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Biomedical subjects

X H Li

Publications and source records attributed to X H Li.

At least 55 records · Page 3Linked to original sources
PubMed1998

DNA-dependent protein kinase phosphorylation of IkappaB alpha and IkappaB beta regulates NF-kappaB DNA binding properties.

Regulation of the IkappaB alpha and IkappaB beta proteins is critical for modulating NF-kappaB-directed gene expression. Both IkappaB alpha and IkappaB beta are substrates for cellular kinases that phosphorylate the amino and carboxy termini of these proteins and regulate their function. In this study, we utilized a biochemical fractionation scheme to purify a kinase activity which phosphorylates residues in the amino and carboxy termini of both IkappaB alpha and IkappaB beta. Peptide microsequence analysis by capillary high-performance liquid chromatography ion trap mass spectroscopy revealed that this kinase was the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). DNA-PK phosphorylates serine residue 36 but not serine residue 32 in the amino terminus of IkappaB alpha and also phosphorylates threonine residue 273 in the carboxy terminus of this protein. To determine the biological relevance of DNA-PK phosphorylation of IkappaB alpha, murine severe combined immunodeficiency (SCID) cell lines which lack the DNA-PKcs gene were analyzed. Gel retardation analysis using extract prepared from these cells demonstrated constitutive nuclear NF-kappaB DNA binding activity, which was not detected in extracts prepared from SCID cells complemented with the human DNA-PKcs gene. Furthermore, IkappaB alpha that was phosphorylated by DNA-PK was a more potent inhibitor of NF-kappaB binding than nonphosphorylated IkappaB alpha. These results suggest that DNA-PK phosphorylation of IkappaB alpha increases its interaction with NF-kappaB to reduce NF-kappaB DNA binding properties.

3T3 Cells↗
PubMed1997

Induction of transplantation tolerance in adult rats by vascularized spleen transplantation.

It was demonstrated by Bitter-Seurmann et al. that tolerance to subsequent skin allografts can be brought about, in some rat strain combinations, by heterotopic spleen allografts. We report here that in adult rats, tolerance can be also induced by vascularized spleen allografts using various strain combinations. DA (RT1av1) rats always accepted major histocompatible complex (MHC)-compatible but minor histocompatibility antigen (miH)-incompatible ACI (RT1av1) spleen grafts spontaneously, and further that those DA rats bearing ACI spleen grafts accepted subsequent ACI skin grafts indefinitely. In contrast, Fischer 344 (RT1lvl) rats always accepted not only the "weak" MHC-incompatible Lewis (RT1l) spleen grafts but also subsequent Lewis skin grafts indefinitely, when recipients were administered a short course of FK506 only at the time of primary spleen transplantation. Furthermore, in a number of MHC- and miH-incompatible strain combinations, recipients always accepted primary spleen grafts indefinitely when given a short course of FK506, but those recipients bearing donor spleens revealed split tolerance, that is, rejected subsequent donor-specific skin grafts but accepted heart grafts indefinitely. We conclude that the spleen seems to be a possible organ to induce transplantation tolerance, and that even if the MHC and miH are mismatched, unresponsiveness to at least heart grafts can be achieved by the administration of additional FK506 at the time of spleen transplantation.

Animals↗
PubMed1997

Importance of epistasis as the genetic basis of heterosis in an elite rice hybrid.

The genetic basis of heterosis was investigated in an elite rice hybrid by using a molecular linkage map with 150 segregating loci covering the entire rice genome. Data for yield and three traits that were components of yield were collected over 2 years from replicated field trials of 250 F(2:3) families. Genotypic variations explained from about 50% to more than 80% of the total variation. Interactions between genotypes and years were small compared with the main effects. A total of 32 quantitative trait loci (QTLs) were detected for the four traits; 12 were observed in both years and the remaining 20 were detected in only one year. Overdominance was observed for most of the QTLs for yield and also for a few QTLs for the component traits. Correlations between marker heterozygosity and trait expression were low, indicating that the overall heterozygosity made little contribution to heterosis. Digenic interactions, including additive by additive, additive by dominance, and dominance by dominance, were frequent and widespread in this population. The interactions involved large numbers of marker loci, most of which individually were not detectable on single-locus basis; many interactions among loci were detected in both years. The results provide strong evidence that epistasis plays a major role as the genetic basis of heterosis.

