amino Acid Sequence↗

PubMed1992

Characterization of a HeLa cDNA clone encoding the human SII protein, an elongation factor for RNA polymerase II.

We present the cloning and sequence characterization of a HeLa cDNA encoding the SII transcription elongation factor. This cDNA clone is distinct from those previously isolated from a human kidney cDNA library [Yoo et al., Nucleic Acids Res. 19 (1991) 1073-1079]. Southern analysis suggests that more than one gene may exist for SII in the human genome. A comparison of deduced amino acid sequences for SII-related proteins from a variety of eukaryotes demonstrates very high similarity, especially within the C-terminal domain.

Amino Acid Sequence↗

PubMed1992

Antitumor activity of magainin analogues against human lung cancer cell lines.

Magainin 1 and magainin 2, originally isolated from African clawed frog Xenopus laevis skin, inhibit the growth of bacteria and fungi. Synthetic magainin A (MAG A) and magainin G (MAG G) are more potent against bacteria and protozoa. In order to determine the antitumor activity of these analogues, we have tested these two analogues against six small cell lung cancer (SCLC) cell lines NCI-H82, NCI-H526, NCI-H678, NCI-H735, NCI-H841, and NCI-H889, which were known to differ by more than 10-fold in their sensitivity to different chemotherapeutic agents, and four normal human fibroblast cell lines. Semiautomated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays of the six SCLC cell lines revealed average concentrations producing 50% inhibition (IC50) values of 2.6 microM (range, 0.49-9.30 microM) for cisplatin, 2.5 microM (range, 0.39-6.00 microM) for etoposide, and 138.8 nM (range, 55.0-450.0 nM) for doxorubicin. The average IC50 of MAG A was 8.64 microM (range, 6.23-11.7 microM) and that of MAG G was 8.82 microM (range, 4.44-12.5 microM) against the SCLC cell lines. Despite a 10-fold difference in sensitivity to standard chemotherapeutic agents, the IC50 of MAG A and MAG G differs by less than 3-fold. The average IC50 against four normal human fibroblast cell lines was 21.1 microM (range, 12.7-25.6 microM) for MAG A and 29.2 microM (range, 21.3-34.8 microM) for MAG G. Combined exposure to the IC50 concentration of MAG A or MAG G plus IC50 of etoposide or cisplatin decreased the percentage of surviving SCLC cells to 29.0% (range, 26.1-31.7%). MAG A or MAG G had an additive effect when used with standard chemotherapeutic agents. These data suggest that MAG A and MAG G have in vitro antitumor activity against SCLC cell lines.

Antimicrobial Cationic Peptides↗

PubMed1992

Molecular and immunological characterization of ADP-ribosylarginine hydrolases.

Mono-ADP-ribosylation is a reversible modification of proteins with NAD:arginine ADP-ribosyltransferases and ADP-ribosylarginine hydrolases catalyzing the forward and reverse reactions, respectively. Hydrolase activities were present in a variety of animal species, with the highest specific activities found in rat and mouse brain, spleen, and testis. Rat and mouse hydrolases were dithiothreitol- and Mg(2+)-dependent, whereas the bovine and guinea pig enzymes were dithiothreitol-independent. A rat brain hydrolase was purified approximately 20,000-fold and represented the major approximately 39-kDa protein on denaturing gels. Immunoaffinity-purified rabbit polyclonal antibodies reacted with 39-kDa proteins from turkey erythrocytes and rat, mouse, and calf brains. A rat brain cDNA library was screened using oligonucleotide and polymerase chain reaction-generated cDNA probes. Inserts from two overlapping clones yielded a composite sequence that included a 1086-base pair open reading frame, which contained amino acid sequences found in the purified hydrolase. A hydrolase fusion protein, synthesized in Escherichia coli, reacted with anti-39-kDa polyclonal antibodies and exhibited Mg(2+)- and dithiothreitol-dependent hydrolase activity. A coding region cDNA hybridized readily to a 1.7-kilobase band in rat and mouse poly(A)+ RNA, but poorly to bovine, chicken, rabbit, and human poly(A)+ RNA. The immunological and molecular biological data are consistent with partial conservation of hydrolase structure across animal species.

Amino Acid Sequence↗

PubMed1992

Evidence for two cDNA clones encoding human GM2-activator protein.

Two cDNAs encoding GM2 activator, pGM2A (648 bp) and GAP (1093 bp), were isolated from human placenta lambda gt11 libraries. The DNA sequence of pGM2A from 1 to 302 was almost identical with GAP, but diverged from 303-648. PCR was used to demonstrate the presence of both species of GM2 activator in placental RNA. Both cDNAs hybridized to mRNAs of approximately 2.3 kb and to identical single bands on genomic Southern blots.

