Abnormal expression of P2X family receptors in Chinese pediatric acute leukemias

Nucleotides are new players in intercellular communication network. P2X family receptors are ATP-gated plasma membrane ion channels with diverse biological functions. Their distribution patterns and significance in pediatric leukemias have not been established. Here we investigated the expression of P2X receptors in BMMC samples from Chinese pediatric acute leukemias. Real-time PCR and Western blot results showed that P2X1, P2X4, P2X5 and P2X7 receptors were simultaneously over expressed in leukemias compared with controls, whereas P2X2, P2X3 and P2X6 were absent or marginally expressed in both groups. It was worth noting that the co-expression feature of them, especially between P2X4 and P2X7, could be observed and the highest expression of P2X7 was detected in relapsed patients. Moreover, concomitant decrease of P2X4, P2X5 and P2X7 expressions was observed at CR stage in a follow-up study. Functional P2X7 was also verified. These results suggested that P2X1, P2X4, P2X5 and P2X7 were hematopoiesis-related P2X receptors, and their signaling, especially for P2X7, might play important roles in pediatric leukemias. P2X receptors might co-operatively contribute to the malignant phenotype in human pediatric leukemias.     

Blockade of sphingosine 1-phosphate receptor 2 signaling attenuates streptozotocin-induced apoptosis of pancreatic β-cells

Sphingosine 1-phosphate (S1P) is a potent sphingolipid mediator that acts through five cognate G protein-coupled receptors (S1P₁-S1P₅) and regulates many critical biological processes. Recent studies indicated that S1P at nanomolar concentrations significantly reduces cytokine-induced apoptosis of pancreatic β-cells in which genes for S1P₁-S1P₄ are co-expressed. However, the S1P receptor subtype(s) involved in this effect remains to be clarified. In this study, we investigated the potential role of S1P₂ in streptozotocin (STZ)-induced apoptosis of pancreatic β-cells and progression of diabetes. S1P₂-deficient (S1P₂^-/-) mice displayed a greater survive ability, lower blood glucose levels, and smaller numbers of TUNEL-positive apoptotic β-cells to administration of a high dose of STZ than wild-type (WT) mice. S1P₂^-/- mice showed higher insulin/glucose ratios (an index of relative insulin deficiency) and larger insulin-positive islet areas to administration of a low dose of STZ than WT mice. Moreover, administration of JTE-013, a S1P₂-specific antagonist, to WT mice ameliorated STZ-induced blood glucose elevation and reduced the incidence of diabetes. Our findings indicate that blockade of S1P₂ signaling attenuates STZ-induced apoptosis of pancreatic β-cells and decreases the incidence of diabetes.     

Kinetic and structural features of betaine aldehyde dehydrogenases: Mechanistic and regulatory implications

The betaine aldehyde dehydrogenases (BADH; EC 1.2.1.8) are so-called because they catalyze the irreversible NAD(P)⁺-dependent oxidation of betaine aldehyde to glycine betaine, which may function as (i) a very efficient osmoprotectant accumulated by both prokaryotic and eukaryotic organisms to cope with osmotic stress, (ii) a metabolic intermediate in the catabolism of choline in some bacteria such as the pathogen Pseudomonas aeruginosa, or (iii) a methyl donor for methionine synthesis. BADH enzymes can also use as substrates aminoaldehydes and other quaternary ammonium and tertiary sulfonium compounds, thereby participating in polyamine catabolism and in the synthesis of γ-aminobutyrate, carnitine, and 3-dimethylsulfoniopropionate. This review deals with what is known about the kinetics and structural properties of these enzymes, stressing those properties that have only been found in them and not in other aldehyde dehydrogenases, and discussing their mechanistic and regulatory implications.     

Reversible Liposome Association Induced by LAH4: A Peptide with Potent Antimicrobial and Nucleic Acid Transfection Activities

We report on the reversible association of anionic liposomes induced by an antimicrobial peptide (LAH4). The process has been characterized for mixed membranes of POPC and POPS at molar ratios of 1:1, 3:1, and 9:1. Although the vesicles remain in suspension in the presence of excess amounts of peptide, the addition of more lipids results in surface charge neutralization, aggregation of the liposomes, and formation of micrometer-sized structures that coexist in equilibrium with vesicles in suspension. At low ratios of anionic lipids, vesicle aggregation is a reversible process, and vesicle disassembly is observed upon inversion of the surface charge by further supplementation with anionic vesicles. In contrast, a different process, membrane fusion, occurs in the presence of high phosphatidylserine concentrations. Upon binding to membranes containing low POPS concentrations, the peptide adopts an in-plane α-helical structure, a secondary structure that is conserved during vesicle association and dissociation. Our finding that peptides are essential for vesicle aggregation contributes to a better understanding of the activity of antimicrobial peptides, and suggests an additional layer of complexity in membrane-protein lipid interactions.     

High expression of the mRNA of cytochrome P450 and phase II enzymes in the lung and kidney tissues of cattle

The objective of this study was to investigate the tissue-specific mRNA expression of different cytochrome P450 (CYP) isoforms, UDP glucuronsyl transferase 1A1 (UGT1A1) and glutathione-S-transferase (GSTA1) in the different tissues (liver, mammary gland, lungs, spleen, kidney cortex, heart, masseter muscle and tongue) of cattle, using quantitative real-time polymerase chain reaction (qPCR). CYP1A1-like mRNA was expressed in all of the tissues examined, including the liver, with the highest expression level in the kidney. CYP1A2-, 2E1- and 3A4-like mRNAs were only expressed hepatically. Interestingly, significant expression of CYP2B6-like mRNA was recorded in the lung tissue, while CYP2C9-like mRNA was expressed in the liver and kidney tissues of the cattle examined. UGT1A1- and GSTA1-like mRNAs were expressed in all of the examined tissues, except the mammary glands, and the highest expression levels were recorded in the kidney. The high expression of UGT1A1 in the lung tissue and GSTA1 in the liver tissue was unique to cattle; this has not been reported for rats or mice. The findings of this study strongly suggest that the liver, kidneys and lungs of cattle are the major organs contributing to xenobiotics metabolism.     

