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T Xia

Publications and source records attributed to T Xia.

At least 19 recordsLinked to original sources
PubMed2002

[TFAR19 enhances the opening of permeability transition pore in the mitochondrial membrane of mice liver].

TFAR19 TF-1 cell apoptosis related gene 19 is a novel apoptosis-related gene cloned from human leukemia cell line TF-1 cells undergoing apoptosis in 1999 (accession number AF014955 in GenBank). The human TFAR19 encodes a protein which shares significant homology to the corresponding proteins of species ranging from yeast to mice. TFAR19 exhibits a ubiquitous expression pattern and its expression is upregulated in tumor cells undergoing apoptosis. Overexpression of TFAR19 could enhance apoptosis of some tumor cells induced by growth factor withdrawal or serum deprivation. But the exact mechanism of TFAR19 is unclear. Mitochondria not only provides energy for the cell, but also plays a critical role on cell death or survival. The release of apoptosis promoting factor, such as cytochrome c from mitochondria, resulted by the damage of mitochondrial membrane integrity, is the key factor controlling apoptosis. The permeability transition pore (PTP) of mitochondria is a protein complex located between the mitochondrial membranes, and it plays an important role in regulating the integrity of mitochondrial membrane. In this study, the effect of recombinant TFAR19 on isolated mitochondrial PTP, membrane potential, and release of cytochrome c was investigated in vitro. The results indicated that recombinant TFAR19 facilitated the isolated mitochondrial PTP opening, decreased the membrane potential, and promoted the release of cytochrome c. The effect of TFAR19 on mitochondria is implemented by opening the mitochondrial PTP. Experimental results implicate that TFAR19 may positively feedback apoptosis signal of mitochondria, forming a positive loop to promote apoptosis.

Animals↗
PubMed2001

Large libraries reveal diverse solutions to an RNA recognition problem.

RNA loops that adopt a characteristic GNRA "tetraloop" fold are common in natural RNAs. Here, we have used in vitro selection by means of mRNA-peptide fusions to select peptides that bind an example of this RNA loop motif. Starting with the RNA recognition domain from the lambda N protein, we have constructed libraries containing 150, 1,600, and 9 trillion different peptide sequences as mRNA-peptide fusions and isolated those capable of high-affinity RNA binding. These selections have resulted in more than 80 different peptides that bind the same RNA loop. The highest affinity peptides exhibit low nanomolar dissociation constants as well as the ability to discriminate RNA hairpins differing by a single loop nucleotide. Thus, our work demonstrates that numerous, chemically distinct solutions exist for a particular RNA recognition problem.

Amino Acid Sequence↗
PubMed2001

Thermodynamics of RNA internal loops with a guanosine-guanosine pair adjacent to another noncanonical pair.

Thermodynamic parameters measured by optical melting are reported for formation of RNA duplexes containing tandem noncanonical pairs with at least one guanosine-guanosine (GG) pair. For selected sequences, imino proton NMR provides evidence that the desired duplex forms and that the structure of a GG pair adjacent to a noncanonical pair depends on context. A GG pair next to a different noncanonical pair is more stable than expected from measurements of adjacent GG pairs. This is likely due to an unfavorable stacking interaction between adjacent GG pairs, where areas of high negative charge probably overlap. The results suggest a model where tandem noncanonical pairs closed by two GC pairs are assigned the following free energy increments at 37 degrees C: 0.8 kcal/mol for adjacent GG pairs, 1.0 kcal/mol for GG next to UU, and -0.3 kcal/mol for all others. These values are adjusted by 0.65 kcal/mol for each closing AU pair.

Base Composition↗
PubMed2001

Relationship between thermal parameters and tumor response in hyperthermia combined with radiation therapy.