Amino Acid Sequence↗

PubMed1992

Oxidative metabolism of polymorphonuclear leukocytes (PMN) in patients with IgA nephropathy.

The production of hydrogen peroxide (H2O2) by neutrophilic polymorphonuclear leukocytes (PMN) after stimulation and the infiltration of PMN in glomeruli were determined in 20 patients with primary IgA nephropathy. The H2O2 production of PMN after the stimulation was measured with a spectrophotometer using horseradish peroxidase as substrate. The results were as follows: 1) when PMN were pretreated with cytochalasin B, H2O2 production after stimulation with heat-aggregated IgG (IgG) or serum-treated zymosan (STZ) was significantly higher in patients with IgA nephropathy than in controls, and 2) there was an increased amount of PMN localized in glomeruli in patients with IgA nephropathy using immunofluorescence of monoclonal anti-PMN antibody. It appeared that the increased renal infiltration of PMN which have a high potential for production of reactive oxygen species might induce the glomerular injuries in patients with IgA nephropathy.

Adult↗

PubMed1992

High-density Escherichia coli cultivation process for hyperexpression of recombinant porcine growth hormone.

Fermentation studies were performed on an Escherichia coli culture that carries a recombinant plasmid composed of an ampicillin-resistant gene, a temperature-regulated pL promoter, and a porcine pituitary cDNA sequence coding for growth hormone. The objective was to achieve high cell density while maintaining the specific expression level of recombinant porcine growth hormone (r-pGH) observed in shake flasks. At a specific expression level of 20% of total cell protein, the cell density of a glucose-limited fed-batch process reached 38 units of OD600 in 14 h, compared to flask cultivation, which resulted in only 1.4 units of OD600 in the same period. The observed critical fermentation conditions for maximal expression included (1) limiting glucose concentration below 1 g l-1 throughout the fed-batch growth and induction phases, (2) keeping postinduction temperature at 42 degrees C for 5-7 h, and (3) maintaining a postinduction growth rate around 0.17-0.21 h-1.

Animals↗

PubMed1992

Comparisons of the effects of calcium carbonate and calcium acetate on zinc tolerance test in hemodialysis patients.

Because aluminum hydroxide, as a phosphate binder, lowered intestinal zinc absorption, we studied the effects of calcium carbonate (CaCO3) and calcium acetate (CaAc), two other phosphate binders, on intestinal Zn absorption in nine patients on hemodialysis and in 11 controls by measuring 1- and 2-hour serum Zn levels after oral administration of 50 mg of elemental Zn as Zn gluconate with or without concomitant administration of 2 g CaCO3 (800 mg elemental Ca) or 3 g CaAc (750 mg elemental Ca). Fasting serum Zn levels were not different between patients and controls (14.0 +/- 2.3 v 14.1 +/- 1.2 mumol/L [91.8 +/- 14.9 v 92.3 +/- 8.0 micrograms/dL]), but the area under the curve of serum Zn increment (AUC) 2 hours after an oral Zn challenge without or with either of two of phosphate binders used was significantly smaller in patients than in controls (P less than 0.05). The AUC after concomitant administration of Zn with CaCO3 did not differ from that of Zn alone in either patients or controls, but it was significantly less in Zn with CaAc than in Zn alone or in Zn with CaCO3 in both groups. The results demonstrate that intestinal Zn absorption after an oral Zn challenge decreased in patients on hemodialysis and concomitant administration of CaAc, but CaCO3 did not decrease intestinal Zn absorption in either group.

Acetates↗

PubMed1992

Penetration of several filter materials by asbestos as a function of fiber dimensions.

The purpose of this research was to determine the penetration of several filter materials commonly used in building air-handling systems by asbestos fibers. An airstream containing tremolite asbestos fibers was passed through these materials and the upstream and downstream fiber concentrations were measured by membrane filtration and scanning electron microscopy. The penetration of these materials was determined as a function of asbestos fiber diameter and length at two typical air velocities. For glass fiber filter materials, the maximum penetrations were 3.5% and 0.1% compared with American Society for Testing and Materials dust spot efficiency ratings of 80% and 90%, respectively. Thus, the glass fiber filters appear to be capable of greatly reducing the concentration of asbestos fibers in a building air-handling system. Roll and panel filter materials consisting of polyester fibers exhibited penetrations from 15% to nearly 90%. Thus, roll and panel filters tested are not recommended for this purpose.

Air Movements↗

PubMed1992

Compound functioning free muscle flap transplantation (lateral half of soleus, fibula, and skin flap).

