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W Li

Publications and source records attributed to W Li.

At least 973 records · Page 54Linked to original sources
PubMed1996

Inhibition of oncogene-mediated transformation by ectopic expression of p21Waf1 in NIH3T3 cells.

The p53-regulated p21Waf1 protein is a universal inhibitor of cyclin-dependent kinases (CDKs). To study the potential tumor-suppressive properties of CDK inhibitors, the ability of p21Waf1 to interfere with oncogene-mediated cellular transformation was analysed in the NIH3T3 cell system. Cotransfection of waf1 together with activated ras or several other oncogenes into NIH3T3 cells potently inhibited the formation of transformed foci in a dose-dependent manner. Expression of the CDK-binding N-terminal half of p21Waf1 (N-p21Waf1) was necessary and sufficient to inhibit Ras-induced focus formation. In contrast, expression of the C-terminal domain (C-p21Waf1) had no effect on Ras-induced focus formation. Immunofluorescence analysis revealed that ectopically expressed p21Waf1 and C-p21Waf1 were localized in the nucleus, while N-p21Waf1 was found in the cytoplasm, with the tendency to accumulate around the nuclear membrane. Surprisingly, stable NIH3T3 transfectants expressing ectopic p21Waf1 grew at the same rate and displayed similar cell cycle distribution as NIH3T3 cells transfected with the same vector containing no insert. However, ectopic p21Waf1 expression did inhibit Ras-mediated anchorage-independent colony formation, indicating that p21Waf1 can selectively interfere with oncogene-mediated transformation without affecting NIH3T3 cell growth, at least at the levels of p21Waf1 expression achieved in these experiments. Transient transfection of waf1 into NIH3T3 cells inhibited Ras-induced transcription from a E2F-responsive element but not from a serum-responsive element, indicating that p21Waf1 acts downstream of early transcriptional events induced by Ras but upstream of E2F-controlled gene transcription. These results provide evidence that p21Waf1 potently suppresses oncogene-mediated cellular transformation of NIH3T3 cells and that it may do so by inhibiting E2F-driven transcription of S phase genes.

3T3 Cells↗
PubMed1996

Monoclonal anti-idiotypic antibody functionally mimics the human gastrointestinal carcinoma epitope GA733.

Anti-idiotypic antibodies (Ab2) that bind to the antigen-combining region of anti-tumor antibodies (Ab1) may functionally, and even structurally, mimic tumor antigen. We have previously demonstrated that polyclonal goat Ab2 directed against anti-human gastrointestinal carcinoma Ab1 GA733 induces anti-anti-idiotypic antibodies (Ab3) in animals that are Ab1-like in their binding specificity and idiotope expression. To obtain more defined Ab2 vaccines with potentially increased specificity and efficacy, a monoclonal Ab2 (FG1) was produced against Ab1 GA733 in rats. The monoclonal Ab2 FG1, similar to the polyclonal Ab2 described previously, induced Ab3 in rabbits that were Ab1-like in their idiotope expression and binding specificity to tumor cells and antigen. Antigen-specific Ab3 induced by Ab2 FG1 were easily detected in unprocessed rabbit sera, whereas the demonstration of such Ab3 after polyclonal Ab2 immunization required purification of the Ab3 from the rabbit sera. In addition, Ab2 FG1 induced antigen-specific humoral and cellular immunity in mice. Murine Ab3 bound specifically to antigen-positive tumor cells. Ab2-immunized mice showed antigen-specific delayed-type hypersensitivity (DTH) reaction, and cultured splenocytes from the immune mice demonstrated specific proliferation and cytokine (interferon-gamma and interleukin-4) secretion upon stimulation with GA733 antigen. However, immune mice were not protected against a challenge with syngeneic GA733 antigen-expressing colon carcinoma cells.

Animals↗
PubMed1996

Regulation of the nuclear factor of activated T cells in stably transfected Jurkat cell clones.

