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Biomedical subjects

P Jiang

Publications and source records attributed to P Jiang.

At least 73 records · Page 4Linked to original sources
PubMed1998

The regulation of Escherichia coli glutamine synthetase revisited: role of 2-ketoglutarate in the regulation of glutamine synthetase adenylylation state.

The regulation of Escherichia coli glutamine synthetase (GS) by reversible adenylylation has provided one of the classical paradigms for signal transduction by cyclic cascades. Yet, many mechanistic features of this regulation remain to be elucidated. We examined the regulation of GS adenylylation state in a reconstituted system containing GS, adenylyltransferase (ATase), the PII signal transduction protein that controls ATase, and the uridylyltransferase/uridylyl-removing enzyme (UTase/UR), which has a role in regulating PII. In this reconstituted bicyclic cascade system, the adenylylation state of GS was regulated reciprocally by the small molecule effectors 2-ketoglutarate and glutamine at physiological effector concentrations. By examination of the individual regulatory monocycles and comparison to the bicyclic system and existing data, we could deduce that the only sensors of 2-ketoglutarate were PII and PII-UMP. At physiological conditions, we observed that the main role of 2-ketoglutarate in bringing about the deadenylylation of GS was to inhibit GS adenylylation, and this was due to the allosteric regulation of PII activity. Glutamine acted as an allosteric regulator of both ATase and UTase/UR. We also compared the regulation of GS adenylylation state to the regulation of phosphorylation state of the transcription factor NRI (NtrC) in a reconstituted bicyclic system containing NRI, the bifunctional kinase/phosphatase NRII (NtrB), PII, and the UTase/UR. This comparison indicated that, at a fixed 2-ketoglutarate concentration, the regulation of GS adenylylation state by glutamine was sharper and occurred at a higher concentration than did the regulation of NRI phosphorylation. The possible biological implications of this regulatory arrangement are discussed.

Adenosine Triphosphate↗
PubMed1998

Enzymological characterization of the signal-transducing uridylyltransferase/uridylyl-removing enzyme (EC 2.7.7.59) of Escherichia coli and its interaction with the PII protein.

The uridylyltransferase/uridylyl-removing enzyme (UTase/UR) of Escherichia coli plays an important role in the regulation of nitrogen assimilation by controlling the uridylylation state of the PII signal transduction protein (PII) in response to intracellular signals. The reversible uridylylation of PII indirectly controls the activity of PII receptors that regulate transcription from nitrogen-regulated promoters and the activity of glutamine synthetase. Here, we present a detailed analysis of the uridylyltransferase and uridylyl-removing activities and their regulation by the small molecule effectors ATP, 2-ketoglutarate, and glutamine. Several important features of enzyme mechanism and regulation were elucidated. Mg2+ appeared to be the physiologically relevant metal ion cofactor for both transferase and uridylyl-removing activities. The transferase reaction proceeded by an ordered bi-bi kinetic mechanism, with PII binding before UTP and pyrophosphate (PPi) released before PII-UMP. The uridylyl-removing reaction proceeded with rapid equilibrium binding of substrate and random release of products. Both reactions were activated by ATP and 2-ketoglutarate, which did so by binding only to PII and PII-UMP. The binding of these effectors to PII and PII-UMP was characterized. Glutamine inhibited the transferase reaction by inhibiting the chemistry step, while glutamine provided nonessential mixed-type activation of the uridylyl-removing activity, lowering the apparent Km and increasing kcat. Our data were consistent with the hypothesis that all effects of glutamine are due to the binding of central complexes at a single glutamine site. By comparing the effects of the activators with their reported in vivo concentrations, we conclude that in intact cells the uridylylation state of PII is regulated mainly by the glutamine concentration and is largely independent of the 2-ketoglutarate concentration. Our kinetic data were consistent with the hypothesis that both transferase and uridylyl-removal reactions occurred at a single active center on the enzyme.

Bacterial Proteins↗
PubMed1998

Endothelial cell death, angiogenesis, and microvascular function after castration in an androgen-dependent tumor: role of vascular endothelial growth factor.

The sequence of events that leads to tumor vessel regression and the functional characteristics of these vessels during hormone-ablation therapy are not known. This is because of the lack of an appropriate animal model and monitoring technology. By using in vivo microscopy and in situ molecular analysis of the androgen-dependent Shionogi carcinoma grown in severe combined immunodeficient mice, we show that castration of these mice leads to tumor regression and a concomitant decrease in vascular endothelial growth factor (VEGF) expression. Androgen withdrawal is known to induce apoptosis in Shionogi tumor cells. Surprisingly, tumor endothelial cells begin to undergo apoptosis before neoplastic cells, and rarefaction of tumor vessels precedes the decrease in tumor size. The regressing vessels begin to exhibit normal phenotype, i.e., lower diameter, tortuosity, vascular permeability, and leukocyte adhesion. Two weeks after castration, a second wave of angiogenesis and tumor growth begins with a concomitant increase in VEGF expression. Because human tumors often relapse following hormone-ablation therapy, our data suggest that these patients may benefit from combined anti-VEGF therapy.

