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Biomedical subjects

L Zhou

Publications and source records attributed to L Zhou.

At least 91 records · Page 5Linked to original sources
PubMed2001

Structure of human DNMT2, an enigmatic DNA methyltransferase homolog that displays denaturant-resistant binding to DNA.

DNMT2 is a human protein that displays strong sequence similarities to DNA (cytosine-5)-methyltransferases (m(5)C MTases) of both prokaryotes and eukaryotes. DNMT2 contains all 10 sequence motifs that are conserved among m(5)C MTases, including the consensus S:-adenosyl-L-methionine-binding motifs and the active site ProCys dipeptide. DNMT2 has close homologs in plants, insects and Schizosaccharomyces pombe, but no related sequence can be found in the genomes of Saccharomyces cerevisiae or Caenorhabditis elegans. The crystal structure of a deletion mutant of DNMT2 complexed with S-adenosyl-L-homocysteine (AdoHcy) has been determined at 1.8 A resolution. The structure of the large domain that contains the sequence motifs involved in catalysis is remarkably similar to that of M.HHAI, a confirmed bacterial m(5)C MTase, and the smaller target recognition domains of DNMT2 and M.HHAI are also closely related in overall structure. The small domain of DNMT2 contains three short helices that are not present in M.HHAI. DNMT2 binds AdoHcy in the same conformation as confirmed m(5)C MTases and, while DNMT2 shares all sequence and structural features with m(5)C MTases, it has failed to demonstrate detectable transmethylase activity. We show here that homologs of DNMT2, which are present in some organisms that are not known to methylate their genomes, contain a specific target-recognizing sequence motif including an invariant CysPheThr tripeptide. DNMT2 binds DNA to form a denaturant-resistant complex in vitro. While the biological function of DNMT2 is not yet known, the strong binding to DNA suggests that DNMT2 may mark specific sequences in the genome by binding to DNA through the specific target-recognizing motif.

Adenosine Triphosphate↗
PubMed2001

Treatment of patients with ovarian carcinoma with pegylated liposomal doxorubicin: analysis of toxicities and predictors of outcome.

BACKGROUND: Pegylated liposomal doxorubicin is a new formulation with activity against epithelial ovarian carcinoma (EOC). The authors sought to determine patient characteristics that may predict for response to this treatment and favorable time to failure as well as survival. METHODS: Eight patients in a Phase I study and 44 patients in two consecutive Phase II studies who were treated with pegylated liposomal doxorubicin (40-60 mg/m2 every 3 weeks for the first two cycles and 40 mg/m2 every 4 weeks thereafter) after failing initial platinum-based chemotherapies for ovarian carcinoma were analyzed. Associations were sought for response, time to failure (TTF), and survival after the treatment and various pretreatment characteristics. RESULTS: Treatment with pegylated liposomal doxorubicin yielded 23% objective responses in measurable disease and 31% overall responses, including serum CA 125-defined responses. The median TTF was 5.2 months (95% confidence interval, 4.1-6.9 months) in all patients, and the median response duration in all responders was 13.2 months (95% confidence interval, 11.9-18.5 months). The overall median survival was 15 months (95% confidence interval, 11-40 months). The main predictive factors were tumor size and baseline hemoglobin level for TTF, and these plus Karnofsky performance status were the main predictive factors for survival. CONCLUSIONS: Pegylated liposomal doxorubicin is an effective drug when it is given as secondary therapy to patients with EOC. Lack of bulky disease is the major predictor for a favorable response, TTF, and survival. The role of this treatment in combination with other effective drugs should be explored in both previously treated and untreated patients with ovarian carcinoma.

Adult↗
PubMed2001

Genetic variation analysis in parkinson disease patients with and without hallucinations: case-control study.

