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N Liu

Publications and source records attributed to N Liu.

At least 199 records · Page 11Linked to original sources
PubMed1996

An integrated computational model of three-dimensional vision.

This article presents the details of and background for a computational model of three-dimensional vision. The basic idea embodied in this model is that a veridical approximation to a three-dimensional scene can best be produced by combining several operators that act on acquired two-dimensional images to reconstruct surface shape and distance. Stereo, shape from shading (SFS), and shape from structured light (SFSL) operators are combined to produce a reconstruction that is superior to any that might be produced by one alone. The advantages and disadvantages of each independent operator and the generic difficulties faced by members of this class of operators are discussed. Collectively, this package of combined algorithms represents a functional model of human spatial vision.

Algorithms↗
PubMed1996

[The disturbance of calcium homeostasis in vascular smooth muscle proliferation after balloon denudation].

OBJECTIVE: To investigate the changes of calcium homeostasis in smooth muscle cells (VSMC) and the role of disturbance of calcium homeostasis in VSMC proliferation after balloon denudation. METHODS: Assay of the cellular incorporation of 3H-leucine and measurement of 45Ca transport were done on the model of balloon-denuded aorta in rat. RESULTS: Endothelial injury induced VSMC proliferation, intimal thickening. After balloon denudation, VSMC calcium influx increased (3 days after balloon denudation, 3.28 +/- 0.14 vs 4.12 +/- 0.28, P < 0.05; 10 days 3.31 +/- 0.09 vs 4.09 +/- 0.21 nmol/10(6) cells, P < 0.01), and calcium efflux decreased, and calcium content increased (3 days after balloon denudation 695 +/- 33 vs 995 +/- 54, P < 0.01; 10 days 709 +/- 32 vs 1022 +/- 94 nmol/10(6) cell, P < 0.01). SR and mitochondria calcium uptake increased. Calcium antagonist, verapamil not only regulated the disturbance of calcium homeostasis, but also inhibited endothelium injury-induced VSMC proliferation. CONCLUSION: The disturbance of calcium homeostasis is probably one of the underlying mechanisms of VSMC proliferation induced by balloon denudation.

Animals↗
PubMed1996

Isolation and identification of metabolites of leukotriene A4 hydrolase inhibitor SC-57461 in rats.

The metabolic fate of SC-57461, N-methyl-N-[3-[4-(phenylmethyl)-phenoxy]propyl]-beta-alanine, a potent and specific inhibitor of the leukotriene A4 hydrolase, was determined by LC/MS/MS, NMR and GC/MS in male Sprague-Dawley rats. The major metabolites of SC-57461 in rats were the desmethyl metabolite, the hydroxylated metabolite, the N-oxide metabolite, the hydroxylamine metabolite, and the propionic acid metabolite. The N-oxide metabolite was found to be stable in the rat plasma and urine, but was unstable in most organic solvents (methanol, acetonitrile, and methylene chloride, etc.) because of the classic Cope reaction of the N-oxide, which led to the formation of the corresponding hydroxylamine product and acrylic acid. The hydroxylamine metabolite and acrylic acid were reactive in the biomatrix and could not be isolated in the in vivo samples. However, formation of the hydroxylamine metabolite and acrylic acid from the N-oxide metabolite in methylene chloride was verified by NMR. The propionic acid metabolite was found to be the common metabolite shared by SC-57461, N-oxide metabolite, as well as the hydroxylamine metabolite, which suggested a sequential metabolism of SC-57461 in rats. The ultimate fate of the propionic acid metabolite was incorporation into rat glycerolipid metabolism as a result of its structural similarity to aryl-substituted propionic acid, a known class of compounds that can be incorporated into rat glycerolipid metabolism. Finally, the isolated hydroxylated metabolite and the N-desmethyl metabolite were found to have excellent inhibitory effects toward leukotriene A4 hydrolase and therefore were the major active metabolites of SC-57461 in rats.

Administration, Oral↗
PubMed1995

Binding of Neu differentiation factor with the extracellular domain of Her2 and Her3.

