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Biomedical subjects

D Li

Publications and source records attributed to D Li.

At least 667 records · Page 37Linked to original sources
PubMed1995

Role of aromatic residues in stabilization of the [Fe4S4] cluster in high-potential iron proteins (HiPIPs): physical characterization and stability studies of Tyr-19 mutants of Chromatium vinosum HiPIP.

The functional role of residue Tyr-19 of Chromatium vinosum HiPIP has been evaluated by site-directed mutagenesis experiments. The stability of the [Fe4S4] cluster prosthetic center is sensitive to side-chain replacements. Polar residues result in significant instability, while nonpolar residues (especially with aromatic side chains) maintain cluster stability. Two-dimensional NMR data of native and mutant HiPIPs are consistent with a model where Tyr-19 serves to preserve the structural rigidity of the polypeptide backbone, thereby maintaining a hydrophobic barrier for exclusion of water from the cluster cavity. Solvent accessibility results in more facile oxidation of the cluster by atmospheric oxygen, with subsequent rapid hydrolysis of the [Fe4S4]3+ core.

Aerobiosis↗
PubMed1995

Codeletion of p15 and p16 in primary malignant mesothelioma.

The p15 and p16 CDK4 inhibitor genes map within the chromosome band 9p21 region deleted frequently in malignant mesothelioma and other cancers. p16 has been implicated recently as a potential target of 9p21 deletions in mesothelioma, but the role of this gene is uncertain because deletions have been detected more often in established cell lines than in primary tumor specimens. We determined p15 and p16 copy number by fluorescence in situ hybridization with a P1 contig in 50 primary mesotheliomas. Codeletion of p15 and p16 was found in 72% of mesotheliomas, including all cases with spindle-cell components (n = 21) and total deletion of p15 and p16 was found in several mesotheliomas that lacked cytogenetic deletion of the chromosome 9 short arm. Point mutations were not found, however, in exon 2 of retained p15 and p16 alleles from seven mesotheliomas. These findings demonstrate that p15, p16 and/or a closely neighboring gene, are the targets of frequent chromosome 9p deletion in primary malignant mesothelioma.

Base Sequence↗
PubMed1995

Usefulness of dobutamine stress echocardiography for the prospective identification of the physiologic significance of coronary narrowings of moderate severity in patients undergoing evaluation for percutaneous transluminal coronary angioplasty.

Dobutamine stress echocardiography (DSE) was performed after coronary angiography to evaluate the need to perform percutaneous transluminal coronary angioplasty (PTCA) for 46 stenoses of moderate severity (50% to 80%) in 46 patients. Patients were divided into 2 groups according to the DSE results in the distribution of the coronary artery with the lesion of moderate severity: group I (n = 32) were those without inducible myocardial ischemia; PTCA was not performed. Group II (n = 14) were those who exhibited myocardial ischemia; PTCA was performed in 12. The 2 groups were comparable in terms of clinical characteristics. Follow-up DSE was performed < or = 48 hours after PTCA, at 3 months, and 6 to 12 months after the first DSE. In group I at 3 months, DSE results were still negative in the distribution of the vessel with the moderately severe lesion in 24 patients; only 1 patient had a positive result, and 8 patients who refused DSE remained clinically stable. At 6 to 12 months (mean 7 +/- 2), 26 patients had negative study results; 3 patients who refused follow-up DSE remained clinically stable. In group II, 12 of 14 patients with inducible ischemia on the initial DSE underwent PTCA. Early follow-up DSE (< or = 48 hours) was negative in 7, and 4 had persistent inducible wall motion abnormalities in the myocardium subtended by the coronary artery in which the PTCA had been performed; 1 study was not performed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Transient acquired thermotolerance in Drosophila, correlated with rapid degradation of Hsp70 during recovery.

Acquired thermotolerance, measured either as increased cell viability following a lethal heat shock or by translational thermotolerance, appears rapidly following a 'priming' heat treatment, but also decays rapidly. 4 hours after priming heating thermotolerance is reduced by > 50% and by 9 hours it is virtually undetectable. Heat-shock protein 70 (Hsp70) turns over with a half-life of approximately 2 hours, and the decline in its intracellular abundance parallels the loss of acquired thermotolerance. Continuous heat shock extends the half-life of Hsp70 to approximately 7 hours. When Hsp70 is expressed at normal temperature using a metallothionein promoter, only partial acquired translational thermotolerance results. The results suggest that acquired thermotolerance is tightly regulated in Drosophila and partly, but not wholly, determined by post-translational regulation of Hsp70 levels.

Adaptation, Physiological↗
PubMed1995

Codeletion of p15 and p16 genes in primary non-small cell lung carcinoma.

