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Biomedical subjects

Y Yuan

Publications and source records attributed to Y Yuan.

At least 235 records · Page 13Linked to original sources
PubMed1995

Substrate recognition by human RNase P: identification of small, model substrates for the enzyme.

RNase P from HeLa cells can efficiently cleave tRNA precursor molecules in vitro but cannot cleave potential substrates from which the D, anticodon and variable loops and stems of the tRNA moiety have all been removed. However, molecules from which the latter subdomains have been removed individually do serve as substrates. We show here that molecules that contain only a 5' leader sequence, the acceptor stem and the T stem and loop of the tRNA domain, and a bulge as small as one nucleotide downstream from nucleotide 7 in the tRNA sequence at the junction of the two stems, can serve as substrates for human RNase P. The identity of the nucleotide in the bulge is important in determining both the efficiency of the cleavage and the conformation of the substrate and/or the enzyme-substrate complex. We also show that the human enzyme locates the appropriate site for cleavage of its substrates in part by 'measuring' the length of the helices in the acceptor and T stems in both model and natural substrates.

Base Sequence↗
PubMed1995

Subnanosecond polarized fluorescence photobleaching: rotational diffusion of acetylcholine receptors on developing muscle cells.

Polarized fluorescence recovery after photobleaching (PFRAP) is a technique for measuring the rate of rotational motion of biomolecules on living, nondeoxygenated cells with characteristic times previously ranging from milliseconds to many seconds. Although very broad, that time range excludes the possibility of quantitatively observing freely rotating membrane protein monomers that typically should have a characteristic decay time of only several microseconds. This report describes an extension of the PFRAP technique to a much shorter time scale. With this new system, PFRAP experiments can be conducted with sample time as short as 0.4 microseconds and detection of possible characteristic times of less than 2 microseconds. The system is tested on rhodamine-alpha-bungarotoxin-labeled acetylcholine receptors (AChRs) on myotubes grown in primary cultures of embryonic rat muscle, in both endogenously clustered and nonclustered regions of AChR distribution. It is found that approximately 40% of the AChRs in nonclustered regions undergoes rotational diffusion fast enough to possibly arise from unrestricted monomer Brownian motion. The AChRs in clusters, on the other hand, are almost immobile. The effects of rat embryonic brain extract (which contains AChR aggregating factors) on the myotube AChR were also examined by the fast PFRAP system. Brain extract is known to abolish the presence of endogenous clusters and to induce the formation of new clusters. It is found here that rotational diffusion of AChR in the extract-induced clusters is as slow as that in endogenous clusters on untreated cells but that rotational diffusion in the nonclustered regions of extract-treated myotubes remains rapid.

Animals↗
PubMed1995

Serologic responses of infertile women to the 60-kd chlamydial heat shock protein (hsp60).

OBJECTIVE: To determine whether women with Chlamydia trachomatis-associated tubal infertility are more likely than other infertile women to have antibodies to a particular region of the 60-kd chlamydial heat shock protein, hsp60. DESIGN: Serologic responses to the chlamydial hsp60 were examined in 43 infertile women seropositive for Chlamydia trachomatis, including 21 women with tubal infertility, 13 women with endometriosis, and 9 women with other causes of infertility. Antibody responses were localized to regions of hsp60 using five nonoverlapping recombinant polypeptides. RESULTS: Sixteen women with tubal infertility had anti-hsp60 antibodies compared with seven women with endometriosis and two women with other causes of infertility. Antibodies of 11 women with tubal infertility reacted predominantly with a region of hsp60 containing amino acids (201 to 300) compared with 1 women without tubal infertility. In contrast, antibodies that localized to the carboxyl terminus, amino acids (401 to 544), were seen equally in all groups. CONCLUSIONS: Among seropositive infertile women, antibodies that localized to amino acids (201 to 300) were immunodominant in those with tubal infertility but not in those with infertility due to other causes.

Adult↗
PubMed1995

Association between GRB2/Sos and insulin receptor substrate 1 is not sufficient for activation of extracellular signal-regulated kinases by interleukin-4: implications for Ras activation by insulin.

