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Q Liu

Publications and source records attributed to Q Liu.

At least 487 records · Page 27Linked to original sources
PubMed1997

Site-directed mutagenesis of the yeast V-ATPase A subunit.

To investigate the function of residues at the catalytic nucleotide binding site of the V-ATPase, we have carried out site-directed mutagenesis of the VMA1 gene encoding the A subunit of the V-ATPase in yeast. Of the three cysteine residues that are conserved in all A subunits sequenced thus far, two (Cys284 and Cys539) appear essential for correct folding or stability of the A subunit. Mutation of the third cysteine (Cys261), located in the glycine-rich loop, to valine, generated an enzyme that was fully active but resistant to inhibition by N-ethylmalemide, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, and oxidation. To test the role of disulfide bond formation in regulation of vacuolar acidification in vivo, we have also determined the effect of the C261V mutant on targeting and processing of the soluble vacuolar protein carboxypeptidase Y. No difference in carboxypeptidase Y targeting or processing is observed between the wild type and C261V mutant, suggesting that disulfide bond formation in the V-ATPase A subunit is not essential for controlling vacuolar acidification in the Golgi. In addition, fluid phase endocytosis of Lucifer Yellow, quinacrine staining of acidic intracellular compartments and cell growth are indistinguishable in the C261V and wild type cells. Mutation of G250D in the glycine-rich loop also resulted in destabilization of the A subunit, whereas mutation of the lysine residue in this region (K263Q) gave a V-ATPase complex which showed normal levels of A subunit on the vacuolar membrane but was unstable to detergent solubilization and isolation and was totally lacking in V-ATPase activity. By contrast, mutation of the acidic residue, which has been postulated to play a direct catalytic role in the homologous F-ATPases (E286Q), had no effect on stability or assembly of the V-ATPase complex, but also led to complete loss of V-ATPase activity. The E286Q mutant showed labeling by 2-azido-[32P]ATP that was approximately 60% of that observed for wild type, suggesting that mutation of this glutamic acid residue affected primarily ATP hydrolysis rather than nucleotide binding.

4-Chloro-7-nitrobenzofurazan↗
PubMed1997

Branch-site selection in a group II intron mediated by active recognition of the adenine amino group and steric exclusion of non-adenine functionalities.

The 2'-hydroxyl on a specific bulged adenosine is the nucleophile during the first step of splicing by group II introns. To understand the means by which the ribozyme core recognizes this adenosine, it was mutagenized and effects on catalytic activity were quantified. The results indicate that a low level of mutational variability is tolerated at the branch-site of group II introns, with no apparent loss of fidelity. Analyses of mutant and modified nucleotides at the branch-site reveal that adenine is recognized primarily through the N6 amino group and by steric exclusion of functionalities found on other bases. The mutational and single atom effects reported here contrast with those observed during spliceosomal processing, suggesting that there are important differences in adenosine recognition by the two systems.

Adenine↗
PubMed1997

Higher frequency of glutathione S-transferase deletions in black children with acute lymphoblastic leukemia.

The genetic polymorphisms in human glutathione S-transferases (GST) M1 and T1 have been associated with race, disease risk, and outcome of some adult cancers. Also, there are racial differences in the incidence and characteristics of childhood acute lymphoblastic leukemia (ALL). Our objectives were to compare the frequency of the null genotype for GSTM1, GSTT1, or both in children with ALL to that in healthy controls, and to determine whether GST genotype was associated with treatment outcome and prognostic factors. We studied GSTM1 and GSTT1 genotypes in somatic cell DNA from black children and white children with ALL and in 416 healthy controls, using a polymerase chain reaction technique. Ninety of 163 (55.2%) white ALL patients and 14 of 34 (41.2%) black patients were GSTM1 null, frequencies not significantly different (P = .19) than healthy controls (53.5% in whites and 27.6% in blacks), although there was a trend toward more null genotypes in black ALL patients. Twenty-three of 163 (14.1%) white ALL patients and 12 of 34 (35.3%) black ALL patients were GSTT1 null, not different (P = .34) than the frequencies in healthy controls (15.0% in whites and 24.1% in blacks). However, the frequency of the "double-null" genotype, lacking both GSTM1 and GSTT1, was higher in black patients with ALL (8 of 34 or 23.5%) than in black controls (3.9%) (P = .0005), but this was not the case in white patients with ALL (10 of 163 or 6.1%) compared to white controls (8.0%) (P = .68). In stratified analyses, the GST double-null genotype was not associated with other characteristics that might differ between whites and blacks with ALL, such as age, T-lineage immunophenotype, presenting white blood cell count, DNA index, or insurance status. The null genotype for GSTM1, GSTT1, or both was not found to be a prognostic factor for disease-free survival or probability of hematologic remission; central nervous system relapse tended to be less common in those with the GSTM1 null genotype (P = .054). The double-null genotype for GSTM1 and GSTT1 is more common among blacks but not whites with childhood ALL. These data suggest that GST genotype, coupled with unidentified additional risk factors, may play a role in risk of childhood ALL in American blacks.