Chromosome band 9p21 is deleted frequently in non-small cell lung carcinoma (NSCLC), and the p15 and p16 cyclin-dependent kinase-4 inhibitor genes map within this deletion region. Recent studies demonstrated deletion of p15 and p16 in NSCLC metastases and cell lines, suggesting a role for these genes in NSCLC progression. We now report p15 and p16 copy number, as determined by fluorescence in situ hybridization with a P1 contig, in 18 primary NSCLCs. Codeletion of p15 and p16 was found in 15 of 18 NSCLCs, and 1 of the 3 tumors with normal p15 and p16 copy number had a nonsense mutation in exon 2 of p16. We conclude that p15 and p16 are deleted and/or mutated in most primary NSCLCs. Two observations, however, support the involvement of at least one additional tumor suppressor gene on chromosome 9. These observations are: (a) the large size (> 100 kb) of most NSCLC p15/p16 deletions; and (b) the absence of exon 2 mutations in most retained NSCLC p15 and p16 alleles.

Adult↗
PubMed1995

Cloning and sequencing of CATR1.3, a human gene associated with tumorigenic conversion.

The human squamous cell carcinoma cell line SCC83-01-82 (SCC) contains mutations in both the H-ras and p53 genes, but it exhibits a nontumorigenic phenotype in nude mice. This cell line can be converted into a cell line with a tumorigenic phenotype, SCC83-01-82CA (CA), by treatment with the mutagen methyl methanesulfonate (MMS). This indicates that additional genetic events leading to expression of a cooperating tumor susceptibility gene(s) may be required for tumorigenicity. To identify the cooperating gene(s), an expression cDNA library was made from tumorigenic Ca cells. The library DNA was transfected into nontumorigenic SCC cells and the transfected SCC cells were then injected into nude mice for the selection of a tumorigenic phenotype. Tumors developed in 3 of the 18 mice after injection. Several new cell lines were established from these transfected cell-induced tumors and designated as CATR cells. Tumor histology and karyotype analysis of these cells indicated that they were of human epithelial cell origin. All the CATR cells have the library vector sequence integrated in their genome. Cell line CATR1 expressed a single message from the integrated library representing a 1.3-kb cDNA insert that was absent from untransfected SCC cells or MMS-converted CA cells. This 1.3-kb cDNA insert was cloned by PCR amplification of reverse-transcribed CATR1 total RNA and was designated CATR1.3. The nucleotide sequence of CATR1.3 encodes a peptide of 79 amino acids, has a long 3' untranslated region, and represents an unknown gene product that was associated with the tumorigenic conversion due to the transfected expression library.

Amino Acid Sequence↗
PubMed1995

Enhancement of Agkistrodon piscivorus piscivorus venom phospholipase A2 activity toward phosphatidylcholine vesicles by lysolecithin and palmitic acid: studies with fluorescent probes of membrane structure.

The activity of phospholipase A2 from snake venom to hydrolyze bilayers of phosphatidylcholines is greatly enhanced by the presence of the hydrolysis products, lysolecithin and fatty acid, in the bilayer. The fluorescence of several probes of membrane structure was used to monitor changes in bilayer physical properties during vesicle hydrolysis. These changes were compared to emission spectra and fluorescence polarization results occurring upon direct addition of lysolecithin and/or fatty acid to the bilayer. The excimer to monomer ratio of 1,3-bis(1-pyrene)propane was insensitive to vesicle hydrolysis, suggesting that changes in the order of the phospholipid chains were not relevant to the effect of the hydrolysis products on phospholipase activity. The fluorescence of 6-propionyl-2-(dimethylamino)-naphthalene (Prodan) suggested that the polarity of the bilayer in the region of the phospholipid head groups increases as the hydrolysis products accumulate in the bilayer. The fluorescence of 6-dodecanoyl-2-(dimethylamino)naphthalene (Laurdan) confirmed that such effects were restricted to the bilayer surface. Furthermore, the lysolecithin appeared to be the product most responsible for these changes. These results suggested that lysolecithin increases the activity of phospholipase A2 during vesicle hydrolysis by disrupting the bilayer surface, making the phospholipid molecules more accessible to the enzyme active site.

2-Naphthylamine↗
PubMed1995

Failure of axon regeneration in postnatal rat entorhinohippocampal slice coculture is due to maturation of the axon, not that of the pathway or target.