Journal Article↗
PubMed1997

Promotion of mouse fibroblast proliferation by IgE-dependent activation of mouse mast cells: role for mast cell tumor necrosis factor-alpha and transforming growth factor-beta 1.

Pathologic fibroblast proliferation or tissue fibrosis develops in certain chronic allergic diseases and in a wide array of other inflammatory disorders in which mast cell activation is also a prominent feature. In this study we investigated a number of potential mechanisms by which IgE-dependent activation of mouse mast cells might influence the proliferation of mouse fibroblasts in vitro. We found that supernatants from in vitro-derived mast cells that had been activated by IgE and specific antigen (but not those from quiescent mast cells) promoted the proliferation of mouse embryonic skin or 3T3 fibroblasts, and we showed that this effect was detectable in the absence of fetal calf serum. We analyzed the kinetics with which the fibroblast-proliferative activity was secreted from bone marrow-derived cultured mast cells and found that it was released both rapidly (i.e., in 30 minutes or less) and for a more prolonged period (i.e., for more than 2 hours) after IgE-dependent mast cell activation. We then measured the levels at which the mast cells produce a number of cytokines that are known to affect fibroblasts (IL-1, IL-6, transforming growth factor-beta 1 [TGF-beta 1], and tumor necrosis factor-alpha [TNF-alpha]) and assessed their relative effects, as recombinant cytokines, on fibroblast proliferation. Our mast cells secreted high levels of TGF-beta 1 and TNF-alpha, intermediate amounts of IL-6, and low levels of IL-1. We titrated the fibroproliferative effects of each of these cytokines and determined that at a dose of 50 pg/ml their rank order of activity was TGF-beta 1 > TNF-alpha > IL-1 > IL-6, with all but IL-6 having significant effects. The ability of supernatants from activated bone marrow-derived cultured mast cells to promote fibroblast proliferation was partially diminished by absorption with neutralizing antibodies against either TNF-alpha or TGF-beta 1, and absorption of the supernatants with a combination of antibodies against TNF-alpha and TGF-beta 1 reduced their ability to induce fibroblast proliferation by approximately 50% (p < or = 0.001, n = 5). These findings show that IgE-dependent activation of mouse mast cells can result in the release of mediators that promote fibroblast proliferation in the absence of any other cell type and suggest that mast cell-derived TNF-alpha and TGF-beta 1 contribute substantially to this effect. They also suggest that these cytokines exert their effects through synergistic interactions with other mast cell mediators.

Animals↗
PubMed1997

Functions of the tobacco etch virus RNA polymerase (NIb): subcellular transport and protein-protein interaction with VPg/proteinase (NIa).

The NIb protein of tobacco etch potyvirus (TEV) possesses several functions, including RNA-dependent RNA polymerase and nuclear translocation activities. Using a reporter protein fusion strategy, NIb was shown to contain two independent nuclear localization signals (NLS I and NLS II). NLS I was mapped to a sequence within amino acid residues 1 to 17, and NLS II was identified between residues 292 and 316. Clustered point mutations resulting in substitutions of basic residues within the NLSs were shown previously to disrupt nuclear translocation activity. These mutations also abolished TEV RNA amplification when introduced into the viral genome. The amplification defects caused by each NLS mutation were complemented in trans within transgenic cells expressing functional NIb, although the level of complementation detected for each mutant differed significantly. Combined with previous results (X. H. Li and J. C. Carrington, Proc. Natl. Acad. Sci. USA 92:457-461, 1995), these data suggest that the NLSs overlap with essential regions necessary for NIb trans-active function(s). The fact that NIb functions in trans implies that it must interact with one or more other components of the genome replication apparatus. A yeast two-hybrid system was used to investigate physical interactions between NIb and several other TEV replication proteins, including the multifunctional VPg/proteinase NIa and the RNA helicase CI. A specific interaction was detected between NIa and NIb. Deletion of any of five regions spanning the NIb sequence resulted in NIb variants that were unable to interact with NIa. Clustered point mutations affecting the conserved GDD motif or NLS II within the central region of NIb, but not mutations affecting NLS I near the N terminus, reduced or eliminated the interaction. The C-terminal proteinase (Pro) domain of NIa, but not the N-terminal VPg domain, interacted with NIb. The effects of NIb mutations within NLS I, NLS II, and the GDD motif on the interaction between the Pro domain and NIb were identical to the effects of these mutations on the interaction between full-length NIa and NIb. These data are compatible with a model in which NIb is directed to replication complexes through an interaction with the Pro domain of NIa.

