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Biomedical subjects

L Wei

Publications and source records attributed to L Wei.

At least 19 recordsLinked to original sources
PubMed1995

Effects of okadaic acid and vanadate on TPA-induced monocytic differentiation in human promyelocytic leukemia cell line HL-60.

Treatment of HL-60 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) (1-5 nM) induced inhibition of cell growth and the appearance of an adherent monocyte-like cell type in a dose- and time-dependent manner. The extent of TPA-induced monocytic differentiation was found to be markedly reduced by okadaic acid (OA) (35 nM). OA had to be present for the early 12 h during treatment with TPA to reduce the induction of monocytic differentiation. The majority of cells (80%) were non-adherent but morphologically resembled mature myelocytes or granulocytes after treatment with TPA (5 nM) in the presence of OA (35 nM). Vanadate (VD), on the other hand, enhanced the extent of monocytic differentiation induced by low-dose of TPA (1 nM). These results indicated that dephosphorylation by tyrosine protein phosphatase and serine-threonine protein phosphatase may play an important role in the induction of monocytic and granulocytic differentiation.

Cell Differentiation↗
PubMed1995

Expression, characterization, and crystallization of the catalytic core of the human insulin receptor protein-tyrosine kinase domain.

The deduced primary sequence of the cytoplasmic protein-tyrosine kinase domain of the insulin receptor contains a conserved kinase homology region (receptor residues 1002-1257) flanked by a juxtamembrane region and a C-terminal tail. A soluble 48-kDa derivative (residues 959-1355) containing these regions but lacking the first six residues of the juxtamembrane region had earlier been synthesized in Sf9 cells using a baculovirus expression system. The catalytic core of the kinase domain was studied first by proteolytic analysis of the 48-kDa kinase and then by expressing a series of truncated kinase domains in transiently transfected COS cells. Based on these studies, two core kinases of 34 (residues 985-1283) and 35 (residues 978-1283) kDa, respectively, were overexpressed in Sf9 cells. Biochemical characterization of the 35-kDa kinase revealed that the core kinase conserved the major functional properties of the native receptor kinase domain. Activity of the 35-kDa kinase toward a synthetic peptide increased more than 200-fold upon autophosphorylation, which occurred exclusively at Tyr-1158, Tyr-1162, and Tyr-1163; the largest increase was observed between bis- and trisphosphorylation of the kinase. The activated 35- and 48-kDa kinases were similar with respect to specific activity and ATP and Mg2+ requirements for peptide phosphorylation. Moreover, autophosphorylation appeared to initiate predominantly at Tyr-1162, immediately followed by phosphorylation at Tyr-1158 and then at Tyr-1163. The rate of autophosphorylation was dependent on enzyme concentration, consistent with a trans-phosphorylation mechanism. Finally, the 35-kDa kinase was crystallized, making possible elucidation of its three-dimensional structure by x-ray crystallography.

Amino Acid Sequence↗
PubMed1995

Small peptide mimics of nerve growth factor bind TrkA receptors and affect biological responses.

Small monomeric cyclic analogs that mimic the beta-turn regions of nerve growth factor (NGF) were designed and synthesized. Potent competitive antagonists were derived from the NGF beta-turn C-D, which inhibited [125I] NGF binding to TrkA receptors and specifically inhibited optimal NGF-mediated neurite outgrowth in PC12 cells. The cyclic beta-turn A'-A" analog also inhibited NGF binding to TrkA receptors but with lower potency. These data indicate that beta-turns C-D and A'-A" are critical for TrkA binding and may confer neurotrophin receptor specificity. Furthermore, structural requirements for binding are absolute, because unconstrained analogs derived from the same regions had no effect. Compounds that mimic NGF will be useful in deciphering the interactions of NGF and its receptors and in rational drug design.

Amino Acid Sequence↗
PubMed1995

Phenotypic features of breast cancer cells overexpressing ornithine-decarboxylase.

