Biomedical subjects

X Xu

Publications and source records attributed to X Xu.

At least 631 records · Page 35Linked to original sources

PubMed1997

Airways responsiveness and development and remission of chronic respiratory symptoms in adults.

BACKGROUND: Many patients with chronic obstructive lung disease show increased airways responsiveness to histamine. We investigated the hypothesis that increased airways responsiveness predicts the development and remission of chronic respiratory symptoms. METHODS: We used data from 24-year follow-up (1965-90) of 2684 participants in a cohort study in Vlagtwedde and Vlaardingen, Netherlands. Increased airways responsiveness was defined as a PC10 value (concentration of histamine for which challenge led to a 10% fall in forced expiratory volume in 1 s) of less than 8 mg/mL. Information on respiratory symptoms was collected by means of a standard questionnaire every 3 years. Logistic regression was used to control for age, area of residence, cigarette smoking status, and sex. FINDINGS: Participants with increased airways responsiveness (1281 observations) were more likely than those without increased airways responsiveness (5801 observations) to develop the following symptoms during any 3-year follow-up interval: chronic cough (odds ratio 1.9 [95% CI 1.2-2.9]), chronic phlegm (2.0 [1.3-3.0]), dyspnoea (2.3 [1.5-3.5]), asthmatic attacks (3.7 [2.2-6.1]), and persistent wheeze (2.7 [1.7-4.4]). The estimate of the odds ratio for the development of any of the six symptoms was 1.7 (1.2-2.3). Participants with increased airways responsiveness were less likely than those without this characteristic to show remission of these respiratory symptoms. The estimate of the odds ratio for the remission of any of the six symptoms was 0.42 (0.28-0.61). INTERPRETATION: These prospective analyses show that increased airways responsiveness is positively associated with the development of chronic respiratory symptoms and negatively associated with the remission of these symptoms in adults.

Adult↗

PubMed1997

Dynamic regulation of c-Jun N-terminal kinase activity in mouse brain by environmental stimuli.

Activation of the recently identified c-Jun N-terminal kinases (JNKs) typically results in programmed cell death (apoptosis) in neurons and other cell types grown in culture. However, the effects of JNK activation in the central nervous system in vivo are unknown. At baseline, JNK activity in mice was on average 17-fold higher in brain than in peripheral organs, whereas JNK protein levels were similar. In brain, JNK was expressed primarily in neurons. Restraining mice or allowing them to explore a novel environment rapidly increased JNK activity 3- to 15-fold in various brain regions, but these manipulations did not increase brain activity of the extracellular signal-regulated kinase. Because noninvasive environmental stimuli that do not induce neurodegeneration elicited prominent increases in JNK activity in the brain, we conclude that acute activation of the JNK cascade in central nervous system neurons does not induce neuronal apoptosis in vivo. In contrast, the high baseline activity of JNK in the brain and the activation of the JNK cascade by environmental stimuli suggest that this kinase may play an important physiological role in neuronal function.

Animals↗

PubMed1997

Structure of the cyclin-dependent kinase inhibitor p19Ink4d.

In cancer, the biochemical pathways that are dominated by the two tumour-suppressor proteins, p53 and Rb, are the most frequently disrupted. Cyclin D-dependent kinases phosphorylate Rb to control its activity and they are, in turn, specifically inhibited by the Ink4 family of cyclin-dependent kinase inhibitors (CDKIs) which cause arrest at the G1 phase of the cell cycle. Mutations in Rb, cyclin D1, its catalytic subunit Cdk4, and the CDKI p16Ink4a, which alter the protein or its level of expression, are all strongly implicated in cancer. This suggests that the Rb 'pathway' is of particular importance. Here we report the structure of the p19Ink4d protein, determined by NMR spectroscopy. The structure indicates that most mutations to the p16Ink4a gene, which result in loss of function, are due to incorrectly folded and/or insoluble proteins. We propose a model for the interaction of Ink4 proteins with D-type cyclin-Cdk4/6 complexes that might provide a basis for the design of therapeutics against cancer. The sequences of the Ink4 family of CDKIs are highly conserved

Amino Acid Sequence↗

PubMed1997

Regeneration studies of an analog of ribonuclease A missing disulfide bonds 65-72 and 40-95.