Amino Acid Sequence↗
PubMed1997

[Studies on pyridonecarboxylic acids as antibacterial agents. XII. Synthesis and antibacterial activity of 6-chloro-1-cyclopropyl-7-(1-piperazinyl)-1, 4-dihydro-4-oxo-quinoline-3-carboxylic acid and analogues].

Sixteen pyridonecarboxylic acids, characterized by having a chlorine atom and a cyclopropyl group at the 6- and 1-position respectively, substituted amino groups at the 7-position, and some substituted groups (chloro, nitro, amino, dimethylamino) at the 8-position, were synthesized. In vitro antibacterial activities of these compounds were tested. The fluoroquinolones ciprofloxacin and norfloxacin were included for comparative purposes. The results showed that both 11 Ca and 11 Cc were 4-8 times more active than ciprofloxacin and norfloxacin against S. aureus-15 in vitro, but with the same activity as ciprofloxacin against E. coli-22 and P. aeruginosa-29.

Animals↗
PubMed1996

Interactions of RecF protein with RecO, RecR, and single-stranded DNA binding proteins reveal roles for the RecF-RecO-RecR complex in DNA repair and recombination.

The products of the recF, recO, and recR genes are thought to interact and assist RecA in the utilization of single-stranded DNA precomplexed with single-stranded DNA binding protein (Ssb) during synapsis. Using immunoprecipitation, size-exclusion chromatography, and Ssb protein affinity chromatography in the absence of any nucleotide cofactors, we have obtained the following results: (i) RecF interacts with RecO, (ii) RecF interacts with RecR in the presence of RecO to form a complex consisting of RecF, RecO, and RecR (RecF-RecO-RecR); (iii) RecF interacts with Ssb protein in the presence of RecO. These data suggested that RecO mediates the interactions of RecF protein with RecR and with Ssb proteins. Incubation of RecF, RecO, RecR, and Ssb proteins resulted in the formation of RecF-RecO-Ssb complexes; i.e., RecR was excluded. Preincubation of RecF, RecO, and RecR proteins prior to addition of Ssb protein resulted in the formation of complexes consisting of RecF, RecO, RecR, and Ssb proteins. These data suggest that one role of RecF is to stabilize the interaction of RecR with RecO in the presence of Ssb protein. Finally, we found that interactions of RecF with RecO are lost in the presence of ATP. We discuss these results to explain how the RecF-RecO-RecR complex functions as an anti-Ssb factor.

Bacterial Proteins↗
PubMed1996

[Clinical observation on aplastic anemia treated with Chinese herbal medicine combined with cord blood infusion].

Forty-eight cases of aplastic anemia (AA) were divided into two groups: the treated group (30 cases) were treated with Chinese herbal medicine and cord blood infusion, the control group (18 cases) were treated with cord blood infusion solely. The total effective rate in the treated group and the control group was 93.3% and 72.2% respectively, the difference between two groups was significant (P < 0.05). Cultures of bone marrow granulocyte-macrophage colony forming units (CFU-GM) in vitro were measured also in both groups. Results showed that 3 months after treatment, the elevation of CFU-GM in the two groups were similar to each other, but after 6 months' treatment, level of CFU-GM in treated group elevated persistently and steadily, while in control group, it decreased slightly as compared with level at 3 months' treatment, suggesting the recovery of bone marrow hematopoiesis of treated group was more stable than that of control group. This study indicated that combined treatment of Chinese herbal medicine and cord blood infusion is an effective method in treating AA.

