Biomedical subjects

J Tang

Publications and source records attributed to J Tang.

At least 271 records · Page 15Linked to original sources

PubMed1998

[Chitosan pin fixation of rabbit proximal tibia osteotomy].

Degradatable chitosan pin, 4 millimeters in diameter and 30 to 40 millimeters in length, was studied radiographically and histologically (oxytetracycline-labeling) at 3, 6, 12, 24 and 48 weeks after the implantation for fixation of a transverse proximal tibia osteotomy in fourty rabbits. The results showed that new bone formation and oxytetracycline uptake were increased 3-6 weeks after operation and the fracture was completely healed 12 weeks after operation, but in two rabbits the chitosan pin broke, in 3 weeks. Histologically, there was a massive inflammation (non-specific foreign body reaction) 3-12 weeks after implantation, which gradually subsided 24 weeks aften operation. Chitosan pin was slowly degradated in bone and was not replaced by normal tissue 48 weeks after operation. The questions to be addressed in future include how to increase the mechanical strength of chitosan pin and how to improve the characteristics of its surface.

Animals↗

PubMed1998

[Expression characteristic of Bacillus thuringiensis cry1 gene in Pseudomonas fluorescens Pfx-18].

The plasmids of lepidopteran-specific Bacillus thuringiensis strain from our laboratory were hybridized with RNA probe of cry 1Aa EcoR I-F fragment labelled using DIG. Cry1 gene was located in 39.3 MD plasmid. The plasmid was digested with Hind III and analysed by southern blot. It appeared both 7.1 kb and of 6.5 kb positive bands. The 7.1 kb fragment was ligated to broad-host-range vector pSUP106 and transformed into Pseudomonas fluorescens Pfx-18. The cloned strain, LZP-1 was obtained. The plasmids of LZP-1 were analysed by PCR. The results showed that gene-type is cry1Ab. SDS-PAGE analysis demonstrated that LZP-1 could express 66 kD insecticidal crystal protein and some small molecular weight peptides. Bioassay showed that motality of 1000-fold diluted fermentation broth was 33% to 3rd instar plulella xyloslelly larvae.

Animals↗

PubMed1998

[Cloning of DNA sequences involved in exopolysaccharide synthesis of Xanthomonas campestris pv. campestris].

By using a cloned DNA segment containing the mutated sequences from the exopolysaccharide-deficient mutant T117 of Xanthomonas campestris pv. campestris as a probe, a 9.4 kb HindIII fragment harbouring DNA sequences corresponding to the mutated site was identified and cloned from the wild-type strain. The fragment could complement the mutant strain T117 in trans and restore the synthesis of exopolysaccharide. This indicates that the fragment contains at least an intact gene which is involved in the exopolysaccharide synthesis of Xanthomonas campestris pv. campestris.

Cloning, Molecular↗

PubMed1998

A comprehensive biochemical and genetic analysis of the yeast U1 snRNP reveals five novel proteins.

The U1 snRNP is essential for recognition of the pre-mRNA 5'-splice site and the subsequent assembly of the spliceosome. Yeast U1 snRNP is considerably more complex than its metazoan counterpart, which suggests possible differences between yeast and metazoa in early splicing events. We have comprehensively analyzed the composition of yeast U1 snRNPs using a combination of biochemical, mass spectrometric, and genetic methods. We demonstrate the specific association of four novel U1 snRNP proteins, Snu71p, Snu65p, Nam8p, and Snu56p, that have no known metazoan homologues. A fifth protein, Npl3p, is an abundant cellular component that reproducibly co-purifies with the U1 snRNP, but its association is salt-sensitive. Therefore, we are unable to establish conclusively whether it binds specifically to the U1 snRNP. Interestingly, Nam8p and Npl3p were previously assigned functions in (pre-m)RNA-metabolism; however, so far, no association with U1 snRNP has been demonstrated or proposed. We also show that the yeast SmB protein is a U1 snRNP component. Yeast U1 snRNP therefore contains 16 different proteins, including seven snRNP core proteins, three homologues of the metazoan U1 snRNP-specific proteins, and six yeast-specific U1 snRNP proteins. We have simultaneously continued the characterization of additional mutants isolated in a synthetic lethal (MUD) screen for genes that functionally cooperate with U1 snRNA. Consistent with the biochemical results, mud10, mud15, and mud16 are alleles of SNU56, NAM8, and SNU65, respectively. mud10 and mud15 affect the in vivo splicing efficiency of noncanonical introns. Moreover, mud10p strongly affects the in vitro formation of splicing complexes, and extracts from the mud15 strain contain a U1 snRNP that migrates aberrantly on native gels. Finally, we show that Nam8p/Mud15p contributes to the stability of U1 snRNP.