Two Jurkat cell clones have been stably transfected with a reporter vector for the nuclear factor of activated T cells (NFAT). Upon stimulation, they express high levels of secreted heat stable placental alkaline phosphatase. With these clones, we demonstrated that NFAT activation induced by phorbol 12-myristate 13-acetate and ionomycin was inhibited by both cyclosporin A (CsA) (IC50 = 8 nM) and FK506 (IC50 = 160 pM), presumably by inhibition of calcineurin activity. Selective phosphatase inhibitors for protein phosphatase 1 (PP1) and 2A (PP2A) that do not inhibit calcineurin, such as okadaic acid and calyculin A, also inhibited NFAT activation with IC50s of 87 nM and 4 nM, respectively, suggesting that okadaic acid and related inhibitors may block NFAT activation through the inhibition of PP1, instead of PP2A. NFAT activation was also inhibited by agents that increase cAMP concentrations such as dibutyryl cAMP, forskolin and prostaglandin E2. These stable Jurkat cell clones provide a convenient and sensitive tool to study NFAT regulation.

Alkaline Phosphatase↗
PubMed1996

Genetic alterations on chromosomes 3 and 9 of esophageal cancer tissues from China.

In previous studies, we had demonstrated that allelic losses in esophageal cancer (EC) tissues are frequently involved in chromosomes 3 and 9 and that EC patients and their blood relatives have low capacity to repair damaged DNA and showed genetic instability. To better define the deleted chromosomal loci and understand the genetic instability in EC tissues, we selected 12 microsatellite markers (D3S1232, D3S1238, D3S1289, D3S1480, D3S647, D3S966, D3S1317, D3S659, D9S156, D9S171, D9S176 and GSN) to examine 36 paired EC tissues for loss of heterozygosity (LOH) and microsatellite instability (MIN) on chromosomes 3 and 9. The frequent LOH was found at D9S156(9p21), D3S647(3p23) and D3S1480(3p14.2), implying the possible existence of tumor suppressor genes near the deleted loci. Higher LOH incidence at D9S156 (9/18) and D3S1480 (8/19) was observed in EC tissues from Beijing, a low EC area. More frequent LOH at D3S647 (6/14) was found in EC tissues from Yangquan, a high EC area. This geographic difference of LOH occurrence was indicative of genetic heterogeneity in the etiology of EC. 24 of 36 (66.7%) EC tissues showed MIN at one or more chromosomal loci. The putative EC suppressor genes on chromosomes 3 and 9 and the molecular basis of the genetic instability associated with EC remain to be elucidated.

Alleles↗
PubMed1996

Pulmonary perfusion: qualitative assessment with dynamic contrast-enhanced MRI using ultra-short TE and inversion recovery turbo FLASH.

The accurate assessment of pulmonary perfusion is especially important in the evaluation of patients with suspected pulmonary embolism, a common and potentially lethal disorder that can be treated by aggressive anticoagulation. In this study, we demonstrate for the first time the use of MR to image pulmonary perfusion in humans by using dynamic imaging after contrast administration. The technique, which uses an inversion recovery turbo FLASH sequence with ultrashort TE (1.4 ms) and 1-s temporal resolution, was tested in a series of eight healthy subjects and in a porcine model of pulmonary embolism. After the administration of gadopentetate dimeglumine in humans and animal models, there was serial enhancement of the systemic veins, right atrium, right ventricle, and pulmonary arteries. The pulmonary arterial tree was visualized beyond the segmental branches, followed by a gradual diffuse increase in signal intensity of the lung parenchyma over a period of 4.0-7.0 s. Pulmonary circulation times ranged from 3.0-3.4 s. Whereas a high dose (20 or 40 ml) of contrast agent tended to produce the most intense parenchymal enhancement, a low dose (5 ml) was best for showing recirculation. In the animal model, a perfusion defect due to a pulmonary embolus was clearly shown and confirmed by cine angiography. It is concluded that MRI of lung perfusion is feasible. With further development, perfusion MRI could eventually have a significant clinical role in the diagnostic evaluation of pulmonary embolism.

Animals↗
PubMed1996

In vivo effects of cardiotrophin-1.

Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 microg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway.

Animals↗
PubMed1996

Alveolar hydatid cyst (AHC): inflammation-induced reactive gastrointestinal (GL) amyloidosis in AHC-infected mice and chemical characterization of the GL amyloid.