BACKGROUND: Visual hallucinations in Parkinson disease (PD) occur in approximately one third of patients treated long-term with dopaminergic medications. In Alzheimer disease, hallucinations and psychosis have been linked to increased representations of B2/B2 homozyogotes for the dopamine receptor gene DRD1 and 1/1 or 2/2 homozygotes for DRD3. In addition, a previous study of PD patients with and without hallucinations did not show differences in D2 and D3 polymorphisms, although careful case-control matching was not performed. Another study linked the apolipoprotein E4 (APOE4) allele to hallucinations in PD. OBJECTIVE: To determine whether the frequency of dopamine receptor genetic variants and APOE alleles in patients with PD with and without chronic visual hallucinations resembles the pattern previously documented in patients with Alzheimer disease. METHODS: We conducted a case-control study of 44 patients with PD and chronic hallucinations and 44 patients with PD who had never hallucinated. Cases and controls were matched for current age and medications. DNA was isolated from blood samples and assayed for DRD1, DRD2, DRD3, DRD4, and APOE polymorphisms. Receptor polymorphisms were genotyped by polymerase chain reaction. Genotypes in hallucinators and nonhallucinators were compared using Mantel-Haenszel tests stratified by pair, and allele frequencies were compared using Wilcoxon signed rank tests within pairs. RESULTS: Neither D1 receptor genotypes (P =.37) nor allele frequencies (P =.38) differed, and there was no predominance of B2/B2 homozygotes in the hallucinators. For D3, there was a higher frequency of allele 2 (P =.047), but there was no significant difference between frequencies of homozygotes vs heterozygotes (P =.39) as reported in Alzheimer disease. D4 receptor distribution of long and short alleles did not differ between the 2 patient groups, and there were too few C alleles (3 of 86) to compare D2 allele genotypes or frequencies. For APOE, 12 cases and 12 controls carried E4 alleles (P>.99). CONCLUSIONS: With careful case-control matching, visual hallucinations in PD are not associated with the pattern seen for patients with Alzheimer disease and visual hallucinations. Furthermore, there was no association between hallucinations and APOE. Similar methods using larger sample sizes might be adapted to test whether specific dopaminergic receptor genetic variants are associated with visual hallucinations in PD. Based on our data, the DRD3 allele 2 may merit further study.

Aged↗
PubMed2001

A murine dopamine neuron-specific cDNA library and microarray: increased COX1 expression during methamphetamine neurotoxicity.

Due to brain tissue heterogeneity, the molecular genetic profile of any neurotransmitter-specific neuronal subtype is unknown. The purpose of this study was to purify a population of dopamine neurons, construct a cDNA library, and generate an initial gene expression profile and a microarray representative of dopamine neuron transcripts. Ventral mesencephalic dopamine neurons were purified by fluorescent-activated cell sorting from embryonic day 13.5 transgenic mice harboring a 4.5-kb rat tyrosine hydroxylase promoter-lacZ fusion. Nine-hundred sixty dopamine neuron cDNA clones were sequenced and arrayed for use in studies of gene expression changes during methamphetamine neurotoxicity. A neurotoxic dose of methamphetamine produced a greater than twofold up-regulation of the mitochondrial cytochrome c oxidase polypeptide I transcript from adult mouse substantia nigra at 12 h posttreatment. This is the first work to describe a gene expression profile for a neuronal subtype and to identify gene expression changes during methamphetamine neurotoxicity.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2001

Murine inter-strain polymorphisms alter gene targeting frequencies at the mu opioid receptor locus in embryonic stem cells.

