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Biomedical subjects

Liping Feng

Publications and source records attributed to Liping Feng.

15 recordsLinked to original sources
PubMed2006

Characterization of progesterone receptor isoform expression in fetal membranes.

OBJECTIVE: To quantify expression of progesterone receptor (PR) messenger RNA (mRNA) isoforms in fetal membranes, and to determine whether these levels change in culture. STUDY DESIGN: Placentas from women undergoing term cesarean delivery before labor were collected. Layers of amnion, chorion, and decidua were separated manually, enzymatically digested, and separated further with the use of a density gradient. RNA was extracted immediately and after culture for 48 hours, then analyzed by quantitative reverse transcription polymerase chain reaction for PR-A, PR-B, and beta-2 microglobulin mRNA expression. Separation of cell types was confirmed by immunohistochemistry. RESULTS: PR isoform expression was identified in fetal membranes, with levels highest in decidua and below the limits of detection in amnion. The ratio of PR-A/PR-B mRNA was not significantly different between cell layers. PR mRNA isoform levels did not differ significantly in fresh versus cultured cells. CONCLUSION: Quantitative reverse transcription polymerase chain reaction was used to quantitate expression of PR mRNA isoforms in cells of fetal membranes and to validate systems for further study of PR with respect to inflammation, infection, and preterm delivery.

Extraembryonic Membranes↗
PubMed2006

Enediynes from aza-enediynes: C,N-dialkynyl imines undergo both aza-Bergman rearrangement and conversion to enediynes and fumaronitriles.

[reaction; see text] Aza-enediynes (C,N-dialkynyl imines) undergo thermal aza-Bergman rearrangement to beta-alkynyl acrylonitriles through 2,5-didehydropyridine (2,5-ddp) intermediates. Certain aza-enediynes also undergo an alternative process affording enediynes and fumaronitriles. Studies employing a specifically (l3)C-labeled aza-enediyne show that the conversion to enediyne is second order in aza-enediyne, proceeds by a "head-to-tail" coupling, and affords the (Z)-enediyne.

Aza Compounds↗
PubMed2005

The neurofibromatosis type 1 gene product neurofibromin enhances cell motility by regulating actin filament dynamics via the Rho-ROCK-LIMK2-cofilin pathway.

Neurofibromin is a neurofibromatosis type 1 (NF1) tumor suppressor gene product with a domain that acts as a GTPase-activating protein and functions, in part, as a negative regulator of Ras. Loss of neurofibromin expression in NF1 patients is associated with elevated Ras activity and increased cell proliferation, predisposing to a variety of tumors of the peripheral and central nervous systems. We show here, using the small interfering RNA (siRNA) technique, that neurofibromin dynamically regulates actin cytoskeletal reorganization, followed by enhanced cell motility and gross cell aggregation in Matrigel matrix. NF1 siRNA induces characteristic morphological changes, such as excessive actin stress fiber formation, with elevated negative phosphorylation levels of cofilin, which regulates actin cytoskeletal reorganization by depolymerizing and severing actin filaments. We found that the elevated phosphorylation of cofilin in neurofibromin-depleted cells is promoted by activation of a Rho-ROCK-LIMK2 pathway, which requires Ras activation but is not transduced through three major Ras-mediated downstream pathways via Raf, phosphatidylinositol 3-kinase, and RalGEF. In addition, the exogenous expression of the NF1-GTPase-activating protein-related domain suppressed the NF1 siRNA-induced phenotypes. Neurofibromin was demonstrated to play a significant role in the machinery regulating cell proliferation and in actin cytoskeletal reorganization, which affects cell motility and adhesion. These findings may explain, in part, the mechanism of multiple neurofibroma formation in NF1 patients.

Actin Depolymerizing Factors↗
PubMed2004

Cre-loxP-controlled periodic Aurora-A overexpression induces mitotic abnormalities and hyperplasia in mammary glands of mouse models.

