Vialinin A, a novel 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenger from an edible mushroom in China

While screening for bioactive compounds from edible mushrooms, a new potent antioxidant, vialinin A (1), together with a known compound, ganbajunin B (2), and a mixture of ganbajunins D (3) and E (4), were isolated from the dry fruiting bodies of Thelephora vialis. The structure of 1, 5',6'-bis(phenylacetoxy)-1,1':4',1'-terphenyl-2',3',4,4'-tetraol, was elucidated by spectroscopic and chemical methods. This compound had strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging activity with an EC(50) value of 14.0 microM, nearly equal to that of butylated hydroxytoluene (BHT; EC(50) = 10.0 microM). A radical scavenging experiment using 1 and DPPH radicals indicated that 1 donated two hydrogen atoms to two molecules of the DPPH radical under hydrophobic conditions.     

Phorbol myristate acetate induces neutrophil death through activation of p38 mitogen-activated protein kinase that requires endogenous reactive oxygen species other than HOCl

Stimulation of normal mouse neutrophils with phorbol 12-myristate 13-acetate resulted in an acceleration of chromatin condensation and phosphatidylserine externalization that was not associated with caspase-3 activation. Caspase-independent death was completely inhibited by GF109203X and SB202190, specific inhibitors for protein kinase C and p38 mitogen-activated protein kinase respectively. Activation of p38 mitogen-activated protein kinase was completely suppressed by GF109203X, indicating that this enzyme is regulated by protein kinase C. On the other hand, cell death was abolished in NADPH oxidase-deficient neutrophils lacking superoxide production. Of note, p38 mitogen-activated protein kinase was activated by phorbol 12-myristate 13-acetate in normal and myeloperoxidase-deficient neutrophils lacking production of HOCl, whereas no activation was observed in NADPH oxidase-deficient neutrophils. These results strongly suggest that activation of p38 mitogen-activated protein kinase is regulated by endogenously generated superoxide or its metabolites other than HOCl, a critical regulator of inducer-stimulated death of neutrophils.     

Glucosamine induces lipid accumulation and adipogenic change in C2C12 myoblasts

Hyperglycemia-induced activation of hexosamine biosynthesis pathway (HBP) has been implicated in the development of insulin resistance in skeletal muscles. In the present study, the content of uridine-5'-diphospho-N-acetylglucosamine, the end product of the HBP, was elevated in skeletal muscle of obese diabetic KKA(y) mice, compared with control mice. To elucidate the effect of elevated HBP in the skeletal muscle, we treated C2C12 myoblasts with glucosamine, an intermediate metabolite of the HBP. Glucosamine induced lipid accumulation and significantly increased the mRNA expression levels of peroxisome proliferator-activated receptor gamma, adiponectin, and aP2 in C2C12 myoblasts. Similar mRNA changes were observed in skeletal muscles of Sprague-Dawley rats treated with glucosamine infusion. Our results provide a possible explanation of hyperglycemia-induced insulin resistance in skeletal muscle.     

An alternative transcript derived from the trio locus encodes a guanosine nucleotide exchange factor with mouse cell-transforming potential

By screening cDNA expression libraries derived from fresh leukemic cells of adult T-cell leukemia for the potential to transform murine fibroblasts, NIH3T3, we have identified a novel transforming gene, designated Tgat. Expression of Tgat in NIH3T3 resulted in the loss of contact inhibition, increase of saturation density, anchorage-independent growth in a semisolid medium, tumorigenicity in nude mice, and increased invasiveness. Sequence comparison revealed that an alternative RNA splicing of the Trio gene was involved in the generation of Tgat. The Tgat cDNA encoded a protein product consisting of the Rho-guanosine nucleotide exchange factor (GEF) domain of a multifunctional protein, TRIO, and a unique C-terminal 15-amino acid sequence, which were derived from the exons 38-46 of the Trio gene and a novel exon located downstream of its last exon (exon 58), respectively. A Tgat mutant cDNA lacking the C-terminal coding region preserved Rho-GEF activity but lost the transforming potential, indicating an indispensable role of the unique sequence. On the other hand, treatment of Tgat-transformed NIH3T3 cells with Y-27632, a pharmacological inhibitor of Rho-associated kinase, abrogated their transforming phenotypes, suggesting the coinvolvement of Rho-GEF activity. Thus, alternative RNA splicing, resulting in the fusion protein with the Rho-GEF domain and the unique 15 amino acids, is the mechanism generating the novel oncogene, Tgat.     