Chromosomal regions near the mu opioid receptor gene are implicated in morphine preference by quantitative trait loci studies. Differences in expression of the mu opioid receptor are expected to contribute to differences in inter-individual (humans) or strain-specific (mice) responses to painful stimuli, opiate drugs, and addictive behaviors. The search for relevant genetic elements is hindered by a lack of inter-strain (or inter-individual) genomic sequence information. This work describes 9.3 kb of DNA sequence surrounding exons 2 and 3 of the murine mu opioid receptor gene from both 129/Sv and C57BL/6 strains. While the exons are perfectly conserved, intronic sequences demonstrate approximately a 2.5% divergence between the strains. Polymorphism within these intronic regions may effect either primary transcript stability or C-terminal splicing. Homologous recombination frequencies of targeting vectors harboring mu opioid receptor gene sequences have also been compared in embryonic stem cells derived from these strains. Non-isogenic targeting reduces homologous recombination in both 129/Sv and C57BL/6 embryonic stem cells by greater than 15-fold. These findings are the first to examine C57BL/6 embryonic stem cells for non-isogenic targeting frequencies and to define polymorphisms that exist between these mouse strains which might contribute to opioid behaviors.

Alleles↗
PubMed2001

Over-expression of beta-1,4-galactosyltransferase I, II, and V in human astrocytoma.

PURPOSE: beta-1,4-Galactosyltransferase (beta-1,4-GalT) I, II, and V are the enzymes responsible for the biosynthesis of N-acetyllactosamine on N-glycans by transferring UDP-galactose to the terminal N-acetylglucosamine (N-GlcNAc) residues with the formation of a beta-1,4-linkage. Neoplasms undergo various changes in the carbohydrate of their glycoconjugates, indicating the possible changes in glycosyltransferases themselves. METHOD: Therefore, we compared the expression of beta-1,4-GalTs between astrocytoma and normal brain tissues. RESULTS: Our reverse-transcription polymerase chain reaction (RT-PCR) results showed that beta-1,4-GalT I transcript was absent in normal adult brain but detectable in grade II, III, and IV astrocytomas; the level of beta-1,4-GalT II transcript was increased in grade II, III, and IV astrocytomas while only a trace amount was found in normal brain; beta-1,4-GalT V transcript existed in normal brain and increased in the process of astrocytoma progress, with the highest level in grade IV astrocytoma. By Ricinus communis agglutinin-1 (RCA-1) lectin blot assay, we also found the more extensive galactosylated bands in astrocytomas compared with normal brain. A major 61kD protein was galactosylated in astrocytoma but not in normal brain tissues. CONCLUSION: These results indicate that the increase of galactosylation in astrocytomas may be caused by the alterations of gene expression of beta-1,4-GalT I, II, and V and that the malignant degree of astrocytoma is correlated with the expression of beta-1,4-GalT V.

Astrocytoma↗
PubMed2001

Emergency contraception with Multiload Cu-375 SL IUD: a multicenter clinical trial.

The objectives of the present study were to evaluate the efficacy and side effects and the benefits and limitations of inserting Multiload intrauterine device (IUD) for emergency contraception. A total of 1013 women requesting emergency contraception was recruited, among whom 843 were parous women and 170 nulliparous women. Multiload Cu-375 SL IUD was inserted within 120 h after unprotected intercourse. A urine test for pregnancy was performed before IUD insertion to rule out pregnancy. Participants were followed-up until 1 week after the expected day of the next menstruation. Pregnancy test or ultrasound scanning were performed if menstruation did not return. Efficacy of preventing unplanned pregnancy was calculated. Efficacy and side effects were compared between the parous and nulliparous groups. The results showed that there were two pregnancies, one in each group. The pregnancy rate was 0.2 per 100 women. The efficacy rate of preventing unwanted pregnancy in the parous group was 98.1% and in the nulliparous group 92.4%. The difference was not significant. Removal of IUD because of pain and bleeding was 2.5% in parous women, but was more in the nulliparous group (10.6%). After the return of menstruation, 95.7% of parous women and 80% of nulliparous women maintained the IUD for contraception. There were two complete expulsions and three partial expulsions of the IUD, but there was no significant changes in menstruation and bleeding pattern, nor was infection or trauma observed. It was concluded that IUD insertion is a safe and effective method for emergency contraception for both parous and nulliparous women. One of the advantages of using an IUD is its long-term contraceptive effect, if the women prefer to continue its use.