The functioning free-muscle transfer is a microneurovascular technique that has proven effective for patients who have a major muscle or muscle group loss for which no other less complicated procedures are available. A new functioning muscle (lateral half of the soleus) transfer was used for forearm reconstruction. This functioning muscle can be transferred alone, or it can be used with overlying skin or nearby fibular bone or both. It was used in a selective complicated case in which not only were major functional muscles lost, but a bone deficiency and skin loss also were seen. The operation was done in one stage with the composite flap (muscle plus bone plus skin). The recovered transferred muscle provided adequate strength and excursion for a functional hand and forearm.

Adolescent↗

PubMed1992

Patch esophagoplasty with free forearm flap for focal stricture of the pharyngoesophageal junction and the cervical esophagus.

Focal stricture of the cervical esophagus can be caused by corrosive injury or irradiation or following esophageal reconstruction. For severe stricture that cannot be relieved by bougie dilatation, surgical correction should be done. Among the operations performed, the myocutaneous flap is considered the first choice. Patch esophagoplasty with a free flap is indicated in the following situations: (1) when the patient is a young woman, (2) when the patient is obese, and (3) following irradiation that renders myocutaneous flaps unreliable. For correction of focal stricture of the cervical esophagus, six patients underwent esophagoplasty with a patch of free forearm flap. In comparison with other methods, this approach is associated with less morbidity and a better aesthetic result. The patients started oral intake at 1 month. Only one patient had minor leakage, and this healed after conservative treatment. The skin patch inserted in the esophageal wall caused no problem in motility, and the patients could eat smoothly after surgery.

Adult↗

PubMed1992

Technique of foot lengthening and shaping with free vascularized iliac osteocutaneous flap.

The iliac osteocutaneous flap has been used widely to replace bony defects of the mandible and the extremities. We report a further application of this flap in foot reconstruction. The iliac osteocutaneous flap proved to be of value to augment both soft tissue and bone in a transmetatarsally amputated foot. This resulted in satisfactory function and an appealing cosmetic result, allowing the patient to wear normal shoes. Flap design and secondary contouring procedures are described for the success of this reconstruction.

Adult↗

PubMed1992

Free forearm flap for closure of difficult oronasal fistulas in cleft palate patients.

There were four patients with palatal clefts who had been operated on many times previously but who still had large oronasal defects due to wound disruption. Moreover, there was considerable scar in the residual palatal tissue, which was contracted in the anteroposterior dimension. These patients were treated with a radial forearm flap transfer. The technical aspects of this reconstruction are emphasized, especially methods to enhance primary healing and to facilitate in setting the flap. Three of the patients were successfully reconstructed with one operation. The fourth had a small area of dehiscence anteriorly that was later closed with advancement of the flap tissue. There were no other complications. With the replacement of healthy tissue, the palate could be pushed further back to achieve better repair of the muscle. This would contribute to better speech function. In every patient, nasal regurgitation was eliminated, and speech quality improved significantly. The radial forearm flap is ideal for intraoral use, providing thin, hairless skin with a long, large-caliber vascular pedicle. It can reconstruct defects in one stage with well-vascularized tissue and minimal dissection of the palate. In a select group of cleft palate patients, this free-tissue transfer should be considered to achieve closure of large oronasal fistulas in patients with dense scar.

Adult↗

PubMed1992

Histiocytic sarcoma in an aging gerbil.

A histiocytic sarcoma in an aging female gerbil is described. The neoplasm primarily involved the spleen and liver, and these organs were considered the primary sites of neoplastic origin. No neoplastic infiltration was noted in the uterus or ovaries as is commonly seen in the female mouse. This is the first report of histiocytic sarcoma in gerbils.

Animals↗

PubMed1992

Molecular cloning and expression of a full-length complementary DNA encoding the guinea pig adrenocortical estrogen sulfotransferase.

