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Biomedical subjects

F Liu

Publications and source records attributed to F Liu.

At least 217 records · Page 12Linked to original sources
PubMed2001

[Effect of increased and decreased bite force on morphology of periodontal tissues].

OBJECTIVE: The aim of this study was to observe the effect of bite force on morphology of periodontal tissues. METHODS: Animal models were induced by extracting the left maxillary molars; the left mandibular molars served as decreased bite force models; the right mandibular molars served as increased bite force models. The dynamic changes of widths of periodontal ligament and cementum were measured. RESULTS: In decreased bite force group, there were significant morphologic changes of periodontal tissues after 1 week. In increased bite force group, there was no significant change. Ligament widths were significantly different after 2, 3 weeks respectively in those two groups, compared with that in control group (P < 0.05). There were significant differences between proximal alveolar wall and distal alveolar wall in width (P < 0.05). CONCLUSION: The histological morphology is closely related to the mechanical condition. Physiological bite force is necessary for periodontal ligament to maintain its physiological structure.

Animals↗
PubMed2001

[Expression of P21 WAF1/CIP1 in human astrocytomas in correlating with P53, MDM2, and cellular proliferation index].

OBJECTIVE: To study the correlation between the expression of p21, p53, MDM2 gene products and the initiation and progression of human astrocytomas. METHODS: The expression of P21, P53, MDM2, and proliferative cell nuclear antigen (PCNA) labeling index using immunohistochemistry in 41 paraffin embedded human astrocytoma samples. As well as the expression of p21 mRNA using mRNA in situ hybridization in 24 fresh human astrocytoma samples stored at -70 degrees C were investigated. In immunohistochemistry, we divided whole tumor cells by positive tumor cell nuclei to obtain labeling index (LI), in this way we could understand the protein product expression of gene in astrocytoma in different patients. In mRNA in situ hybridization, the expression of p21 mRNA was scored according to the rough percentage of positive cells. RESULTS: In p21 mRNA in situ hybridization, the positive staining was present in 87.5%. In immunohistochemistry, positive P21, P53, MDM2, and PCNA staining were presented in 75.6%, 68.3%, 65.9%, 100% respectively. Higher levels of P21 protein expression were seen in higher histological grade (P = 0.001). The association between P21 expression positively correlated with proliferation index. But not with P53 expression and MDM2 expression. The association between P53 expression and proliferation indices were statistically significant, but the expression of P53 was not related to tumor grade. There was no association between MDM2 expression and grade, or cellular proliferation index. Linear stepwise regression analysis showed the parameters affecting tumor grade were PCNA LI (P = 0.000) and P21 LI (P = 0.001). CONCLUSIONS: (1) Both p21 mRNA and P21 protein were overexpressed in human astrocytomas, the overexpression was related to cellular proliferation index, but was not related to P53 expression, suggesting there could be P53-independent pathway to induce the P21 expression, in addition, the overexpression of P21 alone appeared insufficient to suppress tumor growth, provided the participation of PCNA. (2) The expression of P53 protein was associated with proliferation indices, but was not with the tumor malignancy, this indicated that the inactivation of P53 might be the early event in the growth of human astrocytomas. (3) P21 labeling index and cellular proliferation index influenced the tumor histological grade, our data indicated that p21 gene might play a role in the progression of human astrocytomas.

Adolescent↗
PubMed2001

[Nondestructive quantitative analysis of Paracetamoli powder pharmaceutical by artificial neural network and near-infrared spectroscopy].

The application of artificial neural network for pharmaceutical nondestructive quantitative analysis were investigated. Real data set from near infrared reflectance spectra of Paracetamoli powder pharmaceutical were used to build up artificial network to predict unknown samples. The parameters affecting network were discussed. A new network evaluation criterion, the degree of approximation, was employed. Owing to good nonlinear multivariate calibration nature of ANN, the predicted results was reliable.

Acetaminophen↗
PubMed2001

[Using genetic algorithm for quantitative analysis of overlapped spectra in FTIR].

Technique for the quantitative analysis of FTIR spectra, which are serious overlapped in the spectral bands, is studied by genetic algorithm. The multicomponent in the mixture, which contains ten air toxic organic components, such as benzene, phenixin, chlorobenzene, nitrobenzene, phenol, toluene, methanol, o-cresol, m-cresol and p-cresol, is simultaneously determined. The effect of the probability of crossover and the establishment of objective function are discussed. The method of adaptive mutation is used. The results indicate that genetic algorithm has excellent non-linear ability of solution. Mean relative error of each results is really small, generally not bigger than 1%, when the conditions are properly controlled.