Contraceptives, Postcoital↗
PubMed2001

Raloxifene effect on frequency of surgery for pelvic floor relaxation.

OBJECTIVE: To assess the effects of raloxifene therapy on the frequency of surgery for pelvic floor relaxation in postmenopausal women. METHODS: This analysis used safety data through 3 years of treatment from three double-masked, placebo-controlled, randomized trials of raloxifene, which included 6926 postmenopausal women with uteri at entry. Studies 1 and 2 enrolled 969 nonosteoporotic, postmenopausal women who were assigned to 30, 60, or 150 mg per day raloxifene or placebo. Study 3 enrolled 5957 osteoporotic, postmenopausal women randomized to raloxifene 60 or 120 mg per day or placebo. Indications for any reported pelvic operations were identified, including procedures performed for pelvic organ prolapse or urinary incontinence. RESULTS: A total of 34 (1.51%) women in the placebo group and 35 (0.75%) raloxifene-treated women underwent surgical procedures for pelvic floor relaxation. The odds ratio (and 95% confidence interval) for pelvic floor repair in women assigned to raloxifene was 0.50 (0.31, 0.81). Thus, raloxifene therapy was associated with a significantly reduced risk for pelvic floor surgery (P <.005). CONCLUSION: Raloxifene does not increase pelvic floor relaxation. An apparent protective effect on pelvic floor function warrants further investigation.

Aged↗
PubMed2001

Growth inhibition of primary keratinocytes following transduction with a novel TGFbeta-1 containing retrovirus.

Growth and migration of keratinocytes are known to be affected by the addition of exogenous cytokines, such as TGFbeta-1, to culture media. We have developed a retroviral vector, LNTbeta-1, that confers constitutive expression of human TGFbeta-1 to transduced cells. Keratinocytes were exposed to retroviral particles generated in serum-free media, and infected cells were selected for with Geneticin. Transduced keratinocytes remained in culture as single cells instead of a normally grouped growth pattern. While these transduced keratinocytes survived in culture for several weeks, they did not proliferate and seemed arrested in their growth. Keratinocytes transduced with retrovirus not containing the TGFbeta-1 gene appeared normal in their growth pattern. These findings indicate that high-level endogenous expression of TGFbeta-1 in keratinocytes can at least inhibit, and possibly arrest, growth.

Cell Division↗
PubMed2001

Carbon and nitrogen sensing and signaling in plants: emerging 'matrix effects'.

Plants, like other organisms, have developed mechanisms that allow them to sense and respond to changes in levels of carbon and nitrogen metabolites. These mechanisms, in turn, regulate the expression of genes and the activities of proteins involved in C and N transport and metabolism, allowing plants to optimize the use of energy resources. Recent studies, which have involved molecular-genetic, genomic, and cell biological approaches, have begun to uncover the signals and components of C:N sensing and signaling mechanisms in plants. For sugar sensing, analysis of Arabidopsis mutants has revealed intersections with hormone and nitrogen signaling. For nitrogen sensing/signaling, recent progress has identified transcriptional and posttranslational mechanisms of regulation. In all, a complex picture is emerging in which C:N signaling systems are subject to a 'matrix effect' in which downstream responses are dependent upon cell-type, developmental, metabolic, and/or environmental conditions.

Anion Transport Proteins↗
PubMed2001

Determination of total N-nitroso compounds and their precursors in frankfurters, fresh meat, dried salted fish, sauces, tobacco, and tobacco smoke particulates.