Amino Acid Sequence↗

PubMed1998

Relation of time since last birth and parity to survival of young women with breast cancer.

We investigated whether survival was related to recent childbirth or parity in a cohort of 540 women diagnosed with breast cancer before the age of 45 years who were followed for up to 14 years. Women who had given birth within 2 years before their diagnosis of breast cancer were at increased risk of dying, compared with nulliparous women, with an adjusted relative risk of 3.1 (95% confidence interval = 1.8-5.4). There was a moderate association of parity with mortality, with an adjusted relative risk of 1.8 (95% confidence interval = 1.2-2.9) for women with three or more births, compared with nulliparous women.

Adult↗

PubMed1998

The effect of location of transcutaneous electrical nerve stimulation on postoperative opioid analgesic requirement: acupoint versus nonacupoint stimulation.

UNLABELLED: Transcutaneous electrical nerve stimulation (TENS) has been used as a complementary (supplemental) therapy to opioid analgesics for pain relief after surgery. Simultaneous stimulation at a classical Chinese acupoint site and periincisional dermatomes significantly decreases the postoperative analgesic requirement. This sham-controlled study was designed to assess the relative effectiveness of acupoint versus nonacupoint stimulation on the postoperative hydromorphone (HM) requirement, the incidence of opioid-related side effects, and the overall recovery profile. One hundred women undergoing total abdominal hysterectomy or myomectomy procedures with a standardized general anesthesia were randomly assigned to one of four postoperative analgesic treatment regimens (n = 25 each): Group I = sham-TENS (no electrical current) at the Zusanli (ST36) acupoints, Group II = nonacupoint-TENS at the shoulders, Group III = dermatomal-TENS at the level of the surgical incision, and Group IV = acupoint-TENS at the Zusanli acupoints. The frequency of TENS was set in the standard dense-and-disperse mode of 2/100 Hz. The intensity of stimulation was set at 0 mA for patients in Group I and at 9-12 mA for patients in Groups II, III, and IV. A patient-controlled analgesia (PCA) device programmed to deliver bolus doses of HM 0.2-0.4 mg IV on demand with a minimal lockout interval of 10 min was used to quantify the postoperative opioid analgesic requirement. Standard 100-mm visual analog scales were used to assess pain, as well as sedation, fatigue, and nausea, at specific intervals after surgery. The numbers of PCA demands and delivered bolus doses, requirements for supplemental medication, and any opioid-related side effects were recorded. In the first 24 h postoperatively, the opioid requirements in Groups III and IV were decreased by 37% and 39%, respectively, compared with the control (sham) group and 35% and 38%, respectively, compared with Group II. The duration of PCA usage and the incidences of nausea and dizziness were also significantly decreased in Groups III and IV compared with Groups I and II. We conclude that periincisional dermatomal and Zusanli acupoint stimulation were equally effective in decreasing the postoperative opioid analgesic requirement and in reducing opioid-related side effects. Both of these positions were more effective than the nonacupoint (shoulder) location. IMPLICATIONS: The location of the stimulating electrodes seems to be an important determinant of the efficacy of transcutaneous electrical nerve stimulation in decreasing the need for opioid analgesics in the postoperative period. This study demonstrates that transcutaneous electrical nerve stimulation applied at the dermatomal level of the skin incision is as effective as Zusanli acupoint stimulation, and both were more effective than stimulation at a nonacupoint (shoulder) location.

Acupuncture Points↗

PubMed1998

Comparison of the liver and biliary duct development in man and in the rat at the end of the embryonic period.

