Biomedical subjects

Tian Xia

Publications and source records attributed to Tian Xia.

27 records · Page 2Linked to original sources

PubMed2003

The activation domains, the proline-rich domain, and the C-terminal basic domain in p53 are necessary for acetylation of histones on the proximal p21 promoter and interaction with p300/CREB-binding protein.

The p53 transcription factor contains two separate tandem activation domains (AD1 and AD2), a proline-rich domain (PRD), and a C-terminal basic domain (BD). Previously, we have shown that these domains are necessary for transcriptional activity. To further characterize the role of these domains in transactivation, we analyzed the regulation of p21, a well characterized p53 target gene, by various p53 mutants deficient in one or more of these domains. We found that the induction of endogenous p21 is compromised by AD1-deficient p53 (p53(AD1(-))), AD2-deficient p53 (p53(AD2(-))), both AD1- and AD2-deficient p53 (p53(AD1(-)AD2(-))), p53(deltaPRD), which lacks PRD, and p53(deltaBD), which lacks BD. However, p53(AD2(-)), p53(deltaPRD), and p53(deltaBD) are still capable of activating exogenous p21 promoter to an extent comparable with that by wild-type p53. Thus, we performed chromatin immunoprecipitation assay to measure the DNA binding ability of various p53 mutants in vivo. We found that like wild-type p53, these p53 mutants are capable of binding to the p53 response elements in the p21 promoter. In contrast, we found that the extent of acetylated histones on the p21 promoter, especially the proximal promoter, and the amount of interaction with p300/CREB-binding protein, which contain histone acetyltransferase activity, directly correlate with the activity of p53 to induce endogenous p21. Furthermore, we showed that down-regulation of p300/CBP by short interference RNA markedly decreases the ability of p53 to induce endogenous p21. These data lead us to hypothesize that when p53 binds to the responsive element(s) of a target gene, its ability to interact with histone acetyltransferase-containing proteins and subsequently the acetylation of histones bound to the proximal promoter dictate the induction level of a target gene.

Acetylation↗

PubMed2003

Characterization of the 5'-flanking fragment of the human GM3-synthase gene.

To investigate the transcriptional regulation of human GM3-synthase, a 5'-flanking fragment of 1379 bp was cloned by a PCR-based procedure. Analysis of the human genomic sequence showed that the gene consists of seven exons, locates at chromosome 2, and spans over 62 kb. There are a number of potential consensus binding sites in the cloned promoter region, but TATA and CCAAT boxes were not found in the promoter. Primer extension analysis identified two transcription start sites approximately 11 and 57 bp upstream of the exon 1. The transcription activity of the promoter was assessed in human HeLa cells by transient transfection. Of the fragments assayed, the proximal 409 bp fragment exhibits the highest transcription activity. Transcription factors that bound to the 409 bp fragment were pulled down by DNA-coupled magnetic beads. Identities of the pull-down proteins were determined by array analysis. Eight transcription factors were identified, which might either bind to the proximal region or be recruited as co-activators of the transcription factor complexes.

5' Flanking Region↗

PubMed2003

Antibiotic susceptibility of bacteria associated with endodontic abscesses.

Antibiotics to treat endodontic infections are routinely prescribed based on previously published susceptibility tests. There is increased concern that bacteria have increased resistance to the currently recommended antibiotics. The purpose of this investigation was to perform antibiotic susceptibility tests on a panel of bacteria recently isolated from endodontic infections. The bacteria in this study were aseptically aspirated with a needle from endodontic abscesses, cultivated, and identified at the species level. Each of the 98 species of bacteria was tested for antibiotic susceptibility to a panel of six antibiotics using the Etest. The antibiotics were penicillin V, amoxicillin, amoxicillin + clavulanic acid, clindamycin, metronidazole, and clarithromycin. The percentages of susceptibility for the 98 species were penicillin V: 83/98 (85%), amoxicillin: 89/98 (91%), amoxicillin + clavulanic acid: 98/98 (100%), clindamycin: 94/98 (96%), and metronidazole: 44/98 (45%). Metronidazole had the greatest amount of bacterial resistance; however, if it is used in combination with penicillin V or amoxicillin, susceptibility of the combination with penicillin V or amoxicillin increased to 93% and 99%, respectively. Clarithromycin seems to have efficacy, but it is still considered an antibiotic under investigation because the minimum inhibitory concentration has not been established.