Adolescent↗
PubMed1996

[Studies on the chemical constituents of Rhodiola fastigita].

The root and rhizoma of Rhodiola fastigita S. H. Fu. is a traditional Tibetan medicine used for promoting blood circulation and relieving cough. In recent years, it was generally used as a tonic. So, its chemical constituents were studied. A new flavonoid and six known compounds were obtained. The known compounds were: 4'-methoxyl herbacetin (I), rhodiolin (II), dihydrokaempferol (III), daucosterol (IV), tyrosyl (V) and salidroside (VI). The structure of the new flavonoid was elucidated as herbacetin-8-O-alpha-D-lyxopyranoside (VII), by means of UV, IR, MS, 1H and 13C-NMR spectral data and chemical methods.

Flavonoids↗
PubMed1995

Complementation of tobacco etch potyvirus mutants by active RNA polymerase expressed in transgenic cells.

A genetic complementation system was developed in which tobacco etch virus (TEV) polymerase (NIb)-expressing transgenic plants or protoplasts were inoculated with NIb-defective TEV mutants. A beta-glucuronidase (GUS) reporter gene integrated into the genomes of parental and four mutant viruses was used to assay RNA amplification. Two mutants (termed VNN and EDE) contained substitutions affecting the conserved "GDD" polymerase motif or a nuclear localization signal sequence, respectively; one (aD/b) contained a mutation debilitating the NIb N-terminal cleavage site, whereas the other (delta b) lacked the entire NIb sequence. Each mutant was unable to amplify in nontransformed tobacco protoplasts. In contrast, the VNN, EDE, and delta b mutants were complemented to various degrees in NIb-expressing cells, whereas the aD/b mutant was not complemented. The VNN mutant was complemented most efficiently, reaching an average of 11-12% the level of parental TEV-GUS, although in some experiments the level was near 100%. This mutant also replicated in, and spread through, whole transgenic plants to the same level as parental virus. The EDE mutant was complemented relatively poorly, reaching 1% or less of the level of parental TEV-GUS. Despite the close proximity of the EDE substitution to the N-terminal cleavage site, proteolytic processing of NIb was unaffected in an in vitro assay. The delta b mutant was complemented to an intermediate degree in protoplasts, reaching 3.5% the level of parental virus, and replicated and moved systemically in transgenic plants. These data indicate that free NIb supplied entirely in trans can provide all NIb functions essential for RNA amplification. The relative inefficient complementation of the EDE mutant suggests that the resulting mutant protein was transinhibitory.

Biological Assay↗
PubMed1995

In vivo gene therapy for hyperlipidemia: phenotypic correction in Watanabe rabbits by hepatic delivery of the rabbit LDL receptor gene.

Elevations of plasma total or LDL cholesterol are major risk factors for cardiovascular disease. Efforts directed at preventing and treating cardiovascular disease have often focused on reducing the levels of these substances in the blood. The Watanabe Heritable Hyperlipidemic Rabbit, which has exceedingly high plasma cholesterol levels resulting from an LDL receptor deficiency, provides an excellent animal model for testing new treatments. A recombinant adenoviral vector containing the rabbit LDL receptor cDNA was administered to Watanabe rabbits. Plasma total cholesterol levels in the treated animals were reduced from 825.5 +/- 69.8 (mean +/- SD) to 247.3 +/- 61.5 mg/dl 6 d after infusion. These animals also demonstrated a 300-400% increase in plasma levels of HDL cholesterol and apo AI 10 d after treatment. As a result, the LDL:HDL ratio exhibited a dramatic decrease. Because only the rabbit LDL receptor gene was used for treatment, the results strongly suggest that the elevations of plasma HDL cholesterol and apo AI were secondary to a reduction in plasma total cholesterol in the treated animals. These results suggest an inverse relationship between plasma LDL and HDL cholesterol levels and imply that reduction of LDL cholesterol levels may have a beneficial effect on plasma HDL cholesterol.