Hepatic and biliary structures present during embryonic Carnegie stage 23 were analyzed and compared in OFA-IOPS rat and human embryos. The group of embryos was composed of 3 rat specimens-crown rump length (CRL) 16 mm, age 16 days 5 hours post coltus- and of 1 human embryo- CRL 31 mm, age 57 days PC-. The specimens were submitted to serial histological sections with graphic reconstruction. In both species, the basic architecture of liver parenchyma was established including parenchymal cords or plates alternating with hepatic sinusoids. Veinous channels were clearly defined. The intrahepatic biliary system, referred as ductal plates (DP) developed into the periportal connective tissue while the portal spaces were not yet existing. DP was recognized either as a single layered cuboidal structure or as a double layered one dilated to form mature tubular ducts. The latter layout was more frequent in the rat. Except for gallbladder which is never present in the rat, similarity and presence of the same hepatic structure in both species at the end of the embryonic period (stage 23) suggest that the rat is a good experimental model for liver development and will be useful to understand the mechanism of congenital anomalies and specially the involvement of ductal plates in the congenital diseases of intrahepatic bile ducts.

Animals↗

PubMed1997

Structure of a G48H mutant of HIV-1 protease explains how glycine-48 replacements produce mutants resistant to inhibitor drugs.

The crystal structure of human immunodeficiency virus type 1 (HIV-1) protease mutant G48H with peptidic inhibitor U-89360E is described. Comparison with wild-type protease-inhibitor complex shows that mutation of flap residue 48 to histidine allows stabilizing van der Waals contacts between the side chains of His48 and Phe53 as well as between His48 and the P2' and P3' inhibitor subsites. The flap region is less mobile than in the wild-type enzyme. A model of saquinavir-resistant mutant protease G48V in complex with saquinavir predicts interactions similar to those found in the G48H crystal. Energetic calculations confirm the similarity of the His48 and Val48 interactions.

Drug Resistance, Microbial↗

PubMed1997

Alteration of glycosylation renders HIV sensitive to inactivation by normal human serum.

Retroviruses from various mammalian species, excluding humans, are effectively inactivated in normal human serum (NHS). Recent studies have shown that NHS inactivation of retroviruses occurs through natural Ab recognition of a terminal glycosidic moiety on the viral envelope that is acquired during replication in the host cell. This carbohydrate structure (the alpha-galactosyl epitope) is expressed on the cells of most mammals, with the exception of humans and other Old World primates. In this study, NHS sensitivity of HIV was assessed following viral propagation in human cells that were manipulated to express the alpha-galactosyl epitope. HUT-78 cells were transduced with an exogenous alpha1-3-galactosyl transferase gene, which codes for the terminal glycosyl transferase responsible for generation of the alpha-galactosyl epitope. The transduced HUT-78 cells expressed high levels of the alpha-galactosyl epitope on their membrane surface, rendering them sensitive to killing in NHS. Similarly, HIV passaged through these cells acquired the alpha-galactosyl epitope in association with the envelope glycoprotein gp120 and was also effectively inactivated in NHS. Viral inactivation was abolished by the addition of a synthetic disaccharide that contains the alpha-galactosyl epitope, indicating that virolysis is mediated by anti-alpha-galactosyl natural Ab. These results demonstrate that, like other retroviruses bearing the alpha-galactosyl epitope, HIV modified to express this epitope is inactivated in NHS. Furthermore, these data suggest that expression of the alpha-galactosyl epitope on the surface of viruses may have implications in the interspecies transmission of such viruses to humans.

Animals↗

PubMed1997

Synthesis and antiviral activity of C2 analogs of enviroxime: an exploration of the role of critical functionality.

Enviroxime is a potent antiviral agent with broad spectrum activity in tissue culture against both rhinoviruses and enteroviruses. We have synthesized and studied a series of C2-substituted analogs in order to identify critical functionality and examine its role in antiviral activity. We have found that primary amino substitution is the most active. Ab initio calculations indicate that larger groups at C2 may provide a repulsive steric interaction at N3, and in those cases where this undesirable conformation has limited flexibility, the antiviral activity is severely reduced. Further the results show that an amino hydrogen at C2 is strongly hydrogen bonded to the N1 sulfonyl oxygen, which in the case of Enviroxime may act to enhance the activity by holding the second hydrogen in a desirable orientation for interaction at an antiviral site.

