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J Xu

Publications and source records attributed to J Xu.

At least 1,081 records · Page 60Linked to original sources
PubMed1994

Genomic structure and cloned cDNAs predict that four variants in the kinase domain of serine/threonine kinase receptors arise by alternative splicing and poly(A) addition.

Heterodimers of types I and II serine/threonine kinase receptor monomers compose the active receptor complex for ligands of the transforming growth factor beta family. Here we show that the genomic organization of coding sequences for the intracellular domain of a widely expressed type I serine/threonine kinase receptor is similar to that of the activin type II receptor gene. The genomic structure and cDNA clones indicate that poly(A) addition to alternative exons at each of three carboxyl-terminal coding exon-intron junctions may be a common feature of both type I and II receptor genes. The predicted products are monomers truncated at kinase subdomains VII, IX, and X which vary in kinase activity and potential serine, threonine, and tyrosine phosphorylation sites. These results suggest that combinations of variants that affect the signal-transducing intracellular kinase domain of both type I and II receptor monomers within the transforming growth factor beta ligand family may add to the heterogeneity of biological effects of individual ligands in the family.

Alternative Splicing↗
PubMed1994

The contralaterally projecting neurons of the isthmic nucleus in five anuran species: a retrograde tracing study with HRP and cobalt.

The morphology of projection neurons of the isthmic nucleus was studied in Rana esculenta, R. nigromaculata, Bufo marinus, B. bufo gargarizans, and Xenopus laevis from a comparative anatomical point of view. The main point of this work was to provide an anatomical basis for electrophysiological studies. Neurons projecting to the ipsilateral optic tectum were labeled by retrograde transport of horseradish peroxidase and cobaltous lysine complex injected into the optic tectum. Contralaterally projecting cells were filled by injecting the tracer substances into the crossed isthmotectal tract. Cells of the anterior nonrim cortex and the rostral part of the medulla project to the ipsilateral tectum. A band of cells in the middle of the medulla, a few cells in the caudal part of the medulla, and most of the neurons in the rim cortex project to the contralateral tectum. Five types of neurons were distinguished in the rim cortex of R. esculenta. Most of them have piriform perikarya and their dendrites arborize in the rim neuropil. In the medulla of the isthmic nucleus of R. esculenta, seven types of neurons were distinguished. Most of these neurons also exist in the other species. Medullary cells are piriform, fusiform, or multipolar, and are variable in size and in dendritic arborization. The isthmic neurons of the two Ranae and Bufo species are similar. The dominant cell types in Xenopus are multipolar with extensive dendritic arborization, which occupies more space in the nucleus than in the other species. Neurons with narrow dendritic trees may represent a system of fine resolution, and those neurons with extensive dendritic arborization may belong to a coarser system.

Animals↗
PubMed1994

Identification of basic residues involved in substrate binding and catalysis by pyrophosphate-dependent phosphofructokinase from Propionibacterium freudenreichii.

Despite overall low identity of sequence between ATP- and PPi-dependent phosphofructo-1-kinases (PFK), an alignment permits the tentative identification of catalytically important residues in PPi-dependent PFK. Seven basic residues of the PPi-dependent PFK of Propionibacterium freudenreichii, Arg-310, Lys-315, Arg-326, Arg-186, Arg-78, Arg-90, and Lys-148 were chosen on the basis of this alignment for site-directed mutagenesis to neutral residues. Mutants R186A, K315A, and R326A had substantial increases of 43-, 389- and 678-fold, respectively, in Km for fructose 6-phosphate relative to wild-type enzyme and relatively small effects on kcat. The modest kinetic effects of mutations at Arg-78, Arg-90, and Arg-310 were not considered to indicate important roles for these residues. On the other hand, mutant K148M had a Km for PPi that was increased by 132-fold and kcat lowered by a factor of 490. Cho and Cook (Cho, Y.-K., and Cook, P.F. (1988) Biochemistry 28, 4155-4160) concluded on the basis of kinetic and chemical modification data that the enzyme utilizes a proton shuttle mechanism and that two lysines are involved in substrate binding. The present data along with our previous data on mutant D151A support a double proton shuttle mechanism involving Asp-151 and Lys-148 with Lys-148, Arg-326, Lys-315, and perhaps Arg-186 being important for substrate binding.

Amino Acid Sequence↗
PubMed1994

Chromium-induced early changes in renal function among ferrochromium-producing workers.

