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Biomedical subjects

K Xia

Publications and source records attributed to K Xia.

At least 19 recordsLinked to original sources
PubMed2002

Spin-dependent transparency of ferromagnet/superconductor interfaces.

We combine parameter-free calculations of the transmission and reflection matrices for clean and dirty interfaces with a scattering-theory formulation of Andreev reflection (AR) generalized to spin-polarized systems in order to critically evaluate the use of an extended Blonder-Tinkham-Klapwijk (BTK) model to extract values of the spin polarization for ferromagnetic metals from measurements of point-contact AR. Excellent agreement with the experimental conductance data is found for Pb/Cu but it is less good for Pb/Ni and poor for Pb/Co, indicating that the BTK formalism does not describe transport through superconducting/ferromagnetic interfaces correctly.

Journal Article↗
PubMed2002

A novel locus (DSAP2) for disseminated superficial actinic porokeratosis maps to chromosome 15q25.1-26.1.

BACKGROUND: Disseminated superficial actinic porokeratosis (DSAP) is a chronic cutaneous disorder characterized by multiple superficial keratotic lesions surrounded by a slightly raised keratotic border. It develops in teenagers in sun-exposed areas of skin and usually follows an autosomal dominant inheritance pattern. The first locus for DSAP was localized to chromosome 12q23.2-24.1, but no gene responsible for porokeratosis has been identified to date. OBJECTIVES: To determine whether DSAP is a genetically heterogeneous disorder and to identify the disease gene locus in a three-generation Chinese family with DSAP. METHODS: Genetic linkage analysis was carried out in this family using 15 microsatellite markers between D12S1671 and D12S369 on chromosome 12q, followed by a genome-wide scan with 382 microsatellite markers from the autosomes. RESULTS: Genetic linkage analysis with chromosome 12q markers suggested that the locus in this family is not linked to chromosome 12q. A genome-wide scan and fine mapping finally localized the locus for DSAP in this family to a 6.4-cM region between markers D15S1023 and D15S1030 at chromosome 15q25.1-26.1. This DSAP locus was named DSAP2. CONCLUSIONS: The previous results and this study have shown that DSAP is a genetically heterogeneous disorder; a novel locus for DSAP, termed DSAP2, was mapped to a 6.4-cM region between markers D15S1023 and D15S1030.

Adolescent↗
PubMed2001

Association of ethylene dibromide (EDB) with mature cranberry (Vaccinium macrocarpon) fruit.

Ethylene dibromide (EDB), a potential carcinogen, has been used in gasoline mixtures to avoid the accumulation of metallic lead in engines. Ethylene dibromide is present in the environment and in groundwater. Previous analysis has shown that EDB levels have reached up to 16 microg L-1 in the groundwater at two fuel spill plumes in the vicinity of the Massachusetts Military Reservation (MMR) Base and up to 1.69 microg L-1 in the Coonamessett and Quashnet Rivers in Cape Cod, MA (U.S. Air Force IRP, Fact Sheet #98-10, 1998). Groundwater and river water from this area are used to flood some local cranberry bogs for irrigation and harvesting of cranberry fruits. The potential sorption of EDB by cranberry fruits during harvest has caused concern but information regarding its occurrence is not available. In this study, low levels of EDB (0.04-0.15 microg kg-1) were found to be associated with cranberry fruits that were exposed to EDB at levels ranging from 3 to 12 microg L-1 at 10, 20, and 30 degrees C for up to 7 days. Rinsing EDB-exposed cranberry fruits twice with deionized water or once with 0.01 M NaCl solution reduced the amount of EDB associated with the cranberry fruits by 65-72% to a level of 0.02 microg kg-1. Therefore, the EDB most likely is associated with the water residue on the surface of the cranberry fruit rather than being absorbed into the flesh of the fruit during the EDB exposure.

Accidents, Occupational↗
PubMed2001

[Mutation characteristic of STK].

OBJECTIVE: To identify the mutation characteristic of STK(11) gene in Chinese with Peutz-Jeghers syndrome(PJS) and establish the base of the gene diagnosis of PJS. METHODS: STK(11) germline mutation was analysed by DNA sequencing in 18 unrelation patients with PJS. RESULTS: Six novel mutations of STK (11) gene were detected in six unrelation patients. These mutations will lead to production of truncated protein. CONCLUSION: STK (11) gene mutation accounts for one third of the Chinese with PJS. The content of mutation includes single base substitution or deletion and one or two bases insertion. The mutations were widely found in different regions of the whole coding sequence, and 2/3 of those concentr ate in exon 1. Mutation frequency is 66.7% in the family suffering PJS in two or more generations, and 16.7% in the disseminated cases.