Complementary DNA for the guinea pig adrenocortical estrogen sulfotransferase (EST) has been cloned and expressed. Oligonucleotides, based on amino acid sequences of the purified 34-kilodalton protein, were synthesized and used to generate a specific probe by polymerase chain reaction for screening a guinea pig adrenal cDNA library. The polymerase chain reaction rapid amplification of cDNA ends procedure was employed to obtain the 3' and 5' cDNA ends, and a full-length cDNA was constructed. The cloned cDNA consists of 1192 base pairs and encodes a protein of 296 amino acids with a calculated molecular mass of 35,161 daltons. A computer search of the protein data banks revealed significant homology with several sulfotransferases: 71% with bovine placental estrogen sulfotransferase, 52% with rat liver phenol sulfotransferase, 35% with rat liver hydroxysteroid sulfotransferase, and 36% with rat liver senescence marker protein 2. The EST cDNA was inserted into the pcDNA I eukaryotic expression vector and transfected into COS-7 cells. The successful expression of EST cDNA in COS-7 cells was ascertained by Western blot analysis using antibody generated against the protein used to obtain the original amino acid sequence. Additionally, the expressed protein was clearly functional. Only after transfection with EST cDNA was there detectable estradiol sulfotransferase activity in COS-7 cell cytosol. The expressed EST had a single pI of 6.4, whereas native guinea pig adrenocortical EST exhibits four primary charge isoforms. The majority of adrenocortical EST activity focuses as a broad bimodal band in the pH range of 6.6-6.2; additionally, three other discrete immunocross-reactive isoforms are present with pIs of 5.5, 5.4, and 5.2. Antibodies generated against each individual isoform cross-react with all the other isoforms and with the expressed protein. These isoforms were previously reported to be isomers of a pregnenolone-binding protein; however it is now evident that the isoforms and antibodies raised against them are EST specific. Under high stringency hybridization conditions, EST mRNA was only detected in the adrenal gland, where two mRNA species of 1.4 and 1.8 kilobases were evident; when low stringency conditions were used, a faint 1.4-kilobase band was also detected in the liver. Primer extension analysis revealed that the multiple mRNAs do not arise from differential transcription initiation sites, and genomic Southern blot analysis indicated that the multiple mRNAs arise from a single gene.

Adrenal Cortex↗

PubMed1992

Going deep into chemical burns.

This is a five year retrospective study of chemical burn injury in our burn center between 1 January 1987 and 31 December 1991. Of the 1,226 total burn cases, 131 patients had chemical burns. We noted a constant prevailing incidence of 10.7% per year. Males (72%) are more common than females (28%). Most of those injured are in the working age group (65%). Majority of cases had deep full thickness burn involving less than 10% of their total body surface area. Sulfuric acid is the most common chemical agent encountered. We had three mortality cases with deep third degree burns covering 60% of their total body surface area. Some clinical cases are demonstrated. Lastly, proposed solutions for the prevention of chemical burns are cited.

Accidents, Occupational↗

PubMed1992

High resolution electron microscopic investigation of atomic structural images in human atherosclerotic plaque.

Atomic structural images in the calcified matrix of human atherosclerotic plaques were characterized by high-resolution electron microscopy (HREM). The mineral elements distributed in the calcified matrix were analysed by energy dispersive X-ray microanalysis. Careful HREM observations revealed that a large number of microcrystallites and crystal particles with a broad spectrum of crystal size and perfection were embedded in the amorphous matrix of the calcified plaques. The amorphous phase in the calcified matrix was made up of a dense network of granulo-fibrillar substructures. The lattice-fringes with regular arrangement of atom columns along the lattice arrays were clearly demonstrated in the crystalline particles of the calcified plaques. A number of characteristic granulo-fibrillar substructures in the amorphous phase could be seen to be tightly connected to the lattice-fringes in the crystalline phase along the interfaces between the amorphous and crystalline phases. The crystal lattices at the boundary between two crystals were very well matched with the periodicity of visible atoms continuous through the two crystals. The mineral elements such as calcium and phosphorus were detected to be diffusely distributed in the calcified matrix of the atherosclerotic plaques. Based on these findings, it is concluded that: (1) an interlacing network of granulo-fibrillar substructures in the amorphous matrix may play a structural and/or regulatory role for the organic matrix by providing sites for nucleation; and (2) the deposition of the mineral elements may be effective for the transformation of the amorphous nucleation phase to well-crystallized nucleation phase.

Aorta↗

PubMed1992

Anti-HIV plant proteins catalyze topological changes of DNA into inactive forms.

GAP 31, DAP 32 and DAP 30 comprise a new class of plant proteins with potent anti-HIV activity and insignificant cytotoxicity. We report here the identification and characterization of a new DNA enzyme activity in these three proteins. They irreversibly relax and decatenate supercoiled DNA, as well as catalyze double-stranded breakage to form linear DNA. The relaxed molecules are topologically inactive and no longer serve as substrates for DNA gyrase to form supercoils, phenomena similar to those of cellular topoisomerases in the presence of topoisomerase poisons. The ability of these anti-HIV agents to interrupt essential topological interconversions of DNA may provide a novel mechanism for their antiviral and antitumor actions. The presence of this new DNA topological enzyme activity in these plant proteins also suggests that their anti-HIV activity may not be merely a consequence of ribosome inactivation previously recognized.

Amino Acid Sequence↗