Antiviral Agents↗

PubMed1997

Caspase-3-generated fragment of gelsolin: effector of morphological change in apoptosis.

The caspase-3 (CPP32, apopain, YAMA) family of cysteinyl proteases has been implicated as key mediators of apoptosis in mammalian cells. Gelsolin was identified as a substrate for caspase-3 by screening the translation products of small complementary DNA pools for sensitivity to cleavage by caspase-3. Gelsolin was cleaved in vivo in a caspase-dependent manner in cells stimulated by Fas. Caspase-cleaved gelsolin severed actin filaments in vitro in a Ca2+-independent manner. Expression of the gelsolin cleavage product in multiple cell types caused the cells to round up, detach from the plate, and undergo nuclear fragmentation. Neutrophils isolated from mice lacking gelsolin had delayed onset of both blebbing and DNA fragmentation, following apoptosis induction, compared with wild-type neutrophils. Thus, cleaved gelsolin may be one physiological effector of morphologic change during apoptosis.

Actins↗

PubMed1997

Induced direct binding of the adapter protein Nck to the GTPase-activating protein-associated protein p62 by epidermal growth factor.

The SH3-SH3-SH3-SH2 adapter protein Nck links receptor tyrosine kinases, such as EGF and PDGF receptors, to downstream signaling pathways, among which p21cdc42/rac-activated kinase cascade, Sos-activated Ras signaling and the human Wiskott-Aldrich Syndrome protein (WASp)-mediated actin cytoskeleton changes, have been implicated. In EGF stimulated cells, Nck co-immunoprecipitates with a number of phosphotyrosine proteins including the EGF receptor (Li et al., 1992 Mol. Cell. Biol. 12: 5824-2833). To identify the phosphotyrosine protein(s) that directly interacts with Nck and to distinguish it from indirectly associated proteins, preexisting phosphoytrosine protein complexes in the cell lysate were dissociated by heat and SDS prior to the test for binding to Nck. We found that Nck does not directly bind to EGF receptor, instead it binds via its SH2 domain to a 62 kDa phosphotyrosine protein. We present evidence demonstrating that the Nck-bound p62 is related to the previously identified GTPase-activating protein (GAP)-associated phosphotyrosine protein p62. (1) The Nck-bound and the GAP-bound p62 proteins co-migrate with each other in SDS-PAGE. (2) SH2 domains from Nck and GAP compete for binding to p62 in vitro. (3) Purified GST-Nck-SH2 binds directly to the GAP-associated p62. Under these conditions, SH2 domains from PLCgamma, PI-3 kinase, SHC, and Grb2 did not bind p62. (4) Tryptic phosphopeptide maps of the Nck- and the GAP-associated p62 proteins are identical. However, Nck and GAP do not co-immunoprecipitate with each other and apparently bind to different pools of p62. This study suggests that the GAP-associated p62 acts as an SH2 domain docking protein and mediates the interaction between Nck and EGF receptor in response to EGF stimulation.

3T3 Cells↗

PubMed1997

Kinetic properties of saquinavir-resistant mutants of human immunodeficiency virus type 1 protease and their implications in drug resistance in vivo.

In order to study the basis of resistance of human immunodeficiency virus, type 1 (HIV-1), to HIV-1 protease inhibitor saquinavir, the catalytic and inhibition properties of the wild-type HIV-1 protease and three saquinavir resistant mutants, G48V, L90M, and G48V/L90M, were compared. The kinetic parameter kcat/Km was determined for these proteases using eight peptide substrates whose sequences were derived from the natural processing site sequences of HIV-1. The kcat/Km values were determined using conventional steady-state kinetics as well as initial velocities of mixed substrate cleavages under the condition where the substrate concentrations [S]o << Km. The independently determined kcat and Km values for some of the substrates confirmed the accuracy of the mixed-substrate method and also permitted the calculation in all cases of true rather than relative kcat/Km values. The Ki values were also determined. Using a previously described kinetic model [Tang, J., & Hartsuck, J. A. (1995) FEBS Lett. 367, 112-116], the relative processing activities of HIV-1 protease variants were estimated in the saquinavir concentration range of 0-10(-7) M. Although the protease activity of G48V, L90M, and G48V/L90M are only about 10, 7, and 3% of that of the wild-type HIV-1 protease in the absence of inhibitor, the resistance tendencies of the three mutants are clearly manifest by relatively less activity loss as inhibitor concentration becomes higher. Also, the ratios of the activities of the four protease species at certain saquinavir concentrations appear to correlate with the population ratios of the four protease species at different time points of clinical trials. This correlation suggests that the population ratio of the protease species is driven by in vivo saquinavir concentration, which appears to be in the range 10(-10)-10(-9) M during the clinical trials.