AMP-Activated Protein Kinase Kinases↗
PubMed2000

Identification of a locus for disseminated superficial actinic porokeratosis at chromosome 12q23.2-24.1.

Disseminated superficial actinic porokeratosis is an autosomal dominant cutaneous disorder characterized by many uniformly small, minimal, annular, anhidrotic, and keratotic lesions. The genetic basis for this disease is unknown. Using a genomewide search in a large Chinese family, we identified a locus at chromosome 12q23.2-24. 1 responsible for disseminated superficial actinic porokeratosis. The fine mapping study indicates that the disseminated superficial actinic porokeratosis gene is located within a 9.6 cM region between markers D12S1727 and D12S1605, with a maximum two-point LOD score of 20.53 (theta = 0.00) at D12S78. This is the first locus identified for a genetic disease where the major phenotype is porokeratosis. The study provides a map location for isolation of a gene causing disseminated superficial actinic porokeratosis.

China↗
PubMed2000

[The influence of some factors on DNA cycle sequencing].

OBJECTIVE: To study the influence of some factors on DNA cycle sequencing. METHODS: The effects of DNA templates, primers, cycle sequencing reaction conditions as well as purification methods were comparatively analyzed. RESULTS: When the DNA concentration was low, the nucleotide curve showed low ratio of signal to noise, even there were no fluorescent signal. While DNA concentration was too high, the readable length of nucleotides was short. Ions in the DNA template could result in bad sequencing reaction. The Tm value, length and G+C content of primers had no obvious influences on sequencing reaction. The alteration of the denaturing, annealing and extension temperature, or the addition of dimethl sulfoxide or glycerin facilitated sequencing some DNA templates. The fluorescent residues in the purified products of the sequence reaction could interfere the automatic reading of the sequencer, but did not influence the manually proofreading of the sequence. CONCLUSION: The purity and concentration of DNA templates are closely related to sequence data quality. The modification of reaction parameters and usage of additives can help to obtain good result of sequencing some DNA with certain structure. The use of 70% ethanol is recommended to precipitate the extension product.

Sequence Analysis, DNA↗
PubMed1999

Tyrosine phosphorylation of the proto-oncoprotein Raf-1 is regulated by Raf-1 itself and the phosphatase Cdc25A.

There is a growing body of evidence demonstrating that Raf-1 is phosphorylated on tyrosines upon stimulation of a variety of receptors. Although detection of Raf-1 tyrosine phosphorylation has remained elusive, genetic analyses have demonstrated it to be important for Raf-1 activation. Here we report new findings which indicate that Raf-1 tyrosine phosphorylation is regulated in vivo. In both a mammalian and baculovirus expression system, a kinase-inactive allele of Raf-1 was found to be tyrosine phosphorylated at levels much greater than that of wild-type Raf-1. The level of tyrosine phosphate on Raf-1 was markedly increased upon treatment with phosphatase inhibitors either before or after cell lysis. Cdc25A was found to dephosphorylate Raf-1 on tyrosines that resulted in a significant decrease in Raf-1 kinase activity. In NIH 3T3 cells, coexpression of wild-type Raf-1 and phosphatase-inactive Cdc25A led to a marked increase in Raf-1 tyrosine phosphorylation in response to platelet-derived growth factor. These data suggest that the tyrosine phosphorylation of Raf-1 is regulated not only by itself but also by Cdc25A.

3T3 Cells↗
PubMed1999

[Comprehensive evaluation and practical confirmation on processing technology of Daphne genkwa Sieb. et Zucc].

OBJECTIVE: To investigate the effect of five processing methods for D. genkwa. METHOD: Comparing the pharmacodynamic and toxic parameters and related chemical constituents of the processed products with those of crude D. genkwa and vinegar-processed D. genkwa recorded in Chinese Pharmacopoeia. THE RESULT: The vinegar stir-fry method was the best. One hundred kilograms of crud D. genkwa was evenly mixed with 30 kg vinegar diluted in 60 kg water and moistened in a closed container for an hour, then put into a drug-parching machine to get nearly dry with slow fire wenhuo and taken out timely. CONCLUSION: Three repetitions of pilot production have shown that the technology is simple, easy to operate and of good reproducibility, and thus can be used in the production of D. genkwa in slice form.