Adult↗
PubMed1997

Mutation of gene-proximal regulatory elements disrupts human epsilon-, gamma-, and beta-globin expression in yeast artificial chromosome transgenic mice.

Previous studies have defined transcriptional control elements, in addition to the promoters, that both lie near individual human beta-globin locus genes and have been implicated in their differential stage-specific regulation during development (i.e., are believed to directly participate in hemoglobin switching). We have reinvestigated the activities during erythropoiesis that might be conferred by two of the more intensively analyzed of these elements, the epsilon-globin gene 5' silencer and the beta-globin gene 3' enhancer, by deleting them from a yeast artificial chromosome that spans the human beta-globin locus, and then analyzing transgenic mice for expression of all of the human genes. These studies show that sequences within the epsilon-globin "silencer" are not only required for silencing but are also required for activation of epsilon-globin transcription; furthermore, deletion of the silencer simultaneously reduced gamma-globin transcription during the yolk sac stage of erythroid development. Analysis of the adult beta-globin gene 3' enhancer deletion showed that its deletion affects only that gene.

Animals↗
PubMed1997

Molecular cloning and chromosomal localization in human and mouse of the SH2-containing inositol phosphatase, INPP5D (SHIP). Amgen EST Program.

The action of lipid phosphatases on inositol phosphates is thought to be one method that the cell uses to attenuate growth factor- or cytokine-induced mobilization of calcium. We have cloned a cDNA from a mouse spleen library that is virtually identical to the recently described inositol tetraphosphate and phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase, SHIP. Chromosomal localization studies in human and mouse by FISH mapping and interspecies backcrossing in mice have demonstrated that human SHIP is localized to 2q36-q37.1 and that mouse SHIP is localized to 1C5.

Amino Acid Sequence↗
PubMed1997

Epstein-Barr virus in pediatric Hodgkin disease: age and histiotype are more predictive than geographic region.

Epidemiologic studies have implicated Epstein-Barr virus (EBV) in the great majority (80%-100%) of Hodgkin disease (HD) cases in South American countries, versus only 30%-40% in the United States and other industrialized countries. Other EBV-related malignancies are known to be geographically localized, including nasopharyngeal carcinoma in south China and Burkitt lymphoma in equatorial Africa. Some studies, however, have suggested that age and histiotype, rather than geographic region, are the major determinants of the association between EBV and HD. To further characterize this relationship in children, we matched 26 cases of pediatric Hodgkin disease from south Brazil and 26 cases from the U.S.-forhistiotype and age. The Brazilian children (22 males, 4 females) had a median age of 9 years, while the median age of the U.S. group (11 males, 15 females) was 7.5 years. Formalin-fixed, paraffin-embedded biopsy material was examined for EBV early RNA1 (EBER1) expression by in situ hybridization. This antigen was detected solely in Reed-Sternberg cells or their variants in positive samples. The same proportion of cases was positive (15/26 or 58%) in both groups of children. After adjustment for histiotype and age, the association between EBV and HD remained independent of geographic location, but was more frequent in children aged < or = 10 years at diagnosis. These findings support the multiple-etiology hypothesis for Hodgkin disease.

Adolescent↗
PubMed1997

Uterocalin: a mouse acute phase protein expressed in the uterus around birth.

Mouse SIP24/24p3 is a 24 kDa lipocalin expressed in the liver and secreted into the bloodstream during the acute phase response (APR). In this report we show that SIP24/24p3 mRNA and protein are expressed in the uterus around parturition at levels higher than are found in the liver during the APR. Because of the unique expression of this lipocalin in the uterus, we have named this protein uterocalin. Contrary to its expression pattern during the APR, there is little or no expression of uterocalin in the liver during or after pregnancy. Also, unlike the APR, and despite its high level of expression in the uterus, uterocalin was not detected in the blood or amniotic fluid. Day 19 and postpartum uterine samples were examined by immunocytochemistry. Uterocalin was found in the luminal epithelium at day 19 and in the glandular epithelium in postpartum samples. Although some uterocalin remained in the luminal epithelium, most of the uterocalin was found deposited on its luminal surface. The uterus undergoes extensive tissue remodeling during pregnancy and suffers stress and tissue damage around parturition. Uterocalin could be part of the local inflammatory response associated with parturition.