Aurora-A, a serine/threonine mitotic kinase, was reported to be overexpressed in various human cancers, and its overexpression induces aneuploidy, centrosome amplification and tumorigenic transformation in cultured human and rodent cells. However, the underlying mechanisms and pathological settings by which Aurora-A promotes tumorigenesis are largely unknown. Here, we created a transgenic mouse model to investigate the involvement of Aurora-A overexpression in the development of mammary glands and tumorigenesis using a Cre-loxP system. The conditional expression of Aurora-A resulted in significantly increased binucleated cell formation and apoptosis in the mammary epithelium. The surviving mammary epithelial cells composed hyperplastic areas after a short latency. Induction of Aurora-A overexpression in mouse embryonic fibroblasts prepared from the transgenic mice also led to aberrant mitosis and binucleated cell formation followed by apoptosis. The levels of p53 protein were remarkably increased in these Aurora-A-overexpressing cells, and the apoptosis was significantly suppressed by deletion of p53. Given that no malignant tumor formation was found in the Aurora-A-overexpressing mouse model after a long latency, additional factors, such as p53 inactivation, are required for the tumorigenesis of Aurora-A-overexpressing mammary epithelium. Our findings indicated that this mouse model is a useful system to study the physiological roles of Aurora-A and the genetic pathways of Aurora-A-induced carcinogenesis.

Animals↗
PubMed2004

alpha,5-didehydro-3-picoline diradicals from skipped azaenediynes: computational and trapping studies of an aza-Myers-Saito cyclization.

[reaction: see text] On the basis of density functional calculations, the isomerization of skipped azaenediynes (C-alkynyl-N-propargylimines) to azaenyne allenes and subsequent rapid aza-Myers-Saito cyclization to alpha,5-didehydro-3-picoline were predicted. We prepared the N-propargylimine of 1-phenyl-3-tri(isopropyl)silylprop-2-yn-1-one, which undergoes proto-desilylation and isomerization to an azaenyne allene when treated with tetrabutylammonium fluoride. In the presence of 1,4-cyclohexadiene, this azaenyne allene affords 6-phenyl-3-picoline and other products corresponding to the trapping of an alpha,5-didehydro-3-picoline diradical.

Alkynes↗
PubMed2004

PKA phosphorylation and 14-3-3 interaction regulate the function of neurofibromatosis type I tumor suppressor, neurofibromin.

Neurofibromin, a neurofibromatosis type I (NF1) tumor suppressor gene product, has a domain acting as a GTPase activating protein and functions in part as a negative regulator of Ras. Loss of neurofibromin expression in NF1 patients is associated with elevated Ras activity and increased cell proliferation. Therefore, regulation of the function of neurofibromin is heavily involved in cell growth and differentiation. In the present study, we identified a novel cellular neurofibromin-associating protein, 14-3-3, which belongs to a highly conserved family of proteins that regulate intracellular signal transduction events in all eukaryotic cells. The interaction of 14-3-3 is mainly directed to the C-terminal domain (CTD) of neurofibromin, and the cAMP-dependent protein kinase (PKA)-dependent phosphorylation clustered on CTD-Ser (2576, 2578, 2580, 2813) and Thr (2556) is required for the interaction. Interestingly, the increased phosphorylation and association of 14-3-3 negatively regulate the function of neurofibromin. These findings indicate that PKA phosphorylation followed by 14-3-3 protein interaction may modulate the biochemical and biological functions of neurofibromin.

14-3-3 Proteins↗
PubMed2004

[Bioactivity of volatile oils from Myoporum bontioides on Plutella xylostella].

This study showed that the volatile oils from Myoporum bontioides had a significant repellent action on Plutella xylostella. When Plutella xylostella adults entered into the 4-arm selective olfactometer, the preferred times and average staying duration, in the order from more to less, were 3, 1, 4, and 2 arms, which showed a tendency of keeping away from the treatment arms. The males were more sensitive to the volatile oils than the females, when the velocity of flow was 200 ml.min-1. On the first day of the 3rd bioassay, the oviposition deterrent rate and IIPC of the volatile oils on Plutella xylostella adults was 94.48% and 0.0552, respectively. A liquid component of the volatile oils from Myoporum bontioides was isolated, purified, and identified as myoporone.

Animals↗
PubMed2003

Parallel molecular computations of pairwise exclusive-or (XOR) using DNA "string tile" self-assembly.

Self-assembling DNA nanostructures are an efficient means of executing parallel molecular computations. However, previous experimental demonstrations of computations by DNA tile self-assembly only allowed for one set of distinct input to be processed at a time. Here, we report the multibit, parallel computation of pairwise exclusive-or (XOR) using DNA "string tile" self-assembly. A set of DNA tiles encoding the truth table for the XOR logical operation was constructed. Parallel tile self-assembly and ligation led to the formation of reporter DNA strands which encoded both the input and the output of the computations. These reporter strands provided a molecular look-up table containing all possible pairwise XOR calculations up to a certain input size. The computation was readout by sequencing the cloned reporter strands. This is the first experimental demonstration of a parallel computation by DNA tile self-assembly in which a large number of distinct input were simultaneously processed.