Acetic Acid↗
PubMed1998

Mutations in the gene encoding gap junction protein beta-3 associated with autosomal dominant hearing impairment.

Hearing impairment is the most commonly occurring condition that affects the ability of humans to communicate. More than 50% of the cases of profound early-onset deafness are caused by genetic factors. Over 40 loci for non-syndromic deafness have been genetically mapped, and mutations in several genes have been shown to cause hearing loss. Mutations in the gene encoding connexin 26 (GJB2) cause both autosomal recessive and dominant forms of hearing impairment. To study the possible involvement of other members of the connexin family in hereditary hearing impairment, we cloned the gene (GJB3) encoding human gap junction protein beta-3 using homologous EST searching and nested PCR. GJB3 was mapped to human chromosome 1p33-p35. Mutation analysis revealed that a missense mutation and a nonsense mutation of GJB3 were associated with high-frequency hearing loss in two families. Moreover, expression of Gjb3 was identified in rat inner ear tissue by RT-PCR. These findings suggest that mutations in GJB3 may be responsible for bilateral high-frequency hearing impairment.

Adult↗
PubMed1997

X-Ray Absorption and Electron Paramagnetic Resonance Studies of Cu(II) Sorbed to Silica: Surface-Induced Precipitation at Low Surface Coverages

Both EPR and XAFS spectroscopy were used to characterize the sorption of Cu(II) on silica surfaces at extremely low surface coverage (0.8 and 9.9% monolayer). The binding structure of Cu(II) on silica surfaces revealed by XAFS experiment was compared to that predicted by EPR spectra. Our XAFS results show that Cu(II) hydroxide clusters form on silica surfaces even at surface coverage as low as 0.8% of a monolayer. However, we observed low EPR intensity and line-broadening which has been assigned to dipole-dipole interactions between isolated Cu(II) ions. The results of our XAFS studies indicate that the loss of EPR intensity and line-broadening can be traced to Cu(OH)2 clusters on silica surfaces.

Journal Article↗
PubMed1997

Erythropoietin activates Raf1 by an Shc-independent pathway in CTLL-EPO-R cells.

Stimulation of the erythropoietin receptor (EPO-R) or the interleukin-2 receptor (IL-2-R) by their respective ligands has been reported to activate tyrosine phosphorylation of the cytoplasmic protein, Shc. We have recently characterized a cell line, CTLL-EPO-R, that contains functional cell-surface receptors for both EPO and IL-2. Although stimulation with IL-2 or IL-15 resulted in the rapid, dose-dependent tyrosine phosphorylation of Shc, stimulation with EPO failed to activate Shc. EPO, IL-2, and IL-15 activated the tyrosine phosphorylation of the adaptor protein, Shp2, and the association of Shp2/Grb2/cytokine receptor complexes. In addition, EPO, IL-2, and IL-15 activated Raf1 and ERK2, demonstrating that the Raf1/MEK/MAP kinase pathway was activated. These results indicate that multiple biochemical pathways are capable of conferring a mitogenic signal in CTLL-EPO-R. EPO can activate the Raf1/MEK/MAP kinase pathway via Shc-dependent or Shc-independent pathways, and Shc activation is not required for EPO-dependent cell growth in CTLL-EPO-R.

Adaptor Proteins, Signal Transducing↗
PubMed1997

[Giant-cell tumor of bone: a review of diagnosis and treatment of 105 cases].

OBJECTIVE: To summarize the experience in the diagnosis and treatment of giant-cell tumor of bone, the selection of various operation methods and their effects were evaluated and discussed. METHODS: From 105 cases of giant-cell tumor of bone data were collected and reviewed. The clinical features were analyzed in association with radiological and histological characteristics. Prognosis was assessed by long-term follow-up. RESULTS: Among 105 cases, one had multiple giant-cell tumors and two had distant metastases. In some cases, the radiological and histological appearances didn't accord with the clinical findings. The recurrence rate was 36% in patients treated with curettage. Although no recurrence was seen in patients treated by local excision, the joint function could not be fully retained. CONCLUSION: Diagnosis should be made on the basis of integrated clinical, radiological and pathological manifestations. Early diagnosis and operation are important. The function of joint must be retained as much as possible. Pre-operative embolization of tumor of sacrum and pelvis is very helpful to ensure operative success and to minimize recurrence.

Adolescent↗
PubMed1996

The cytokine-activated tyrosine kinase JAK2 activates Raf-1 in a p21ras-dependent manner.