Androgens↗
PubMed1998

A randomized trial of the effect of ritonavir in maintaining quality of life in advanced HIV disease. Advanced HIV Disease Ritonavir Study Group.

BACKGROUND: The aim of treatment for HIV disease is prolonging survival and improvement in health-related quality of life. Ritonavir is a potent, orally bioavailable HIV protease inhibitor with demonstrated impact on surrogate endpoints, AIDS-defining disease, and mortality. OBJECTIVES: To evaluate the effect of ritonavir combined with reverse transcriptase inhibitor therapy on patient functioning and well-being. METHODS: An international, multicenter randomized placebo-controlled clinical trial of ritonavir was conducted in HIV-infected patients with CD4 cell counts < or = 100 x 10(6)/l. A total of 1090 patients were randomized to ritonavir and continued treatment with as many as two nucleoside agents (n=543) or placebo and continued treatment with as many as two nucleoside agents (n=547). Health-related quality of life was measured at baseline and after 3 and 6 months of treatment using the Medical Outcomes Study HIV Health Survey (MOS-HIV) and HIV-related symptoms scale. MOS-HIV contains 10 subscales and two summary scores (physical health and mental health). RESULTS: The two treatment groups were comparable on baseline CD4 cell counts, demographic characteristics, and MOS-HIV and HIV symptom subscale scores. After 3 months, statistically significant differences (P < 0.03) favoring the ritonavir-treated patients were seen on the physical health summary, mental health summary, and general health perceptions, social function, mental health, and energy/fatigue subscales. After 6 months of ritonavir therapy, significant differences were observed on physical health and mental health summary scores (P < 0.001), and on measures of general health perceptions, physical function, role function, social function, cognitive function, mental health, health distress, energy/fatigue, and overall ratings of quality of life (P < 0.01). Ritonavir-treated patients reported fewer fever symptoms and neurologic symptoms than the placebo group after 6 months of treatment (P < 0.005). CONCLUSIONS: Ritonavir therapy, combined with other antiretroviral treatments, significantly contributes to maintenance of functioning and well-being over at least 6 months in patients with advanced HIV disease.

Adult↗
PubMed1998

Membrane protein proteolysis assayed by fluorescence quenching: assay of O-sialoglycoprotein endopeptidase.

The assay of the O-sialoglycoprotein endopeptidase of Pasteurella haemolytica has previously used the cleavage of 125I-labeled glycophorin A, measured by SDS-PAGE, autoradiography, gel-slicing, and scintillation counting. A new assay is based on the increased fluorescence which results from proteolytic cleavage of a fluorescence-quenched micellar substrate, 4,4-difluor-5,7-dimethyl-4-bora-3 alpha, 4 alpha-diaza-s-indacene-3-propionic acid conjugated to glycophorin A (BODIPY-FL-glycophorin A). Micellar association of glycophorin A molecules results in 97% fluorescence quenching despite a low molar ratio of BODIPY-FL-glycophorin A. Proteolysis of the membrane protein causes greatly enhanced fluorescence which is used for a rapid one-step proteolysis assay. Direct monitoring of proteolysis in microcuvettes, or routine assay in microtiter plates can be used. Reproducibility is higher than with the radiolabeled substrate and the K(m) values for the two substrates are similar. The assay is suitable for the O-sialoglycoprotein endopeptidase activity of chromatographically purified enzyme or unpurified bacterial culture supernatants and can be used to monitor inhibition of the O-sialoglycoprotein endopeptidase by neutralizing antibodies. The O-sialoglycoprotein endopeptidase assay employing BODIPY-FL-glycophorin A provides a rapid and nonradioactive method for the assay of this highly specific enzyme.

Boron Compounds↗
PubMed1998

Diffusion, perfusion, and T2 magnetic resonance imaging of anti-intercellular adhesion molecule 1 antibody treatment of transient middle cerebral artery occlusion in rat.