Urinary biochemical indicators of renal injury were examined in 84 male and 38 female ferrochromium-producing workers exposed to water-soluble chromium compounds [Cr(VI)]. The indicators examined included urinary chromium (U-Cr), alkaline phosphatase (ALP), gamma-glutamyl transferase (gamma-GT), glutamic-oxalacetic and glutamic-pyruvic transaminases (GOT & GPT), lactate dehydrogenase (LDH), N-acetyl-beta-D-glucosaminidase (NAG), total protein (TPr) and beta 2-microglobulin (beta 2-MG). The U-Cr levels in the exposed group were approximately 1.8 times that of the control group. Compared to controls, the activities of gamma-GT, NAG, ALP, GOT and LDH in the urine of workers were significantly increased whenever U-Cr concentration exceeded 45 microgram/g creatinine. The activities of gamma-GT, GOT and NAG were elevated in workers employed for longer than ten years. However, no clear dose-response relationships nor time-effect relationships were found. The present results suggest that long-term exposure to water-soluble chromium [Cr(VI)] produces chronic renal injury. The site of the injury appears to mainly involve the proximal tubule. U-Cr concentrations of > 15 microgram/g creatinine can be proposed as a threshold dosage for nephrotoxicity, and gamma-GT, NAG and ALP are early sensitive indicators of the most valuable for evaluating the renal injury.

Acetylglucosaminidase↗
PubMed1994

Fibroblast growth factor receptor (FGFR) 3. Alternative splicing in immunoglobulin-like domain III creates a receptor highly specific for acidic FGF/FGF-1.

Fibroblast growth factors (FGF) regulate the growth and differentiation of cells through complex combinatorial signaling pathways. There are nine ligands that interact with a family of four tyrosine kinase FGF receptors (FGFR). Diversity in FGF signaling is determined in part by the affinity of specific ligand-receptor pairs. Alternative splicing in the FGFR ligand binding domain generates additional receptor isoforms with novel ligand affinities. For example, splicing events in the ligand binding domain of FGFR2 dramatically increases its affinity for keratinocyte growth factor (KGF/FGF-7). We have identified an alternatively spliced form of the FGFR3 mRNA, corresponding to known splice variants of FGFRs 1 and 2. We demonstrate both by binding studies on genetically engineered soluble receptors and by the mitogenic response of growth factor-dependent cell lines that this splice variant of FGFR3 (FGFR3 IIIb), by binding only acidic FGF (aFGF/FGF-1), has the most restricted ligand binding properties of any FGFR thus far described. Furthermore, by constructing a chimeric receptor that contains the homologous exon from FGFR2, we demonstrate that this single domain from FGFR2 is sufficient to confer upon FGFR3 the ability to bind KGF/FGF-7. The uniquely limited repertoire of ligands that interact with this receptor suggests that a novel ligand for FGFR3 IIIb exists.

Alternative Splicing↗
PubMed1994

Inhibition of mechanical strain-induced fetal rat lung cell proliferation by gadolinium, a stretch-activated channel blocker.

Normal growth of the fetal lung is dependent upon fetal breathing movements. We have previously demonstrated that mechanical strain, simulating fetal breathing movements, stimulated DNA synthesis and cell division by reaggregated alveolar-like structures of fetal rat lung cells. Herein, we report that both intracellular and extracellular calcium modulate strain-induced proliferative activity. Strain-induced cell proliferation was inhibited by BAPTA/AM, an intracellular calcium chelator. The intracellular calcium modulators, cyclopiazonic acid and 2,5-di-(tert-butyl)-1,4-benzohydroquinone, increased DNA synthesis of unstrained cultures and partially reduced strain-induced cell growth activity. A similar effect was noted with the calcium ionophore A23187. Extracellular Ca2+ increased DNA synthesis in unstrained cultures in a concentration-dependent fashion. The stimulatory effect of strain on DNA synthesis was also dependent on the calcium concentration in the medium. Furthermore, strain-enhanced DNA synthesis was inhibited by the presence of a divalent ion chelator, EGTA, in the medium. Mechanical strain increased 45Ca2+ influx within 1 min after the onset of strain. This rapid entry of calcium was not affected by calcium channel blockers, such as verapamil or Ni2+. Calcium channel blockers verapamil, nifedipine, Ni2+, Co2+, or La3+ also did not inhibit strain-induced cell growth activity. In contrast, gadolinium, a stretch-activated channel blocker, inhibited strain-induced 45Ca2+ influx and suppressed strain-enhanced DNA synthesis. We conclude that the entry of calcium into cells through stretch-activated ion channels plays a critical role in strain-induced fetal lung cell proliferation.

Animals↗
PubMed1994

Monocyte chemoattractant protein 1 (MCP-1) expression occurs in toxic rat liver injury and human liver disease.