Acute-Phase Proteins↗
PubMed1997

Soluble oligonucleosomal complexes in synovial fluid from inflamed joints.

OBJECTIVE: To determine whether soluble oligonucleosomal DNA, typical of that released during apoptotic cell death, is present in synovial fluids from inflamed joints and, if so, whether it is present in sufficient concentrations to have pathophysiologic significance. METHODS: Fifty synovial fluid specimens from 46 patients were studied, 41 from joints with a variety of inflammatory disorders and 9 from osteoarthritic joints. DNA from freshly collected synovial fluid was isolated and quantitated by microfluorometry, and the oligonucleosomal fraction was measured by radiolabeling, gel electrophoresis, and autoradiography. Specific immunoprecipitation with monoclonal antihistone antibody, after DNA radiolabeling in whole synovial fluid, was used to detect histone binding. RESULTS: DNA with a typical oligonucleosomal ladder was observed in most specimens. The mean +/- SD oligonucleosomal DNA concentration was 14.1 +/- 18.5 microg/ml in synovial fluids from inflamed joints, considerably higher than that in osteoarthritic synovial fluids. Additionally, the DNA was shown to be complexed with histone, as would be expected. Control experiments were performed to show that the oligonucleosomal DNA was present in soluble form and did not arise due to in vitro artifact. The DNA concentrations were found to correlate significantly with the concentrations of synovial fluid leukocytes, most of which were neutrophils. CONCLUSION: Synovial fluids from inflamed joints contain oligonucleosomal DNA typical of that released during apoptotic cell death. The probable source is fluid-phase neutrophils undergoing apoptotic cell death, although this was not directly demonstrated. The concentrations are sufficient to have biologic activity similar to that shown in vitro, including lymphoproliferation and stimulation of interleukin-6 secretion. A mechanism by which oligonucleosomal DNA may contribute to perpetuation of rheumatoid synovitis is proposed. If it is generalizable to other sites of inflammation, as seems probable, similar oligonucleosomal DNA release accompanying inflammation may play a pathogenetic role in other disorders, including systemic lupus erythematosus.

DNA↗
PubMed1997

The effect of epidermal growth factor on the septic complications of acute pancreatitis.

Bacterial translocation (BT) from the gastrointestinal tract to mesenteric lymph nodes (MLN) and other extraintestinal organs is an important source of infection in acute pancreatitis (AP). Epidermal growth factor (EGF), a peptide hormone with trophic effects on gut mucosa, has decreased intestinal mucosal injury in septic rats and decreased burn-induced BT in mice. The purpose of this study is to examine whether EGF could affect BT in acute necrotizing pancreatitis. Forty-eight male Sprague-Dawley rats (250-350 g) were studied. AP was induced in Group I and Group II by pressure injection of 3% taurocholate and trypsin into the biliopancreatic duct (1 ml/kg of body weight). Group III and Group IV underwent laparotomy without induction of acute pancreatitis. Group I rats received human recombinant EGF (100 micrograms/kg, subcutaneously twice daily) and Group II rats received a similar volume of 0.1% bovine serum albumin as a placebo postoperatively. Group III and Group IV received EGF and placebo, respectively. At 48 hr postoperatively, blood was drawn for culture and amylase determinations. Jejunum and ileum were obtained to measure mucosal protein content, mucosal thickness, villus height, and crypt depth. Specimens from MLN, spleen, liver, pancreas, and cecum were harvested for pathology and culture of gram positive (G+), gram negative (G-), and anaerobic bacteria. Ileal mucosal protein levels were increased significantly in Group I (1.96 +/- 0.14 mg/cm) compared to Group II (0.95 +/- 0.15 mg/cm intestinal segment) (P < 0.01). Jejunal and ileal mucosal thickness, villus height, and crypt depth in Group I were significantly increased when compared to Group II (P < 0.05). All 12 rats in Group II had BT to MLN compared to 58% (7 of 12 rats) in Group I (P < 0.05). Thirty-three percent (4 of 12 rats) had BT to distant sites such as pancreas, spleen, liver, and/or blood in Group I vs 83% (10 of 12 rats) in Group II (P < 0.05). EGF treatment minimizes intestinal damage, decreases BT to MLN and bacterial spread to distant sites, and may be beneficial in preventing septic complications in AP.

Acute Disease↗
PubMed1997

Relationship between GHRP-6 and TPA in the regulation of growth hormone secretion by human pituitary somatotrophinomas.

