Biomedical subjects

Xiao-Ping Zhang

Publications and source records attributed to Xiao-Ping Zhang.

15 recordsLinked to original sources

PubMed2006

Rad54: the Swiss Army knife of homologous recombination?

Homologous recombination (HR) is a ubiquitous cellular pathway that mediates transfer of genetic information between homologous or near homologous (homeologous) DNA sequences. During meiosis it ensures proper chromosome segregation in the first division. Moreover, HR is critical for the tolerance and repair of DNA damage, as well as in the recovery of stalled and broken replication forks. Together these functions preserve genomic stability and assure high fidelity transmission of the genetic material in the mitotic and meiotic cell divisions. This review will focus on the Rad54 protein, a member of the Snf2-family of SF2 helicases, which translocates on dsDNA but does not display strand displacement activity typical for a helicase. A wealth of genetic, cytological, biochemical and structural data suggests that Rad54 is a core factor of HR, possibly acting at multiple stages during HR in concert with the central homologous pairing protein Rad51.

Adenosine Triphosphatases↗

PubMed2006

cAMP signal transduction induces eNOS activation by promoting PKB phosphorylation.

The objective of this study was to determine whether activation of protein kinase B (PKB) is involved in the production of nitric oxide (NO) induced by cAMP signal transduction. Mongrel dogs were used for this study. Coronary microvessels were isolated from the left ventricular free wall of these dog hearts. Forskolin (an activator of adenylyl cyclase that increases intracellular cAMP level) and 8-bromo-cAMP (a membrane-permeable cAMP analog) were used to stimulate NO release and activation of PKB and endothelial NO synthase (eNOS) in these blood vessels. We found that forskolin and 8-bromo-cAMP increased NO release (quantified by using the Griess reaction) from coronary microvessels by 80 +/- 6 and 78 +/- 11 pmol/mg (mean +/- SE), respectively (P < 0.05 vs. control). Western blot analysis showed that forskolin elicited a significant increase in eNOS phosphorylation (59 +/- 11%) at serine-1177 (a positively regulatory phosphorylation site for eNOS) and a significant increase in dephosphorylation (28 +/- 6%) at threonine-495 (a negatively regulatory phosphorylation site of eNOS) (P < 0.05 vs. control). Interestingly, forskolin also increased the phosphorylation of PKB at serine-473 (by 49 +/- 17%) and threonine-308 (by 53 +/- 17%), respectively (P < 0.05 vs. control; phosphorylation of both sites is required for a full activation of PKB). N(omega)-nitro-l-arginine methyl ester (an NOS inhibitor) blocked NO formation, Rp diastereomer of cAMP (a PKA inhibitor), and LY-294002 [a PI3-kinase (an activator of PKB) inhibitor] prevented the production of NO, phosphorylation of PKB, and eNOS induced by forskolin. Our data clearly show an involvement of PKB activation in cAMP signal-induced NO production. We are reporting for the first time that cAMP signal transduction stimulates eNOS activation through a PKB-mediated mechanism.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2006

The Rad51/RadA N-terminal domain activates nucleoprotein filament ATPase activity.

Proteins in the RecA/RadA/Rad51 family form helical filaments on DNA that function in homologous recombination. While these proteins all have the same highly conserved ATP binding core, the RadA/Rad51 proteins have an N-terminal domain that shows no homology with the C-terminal domain found in RecA. Both the Rad51 N-terminal and RecA C-terminal domains have been shown to bind DNA, but no role for these domains has been established. We show that RadA filaments can be trapped in either an inactive or active conformation with respect to the ATPase and that activation involves a large rotation of the subunit aided by the N-terminal domain. The G103E mutation within the yeast Rad51 N-terminal domain inactivates the filament by failing to make proper contacts between the N-terminal domain and the core. These results show that the N-terminal domains play a regulatory role in filament activation and highlight the modular architecture of the recombination proteins.

Adenosine Triphosphatases↗

PubMed2006

Identification of an HLA-A*0201-restricted cytotoxic T-lymphocyte epitope in rotavirus VP6 protein.

The function of cytotoxic T lymphocytes (CTLs) in rotavirus (RV) infection in humans is poorly understood. To date, no RV-specific human leukocyte antigen (HLA) class I-restricted T-cell epitopes have been described. In this study, four peptides derived from human RV Wa strain VP6 protein were predicted by computer algorithms and verified by an HLA*0201-binding assay. Two peptides with high affinity for HLA-A*0201 molecules were further assessed. The CTLs induced in vitro by P340-348 (TLLANVTAV)-loaded autologous dendritic cells from peripheral blood lymphocytes of HLA-A*0201-matched healthy donors released gamma interferon specifically upon stimulation with P340-348-loaded T2 cells. The CTLs lysed both P340-348-loaded T2 cells and human RV Wa strain-infected HLA-A*0201(+) Caco-2 cells in an antigen-specific and HLA-A*0201-restricted manner. At the same time, P340-348 was shown to be immunogenic in vivo in HLA-A*0201/Kb transgenic mice. It is proposed that P340-348 is an HLA-A*0201-restricted CTL epitope.

