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G Chu

Publications and source records attributed to G Chu.

At least 55 records · Page 3Linked to original sources
PubMed1996

Isolation of a cDNA encoding a UV-damaged DNA binding factor defective in xeroderma pigmentosum group E cells.

XPE binding factor (XPE-BF) is deficient in a subset of patients from xeroderma pigmentosum complementation group E. Binding activity copurifies with a 125 kDa polypeptide (p125) that binds to DNA damaged by ultraviolet (UV) radiation and many other agents. We isolated cDNA encoding a polypeptide with a predicted amino acid sequence that matched the sequences of eleven tryptic peptides derived from digestion of XPE-BF purified from human placenta. In vitro transcription and translation of the cDNA yielded a polypeptide of 125 kDa that bound specifically to UV-damaged DNA. Therefore the cDNA encodes either all or the major component of XPE-BF.

Amino Acid Sequence↗
PubMed1996

Xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy: do the genes explain the diseases?

Xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy are three distinct human syndromes associated with sensitivity to ultraviolet radiation. We review evidence that these syndromes overlap with each other and arise from mutations in genes involved in nucleotide-excision repair and RNA transcription. Attempts have been made to explain the syndromes in terms of defects in repair and transcription. These two biochemical pathways do not easily account for all the features of the syndromes. Therefore, we propose a third pathway, in which the syndromes are due, in part, to defects in a demethylation mechanism involving the excision of methylated cytosine. Perturbation of demethylation could affect the developmentally regulated expression of some genes.

Animals↗
PubMed1996

Laser palliation of inoperable malignant dysphagia: initial and at death.

BACKGROUND: Nd: YAG laser therapy has been shown to be highly effective in the palliation of dysphagia due to inoperable esophageal malignancy. However, the duration of response and the degree of palliation present at death have not been adequately addressed. METHODS: Seventy consecutive patients with inoperable malignant dysphagia (mean age, 70 years; 48 men, 22 women) underwent palliative laser therapy. Dysphagia was assessed on a 5-point scale (0, normal; 4, complete dysphagia) before and after laser therapy and within 2 weeks of death. RESULTS: Ninety-six percent of patients were palliated initially (70% successful, 26% partial). Mean swallowing score improved from 2.3 to 1.1 (p < 0.001) with a mean of 1.9 initial treatment sessions. Swallowing score remained improved in the last two weeks of life at a mean of 1.7 (p < 0.001). Seventy-three percent of patients were palliated at death (36% successful, 37% partial); median survival was six months. The mean total number of laser sessions was 3.4, with a mean time interval between laser sessions of 27.2 days. Complications included one perforation (1.4%) resulting in death. CONCLUSION: Endoscopic laser therapy provides safe and effective initial palliation of inoperable malignant dysphagia. In the majority of patients the palliation is maintained until death.

Aged↗
PubMed1996

Ku86 defines the genetic defect and restores X-ray resistance and V(D)J recombination to complementation group 5 hamster cell mutants.

X-ray-sensitive hamster cells in complementation groups 4, 5, 6, and 7 are impaired for both double-strand break repair and V(D)J recombination. Here we show that in two mutant cell lines (XR-V15B and XR-V9B) from group 5, the genetic defects are in the gene encoding the 86-kDa subunit of the Ku autoantigen, a nuclear protein that binds to the double-stranded DNA ends. These mutants express Ku86 mRNA containing deletions of 138 and 252 bp, respectively, and the encoded proteins contain internal, in-frame deletions of 46 and 84 amino acids. Two X-ray-resistant revertants of XR-V15B expressed two Ku86 transcripts, one with and one without the deletion, suggesting that reversion occurred by activation of a silent wild-type allele. Transfection of full-length cDNA encoding hamster Ku86 into XR-V15B cells resulted in a complete rescue of DNA-end-binding (DEB) activity and Ku70 levels, suggesting that Ku86 stabilizes the Ku70 polypeptide. In addition, cells expressing wild-type levels of DEB activity were fully rescued for X-ray resistance and V(D)J recombination, whereas cells expressing lower levels of DEB activity were only partially rescued. Thus, Ku is an essential component of the pathway(s) utilized for the resolution of DNA double-strand breaks induced by either X rays or V(D)J recombination, and mutations in the Ku86 gene are responsible for the phenotype of group 5 cells.