JAK2, a member of the Janus kinase superfamily was found to interact functionally with Raf-1, a central component of the ras/mitogen-activated protein kinase signal transduction pathway. Interferon-gamma and several other cytokines that are known to activate JAK2 kinase were also found to stimulate Raf-1 kinase activity toward MEK-1 in mammalian cells. In the baculovirus coexpression system, Raf-1 was activated by JAK2 in the presence of p21ras. Under these conditions, a ternary complex of p21ras, JAK2, and Raf-1 was observed. In contrast, in the absence of p21ras, coexpression of JAK2 and Raf-1 resulted in an overall decrease in the Raf-1 kinase activity. In addition, JAK2 phosphorylated Raf-1 at sites different from those phosphorylated by pp60v-src. In mammalian cells treated with either erythropoietin or interferon-gamma, a small fraction of Raf-1 coimmunoprecipitated with JAK2 in lysates of cells in which JAK2 was activated as judged by its state of tyrosine phosphorylation. Taken together, these data suggest that JAK2 and p21ras cooperate to activate Raf-1.

Animals↗
PubMed1996

Role of protein kinase A and the serine-rich region of herpes simplex virus type 1 ICP4 in viral replication.

Efficient expression of herpes simplex virus genes requires the synthesis of functional ICP4, a nuclear phosphoprotein that contains a prominent serine-rich region between amino acids 142 and 210. Residues in this region not only are potential sites for phosphorylation but also are involved in the functions of ICP4. By comparing the growth of a virus in which this region is deleted (d8-10) with wild-type virus (KOS) in PC12 cells or PC12 cells that are deficient in cyclic AMP-dependent protein kinase (PKA), two observations were made: (i) the growth of wild-type virus was impaired by 1 to 2 orders of magnitude in the PKA-deficient cells, indicating the involvement of PKA in the growth cycle of herpes simplex virus type 1, and (ii) while the growth of d8-10 was impaired by almost 2 orders of magnitude in wild-type cells, it was not further impaired (as was that of wild-type virus) in PKA-deficient cells, implicating the region deleted in d8-10 as a possible target for cellular PKA. In trigeminal'ganglia of mice, the d8-10 mutant virus grew poorly; however, it established latency in nearly 90% of ganglia tested. Studies of the phosphorylation of wild-type and d8-10 ICP4 proteins revealed that the serine-rich region is a major determinant for phosphorylation of ICP4 in vivo and that the phosphorylation state could change as a function of the PKA activity. Consistent with this observation, the serine-rich region of ICP4 was shown to be a target for PKA in vitro. While intact ICP4 was readily phosphorylated by ICP4 in vitro, the d8-10 mutant ICP4 was not. Moreover, a synthethic peptide representing a sequence in the serine tract that is predicted to be a substrate for PKA was phosphorylated by PKA in vitro, having a Km within the physiological range. These data suggest that PKA plays a role in viral growth through phosphorylation of one or more sites on the ICP4 molecule.

Amino Acid Sequence↗
PubMed1996

Analysis of phosphorylation sites of herpes simplex virus type 1 ICP4.

The herpes simplex virus ICP4 protein is required for induction of early and late viral gene transcription as well as for repression of expression of its own gene and several other viral genes. Several electrophoretic forms of ICP4 have been observed, and phosphorylation is thought to contribute to this heterogeneity and possibly to the multiple functions of ICP4. To define the complexity of the site(s) of phosphorylation of ICP4 and to initiate mapping of this site(s), we have performed two-dimensional phosphopeptide mapping of wild-type and mutant forms of ICP4 labeled in infected cells or in vitro. Wild-type ICP4 labeled in infected cells shows a complex pattern of phosphopeptides, and smaller mutant forms of ICP4 show progressively fewer phosphopeptides, arguing that multiple sites on ICP4 are phosphorylated. The serine-rich region of ICP4, residues 175 to 198, was shown to be a site for phosphorylation. Furthermore, the serine-rich region itself or the phosphorylation of this region increases phosphorylation of all phosphopeptides. A mutant ICP4 molecule lacking the serine-rich region showed low levels of phosphorylation by protein kinase A or protein kinase C in vitro. These results suggest that there may be a sequential phosphorylation of ICP4, with phosphorylation of the serine-rich region stimulating phosphorylation of the rest of the molecule. In addition, purified ICP4 showed an associated kinase activity or an autophosphorylation activity with properties different from those of protein kinase A or protein kinase C.

Amino Acid Sequence↗