BACKGROUND: In hyperthermia for cancer therapy, thermal parameters related to tumor response have not yet been clarified. We investigated thermal parameters that could predict tumor response to hyperthermia combined with radiotherapy in locally advanced malignancies. METHODS: Fifty-four patients with locally advanced malignancies who were treated by hyperthermia in combination with radiation therapy were enrolled in this study. Local hyperthermia was induced by ultrasound heating equipment for 60 min, within 30 min after irradiation, twice a week, for a total of six to ten sessions. Radiation therapy was administered with a conventional fractionation regimen, at a total dose of 40-70 Gy. Multi-point thermometry results were obtained with every 10-s temperature data acquisition. An average of seven interstitial sites per tumor was monitored for each treatment. Univariate logistic regression analysis was used to investigate the relationship between tumor response and minimum, maximum, and average intratumor temperature (Tmin, Tmax, Tav); the cumulative minutes of treatment at temperatures exceeded by 90%, 50%, and 10% of the measured intratumoral temperatures (T90, T50, T10); and cumulative minutes of the temperature that achieved above the index temperature value in the tumor center ((Cum min T(center) > T(index)). RESULTS: Complete and partial response rates were 32.6% and 46.2%, respectively. Univariate logistic regression analysis revealed that the temperature parameters with predictive probability were highest for Cum min T(center) > 42.5 degrees C, followed by > 42 degrees C and > 41 degrees C; and T90. Cum min T(center) > 42.5 degrees C was most significantly associated with complete tumor response (P < 0.001). CONCLUSION: These results strongly suggest that hyperthermia is a useful adjunct to radiotherapy for increasing the local control of advanced malignancies, and that Cum min T(center) > 42.5 degrees C could be an important thermal parameter for predicting tumor response.

Adult↗
PubMed2001

Isolation and characterization of a Na+/H+ antiporter gene from the halophyte Atriplex gmelini.

With a homologous gene region we successfully isolated a Na+/H+ antiporter gene from a halophytic plant, Atriplex gmelini, and named it AgNHX1. The isolated cDNA is 2607 bp in length and contains one open reading frame, which comprises 555 amino acid residues with a predicted molecular mass of 61.9 kDa. The amino acid sequence of the AgNHX1 gene showed more than 75% identity with those of the previously isolated NHX1 genes from glycophytes, Arabidopsis thaliana and Oryza sativa. The migration pattern of AgNHX1 was shown to correlate with H+-pyrophosphatase and not with P-type H+-ATPase, suggesting the localization of AgNHX1 in a vacuolar membrane. Induction of the AgNHX1 gene was observed by salt stress at both mRNA and protein levels. The expression of the AgNHX1 gene in the yeast mutant, which lacks the vacuolar-type Na+/H+ antiporter gene (NHX1) and has poor viability under the high-salt conditions, showed partial complementation of the NHX1 functions. These results suggest the important role of the AgNHX1 products for salt tolerance.

Amino Acid Sequence↗
PubMed2001

Cimetidine inhibits production of interferon gamma and tumor necrosis factor alpha by splenocytes in aplastic anemic mice.

AIM: To study the effects of cimetidine (Cim) on the production of interferon gamma (IFN gamma) and tumor necrosis factor alpha (TNF alpha) by splenocytes in immune-derived aplastic anemic (AA) mice. METHODS: Aplastic anemic mice model was constructed first, and then the splenocytes were induced to secrete IFN gamma and TNF alpha. Concentration of IFN gamma was assayed using sandwich ELISA, while that of TNF alpha was measured with L929 cytotoxicity methods. RESULTS: (1) Concentrations of IFN gamma and TNF alpha secreted by splenocytes from AA mice were (137 +/- 36) ng/L and (6 +/- 3) microg/L, respectively, much more than the irradiated and the control mice. (2) Treatment with Cim 10 micromol/L reduced the concentrations of IFN gamma and TNF alpha to (14 +/- 8) ng/L and (2.7 +/- 0.6) microg/L, respectively. CONCLUSION: Cim could effectively reduce the production of IFN gamma and TNF alpha from splenocytes of AA mice.

Anemia, Aplastic↗
PubMed2000

Expanded CUG repeat RNAs form hairpins that activate the double-stranded RNA-dependent protein kinase PKR.