Insulin receptor substrate 1 (IRS-1) mediates the activation of a variety of signaling pathways by the insulin and insulin-like growth factor 1 receptors by serving as a docking protein for signaling molecules with SH2 domains. We and others have shown that in response to insulin stimulation IRS-1 binds GRB2/Sos and have proposed that this interaction is important in mediating Ras activation by the insulin receptor. Recently, it has been shown that the interleukin (IL)-4 receptor also phosphorylates IRS-1 and an IRS-1-related molecule, 4PS. Unlike insulin, however, IL-4 fails to activate Ras, extracellular signal-regulated kinases (ERKs), or mitogen-activated protein kinases. We have reconstituted the IL-4 receptor into an insulin-responsive L6 myoblast cell line and have shown that IRS-1 is tyrosine phosphorylated to similar degrees in response to insulin and IL-4 stimulation in this cell line. In agreement with previous findings, IL-4 failed to activate the ERKs in this cell line or to stimulate DNA synthesis, whereas the same responses were activated by insulin. Surprisingly, IL-4's failure to activate ERKs was not due to a failure to stimulate the association of tyrosine-phosphorylated IRS-1 with GRB2/Sos; the amounts of GRB2/Sos associated with IRS-1 were similar in insulin- and IL-4-stimulated cells. Moreover, the amounts of phosphatidylinositol 3-kinase activity associated with IRS-1 were similar in insulin- and IL-4-stimulated cells. In contrast to insulin, however, IL-4 failed to induce tyrosine phosphorylation of Shc or association of Shc with GRB2. Thus, ERK activation correlates with Shc tyrosine phosphorylation and formation of an Shc/GRB2 complex. Thus, ERK activation correlates with Shc tyrosine phosphorylation and formation of an Shc/GRB2 complex. Previous studies have indicated that activation of ERks in this cell line is dependent upon Ras since a dominant-negative Ras (Asn-17) blocks ERK activation by insulin. Our findings, taken in the context of previous work, suggest that binding of GRB2/Sos to Shc may be the predominant mechanism whereby insulin as well as cytokine receptors activate Ras.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Interaction of neutrophils and endothelium in isolated coronary venules and arterioles.

This study reports measurements of porcine neutrophil dynamics in isolated microvessels. Porcine coronary venules and arterioles were isolated, cannulated, and perfused with fluorescently labeled neutrophils at a series of flow velocities. In venules (62.50 +/- 5.41 microns diam) under control conditions, rolling neutrophils were often observed at intraluminal flow velocities ranging from 600 to 6,000 microns/s, and the rolling fraction varied inversely as a function of flow velocity. There was no significant adherence under the control conditions at any of the various flow velocities. Pretreatment of the neutrophils with human recombinant complement 5a (C5a, 10(-8) M) increased adherence at low flow velocities but did not alter the rolling fraction. In contrast to venules, rolling neutrophils were not observed in arterioles (58.80 +/- 5.6 microns diam). Furthermore, neutrophils that were pretreated with C5a did not adhere to the arteriolar endothelium even at low flow velocities. We suggest that 1) isolated microvessels perfused with fluorescently labeled neutrophils are suitable models for the study of the interaction between neutrophils and the microvascular endothelium, 2) shear force plays an important role in neutrophil rolling in coronary venules but is not the major factor that prevents neutrophil rolling and adherence in arterioles, and 3) C5a causes neutrophil adherence in venules but not in arterioles, indicating that different mechanisms underlie the interaction between neutrophils and endothelium in venules and arterioles.

Animals↗
PubMed1995

[Measurement of the reserve function of inspiratory muscle and its clinical significance].

The principles of measuring inspiratory muscle tension-time index (TTim) and the ratio of the works of inspiration over the maximal works of inspiration (Wi/Wi(max)) were investigated and their formulae were deduced, i.e. TTim = (Pi x Ti)/(MIP x Ttot) and Wi/Wi(max) = (Pi x VT)/(MIP x IC). The importance of the inspiratory pressure and the maximal inspiratory pressure (MIP) measured at function residual capacity (FRC) level was emphasized. Both TTim and Wi/Wi(max) were measured in 35 normal subjects and 89 patients with chronic obstructive pulmonary disease (COPD). The results showed that normal value of TTim was 0.0253 +/- 0.0055 which corresponds to the normal value of the diaphragm tension-time index (TTdi = 0.02-0.03) reported by Bellemare. Patients with COPD had a mean TTim much higher than that of normals (P < 0.01). The works of inspiration (Wi) in patients with COPD increased, while the maximal works of inspiration (Wi(max)) declined, so Wi/Wi(max) became significantly greater than that of normals (P < 0.01). The results also showed that there was a linear relationship between Pi/Pimax and TTim or Wi/Wimax (r = 0.7891, 0.9738, 0.6459, 0.9327, P < 0.01). Therefore, we suggest that both TTim and Wi/Wimax can be used as clinical indices to reflect the reserve function of inspiratory muscles.

