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Biomedical subjects

H Niu

Publications and source records attributed to H Niu.

At least 19 recordsLinked to original sources
PubMed2006

Nanofluidic channels fabrication and manipulation of DNA molecules.

Nanofluidic channel arrays, which have a width of about 40 nm, depth of 60 nm and length of 50 mum, were created using a focused-ion-beam milling instrument on a silicon nitride film swiftly and exactly, as is necessary. Stained -DNA molecules were put inside these sub-100 nm conduits by capillary force and they were stretched and transferred along these conduits, which were dealt with activating reagent Brij aqueous solution in advance. The movements of DNA molecules in these channels were discussed. These nano-structure channels may be useful in the study and analysis of the statics as well as the dynamics of single biomolecules.

DNA↗
PubMed2002

A fast automatic RBS/w channeling system for damage depth profiling.

A computer-aided data acquisition coupling with goniometer-control system dedicated for damage depth profile measurements is established. The channeling direction searching is performed along tilt and azimuth directions. The system includes a computer code to convert the measured spectra into damage depth profile. The analyzing time for each sample requires approximately 20-30 min. The damage depth profiles of the self-implanted (100) silicon samples are in reasonable agreement with the calculated results yielded by the SRIM Monte-Carlo simulation code.

Journal Article↗
PubMed2001

Antitumor activity of expanded human tumor-infiltrating gammadelta T lymphocytes.

BACKGROUND: The objective of this study was to investigate the antitumor activity of selectively expanded gammadelta T cells in tumor-infiltrating lymphocytes (gammadeltaTILs) or tumor ascites lymphocytes (gammadeltaTALs) from patients with colorectal and ovarian epithelial carcinoma (OEC) in vitro and in vivo. METHODS: gammadeltaTILs/TALs were expanded by the solid-phase antibody method; their cytolytic and proliferative activities in vitro were detected by the MTT method and 3H-TdR incorporation and their effect in vivo was evaluated by the nude mice model. RESULTS: Expanded gammadeltaTILs from colorectal tumors demonstrated marked cytotoxicities to allogeneic human colon adenocarcinoma HR8348 and lymphoma Daudi cells, as well as xenogeneic murine thymoma EL-4 cell lines. Cytokines, including IL-2, IL-4, IL-12, IL-15, TNF-alpha and INF-gamma, could promote the cytotoxicities of gammadeltaTILs to tumor cells, whereas IL-10, GM-CSF and TFG-beta had no effect on such killing activities. Rested gammadeltaTILs could proliferate strongly in response to mitomycin C-treated Daudi and EL-4 tumor cells, but not to HR8348 tumor cells, suggesting that the latter might possess only cytotoxicity-related antigen recognized by gammadeltaTILs. Either alphabetaTILs or gammadeltaTILs from patients with OEC displayed cytotoxicities to allogeneic or autologous OEC cell lines at a similar strength in vitro. Transferring gammadeltaTILs into Daudi cell-bearing BALB/c nude mice with an injection of IL-2 was able to maintain a high survival rate of the mice for 30 days, when compared with mice treated with alphabetaTILs or without any treatment (p < 0.05). Without coinjection of IL-2, after 3 months of Daudi tumor inoculation, a high survival rate was observed in gammadeltaTIL-treated mice. Similarly, adoptive gammadeltaTALs from the ascites of patients with OEC transferred into nude mice displayed a stronger antitumor response to OEC SKOV3 cells than alphabetaTALs in vivo. Tumor volumes in gammadeltaTAL-treated mice were smaller than in alphabetaTAL-treated or non-TAL-treated mice within the period from day 23 to day 50 after tumor inoculation (p < 0.05). Fifty days after SKOV3 tumor inoculation, a decreasing trend of carcinogenic rate was observed in gammadeltaTAL-treated nude mice. CONCLUSION: Taken together, our results suggest that gammadeltaT cells could be a new candidate for adoptive immunotherapy in the future treatment of patients with cancer.

Adenocarcinoma↗
PubMed2000

Characterization of the interaction between the nuclease and reverse transcriptase activity of the yeast telomerase complex.