Mutants of bovine pancreatic ribonuclease A (RNase A) that contain four of the eight cysteine residues found in the wild-type protein were prepared. Cysteine residues 40, 65, 72, and 95 were replaced by serine to form [C40S,C65S,C72S,C95S] RNase A or by alanine to form [C40A,C65A,C72A,C95A] RNase A, which contain the following four cysteine residues: 26, 58, 84, and 110. The substitutions resulted in deletion of wild-type disulfide bonds, 65-72 and 40-95. These mutants were prepared to investigate interactions that may be important for the folding and unfolding of the wild-type protein. The mutant protein was expressed and purified in an unfolded sulfonated form. Upon regeneration of the native form from the reduced mutant with DTTox, all three of the possible two-disulfide pairings, including the native one, formed. One-dimensional 1H NMR spectra demonstrated that the conformations of these three species are similar and are predominantly disordered; however, there is evidence of local structure in the vicinity of one histidine residue. It was also shown that disulfide pairing is not completely random and that both entropic factors and enthalpic interactions contribute to the formation of the native-disulfide bonds. The presence of more than a statistical population of native-disulfide pairings indicates that specific local interactions present in the reduced protein direct the preferential formation of native-disulfide bonds in the two-disulfide mutant.

Animals↗

PubMed1997

Maternal menstrual history and small-for-gestational-age births in a population-based Chinese birth cohort.

The relationship between maternal menstrual history and small-for-gestational-age (SGA) births is examined in a population-based birth cohort of 5291 mothers with singleton births and 28 completed gestational weeks in Qingdao, China, in 1992. Multivariate analyses suggest that the length of the menstrual cycle and age at menarche had independent effects on SGA after controlling for sex of the infant, physical size of the mother, blood pressure at the first antenatal visit, parity, gestational week at the first antenatal visit, number of antenatal visits, number of previous spontaneous abortions and maternal educational attainment and occupation. The relative risk (RR) of SGA among thin mothers (BMI < = 21) is 1.63 (95% confidence interval (CI) 1.16-2.29) if the mother's menarche started after 14 years (reference to < = 14 years), 1.75 (95% CI 0.96-3.20) if the mother's menstrual cycle was 29-30 days and 2.92 (95% CI 1.42-6.03) if the menstrual cycle > = 31 days ( < = 28 as a reference category for both). Among normal weight mothers (BMI 21-24), only a menstrual cycle equal or longer than 31 days still had a significant effect on SGA (RR 2.17, 95% CI 1.18-4.08), and among fat mothers no significant effects were observed. The results encourage further evaluation of the association between maternal menstrual background and fetal development among other ethnic populations and exploration of the possible biological mechanisms behind this relationship.

Adult↗

PubMed1997

Regression of left ventricular hypertrophy with captopril restores normal ventricular action potential duration, dispersion of refractoriness, and vulnerability to inducible ventricular fibrillation.

BACKGROUND: Left ventricular hypertrophy (LVH) is associated with multiple cellular electrophysiological abnormalities, susceptibility to ventricular arrhythmias, and an increased risk of sudden death. Several pharmacological therapies have been shown to produce regression of hypertrophy, but the value of regression is unclear. The present study examines whether pharmacological regression of LVH has effects on the susceptibility to ventricular arrhythmia or the cellular electrophysiological abnormalities of LVH. METHODS AND RESULTS: Rabbits underwent unilateral renal artery banding and contralateral nephrectomy to induce LVH or were placed in the control group. Both groups were studied 3 months later by in vivo and in vitro electrophysiological techniques. Banded rabbits had increased mean arterial pressure, increased left ventricular weight and wall thickness, increased dispersion of refractoriness, and lower ventricular fibrillation thresholds than control rabbits. Action potential duration and cell capacitance were also greater in the banded group. Additional rabbits were treated beginning 3 months after banding with either captopril (5 mg x kg(-1) x d(-1)) or vehicle added to their diet for an additional 3 months. These rabbits and age-matched controls were then studied by in vivo and in vitro electrophysiological techniques. In banded rabbits that received vehicle and were studied 6 months after banding, increased dispersion of refractoriness, a lower ventricular fibrillation threshold, and action potential prolongation persisted and were unchanged from animals studied 3 months after banding. Captopril, started 3 months after banding, caused regression of hypertrophy and normalization of the in vivo and in vitro electrophysiological abnormalities. Addition of captopril to the tissue bath during in vitro electrophysiological study showed no effect on cells from control or banded rabbits. CONCLUSIONS: Pharmacological regression of LVH with captopril normalizes the in vivo and in vitro electrophysiological abnormalities of ventricular hypertrophy and reduces the vulnerability to ventricular fibrillation in a renovascular model of LVH.