The effect of anti-intercellular adhesion molecule-1 (anti-ICAM-1) antibody treatment of transient (2 h) middle cerebral artery (MCA) occlusion in the rat was measured using diffusion (DWI)-, T2 (T2I)- and perfusion (PWI)-weighted magnetic resonance imaging. Rats were treated upon reperfusion with an anti-ICAM-1 monoclonal antibody (n=11) or a control antibody (n=7). DWI, T2I and PWI were performed before, during, and after induction of focal cerebral ischemia from 1 h to 7 days. In both groups, the apparent diffusion coefficient of water (ADCw) and cerebral blood flow (CBF) values in the ischemic region significantly declined from the preischemic ADCw values (p<0. 05). The post ischemic increase in T2 of the control group was significantly higher at 48 h than in the anti-ICAM-1 treated group (p<0.05). CBF was not significantly different between the two groups. The temporal profiles of MRI cluster analysis, which combines ADCw and T2 maps into a single image, was significantly different between groups. These data suggest that the neuroprotective effect of anti-ICAM-1 antibody treatment is reflected in reductions of T2 and lesion growth during reperfusion and may not be associated with increased cerebral perfusion.

Animals↗
PubMed1998

Mutant human presenilin 1 protects presenilin 1 null mouse against embryonic lethality and elevates Abeta1-42/43 expression.

Mutations in presenilin 1 (PS1) are linked to early onset of familial Alzheimer's disease (FAD) and are shown to foster production of Abeta1-42/43 in FAD patients and transgenic mice. PS1 null mice are embryonic lethal and exhibit axial skeleton malformation and CNS defects. We show that transgenic mouse lines expressing either the wild-type human PS1 protein or human PS1 with the A246E FAD mutation can rescue the PS1 knockout mouse from embryonic lethality to similar degrees, indicating that the mutation does not lead to loss of PS1 function during development. Furthermore, a 50% reduction of PS1 activity in PS1(+/-) mice does not lead to Abeta1-42/43 increase, whereas expression of human mutant PS1 on murine PS1 null background is sufficient to elevate Abeta1-42/43, supporting a gain-of-function activity as the result of the PS1 mutation.

Alzheimer Disease↗
PubMed1998

Inner ear damage in guinea pigs exposed to stable and impulse noise.

OBJECTIVE: To investigate the inner ear damage after exposure to stable noise, impulse noise and stable plus impulse noise in guinea pigs. METHODS: Ninety-six healthy guinea pigs were divided into 3 equal groups. (1) Stable noise group: exposed to 110 dBA stable noise for 3 days, 4 hours per day. (2) Impulse noise group: exposed to 165 dBA simulated cannon fire impulse noise 10 times successively at an interval of 10 seconds. (3) stable plus impulse noise group: exposed to the same stable noise as that in the first group, then after a 2-hour rest, the animals were followed with impulse noise exposures as that in the second group. After those exposure, each of the 3 groups was further divided into 4 subgroups according to the time after the noise exposure, namely, the right after, 7 d, 14 d and 30 d groups. The evoked cortical potential responses to click and tone burst stimulation sound were examined. The surface preparation and celloidine embedded serial section of the cochlea were observed under a light microscope. RESULTS: Both the stable and impulse noise could increase the hearing threshold and damage the inner ear hair cells. The damage in the first group was relatively slight, whereas in group 3 the damage was more severe than that in the other 2 groups. CONCLUSION: For seamen who are working in heavy noise environment, corresponding measures should be taken to protect their ears from noise which induces hearing loss.

Animals↗
PubMed1998

[Applied anatomy of the temporal and frontal regions in endoscopic temporal lifting].

OBJECTIVE: This anatomic study was carried out in a bid to decrease damage of the temporal branch of the face nerve in endoscopic temporal lifting. METHODS: We dissected the frontal-temporal region and located the temporal branch on 36 sides of adult head specimens. RESULTS: It was found that the temporal branch is deep to the temporoparietal fascia and frontal muscle. The temporal branch has one to four branches in general. The first one is 8.1 +/- 2.1 mm anterior to articular tubercle and 33.8 +/- 4.9 mm superior to the bony lateral canthus. The temporal branches locate below a line drawn from the articular tubercle to 40 mm above the bony lateral canthus. CONCLUSION: It is suggested that the operation incisions in the temporal region be selected above this line.

Adult↗
PubMed1998

[Changes in distortion product otoacoustic emissions and hair cells after noise exposure in guinea pigs].