Horizontal slices which included the entorhinal area in continuity with the hippocampus were taken from the ventral levels of the cerebral hemispheres of rat pups from two age groups, from the 6th to the 8th postnatal days ('young') and the 12th to the 15th days ('old'). The slices were divided into an entorhinal part and a hippocampal part (which consisted of the hippocampus proper, dentate gyrus and subiculum) by a knife cut passing through the deep white matter of the entorhinal area. The slices were recombined in their normal orientation by matching the cut edges in the following age combinations: young/young, old/old, young/old and old/young. After 14 days in culture, crystals of biocytin were placed on the superficial layers of the entorhinal area. In the young/young combination the same placement of biocytin simultaneously labelled projections passing in both directions across the interface, i.e. (i) orthograde transport of biocytin taken up by entorhinal projection neurons resulted in labelling of axons passing from the entorhinal area across the interface between the cocultures to reach the correct terminal zone in the outer molecular layer of the dentate gyrus, and (ii) retrograde transport of biocytin taken up by axons and their terminals in the entorhinal area labelled the slender subicular and adjacent hippocampal field CA1 pyramidal cells whose axons project to the entorhinal area. In the old/old cocultures there were no projections in either direction. In the mixed age combinations, young entorhinal cortical tissue projected correctly across the interface to old dentate gyrus, but old entorhinal tissue did not project to young dentate gyrus.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1995

Cloning and expression of cDNA encoding a protein that binds a palindromic promoter element essential for induction of fungal cutinase by plant cutin.

Previous studies showed that a palindromic sequence located at -159 base pairs is essential for induction of cutinase gene in Fusarium solani f. sp. pisi (Nectria haematococca mating type VI) by the hydroxy fatty acids from plant cutin and that a 50-kDa nuclear protein binds to a promoter that contains this element. Screening of a phage lambda gt11 expression library with the concatenated palindromic sequence as the probe identified a cDNA encoding a palindrome-binding protein (PBP). Nucleotide sequence of this cDNA revealed an open reading frame that would code for PBP with a calculated molecular weight of 49,847. This PBP contains a putative nuclear localization signal and a zinc finger motif sharing homology with the zinc finger DNA binding domains of transcription factors from mammals, Saccharomyces cerevisiae, Neurospora crassa, and Ustilago maydis. A highly basic region immediately adjacent to the carboxyl side of the zinc finger was also observed. PBP expressed in Escherichia coli showed specific binding to the palindromic DNA fragment.

Activating Transcription Factor 2↗
PubMed1995

Surface signaling in pathogenesis.

Surface signaling plays a major role in fungal infection. Topographical features of the plant surface and chemicals on the surface can trigger germination of fungal spores and differentiation of the germ tubes into appressoria. Ethylene, the fruit-ripening hormone, triggers germination of conidia, branching of hyphae, and multiple appressoria formation in Colletotrichum, thus allowing fungi to time their infection to coincide with ripening of the host. Genes uniquely expressed during appressoria formation induced by topography and surface chemicals have been isolated. Disruption of some of them has been shown to decrease virulence on the hosts. Penetration of the cuticle by the fungus is assisted by fungal cutinase secreted at the penetration structure of the fungus. Disruption of cutinase gene in Fusarium solani pisi drastically decreased its virulence. Small amounts of cutinase carried by spores of virulent pathogens, upon contact with plant surface, release small amounts of cutin monomers that trigger cutinase gene expression. The promoter elements involved in this process in F. solani pisi were identified, and transcription factors that bind these elements were cloned. One of them, cutinase transcription factor 1, expressed in Escherichia coli, is phosphorylated. Several protein kinases from F. solani pisi were cloned. The kinase involved in phosphorylation of specific transcription factors and the precise role of phosphorylation in regulating cutinase gene transcription remain to be elucidated.

Amino Acid Sequence↗
PubMed1995

Gonadotropin-releasing hormone overcomes follicle-stimulating hormone's inhibition of insulin-like growth factor-5 synthesis and promotion of its degradation in rat granulosa cells.

The effect of a gonadotropin-releasing hormone-agonist (GnRH-a) on the synthesis of insulin-like growth factor-binding protein-5 (IGFBP-5), a physiological marker for atresia, was investigated. Granulosa cells obtained from diethylstilbestrol (DES)-treated immature female rats were cultured in serum-free medium for 72 h with GnRH-a and the conditioned media were subjected to immunoblot analysis using rat IGFBP-5 specific antibody. GnRH-a caused a dose-dependent (ED50 = 8.6 x 10(-11) M) accumulation of IGFBP-5, which migrated as 35 (non-glycosylated) and 36 kDa (glycosylated) bands under reducing conditions. A maximally effective dose of GnRH-a (10(-9) M) caused a 4-fold increase in IGFBP-5 accumulation. In contrast, increasing doses of porcine follicle-stimulating hormone (pFSH) caused a biphasic effect on IGFBP-5 accumulation. A low dose of pFSH (0.25 ng/ml) increased and higher doses of pFSH (22.5 ng/ml) decreased the 35 and 36 kDa IGFBP-5 bands. In the presence of high doses of pFSH (20.75 ng/ml), a 22 kDa band corresponding to a cleaved IGFBP-5 fragment appeared in the media. When the granulosa cells were cultured with a saturating dose of pFSH, co-addition of GnRH-a dose dependently inhibited the FSH effects (ED50 = (2.3-3.7) x 10(-10) M). The GnRH-a effects were completely blocked by co-incubation with GnRH-antagonist. IGFBP-5 mRNA accumulation levels were increased by GnRH-a in a dose dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Isolation and initial characterization of a newfound hantavirus from California.