Considerable evidence suggests that monocytes/macrophages play a crucial role in the process of liver injury and repair. Recent investigations have focused on the function of various macrophage-produced cytokines in liver disease. Much is still unknown, however, about the mechanism of macrophage recruitment and activation during liver disease. To further define this process, the gene expression of the monocyte chemoattractant monocyte chemoattractant protein 1 (MCP-1) was examined in animal and human liver disease. MCP-1 mRNA was not found in normal rat liver by Northern blot analysis. After single-dose treatments with the hepatotoxins carbon tetrachloride and galactosamine, MCP-1 mRNA was detectable beginning at 2 and 4 h after treatment, respectively, and was expressed continuously until 60-72 h. During chronic carbon tetrachloride administration, MCP-1 mRNA levels were elevated for the entire 10 weeks of treatment with peak levels of expression occurring early (weeks 1-3) and late (weeks 8-10) in this model. Isolated liver cell fractions from rats treated for 3 weeks with carbon tetrachloride revealed the major cellular source of MCP-1 mRNA to be fat-storing or Ito cells, with some expression occurring in the endothelial cell fraction. Studies of potential inducers of hepatic MCP-1 expression showed that lipopolysaccharide, tumor necrosis factor-alpha, and interleukin-1 alpha and beta treatments all led to MCP-1 expression. Finally, studies of human liver samples revealed MCP-1 gene expression in nondiseased liver and greatly increased levels in livers from patients with fulminant hepatic failure. These data implicate MCP-1 from fat-storing cells as a modulator of the process of liver injury and further support a role for MCP-1 in the pathogenesis of human disease.

Animals↗
PubMed1994

Characterization of 10 new polymorphic dinucleotide repeats and generation of a high-density microsatellite-based physical map of the BRCA1 region of chromosome 17q21.

A familial early onset breast cancer gene (BRCA1) has been localized to chromosome 17q21. To aid in the identification of this gene a number of new microsatellite markers from the D17S857 to D17S78 region were isolated and characterized. These markers, along with previously published markers from the region, were localized on a physical map by STS content mapping of cosmids from the BRCA1 interval. This high-density STS map of the BRCA1 region will be useful for linkage studies of families with apparent inherited breast cancer and for loss of heterozygosity analysis of breast tumor DNAs.

Alleles↗
PubMed1994

Expression of the glycoprotein H of murine cytomegalovirus and identification of an N-terminal antibody-binding region.

A series of overlapping fragments spanning the entire coding sequence of the gH gene of murine cytomegalovirus (MCMV) were expressed in Escherichia coli as fusion proteins with glutathione S-transferase (GST) using the pGEX expression system. A region of antibody-binding was mapped to the NH2-terminus of glycoprotein H (gH) between amino acid residues 26 and 90 on the basis of the reactivity of GST-gH fusion proteins with polyclonal antibodies to MCMV in Western blot analysis. Antibodies to gH were generated in mice immunized with the GST-gH fusion protein SK and shown to react with an 87-kDa polypeptide present in virion particles which was conserved in MCMV isolates obtained from diverse locations. They also recognized the gH protein in MCMV-infected cells, as well as gH expressed in Chinese Hamster Ovary cells. The antibodies to gH had a significant ELISA titer but no neutralizing activity in vitro. The antibody response to the GST-gH fusion protein did not modify the level of MCMV replication in the spleens of mice.

Animals↗
PubMed1994

Expression of major histocompatibility complex class II antigen on amoeboid microglial cells in early postnatal rat brain following intraperitoneal injections of lipopolysaccharide.

In rats given two single intraperitoneal injections of lipopolysaccharide (LPS) at 1 and 4 days of age and killed at 7 days of age, 11.5--12% of amoeboid microglial cells (AMC) in the supraventricular corpus callosum were induced to express major histocompatibility complex (MHC) class II antigen, as detected with monoclonal antibody OX-6. The MHC class II antigen induced was colocalized with MHC class I antigen and type 3 complement receptors on the same cells. The expression of MHC class II antigen on the plasma membrane of AMC was confirmed in immunoelectron microscopy. Although OX-6-positive AMC often assumed a perivascular position, the majority of them, however, were far removed from the blood vessels. The cytoplasmic processes of the perivascular OX-6-positive AMC appeared to rest directly on the vascular lamina, and in some section profiles they were in contact with a large surface area of the outer wall of small blood vessels. It is concluded from this study that although MHC class II antigen is not constitutively present on AMC, it is, however, inducible under stimulation with LPS. It is, therefore, suggested that the OX-6-positive AMC, especially the perivascular AMC, may have the potentiality to function as antigen-presenting cells in the developing brain when challenged by LPS.