Dose-Response Relationship, Drug↗

PubMed1997

The crystal structure of bovine bile salt activated lipase: insights into the bile salt activation mechanism.

BACKGROUND: The intestinally located pancreatic enzyme, bile salt activated lipase (BAL), possesses unique activities for digesting different kinds of lipids. It also differs from other lipases in a requirement of bile salts for activity. A structure-based explanation for these unique properties has not been reached so far due to the absence of a three-dimensional structure. RESULTS: The crystal structures of bovine BAL and its complex with taurocholate have been determined at 2.8 A resolution. The overall structure of BAL belongs to the alpha/beta hydrolase fold family. Two bile salt binding sites were found in each BAL molecule within the BAL-taurocholate complex structure. One of these sites is located close to a hairpin loop near the active site. Upon the binding of taurocholate, this loop becomes less mobile and assumes a different conformation. The other bile salt binding site is located remote from the active site. In both structures, BAL forms similar dimers with the active sites facing each other. CONCLUSIONS: Bile salts activate BAL by binding to a relatively short ten-residue loop near the active site, and stabilize the loop in an open conformation. Presumably, this conformational change leads to the formation of the substrate-binding site, as suggested from kinetic data. The BAL dimer observed in the crystal structure may also play a functional role under physiological conditions.

Animals↗

PubMed1997

Fumonisin B1-induced sphingolipid depletion inhibits vitamin uptake via the glycosylphosphatidylinositol-anchored folate receptor.

The folate receptor, like many glycosylphosphatidylinositol-anchored proteins, is found associated with membrane domains that are insoluble in Triton X-100 at low temperature and that are enriched in cholesterol and sphingolipids. Depletion of cellular cholesterol has been shown to inhibit vitamin uptake by this receptor (Chang, W. -J., Rothberg, K. G., Kamen, B. A., and Anderson, R. G. W. (1993) J. Cell Biol. 118, 63-69), suggesting that these domains regulate this process. In this study, the importance of sphingolipids for folate receptor function was investigated in Caco-2 cells using fumonisin B1, a mycotoxin that inhibits the biosynthesis of these lipids. The folate receptor-mediated transport of 5-methyltetrahydrofolate was almost completely blocked in cells in which sphingolipids had been reduced by approximately 40%. This inhibition was dependent on the concentration and duration of the treatment with the mycotoxin and was mediated by the sphingolipid decrease. Neither receptor-mediated nor facilitative transport was inhibited by fumonisin B1 treatment, indicating that the effect of sphingolipid depletion was specific for folate receptor-mediated vitamin uptake. A concurrent loss in the total amount of folate binding capacity in the cells was seen as sphingolipids were depleted, suggesting a causal relationship between folate receptor number and vitamin uptake. These findings suggest that dietary exposure to fumonisin B1 could adversely affect folate uptake and potentially compromise cellular processes dependent on this vitamin. Furthermore, because folate deficiency causes neural tube defects, some birth defects unexplained by other known risk factors may be caused by exposure to fumonisin B1.

Biological Transport↗

PubMed1997

Influence of iron-removal procedures on sequential electron transfer in photosynthetic bacterial reaction centers studied by transient EPR spectroscopy.

