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W Yan

Publications and source records attributed to W Yan.

At least 37 records · Page 2Linked to original sources
PubMed2001

Translational regulation as a novel mechanism for the development of cellular drug resistance.

Cellular drug resistance is one of the principal obstacles to the clinical efficacy of cancer chemotherapy. In this review, we describe the potential role for translational regulation as a novel mechanism for modulating chemosensitivity. The evidence for the translational control of thymidylate synthase, dihydrofolate reductase, and p53 will be presented, as will experimental data showing how disruptions in this important regulatory process can lead to the rapid emergence of cellular drug resistance.

Antineoplastic Agents↗
PubMed2001

Rescue of embryonic lethality in Mdm4-null mice by loss of Trp53 suggests a nonoverlapping pathway with MDM2 to regulate p53.

The p53 protein can inhibit cell cycling or induce apoptosis, and is thus a critical regulator of tumorigenesis. This protein is negatively regulated by a physical interaction with MDM2, an E3 ubiquitin ligase. This interaction is critical for cell viability; loss of Mdm2 causes cell death in vitro and in vivo in a p53-dependent manner. The recently discovered MDM2-related protein MDM4 (also known as MDMX) has some of the same properties as MDM2. MDM4 binds and inhibits p53 transcriptional activity in vitro. Unlike MDM2, however, MDM4 does not cause nuclear export or degradation of p53 (refs. 9,10). To study MDM4 function in vivo, we deleted Mdm4 in mice. Mdm4-null mice died at 7.5-8.5 dpc, owing to loss of cell proliferation and not induction of apoptosis. To assess the importance of p53 in the death of Mdm4-/- embryos, we crossed in the Trp53-null allele. The loss of Trp53 completely rescued the Mdm4-/- embryonic lethality. Thus, MDM2 and MDM4 are nonoverlapping critical regulators of p53 in vivo. These data define a new pathway of p53 regulation and raise the possibility that increased MDM4 levels and the resulting inactivation of p53 contribute to the development of human tumors.

Animals↗
PubMed2001

Induction of basic helix-loop-helix protein DEC1 (BHLHB2)/Stra13/Sharp2 in response to the cyclic adenosine monophosphate pathway.

DEC1 (BHLHB2)/Stra13/Sharp2, a basic helix-loop-helix (bHLH) transcription factor has been suggested to be involved in the control of proliferation and/or differentiation of several cells including nerve cells, fibroblasts and chondrocytes. In the present study, we examined the effect of parathyroid hormone (PTH), dibutyryl cAMP (Bt2cAMP) and forskolin on the expression of DEC1 in various cells. In rabbit chondrocyte cultures, PTH or Bt2cAMP increased the DEC1 mRNA level within 1 h. Thereafter, the DEC1 mRNA level rapidly decreased to the basal level at 3 h, and increased at 6-24 h. In cultures of a mouse embryo prechondrogenic cell line ATDC5, PTH or forskolin, an activator of adenylate cyclase, also increased the DEC1 mRNA level within 1 h. Furthermore, in all evaluated cell lines of human fibroblasts, canine epithelial cells, human carcinoma, human glioblastoma and human melanoma, Bt2cAMP increased the DEC1 mRNA level within 1-3 h. Studies with actinomycin D and cycloheximide indicated that the enhancement of DEC1 mRNA by cAMP was not due to mRNA stabilization and did not require new protein synthesis. These findings suggest that DEC1 is a novel direct target for cAMP in wide types of cells, and that the bHLH protein is involved in the control of gene expression in cAMP-activated cells.

Animals↗
PubMed2001

Drug targeting Mycobacterium tuberculosis cell wall synthesis: genetics of dTDP-rhamnose synthetic enzymes and development of a microtiter plate-based screen for inhibitors of conversion of dTDP-glucose to dTDP-rhamnose.