Adult↗
PubMed1995

Methylmercury acts at multiple sites to block hippocampal synaptic transmission.

To explore the mechanisms by which methylmercury (MeHg) blocks central synaptic transmission, intracellular recordings of action potentials and resting membrane potentials were made in CA1 neurons of rat hippocampal slices. At 4 to 100 microM, MeHg blocked action potentials in a concentration- and time-dependent manner. MeHg also depolarized Ca1 neuronal membranes. However, this effect occurred more slowly than block of action potentials because the resting membrane potentials remained unchanged when threshold stimulation-evoked action potentials were blocked. Thus, MeHg may initially alter the threshold level of neuronal membrane excitability and subsequently depolarize the membrane leading to block of synaptic transmission. To identify potential sites of action of MeHg, effects of MeHg on the responses of CA1 neurons to orthodromic stimulation of Schaffer collaterals, antidromic stimulation of the alveus, direct injection of current at cell soma and iontophoretic application of glutamate were compared. At 20 and 100 microM, MeHg blocked action potentials evoked by stimulation of Schaffer collaterals and by current injection at the cell soma at similar times. In contrast, action potentials evoked by stimulation of the alveus were blocked more rapidly by 100 microM MeHg than were action potentials evoked by current injection at CA1 neuronal soma. MeHg also blocked the responses of CA1 neurons to iontophoresis of glutamate, but time to block of these responses was slower than block of the corresponding orthodromically-evoked responses by stimulation of Schaffer collaterals. Compared to excitatory postsynaptic potentials, inhibitory postsynaptic potentials appeared to be more sensitive to MeHg, because block of inhibitory postsynaptic potentials occurred before block of excitatory postsynaptic potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Effects of hypoxic endothelial cell conditioned medium on proliferation and collagen synthesis of smooth muscle cells and inhibitory effects of radix salviae miltiorrhizae.

The effects of hypoxic endothelial cell conditioned medium (HECCM) on proliferation and collagen synthesis of cultured porcine pulmonary arterial smooth muscle cells (PASMCs) were studied by 3H-thymidine (3H-TdR) and 3H-proline incorporations, image analysis for determination of DNA content and colorimetric assay using MTT, and the inhibitory effects of radix salviae miltiorrhizae (RSM) on them were also investigated. The results showed that HECCM could induce enhancement of the enzymatic activity of mitochondria, increase of the nucleic DNA content and increases of the 3H-TdR and 3H-proline incorporation in PASMCs. The 3H-proline incorporation in PASMCs cultured in HECCM was 1.83 times as much as that cultured in normoxic endothelial cell conditioned medium (NECCM). Compared with the control, Chinese herb medicine RSM could inhibit the proliferation of PASMCs cultured in HECCM and decrease the 3H-proline incorporation in PASMCs cultured in both HECCM and NECCM (P < 0.001). However, RSM had no effects on the nucleic DNA content and 3H-TdR incorporation into DNA of PASMCs cultured in NECCM. It suggests that hypoxia may stimulate the endothelia to synthesize and secrete some cytokines which can stimulate the proliferation and the synthesis of collagen of PASMCs and RSM can inhibit this process.

Animals↗
PubMed1995

[Preoperative evaluation of hepatic functional reserve for patients with primary liver carcinoma].

The retention rate of indocyanine green at 15 minutes (ICGR15) and routine hepatic function tests were performed preoperatively in 122 cases of patients with primary liver carcinomas in order to evaluate the hepatic functional reserve. These patients were divided into 3 groups according to the post-operative changes of hepatic function. 87, 24 and 11 cases showed good recovery (group good), mild liver dysfunction (group mild) and severe liver dysfunction (group severe) respectively, after operation. The differences of Pugh's points, ALT, ALP and gamma-GT between each two groups were not significant. But, the differences of ICGR15 were very significant. We also divided all cases into 3 groups according to the value of ICGR15. The incidence of liver dysfunction was 6.0% in group A (ICGR15 < 10.0%), 27.8% in group B (ICGBR15 = 10.0%-20.0%) and 76.5% in group C (ICGR15 > 20.0%), respectively. The difference of the incidences of liver dysfunction in these 3 groups was very significant. The higher the ICGR15, the more the incidence of liver dysfunction. These results demonstrated that ICGR15 is a good indicator to judge hepatic functional reserve for patients with primary liver carcinoma.