Telomerase is a ribonucleoprotein that mediates extension of the dG-rich strand of telomeres in most eukaryotes. Like telomerase derived from ciliated protozoa, yeast telomerase is found to possess a tightly associated endonuclease activity that copurifies with the polymerization activity over different affinity-chromatographic steps. As is the case for ciliate telomerase, primers containing sequences that are not complementary to the RNA template can be efficiently cleaved by the yeast enzyme. More interestingly, we found that for the yeast enzyme, cleavage site selection is not stringent, since blocking cleavage at one site by the introduction of a nonhydrolyzable linkage can lead to the utilization of other sites. In addition, the reverse transcriptase activity of yeast telomerase can extend either the 5'- or 3'-end fragment following cleavage. Two general models that are consistent with the biochemical properties of the enzyme are presented: one model postulates two distinct active sites for the nuclease and reverse transcriptase, and the other invokes a multimeric enzyme with each protomer containing a single active site capable of mediating both cleavage and extension.

Binding Sites↗
PubMed1998

Antigen receptor signaling induces MAP kinase-mediated phosphorylation and degradation of the BCL-6 transcription factor.

The bcl-6 proto-oncogene encodes a POZ/zinc finger transcriptional repressor expressed in germinal center (GC) B and T cells and required for GC formation and antibody affinity maturation. Deregulation of bcl-6 expression by chromosomal rearrangements and point mutations of the bcl-6 promoter region are implicated in the pathogenesis of B-cell lymphoma. The signals regulating bcl-6 expression are not known. Here we show that antigen receptor activation leads to BCL-6 phosphorylation by mitogen-activated protein kinase (MAPK). Phosphorylation, in turn, targets BCL-6 for rapid degradation by the ubiquitin/proteasome pathway. These findings indicate that BCL-6 expression is directly controlled by the antigen receptor via MAPK activation. This signaling pathway may be crucial for the control of B-cell differentiation and antibody response and has implications for the regulation of other POZ/zinc finger transcription factors in other tissues.

B-Lymphocytes↗
PubMed1998

Nonviral vector-mediated thymidine kinase gene transfer and ganciclovir treatment in leiomyoma cells.

OBJECTIVE: To test the hypotheses that ganciclovir is cytotoxic to leiomyoma cells transfected with herpes simplex virus thymidine kinase and that estrogen modulates the responsiveness of tumor cells to this gene therapy approach. METHODS: Human and rat cultured uterine leiomyoma cells were transfected with plasmids encoding the beta-galactosidase gene, thymidine kinase gene, or a control plasmid. Transfection efficiency was monitored by measuring beta-galactosidase enzyme activity. Ganciclovir cytotoxicity in thymidine kinase-transfected cells was assessed by monitoring cell viability using trypan blue exclusion. The "bystander effect," a phenomenon in which thymidine kinase-expressing cells exposed to ganciclovir are toxic to adjacent thymidine kinase-nonexpressing cells, was assessed when thymidine kinase vector-transfected cells were cocultured with control plasmid-transfected cells at various percentages before exposure to ganciclovir. The effect of estradiol on ganciclovir-thymidine kinase-mediated cytotoxicity was assessed in estrogen-responsive rat leiomyoma cells. RESULTS: A thymidine kinase-ganciclovir-mediated "bystander effect" was demonstrated, with 48.6% (human) and 65.6% (rat) cell death when 5% of the leiomyoma cells were transfected with the pNGVL1-tk vector, with 0.84% and 1.9% of the cells expected to express thymidine kinase as based on the 16.7% and 39.8% transfection efficiency determined by the reporter gene assay in human and rat leiomyoma cells, respectively. Estradiol promoted cell growth and enhanced the "bystander effect" in rat leiomyoma cells. CONCLUSION: These findings demonstrate the feasibility of using thymidine kinase gene therapy as a novel treatment for uterine leiomyomas. The effect of estrogen may provide a mechanism to enhance the tumor-suppressive effect of this approach.

Animals↗
PubMed1997

Mapping of amino acid residues in the p34 subunit of human single-stranded DNA-binding protein phosphorylated by DNA-dependent protein kinase and Cdc2 kinase in vitro.

Human single-stranded DNA-binding protein (HSSB, also called RPA), is a heterotrimeric complex that consists of three subunits, p70, p34, and p11. HSSB is essential for the in vitro replication of SV40 DNA and nucleotide excision repair. It also has important functions in other DNA transactions, including DNA recombination, transcription, and double-stranded DNA break repair. The p34 subunit of HSSB is phosphorylated in a cell cycle-dependent manner. Both Cdc2 kinase and the DNA-dependent protein kinase (DNA-PK) phosphorylate HSSB-p34 in vitro. In this study, we show that efficient phosphorylation of HSSB-p34 by DNA-PK requires Ku as well as DNA. The DNA-PK phosphorylation sites in HSSB-p34 have been mapped at Thr-21 and Ser-33. Kinetic studies demonstrated that a phosphate residue is first incorporated at Thr-21 followed by the incorporation of a second phosphate residue at Ser-33. We also identified Ser-29 as the major Cdc2 kinase phosphorylation site in the p34 subunit.