Action Potentials↗

PubMed1997

Glutamine235 and arginine272 in human melanocortin 5 receptor determines its low affinity to MSH.

The human melanocortin 5 receptor (hMC5R) in the melanocortin receptor family has been identified as the receptor with low affinity towards alpha-MSH. Here we show that the glutamine at position 235 and arginine at the position 272 in the hMC5R are contributing to the low affinity of this receptor. Glutamine235 and arginine272 in hMC5R were mutated to lysine (Q235K) and cysteine (R272C), respectively, residues which are conserved at these positions in other melanocortin receptor subtypes. Upon these mutations affinity of alpha-MSH for hMC5R was increased 10-fold for Q235K and 690-fold for R272C mutants, respectively. The results explain the unusually low affinity of the hMC5R to the melanocortic ligands and suggest the importance of these conserved residues in maintaining the high affinity form of melanocortin receptors.

Amino Acid Sequence↗

PubMed1997

The immunosuppressive metabolite of leflunomide, A77 1726, affects murine T cells through two biochemical mechanisms.

The immunosuppressive metabolite of leflunomide, A77 1726, inhibits the enzymatic activity of protein tyrosine kinases and of dihydro-orotic acid dehydrogenase, an enzyme involved in pyrimidine biosynthesis. Here murine CTLL cell lines were studied to determine which of the biochemical targets of A77 1726 was responsible for the observed inhibition of proliferation and cytotoxic activity. At low concentrations of A77 1726, pyrimidine biosynthesis is the target, since inhibition of proliferation correlates with a reduction in pyrimidine NTP levels and is reversed by uridine. At higher concentrations of A77 1726, uridine no longer reverses the inhibition of proliferation even though pyrimidine NTP levels are restored. This second mechanism for inhibiting proliferation is probably inhibition of protein tyrosine kinases, since these higher concentrations of A77 1726 inhibit IL-2-induced tyrosine phosphorylation of Jak1 and Jak3, the protein tyrosine kinases initiating signaling by the IL-2R. Tyrosine phosphorylation of the beta-chain of the IL-2R, which is required for IL-2-driven proliferation, is also inhibited by A77 1726. Cytotoxicity of a CTLL line that overexpresses the Lck protein tyrosine kinase is inhibited by A77 1726; this inhibition is not affected by uridine, but does correlate with inhibition of an Lck in vitro kinase reaction. These studies establish that inhibition of pyrimidine biosynthesis and that of protein tyrosine kinase both contribute to the effects of A77 1726 on CTLL cell lines.

Aniline Compounds↗

PubMed1997

In vivo mechanism by which leflunomide controls lymphoproliferative and autoimmune disease in MRL/MpJ-lpr/lpr mice.

