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T Hsieh

Publications and source records attributed to T Hsieh.

At least 19 recordsLinked to original sources
PubMed1992

Incomplete reversion of double stranded DNA cleavage mediated by Drosophila topoisomerase II: formation of single stranded DNA cleavage complex in the presence of an anti-tumor drug VM26.

Anti-tumor drug VM26 greatly stimulates topoisomerase II mediated DNA cleavage by stabilizing the cleavable complex. Addition of a strong detergent such as SDS to the cleavable complex induces the double stranded DNA cleavage. We demonstrate here that heat treatment can reverse the double stranded DNA cleavage; however, topoisomerase II remains bound to DNA even in the presence of SDS. This reversed complex has been shown to contain single strand DNA breaks with topoisomerase II covalently linked to the nicked DNA. Chelation of Mg++ by EDTA and the addition of salt to a high concentration also reverse the double strand DNA cleavage, and like heat reversion, topoisomerase II remains bound to DNA through single strand DNA break. The reversion complex can be analyzed and isolated by CsCl density gradient centrifugation. We have detected multiple discrete bands from such a gradient, corresponding to protein/DNA complexes with 1, 2, 3, ..... topoisomerase II molecules bound per DNA molecule. Analysis of topoisomerase II/DNA complexes isolated from the CsCl gradient indicates that there are single stranded DNA breaks associated with the CsCl stable complexes. Therefore, topoisomerase II/DNA complex formed in the presence of VM26 cannot be completely reversed to yield free DNA and enzyme. We discuss the possible significance of this finding to the mechanism of action of VM26 in the topoisomerase II reactions.

Animals↗
PubMed1992

Eustachian tube dysfunction in patients with nasopharyngeal carcinoma, pre- and post-irradiation.

Eustachian tube function tests were performed in 34 patients with nasopharyngeal carcinoma before and after irradiation. Tubal dysfunction prior to irradiation in these patients was due to functional impairment. However, tubal dysfunction after irradiation was due to both organic obstruction and functional impairment. Organic obstruction of the tube was found to be severe with higher dosages of irradiation (to 80 Gy) resulting in subsequent otitis media. In our experience, higher doses of irradiation should be avoided if possible, but insertion of a ventilation tube should be done if a high dose of irradiation is planned.

Adult↗
PubMed1989

Nuclease protection by Drosophila DNA topoisomerase II. Enzyme/DNA contacts at the strong topoisomerase II cleavage sites.

A DNA consensus sequence for topoisomerase II cleavage sites was derived previously based on a statistical analysis of the nucleotide sequences around 16 sites that can be efficiently cleaved by Drosophila topoisomerase II (Sander, M., and Hsieh, T. (1985) Nucleic Acids Res. 13, 1057-1072). A synthetic 21-mer DNA sequence containing this cleavage consensus sequence was cloned into a plasmid vector, and DNA topoisomerase II can cleave this sequence at the position predicted by the cleavage consensus sequence. DNase I footprint analysis showed that topoisomerase II can protect a region of approximately 25 nucleotides in both strands of the duplex DNA, with the cleavage site located near the center of the protected region. Similar correlation between the DNase I footprints and strong topoisomerase II cleavage sites has been observed in the intergenic region of the divergent HSP70 genes. This analysis therefore suggests that the strong DNA cleavage sites of Drosophila topoisomerase II likely correspond to specific DNA-binding sites of this enzyme. Furthermore, the extent of DNA contacts made by this enzyme suggests that eucaryotic topoisomerase II, in contrast to bacterial DNA bacterial DNA gyrase, cannot form a complex with extensive DNA wrapping around the enzyme. The absence of DNA wrapping is probably the mechanistic basis for the lack of DNA supercoiling action for eucaryotic topoisomerase II.

Animals↗
PubMed1989

Structure of the Drosophila DNA topoisomerase II gene. Nucleotide sequence and homology among topoisomerases II.

We have determined the nucleotide sequence of the Drosophila DNA topoisomerase II gene. Data from primer extension and S1 nuclease protection experiments were combined with comparisons of genomic and cDNA sequences to determine the structure of the mature messenger RNA. This message has a large open reading frame of 4341 nucleotides. The length of the predicted protein is 1447 amino acids with a molecular weight of 164,424. Topoisomerase II can be divided into three domains: (1) an N-terminal region with homology to the B (ATPase) subunit of the bacterial type II topoisomerase, DNA gyrase; (2) a central region with homology to the A (breaking and rejoining) subunit of DNA gyrase; (3) a C-terminal region characterized by alternating stretches of positively and negatively charged amino acids. DNA topoisomerase II from the fruit fly shares significant sequence homology with those from divergent sources, including bacteria, bacteriophage T4 and yeasts. The location and distribution of homologous stretches in these sequences are analyzed.