Animals↗
PubMed1994

Identification of chromosomal structural alterations in human ovarian carcinoma cells using combined GTG-banding and repetitive fluorescence in situ hybridization (FISH).

In order to identify chromosomal structural alterations in the ovarian carcinoma cell line MLS/P, fluorescence in situ hybridization with centromeric probes for chromosomes 1, 8, 9, 13/21, 14/22, 15, 17, and X and whole chromosome painting probes for chromosomes 1, 3, 4, 5, 7, 8, 9, 10, 12, 13, 14, 17, 19, 22, and X were performed subsequent to GTG-banding. This combined approach identified 14 of the 18 clonal structurally rearranged chromosomes, with the X chromosome involved in three aberrations. In contrast, only eight of the 14 rearrangements were identifiable by G-banding alone. These results indicate that the combined G-banding and FISH approach can significantly improve the cytogenetic analysis of human neoplasia.

Azure Stains↗
PubMed1994

Upregulation and induction of major histocompatibility complex class I and II antigens on microglial cells in early postnatal rat brain following intraperitoneal injections of recombinant interferon-gamma.

Interferon-gamma when given intraperitoneally by single daily injection into one-day-old rats upregulated the expression of major histocompatibility complex class I antigen on ramified microglial cells in cerebral cortex and induced the expression of major histocompatibility complex class II antigen both on amoeboid and ramified microglial cells present in corpus callosum and cerebral cortex, respectively. In rats receiving single daily injections of interferon-gamma over a period of three consecutive days and killed at the age of seven days, the endothelium exhibited a moderate to weak immunoreaction for major histocompatibility complex class I antigen as detected with the monoclonal antibody OX-18. The immunoreactivity of major histocompatibility complex class I antigen on amoeboid microglial cells was comparable to that of control rats. On the other hand, it was remarkably enhanced on ramified microglial cells and was further intensified with four or six injections of interferon-gamma. In the latter, the endothelial cells also showed a stronger immunoreactivity with OX-18. In rats given three successive injections of interferon-gamma and killed at the age of seven days, 7.5% of amoeboid microglial cells in corpus callosum were induced to exhibit major histocompatibility complex class II antigen as detected with OX-6. An upsurge of the amoeboid microglial cells with major histocompatibility complex class II antigen amounting to about 40% was observed following four and six injections of interferon-gamma. A minimum of four successive injections of interferon-gamma were needed to elicit the expression of major histocompatibility complex class II antigen on ramified microglial cells in cerebral cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Lipopolysaccharide-lipophorin complex formation in insect hemolymph: a common pathway of lipopolysaccharide detoxification both in insects and in mammals.

The formation of the lipophorin-lipopolysaccharide (LPS) complex in Bombyx mori hemolymph and its role in LPS detoxification were explored. LPS, an antibacterial protein inducer in insects, was injected into B. mori larvae. Analytical density gradient ultracentrifugation revealed that after injection the LPS peak shifts to a zone of lower density with time. The shifted peak was identified as the lipophorin-LPS complex. This complex formation was also achieved in an in vitro mixture of cell-free hemolymph and LPS at 25 degrees C but not at 1 degree C. The lipophorin-LPS complex had a significantly lower capacity to elicit the mRNA of cecropin B, an antibacterial protein. The biological activity of reextracted LPS from the complex was slightly reduced in the Limulus test and no structural modification was observed in sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). These results suggested that the formation of lipophorin-LPS strikingly reduces the cecropin inducibility of LPS without any structural change in LPS. Similar serum lipoprotein-LPS complex formation and reduction of biological activities of LPS were also observed in mammals. We, therefore, suggest that the formation of the serum lipoprotein-LPS complex is a common pathway to inactivate LPS both in insects and in mammals.

Animals↗
PubMed1994

Mice deficient for the CD40 ligand.

To study the potential roles of CD40L in immune responses, we generated CD40L-deficient mice by gene targeting. Similar to the effects of CD40L mutations in humans (hyper-IgM syndrome), CD40L-deficient mice have a decreased IgM response to thymus-dependent antigens, fail altogether to produce an antigen-specific IgG1 response following immunization, yet respond normally to a T-independent antigen, TNP-Ficoll. Moreover, these mice do not develop germinal centers in response to thymus-dependent antigens, suggesting an inability to develop memory B cell responses. Although CD40L-deficient mice have low levels of most circulating immunoglobulin isotypes, they do not exhibit the spontaneous hyper-IgM syndrome seen in humans, at least up to 12 weeks of age. In summary, our study confirms the important role of CD40-CD40L interactions in thymus-dependent humoral immune responses and germinal center formation.

Animals↗