The interaction of neu differentiation factor (NDF) with the extracellular domains of Her2 (sHer2) and Her3 (sHer3) have been studied using native gels, light scattering, and sedimentation equilibrium. The full-length NDF beta 2 was shown to bind sHer3 with a dissociation constant of 26 +/- 9 nM, while it showed a 1000-fold weaker binding to sHer2. Taken together, these results demonstrate that NDF is a high affinity ligand for Her3, but not for Her2. No increase in affinity of the NDF beta 2 for sHer3 was observed upon addition of sHer2 to the NDF beta 2-sHer3 mixture. Binding of NDF beta 2 to sHer3 did not induce receptor dimerization or oligomerization, the stoichiometry being one sHer3 per one NDF molecule. This finding suggests that transmembrane and/or intracellular domains of receptor family members or perhaps additional unidentified components may be involved in NDF induced dimerization and autophosphorylation, or alternatively, that dimerization is not the mechanism for Her3 autophosphorylation and signal transduction.

Animals↗
PubMed1995

Presence of an additional PstI fragment in intron 1 of the chicken growth hormone-encoding gene.

A previously unreported 196-bp PstI fragment was found in intron 1 of the gene encoding chicken growth hormone (cGH) when a PCR assay for an MspI restriction fragment length polymorphism was established. A pair of PCR primers was designed according to the published cGH sequence and used to amplify a fragment which contained two MspI sites, one polymorphic and another non-polymorphic. However, amplification of genomic DNA from two strains of meat-type chickens and three strains of White Leghorn chickens yielded a PCR product which was about 200 bp larger than expected. The fragment from one of the meat-type chickens was subcloned into the vector pCR-Script SK+, and sequenced. It revealed the presence of an extra fragment of 196 bp which was flanked by the PstI sites and occurred at nt +308 of the previously reported cGH sequence.

Animals↗
PubMed1995

Correction of chromosomal instability and sensitivity to diverse mutagens by a cloned cDNA of the XRCC3 DNA repair gene.

The mutagen-sensitive CHO line irs1SF was previously isolated on the basis of hypersensitivity to ionizing radiation and was found to be chromosomally unstable as well as cross-sensitive to diverse kinds of DNA-damaging agents. The analysis of somatic cell hybrids formed between irs1SF and human lymphocytes implicated a human gene (defined as XRCC3; x-ray repair cross-complementing), which partially restored mitomycin C resistance to the mutant. A functional cDNA that confers mitomycin C resistance was transferred to irs1SF cells by transforming them with an expression cDNA library and obtaining primary and secondary transformants. Functional cDNA clones were recovered from a cosmid library prepared from a secondary transformant. Transformants also showed partial correction of sensitivity to cisplatin and gamma-rays, efficient correction of chromosomal instability, and substantially improved plating efficiency and growth rate. The XRCC3 cDNA insert is approximately 2.5 kb and detects an approximately 3.0-kb mRNA on Northern blots. The cDNA was mapped by fluorescence in situ hybridization to human chromosome 14q32.3, which was consistent with the chromosome concordance data of two independent hybrid clone panels.

Animals↗
PubMed1995

Neu differentiation factor inhibits EGF binding. A model for trans-regulation within the ErbB family of receptor tyrosine kinases.

Neu differentiation factor (NDF, or heregulin) and epidermal growth factor (EGF) are structurally related proteins that bind to distinct members of the ErbB family of receptor tyrosine kinases. Here we show that NDF inhibits EGF binding in a cell type-specific manner. The inhibitory effect is distinct from previously characterized mechanisms that involve protein kinase C and receptor internalization because it occurred at 4 degrees C and displayed reversibility. The extent of inhibition correlated with both receptor saturation and affinity of different NDF isoforms, and it was abolished upon overexpression of either EGF receptor or ErbB-2. Binding kinetics and equilibrium analyses indicated that NDF reduced the affinity, rather than the number, of EGF receptors, through an acceleration of the rate of ligand dissociation and deceleration of the association rate. On the basis of co-immunoprecipitation of EGF and NDF receptors, we attribute the inhibitory effect to the formation of receptor heterodimers. According to this model, EGF binding to NDF-occupied heterodimers is partially blocked. This model of negative trans-regulation within the ErbB family is relevant to other subgroups of receptor tyrosine kinases and may have physiological implications.

Breast Neoplasms↗
PubMed1995

ErbB-3 mediates differential mitogenic effects of NDF/heregulin isoforms on mouse keratinocytes.