Algorithms↗
PubMed2001

[Genetic algorithms and its application to spectral analysis].

Genetic algorithm derived from the principle of natural selection and the concepts of genetics is a global search method, which is not only highly effective but also parallel. Its essential theory, operating method, application to spectral analysis and trend of development are reviewed with 66 references.

Algorithms↗
PubMed2001

Systemic administration of naked DNA: gene transfer to skeletal muscle.

Skeletal muscle is a promising target tissue for the gene therapy of both muscle and non-muscle disorders. Gene transfer into muscle tissue can produce a variety of physiologically active proteins and may ultimately be applied to the treatment of many diseases. A variety of methods have been studied to transfer genes into skeletal muscle, including viral and non-viral vectors. In this review, we discuss recent developments in the non-viral delivery of genes to muscles.

Animals↗
PubMed2000

Unique dynamic appearance of a Ge-Si ad-dimer on Si(001).

We carry out a comparative study of the energetics and dynamics of Si-Si, Ge-Ge, and Ge-Si ad-dimers on top of a dimer row in the Si(001) surface, using first-principles calculations. The dynamic appearance of a Ge-Si dimer is distinctively different from that of a Si-Si or Ge-Ge dimer, providing a unique way for its identification by scanning tunneling microscopy (STM). Its "rocking" motion, observed in STM, actually reflects a 180 degrees rotation of the dimer, involving a piecewise-rotation mechanism. The calculated energy barrier of 0.74 eV is in good agreement with the experimental value of 0.82 eV.

Journal Article↗
PubMed2000

Mechanism of phosphorylation of protein kinase B/Akt by a constitutively active 3-phosphoinositide-dependent protein kinase-1.

Phosphorylation of Thr(308) in the activation loop and Ser(473) at the carboxyl terminus is essential for protein kinase B (PKB/Akt) activation. However, the biochemical mechanism of the phosphorylation remains to be characterized. Here we show that expression of a constitutively active mutant of mouse 3-phosphoinositide-dependent protein kinase-1 (PDK1(A280V)) in Chinese hamster ovary cells overexpressing the insulin receptor was sufficient to induce PKB phosphorylation at Thr(308) to approximately the same extent as insulin stimulation. Phosphorylation of PKB by PDK1(A280V) was not affected by treatment of cells with inhibitors of phosphatidylinositol 3-kinase or by deletion of the pleckstrin homology (PH) domain of PKB. C(2)-ceramide, a cell-permeable, indirect inhibitor of PKB phosphorylation, did not inhibit PDK1(A280V)-catalyzed PKB phosphorylation in cells and had no effect on PDK1 activity in vitro. On the other hand, co-expression of full-length protein kinase C-related kinase-1 (PRK1/PKN) or 2 (PRK2) inhibited PDK1(A280V)-mediated PKB phosphorylation. Replacing alanine at position 280 with valine or deletion of the PH domain enhanced PDK1 autophosphorylation in vitro. However, deletion of the PH domain of PDK1(A280V) significantly reduced PDK1(A280V)-mediated phosphorylation of PKB in cells. In resting cells, PDK1(A280V) localized in the cytosol and at the plasma membrane. However, PDK1(A280V) lacking the PH domain localized predominantly in the cytosol. Taken together, our findings suggest that the wild-type PDK1 may not be constitutively active in cells. In addition, activation of PDK1 is sufficient to phosphorylate PKB at Thr(308) in the cytosol. Furthermore, the PH domain of PDK1 may play both positive and negative roles in regulating the in vivo function of the enzyme. Finally, unlike the carboxyl-terminal fragment of PRK2, which has been shown to bind PDK1 and allow the enzyme to phosphorylate PKB at both Thr(308) and Ser(473), full-length PRK2 and its related kinase PRK1/PKN may both play negative roles in PKB-mediated downstream biological events.

3-Phosphoinositide-Dependent Protein Kinases↗
PubMed2000

Creation of "quantum platelets" via strain-controlled self-organization at steps.

We demonstrate, by both theory and experiment, the strain-induced self-organized formation of "quantum platelets," monolayer-thick islands of finite dimensions. They form at the early stage of heteroepitaxial growth on a substrate with regularly spaced steps, and align along the steps. In the direction perpendicular to substrate steps, the island position and spacing can be preselected through substrate miscut. Along the steps, the island size and density are controlled by self-organized growth.