An L-rhamnosyl residue plays an essential structural role in the cell wall of Mycobacterium tuberculosis. Therefore, the four enzymes (RmlA to RmlD) that form dTDP-rhamnose from dTTP and glucose-1-phosphate are important targets for the development of new tuberculosis therapeutics. M. tuberculosis genes encoding RmlA, RmlC, and RmlD have been identified and expressed in Escherichia coli. It is shown here that genes for only one isotype each of RmlA to RmlD are present in the M. tuberculosis genome. The gene for RmlB is Rv3464. Rv3264c was shown to encode ManB, not a second isotype of RmlA. Using recombinant RmlB, -C, and -D enzymes, a microtiter plate assay was developed to screen for inhibitors of the formation of dTDP-rhamnose. The three enzymes were incubated with dTDP-glucose and NADPH to form dTDP-rhamnose and NADP(+) with a concomitant decrease in optical density at 340 nm (OD(340)). Inhibitor candidates were monitored for their ability to lower the rate of OD(340) change. To test the robustness and practicality of the assay, a chemical library of 8,000 compounds was screened. Eleven inhibitors active at 10 microM were identified; four of these showed activities against whole M. tuberculosis cells, with MICs from 128 to 16 microg/ml. A rhodanine structural motif was present in three of the enzyme inhibitors, and two of these showed activity against whole M. tuberculosis cells. The enzyme assay was used to screen 60 Peruvian plant extracts known to inhibit the growth of M. tuberculosis in culture; two extracts were active inhibitors in the enzyme assay at concentrations of less than 2 microg/ml.

Carbohydrate Dehydrogenases↗
PubMed2001

Bitter taste transduced by PLC-beta(2)-dependent rise in IP(3) and alpha-gustducin-dependent fall in cyclic nucleotides.

Current evidence points to the existence of multiple processes for bitter taste transduction. Previous work demonstrated involvement of the polyphosphoinositide system and an alpha-gustducin (Galpha(gust))-mediated stimulation of phosphodiesterase in bitter taste transduction. Additionally, a taste-enriched G protein gamma-subunit, Ggamma(13), colocalizes with Galpha(gust) and mediates the denatonium-stimulated production of inositol 1,4,5-trisphosphate (IP(3)). Using quench-flow techniques, we show here that the bitter stimuli, denatonium and strychnine, induce rapid (50-100 ms) and transient reductions in cAMP and cGMP and increases in IP(3) in murine taste tissue. This decrease of cyclic nucleotides is inhibited by Galpha(gust) antibodies, whereas the increase in IP(3) is not affected by antibodies to Galpha(gust). IP(3) production is inhibited by antibodies specific to phospholipase C-beta(2) (PLC-beta(2)), a PLC isoform known to be activated by Gbetagamma-subunits. Antibodies to PLC-beta(3) or to PLC-beta(4) were without effect. These data suggest a transduction mechanism for bitter taste involving the rapid and transient metabolism of dual second messenger systems, both mediated through a taste cell G protein, likely composed of Galpha(gust)/beta/gamma(13), with both systems being simultaneously activated in the same bitter-sensitive taste receptor cell.

Animals↗
PubMed2001

CaMKIV/Gr is dispensable for spermatogenesis and CREM-regulated transcription in male germ cells.

The calcium/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is expressed in male germ cells and spermatids and has been implicated in controlling the differentiation of germ cells into mature spermatozoa. The function of CaMKIV/Gr in spermatogenesis was investigated using CaMKIV/Gr-deficient mice generated by targeted gene disruption. CaMKIV/Gr-deficient males exhibited normal spermatogenesis, and their fertility was similar to that of wild-type littermates. Notwithstanding the function of CaMKIV/Gr as an activator of cAMP response element (CRE)-dependent transcription, mRNA levels of several testis-specific CRE modulator (CREM)-regulated genes were unaltered. These results indicate that CaMKIV/Gr is not essential for spermatogenesis or for CRE-regulated gene transcription in the testis.

Alternative Splicing↗
PubMed2001

Altered structure and function of reproductive organs in transgenic male mice overexpressing human aromatase.