Amino Acid Sequence↗
PubMed1989

Effect of cranial irradiation on hypothalamus and pituitary functions.

Hypopituitarism can occur after cranial irradiation for tumors distant from the pituitary gland. Recent studies have suggested that this is hypothalamic in origin. Hypothalamic and pituitary functions were studied in 11 patients, 4 men and 7 women, 4.5 years or more after radiotherapy for nasopharyngeal carcinomas. The estimated average total dose was 5000 cGys for the hypothalamus and pituitary gland. Except for 2 women with amenorrhea and 4 men with impotency, the patients did not have evident endocrine deficiency. Baseline hormone profiles revealed normal T4, T3 and cortisol levels, 6 with elevated prolactin, 3 with reduced testosterone and 3 with slightly elevated basal TSH. The four menopausal women had impaired gonadotropin response to LHRH (100 micrograms, i.v.). Four (1 menstruating, 1 amenorrheic, 2 menopausal) women did not reach peak FSH response 4 hours after LHRH injection. The other amenorrheic woman had minimal FSH and LH response to LHRH which persisted even after 8 days of pulsatile infusion of LHRH (1 microgram/90min). TSH response to TRH (400 micrograms, i.v.) was delayed in 7 patients. GH response to human GRH (1 microgram/kg, i.v.) was impaired in 6 patients (maximal GH less than 5 mU/l). ACTH response to ovine CRH (1 microgram/kg, i.v.) was impaired in 3 patients (less than 50% elevation from baseline). Three patients who had normal GRH tests had impaired GH response to insulin hypoglycemia. Six patients had an empty sella on CT scan. From this study the following conclusions are drawn: (1) Among the four axes, GH is the most vulnerable. (2) The insulin tolerance test is still the best single test for evaluation of hypothalamic function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Malignant fibrous histiocytoma of the head and neck: report of 5 cases.

Malignant fibrous histiocytoma is a rare tumor in the head and neck region. This paper describes 5 cases, one was primary, and the remaining 4 cases were supposed to be secondary to previous radiotherapy for malignant diseases in the head and neck region. Three cases were in the maxillary sinus and two at the tongue base. All patients received surgical treatment with or without postoperative irradiation. Two patients survived more than 3 years after surgical intervention.

Adult↗
PubMed1988

Extension of nasopharyngeal carcinoma and otitis media with effusion.

In 35 patients with nasopharyngeal carcinoma that occupied the fossa of Rosenmüller, the relationship of the tumor, assessed by computed tomographic scans, to otitis media with effusion and ventilatory function of the eustachian tube was examined. Incidence of otitis media with effusion was low when the tumor was limited to the fossa of Rosenmüller (stage I), and high when the tumor extended from the fossa to the parapharyngeal space (stage II). Passive opening of the eustachian tube remained normal until the tumor occupied the parapharyngeal space (stage III). However, active tubal opening was impaired in stage I and the impairment increased with the tumor stage. These results indicate that tumor extension from the fossa of Rosenmüller to the parapharyngeal space and resultant poor active tubal opening cause the development of otitis media with effusion in patients with nasopharyngeal carcinoma.

Adult↗
PubMed1987

Sequence dependence of Drosophila topoisomerase II in plasmid relaxation and DNA binding.

The sequence dependence of Drosophila topoisomerase II supercoil relaxation and binding activities has been examined. The DNA substrates used in binding experiments were two fragments from Drosophila heat shock locus 87A7. One of these DNA fragments includes the coding region for the heat shock protein hsp70, and the other includes the intergenic non-coding region that separates two divergently transcribed copies of the hsp70 gene at the locus. The intergenic region was previously shown to have a much higher density of topoisomerase cleavage sites than the hsp70 coding region. Competition nitrocellulose filter binding assays demonstrate a preferential binding of the intergene fragment, and that binding specificity increases with increasing ionic strength. Dissociation kinetics indicate a greater kinetic stability of topoisomerase II complexes with the intergene DNA fragment. To study topoisomerase II relaxation activity, we used supercoiled plasmids that contained the same fragments from locus 87A7 cloned as inserts. The relative relaxation rates of the two plasmids were determined under several conditions of ionic strength, and when the plasmid substrates were included in separate reactions or when they were mixed in a single reaction. The relaxation properties of these two plasmids can be explained by a coincidence of high-affinity binding sites, strong cleavage sites, and sites used during the catalysis of strand passage events by topoisomerase II. Sequence dependence of topoisomerase II catalytic activity may therefore parallel the sequence dependence of DNA cleavage by this enzyme.