In order to observe the changes in distortion product otoacoustic emissions (DPOAE) and hair cells after noise exposure, sixteen healthy guinea pigs were used. The animals were divided into 3 groups. Group 1 was normal animals. Group 2 and 3 were animal right and 7 days after exposed to 115 dB SPL simulated submarine engine room noise for 4 hours, respectively. The DPOAE audiogram and I/O function were measured before and after exposure. The changes of hair cells were observed by light microscope and scanning electron microscope. The amplitudes of DPOAE disappeared right after noise exposure(P < 0.01) and recovered to normal at 7 days after exposure (P > 0.05). The light microscopy and scanning electron microscopy showed the stereocilia of the outer hair cells were disarrangement and some disappeared at 2,3,4 kHz regions of the cochlea. The results indicated that the normal outer cells can regulate and compensate the function of some damaged outer hair cells which result in a normal DPOAE in mild damaged cochlea.

Animals↗
PubMed1998

[Chemical constituents of Cichorium intybus L].

OBJECTIVE: To investigate the chemical constituents of Cichorium intybus. METHOD: Constituents were separated by means of solvent extraction and chromatography on silical gel. The structures were established by spectral analysis and chemical evidence. RESULT: Seven compounds were isolated from the roots of C. intybus and four of them were identified as alpha-amyrin, taraxerone, baurenyl acetate and beta-sitosterol. CONCLUSION: All the four compounds were obtained from the plant for the first time.

Cichorium intybus↗
PubMed1998

[Study on the contents of HBV DNA in sera of patients with hepatic diseases by QPCR technique].

In order to test the content of serum HBV DNA for evaluating the effectiveness of clinical antiviral treatment and the relation of serum HBV DNA level to state of illness and prognosis, a QPCR method of energy transfer in amplification by semi-nested fluorescein labeled primer was established. Serum HBV DNA contents of 63 cases of hepatic diseases with abnormal liver function were detected by QPCR, PCR and ELISA. The positive detectable rate of the three methods were compared. The results showed that the positive detectable rate of QPCR was 82.54%, PCR 71.43% and ELISA 63.50%. The detectable rate of QPCR was compared with PCR, and uniformity rate of the both methods was 88.89%, P < 0.05; the positive results of QPCR were compared with ELISA, and their uniformity rate was 80.95%, P < 0.05; when serum average content (mean +/- s) of HBV DNA by QPCR method was compared with serum average titer of HBV by ELISA method, serum HBV-DNA average content of the group in which both QPCR and ELISA were positive was much higher than that of the group of QPCR(+) and ELISA(-), P < 0.05; serum QPCR-HBV-DNA of 30 cases of healthy persons were all negative. The results indicated that QPCR method is of highest positive detectable rate and more specific in detecting serum HBV DNA and had no nonspecific amplifying reaction. It has the superiority of detecting low level serum HBV DNA.

Adult↗
PubMed1997

Risk of tongue cancer associated with tobacco smoking and alcohol consumption: a case-control study.

Recent studies indicate that cancer of the tongue is increasing rapidly among the younger population in many parts of the world. Few studies, however, have directly examined the risk factors for the disease. A case-control study was conducted in Beijing, China to investigate risk factors for tongue cancer. A total of 111 cases and 111 controls aged 20-80 years were included in this study. The results show that risk of tongue cancer is significantly elevated among ex-smokers (OR = 2.24, 95% CI = 1.09-4.62) and among current smokers (OR = 2.73, 95% CI = 1.26-5.91). The risk increases with increasing tobacco consumption, as reflected by both cigarette equivalents smoked per day and lifetime pack-years of tobacco smoking. Quitting smoking was associated with a reduction of the risk of tongue cancer. The numbers of cases in the study, however, is small, preventing further analyses during the years after quitting smoking. Overall, alcohol drinking was not found to be significantly associated with the risk of tongue cancer in this study (OR = 1.20, 95% CI = 0.58-2.50 for current drinkers). However, a marginally significant association was found for those who drank spirits at least 5 days a week (OR = 2.34, 95% CI = 0.90-6.06). A suggestion of effect modification for smoking and alcohol drinking was observed in this study.

Adult↗
PubMed1997

Structure/function analysis of the PII signal transduction protein of Escherichia coli: genetic separation of interactions with protein receptors.