Aromatization of androgens is a key step in estrogen production, and it regulates the delicate balance between estrogens and androgens in the gonads and sex steroid target tissues. In the present study, we generated transgenic mice (AROM(+)) bearing the human ubiquitin C promoter/human P450 aromatase fusion gene. AROM(+) male mice are characterized by an imbalance in sex hormone metabolism, resulting in elevated serum E(2) concentrations, combined with significantly reduced testosterone and FSH levels, and elevated levels of PRL and corticosterone. AROM(+) males present a multitude of severe structural and functional alterations in the reproductive organs, such as cryptorchidism associated with Leydig cell hyperplasia, dysmorphic seminiferous tubules, and disrupted spermatogenesis. The males also have small or rudimentary accessory sex glands with abnormal morphology; a prominent prostatic utricle with squamous epithelial metaplasia, and edema in the ejaculatory ducts and vas deferens. In addition, the abdominal muscle wall is thin, and the adrenal glands are enlarged, with cortical hyperplasia. Some of the abnormalities, such as undescended testes and undeveloped prostate, resemble those observed in animals exposed perinatally to high levels of exogenous estrogen, indicating that the elevated aromatase activity results in excessive estrogen exposure during early phases of development. Some of the disorders in the reproductive organs, furthermore, can be explained by the fact that AROM(+) males are hypoandrogenic, and have elevated levels of serum PRL and corticosterone. Thus, the AROM(+) mouse model provides a novel tool to investigate the consequences of a prolonged increase in conversion of androgens to estrogens which results in complex hormonal disturbances altering the structure and function of various male reproductive organs.

Abdominal Muscles↗
PubMed2001

The expression and regulation of Bcl-2-related ovarian killer (Bok) mRNA in the developing and adult rat testis.

OBJECTIVE: To study the role of Bcl-2-related ovarian killer (Bok) in the regulation of apoptosis in the testis of developing and adult rat. METHODS: Bok mRNA expression was analyzed by Northern hybridization before and after culturing rat seminiferous tubules in vitro. Seminiferous tubules were cultured with different hormones and growth factors. Changes in the expression level of Bok mRNA during testicular development was analyzed by Northern hybridization. Localization of Bok mRNA was verified by in situ hybridization. RESULTS: Bok mRNA was highly expressed in the rat testis, varying during development. Highest expression levels were found in immature rats. Highest hybridization intensity appeared to be in spermatogonia, pachytene spermatocytes and Sertoli cells. Treatment with FSH was able to inhibit spontaneous increase of Bok mRNA expression that occurred in the defined stages of the rat seminiferous epithelium. CONCLUSIONS: FSH protects germ cells from apoptosis and this protective effect may at least partly be due to the inhibition of Bok gene expression. The amount of apoptosis varies during testicular development and highest expression of Bok mRNA occurs at the time of apoptosis, suggesting a possible role for Bok in its regulation.

Animals↗
PubMed2001

Epidemiology of Necator americanus hookworm infections in Xiulongkan Village, Hainan Province, China: high prevalence and intensity among middle-aged and elderly residents.

Hookworm is highly endemic to Hainan Province, an island located in the South China Sea. To investigate the prevalence and intensity of infection in the area, the village of Xiulongkan was surveyed between April and July 1998. A cross-sectional study was conducted in which fecal samples of 80% of the village residents (631 individuals) were tested for the presence of helminth eggs. Hookworm was the predominant intestinal helminth in Xiulongkan, where it was determined that 60% of those tested were infected. Necator americanus was the predominant species of hookworm in this population. The prevalence of hookworm increased with age, and then leveled to a plateau for ages 41 yr and up. This observation was in contrast to infections with Ascaris lumbricoides, where the highest prevalences occurred among school-aged children. Women had a significantly higher prevalence of hookworm than men and this difference emerged in early adulthood. The intensity of hookworm infection also significantly increased with age, with the highest intensity infections occurring among middle-aged and elderly residents. Females were more likely to have moderate or heavy infections, whereas males were more likely to have light infections. The rates of hookworm transmission are particularly high among the middle-aged and elderly residents of Xiulongkan.

Adolescent↗
PubMed2001

[Study of fungus polysaccharides compounds (FPC) in inducing the apoptosis of liver cancer cell Bel-7402].

To observe the influence of fungus polysaccharides compounds (FPC) in inducing human liver cancer cell Bel-7402 apoptosis in cell cultivating in vitro, the authors analyzed tumor inhibitive gene P53 expression in Bel-7402 apoptosis by applying double immuno-marker. The result showed that the multilevel of FPC could all apparently induce Bel-7402 apoptosis. With the enhancement of FPC concentration, the authors observed chromatin condensation in some phases companying with the characteristic apoptosis. In the meantime, it could also greatly reduce the G1 and S, with obviously dose-response relationship. The percentage of cell apoptosis increased with the enhancing of concentration. In the high-level group the authors found typical DNA ladder eletrophoresis stripe. The result showed that the mechanism of the FPC antineoplastic effect had an intimate relation with its induction to apoptosis and that the result of FPC inducing tumor cell apoptosis had the character of P53 independence.