Polyamines (PA) have been shown to be critical mediators of estradiol-induced breast cancer cell proliferation. This finding suggests that constitutive activation of the PA pathway may promote tumor progression, possibly leading to hormone independence. To test this hypothesis, we transfected hormone-responsive MCF-7 breast cancer cells with a complementary DNA coding for ornithine-decarboxylase (ODC), the first rate-limiting enzyme in PA biosynthesis. Marked ODC overexpression observed in stably transfected clones was associated with a selective increase in cellular putrescine content, while spermidine and spermine levels were not altered. ODC-overexpressing MCF-7 cells were resistant to the antiproliferative effects of low but not high concentrations of the enzyme inhibitor, alpha-difluoromethylornithine. In agreement with our hypothesis, sensitivity to the growth-promoting action of estradiol was reduced by approximately one third (P < 0.001) in ODC-overexpressing MCF-7 cells compared with vector-only transfected clones. Basal growth under anchorage-dependent conditions was only marginally increased by ODC overexpression (P = 0.048), while clonogenicity in soft agar was actually reduced. These data suggest that activation of PA biosynthesis may contribute in part to the acquisition of estrogen independence by breast cancer cells. Since only putrescine content was increased as a result of ODC overexpression, these data may underestimate the overall influence of the PA pathway on breast cancer phenotype.

Breast Neoplasms↗
PubMed1995

Polyamine profiles and growth properties of ornithine decarboxylase overexpressing MCF-7 breast cancer cells in culture.

To determine the direct influence of the polyamine (PA) pathway on breast cancer phenotype, we employed a transfection approach to induce overexpression of the PA biosynthetic enzyme ornithine decarboxylase (ODC) in the hormone-responsive MCF-7 breast cancer cell line. Using a modified calcium phosphate method and an ODC cDNA coding for a truncated and more stable enzyme, we were able to achieve a moderate to marked degree of ODC overexpression (up to 150-fold) in a transient transfection system. ODC-overexpressing MCF-7 cells exhibited a selective increase in cellular putrescine content, while the levels of spermidine and spermine remained unaffected. Under defined culture conditions, overexpression of ODC resulted in a consistent but modest increase in [3H]thymidine incorporation into DNA which was similar in the presence and absence of 17-beta-estradiol, TGF-alpha, and IGF-I. In the presence of serum, the effect of ODC overexpression on basal [3H]-thymidine incorporation into DNA was inconsistent, possibly as a result of subtle differences in culture conditions. Overall, our results support the hypothesis that activation of the PA biosynthetic pathway may confer a growth advantage to breast cancer cells.

Breast Neoplasms↗
PubMed1995

7,12-dimethylbenz[a]anthracene induces oxidative DNA modification in vivo.

Initiation and promotion are major stages in the multistage carcinogenesis process. Formation of initiating carcinogen-DNA base adducts leads to heritable genetic changes, but the tumor-promoting events induced by complete carcinogens have not, as yet, been elucidated. Oxidant production and oxidative DNA damage induced by phorbol esters (i.e., 12-O-tetradecanoyl-phorbol-13-acetate) are associated with tumor promotion, while antioxidants and inhibitors of oxidative DNA damage suppress promotion and carcinogenesis. Our goal was to establish whether a carcinogen that requires oxidative metabolism for its activity can also induce oxidant production and DNA base oxidation. We found that topical treatment of SENCAR mice with 7,12-dimethylbenz[a]anthracene, which induces tumors in 40-50% of the mice, also causes hydrogen peroxide production and formation of oxidized bases (i.e., 8-hydroxyl-2'-deoxyguanosine and 5-hydroxymethyl-2'-deoxyuridine) in epidermal DNA. The levels of oxidized bases were of comparable magnitude to those mediated by the potent tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. The oxidized bases persisted over several weeks in epidermal DNA. These oxidative events appear to be temporally associated with inflammatory responses that include edema and polymorphonuclear leukocyte infiltration, which remained elevated over longer periods of time and at higher levels than those induced by phorbol ester. Because these processes are usually associated with tumor promotion, our results support the conjecture that oxidative events may be involved in what is operationally referred to as the tumor promotion process by 7,12-dimethylbenz[a]anthracene.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1995

Nicotine raises the influx of permeable solutes across the rat blood-brain barrier with little or no capillary recruitment.