Amoxicillin↗

PubMed2003

Efficacy of calcium hydroxide: chlorhexidine paste as an intracanal medication in bovine dentin.

The purpose of this study was to evaluate the antibacterial efficacy of an intracanal medication composed of calcium hydroxide with 2% chlorhexidine. Dentin from 24 bovine incisors was used. The incisors were made into standardized cylindrical segments of dentin and infected with Enterococcus faecalis. They were then treated with an intracanal paste composed of calcium hydroxide and sterile water or an intracanal paste composed of calcium hydroxide and 2% chlorhexidine for 1 week. Dentin shavings were collected, suspended in solution, and spread on brain-heart infusion agar. After incubation, colony-forming units were enumerated. The amount of bacteria per mg of dentin was determined. The calcium hydroxide paste with 2% chlorhexidine was significantly more effective at killing E. faecalis in the dentinal tubules than calcium hydroxide with water.

Animals↗

PubMed2003

Occurrence of Actinomyces in infections of endodontic origin.

Species of Actinomyces have been associated with endodontic treatment that failed to heal. In this study polymerase chain reaction was used with a pair of universal primers for Actinomyces and species-specific primers to evaluate the contents of infected root canals and aspirates from abscesses or cellulitis for the presence of Actinomyces israelii, A. naeslundii, and A. viscosus. DNA was extracted from 131 clinical samples. DNA from 2 of the original 131 samples was not available for polymerase chain reaction with the universal primer for Actinomyces and A. naeslundii. DNA reacting with the universal primer for Actinomyces was detected in 72 of 129 (55.8%) clinical samples. Of those 41 of 51 (80.4%) were from infected root canals, 22 of 48 (45.8%) were from abscesses, and 9 of 30 (30%) were associated with cellulitis. A. viscosus was detected in 42 of 131 (32.1%) clinical samples. Of those 31 of 52 (59.6%) were from infected root canals, 6 of 43 (14%) were from abscesses, and 5 of 36 (13.9%) were associated with cellulitis. A. israelii was detected in 31 of 131 (23.7%) clinical samples. Of those 14 of 52 (26.9%) were from infected root canals, 11 of 43 (25.6%) were from abscesses, and 6 of 36 (16.7%) were associated with cellulitis. A. naeslundii was detected in 11 of 131 (8.5%) clinical samples. Of those 7 of 51 (13.7%) were from infected root canals, 2 of 48 (4.2%) were from abscesses, and 2 of 30 (6.7%) were associated with cellulitis.

Actinomyces↗

PubMed2003

Identification of spirochetes (treponemes) in endodontic infections.

The purpose of this study was to determine the prevalence of spirochetes in asymptomatic infected root canals and in endodontic abscesses/cellulitis. Aseptic clinical samples were collected using paper points from 54 infected root canals and from aspirates of 84 abscesses/cellulitis. Oligonucleotide primers were produced for PCR identification of Treponema vincentii, T. pectinovorum, T. medium, T. amylovorum, T. denticola, T. maltophilum, and T. socranskii. PCR detected spirochetes in 51 of 84 (60.7%) samples from abscesses/cellulitis and in 20 of 54 (37.0%) samples from asymptomatic infected root canals. T. socranskii was the most frequently detected (44.9%), followed by T. maltophilum (29.7%), T. denticola (28.9%), T. pectinovorum (13.7%), and T. vincentii (5.1%). The number of treponema species detected ranged from 1 to 5 species per sample. The mean numbers of species detected were 2.3 in abscesses/cellulitis and 2.6 in infected root canals. Significant association among species was found between T. maltophilum and T. socranskii, as well as between T. maltophilum and T. denticola by determining the odds ratio (> 2.0).