Total N-nitroso compounds (NOC) and NOC precursors (NOCP) were determined in extracts of food and tobacco products. Following Walters' method, NOC were decomposed to NO with refluxing HBr/HCl/HOAc/EtOAc and NO was measured by chemiluminescence. NOC were determined after sulfamic acid treatment to destroy nitrite, and NOCP were determined after treatment with 110 mM nitrite and then sulfamic acid. Analysis without HBr gave results < or =20% of those with HBr. This NOC method was efficient for nitrosamines but not nitrosoureas. The standard nitrosation for determining NOCP gave high yields for readily nitrosated amines, including 1-deoxy-1-fructosylvaline, but not for simple amines, dipeptides, and alkylureas. Mean NOC and NOCP results were (respectively, in micromol/kg of product) 5.5 and 2700 for frankfurters, 0.5 and 660 for fresh meat, 5.8 and 5800 for salted, dried fish, and 660 and 2900 for chewing tobacco (all for aqueous extracts) and 220 and 20000 nmol/cigarette for MeCN extracts of cigarette smoke filter pads.

Animals↗
PubMed2001

Intramuscular electroporation delivery of IFN-alpha gene therapy for inhibition of tumor growth located at a distant site.

Although electroporation has been shown in recent years to be a powerful method for delivering genes to muscle, no gene therapy via electro-injection has been studied for the treatment of tumors. In an immunocompetent tumor-bearing murine model, we have found that delivery of a low dose of reporter gene DNA (10 microg) to muscle via electroporation under specific pulse conditions (two 25-ms pulses of 375 V/cm) increased the level of gene expression by two logs of magnitude. Moreover, administration of 10 microg of interferon (IFN)-alpha DNA plasmid using these parameters once a week for 3 weeks increased the survival time and reduced squamous cell carcinoma (SCC) growth at a distant site in the C3H/HeJ-immunocompetent mouse. IFN-alpha gene therapy delivered to muscle using electroporation demonstrated statistically significant (P < 0.05) therapeutic efficacy for treating SCC located at a distant site, compared with interleukin (IL)-2 or endostatin gene, also delivered by electro-injection. The increased therapeutic efficacy was associated with a high level and extended duration of IFN-alpha expression in muscle and serum. We also discovered that the high level of IFN-alpha expression correlated with increased expression levels of the antiangiogenic genes IP-10 and Mig in local tumor tissue, which may have led to the reduction of blood vessels observed at the local tumor site. Delivery of increasing doses (10-100 microg) of IFN-alpha plasmid DNA by injection alone did not increase antitumor activity, whereas electroporation delivery of increasing doses (10-40 microg) of IFN-alpha plasmid DNA did increase the survival time. Our data clearly demonstrate the potential utility of electroporation for delivery of gene therapy to muscle for the treatment of residual or disseminated tumors.

Animals↗
PubMed2001

Synchronization of separation and determination based on multichannel mode-filtered light detection with capillary electrophoresis.

A novel method for the synchronization of separation and determination is described, in which a mode-filtered light detector is used as an online detector in capillary electrophoresis. An instrument is described which has been developed for this purpose. The round capillary used in conventional capillary electrophoresis is replaced by an annular column, which is constructed from a naked optical fibre inserted into a fused-silica capillary. In fact, the annular electrophoresis column itself forms part of the mode-filtered light sensor. Along the side of the annular column are several detection channels for gathering and transmitting the mode-filtered light to a charge-coupled device (CCD). Every channel provides information on the sample from the point at which it is located. Using capillary isotachophoresis incorporating the annular column, the analytes in a sample containing alanine (10.0 mM) and glycine (9.7 mM) were simultaneously separated and determined using multichannel mode-filtered light detection with a detection limit of 1.5 mM.

Journal Article↗
PubMed2001

TFIIAalpha/beta-like factor is encoded by a germ cell-specific gene whose expression is up-regulated with other general transcription factors during spermatogenesis in the mouse.