The PII protein, encoded by glnB, is known to interact with three bifunctional signal transducing enzymes (uridylyltransferase/uridylyl-removing enzyme, adenylyltransferase, and the kinase/phosphatase nitrogen regulator II [NRII or NtrB]) and three small-molecule effectors, glutamate, 2-ketoglutarate, and ATP. We constructed 15 conservative alterations of PII by site-specific mutagenesis of glnB and also isolated three random glnB mutants affecting nitrogen regulation. The abilities of the 18 altered PII proteins to interact with the PII receptors and the small-molecule effectors 2-ketoglutarate and ATP were examined by using purified components. Results with certain mutants suggested that the specificity for the various protein receptors was altered; other mutations affected the interaction with all three receptors and the small-molecule effectors to various extents. The apex of the large solvent-exposed T loop of the PII protein (P. D. Carr, E. Cheah, P. M. Suffolk, S. G. Vasudevan, N. E. Dixon, and D. L. Ollis, Acta Crytallogr. Sect. D 52:93-104, 1996), which includes the site of PII modification, was not required for the binding of small-molecule effectors but was necessary for the interaction with all three receptors. Mutations altering residues of this loop or affecting the nearby B loop of PII, which line a cleft between monomers in the trimeric PII, affected the interactions with protein receptors and the binding of small-molecule ligands. Thus, our results support the predictions made from structural studies that the exposed loops of PII and cleft formed at their interface are the sites of regulatory interactions.

Adenosine Triphosphate↗
PubMed1997

Probing interactions of the homotrimeric PII signal transduction protein with its receptors by use of PII heterotrimers formed in vitro from wild-type and mutant subunits.

The homotrimeric PII signal transduction protein of Escherichia coli interacts with two small-molecule effectors, 2-ketoglutarate and ATP, regulates two protein receptors, the kinase/phosphatase nitrogen regulator II (NRII) and the glutamine synthetase (GS) adenylyltransferase (ATase), and is subject to reversible uridylylation, catalyzed by the uridylyltransferase/uridylyl-removing enzyme (UTase/UR). The site of PII uridylylation, Y51, is located at the apex of the solvent-exposed T-loop (E. Cheah, P. D. Carr, P. M. Suffolk, S. G. Vasudevan, N. E. Dixon, and D. L. Ollis, Structure 2:981-990, 1994), and an internally truncated PII lacking residues 47 to 53 formed trimers that bound the small-molecule effectors but were unable to be uridylylated or activate NRII and ATase (P. Jiang, P. Zucker, M. R. Atkinson, E. S. Kamberov, W. Tirasophon, P. Chandran, B. R. Schefke, and A. J. Ninfa, J. Bacteriol. 179:4342-4353, 1997). We investigated the ability of heterotrimers containing delta47-53 and wild-type subunits to become uridylylated and activate NRII and ATase. Heterotrimers were formed by denaturation and renaturation of protein mixtures; when such mixtures contained a fivefold excess of A47-53 subunits, the wild-type subunits were mostly redistributed into trimers containing one wild-type subunit and two mutant subunits. The resulting population of trimers was uridylylated and deuridylylated by UTase/UR, stimulated the phosphatase activity of NRII, and stimulated adenylylation of GS by ATase. In all except the ATase interaction, the activity of the hybrid trimers was greater than expected based on the number of wild-type subunits present. These results indicate that a single T-loop region within a trimer is sufficient for the productive interaction of PII with its protein receptors. We also formed heterotrimers containing wild-type subunits and subunits containing the G89A alteration (P. Jiang, P. Zucker, M. R. Atkinson, E. S. Kamberov, W. Tirasophon, P. Chandran, B. R. Schefke, and A. J. Ninfa, J. Bacteriol. 179: 4342-4353, 1997). The G89A mutant form of PII does not bind the small-molecule effectors, does not interact with UTase or with NRII, and interacts poorly with ATase. Heterotrimers formed with a 10/1 starting ratio of G89A to wild-type subunits interacted with UTase/UR and ATase to a lesser extent than expected based on the number of wild-type subunits present but activated NRII slightly better than expected based on the number of wild-type subunits present. Thus, intersubunit interactions within the PII trimer can adversely affect the activity of wild-type subunits and may affect the interactions with the different receptors in a variable way. Finally, we formed heterotrimers containing delta47-53 and G89A mutant subunits. These heterotrimers were not uridylylated, did not interact with NRII, and interacted with the ATase only to the extent expected based on the number of G89A subunits present. Thus, the G89A subunits, which contain an intact T-loop region, were not "repaired" by inclusion in heterotrimers along with delta47-53 subunits.

Bacterial Proteins↗
PubMed1997

[Effect of perilymphatic fistula on distortion product otoacoustic emissions in guinea pigs].

Perilymphatic fistula was induced in 11 healthy guinea pigs to study its effects on distortion product otoacoustic emissions (DPOAEs). DPOAE amplitudes decreased significantly right after formation of the fistula (P < 0.01), and recurred to near pretreatment level in animals whose fistula healed. The amplitude remained below pretreatment level 18 days after fistulization in those animals whose fistula failed to heal. Under light microscope, the organ of Corti was seen normal. The authors feel that DPOAEs may be helpful in detecting perilymphatic fistula.

Acoustic Stimulation↗