Amino Acid Sequence↗
PubMed1996

Comparison of three faecal occult blood tests in the detection of colorectal neoplasia.

METHODS AND AIMS: For the detection of colorectal neoplasia, 192 consecutive patients had colonoscopy to evaluate the sensitivity and specificity of three faecal occult blood tests (FOBT). Of 160 evaluable patients (96 female, mean age 51.9), 21 patients (13.1%) had adenomas and three patients (1.9%) had colorectal carcinoma. RESULTS: When comparing all three faecal occult blood tests for the detection of colorectal neoplasia, the sensitivity of Monohaem (43.8%) was superior to both Hemoccult II (25%) and to BM-Test colon albumin (25%). The specificity of Monohaem (94.6%) was greater than both Hemoccult II (88%) and BM-Test colon albumin (89%). Using McNemar's test, Monohaem was a more accurate FOBT than Hemoccult II and BM-Test albumin (p < 0.05). In the 21 patients with adenomatous polyps, FOBT sensitivity seemed to be dependent on polyp size, but not polyp site. CONCLUSIONS: Monohaem, a feacal occult blood test that uses a monoclonal antibody that is specific for human haemoglobin, is a more accurate test in the detection of colorectal neoplasia and should possibly be used in colorectal cancer screening programmes.

Adenoma↗
PubMed1996

Compensatory mechanisms associated with the hyperdynamic function of phospholamban-deficient mouse hearts.

Phospholamban ablation is associated with significant increases in the sarcoplasmic reticulum Ca(2+)-ATPase activity and the basal cardiac contractile parameters. To determine whether the observed phenotype is due to loss of phospholamban alone or to accompanying compensatory mechanisms, hearts from phospholamban-deficient and age-matched wild-type mice were characterized in parallel. There were no morphological alterations detected at the light microscope level. Assessment of the protein levels of the cardiac sarcoplasmic reticulum Ca(2+)-ATPase, calsequestrin, myosin, actin, troponin I, and troponin T revealed no significant differences between phospholamban-deficient and wild-type hearts. However, the ryanodine receptor protein levels were significantly decreased (25%) upon ablation of phospholamban, probably in an attempt to regulate the release of Ca2+ from the sarcoplasmic reticulum, which had a significantly higher diastolic Ca2+ content in phospholamban-deficient compared with wild-type hearts (16.0 +/- 2.2 versus 8.6 +/- 1.0 mmol Ca2+/kg dry wt, respectively). The increases in Ca2+ content were specific to junctional sarcoplasmic reticulum stores, as there were no alterations in the Ca2+ content of the mitochondria or A band. Assessment of ATP levels revealed no alterations, although oxygen consumption increased (1.6-fold) to meet the increased ATP utilization in the hyperdynamic phospholamban-deficient hearts. The increases in oxygen consumption were associated with increases (2.2-fold) in the active fraction of the mitochondrial pyruvate dehydrogenase, suggesting increased tricarboxylic acid cycle turnover and ATP synthesis. 31P nuclear magnetic resonance studies demonstrated decreases in phosphocreatine levels and increases in ADP and AMP levels in phospholamban-deficient compared with wild-type hearts. However, the creatine kinase activity and the creatine kinase reaction velocity were not different between phospholamban-deficient and wild-type hearts. These findings indicate that ablation of phospholamban is associated with downregulation of the ryanodine receptor to compensate for the increased Ca2+ content in the sarcoplasmic reticulum store and metabolic adaptations to establish a new energetic steady state to meet the increased ATP demand in the hyperdynamic phospholamban-deficient hearts.

Animals↗
PubMed1995

[Gastric eosinophilic granuloma: report on 12 patients].