Electron spin polarized electron paramagentic resonance (ESP EPR) spectra were obtained with deuterated iron-removed photosynthetic bacterial reaction centers (RCs) to specifically investigate the effect of the rate of primary charge separation, metal-site occupancy, and H-subunit content on the observed P865+QA- charge-separated state. Fe-removed and Zn-substituted RCs from Rb. sphaeroides R-26 were prepared by refined procedures, and specific electron transfer rates (kQ) from the intermediate acceptor H- to the primary acceptor QA of (200 ps)-1 vs (3-6 ns)-1 were observed. Correlation of the transient EPR and optical results shows that the observed slow kQ rate in Fe-removed RCs is H-subunit-independent, and, in some cases, independent of Fe-site occupancy as Zn2+ substitution does not ensure retention of the native kQ. In addition, shifts in the optical spectrum of P865 and differences in the high-field region of the Q-band ESP spectrum for Fe-removed RCs with slow kQ indicate possible structural changes near P865. The experimental X-band and Q-band spin-polarized EPR spectra for deuterated Fe-removed RCs where kQ is at least 15-fold slower at room temperature than the (200 ps)-1 rate observed for native Fe-containing RCs have different relative amplitudes and small g-value shifts compared to the spectra of Zn-RCs which have a kQ unchanged from native RCs. These differences reflect the trends in polarization predicted from the sequential electron transfer polarization (SETP) model [Morris et al. (1995) J. Phys. Chem. 99, 3854-3866; Tang et al. (1996) Chem. Phys. Lett. 253, 293-298]. Thus, SETP modeling of these highly resolved ESP spectra obtained with well-characterized proteins will provide definitive information about any light-induced structural changes of P865, H, and QA that occur upon formation of the P865+QA- charge-separated state.

Electron Spin Resonance Spectroscopy↗

PubMed1997

Identification and characterization of a yeast homolog of U1 snRNP-specific protein C.

U1C is one of the three human U1 small nuclear ribonucleoprotein (snRNP)-specific proteins and is important for efficient complex formation between U1 snRNP and the pre-mRNA 5' splice site. We identified a hypothetical open reading frame in Saccharomyces cerevisiae as the yeast homolog of the human U1C protein. The gene is essential, and its product, YU1C, is associated with U1 snRNP. YU1C depletion gives rise to normal levels of U1 snRNP and does not have any detectable effect on U1 snRNP assembly. YU1C depletion and YU1C ts mutants affect pre-mRNA splicing in vivo, and extracts from these strains form low levels of commitment complexes and spliceosomes in vitro. These experiments indicate a role for YU1C in snRNP function. Structure probing with RNases shows that only the U1 snRNA 5' arm is hypersensitive to RNase I digestion when YU1C is depleted. Similar results were obtained with YU1C ts mutants, indicating that U1C contributes to a proper 5' arm structure prior to its base pairing interaction with the pre-mRNA 5' splice site.

Amino Acid Sequence↗

PubMed1997

TGF-beta down-regulates stromal IL-7 secretion and inhibits proliferation of human B cell precursors.

Development of lymphoid progenitors in vivo requires interaction with a bone marrow stromal microenvironment containing multiple cytokines involved in the development of nonlymphoid hemopoietic lineages. We tested the effect of one such cytokine, TGF-beta, on the proliferation of early human clonogenic lymphoid progenitors using a stroma-dependent in vitro culture system. TGF-beta caused a dose-dependent inhibition of lymphoid progenitor colonies that was reversible at low TGF-beta doses by addition of exogenous IL-7 to the cultures. IL-7 was unable to reverse the inhibitory effect of higher TGF-beta concentrations or inhibition caused by IL-1alpha, IL-4, or TNF-alpha. Stromal IL-7 mRNA expression and protein secretion were markedly down-regulated by TGF-beta, suggesting that inhibition of stromal IL-7 secretion partially accounts for the inhibitory effect of TGF-beta on lymphopoiesis in this culture system. It is likely that higher TGF-beta concentrations do not inhibit lymphopoiesis by down-regulating IL-7 receptor expression, since this cytokine did not reduce IL-7R alpha or gamma c mRNA levels in normal B cell precursors. Since direct stromal contact is required for in vitro lymphopoiesis, the potential regulation of the IL-7 pathway by cell adhesion was examined. Adhesion of human B cell precursors to stroma did not alter stromal IL-7 expression or expression of IL-7R alpha or gamma c-chains by B cell precursors. These results indicate that TGF-beta is a significant negative regulator of stroma-dependent proliferation of early human lymphoid progenitors and acts in part by down-regulating stromal IL-7 secretion.

B-Lymphocytes↗