A high incidence of GI amyloidosis has been described in patients with various forms of systemic amyloidosis but its evolution and progression in different subregions of the GI tract are not well documented. These aspects including the chemical nature of GI amyloid were examined in the AHC mouse model of inflammation-associated reactive amyloidosis. C57BL/6 mice were infected intraperitoneally with 250 AHC. Paraffin sections from the stomach and the small and large intestines of AHC mice were stained at different time intervals with Congo red or immunocytochemically with monospecific RAA. The submucosal blood vessels at 1 week postinfection were found to be the first target of amyloid deposition. With time the amyloid deposits extended to the mucosa and the Peyer's patches and immunoreacted with RAA; ileum was the most severely affected region. Amyloid was extracted from the GI tract and purified by size exclusion chromatography using 5 M guanidine-formic acid, pH 3. The purified amyloid was identified by Western blotting using RAA and by partial N-terminal microsequencing up to 10 cycles. The GI amyloid showed homology with murine SAA2, although SAA2 mRNA is not expressed in murine GI tract. These results shows that (a) the GI amyloid is derived, similar to that of splenic/hepatic amyloid, from circulating SAA2 and (b) the GI tract submucosal blood vessels are the first target of AA deposition. The data also suggest that AA-mediated damage to the submucosal blood capillaries may lead to SAA leakage followed by cascading of AA deposition in other layers of the GI tract.

Amino Acid Sequence↗
PubMed1996

Mg2+ antagonism on Ni(2+)-induced changes in microtubule assembly and cellular thiol homeostasis.

As an essential metal for cell metabolism, Mg2+ is known to exert antagonism on Ni2+ genotoxic and other effects. This study examined the influence of Mg2+ on Ni(2+)-induced changes in microtubule (MT) assembly in vitro, cytoplasmic MT organization, cellular glutathione (GSH), and cytoskeletal and cytosolic protein sulfhydryls (PSH). As determined by a turbidity assay at 27 degrees C, Ni2+ enhanced the in vitro MT assembly in a Pipes buffer by shortening the initial lag (nucleation phase) and increasing the rate of polymerization with a higher final plateau. However, presence of 1 mM exogenous MgCl2 abolished the Ni2+ enhancing effect. Exposure of 3T3 cells to 2 mM NiCl2 for 20 hr resulted in perinuclear bundling of MTs and decreases in cytoskeletal and cytosolic PSH and cellular GSH levels. However, coincubation of cells with MgCl2 (1.25-20 mM) added to the culture medium markedly diminished the Ni2+ injury to MT organization. Under these conditions the Ni2+ interference with PSH was blocked such that both the cytoskeletal and cytosolic PSH levels returned to the range of control cells without metal treatment. Treatment of cells with Mg2+ (1.25-5 mM) for 20 hr slightly increased, while with higher Mg2+ doses (> 10 mM) decreased, cellular GSH content. Importantly, in Ni(2+)-treated cultures, addition of Mg2+ (1.25-10 mM) elevated GSH levels to > or = 200% of that in cells treated with Ni2+ alone. Furthermore, these Ni2+ and Mg2+ (1.25-10 mM) treated cells actually maintained GSH levels which were essentially unchanged from the basal level of control cells with no metal treatment. Although Mg2+ replacement of Ni2+ bound to MT proteins could be an important mechanism, cellular GSH may also be a critical factor in Mg2+ antagonism on Ni(2+)-enhanced MT assembly in view of the essential role of tubulin PSH in modulating MT assembly and, in turn, the GSH modulation of PSH.

3T3 Cells↗
PubMed1996

Nickel (Ni2+) enhancement of alpha-tubulin acetylation in cultured 3T3 cells.

Stable microtubules (MTs) are well known to contain acetylated alpha-tubulin. Ni2+-induced MT bundling may be accompanied with such tubulin post-translational modification. To explore this possibility as a mechanism of Ni2+-induced cytoskeletal injury, we have examined acetylated alpha-tubulin levels in cultured 3T3 cells by both immunoprecipitation assays and fluorescent staining of MTs using a monoclonal antibody (clone 6-11B-1) specific for acetylated artubulin. Cell extracts prepared from [35S]methionine labeled cultures in the presence or absence of Ni2+ were immunoprecipitated and analyzed by SDS-PAGE followed by autoradiography. A predominant protein band (molecular mass 55 kDa), representing acetylated alpha-tubulin, appeared in Ni2+-treated cells in a dose and time-dependent manner whereas the corresponding labeled protein band was only barely detectable in control cells. Consistent with the immunoblot findings, MTs in control 3T3 cells in the absence of Ni2+ were not labeled by the 6-11B-1 antibody except for some short, discontinuous segments localized in the cell center or the perinuclear MT organizing center area. In contrast, treatment of cells with NiCl2 (2 mM for 20 hr) resulted in, as expected, the formation of MT bundles that were intensely stained by the 6-11B-1 monoclonal antibody specific for acetylated alpha-tubulin. Furthermore, MTs containing acetylated alpha-tubulin in Ni2+-treated cells were resistant to disassembly induced by nocodazole, and at least partially resistant to cold temperature (0 degrees C), which also depolymerizes MTs. Since acetylated alpha-tubulin serves as a marker for the presence of stable MTs, the marked enhancement of alpha-tubulin acetylation in Ni2+-treated cells indicates that stabilization of MTs may be an important mechanism by which Ni2+ induces cell injury since stabilized MTs in turn should favor MT bundling, an unusual form of cytoskeletal perturbation in response to Ni2+ exposure.