Nicotine (1.75 mg/kg s.c.) was administered to rats to raise local CBF (lCBF) in various parts of the brain, test the capillary recruitment hypothesis, and determine the effects of this increase in lCBF on local solute uptake by brain. lCBF as well as the local influx rate constants (K1) and permeability-surface area (PS) products of [14C]antipyrine and [14C]-3-O-methyl-D-glucose (3OMG) were estimated by quantitative autoradiography in 44 brain areas. For this testing, the finding of significantly increased PS products supports the capillary recruitment hypothesis. In 17 of 44 areas, nicotine treatment increased lCBF by 30-150%, K1 of antipyrine by 7-40%, K1 of 3OMG by 5-27%, PS product of antipyrine by 0.20% (mean 7%), and PS product of 3OMG by 0-23% (mean 8%). Nicotine had no effect on blood flow or influx in the remaining 27 areas. The increases in lCBF and K1 of antipyrine were significant, whereas those in K1 of 3OMG and in PS for both antipyrine and 3OMG were not statistically significant. The lack of significant changes in PS products implies that in brain areas where nicotine increased blood flow: (a) essentially no additional capillaries were recruited and (b) blood flow within brain capillary beds rises by elevating linear velocity. The K1 results indicate that the flow increase generated by nicotine will greatly raise the influx and washout rates of highly permeable materials, modestly elevate those of moderately permeable substances, and negligibly change those of solutes with extraction fractions of < 0.2, thereby preserving the barrier function of the blood-brain barrier.

3-O-Methylglucose↗
PubMed1995

Ministrokes in rat barrel cortex.

BACKGROUND AND PURPOSE: Many stroke models in rats are based on occlusion of the middle cerebral artery, which supplies a significant portion of multifunctional cortical and deep structures in the cerebral hemisphere. The purpose of this study was to develop a model for direct observation in real time of blood flow in and around focal ischemic regions of the cortex of known function. METHODS: Cranial windows were placed over the parietal cortex of adult Wistar and Sprague-Dawley rats anesthetized with ketamine and xylazine. Whisker barrel cortex responding to stimulation of the contralateral whiskers was identified by an intrinsic optical signal. Transits of vital dyes were recorded by videomicroscopy before and after ligation of three to six branches and major collaterals of the middle cerebral artery through the dura. Infarcts were demonstrated with triphenyl-tetrazolium chloride staining; their relation to barrel cortex was determined by Nissl and cytochrome oxidase histology. RESULTS: Reduced blood flow in small ischemic regions was outlined by patient blue violet in the surrounding nonischemic area; arteriovenous latencies increased more than four times in ischemic cortex. Infarcts,typically 3 mm or less, were seen at 24 hours in 8 of 16 Wistar and 9 of 9 Sprague-Dawley rats. The ministrokes were confirmed by histology to be in the somatosensory cortex. CONCLUSIONS: This model of local ischemia, produced deliberately in the functionally defined barrel cortex in rats, leads to ministrokes. Changes can be followed by videomicroscopy as they develop, and processes of recovery can potentially be monitored. Infarcts are confirmed by histology for their location and extent in the somatic representation.

Animals↗
PubMed1995

[Chemical constituents of Astragalus chinensis L].

Three compounds have been isolated from the seeds of Astragalus chinensis. Their structures were identified on the basis of spectral data (UV, 13CNMR, 1HNMR, IR and MS) as octacosane, daucosterol and kaempferol.

Alkanes↗
PubMed1995

Characterizing oriented protein structural sites using biochemical properties.