TFIIAalpha/beta-like factor (ALF) is a testis-specific counterpart of the large subunit of human general transcription factor TFIIA. Northern analysis shows that ALF mRNA first appears in mouse testis at Postnatal Day 14. Similarly, expression of the general transcription factors TBP, TRF2, TFIIAalpha/beta, TFIIAgamma, and TFIIIB(90) is also increased beginning at Postnatal Day 14, suggesting that there is a coordinated induction of many general transcription factors during male germ cell differentiation. Analysis of male germ cells separated by Staput sedimentation shows that ALF is present in pachytene spermatocytes and haploid spermatids. In addition, in situ hybridization experiments with adult mouse testis shows that ALF is present in haploid spermatids. Searches of the human genome sequence database using the basic local alignment search tool reveal that the ALF and TFIIAalpha/beta(GTF2A1) genes are both composed of nine exons, whereas the TFIIAgamma (GTF2A2) gene is composed of five exons. Furthermore, nucleotide and amino acid comparisons among human and mouse ALF, TFIIAalpha/beta, and TFIIAgamma cDNA sequences show that ALF has diverged more rapidly than either TFIIAalpha/beta or TFIIAgamma. Finally, the ALF and SBLF (Stoned B-Like Factor) sequences present in the chimeric SALF cDNA are both present on human chromosome 2, and an analysis of the corresponding genes suggests a model for the formation of SALF.

Amino Acid Sequence↗
PubMed2001

Dichotomy of AML1-ETO functions: growth arrest versus block of differentiation.

The fusion gene AML1-ETO is the product of t(8;21)(q22;q22), one of the most common chromosomal translocations associated with acute myeloid leukemia. To investigate the impact of AML1-ETO on hematopoiesis, tetracycline-inducible AML1-ETO-expressing cell lines were generated using myeloid cells. AML1-ETO is tightly and strongly induced upon tetracycline withdrawal. The proliferation of AML1-ETO(+) cells was markedly reduced, and most of the cells eventually underwent apoptosis. RNase protection assays revealed that the amount of Bcl-2 mRNA was decreased after AML1-ETO induction. Enforced expression of Bcl-2 was able to significantly delay, but not completely overcome, AML1-ETO-induced apoptosis. Prior to the onset of apoptosis, we also studied the ability of AML1-ETO to modulate differentiation. AML1-ETO expression altered granulocytic differentiation of U937T-A/E cells. More significantly, this change of differentiation was associated with the down-regulation of CCAAT/enhancer binding protein alpha (C/EBPalpha), a key regulator of granulocytic differentiation. These observations suggest a dichotomy in the functions of AML1-ETO: (i) reduction of granulocytic differentiation correlated with decreased expression of C/EBPalpha and (ii) growth arrest leading to apoptosis with decreased expression of CDK4, c-myc, and Bcl-2. We predict that the preleukemic AML1-ETO(+) cells must overcome AML1-ETO-induced growth arrest and apoptosis prior to fulfilling their leukemogenic potential.

Apoptosis↗
PubMed2001

Computer model for action potential propagation through branch point in myelinated nerves.

A mathematical model is developed for simulation of action potential propagation through a single branch point of a myelinated nerve fiber with a parent branch bifurcating into two identical daughter branches. This model is based on a previously published multi-layer compartmental model for single unbranched myelinated nerve fibers. Essential modifications were made to couple both daughter branches to the parent branch. There are two major features in this model. First, the model could incorporate detailed geometrical parameters for the myelin sheath and the axon, accomplished by dividing both structures into many segments. Second, each segment has two layers, the myelin sheath and the axonal membrane, allowing voltages of intra-axonal space and periaxonal space to be calculated separately. In this model, K ion concentration in the periaxonal space is dynamically linked to the activity of axonal fast K channels underneath the myelin in the paranodal region. Our model demonstrates that the branch point acts like a low-pass filter, blocking high-frequency transmission from the parent to the daughter branches. Theoretical analysis showed that the cutoff frequency for transmission through the branch point is determined by temperature, local K ion accumulation, width of the periaxonal space, and internodal lengths at the vicinity of the branch point. Our result is consistent with empirical findings of irregular spacing of nodes of Ranvier at axon abors, suggesting that branch points of myelinated axons play important roles in signal integration in an axonal tree.

Action Potentials↗