Animals↗

PubMed2006

Multiscale fragile watermarking based on the Gaussian mixture model.

In this paper, a new multiscale fragile watermarking scheme based on the Gaussian mixture model (GMM) is presented. First, a GMM is developed to describe the statistical characteristics of images in the wavelet domain and an expectation-maximization algorithm is employed to identify GMM model parameters. With wavelet multiscale subspaces being divided into watermarking blocks, the GMM model parameters of different watermarking blocks are adjusted to form certain relationships, which are employed for the presented new fragile watermarking scheme for authentication. An optimal watermark embedding method is developed to achieve minimum watermarking distortion. A secret embedding key is designed to securely embed the fragile watermarks so that the new method is robust to counterfeiting, even when the malicious attackers are fully aware of the watermark embedding algorithm. It is shown that the presented new method can securely embed a message bit stream, such as personal signatures or copyright logos, into a host image as fragile watermarks. Compared with conventional fragile watermark techniques, this new statistical model based method modifies only a small amount of image data such that the distortion on the host image is imperceptible. Meanwhile, with the embedded message bits spreading over the entire image area through the statistical model, the new method can detect and localize image tampering. Besides, the new multiscale implementation of fragile watermarks based on the presented method can help distinguish some normal image operations such as JPEG compression from malicious image attacks and, thus, can be used for semi-fragile watermarking.

Algorithms↗

PubMed2006

[PPARalpha agonist--fenofibrate inhibits LPS-induced tissue factor expression in THP-1 cells].

This study was aimed to investigate the influence of PPARalpha agonist on the expression of TF (tissue factor) in THP-1 cells. THP-1 cells were pretreated with different concentrations of PPARalpha agonist (fenofibrate) for definite time. Lipopolysaccharide (LPS)-induced TF mRNA and protein levels were detected by RT-PCR and Western blot respectively. The results showed that fenofibrate decreased tissue factor protein and mRNA expression in supernatants of LPS-stimulated human monocytes in a concentration-dependent manner (P < 0.05 - 0.01, n = 5). It is concluded that fenofibrate inhibit TF expression induced by LPS in THP-1 cells, which may be involved in the anti-atherosclerotic effects of PPARalpha agonist.

Depression, Chemical↗

PubMed2005

Gly-103 in the N-terminal domain of Saccharomyces cerevisiae Rad51 protein is critical for DNA binding.

Rad51 is a homolog of the bacterial RecA protein and is central for recombination in eukaryotes performing homology search and DNA strand exchange. Rad51 and RecA share a core ATPase domain that is structurally similar to the ATPase domains of helicases and the F1 ATPase. Rad51 has an additional N-terminal domain, whereas RecA protein has an additional C-terminal domain. Here we show that glycine 103 in the N-terminal domain of Saccharomyces cerevisiae Rad51 is important for binding to single-stranded and duplex DNA. The Rad51-G103E mutant protein is deficient in DNA strand exchange and ATPase activity due to a primary DNA binding defect. The N-terminal domain of Rad51 is connected to the ATPase core through an extended elbow linker that ensures flexibility of the N-terminal domain. Molecular modeling of the Rad51-G103E mutant protein shows that the negatively charged glutamate residue lies on the surface of the N-terminal domain facing a positively charged patch composed of Arg-260, His-302, and Lys-305 on the ATPase core domain. A possible structural explanation for the DNA binding defect is that a charge interaction between Glu-103 and the positive patch restricts the flexibility of the N-terminal domain. Rad51-G103E was identified in a screen for Rad51 interaction-deficient mutants and was shown to ablate the Rad54 interaction in two-hybrid assays (Krejci, L., Damborsky, J., Thomsen, B., Duno, M., and Bendixen, C. (2001) Mol. Cell. Biol. 21, 966-976). Surprisingly, we found that the physical interaction of Rad51-G103E with Rad54 was not affected. Our data suggest that the two-hybrid interaction defect was an indirect consequence of the DNA binding defect.

Adenosine Triphosphatases↗

PubMed2005

Bidirectional labeling and registration scheme for grayscale image segmentation.

In this paper, we introduce a new image segmentation scheme that is based on bidirectional labeling and registration and prove that its segmentation performance is equivalent to that of the conventional watershed segmentation algorithm. The proposed bidirectional labeling and registration scheme, which we refer to as bidirectional labeling and registration scheme (BIDS), involves only linear scans of image pixels. It uses one-dimensional operations rather than the queues that are used in traditional segmentation algorithms, which are two-dimensional problems. BIDS also provides unique labels for individual homogeneous regions. In addition to achieving the same segmentation results, BIDS is four times less computationally complex than the conventional watershed by immersion technique.