Characterization of two NADPH: Cytochrome P450 reductases from cotton (Gossypium hirsutum)

Cytochrome P450 monooxygenases (P450s) are commonly involved in biosynthesis of endogenous compounds and catabolism of xenobiotics, and their activities rely on a partner enzyme, cytochrome P450 reductase (CPR, E.C.1.6.2.4). Two CPR cDNAs, GhCPR1 and GhCPR2, were isolated from cotton (Gossypium hirsutum). They are 71% identical to each other at the amino acid sequence level and belong to the Class I and II of dicotyledonous CPRs, respectively. The recombinant enzymes reduced cytochrome c, ferricyanide and dichlorophenolindophenol (DCPIP) in an NADPH-dependent manner, and supported the activity of CYP73A25, a cinnamate 4-hydroxylase of cotton. Both GhCPR genes were widely expressed in cotton tissues, with a reduced expression level of GhCPR2 in the glandless cotton cultivar. Expression of GhCPR2, but not GhCPR1, was inducible by mechanical wounding and elicitation, indicating that the GhCPR2 is more related to defense reactions, including biosynthesis of secondary metabolites.     

Inhibitor and substrate activities of sesquiterpene olefins toward (+)-δ-cadinene-8-hydroxylase, a cytochrome P450 monooxygenase (CYP706B1)

Several lines of evidence indicate that (+)-δ-cadinene-8-hydroxylase (CYP706B1) plays an important role in biosynthesis of gossypol in Gossypium arboreum L. ( [Luo et al., 2001] and [Wang et al., 2003]). The catalytically active enzyme has been expressed in yeast microsomes. Some microsomal preparations conjugated the hydroxylated (+)-δ-cadinene to a moiety that has not yet been identified. However, when microsomes were treated with n-octyl-β-d-glucoside (OG), a non-ionic detergent, (+)-δ-cadinene was reproducibly converted to the free alcohol, 8-hydroxy-(+)-δ-cadinene. OG had little effect on K_m and slightly stimulated apparent V_max. Enzymic activity was more than 10-fold more sensitive to inhibition by the N-substituted imidazole clotrimazole than to miconazole. Sesquiterpene olefins (−)-δ-cadinene, (−)-α-cubebene, (−)-α-muurolene, α-humulene, and a mixture of (−)- and (+)-α-copaene were inhibitory to hydroxylation of (+)-δ-cadinene. In addition, (−)-α-cubebene, (−)-α-muurolene, α-humulene, and, to a smaller extent, (−)-δ-cadinene served as alternative substrates for (+)-δ-cadinene-8-hydroxylase and were converted to mono-hydroxylated products. Of the five olefins tested, α-humulene and α-copaene are found in lysigenous glands of cotton (Elzen et al., 1985), which are also the site of gossypol accumulation ( [Bell et al., 1978] and [Mace et al., 1976]) and the probable site of its biosynthesis.     

Sorgoleone

Sorgoleone, a major component of the hydrophobic root exudate of sorghum [Sorghum bicolor (L.) Moench], is one of the most studied allelochemicals. The exudate also contains an equivalent amount of a lipid resorcinol analog as well as a number of minor sorgoleone congeners. Synthesis of sorgoleone is constitutive and compartmentalized within root hairs, which can accumulate up to 20 μg of exudate/mg root dry weight. The biosynthesis pathway involves unique fatty acid desaturases which produce an atypical 16:3 fatty acyl-CoA starter unit for an alkylresorcinol synthase that catalyzes the formation of a pentadecatrienylresorcinol intermediate. This intermediate is then methylated by SAM-dependent O-methyltransferases and dihydroxylated by cytochrome P450 monooxygenases. An EST data set derived from a S. bicolor root hair-specific cDNA library contained all the candidate sequences potentially encoding enzymes involved in the sorgoleone biosynthetic pathway. Sorgoleone interferes with several molecular target sites, including inhibition of photosynthesis in germinating seedlings. Sorgoleone is not translocated acropetally in older plants, but can be absorbed through the hypocotyl and cotyledonary tissues. Therefore, the mode of action of sorgoleone may be the result of inhibition of photosynthesis in young seedlings in concert with inhibition of its other molecular target sites in older plants. Due to its hydrophobic nature, sorgoleone is strongly sorbed in soil which increases its persistence, but experiments show that it is mineralized by microorganisms over time.     

DNA binding and nuclease activity of a one-dimensional heterometallic nitrosyl complex

The interaction of a structurally characterized Sr–Fe nitrosyl complex with DNA has been studied by UV–vis and fluorescence spectroscopy, viscometric, and gel electrophoresis techniques. From the absorption titration studies the intrinsic binding constant of the complex with DNA was calculated to be 1.6 × 10⁴ M⁻¹. Fluorimetric studies indicate that the complex compete with EB in binding to DNA. The complex shows nuclease activity on pUC19 supercoiled DNA in presence of H₂O₂.