12 patients with gastric eosinophilic granuloma (GEG) were diagnosed mistakenly to be stomach cancer before operations, including 3 patients with acute massive hemorrhage from upper alimentary tract and 2 patients with pyloric obstruction. Operations were given to all. No relapses were noted after operation.

Adult↗
PubMed1994

Restoration of X-ray resistance and V(D)J recombination in mutant cells by Ku cDNA.

Three genetic complementation groups of rodent cells are defective for both repair of x-ray-induced double-strand breaks and V(D)J recombination. Cells from one group lack a DNA end-binding activity that is biochemically and antigenically similar to the Ku autoantigen. Transfection of complementary DNA (cDNA) that encoded the 86-kilodalton subunit of Ku rescued these mutant cells for DNA end-binding activity, x-ray resistance, and V(D)J recombination activity. These results establish a role for Ku in DNA repair and recombination. Furthermore, as a component of a DNA-dependent protein kinase, Ku may initiate a signaling pathway induced by DNA damage.

Animals↗
PubMed1994

Xeroderma pigmentosum group E binding factor recognizes a broad spectrum of DNA damage.

Xeroderma pigmentosum complementation group E binding factor (XPE-BF) is a damaged DNA binding protein that is deficient in a subset of patients from complementation group E of xeroderma pigmentosum. The protein recognizes various forms of DNA damage including some cyclobutane pyrimidine dimers, 6-4 photoproducts, cis-diamminedichloroplatinum(II) adducts, and single-stranded DNA. We now show that it also recognizes damage induced by nitrogen mustard; N-methyl-N'-nitro-N-nitrosoguanidine, and depurination, but has no detectable affinity for DNA adducts generated by trans-diamminedichloroplatinum(II), 4-nitroquinoline-N-oxide, 8-methoxypsoralen, or enzymatically methylated cytosine and adenine. The failure to recognize 4-nitroquinoline-N-oxide and 8-methoxypsoralen adducts is consistent with previous reports that XPE cells carry out wild-type levels of repair synthesis after DNA damage by those drugs. These results demonstrate that XPE-BF is a versatile damage recognition protein, but suggest that other proteins must contribute to the recognition of DNA lesions for the human excision repair pathway.

4-Nitroquinoline-1-oxide↗
PubMed1994

Involvement of the Ku autoantigen in the cellular response to DNA double-strand breaks.

The Ku autoantigen is a well-characterized heterodimer of 70 and 86 kDa that binds to DNA ends, but its cellular function has been obscure. An electrophoretic mobility-shift assay and Ku antisera were used to show that Ku or a closely related protein was deficient in three mutant hamster cell lines from x-ray-sensitive complementation group 5, which is characterized by defects in DNA double-strand break repair and V(D)J recombination. Furthermore, Ku protein expression was restored when the cells reverted to x-ray resistance. The Ku p86 gene maps to human chromosome 2q33-35, and group 5 cells are rescued by almost precisely the same region, 2q34-36. Thus, biochemical and genetic evidence suggests that Ku is involved in pathways for DNA recombination and repair. By its association with a DNA-dependent protein kinase activated by DNA ends, Ku may also initiate a signaling pathway induced by DNA damage, perhaps for cell cycle arrest.

Animals↗
PubMed1994

Cellular responses to cisplatin. The roles of DNA-binding proteins and DNA repair.

The anticancer drug cisplatin provokes a complex response in the cell. A lethal dose of the drug kills cells primarily by forming DNA adducts, causing G2 arrest in the cell cycle, and then triggering apoptosis. A sublethal dose induces drug resistance by several mechanisms, including changes in drug uptake and efflux, glutathione and metallothionein levels, and DNA repair. Cisplatin-DNA adducts bind several cellular proteins, including some that enhance survival of the cell by mediating DNA repair and others that hasten its death by conferring sensitivity to the drug.