DNA↗
PubMed2003

Directed nucleation assembly of DNA tile complexes for barcode-patterned lattices.

The programmed self-assembly of patterned aperiodic molecular structures is a major challenge in nanotechnology and has numerous potential applications for nanofabrication of complex structures and useful devices. Here we report the construction of an aperiodic patterned DNA lattice (barcode lattice) by a self-assembly process of directed nucleation of DNA tiles around a scaffold DNA strand. The input DNA scaffold strand, constructed by ligation of shorter synthetic oligonucleotides, provides layers of the DNA lattice with barcode patterning information represented by the presence or absence of DNA hairpin loops protruding out of the lattice plane. Self-assembly of multiple DNA tiles around the scaffold strand was shown to result in a patterned lattice containing barcode information of 01101. We have also demonstrated the reprogramming of the system to another patterning. An inverted barcode pattern of 10010 was achieved by modifying the scaffold strands and one of the strands composing each tile. A ribbon lattice, consisting of repetitions of the barcode pattern with expected periodicity, was also constructed by the addition of sticky ends. The patterning of both classes of lattices was clearly observable via atomic force microscopy. These results represent a step toward implementation of a visual readout system capable of converting information encoded on a 1D DNA strand into a 2D form readable by advanced microscopic techniques. A functioning visual output method would not only increase the readout speed of DNA-based computers, but may also find use in other sequence identification techniques such as mutation or allele mapping.

Base Sequence↗
PubMed2003

Neurofibromatosis type I tumor suppressor neurofibromin regulates neuronal differentiation via its GTPase-activating protein function toward Ras.

Neurofibromin, the neurofibromatosis type 1 (NF1) gene product, contains a central domain homologous to a family of proteins known as Ras-GTPase-activating proteins (Ras-GAPs), which function as negative regulators of Ras. The loss of neurofibromin function has been thought to be implicated in the abnormal regulation of Ras in NF1-related pathogenesis. In this study, we found a novel role of neurofibromin in neuronal differentiation in conjunction with the regulation of Ras activity via its GAP-related domain (GRD) in neuronal cells. In PC12 cells, time-dependent increases in the GAP activity of cellular neurofibromin (NF1-GAP) were detected after NGF stimulation, which were correlated with the down-regulation of Ras activity during neurite elongation. Interestingly, the NF1-GAP increase was due to the induction of alternative splicing of NF1-GRD type I triggered by the NGF-induced Ras activation. Dominant-negative (DN) forms of NF1-GRD type I significantly inhibited the neurite extension of PC12 cells via regulation of the Ras state. NF1-GRD-DN also reduced axonal and dendritic branching/extension of rat embryonic hippocampal neurons. These results demonstrate that the mutual regulation of Ras and NF1-GAP is essential for normal neuronal differentiation and that abnormal regulation in neuronal cells may be implicated in NF1-related learning and memory disturbance.

Alternative Splicing↗
PubMed2003

An extremely facile aza-Bergman rearrangement of sterically unencumbered acyclic 3-aza-3-ene-1,5-diynes.

The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkynyl imines) have not previously been elucidated. Here we report our kinetic studies of the aza-Bergman reactions of a series of 6-triisopropylsilyl and 6-unsubstituted 1-phenyl-4-aryl-3-aza-3-ene-1,4-diynes in which the aryl group is phenyl, o-(methoxy)phenyl, or p-(methoxy)phenyl. These aza-enediynes are prepared as single isomers in modest yield from the corresponding 1-aryl-3-(triisopropylsilyl)propynone oximes. These aza-enediynes undergo aza-Bergman reaction followed by a rapid retro-aza-Bergman cyclization to afford beta-alkynyl acrylonitrile products. In no case are products corresponding to trapping the intermediate 2,5-didehydropyridine diradical isolated. While the rate of aza-Bergman cyclization is not greatly affected by the nature of the 4-aryl substituent, the rate is very dependent on the nature of the 6-substituent. 1-Phenyl-4-aryl-3-aza-3-ene-1,5-diynes that lack a 6-substituent undergo aza-Bergman cyclization spontaneously at 20 degrees C with first-order half-lives of 36-78 min. The effect of solvent on the kinetics of aza-Bergman cyclization of 1,4-diphenyl-3-aza-3-ene-1,5-diyne was investigated. The rate of this cyclization is solvent dependent, proceeding more rapidly in less polar solvents.