Algorithms↗

PubMed2004

[Effects of Shendan Jianyi Capsule on aldose reductase activity of kidney in diabetic rats].

OBJECTIVE: To evaluate the effects of Shendan Jianyi Capsule (SDJYC) on aldose reductase (AR) activity of the kidney in diabetic rats and the significance of prevention and treatment of diabetic nephropathy with Chinese natural herbs. METHODS: Diabetic Wistar rats were treated with SDJYC and sorbinil respectively, and the AR activity in kidney, urine protein and the activity of Na(+)-K(+)-ATPase were tested. RESULTS: The AR activity in diabetic rats was decreased obviously after being treated with sorbinil or SDJYC. The activity of Na(+)-K(+)-ATPase in diabetic rats decreased obviously at the end of the eighth week, and increased after being treated with sorbinil and SDJYC. There was no difference between two treated groups after the treatment. It demonstrated that the inhibition of AR activity could improve the activity of Na(+)-K(+)-ATPase and SDJYC had the same effect. CONCLUSIONS: SDJYC exerts effects by inhibiting the activity of AR.

Aldehyde Reductase↗

PubMed2003

[Effects of hyperbaric oxygenation on rabbits 'testes with varicocele].

OBJECTIVE: To study the mechanism of male infertility caused by varicocele by evaluating the effects of hyperbaric oxygenation (HBO) therapy on the testicular tissue morphology and function of rabbit model with varicocele(VC). METHODS: Twenty-four mature male rabbits were randomly divided into three groups: pseudo-operation, VC model and VC model administered by HBO. Experimental varicocele was induced by partial ligation of the left "lumbotesticular" trunk vein in rabbits. HBO was administered to one of the two groups of VC model rabbits after the operation. Weight and volume of both testes, parameters of seminal fluid, histological changes of testicular tissues, MTDs, TFI, and Sertoli cell index (SI) of seminiferous tubules were studied. RESULTS: The average weight and volume of the left testes significantly increased in the rabbits treated by HBO. The semen quality was improved, and MTDs increased significantly compared with VC group(P < 0.0001). The testicular tissue morphology became nearly normal in VC + HBO group. CONCLUSIONS: 1. Both the structure and spermatogenetic function of testes can be damaged by the presence of varicocele; 2. Chronic ischemia, anoxia and microcircular dysfunction may be the key process and essential factor that make varicocele contributive to testicular damage and spermatogenetic dysfunction; 3. HBO can effectively alleviate, even eliminate, chronic ischemia, anoxia and microcircular dysfunction in testicular tissues with varicocele, and thus protect the structure and functions of testes.

Animals↗

PubMed2003

Detection of gastric cancer and premalignant lesions by novel marker glycoprotein 87 using monoclonal antibody Adnab-9.

Gastric adenocarcinoma (GC), the second most frequent cancer in the world, is highly prevalent in Asia. A screening test for early-stage GC would represent a major advance in the management of this disease. Associated conditions such as chronic atrophic gastritis (CAG) with intestinal metaplasia are manifested by specialized intestinalized tissue that often includes Paneth cells. Adenoma-associated antigen glycoprotein 87 (GP87), defined by the Adnab-9 monoclonal antibody and shed into the gut, is associated with epithelial cells, some of which resemble Paneth cells. We evaluated the diagnostic value of GP87 for cancer and gastric premalignant lesions. One hundred and seven sections of normal, benign, and premalignant gastric mucosa and 79 sections of pericancerous tissue were evaluated for expression of GP87 by immunohistochemistry. Eighty-two patients with GC, 34 patients with benign chronic disease, 35 patients with premalignant conditions, and 80 normal controls were evaluated by ELISA for GP87 in feces and gastric juice. Adnab-9 immunostaining for GP87 was significantly positive in CAG and intestinal metaplasia (>77.8%), compared with 0% in normal controls (P < 0.05). Fecal GP87 was positive in 79.3% of patients with gastric cancer, including early-stage lesions, and in 84% of patients with CAG versus 10% of controls (P < 0.05). Positive proportions for each pathological group in tissue correlated with that in feces (r = 0.99; P < 0.02). GP87 is differentially expressed in premalignant gastric lesions that appear to be the origin for fecal GP87, which may be useful for early detection of GC.

Animals↗

PubMed2002

cAMP signal transduction, a potential compensatory pathway for coronary endothelial NO production after heart failure.