Animals↗
PubMed1986

Protein kinase C phosphorylates topoisomerase II: topoisomerase activation and its possible role in phorbol ester-induced differentiation of HL-60 cells.

DNA topoisomerase II from Drosophila was phosphorylated effectively by protein kinase C. With a Km of about 100 nM, the reaction was rapid, occurring at 4 degrees C as well as at 30 degrees C and requiring as little as 0.6 ng of the protein kinase per 170 ng of topoisomerase. About 0.85 mol of phosphate could be incorporated per mol of topoisomerase II, with phosphoserine as the only phospho amino acid produced. The reaction was dependent on Ca2+ and phosphatidylserine and was stimulated by phorbol esters. Calmodulin-dependent protein kinase II, but not cyclic AMP-dependent protein kinase, was also able to phosphorylate the topoisomerase. Phosphorylation of topoisomerase II by protein kinase C resulted in appreciable activation of the topoisomerase, suggesting that it may represent a possible target for the regulation of nuclear events by protein kinase C. This possibility is supported by the finding that the phorbol ester-induced differentiation of HL-60 cells was blocked by the topoisomerase II inhibitors novobiocin and 4'-(9-acridinylamino)methanesulfon-m-anisidide(m-AMSA), but not by the inactive analog o-AMSA.

Aminoacridines↗
PubMed1979

A protein that preferentially binds Drosophila satellite DNA.

Using a nitrocellulose filter binding assay, we have detected and partially purified a protein from embryos of Drosophila melanogaster that preferentially binds to a highly repeated satellite DNA of the same species. Formation of the satellite DNA-protein complex requires physiological conditions of salt and temperature, but once formed, the complex is stable in high salt (1 M NaCl) or at low temperature. Optimal formation of the specific complex also requires the satellite DNA to be in a supertwisted conformation. The protein interacts with a limited region within the 359-base-pair repeated sequence of the satellite DNA.

Animals↗
PubMed1978

Physiochemical studies on interactions between DNA and RNA polymerase. Ultraviolet absorption measurements.

The interaction between Escherichia coli RNA polymerase and a restriction fragment of coliphage T7 DNA containing four promoter sites for the coli enzyme has been studied by difference uv absorption spectroscopy in a low ionic strength buffer containing 10 mm MgCl2 and 50 mM KCl. The binding of the enzyme to the DNA is accompanied by a hyperchromic shift which shows a maximum around 260 nm, and increases with increasing temperature in the temperature range studied (4-40 degrees C). Measurements were also carried out with whole T7 DNA and a restriction fragment containing no promoter site. A comparison of the results obtained with the various DNAs suggests that the binding of an RNA polymerase to a promoter site in the low ionic strength medium causes the disruption of a short segment of the DNA helix, of the order of ten pairs; the binding of an enzyme molecule to a promotor site appears to have a cooperative effect on the binding of the enzyme molecules to adjacent non-promoter sites with concomitant disruption of DNA base pairs.

Binding Sites↗
PubMed1977

Prognosis of nasopharyngeal carcinoma by Epstein-Barr virus antibody titer.

A total of 433 samples of serum were collected from 305 patients with histopathologically proved anaplastic nasopharyngeal carcinoma (NPC). Antibodies against viral capsid antigens (VCA) of Epstein-Barr (EB) virus were titrated by means of indirect fluorescent antibody technique, using P3HR-1 cells as the target. High anti-VCA antibody titer in patients with NPC was found beginning to decline at the end of radiotherapy. Most (66.7%) of the patients were found to have a detectable reduction in antibody titer within six months after radiotherapy. Persistent high antibody titer after treatment correlates to high risk of the recurrence of the disease. This prognostic importance of anti-VCA titer becomes apparent at the end of radiotherapy, significant (P less than .05) within one year after treatment, and highly significant (P less than .0005) over one year after treatment.

Antibodies, Viral↗