Myotonic dystrophy is caused by an expanded CTG repeat in the 3' untranslated region of the DM protein kinase (DMPK) gene. The expanded repeat triggers the nuclear retention of mutant DMPK transcripts, but the resulting underexpression of DMPK probably does not fully account for the severe phenotype. One proposed disease mechanism is that nuclear accumulation of expanded CUG repeats may interfere with nuclear function. Here we show by thermal melting and nuclease digestion studies that CUG repeats form highly stable hairpins. Furthermore, CUG repeats bind to the dsRNA-binding domain of PKR, the dsRNA-activated protein kinase. The threshold for binding to PKR is approximately 15 CUG repeats, and the affinity increases with longer repeat lengths. Finally, CUG repeats that are pathologically expanded can activate PKR in vitro. These results raise the possibility that the disease mechanism could be, in part, a gain of function by mutant DMPK transcripts that involves sequestration or activation of dsRNA binding proteins.

Base Pairing↗
PubMed2000

Isolation and identification of Prevotella tannerae from endodontic infections.

Black-pigmented bacteria are often isolated from endodontic infections. Five strains of black-pigmented bacteria isolated from endodontic infections could not be identified in our laboratory. The purpose of this study was to sequence the 16S rRNA gene of the five unknown isolates and identify the organisms. The 16S rRNA genes from the unknown organisms were cloned, sequenced, and determined to be Prevotella tannerae. In addition, samples from endodontic infections were surveyed for the presence of the organism. When 118 samples from endodontic infections were examined using polymerase chain reaction with specific primers for P. tannerae, 60% of the samples were positive for the presence of the organism. This suggests that P. tannerae is commonly present in endodontic infections and could be a potential pathogen.

Bacteroidaceae Infections↗
PubMed2000

Occurrence of Candida albicans in infections of endodontic origin.

Microorganisms are recognized as the etiological agent for the majority of pulpal and periradicular disease. Although bacteria have been the most studied, fungi have also been associated with infected root canals. The purpose of this study was to evaluate the contents of infected root canals and aspirates of cellulitis/abscesses of endodontic origin for the presence of Candida albicans using the polymerase chain reaction (PCR). PCR primers specific for the 18S ribosomal RNA gene of C. albicans were used to survey 24 samples taken from infected root canals and 19 aspirates from periradicular infections of endodontic origins. The presence of C. albicans was detected in 5 of 24 (21%) samples taken from root canals, but none was detected in the periradicular aspirates. The results indicate that PCR is an extremely sensitive molecular method that may be used to identify C. albicans directly in samples from infections of endodontic origin.

Candida albicans↗
PubMed2000

[Expression of VEGF and tumor angiogenesis in bladder cancer].

OBJECTIVE: To evaluate expression of vascular endothelial growth factor (VEGF) and its relation to angiogenesis in bladder cancer. METHODS: The expression of VEGF by immunohistochemical staining was examined in 68 cases of primary transitional carcinoma (TCC) and 7 subjects with normal urothelium. Microvessel density (MVD) in 40 cases of invasive bladder cancer was determined by Factor VIII immunohistochemical staining. RESULTS: The expression of VEGF was negative or low level in all normal bladder tissue but high in bladder cancer. VEGF and MVD were closely related to tumor cell nuclear grade and clinical stage. The average MVD was higher in the cases with the high level expression of VEGF, than in those with the low level expression of VEGF. CONCLUSIONS: This study indicates that VEGF is positively correlated with the occurrence and progression of bladder cancer. VEGF is one of the primary angiogenic factors for bladder cancer, and is able to induce tumor angiogenesis and accelerate tumor growth. Quantification of VEGF may provide a valuable marker for a poorer prognosis of patients.

Adult↗
PubMed1999

Rapid colorimetric assay of urinary beta-galactosidase and N-acetyl-beta-D-glucosaminidase with Cobas Mire Auto-analyzer.