Animals↗
PubMed1994

A novel role for DNA photolyase: binding to DNA damaged by drugs is associated with enhanced cytotoxicity in Saccharomyces cerevisiae.

DNA photolyase binds to and repairs cyclobutane pyrimidine dimers induced by UV radiation. Here we demonstrate that in the yeast Saccharomyces cerevisiae, photolyase also binds to DNA damaged by the anticancer drugs cis-diamminedichloroplatinum (cis-DDP) and nitrogen mustard (HN2) and by the alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Surprisingly, mutations in photolyase were associated with resistance of yeast cells to cis-DDP, MNNG, 4-nitroquinoline oxide (4NQO), and HN2. Transformation of yeast photolyase mutants with the photolyase gene increased sensitivity to these agents. Thus, while the binding of photolyase to DNA damaged by UV radiation aids survival of the cell, binding to DNA damaged by other agents may interfere with cell survival, perhaps by making the lesions inaccessible to the nucleotide excision repair system.

4-Nitroquinoline-1-oxide↗
PubMed1994

A DNA end-binding factor involved in double-strand break repair and V(D)J recombination.

We have identified a nuclear factor that binds to double-stranded DNA ends, independently of the structure of the ends. It had equivalent affinities for DNA ends created by sonication or by restriction enzymes leaving 5', 3', or blunt ends but had no detectable affinity for single-stranded DNA ends. Since X rays induce DNA double-strand breaks, extracts from several complementation groups of X-ray-sensitive mammalian cells were tested for this DNA end-binding (DEB) activity. DEB activity was deficient in three independently derived cell lines from complementation group 5. Furthermore, when the cell lines reverted to X-ray resistance, expression of the DEB factor was restored to normal levels. Previous studies had shown that group 5 cells are defective for both double-strand break repair and V(D)J recombination. The residual V(D)J recombination activity in these cells produces abnormally large deletions at the sites of DNA joining (F. Pergola, M. Z. Zdzienicka, and M. R. Lieber, Mol. Cell. Biol. 13:3464-3471, 1993, and G. Taccioli, G. Rathbun, E. Oltz, T. Stamato, P. Jeggo, and F. Alt, Science 260:207-210, 1993), consistent with deficiency of a factor that protects DNA ends from degradation. Therefore, DEB factor may be involved in a biochemical pathway common to both double-strand break repair and V(D)J recombination.

Animals↗
PubMed1993

Massive cisplatin overdose by accidental substitution for carboplatin. Toxicity and management.

BACKGROUND: Unlike the related drug carboplatin, cisplatin is highly nephrotoxic and must be given with vigorous intravenous hydration at a much lower dose. As the result of an accidental substitution of cisplatin for carboplatin, a 68-year-old woman received a massive overdose of cisplatin without intravenous hydration. METHODS: Laboratory documentation included measurements of platinum concentrations by atomic absorption spectroscopy and of xeroderma pigmentosum group E (XPE) binding factor, a protein that is involved in the recognition step of DNA repair. RESULTS: Toxicities included severe emesis, myelosuppression, renal failure, and deafness, which are well known. Other toxicities were seizures, hallucinations, loss of vision, and hepatic toxicity, which were unusual and may have been caused by the magnitude of the overdose. As late as day 19, there was a continued cellular response from cisplatin, as evidenced by decreased levels of XPE binding factor in extracts from the patient's peripheral blood lymphocytes. Plasmapheresis was effective in lowering the platinum concentration from greater than 2900 ng/ml to 200 ng/ml and appeared to be of clinical benefit. Even after the onset of renal failure, hydration to increase urine volume resulted in increased urinary excretion of platinum. Granulocyte-macrophage colony-stimulating factor (GM-CSF) was used to ameliorate myelosuppression. The patient received a transplanted kidney from her monozygotic twin sister and survived with no clinically significant deficit except for deafness. CONCLUSION: No previous reports exist of survival after such a high dose of cisplatin without intravenous hydration. In the future, patients may benefit from similar management and heightened awareness of the possibility of accidental substitution.

Aged↗