Antineoplastic Agents↗
PubMed2001

[The development and identification of animal osteoblasts from bone marrow culture].

This study was aimed to evaluate a modified method for animal osteoblast marrow culture on the basis of previously published method. The marrow mononuclear cells(MMNC) in femoral bone-marrow of SD rat were gained with Ficoll-Hapaque centrifuge, which were then cultured in 5 x 10(5) cells/cm3 on the 96-well culture plates with RPMI 1640 medium containing 30% horse serum in a humidified atmosphere of 5% carbon dioxide at 37 degree Celsius. The medium was changed every three days. Cultured cells were identified with inverted microscopy for observing the shape of living cells, and with Wright-Geimsa mixture stain and Alkaline phosphatase (ALP) stain. In order to avoid false positive reaction, we caused damage to the ALP in cultured cells and stained the cells with ALP again for comparison. The results of inverted microscopy showed that the small spherical mononuclear cells became polygonal, spindle-shaped or squamous successively from the fifth day onward. Wright-Geimsa staining showed the specific property of osteoblast. ALP stain positive reaction was between "2+" and "3+", then ALP stain negative reaction was noticed after the damage to ALP. These data demonstrated that MMNC in SD rat could become osteoblast in RPMI 1640 medium containing 30% horse serum. The modified osteoblast marrow culture method has the advantages of short time, less risk of contamination and higher efficiency.

Animals↗
PubMed2001

[Apoptosis-related genes cloned by improved subtractive hybridization].

OBJECTIVE: To clone apoptosis-related genes induced by all-trans retinoic acid (ATRA) from human breast cancer cell line MCF-7, and to analyze the association between the cloned genes and apoptosis. METHODS: An apoptotic cell model of MCF-7 cells was constructed with ATRA induction. The apoptosis-related genes were cloned by improved PCR-based subtractive hybridization. RESULTS: Twelve differentially expressed clones were screened out. After exclusion of false positive clones by reverse dot blotting, 5 clones containing fragments of 0.5-1.5 kb were sequenced. The results of sequencing were compared with BLAST. A novel gene, named apmcf-1, coding for 47 amino acids was identified. This gene was accepted by GenBank, (Accession number: AF141882). The result of reverse dot blotting showed that it was related to apoptosis. The other 4 genes were already known. Three of them were related to apoptosis as previously reported. Two of them, hsp-90 and rb-L3, had little information about their relationship with apoptosis. CONCLUSION: ATRA-induced tumor cell apoptosis is a complex process with multiple genes involved.

Apoptosis↗
PubMed2001

[The role of p38 MAPK in LPS induced ICAM-1 expression on endothelial cell].

OBJECTIVE: To study the role of p38 mitogen-activated protein kinase (MAPK) in lipopolysaccharide (LPS) induced expression of intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cell (HUVEC). METHODS: HUVEC was harvested and cultured before being divided into two groups, i,e. stimulating group (S) and priming group (P). In S group, the cultured endothelial cell was stimulated by LPS. In P group, endothelial cell was pre-treated with SB 203580 2 hours before LPS stimulation. The expressions of ICAM-1 mRNA and protein in HUVEC of two groups and their dose-effect relationship with stimulator and inhibitor were observed. Furthermore the p38 mRNA activity of HUVEC was detected. RESULTS: After LPS stimulation, ICAM-1 molecule on the surface of endothelium increased significantly at 8 to 36 hours. Cytoplasmic mRNA increased obviously at 2 hours. The activity of p38 MAPK increased at 15 min and reached peak value at 30 to 60 min after that HUVEC was stimulated by LPS. CONCLUSION: Inhibitor SB 203580 of p38 might significantly inhibit the inducing effect of LPS. LPS could regulate the expression of ICAM-1 gene and protein in HUVEC by activating p38 MAPK signal transduction passage.

Cells, Cultured↗
PubMed2001

[Effect of monascus on improving the hemorheology of rats with high blood lipids].