Two activities have been identified for the immunosuppressive metabolite of leflunomide, A77 1726: inhibition of dihydroorotate dehydrogenase (DHO-DHase), an enzyme involved in the biosynthesis of pyrimidine nucleotides (PyN); and inhibition of protein tyrosine kinases. The in vitro potency of A77 1726 as a DHO-DHase inhibitor is reported to be 10- to 500-fold greater than as a tyrosine kinase inhibitor. These observations suggested that the immunosuppressive efficacy of leflunomide in vivo is related to inhibition of DHO-DHase. However, observations that patients with disorders in the PyN synthetic pathway are not overtly immunodeficient militate against this hypothesis. We investigated the effects of leflunomide in vivo and report that amelioration of lymphoproliferative and autoimmune diseases in MRL/MpJ-lpr/lpr (lpr/lpr) mice by leflunomide is not accompanied by reduced PyN concentrations in lymph node cells. Our hypothesis that lymphocytes could salvage serum uridine to counter the effects of reduced PyN synthesis in vivo was supported by in vitro studies. Finally, we observed that amelioration of disease correlated with a reduction of tyrosine phosphorylated proteins in lymph node cells of lpr/lpr mice. These observations suggest that the primary mechanism by which leflunomide prevents autoimmune and lymphoproliferative diseases in lpr/lpr mice is not depletion of PyN, but correlates with reduced tyrosine phosphorylation concentrations in lymph node cells.

Aniline Compounds↗

PubMed1997

Polarized expression of Ca2+ channels in pancreatic and salivary gland cells. Correlation with initiation and propagation of [Ca2+]i waves.

In polarized epithelial cells [Ca2+]i waves are initiated in discrete regions and propagate through the cytosol. The structural basis for these compartmentalized and coordinated events are not well understood. In the present study we used a combination of [Ca2+]i imaging at high temporal resolution, recording of Ca2+-activated Cl- current, and immunolocalization by confocal microscopy to study the correlation between initiation and propagation of [Ca2+]i waves and localization of Ca2+ release channels in pancreatic acini and submandibular acinar and duct cells. In all cells Ca2+ waves are initiated in the luminal pole and propagate through the cell periphery to the basal pole. All three cell types express the three known inositol 1,4,5-trisphosphate receptors (IP3Rs). Expression of IP3Rs was confined to the area just underneath the luminal and lateral membranes, with no detectable receptors in the basal pole or other regions of the cells. In pancreatic acini and SMG ducts IP3R3 was also found in the nuclear envelope. Expression of ryanodine receptor was detected in submandibular salivary gland cells but not pancreatic acini. Accordingly, cyclic ADP ribose was very effective in mobilizing Ca2+ from internal stores of submandibular salivary gland but not pancreatic acinar cells. Measurement of [Ca2+]i and localization of IP3Rs in the same cells suggests that only a small part of IP3Rs participate in the initiation of the Ca2+ wave, whereas most receptors in the cell periphery probably facilitate the propagation of the Ca2+ wave. The combined results together with our previous studies on this subject lead us to conclude that the internal Ca2+ pool is highly compartmentalized and that compartmentalization is achieved in part by polarized expression of Ca2+ channels.

Adenosine Diphosphate Ribose↗

PubMed1997

Polarized expression of Ca2+ pumps in pancreatic and salivary gland cells. Role in initiation and propagation of [Ca2+]i waves.

The present study was aimed at localization of plasma membrane (PMCA) and intracellular (SERCA) Ca2+ pumps and characterizing their role in initiation and propagation of Ca2+ waves. Specific and polarized expression of Ca2+ pumps was observed in all epithelial cells examined. Immunolocalization revealed expression of PMCA in both the basolateral and luminal membranes of all cell types. SERCA2a appeared to be expressed in the luminal pole, whereas SERCA2b was expressed in the basal pole and the nuclear envelope of pancreatic acini. Interestingly, SERCA2b was found in the luminal pole of submandibular salivary gland acinar and duct cells. These cells expressed SERCA3 in the basal pole. To examine the significance of the polarized expression of SERCA and perhaps PMCA pumps in secretory cells, we compared the effect of inhibition of SERCA pumps with thapsigargine and partial Ca2+ release with ionomycin on Ca2+ release evoked by agonists and Ca2+ uptake induced by antagonists. Despite their polarized expression, Ca2+ uptake by SERCA pumps and Ca2+ efflux by PMCA resulted in uniform reduction in [Ca2+]i. Surprisingly, inhibition of the SERCA pumps, but not Ca2+ release by ionomycin, eliminated the distinct initiation sites and propagated Ca2+ waves, leading to a uniform increase in [Ca2+]i. In addition, inhibition of SERCA pumps reduced the rate of Ca2+ release from internal stores. The implication of these findings to rates of Ca2+ diffusion in the cytosol, compartmentalization of Ca2+ signaling complexes, and mechanism of Ca2+ wave propagation are discussed.