Journal Article↗
PubMed2000

Regulation of somatic growth by the p160 coactivator p/CIP.

A family of p160 coactivators was initially identified based on ligand-dependent interactions with nuclear receptors and thought to function, in part, by recruiting CREB-binding protein/p300 to several classes of transcription factors. One of the p160 factors, p/CIP/AIB1, often amplified and overexpressed in breast cancer, also exhibits particularly strong interaction with CREB-binding protein/p300. In this manuscript, we report that p/CIP, which exhibits regulated transfer from cytoplasm to nucleus, is required for normal somatic growth from embryonic day 13.5 through maturity. Our data suggest that a short stature phenotype of p/CIP gene-deleted mice reflect both altered regulation of insulin-like growth factor-1 (IGF-1) gene expression in specific tissues and a cell-autonomous defect of response to IGF-1, including ineffective transcriptional activities by several classes of regulated transcription factors under specific conditions. The actions of p/CIP are therefore required for full expression of a subset of genes critical for regulating physiological patterns of somatic growth in mammals.

Animals↗
PubMed2000

Distinct roles of the adaptor protein Shc and focal adhesion kinase in integrin signaling to ERK.

It has been proposed that integrins activate ERK through the adaptor protein Shc independently of focal adhesion kinase (FAK) or through FAK acting on multiple target effectors, including Shc. We show that disruption of the actin cytoskeleton by cytochalasin D causes a complete inhibition of FAK but does not inhibit Shc signaling and activation of ERK. We have then generated primary fibroblasts carrying a targeted deletion of the segment of beta(1) subunit cytoplasmic domain required for activation of FAK. Analysis of these cells indicates that FAK is not necessary for efficient tyrosine phosphorylation of Shc, association of Shc with Grb2, and activation of ERK in response to matrix adhesion. In addition, integrin-mediated activation of FAK does not appear to be required for signaling to ERK following growth factor stimulation. To examine if FAK could contribute to the activation of ERK in a cell type-specific manner through the Rap1/B-Raf pathway, we have used Swiss-3T3 cells, which in contrast to primary fibroblasts express B-Raf. Dominant negative studies indicate that Shc mediates the early phase and peak, whereas FAK, p130(CAS), Crk, and Rap1 contribute to the late phase of integrin-dependent activation of ERK in these cells. In addition, introduction of B-Raf enhances and sustains integrin-mediated activation of ERK in wild-type primary fibroblasts but not in those carrying the targeted deletion of the beta(1) cytoplasmic domain. Thus, the Shc and FAK pathways are activated independently and function in a parallel fashion. Although not necessary for signaling to ERK in primary fibroblasts, FAK may enhance and prolong integrin-mediated activation of ERK through p130(CAS), Crk, and Rap1 in cells expressing B-Raf.

3T3 Cells↗
PubMed2000

Cleavage of symmetric immobile DNA junctions by Escherichia coli RuvC.

The Holliday junction is a key DNA intermediate in the process of genetic recombination. It consists of two double-helical domains composed of homologous strands that flank a branch point; two of the strands are roughly helical, and two form the crossover between the helices. RuvC is a Holliday junction resolvase that cleaves the helical strands at a symmetric sequence, leading to the production of two recombinant molecules. We have determined the position of the cleavage site relative to the crossover point by the use of symmetric immobile junctions; these are DNA molecules containing two crossover points, one held immobile by sequence asymmetry and the second a symmetric sequence, but held immobile by torsional coupling to the first junction. We have built five symmetric immobile junctions, in which the tetranucleotide recognition site is moved stepwise relative to the branch point. We have used kinetic analysis of catalysis, gel retardation, and hydroxyl radical hypersensitivity to analyze this system. We conclude that the internucleotide linkage one position 3' to the crossover point is the favored site of cleavage.

Bacterial Proteins↗
PubMed2000

Direct evidence for spontaneous branch migration in antiparallel DNA Holliday junctions.