The family of Neu differentiation factors (NDFs, or heregulins) includes a dozen secreted glycoproteins, whose receptor binding domain displays two variants, alpha and beta, and they bind to two receptor tyrosine kinases, ErbB-3 and ErbB-4. Certain isoforms were reported to induce growth-arrest and differentiation of mammary tumor cells, while other breast cancer cell lines responded mitogenically. The present study addressed the biologic effects of various NDF isoforms on normal EGF-dependent epithelial cells, Balb/MK keratinocytes, that can undergo either proliferation or differentiation. We found that beta isoforms of NDF induced a mitogenic effect, that was significantly smaller than the maximal response to EGF. By contrast with NDF-beta, NDF-alpha isoforms exerted almost no mitogenic effect, but they were sufficient to maintain keratinocytes in culture. Consistent with their higher mitogenic potency, NDF-beta isoforms bound to Balb/MK cells with higher affinity (Kd = 2.2 nM) than alpha isoforms, however both groups shared their receptor, that we identified as ErbB-3. No transcript of ErbB-4 was detectable in the keratinocytes, but these cells express multiple NDF mRNAs and also ErbB-2. We conclude that different isoforms of NDF induce distinct growth regulatory effects on cultured keratinocytes, through direct interaction with ErbB-3.

Animals↗
PubMed1995

Studies on the structure and function of glycosylated and nonglycosylated neu differentiation factors. Similarities and differences of the alpha and beta isoforms.

Comparative analyses of both glycosylated and nonglycosylated neu differentiation factor (NDF) isoforms revealed significant similarities and differences of their overall structures and functions. Biophysical analyses confirmed that all NDF isoforms are monomeric, but have an extended ellipsoidal shape in solution. All full-length NDFs are similar in secondary and tertiary structures and they contain no alpha-helix but are abundant in beta-strand structures. A small NDF fragment containing only the epidermal growth factor domain is also rich in beta-strand structures, but exhibits tertiary structure different from the long NDF forms. Monoclonal antibodies that selectively recognize epidermal growth factor domains of human NDF-alpha and -beta can specifically bind the respective NDF-alpha and -beta isoforms independent of NDF origins. Western blot analysis and quantitative binding assays further identify that an NDF preparation produced naturally from Rat1-EJ cells contains both alpha and beta isoforms in a 3 to 2 ratio. In receptor-binding competition experiments, human and rat NDF-beta isoforms have higher affinity than NDF-alpha isoforms. NDF-beta isoforms can dramatically enhance the stimulation of DNA synthesis for transfected NIH3T3 cells that overexpress HER-3 and HER-4 receptors, while NDF-alpha isoforms can only stimulate proliferation of HER-4-transfected cells with lower activity. Taken together, NDF-alpha and -beta isoforms share similar gross protein conformations but are biologically distinct.

3T3 Cells↗
PubMed1995

Allele-specific PCR reveals that CYP6D1 is on chromosome 1 in the house fly, Musca domestica.

A cytochrome P450, termed P450lpr, is the major P450 responsible for pyrethroid resistance in the Learn-PyR (LPR) strain of house fly. Recently, the putative gene (CYP6D1) coding for P450lpr has been sequenced from the LPR and aabys strains of house fly. Allele-specific polymerase chain reaction (ASPCR) was used for linkage group analysis with backcross progeny from the wild type LPR strain and a multiple marker strain (aabys). We found that CYP6D1 is linked to chromosome 1. The possible role of regulatory or modifying genes responsible for elevated P450lpr expression is discussed in relation to the chromosomal linkage of CYP6D1.

Alleles↗
PubMed1995

High-level expression of prochymosin in Escherichia coli: effect of the secondary structure of the ribosome binding site.