A rapid and simple colorimetric method for the assay of urinary beta-galactosidase (GAL) and N-acetyl-beta-D-glucosaminidase (NAG) using 4-nitrophenyl-glycosides as the substrates and a Cobas Mire Auto-analyzer is described. Optimal conditions for this method including substrate concentration, ionic strength, pH and incubation time were characterized. Endogenous substances in urine did not interfere with the assays. Incubation time could be shortened to 10 minutes. A small volume of an alkaline buffer to terminate the enzyme reaction achieved better sensitivity and accuracy. Buffer-substrate solutions were stable for at least one week at 4 degrees C. Normal values of the two urinary enzymes are also reported.

Acetylglucosaminidase↗
PubMed1999

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and polymerase chain reaction for differentiation of Prevotella intermedia and Prevotella nigrescens.

Isolates previously thought to be Prevotella intermedia have been shown to be a closely related species now known as Prevotella nigrescens. The purpose of this study was to determine the efficacy of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and polymerase chain reaction (PCR) to differentiate endodontic isolates of P. nigrescens from P. intermedia. Fifty-six strains of black-pigmented bacteria isolated from endodontic infections and conventionally identified as P. intermedia were used in this study. Using SDS-PAGE, novel polypeptide bands were used to differentiate P. nigrescens from P. intermedia. PCR was accomplished with specific primers for the 16S ribosomal RNA gene of both strains. Of 56 endodontic isolates, 41 (73%) strains were identified by SDS-PAGE as P. nigrescens and 15 (27%) strains as P. intermedia. Of the 41 strains of P. nigrescens identified by SDS-PAGE, PCR identified 37 strains as P. nigrescens. Restriction endonuclease digestion of amplified 16S ribosomal RNA genes indicated that the remaining four strains originally identified by SDS-PAGE as P. nigrescens were actually strains of Prevotella distinct from P. nigrescens and P. intermedia. Of 15 strains of P. intermedia identified by SDS-PAGE, PCR identified 14 strains as P. intermedia; but, one strain was identified as P. nigrescens. The results indicated that PCR was a more precise method than SDS-PAGE to differentiate P. intermedia from P. nigrescens. This study confirms that P. nigrescens is more commonly isolated in pure culture from endodontic infections than P. intermedia.

Bacterial Typing Techniques↗
PubMed1999

Association of black-pigmented bacteria with endodontic infections.

Black-pigmented bacteria (BPB) have been associated with endodontic infections. The purpose of this study was to evaluate further the presence of BPB with the clinical signs and symptoms associated with endodontic infections. Microbial samples were collected from the root canals of 40 intact teeth with necrotic pulps and apical periodontitis. Conventional laboratory methods were used for identification of the strains of BPB isolated in pure culture. In addition, the polymerase chain reaction and specific primers for 16S r-RNA genes were used to differentiate Prevotella nigrescens from Prevotella intermedia. Twenty-two (55%) samples were positive for the growth of BPB. Of those, 11 of 22 (50%) were identified as P. nigrescens, 8 of 22 (36%) were P. intermedia, 2 of 22 (9%) were Porphyromonas gingivalis, and 1 of 22 (5%) was Prevotella melaninogenica. Sixteen of the 22 root canals positive for the growth of BPB were associated with purulent drainage either from the root canal or an associated sinus tract. Statistical analysis did not show a significant relationship for the presence of BPB with clinical signs and symptoms.

Bacterial Typing Techniques↗
PubMed1999

Survey for collagenase gene prtC in Porphyromonas gingivalis and Porphyromonas endodontalis isolated from endodontic infections.