3T3 Cells↗
PubMed1996

Cultured retinal capillary pericytes die by apoptosis after an abrupt fluctuation from high to low glucose levels: a comparative study with retinal capillary endothelial cells.

A number of clinical observations concerning cases of glycemic fluctuation have prompted us to study whether or not a rapid change in blood glucose concentration can aggravate retinal microvascular pathology during the early stage of diabetic retinopathy. We conducted a comparative study of retinal capillary pericytes and endothelial cells in vitro. Both types of cells, either in single culture or in co-culture, were initially incubated in medium with high glucose (20-40 mmol/l), followed by a rapid reduction of glucose to 3.5, 1, or 0.5 mmol/1. This type of reduction of extracellular glucose resulted in depletion of intracellular glucose, occurring much faster in pericytes than in endothelial cells. The abrupt reduction in glucose caused pericyte cell shrinkage and nuclear condensation associated with DNA fragmentation, followed by loss of cell viability. All of these pericyte changes are apoptosis-like characteristics. This apoptotic process was prevented by the addition of cycloheximide, a protein synthesis inhibitor, or by platelet-derived growth factor BB, which is known competent factor for pericyte growth. In analysis of signalling pathways during the abrupt fluctuation of glucose, the occurrence of pericyte apoptosis was an intracellular calcium-dependent, protein kinase C and protein kinase A mediated, and poly (ADP-ribose) synthetase-dependent process. Interestingly, a larger degree of DNA fragmentation was observed with a higher magnitude and a longer duration of pre-existing hyperglycaemia. These results suggest that the magnitude and duration of pre-existing hyperglycaemia prime the apoptotic responsiveness of pericytes. Retinal capillary endothelial cells, after an identical glucose fluctuation treatment did not undergo an apoptotic process.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1996

Dose-response relationship of cytochrome P4501b1 mRNA induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin in livers of C57BL/6J and DBA/2J mice.

The dose-response relationship of cytochrome P4501b1 (Cyp1b1) and Cyp1a1 induction in livers of TCDD-treated female C57BL/6J and DBA/2J mice are described. The animals were treated i.p. with 0.001, 0.01, 0.1, 1, 10 and 50 micrograms TCDD/kg for 24 h, and Cyp1b1 and Cyp1a1 mRNA expression was analyzed by RT-PCR. In the livers of both mouse strains, the Cyp1b1 and Cyp1a1 mRNA content was increased after TCDD exposure in a dose-dependent manner. These effects were more pronounced in TCDD-responsive C57BL/6J mice than in the less responsive DBA/2J mice, although Cyp1a1 was more responsive to TCDD than Cyp1b1 in both strains. The calculated ED50 values for Cyp1b1 and Cyp1a1 induction in livers of TCDD-treated C57BL/6J mice were 1.3 and 0.08 micrograms TCDD/kg, respectively. The corresponding values for half-maximal induction response in livers of DBA/2J mice were 3.4 micrograms TCDD/kg for Cyp1b1 and 1.5 micrograms TCDD/kg for Cyp1a1. These results show that Cyp1b1 mRNA expression is less inducible by TCDD than Cyp1a1. Both genes are highly inducible in TCDD-responsive C57BL/6J mice expressing the high affinity arylhydrocarbon receptor (Ah receptor), suggesting that Cyp1b1, like Cyp1a1, is a potential Ah receptor-regulated gene.