Animals↗

PubMed1997

Fibroblast growth factor receptor-1 (FGFR-1) is essential for normal neural tube and limb development.

Fibroblast growth factor receptor-1 (FGFR-1) is a membrane-spanning tyrosine kinase that serves as a high-affinity receptor for fibroblast growth factors. It has recently been shown that FGFR-1 mutant embryos die during gastrulation displaying severe growth retardation and defective mesodermal structures. This early lethality has obscured functions of FGFR-1 that might occur later in development. To circumvent these embryonic defects, we generated chimeras by injecting FGFR-1-deficient (R1-/-) ES cells into wild-type blastocysts. We found that the fgfr-1 gene plays an important role after gastrulation and that it acts in a cell-autonomous fashion. Embryos with a high contribution of R1-/- cells replicate the FGFR-1 null phenotype and die during gastrulation. In contrast, the majority of embryos with a low contribution of R1-/- cells complete gastrulation and display malformations of posterior structures at later stages of embryogenesis. These abnormalities include truncation of embryonic structures, limb bud malformation, partial duplication of the neural tube, tail distortion, and spina bifida caused by the amplification of neural tissue in the posterior portion of the spinal cord. Thus, FGFR-1 plays a role in neurulation, suggesting that there may be a connection between FGFR-1-mediated signal pathways and neural tube defects, the most common malformations in the human central nervous system.

Animals↗

PubMed1997

Interaction between Cdc37 and Cdk4 in human cells.

Using the yeast two-hybrid system we have identified novel potential Cdk4 interacting proteins. Here we described the interaction of Cdk4 with a human homologue of the yeast Drosophila CDC37 gene products. Cdc37 protein specifically interacts with Cdk4 and Cdk6, but not with Cdc2, Cdk2, Cdk3, Cdk5 and any of a number of cyclins tested. Cdc37 is not an inhibitor nor an activator of the Cdk4/cyclin D1 kinase, while it appears to facilitate complex assembly between Cdk4, and cyclin D1 in vitro. Cdc37 competes with p16 for binding to Cdk4, suggesting that p16 might exert part of its inhibitory function by affecting the formation of Cdk4/cyclin D1 complexes via Cdc37.

Amino Acid Sequence↗

PubMed1997

A mutant Rel-homology domain promotes transcription by p50/NFkappaB1.

Previous studies showed that the binding of p50/NFkappaB1 to particular kappaB DNA sites altered its conformation in a way that correlated with transcriptional activation. Here, we investigated the effects of protein-protein interactions on the transcriptional activity of p50. We show that the association of p50 with a mutant Rel-homology domain (RHD) defective for DNA binding led to synergistic activation of kappaB site-dependent transcription, whereas neither protein alone had any effect. Partial proteolytic analysis showed that the conformation of p50 in these complexes differed from that in wild-type c-Rel-RHD/p50 complexes, and correlated with activated transcription. These results suggest that the Rel-homology domain can act as an allosteric effector to promote transcription by p50/NFkappaB1 and that the configuration of p50 is important for its activity. This also suggests that Rel proteins can promote transcription by other Rel-family members without binding to their DNA recognition site. These studies emphasize the important role of protein-protein interactions in Rel and NFkappaB-mediated transcription.

Animals↗

PubMed1997

The complete mitochondrial genome of the wallaroo (Macropus robustus) and the phylogenetic relationship among Monotremata, Marsupialia, and Eutheria.