A fatal case of hantavirus pulmonary syndrome (HPS) in northern California prompted our attempt to isolate viruses from local rodents. From tissues of two deer mice, Peromyscus maniculatus, two hantaviruses (Convict Creek virus 107 and 74, CC107 and CC74) were established in cell culture. Viral antigens, proteins, and RNAs of the first and archetypical isolate (CC107) were examined, and portions of the medium (M) and small (S) genome segments of both isolates were sequenced. Antigenically, CC107 virus and the second isolate, CC74 virus, were more closely related to Puumala virus than Hantaan (HTN) virus, though distinct from both. Northern blots of viral RNAs showed the large and M segments of CC107 to be the same size as those of HTN virus, whereas the S segment was larger. Protein gels did not reveal CC107 to have a substantially larger nucleocapsid protein than HTN virus. Partial nucleotide sequence comparisons of CC107 and CC74 viruses revealed their M segments to be highly similar to one another, while their S segments differed by more than 10%. Nucleotide and deduced amino acid sequence comparisons showed the California isolates to be closely related to the newfound hantaviruses first detected in the Four Corners area and since incriminated in HPS through wide areas of the United States.

Amino Acid Sequence↗
PubMed1995

Complete nucleotide sequences of the M and S segments of two hantavirus isolates from California: evidence for reassortment in nature among viruses related to hantavirus pulmonary syndrome.

We report the complete nucleotide sequence of the M and the S genome segments and a portion of the L segments of two hantavirus isolates from Peromyscus maniculatus trapped in eastern California. The isolates, Convict Creek 107 and 74 (CC107 and CC74) are genetically similar to viruses known to cause hantavirus pulmonary syndrome in New Mexico. CC107 and CC74 each have an M segment consisting of 3696 nucleotides with a coding potential of 1140 amino acids in the virus complementary-sense RNA (cRNA). The S segments of CC107 and CC74 are 2083 and 2047 nucleotides long, respectively, and each has an ORF in the cRNA capable of encoding a protein of 428 amino acids. Unusually long 3' noncoding regions of 757 and 721 nucleotides follow the S segment ORF of CC107 and CC74, respectively, and include numerous imperfect repetitive sequences. Whereas the M and S segments of any given hantavirus typically appear to diverge at comparable rates from homologous genes of any other hantavirus, CC107 and CC74 have M segments that differ by only 1% from one another but S segments that differ by 13%. After trivial explanations are rendered improbable, i.e., by consideration of the genetics of closely and distantly related hantaviruses, the most likely explanation for our data is that hantavirus genome segment reassortment occurred within rodent populations in California.

Animals↗
PubMed1995

Hepatitis E virus (87A strain) propagated in A549 cells.

A strain of hepatitis E virus (HEV), the 87A strain isolated in 2BS cells from the feces of a patient with hepatitis E, has been reported previously. In this study, the 87A strain was propagated in A549 cells, and the marked cytopathic effect (CPE) appeared in the infected monolayer cells. The size of this virus is about 30 nm in diameter. Furthermore, HEV-RNA from the supernatants of the virus of different passages was detected by polymerase chain reaction (PCR) amplification using ET1.1 HEV primers. A band of HEV for 239 bp from PCR products was revealed by electrophoresis. PCR products of the fourth passage were sequenced. These results show that the 87A virus replicates in the A549 cell line.

Animals↗
PubMed1995

Identification of potential redox-sensitive cysteines in cytosolic forms of fructosebisphosphatase and glyceraldehyde-3-phosphate dehydrogenase.

Tertiary-structure modeling suggests the occurrence of disulfide bonds in the cytosolic form of fructose-bisphosphatase (EC 3.1.3.11) in spinach (Spinacia oleracea L.), sugarbeet (Beta vulgaris L.) and potato (Solanum tuberosum L.). Redox modulation could then control the AMP sensitivity of fructosebisphosphatase in the cytosol, as suggested by the experiments of E. Khayat et al. (1993, Plant Physiol. 101, 57-64). Modeling also reveals two cysteine residues correctly positioned to form a disulfide bond and hence potentially redox-sensitive in the cytosolic glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) from the facultative crassulacean metabolism plant Mesembryanthemum crystallinum L.

Amino Acid Sequence↗