A protein site is a region of a three-dimensional protein structure with a distinguishing functional or structural role. Certain sites recur in different protein structures (for example catalytic sites, calcium binding sites, and some types of turns), but maintain critical shared features. To facilitate the analysis of such protein sites, we have developed a computer system for analyzing the spatial distributions of biochemical properties around a site. The system takes a set of similar sites and a set of control nonsites, and finds differences between them. Specifically, it compares distributions of the properties surrounding the sites with those surrounding the nonsites, and reports statistically significant differences. In this paper, we use our method to analyze the features in the active site of the serine protease enzymes. We compare the use of radial distributions (shells) with 3-D grids (blocks) in the analysis of the active site. We demonstrate three different strategies for focusing attention on significant findings, based on properties of interest, spatial volumes of interest, and on the level of statistical significance. Finally, we show that the program automatically identifies conserved sequential, secondary structural and biophysical features of the serine protease active site, using noncatalytic histidine residues as a control environment.

Algorithms↗
PubMed1995

[Mutagenicity and anti-mutagenicity assay of airborne suspended particles in Shijiazhuang city].

Samples of airborne suspended particles collected from five air monitoring sites in Shijiazhuang City in 1993 were analyzed with rapid synchronous mutagenicity and anti-mutagenicity tests. It revealed airborne suspended particles collected had direct and indirect mutagenicity, but no anti-mutagenicity, and there was seasonal difference in their mutagenicity, which showed a decreasing trend with an order of winter, spring, summer and autumn. Mutagenicity related positively to air concentrations of total suspended particles and sulfur dioxide, inversely to those of ozone, and did not related to those of nitrogen oxide and carbon monoxide.

Air Pollutants↗
PubMed1995

[Alkaloid constituents in the seeds of Sophora viciifolia Hance].

Six alkaloids were isolated from the mature seeds of Sophora viciifolia for the first time. On the basis of physicochemical and spectroscopic analysis, their structures have been identified as oxymatrine, oxysophocarpine, matrine, sophocarpine, sophoramine and sophoridine.

Alkaloids↗
PubMed1995

[Fecundify after treatment of tubal pregnancy].

UNLABELLED: This study is a follow-up analysis of 103 patients who desired to preserve their fertile ability after treatment of tubal pregnancy. Among the 103 cases, 58 were treated by unilateral salpingectomy, 15 by salpingostomy and 30 by drug conservative therapy. RESULTS: 67 cases had intrauterine pregnancy and 9 cases repeated ectopic pregnancy. The intrauterine pregnancy rate of the surgical group (71.2%) was higher than that of the nonsurgical group (50.0%). And the pregnancy rate of salpingostomy group (86.7%) was higher than that of salpingectomy group (67.2%). No repeated ectopic pregnancy occurred in the salpingostomy group. After three months of treatment, 45 cases were randomly sampled for tubal patency test. Bilateral tubal patency rate in salpingostomy group was 93.3% and in drug treatment group was 20.0%. These results indicated that tubal patency is an essential factor for normal pregnancy. Prevention of post-operative adhesion and treatment of pelvic inflammatory disease are important for increasing intrauterine pregnancy rate and decreasing repeated ectopic pregnancy rate.

Fallopian Tube Patency Tests↗
PubMed1994

Structural determinants of substrate selection by the human insulin-receptor protein-tyrosine kinase.

Using NMR spectroscopy to visualise tyrosine phosphorylation kinetics in real time, we have investigated the sequence-dependent determinants of the selectivity of the human insulin receptor protein-tyrosine kinase for different tyrosine residues. The peptides used encompass the multiple-tyrosine-containing autophosphorylation site sequences from the insulin receptor kinase core domain (Tyr1158, Tyr1162 and Tyr1163) and from its specific C-terminal tail domain (Tyr1328 and Tyr1334). Comparison of the phosphorylation kinetics with those found for the tyrosine residues on a peptide comprising the regulatory tyrosine phosphorylation site of cdc2 points to the role of the primary sequence context of the phosphate acceptor. The particularly deleterious influence of a basic residue immediately C-terminal to the tyrosine is discussed in relation to the autophosphorylation properties of the regulatory loop regions of the insulin and epidermal growth factor receptor kinases. The data further suggest that receptor tyrosine kinase active sites and their substrate targets act in concert to ensure that specific downstream effects are activated.

Amino Acid Sequence↗