Adult↗
PubMed1995

[Simultaneous bilateral total knee replacement for the patients with serious rheumatoid disease].

This retrospective study reviews 57 patients with serious rheumatoid disease who had bilateral total knee arthroplasties simultanneously between 1987 and 1994. The short follow-up results revealed that there was no increase in complications in the patients with simultaneous bilateral procedures, and nearly identical postoperative results to those observed among patients with single joint replacement. Advantage of simultaneous bilateral total arthroplasty include reduction in hospital cost, the need for less invasive surgical event and the ability to rehabilitate the patient symmetrically.

Adult↗
PubMed1994

Tyrosine kinases regulate the cytoskeletal attachment of integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) and the cellular retraction of fibrin polymers.

Integrins promote cell-substratum and cell-cell adhesion by acting as transmembrane linker molecules between extracellular adhesion proteins and the actin-rich cytoskeleton. The integrin alpha IIb beta 3 (platelet glycoprotein IIb/IIIa) is essential for platelet spreading, aggregation, fibrin clot retraction, and for the transduction of extracellular signals. We examined the effect of the specific tyrosine kinase inhibitor herbimycin A on integrin and cytoskeletal-mediated events in thrombin-stimulated platelets. Incubation of washed platelets for 24 h with herbimycin A (5 microM) abolished the thrombin-stimulated cytoskeletal enzyme activity of pp60c-src in parallel with a reduction in the tyrosine phosphorylation of multiple platelet proteins, as assessed with anti-phosphotyrosine immunoblots. However, thrombin-induced activation of protein kinase C and the production of thromboxane A2 were not altered by herbimycin A. Despite the absence of cytoskeletal pp60c-src enzyme activity, platelet shape change, aggregation, and serotonin release were unaltered following platelet stimulation with thrombin (0.05-1.0 unit/ml). Herbimycin A-treated platelets also demonstrated normal platelet aggregation in response to collagen (5 micrograms/ml), ionophore A23187 (2 microM), and ADP/adrenaline (10 microM each). However, the ability of herbimycin A-treated platelets to retract fibrin gels was significantly reduced. This defect in clot retraction was associated with reduced incorporation of integrin alpha IIb beta 3 into the cytoskeletal fraction of thrombin-aggregated platelets. Our studies suggest that tyrosine kinases in platelets regulate the cytoskeletal attachment of alpha IIb beta 3, as an essential process for the transmission of cellular contractile forces to fibrin polymers.

Benzoquinones↗
PubMed1994

Adhesion receptor activation of phosphatidylinositol 3-kinase. von Willebrand factor stimulates the cytoskeletal association and activation of phosphatidylinositol 3-kinase and pp60c-src in human platelets.

The cytoskeleton participates in the coordinated regulation of intracellular signaling molecules, following agonist stimulation of cells. We have demonstrated that von Willebrand factor (vWF) induced the cytoskeletal association and activation of phosphatidylinositol 3-kinase (PtdIns 3-kinase) in human platelets. The activation of PtdIns 3-kinase coincided with the tyrosine phosphorylation of multiple platelet proteins, as assessed by anti-phosphotyrosine immunoblotting. One of these tyrosine-phosphorylated proteins, pp60c-src, became specifically enriched in the cytoskeletal fraction of vWF-stimulated platelets. The vWF-stimulated cytoskeletal association of PtdIns 3-kinase and pp60c-src required platelet stirring and aggregation, was specifically blocked by an anti-GPIb monoclonal antibody, and was not observed in platelets lacking the glycoprotein Ib/IX complex (Bernard-Soulier syndrome). Pretreatment of normal platelets with 5 mM EDTA (37 degrees C for 90 min) or RGDS (2 mM), which disrupts the binding of various adhesive proteins to platelet integrins and inhibits fibrinogen-mediated platelet aggregation, did not alter the vWF-stimulated activation and cytoskeletal association of PtdIns 3-kinase and pp60c-src. Pretreatment of platelets with acetylsalicylic acid (1 mM) completely abolished vWF-stimulated production of thromboxane A2, dense granule release, and the activation of protein kinase C, without altering the activation and cytoskeletal translocation of PtdIns 3-kinase and pp60c-src. Our results suggest that vWF binding to the platelet adhesion receptor glycoprotein Ib/IX can mediate activation and translocation of both tyrosine and lipid kinase(s) independent of other agonists.