Regulation of the expression of prochymosin cDNA in Escherichia coli at the translational level was studied by mutating the regions between the Shine-Dalgarno (SD) sequence and the initiation codon and upstream of the SD signal. Results revealed that expression plasmids with a distance of 7-10 bp from SD to ATG have the potential to be expressed at higher levels. However, an approximately 20-fold variation in expression was observed with plasmids harboring different base composition but identical distance in the spacer. Analysis of the predicted secondary structure of ribosome binding sites (RBS) indicates that the control of expression by base composition is mediated by the secondary structure of the RBS. An unfolded state of the RBS is required for high expression. Therefore, a vector for enhanced translation can be designed and constructed via prediction of the secondary structure of the proposed RBS and mutagenesis. Based on this strategy, high-level expression of prochymosin, up to 39% of the total cellular proteins, was achieved. The 9-base sequence proposed by Olins and Rangwala as a translational enhancer did not exhibit an additive effect on prochymosin expression. This is probably because the affinity of the SD sequence used in this study to 16S rRNA is strong enough that no additional element is required to facilitate the formation of the translation initiation complex.

Base Sequence↗
PubMed1995

Onset of expression of the alpha subunit of Ca2+/calmodulin-dependent protein kinase II and a novel related protein in the developing retina.

Calcium-calmodulin-dependent protein kinase II is an abundant protein in the nervous system and has been associated with many aspects of neuronal function, including events related to synaptic transmission. The purpose of this study is to correlate the onset of expression of this kinase with a specific developmental event in retinal morphogenesis using a monoclonal antibody to the 50-kDa alpha-subunit. Microscopy showed the antigen to be associated with the plexiform layers of the retina. Western blots demonstrated that the onset of expression of the alpha-subunit coincided in time with the initial formation of the plexiform layers. However, the onset of expression of the 50-kDa alpha-subunit was preceded by the earlier embryonic appearance of a related 82.5-kDa antigen that was recognized by the antibody. The amount of this latter protein declined as the amount of the alpha-subunit increased in retinal homogenates. Although this related 82.5 kDa protein disappeared from blots of retinal homogenates after embryonic d 14, it could be detected in concentrated supernatant fractions isolated from the retinae of hatched chicks. Microscopy showed that a subset of retinal cells and their processes contained this antigen in early embryonic chicks. Finally, the 50 kDa alpha-subunit of kinase II and the 82.5 kDa novel antigen were shown to be separable by differential centrifugation.

Animals↗
PubMed1995

Neu differentiation factor is a neuron-glia signal and regulates survival, proliferation, and maturation of rat Schwann cell precursors.

We show that beta forms of Neu differentiation factor (NDF), homologous to acetylcholine receptor-inducing activity, glial growth factor, and heregulin, prevent apoptotic death and stimulate DNA synthesis of the E14 Schwann cell precursor, an early cell in the rat Schwann cell lineage. When precursors are exposed to NDF in defined medium, they generate Schwann cells without the requirement for DNA synthesis and with a time course that is similar to that with which Schwann cells appear in embryonic nerves in vivo. Furthermore, a neuronal signal that also mediates precursor survival and maturation is blocked by the extracellular domain of the ErbB4 NDF receptor, a protein that specifically blocks the action of NDFs. These observations provide important evidence that NDF is one of the hitherto elusive neuron-glia signaling molecules long proposed to regulate development in the Schwann cell lineage.

Animals↗
PubMed1995

Thrombocytopenia with absent radii (TAR) syndrome: a new increased cellular radiosensitivity syndrome.

A 70-year-old woman with congenital absence of both radii but preservation of the thumb developed a marked pancytopenia after two i.v. injections of 1 g of 5-fluorouracil (5-FU) 1 week apart. She developed bloody diarrhoea after nine fractions of 2 Gy to parallel opposed 16 x 15 cm abdominal fields. This unusual response prompted an investigation of the radiosensitivity of the patient's cells by the sensitive G2 assay of transformed lymphocytes. The radiosensitivity of the patient's lymphoblastoid line appeared to be intermediate between that of normal individuals and an ataxia telangiectasia line. The clinical response and in vitro radiosensitivity testing suggest that the thrombocytopenia with absent radii (TAR) syndrome appears to be one of the inherited impaired DNA repair syndromes and is a very newly described radiation sensitivity syndrome. The development of three separate primary cancers in this patient (small bowel, ovary and bladder) suggests there is an increased risk of neoplasia in this condition.

Aged↗
PubMed1995

Systematic transesophageal echocardiography for detection of mediastinal lesions in patients with multiple injuries.