The complete mitochondrial DNA (mtDNA) (16,896 nt) of the wallaroo (Macropus robustus) was sequenced. The concatenated amino acid sequences of 12 mitochondrial protein-coding genes of the wallaroo plus those of a number of other mammals were included in a phylogenetic study of early mammalian divergences. The analysis joined monotremes and marsupials (the Marsupionta hypothesis) to the exclusion of eutherians. The analysis rejected significantly the commonly acknowledged Theria hypothesis, according to which Marsupialia and Eutheria are grouped together to the exclusion of Monotremata. The region harboring the gene for lysine tRNA (tRNA-Lys) in the mtDNA of other vertebrates is in the wallaroo occupied by a sequence (tRNA-Lys) that lacks both an anticodon loop as well as the anticodon for the amino acid lysine. An alternative tRNA-Lys gene was not identified in any other region of the mtDNA of the wallaroo, suggesting that a tRNA-Lys of nuclear origin is imported into marsupial mitochondria. Previously described RNA editing of tRNA-Asp and rearrangement of some tRNA genes were reconfirmed in the mtDNA of the wallaroo. The divergence between Monotremata/Marsupialia and Eutheria was timed to approximately 130 million years before present (MYBP). The same calculations suggested that Monotremata and Marsupialia diverged approximately 115 MYBP and that Australian and American marsupials separated approximately 75 MYBP. The findings also show that many, probably most, extant eutherian orders had their origin in middle to late Cretaceous times, 115-65 MYBP.

Animals↗

PubMed1997

Guanine nucleotide binding properties of Rac2 mutant proteins and analysis of the responsiveness to guanine nucleotide dissociation stimulator.

The Rac GTPases are currently being subjected to intensive study due to their involvement in a wide array of cellular phenomena. Many studies of Rac function have relied upon the use of relatively uncharacterized Rac dominant active, dominant negative, and effector domain mutants on the basis of the analogy to Ras structure. We have generated and purified such Rac2 mutants and characterized their guanine nucleotide binding properties in vitro. The Rac2 G12V and Q61L activating mutations were shown to hydrolyze bound GTP very slowly and were unresponsive to p190 Rac GTPase-activating protein. Distinct differences in the kinetics of nucleotide binding to individual mutant proteins were observed, accounting for the behavior of these proteins in biological assays. The structural features required for the responsiveness of Rac2 to the guanine nucleotide exchange protein smgGDS were examined. We show that guanine nucleotide exchange by smgGDS is dependent upon intact switch 1 and switch 2 regions in Rac2. Functional interactions between the switch 1 and switch 2 regions and the G12V mutation of Rac2 are described. These data form the basis for rational use of Rac mutants in biological studies.

GTP Phosphohydrolases↗

PubMed1997

Functional localization of pain perception in the human brain studied by PET.

To elucidate the functional localization and somatotopic organization of pain perception in the human cerebral cortex, we studied the regional cerebral blood flow using positron emission tomography during selective painful stimulation in six normal subjects. Response to a painful stimulus was elicited using a special CO2 laser, which selectively activates nociceptive receptors, to the hand and foot. Multiple brain areas, including bilateral secondary somatosensory cortices (SII) and insula, and the frontal lobe and thalamus contralateral to the stimulus side, were found to be involved in the response to painful stimulation. While our data indicate that the bilateral SII play an important role in pain perception, they also indicate that there is no pain-related somatotopic organization in the human SII or insula.

Adult↗

PubMed1997

A single genetic origin for a common Caucasian risk factor for venous thrombosis.

A common genetic risk factor for venous thrombosis among Caucasoid subpopulations is a polymorphism, nt G1691A, in blood coagulation factor V that replaces Arg506 with Gln and imparts resistance of factor Va to the anticoagulant, activated protein C. Haplotype analyses using six dimorphic sites in the factor V gene for 117 Caucasian subjects of Jewish, Arab, Austrian, and French origin who were homozygous for nt A1691 compared with 167 controls (nt G1691) support a single origin for this polymorphism. The nt G1691A mutation is estimated to have arisen circa 21,000 to 34,000 years ago, ie, after the evolutionary divergence of Africans from non-Africans and of Caucasoid from Mongoloid subpopulations.

Arginine↗