Collagenase is a potential virulence factor shown to be expressed by Porphyromonas gingivalis associated with periodontal disease. The purpose of this study was to use the polymerase chain reaction (PCR) to detect the presence of the collagenase gene (prtC) in 21 strains of Porphyromonas species isolated from endodontic infections. Type strains for P. gingivalis (ATCC 33277), P. endodontalis (ATCC 35406), Prevotella intermedia (ATCC 25611), and Prevotella nigrescens (ATCC 33563) were used as controls. When PCR primers specific for the 16S ribosomal RNA gene of P. gingivalis or P. endodontalis were used, 16 of the strains were identified as P. gingivalis, and five strains were identified as P. endodontalis. The presence of the prtC gene for collagenase was detected using PCR. Amplicons were analyzed by agarose gel electrophoresis, with an 815 bp amplicon representing the presence of the collagenase gene. Type strain ATCC 33277 and all 16 clinical isolates of P. gingivalis produced the collagenase gene amplicon. Neither type strain ATCC 35406 nor the five strains from clinical isolates of P. endodontalis produced the collagenase gene amplicon. These results indicate that P. gingivalis from endodontic infections possesses the prtC gene. P. endodontalis does not seem to exhibit prtC. The virulence of P. gingivalis may be related to its production of collagenase.

Bacterial Proteins↗
PubMed1999

PhhB, a Pseudomonas aeruginosa homolog of mammalian pterin 4a-carbinolamine dehydratase/DCoH, does not regulate expression of phenylalanine hydroxylase at the transcriptional level.

Pterin 4a-carbinolamine dehydratase is bifunctional in mammals. In addition to playing a catalytic role in pterin recycling in the cytoplasm, it plays a regulatory role in the nucleus, where it acts as a dimerization-cofactor component (called DCoH) for the transcriptional activator HNF-1alpha. A thus far unique operon in Pseudomonas aeruginosa contains a gene encoding a homolog (PhhB) of the regulatory dehydratase, together with genes encoding phenylalanine hydroxylase (PhhA) and aromatic aminotransferase (PhhC). Using complementation of tyrosine auxotrophy in Escherichia coli as a functional test, we have found that the in vivo function of PhhA requires PhhB. Strikingly, mammalian DCoH was an effective substitute for PhhB, and either one was effective in trans. Surprisingly, the required presence of PhhB for complementation did not reflect a critical positive regulatory effect of phhB on phhA expression. Rather, in the absence of PhhB, PhhA was found to be extremely toxic in E. coli, probably due to the nonenzymatic formation of 7-biopterin or a similar derivative. However, bacterial PhhB does appear to exert modest regulatory effects in addition to having a catalytic function. PhhB enhances the level of PhhA two- to threefold, as was demonstrated by gene inactivation of phhB in P. aeruginosa and by comparison of the levels of expression of PhhA in the presence and absence of PhhB in Escherichia coli. Experiments using constructs having transcriptional and translational fusions with a lacZ reporter indicated that PhhB activates PhhA at the posttranscriptional level. Regulation of PhhA and PhhB is semicoordinate; both PhhA and PhhB are induced coordinately in the presence of either L-tyrosine or L-phenylalanine, but PhhB exhibits a significant basal level of activity that is lacking for PhhA. Immunoprecipitation and affinity chromatography showed that PhhA and PhhB form a protein-protein complex.

Escherichia coli↗
PubMed1999

Lymphocyte subsets and sister-chromatid exchanges in the students exposed to formaldehyde vapor.

The present report evaluates the effects of formaldehyde (FA) exposure on peripheral lymphocytes by using both genetic and immunological parameters. Twenty-three non-smoking students in the study had inhalation exposure to 0.508 +/- 0.299 mg/m3 of FA for a period of 8 weeks (3h x 3 times each week) during anatomy classes. As for composition of lymphocyte subsets after FA exposure, significant increase was found in the percentage of CD19 (B cells), while significant decrease was observed in CD3 (total T cells), CD4 (T helper-inducer cells), and CD8 (T cytotoxic-suppressor cells) with a P < 0.01. Increase in the ratio of T-helper-inducer cells to T-cytotoxic-suppressor cells (T4/T8) was also observed with statistical significance after exposure (P < 0.001). In the meanwhile, no significant difference (P > 0.05) was reported between lymphocyte proliferation rate and sister-chromatid exchange (SCE) at the exposure level and duration. It is suggested that the lymphocyte subsets may be most susceptible to the effects of FA, though a single immunological endpoint is rarely related with pathophysiological interpretation.

Adult↗