Growth hormone releasing peptide (GHRP-6) is a synthetic hexapeptide which specifically stimulates secretion of growth hormone (GH) by pituitary somatotrophs. Phorbel ester, 1, 2 tetradecanoylphorbol 13 acetate (TPA) can also stimulate releasing of GH. The precise intracellular mechanism has not been entirely deciphered. We used cell cultures of human pituitary somatotrophinomas to investigate the relation between GHRP-6 and TPA on membrane phosphatidylinositol (PI) turnover and GH secretion. The results showed that the working mechanisms of GHRP-6 and TPA are not identical, although they all can stimulate GH secretion in human pituitary somatotrophinomas. This indicates that PI-PKC signal transduction system may play a crucial role in the regulation of GH secretion.

Adenoma↗
PubMed1997

Interleukin-11 improves survival and reduces bacterial translocation and bone marrow suppression in burned mice.

PURPOSE: Major burns are associated with a high mortality, an increased rate of bacterial translocation, and bone marrow suppression. This study evaluates the effect of interleukin-11 (IL-11), a bone marrow-derived growth factor on survival, intestinal cytoarchitecture, bacterial translocation, and bone marrow suppression in a highly lethal murine burn model with a lethal dose greater than 50. METHODS: C3H/HeJ 8 to 10-week-old mice underwent a standardized 32% total body surface area (TBSA) scald burn using a burn template. Mice were divided equally between groups receiving IL-11 (125 micrograms/kg, twice daily, subcutaneously [SC]) and 0.1% same-volume Bovine Serum Albumin (BSA) (0.2 mL, twice daily, sc). Animals were evaluated for mesenteric lymph node bacterial counts, intestinal mucosal villus height, number of mucosal crypt cell mitoses per 100 crypts, and peripheral platelet and total lymphocyte counts. Survival was calculated to 7 days postburn. RESULTS: At 24 hours postburn, IL-11-treated mice had significantly less enteric bacteria cultured from mesenteric lymph nodes (P < .001), increased intestinal crypt cell mitoses (P = .002) and intestinal villus height (P = .002), increased peripheral platelet (P = .002) and lymphocyte counts (P = .004), and an improved survival compared with BSA controls (P = .003). CONCLUSION: These data show that IL-11 improves survival, intestinal cytoarchitecture, reduces bacterial translocation, and reduces bone marrow suppression after a 32% TBSA burn in mice. These data imply that IL-11 cytokine therapy may be a useful adjunct in extensive burn injury.

Animals↗
PubMed1997

Histology of rat small bowel transplants: cyclosporine A ameliorates features of rejection including apoptosis and ganglion cell reduction.

The histology of rat small bowel transplants (SBT) was examined in orthotopic isografts and allografts with and without immunosuppression. Lewis to Lewis isografts were examined 7 days after transplant, and LBNF1 to Lewis allografts were examined 2, 4, 7, and 10 days after transplant; one group received cyclosporine A (CyA), and their allografts were examined 7 days after transplant. Compared with similar intestinal segments from unoperated animals, allografts at 4, 7, and 10 days after surgery showed progressive inflammation, cryptitis, villous atrophy, and transmural necrosis. In contrast, SBT in animals given CyA did not significantly differ from normal in any histological parameter. The number of apoptotic structures per 100 crypts in SBT at day 4 (58.25 +/- 32.98) and day 7 (31.86 +/- 27.63) after transplant were significantly increased compared with unoperated bowel (5.23 +/- 13.41) (P < .05); the number in CyA-treated allografts (11.57 +/- 29.56) did not differ significantly from normal. The number of intermyenteric ganglion cells was significantly reduced (P< .05) in allografts 7 and 10 days after transplant (mean and [range] = 31 [18 to 38] and 25 [23 to 27], respectively) but the number in allografts from CyA-treated animals (47 [24 to 72]) did not differ from unoperated bowels (52 [30 to 88]). We conclude that CyA treatment significantly reduces the histological abnormalities associated with transplant rejection including adverse effects on epithelial and ganglion cells; therefore, the absorptive capacity and motility characteristics of the CyA-treated SBT should be preserved compared with untreated allograft controls.

Animals↗
PubMed1997

In vitro calcium phosphate formation on a natural composite material, bamboo.