Bacterial Typing Techniques↗

PubMed2002

A study on permeability transition pore opening and cytochrome c release from mitochondria, induced by caspase-3 in vitro.

We recently described that there is a feedback amplification of cytochrome c release from mitochondria by caspases. Here we investigated how caspases impact on mitochondria to induce cytochrome c release and found that recombinant caspase-3 induced opening of permeability transition pore and reduction of membrane potential in vitro. These events were inhibited by Bcl-xL, cyclosporin A and z-VAD.fmk. Moreover, caspase-3 stimulated the rate of mitochondrial state 4 respiration, superoxide production and NAD(P)H oxidation in a Bcl-xL- and cyclosporin A-inhibitable manner. These results suggest that caspase-3 induces cytochrome c release by inducing permeability transition pore opening which is associated with changes in mitochondrial respiration and redox potential.

Amino Acid Chloromethyl Ketones↗

PubMed2002

Microbial leakage evaluation of the continuous wave of condensation.

Coronal leakage has been recognized as a cause of pulpal and periradicular disease. Although cleaning and shaping of the root canal system is considered paramount, obturation of the system is an important step in endodontic success. The purpose of this study was to evaluate coronal bacterial leakage in teeth obturated with the System B continuous wave of condensation technique, followed by an Obtura II backfill, versus teeth obturated using the lateral condensation technique. Sixty single-rooted bilaterally matched teeth were evaluated in this study. An anaerobic bacterial leakage model was used. Results indicate that microbial coronal leakage occurs more quickly using lateral condensation than with the System B continuous wave of condensation and Obtura II backfill. This difference was statistically significant (p < or = 0.05). However, there was no statistical difference between groups 1 and 2 in the numbers of teeth that demonstrated bacterial leakage at the end of the study.

Case-Control Studies↗

PubMed2002

Down stream involvement of the bile duct in hepatolithiasis.

OBJECTIVE: To evaluate the down stream involvement of the bile duct in hepatolithiasis. METHODS: Mechanical damage to bile duct epithelia and long standing cholangitis as result of hepatolithiasis play an important role in the carcinogenesis of bile duct epithelia and stricture of the intra- and extra-hepatic bile duct. Macromorphological and microscopic changes in bile duct mucosa of 100 consecutive patients with hepatolithiasis were investigated using intra- or post-operative cholangioscopy. Biopsy specimens of lesions obtained during cholangioscopy were studied with immunohistochemical staining and flow cytometry to determine proliferative activity and DNA content. Five cases of well-proven cholangiocarcinoma were simultaneously studied as controls. RESULTS: Of the 100 patients, those with chronic cholangitis accounted for 86% (86/100), proliferative lesions 11% (11/100), adenomatous polyps 1% (1/100), and adenocarcinoma 2% (2/100). The obvious mucosal lesion associated with hepatolithiasis was located down-stream of the bile duct, predominantly in the hilar region, e.g. orifices of the right/left hepatic duct and common hepatic duct (73% mucosa lesions in the hilar region). The intensity of cancer embryonic antigen stain and the proliferative cell nuclear antigen index increased with the development of bile duct lesions. Aneuploid DNA presented mainly in the high degree malignant adenocarcinomas (> 80% of cases). CONCLUSIONS: The obvious mucosal lesions associated with hepatolithiasis were located down-stream of the bile duct, predominantly in the hilar region (73% of mucosal lesions). The proliferative activity of examined bile duct mucosa lesions increased with the development of pathological deterioration, which may contribute to the development of hilar bile duct stricture and hilar cholangiocarcinoma.

Adult↗