The Holliday junction is a central intermediate in genetic recombination. It contains four strands of DNA that are paired into four double helical arms flanking a branch point. In naturally occurring Holliday junctions, the sequence flanking the branch point contains 2-fold (homologous) symmetry. As a consequence of this symmetry, the junction can undergo a conformational isomerization known as branch migration, which relocates the site of branching. In the absence of proteins and in the presence of Mg(2+), the four arms are known to stack in pairs, forming two helical domains whose orientations are antiparallel. Nevertheless, the mechanistic models proposed for branch migration are all predicated on a parallel alignment of helical domains. Here, we have used antiparallel DNA double crossover molecules to demonstrate that branch migration can occur in antiparallel Holliday junctions. We have constructed a DNA double crossover molecule with three crossover points. Two adjacent branch points in this molecule are flanked by symmetric sequences. The symmetric crossover points are held immobile by the third crossover point, which is flanked by asymmetric sequences. Restriction of the helices that connect the immobile junction to the symmetric junctions releases this constraint. The restricted molecule undergoes branch migration, even though it is constrained to an antiparallel conformation.

Base Sequence↗
PubMed2000

Combinatorial roles of the nuclear receptor corepressor in transcription and development.

Transcriptional repression plays crucial roles in diverse aspects of metazoan development, implying critical regulatory roles for corepressors such as N-CoR and SMRT. Altered patterns of transcription in tissues and cells derived from N-CoR gene-deleted mice and the resulting block at specific points in CNS, erythrocyte, and thymocyte development indicated that N-CoR was a required component of short-term active repression by nuclear receptors and MAD and of a subset of long-term repression events mediated by REST/NRSF. Unexpectedly, N-CoR and a specific deacetylase were also required for transcriptional activation of one class of retinoic acid response element. Together, these findings suggest that specific combinations of corepressors and histone deacetylases mediate the gene-specific actions of DNA-bound repressors in development of multiple organ systems.

Animals↗
PubMed2000

Down-regulation of N-acetylglucosaminyltransferase V by tumorigenesis- or metastasis-suppressor gene and its relation to metastatic potential of human hepatocarcinoma cells.

The effects of transfection of the metastasis suppressor gene nm23-H1 and cell-cycle related tumor-suppressor gene p16 on the activity of N-acetylglucosaminyltransferase V (GnT-V) and their relations to cancer metastatic potential were investigated. After transfection of nm23-H1 into 7721 human hepatocarcinoma cells and A549 human lung cancer cells, the activities of GnT-V were decreased by 28%-42% in the cells. In contrast, when p16 was transfected into these two cell lines, the decrease of GnT-V activity was only observed in A549 cells. This was probably to be due to the obvious expression of p16 gene in parental 7721 cells and the deletion of p16 in A549 cells. The decrease of GnT-V mRNA was only observed in nm23-H1-transfected cells, but not in p16-transfected A549 cells, suggesting that these two genes regulated GnT-V via different mechanisms. Horseradish peroxidase (HRP)-lectin staining showed that the 7721 cells transfected with nm23-H1 or the A549 cells transfected with p16 displayed a decreased intensity with HRP-leucoagglutinating phytohemagglutinin and increased intensity with HRP-concanavalin A, indicating the decline of beta1,6 N-acetylglucosamine branching structure on the asparagine-linked glycans of cell-surface and intracellular glycoproteins. The nm23-H1 transfected 7721 cells also displayed some changes in metastasis-related phenotypes, including the increase in cell adhesion to fibronectin (Fn), the decline in cell adhesion to laminin (Ln), and the decreased cell migration and invasion through matrigel. Transfection of antisense GnT-V cDNA into 7721 cells resulted in a decrease of GnT-V activity, an increase of cell adhesion to Fn or Ln, and a decrease in cell migration and invasion through matrigel. These phenotypes bore similarity to those of the 7721 cells transfected with nm23-H1. Our findings indicate that the down-regulation of GnT-V by nm23-H1 contributes to the alterations in metastasis-related phenotypes, and is an important molecular mechanism of metastasis suppression mediated by nm23-H1.

Adenocarcinoma↗
PubMed2000

Thermal roughening of a thin film: A new type of roughening transition

The equilibrium thermal roughening of thin Ge layers (one and two monolayers) deposited on Si(001) has been investigated with low-energy electron microscopy. A Ge-coverage-dependent roughening is observed. For two monolayers, the temperature at which imaging contrast is lost due to surface roughness is 900+/-25 degrees C, between the roughening temperatures of Ge(001) and Si(001). Lower Ge coverages move this temperature closer to that of Si(001). The roughening is confined to the Ge overlayers. It is believed that this phenomenon represents a new type of surface roughening transition that should be generally applicable for heteroepitaxial films.

Journal Article↗