Animals↗
PubMed1995

[Study of treating experimental ulcerative colitis of spleen deficiency type with "guben yichang tablet" in guinea pigs].

Guinea pigs were perfused with the extract of senna (20%). 3 days later glacial acetic acid (5%) was given intra-anally so as to replicate the animal model of Spleen Deficiency (SD) and ulcerative colitis which is the disease of Western medicine combined with the Syndrome in TCM. The model animals showed the symptoms of SD such as loose stool, anorexia, wasting, aversion of cold, laziness and loss of hair luster and the symptoms of ulcerative colitis such as abdominal distension and mucous bloody stool. The colonic lesion were observed by eyes that the mucosa were edematous, congestive with ulcerative foci. The pathological examinations showed edema and congestion in submucous layers; large amount of inflammatory cell infiltration; and the scaling and ulcer formation of epithelium mucosae. The above-mentioned symptoms and pathological changes were the same as SD and ulcerative colitis in clinical practice. The new medicine "Guben Yichang Tablet" against ulcerative colitis was given to guinea pigs for 7 days could abate their symptoms, increase their body weights and decrease the size of colonic ulcer and edema.

Animals↗
PubMed1994

Gene therapy for phenylketonuria: phenotypic correction in a genetically deficient mouse model by adenovirus-mediated hepatic gene transfer.

Classical phenylketonuria (PKU), which predisposes affected individuals to severe mental retardation, is caused by a deficiency of hepatic phenylalanine hydroxylase (PAH). A recombinant adenoviral vector containing the human PAH cDNA was constructed and administered to PAH-deficient mice (strain PAHenu2). The hyperphenylalaninemic phenotype of these animals was completely normalized within 1 week of treatment. Although this therapeutic effect did not persist, analysis of the relationship between hepatic PAH activity and serum phenylalanine levels indicated that only 10-20% of normal enzymatic activity in the mouse liver is sufficient to restore normal serum phenylalanine levels. These results demonstrate that PKU and other metabolic disorders secondary to hepatic deficiencies can be completely corrected by gene therapy when more persistent vector systems are developed.

Adenoviridae↗
PubMed1994

[Effects of rhizoma zedoariae on nickel sulfide induced unscheduled DNA synthesis of human lymphocytes].

The study was designed to investigate the toxic effects of Rhizoma Zedoariae (RZ) and nickel sulfide, and the effect of RZ on nickel sulfide induced unscheduled DNA synthesis (UDS) of human lymphocytes using an UDS assay of human lymphocytes. The results showed that TZ did not induce UDS, it could inhibit 3H-TdR incorporation with intracellular DNA when its' dose was 1 g/ml, that nickel sulfide and ultraviolet could largely induce UDS, that might be inhibited by RZ with a dose dependent relationship. These suggested that nickel sulfide induced damage of DNA might be inhibited by RZ, RZ was not mutagenic and DNA synthesis might be inhibited when the RZ dose amounted to 1 g/ml.

DNA↗
PubMed1994

[Distribution of pre-core A83 point mutation in hepatitis B virus infections].

We designed a mispairing primer, which could introduce a Bsu36I restriction site into the amplified fragment of A83 mutant. Following PCR, the 102bp was diagnosed by the restriction endonuclease, and the variation was detected by demonstration of 82bp and 20bp bands on gel electrophoresis (RFLP). With the method, 77 cases of acute and chronic HBV infections were analysed. Among those, 31 (65%) mutants were detected in 48 anti-HBe-positive cases, and in 29 HBeAg-positive cases, 11 (38%) were co-infected with mutated and wild isolates. No pre C defect was found in acute hepatitis B and chronic asymptomatic carriers, suggesting that mutation occurs only after immune selection. The HBeAg defective variant appears to be involved in the loss of virus tolerance, and therefore in the pathogenesis of acute exacerbation of chronic carriage as demonstrated in this study. The various chronic liver diseases had an approximate mutation frequency, and it seems that A83 mutation nearly makes HBV infection persist.

Antigenic Variation↗