OBJECTIVE: This study investigated whether cAMP signal transduction regulates coronary microvascular NO production after heart failure (HF), a state in which endothelial NO synthase (eNOS) is downregulated. METHODS AND RESULTS: Myocardial microvessels were isolated. Nitrite, the hydration product of NO, from these vessels was quantified by using the Griess reaction. Forskolin (10(-4) mol/L), 8-bromo-cAMP (10(-2) mol/L), isoproterenol (10(-4) mol/L), or adrenomedullin (10(-6) mol/L) significantly increased nitrite release by 78+/-8, 84+/-14, 71+/-11, and 73+/-15 pmol/mg, respectively, from isolated microvessels from normal canine hearts (P<0.05 versus control). Bradykinin (10(-5) mol/L) and acetylcholine (10(-5) mol/L) increased nitrite release by 83+/-13 and 72+/-6 pmol/mg, respectively (P<0.05 versus control). However, NO production induced by bradykinin and acetylcholine was markedly reduced after HF (46+/-7 and 39+/-7 pmol/mg, respectively; P<0.05 versus normal), reflecting eNOS downregulation (55% in eNOS protein). Surprisingly, NO production in response to forskolin, 8-bromo-cAMP, isoproterenol, and adrenomedullin not only was preserved but also was substantially enhanced in these microvessels after HF (121+/-14, 124+/-21, 107+/-18, and 122+/-16 pmol/mg, respectively; P<0.05 versus normal group) and was associated with an upregulation of protein kinase B (220% increase in protein kinase B protein). All these responses were in an NO synthase or a protein kinase A inhibitor-blockable manner. CONCLUSIONS: Our data indicate that cAMP signal transduction may be an important potential compensatory pathway to increase myocardial microvascular NO production after HF when eNOS is downregulated.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2002

Interaction of plant mitochondrial and chloroplast signal peptides with the Hsp70 molecular chaperone.

Most mitochondrial and chloroplast proteins are synthesized on cytosolic polyribosomes as precursor proteins, with an N-terminal signal sequence that targets the precursor to the correct organelle. In mitochondria, the chaperone Hsp70 functions as a molecular motor, pulling the precursor across the mitochondrial membranes; 97.0% of plant mitochondrial presequences contain an Hsp70 binding site. In chloroplasts, the outer envelope, intermembrane space and a stromal Hsp70 are thought to participate in protein import; 82.5% of chloroplast transit peptides have an Hsp70 binding site. The interaction of signal peptides with Hsp70 during the import process is supported by biochemical and bioinformatic studies.

Amino Acid Sequence↗

PubMed2002

Paradoxical release of nitric oxide by an L-type calcium channel antagonist, the R+ enantiomer of amlodipine.

Amlodipine is a mixture of two enantiomers, one having L-type channel blocking activity (S-) and the other about 1,000-fold weaker activity and of little known other activity (R+). To determine whether the R+ enantiomer releases nitric oxide, the ability of amlodipine, its enantiomers, and nitrendipine to release nitric oxide in isolated coronary microvessels and to regulate cardiac tissue oxygen consumption via nitric oxide release was studied in vitro. Amlodipine and the R+ enantiomer released nitric oxide in a concentration-dependent fashion, increasing nitrite release from coronary microvessels by 57 +/- 12 and 45 +/- 5 pmol/mg/20 min at 10(-6) M (p < 0.05 from control). Nitrite release was entirely blocked by N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, and HOE-140, a B2-kinin receptor antagonist. The S- enantiomer had no effect on nitrite release at any concentration. Amlodipine and the R+ enantiomer also reduced oxygen consumption in canine cardiac tissue in vitro and this was in an L-NAME-blockable manner. The S- enantiomer of amlodipine had no effect. This study shows that the R+ enantiomer of amlodipine is responsible for the release of nitric oxide and not the S- enantiomer (the L-type calcium channel blocking portion of amlodipine). Interestingly, nitric oxide release is dependent on the production of kinins because it is blocked by HOE-140. This study defines a potentially important property by which calcium channel blockers may release nitric oxide and may contribute to their use in the treatment of cardiovascular disease.

Amlodipine↗

PubMed2000

Assay of Adenylyl Cyclase Activity by Ion-exchange High-performance Liquid Chromatography.

Adenylyl cyclase(AC)activity was determined by directly quantifying the product cAMP with ion-exchange HPLC. When AC reaction was terminated, the reaction mixture was kept at 0 degrees for 2 h to remove residual ATP utilizing the action of ATP-hydrolyzing enzymes existed in the crude AC preparation of membrane pellet. Papaverine was removed by the dichloromethane extraction, and cAMP was quantified by chromatography on a WAX-1 HPLC column with baseline-resolution. It was found that cAMP was linearly formed within 10 min of the reaction, and the amount of cAMP formed was proportional to the amount of enzyme. Mouse brain AC activity determined by this method was 42 nmol/min per gram of protein, similar to that obtained by the classical [(3)H] labeled ATP method. This ion-exchange HPLC was more rapid and convenient.

Journal Article↗