Amino Acid Sequence↗
PubMed1997

Dexamethasone regulates basic fibroblast growth factor, nerve growth factor and S100beta expression in cultured hippocampal astrocytes.

Glucocorticoids regulate hippocampal neuron survival during fetal development, in the adult, and during aging; however, the mechanisms underlying the effects are unclear. Since astrocytes contain adrenocortical receptors and synthesize and release a wide variety of growth factors, we hypothesized that glucocorticoids may alter neuron-astrocyte interactions by regulating the expression of growth factors in hippocampal astrocytes. In this study, three growth factors, which are important for hippocampal neuron development and survival, were investigated: basic fibroblast growth factor (bFGF), nerve growth factor (NGF), and S100beta. Enriched type I astrocyte cultures were treated with 1 microM dexamethasone (DEX), a synthetic glucocorticoid, for up to 120 h. Cells and culture medium were collected and total RNA and protein were measured at 6, 12, 24, 48, 72, 96 and 120 h after the initiation of hormone treatment. Growth factor mRNA levels were measured and quantified using solution hybridization-RNase protection assays and protein levels were quantified using ELISA methods. We report that DEX stimulates the bFGF mRNA levels over the 120-h treatment. In contrast, DEX suppresses NGF mRNA continuously over the same period of treatment. DEX induces a biphasic response in S100beta mRNA levels. In addition, some of the changes in gene expression are translated into parallel changes in protein levels of these growth factors. Our results demonstrate that dexamethasone can differentially regulate the expression of growth factors in hippocampal astrocytes in vitro. This suggests that one of the mechanisms through which glucocorticoids affect hippocampal functions may be by regulating the expression of astrocyte-derived growth factors.

Animals↗
PubMed1997

[The value of electronystagmography in differential diagnosis of vertigo].

Findings of electronystagmography (ENG) in 645 patients with vertigo were analysed. Two hundred and twelve cases showed vestibular peripheral vertigo, 394 cases vestibular central vestigo, and 39 cases other types of vertigo. The ENGs in patients with vestibular peripheral vertigo were charazterized mainly by the vestibular abnormal caloric responses, spontaneous and benign positional nystagmuses were also obsedrved at the same time. Different degrees and various combinations of the abnormal responses shown in optokinetic central test were the most characteristic of ENG in patients with vestibular central vertigo. The results suggest that ENG is particularly useful for differentiating peripheral and central vertigo.

Adolescent↗
PubMed1996

Studies on the in vitro phosphorylation of HSSB-p34 and -p107 by cyclin-dependent kinases. Cyclin-substrate interactions dictate the efficiency of phosphorylation.

Cyclin-dependent kinases (Cdks) are required for cell cycle progression. Two potentially significant Cdk substrates in human cells are the human single-stranded binding protein (HSSB or RPA), which plays an essential role in DNA replication, repair, and recombination, and the tumor suppressor p107 which acts to negatively regulate cell growth. In this report we describe the in vitro phosphorylation of these two proteins by Cdks in an attempt to understand how cyclin-substrate interactions direct phosphorylation efficiencies. We show that cyclin A-Cdk2 efficiently phosphorylates the p34 subunit of HSSB (HSSB-p34) alone or as a part of the heterotrimeric complex. In contrast, cyclin E-Cdk2 that is active in phosphorylating histone H1, does not support the phosphorylation of the p34 subunit of HSSB. We provide evidence that this differential phosphorylation results from a specific interaction between HSSB-p34 and cyclin A, but not cyclin E. Thus the observed cell cycle-dependent phosphorylation of HSSB-p34 at the G1 to S transition is most likely catalyzed by cyclin A-Cdk2 initiated by the direct interaction between cyclin A and the HSSB-p34 subunit. These studies are consistent with our previous observation that p107, which directly binds cyclin A, is efficiently phosphorylated by cyclin A-Cdk2 but not cyclin B-associated kinases. Here we further demonstrate that cyclin A only complexes with p107 in its unphosphorylated form. These data suggest a catalytic mechanism by which Cdk acts: substrate targeting by a cyclin-substrate interaction followed by dissociation of the Cdk upon phosphate incorporation allowing the Cdk to become available for the next cycle of phosphorylation.