Animals↗
PubMed1996

Inhibition of rat C6 glioblastoma tumor growth by expression of insulin-like growth factor I receptor antisense mRNA.

The expression of insulin-like growth factor I receptor (IGF-IR) antisense mRNA inhibits the growth of C6 rat glioblastoma cells both in vitro and in vivo [Cancer Res (1994) 54:2218]. Moreover, the injection of C6 cells expressing an antisense mRNA to the IGF-IR into syngeneic rats prevents subsequent wild-type tumorigenesis and induces regression of established tumors. For the study of immune function in syngeneic rats, C6 cells expressing either IGF-IR sense or IGF-IR antisense mRNA were injected and splenic lymphocyte function analyzed in vitro after 2 weeks. Cytotoxic, CD8+ lymphocytes from animals injected with IGF-IR antisense cells, but not from those treated with IGF-IR sense cells, proliferated in vitro in response to wild-type C6 cells. Wild-type C6 cells or IGF-IR-sense-RNA-expressing cells rapidly formed tumors upon subcutaneous injection into athymic nude mice. IGF-IR antisense cells were weakly tumorigenic, exhibiting a six- to tenfold increase in tumor latency. Injection of IGF-IR antisense C6 cells mildly delayed the development of wild-type tumors, and did not induce the regression of established wild-type C6 tumors in athymic nude mice. Thus, these findings demonstrate the stimulation of a cellular immune response in rats following the injection of IGF-IR antisense cells. However, studies of athymic nude mice indicate that expression of IGF-IR antisense mRNA also inhibits C6 cells tumorigenicity by additional mechanisms.

Animals↗
PubMed1996

Anti-idiotype cancer vaccines: past and future.

Anti-idiotypic antibodies (Ab2) binding to the antigen-combining site of antitumor antibodies (Ab1) can induce anti-anti-idiotypic antibodies (Ab3) that specifically bind to the tumor antigen recognized by Ab1. Furthermore, Ab2, mimicking tumor antigens, have been shown to induce anti-anti-idiotypic proliferative T lymphocytes of the helper and suppressor type, as well as cytotoxic lymphocytes. The immunomodulatory activities of Ab2 have been demonstrated both in animals and in patients. The demonstration of tumor growth inhibition by anti-idiotypes in preclinical and phase I clinical studies emphasizes that randomized control trials should be performed to demonstrate clinical efficacy of Ab2 vaccines.

Animals↗
PubMed1996

Animal model for the pathogenesis of reactive amyloidosis.

The pathogenesis of amyloidosis is not well understood. Here, Zafer Ali-Khan, Weihua Li and Sic L. Chan present a metazoan parasite mouse model of reactive amyloidosis, review the relationship between chronic inflammation and multiorgan AA amyloidosis and postulate how ubiquitin might function in the processing of serum amyloid A and in AA amyloid formation in the endosomes-lysosomes of activated murine reticuloendothetial cells.

Journal Article↗
PubMed1996

Temporal correlation of blood scattering signals in vivo from radiofrequency intravascular ultrasound.

One limitation encountered using high frequency intravascular ultrasound (IVUS) is the echogenicity of blood, which increases dramatically at frequencies of 20-40 MHz. Because of the higher velocity of moving blood particles, the echo pattern of flowing blood shows more variations in time than that of the wall. To investigate the time-varying characteristics of the blood scattering measurements were performed on the radiofrequency (RF) data collected in vivo from five pig experiments. After positioning the echo catheter inside the iliac artery, an M-mode sequence of 30 RF traces was acquired at a high pulse repetition rate (5 kHz). The RF correlation time was measured on the regions of blood and the arterial wall. Two processing techniques, temporal averaging and correlation, were tested for suppression of the blood echo intensity. The correlation time Tc measured in the blood region was approximately 1 ms, which was shorter than that measured in the wall region (Tc >> 6 ms). The correlation values calculated in a small window showed a large variation in the blood region while the wall region produced a constant high output. After processing eight consecutive RF traces (delta T = 200 microseconds), the temporal averaging method results in a 50% intensity reduction in the blood region. Using the correlation output as a weighting function, the blood echo intensity can be further reduced to only 10% of its original value. Application of the RF correlation processing to a cross-sectional image data demonstrates the feasibility of this technique to remove most of the blood echoes and enhance the image contrast of the luminal interface.

Animals↗