The effects of monascus on the hemorheology of rats with high blood lipids were observed. Wistar rats were fed with high cholesterol to establish a model of hypercholesterolemia. Monascus at the dosage of 0.0, 0.6, 1.2 g/(d.kg BW) was administrated for 28 days. Normal control group was fed with standard rat chow. Rats in 0.0 g/kg BW group became hypercholesterolemia clearly. Monascus decreased TC, TG, and increased HDL-C significantly in the experimental groups. Monascus can significantly increase the deformability of erythrocyte(IDEI) and decrease aggregation index(AI), platelet adhesion rate(PADT) and blood viscosity at the shear rate of 5 s-1. No significant difference of platelet aggregation (PAGT) in groups was observed.

Animals↗
PubMed2001

[Influence of the hearing loss level and auditory sensation curve type on click evoked SP/AP amplitude ratio in Menière's disease].

OBJECTIVE: To assess the influence of hearing loss level and auditory sensation curve type on click evoked SP/AP amplitude ratio (negative summating potential/action potential) in the diagnosis of Meniere's disease. METHOD: AP and SP was recorded with tympanic ECochG in normal controls (50 ears), patients with sensorineural hearing loss (SNHL) and patients with Meniere's disease (90 ears) which were further divided based upon the degree of hearing loss and audiometric configuration. SP/AP amplitude ratio was calculated and analyzed. RESULT: AP latency in the three groups had no significant differences. AP amplitude in normal hearing subjects was higher than other two patients groups (P < 0.05). Amplitude of SP of control group was higher than that of SNHL group (P < 0.01), but lower than Meniere's disease group (P < 0.01). SP/AP amplitude ratio in Meniere's disease ears was (48.09 +/- 14.83)%, which was significantly higher than that of SNHL group (20.20 +/- 15.00)% (P < 0.01) and normal group (23.85 +/- 8.05)% (P < 0.01). In Meniere's disease ears, SP/AP amplitude ratio was positively correlated to pure tone thresholds (r = 0.5601 P < 0.01). An elevated SP/AP ratio was found in 73% of the Meniere's ears and 6% of the SNHL ears. SP/AP ratio among the different levels of hearing loss in Meniere's disease ears, of the ears with mild hearing loss was lower than those with moderate (P < 0.01) and severe hearing loss (P < 0.01), but between later groups there was no statistical significant difference (P > 0.05). Positive rate of SP/AP ratio was 63% in mild, 83% in moderate, 73% in severe hearing loss ears respectively. SP/AP amplitude ratio in patients with low tone auditory curve type was lower than that with flat type(P < 0.05), the latter had no significant difference (P > 0.05) compared with high tone type. Positive rate was 67.57% in low tone type, 75% in high tone type and 78% in flat tone type respectively. CONCLUSION: Results suggests the increase of SP/AP ratio was of clinical significance in the diagnosis of Meniere's disease, and was with advancing pure tone thresholds in certain range of hearing loss levels. Click evoked SP/AP amplitude ratio was affected by degree of hearing loss and auditory sensation curve as well, perhaps the influence of the former on SP/AP ratio was considerable significant.

Action Potentials↗
PubMed2001

[Transconjunctival approach to the fractures of the orbital floor and infraorbital rim].

OBJECTIVE: To study the surgical approach to the orbital floor and infraorbital rim. METHOD: 15 cases of fractures of the orbital floor and infraorbital rim were treated with the transconjunctival approach. RESULT: All fractures of the orbital floor and infraorbital rim were repositioned and fixed through transconjunctival approach. Except for 1 case with mild canthal malposition, no other complication was observed. CONCLUSION: The transconjunctival approach can provide adequate exposure of the infraorbital rim and orbital floor without scar formation in the face.

Adolescent↗
PubMed2001

[Study on the hypotensive effect of manascus].

The hypotensive effect of manascus was studied by using three well established rat models with hypertension: spontaneously hypertensive rat (SHR), renalvascular hypertensive rat (RHR, 2K1C) and DOCA-salt hypertensive rat. Manascus of 0.0, 0.4, 0.8, 1.2 g/kg BW (p.o.) were administrated daily to these animals for 3-4 weeks. Systolic blood pressure (SBP) and heart rate were measured once a week by using tail-cuff method. The hypotensive effect of manascus was observed in SHR and DOCA-salt hypertensive rats; and the effect was more potent in DOCA-salt hypertensive rat. Manascus showed less potential hypotensive effect in RHR.

Animals↗