Journal Article↗
PubMed2003

Ex vivo evaluation of a novel polyiodinated compound for early detection of atherosclerosis.

Atherosclerosis is a primary cause of heart disease and stroke; it is the underlying cause of about 50% of all deaths in Western countries. It is known that early detection of atherosclerotic lesions would significantly reduce the risk of mortality. The objective of this study was to develop a radioimaging method for early detection of atherosclerotic plaques. A novel polyiodinated cholesterol analog, cholesteryl 1,3-diiopanoate glyceryl ether (C2I, patent pending), was synthesized and radiolabeled with 125I. 125I-C2I was incorporated into acetylated low-density lipoprotein (AcLDL), which is considered to be an atherosclerotic plaque-seeking carrier. 125I-C2I was also prepared as a chylomicron-like emulsion. Transgenic mice deficient in apoE and low-density lipoprotein receptors (LDLR), known as apoE/LDLR double knockout, were used as an animal model of early atherosclerosis. 125I-C2I/AcLDL or 125I-C2I emulsion was injected into the apoE/LDLR knockout mice via the tail vein, and the mice were killed humanely 24 h after injection. Various tissues including aorta were removed and radioactivity was determined. The aorta samples were also imaged to determine the accumulation of radioactivity from C2I. The images were compared to the atherosclerotic lesions revealed by histological studies. It was found that both 125I-C2I/AcLDL and 125I-C2I emulsion resulted in accumulation of radioactivity at the site of early atherosclerotic lesions, and they therefore may be useful for early detection of atherosclerosis.

Animals↗
PubMed2003

Acetylated low-density lipoprotein-encapsulated cholesteryl 1,3-diiopanoate glyceryl ether for the detection of atherosclerosis in rabbits.

UNLABELLED: A cholesteryl ester analog, cholesteryl 1,3-diiopanoate glyceryl ether (C2I), was synthesized and investigated for its potential use for the detection of atherosclerotic lesions in rabbits. METHODS: (125)I-labeled C2I was incorporated into acetylated low-density lipoprotein (AcLDL). The resultant complex, (125)I-C2I-AcLDL, was injected intravenously into 2 groups of rabbits, fed cholesterol and normal chow, at a dose of 555 kBq/kg. Tissue samples were taken 24 h after injection for the biodistribution study. Atherosclerotic lesions and C2I deposition in aortic samples were examined by Sudan IV staining and autoradiography, respectively. RESULTS: The levels of C2I in blood and aortic samples in cholesterol-fed animals were 2- to 3-fold higher than those in the control group (P < 0.05). The autoradiography results correlated well with the Sudan IV staining results, indicating sites of C2I deposition superimposed on lesion sites. CONCLUSION: C2I was preferentially taken up and retained at atherosclerotic lesion sites, suggesting its potential use for the detection of early atherosclerosis.

Animals↗
PubMed2002

[Serological investigations on patients with hemolytic uremic syndromes due to enterohemorrhagic Escherichia coli O157:H7 infection].

OBJECTIVE: To investigate the etiological agent of patients with diarrhea followed by acute kidney failure symptoms in China, 1999. METHODS: Western blot was used to detect serum specific antibodies of patients against entero-haemorrhagic Escherichia coli hemolysin (EHEC-Hly) and lipo-polysaccharide of E. coli O157. RESULTS: Twenty-one and 16 of 42 patients showed positive reaction of specific IgG or IgM antibodies against EHEC-Hly respectively. Eleven of 42 serum samples were positive for having both IgG and IgM antibodies while 26 of 42 samples were positive for IgG or IgM. For E. coli O157 LPS test, 24 and 24 of 42 samples showed positive for IgG or IgM antibodies respectively. In 42 samples, 20 were positive for IgG and IgM while 29 were positive for IgG or IgM. CONCLUSIONS: Twenty-two of 42 samples were reacted with EHEC-Hly and E. coli O157 LPS, but 34 of 42 samples were positive for EHEC-Hly or E. coli O157. In combination of western blot results, bacterial isolation clinical symptoms and epidemiological investigation findings, it was reasonable to conclude that this cluster of patients with distinguish clinical symptoms was caused by E. coli O157:H7, which had never been reported in China. Hence serological methods with EHEC-Hly and E. coli O157 LPS are valuable for diagnosis of infections of E. coli O157:H7, when bacterial isolation is failed.

Adult↗