Base Sequence↗
PubMed1996

Rat ribosomal RNA gene can utilize primate RNA polymerase I transcription machinery: lack of absolute species specificity in rDNA transcription.

The transcriptional activity of rodent ribosomal RNA gene (rDNA) in the primate cell was examined in the light of reported species specificity of eukaryotic ribosomal RNA synthesis. The present study showed that rat rDNA can be transcribed in HeLa nuclear extract whereas mouse rDNA was not transcribed in the heterologous extract. Rat and mouse rDNA transcription factors were interchangeable with respect to efficiency and accuracy of transcription. The initiation of rat ribosomal gene transcription by RNA polymerase I occurred at the +1 site in the heterologous extract. Initiation of transcription at the correct site also occurred in vivo following transfection of cloned rat rDNA into the primate (COS-7) cells. These data indicate that rat ribosomal RNA gene can be expressed in the primate system in vitro and in vivo. The absolute lack of species specificity in rDNA transcription has been discussed based on the present data and other reports.

Animals↗
PubMed1995

Chromosomal translocations cause deregulated BCL6 expression by promoter substitution in B cell lymphoma.

The BCL6 gene codes for a zinc-finger transcription factor and is involved in chromosomal rearrangements in 30-40% of diffuse large-cell lymphoma (DLCL). These rearrangements cluster within the 5' regulatory region of BCL6 spanning its first non-coding exon. To determine the functional consequences of these alterations, we have analyzed the structure of the rearranged BCL6 alleles and their corresponding RNA and protein species in two DLCL biopsies and one tumor cell line which carried the t(3;14)(q27;q32) translocation involving the BCL6 and immunoglobulin heavy-chain (IgH) loci. In all three cases, the breakpoints were mapped within the IgH switch region and the BCL6 first intron, leading to the juxtaposition of part of the IgH locus upstream and in the same transcriptional orientation to the BCL6 coding exons. An analysis of cDNA clones showed that these recombinations generate chimeric IgH-BCL6 transcripts which initiated from IgH germline transcript promoters (I mu or I gamma 3), but retain a normal BCL6 coding domain. In the tumor cell line, the chimeric I gamma 3-BCL6 allele, but not the germline BCL6 gene, was transcriptionally active and produced a normal BCL6 protein. These findings indicate that t(3;14) translocations alter BCL6 expression by promoter substitution and imply that the consequence of these alterations is the deregulated expression of a normal BCL6 protein.

Alleles↗
PubMed1995

E1BF/Ku interacts physically and functionally with the core promoter binding factor CPBF and promotes the basal transcription of rat and human ribosomal RNA genes.

We have previously characterized an RNA polymerase (pol) I transcription factor, E1BF, from rat cells. This protein is immunologically related to Ku autoantigen and is required in pol-I directed transcription of rodent ribosomal RNA gene (rDNA). Glycerol density gradient fractionation and in situ UV cross-linking analysis of the purified factor showed directly that it consists of a heterodimer of 85 and 72 kDa polypeptides. E1BF also interacted with the human core promoter and augmented transcription of human rDNA as much as fivefold in HeLa nuclear extract, whereas transcription from adenovirus major late promoter, CMV or SV40 early promoters by pol II and of U6 and 5S RNA genes by pol III were either unaffected or minimally inhibited by the antibodies. Purified rat E1BF partially restored the suppression of human rDNA transcription by anti-Ku antibodies. Immunoprecipitation of rat cell extract with the anti-Ku antibodies followed by SDS-PAGE of the precipitated proteins and Southwestern analysis showed that E1BF interacts with CPBF, a core promoter binding factor. When the majority of CPBF and E1BF was removed from the reaction mixture by preincubation with a core promoter oligo nucleotide fragment, rDNA transcription was severely impaired. Addition of exogenous CPBF or E1BF to such a reaction resulted in significant restoration of the transcription, whereas inclusion of both factors caused further enhancement of rDNA transcription. These data demonstrate that E1BF is a basal pol I transcription factor that interacts with a core promoter binding factor both physically and functionally, and that is not a general pol II or pol III transcription factor.

Adenoviridae↗