A prospective study assessing the interest in and the results of systematic transesophageal echocardiography (TEE) examination in nonselected intubated multiple injury patients was carried out from January 1992 through June 1993. Seventy patients were included and divided into two groups according to the results of admission screening, including clinical examination, EKG, CK-MB and chest radiograph. Group 1 (60 patients) had abnormalities on initial screening, while group 2 (10 patients) had no symptom of thoracic or mediastinal injury. TEE was performed within 48 hours following admission and its results were compared with those of the initial screening. TEE usefulness was evaluated on a score grade from 0 (no interest) to 4 (outstanding interest). Myocardial contusion was suspected in 25 patients. TEE invalidated 18 suspected and found 5 unsuspected myocardial contusions. Pericardial effusion was suspected in only one case, while TEE documented 13 additional cases. A mediastinal enlargement was seen in 13 patients, but TEE invalidated aortic lesions in all these cases and made an unsuspected diagnosis of aortic tears. Eight cases of severe hypovolemia and seven cases of left ventricle dysfunction were detected by TEE. The score of interest showed that TEE allowed new interesting diagnoses in 70% of group I patients and in 33% of group II patients. TEE is of utmost importance in multiple injury patients, with or without any evidence of thoracic or mediastinal injury, providing a safe and rapid examination of the mediastinal structures and an evaluation of the hemodynamic status.

Adult↗
PubMed1995

Molecular mechanisms involved in increased expression of a cytochrome P450 responsible for pyrethroid resistance in the housefly, Musca domestica.

Cytochrome P450 Ipr is a developmentally regulated P450 responsible for monooxygenase-mediated pyrethroid resistance in the LPR strain of housefly. CYP6D1, the gene coding for P450 Ipr, has recently been sequenced. We investigated the molecular basis for CYP6D1-mediated pyrethroid resistance by comparison of mRNA levels, gene sequences, and gene copy number between LPR and pyrethroid susceptible strains of housefly. CYP6D1 mRNA levels were elevated in the LPR strain to a similar level as P450 Ipr protein, suggesting that over-expression of this important P450 in the resistant strain is probably due to increased transcription. Southern blots of susceptible and LPR strain DNA suggest that gene amplification is probably not involved in the increased expression of CYP6D1 protein. Five alleles of CYP6D1 were discovered and their possible role in resistance is discussed.

Amino Acid Sequence↗
PubMed1995

Neu differentiation factor upregulates epidermal migration and integrin expression in excisional wounds.

Neu differentiation factor (NDF) is a 44-kD glycoprotein which was isolated from ras-transformed rat fibroblasts and indirectly induces tyrosine phosphorylation of the HER-2/neu receptor via binding to either the HER-3 or HER-4 receptor. NDF contains a receptor binding epidermal growth factor (EGF)-like domain and is a member of the EGF family. There are multiple different isoforms of NDF which arise by alternative splicing of a single gene. To date, in vivo biologic activities have not been demonstrated for any NDF isoform. Since NDF, HER-2/neu, and HER-3 are present in skin, and other EGF family members can influence wound keratinocytes in vivo, we investigated whether NDF would stimulate epidermal migration and proliferation in a rabbit ear model of excisional wound repair. In this model, recombinant human NDF-alpha 2 (rhNDF-alpha 2), applied once at the time of wounding, induced a highly significant increase in both epidermal migration and epidermal thickness at doses ranging from 4 to 40 micrograms/cm2. In contrast, rhNDF-alpha 1, rhNDF-beta 1, and rhNDF-beta 2 had no apparent biologic effects in this model. rhNDF-alpha 2 also induced increased neoepidermal expression of alpha 5 and alpha 6 integrins, two of the earliest integrins to appear during epidermal migration. In addition, rhNDF-alpha 2-treated wounds exhibited increased neoepidermal expression of cytokeratin 10 and filaggrin, both epidermal differentiation markers. NDF alpha isoforms were expressed in dermal fibroblasts of wounded and unwounded skin, while both HER-2/neu and HER-3 were expressed in unwounded epidermis and dermal adnexa. In wounds, HER-2/neu expression was markedly decreased in the wound neoepidermis while neoepidermal HER-3 expression was markedly upregulated. Taken together, these results suggest that endogenous NDF-alpha 2 may function as a paracrine mediator directing initial epidermal migration during cutaneous tissue repair.

Animals↗