A natural self-reinforced composite material, bamboo, is studied for the first time as a biomedical material. Its anatomical structure was investigated and its mechanical properties were measured and compared with those of some common bone-bonding or bone-repairing biomaterials. It is found that, among all kinds of biomaterials, bamboo has the closest modulus of elasticity to human long bone. The cytotoxicity of bamboo was tested using the agar overlay method before and after heat or chemical treatments. The results reveal that ethanol, methanol and toluene can remove toxic leachable components from bamboo to some extent through extraction. After grafting a polymer whose molecule includes poly(ethylene glycol), alpha,omega-di(aminopropyl)poly(ethylene glycol) 800 on bamboo, bamboo has the ability to form a calcium phosphate coating after being immersed in calcification solution (simulated body fluid and accelerated calcification solution). The characteristics and the morphology of the mineral formed on bamboo were studied by infrared spectroscopy and scanning electron microscopy.

Apatites↗
PubMed1997

Formation and characteristics of the apatite layer on plasma-sprayed hydroxyapatite coatings in simulated body fluid.

Plasma-sprayed hydroxyapatite (HA) coatings were incubated in simulated body fluids (SBFs) for different periods of time to investigate the nucleation and growth of apatite on their surface. The layer that formed was recognized as having similarities to bone apatite because it is poorly crystallized, non-stoichiometric or calcium deficient, and contains carbonate and magnesium. Scanning electron microscopy (SEM) and infrared spectroscopy (IR) were employed to investigate the morphological changes of the coating surface and the structure of the grown layer respectively. In the first few hours, calcium and phosphate ions dissolved from the coatings so as to increase their local supersaturation to a higher degree, thereafter followed by the nucleation and growth of apatite. The nucleation occurred firstly on the recessed regions, inside pores and cracks where the higher supersaturation was readily maintained. Only after 24 h incubation was a complete layer formed on the surface of the coating. There is no obvious interface between the grown layer and the underlying coating. Heat treatment in the air made the apatite transform into biphasic calcium phosphate of HA and tricalcium phosphate, with a blue colour because of trace manganese ions. The heat-treated HA coating showed no dissolution by SEM observation. This resulted in no precipitation on the surface. When SBF was used with two-fold higher ion concentrations, the apatite layer formed slowly in 72 h without dissolution of the coating surface. This may mean that the microenvironment with a sufficiently high degree of supersaturation of calcium and phosphate ions is crucial for apatite to nucleate and grow in SBF, while the HA crystalline structure is not critical in the nucleation process, as expected.

Apatites↗
PubMed1997

Nano-apatite/polymer composites: mechanical and physicochemical characteristics.

Hydrothermally synthesized acicular nano-apatite (Nap) was used as filler to make composites with a polyethylene glycol/poly(butylene terephthalate) (PEG/PBT) block copolymer (Polyactive 70:30). The Nap had a particle diameter of 9-25 nm and a length of 80-200 nm. The mechanical properties and the physiochemical characteristics of the composites, such as Young's modulus, swelling degree in water and the calcification behaviour, have been determined. It was found that Nap had a strong ability to promote the calcification of composites when incorporated into Polyactive 70:30, while poly(acrylic acid) (PAA) coating of Nap had an adverse effect on the calcification of composites, presumably due to the formation of complexes between PAA and PEG segments. Nap had a prominent stiffening effect for Polyactive 70:30 in the dry state, but had a poor stiffening effect for composites in an aqueous environment due to the hygroscopic nature and/or the formation of aggregates. PAA coating on Nap had almost no additional effect on the mechanical properties of composites either in the dry state or in an aqueous environment. To reinforce the polymer by Nap, achieving a more homogeneous dispersion of Nap in the polymer matrix and surface modifications to render the powders less hygroscopic appear to be necessary.

Acrylic Resins↗
PubMed1997

Fast precipitation of calcium phosphate layers on titanium induced by simple chemical treatments.

A simple two-step chemical treatment, i.e. etching with HCl and H2SO4 followed by immersion in boiling dilute NaOH solution, has been developed by our group to prepare bioactive microporous titanium surfaces allowing fast deposition of a calcium phosphate layer (CPL) from an in vitro supersaturated calcification solution (SCS). In this work, a precalcification (Pre-Ca) procedure was applied by soaking the two-step treated titanium in Na2HPO4 and then saturated Ca(OH)2 solution before immersion in SCS to accelerate further the CPL precipitation. The treated titanium surfaces with Pre-Ca were characterized after 1, 2, 4, 8 and 16 h of immersion in SCS by means of scanning electron microscopy together with energy dispersive X-ray analysis, X-ray diffraction and infrared absorption analysis. It was observed that the CPL precipitation rate with Pre-Ca averaged 1 microm h-1, twice as fast as without Pre-Ca. No precipitation was observed on untreated titanium with Pre-Ca up to day 14 of immersion in the SCS.

Calcium Hydroxide↗