Aspirin↗
PubMed1994

Selection of guide sequences that direct efficient cleavage of mRNA by human ribonuclease P.

Any RNA, when in a complex with another oligoribonucleotide known as an external guide sequence (EGS), can become a substrate for ribonuclease P. Simulation of evolution in vitro was used to select EGSs that bind tightly to a target substrate messenger RNA and that increase the efficiency of cleavage of the target by human ribonuclease P to a level equal to that achieved with natural substrates. The most efficient EGSs form transfer RNA precursor-like structures with the target RNA, in which the analog of the anticodon stem has been disrupted, an indication that selection for the optimal substrate for ribonuclease P yields an RNA structure different from that of present-day transfer RNA precursors.

Anticodon↗
PubMed1994

Human RNaseP RNA and nucleolar 7-2 RNA share conserved 'To' antigen-binding domains.

RNase P in both prokaryotes and eukaryotes is a ribonucleoprotein that cleaves tRNA precursors to generate the 5' termini of the mature tRNAs. Many patients with autoimmune diseases produce antibodies against a 40 kDa protein (designated To or Th antigen) which is an integral component of eukaryotic RNaseP as well as nucleolar 7-2 RNP which is identical to the mitochondrial RNA processing (MRP) RNP. Interestingly, the To antigen found in human cells and the C5 protein, the only protein component of E. coli RNaseP, are antigenically related. In this study, we show that a 56 nucleotide-long sequence, corresponding to nucleotides 20-75 near the 5' end of human RNaseP RNA, is sufficient to bind the To antigen. We previously showed that the human To antigen binds to a short distinct structural domain near the 5' end of human 7-2/MRP RNA. There is no obvious primary sequence homology between the To antigen binding sites in RNaseP RNA and 7-2/MRP RNA; however, these sequences are capable of assuming a similar secondary structure which corresponds to the recently proposed 'cage' structure for RNaseP RNAs and 7-2/MRP RNA (Forster and Altman (1989) Cell 62: 407-409). These data are supportive of the idea that these two RNAs may have evolved from a common progenitor molecule.

Antibodies↗
PubMed1994

[Comparative study on three serologic tests for detecting antibodies in cases with bancroftian microfilaremia].

A comparative study was conducted for detecting antibody levels of bancroftian microfilaremia cases by using three serologic tests, IFAT, ELISA and dot-ELISA. A total of 102 serum specimens were collected from bancroftian microfilaremia cases. The positive rate was 89.2% (91/102) with IFAT (serum dilution > or = 1:20), 84.3% (86/102) with ELISA (OD value > or = 0.440) and 89.2% (91/102) with dot-ELISA (serum dilution > or = 1:80), respectively (P > 0.05); while in healthy individuals from non-endemic areas the false positive rate was 0(0/30), 1.8(1/55) and 0(0/54), respectively. The results indicated that there were no statistically significant differences among the three serologic tests. There was no correlation found in this study between microfilaria density and the antibody level. It was also proved that the detection rate of the combined use of either 2 or 3 tests was higher than each of the three tests; the positive rates being 94.1%-98.0%.

Animals↗
PubMed1994

66A-078:a kappa-opiate receptor agonist for amelioration of spinal spasticity.

The effect and mechanism of kappa opiate receptor agonist and high-frequency electrostimulation of acupoints in treating spinal spasticity were studied. The spinal spastic models were made by gradual mechanical compression on the cervical spinal cord of rabbits. 24 prepared rabbits were divided into 3 groups randomly, and each group with 8 rabbits was given intrathecally kappa-receptor agonist 66A-078, kappa-receptor antagonist +66A-078 and normal saline respectively. The degree of spasticity was quantified by both clinical score and electrophysiological examinations. The result showed that the spasticity was markedly inhibited by intrathecal injection of 66A-078 and that the kappa-receptor antagonist (naloxone) reversed this effect. We can infer that the antispastic effect of 66A-078 is mediated by kappa-receptors. This result is helpful in explaining the immediate antispastic mechanism of high-frequency electrostimulation of acupoints discussed in previous study.

Animals↗