Construction of a novel human artificial chromosome vector for gene delivery

Potential problems of conventional transgenes include insertional disruption of the host genome and unpredictable, irreproducible expression of the transgene by random integration. Alternatively, human artificial chromosomes (HACs) can circumvent some of the problems. Although several HACs were generated and their mitotic stability was assessed, a practical way for introducing exogenous genes by the HACs has yet to be explored. In this study, we developed a novel HAC from sequence-ready human chromosome 21 by telomere-directed chromosome truncation and added a loxP sequence for site-specific insertion of circular DNA by the Cre/loxP system. This 21HAC vector, delivered to a human cell line HT1080 by microcell fusion, bound centromere proteins A, B, and C and was mitotically stable during long-term culture without selection. The EGFP gene inserted in the HAC vector expressed persistently. These results suggest that the HAC vector provides useful system for functional studies of genes in isogenic cell lines.     

Human chromosome 21q22.2-qter carries a gene(s) responsible for downregulation of mlc2a and PEBP in Down syndrome model mice

Congenital heart disease (CHD) is a major clinical manifestation of Down syndrome (DS). We recently showed that chimeric mice containing a human chromosome 21 (Chr 21) exhibited phenotypic traits of DS, including CHD. Our previous study showed that myosin light chain-2a (mlc2a) expression was reduced in the hearts of chimeric mice and DS patients. We found that phosphatidylethanolamine binding protein (PEBP) was also downregulated in Chr 21 chimeras in this study. As mlc2a is involved in heart morphogenesis, and PEBP controls the proliferation and differentiation of different cell types, these genes are candidates for involvement in DS-CHD. The DS-CHD candidate region has been suggested to span between PFKL and D21S3, which is the STS marker near the ETS2 loci. To identify gene(s) or a gene cluster on Chr 21 responsible for the downregulation of mlc2a and PEBP, we fragmented Chr 21 at the EST2 loci, by telomere-directed chromosome truncation in homologous recombination-proficient chicken DT40 cells. The modified Chr 21 was transferred to mouse ES cells by microcell-mediated chromosome transfer (MMCT), via CHO cells. We used ES cell lines retaining the Chr 21 truncated at the ETS2 locus (Chr 21E) to produce chimeric mice and compared overall protein expression patterns in hearts of the chimeras containing the intact and the fragmented Chr 21 by two-dimensional electrophoresis. While mouse mlc2a and PEBP expression was downregulated in the chimeras containing the intact Chr 21, the expression was not affected in the Chr 21E chimeras. Therefore, we suggest that Chr 21 gene(s) distal from the ETS2 locus reduce mouse mlc2a and PEBP expression in DS model mice and DS. Thus, this chromosome engineering technology is a useful tool for identification or mapping of genes that contribute to the DS phenotypes.     

Characterization of human CD4 helper T cell responses against Aurora kinase A

Aurora kinase A (Aurora-A) is a cell cycle-associated serine–threonine kinase that is overexpressed by various types of cancer and is highly associated with poor prognosis. Since the expression of Aurora-A in normal tissues has been shown to be significantly lower as compared to tumor cells, this protein is being considered as a potential tumor-associated antigen for developing immunotherapies. The goal in the present study was to identify CD4 helper T lymphocyte (HTL) epitopes for Aurora-A for the design of T cell-based immunotherapies against Aurora-A-expressing tumors. Synthetic peptides corresponding to potential HTL epitopes were identified from Aurora-A and used to stimulate CD4 T lymphocytes in vitro to generate antigen-specific HTL clones that were evaluated for antigen specificity, MHC restriction and for their ability to interact with Aurora-A-expressing tumor cells. The results show that two peptides (Aurora-A_161–175 and Aurora-A_233–247) were effective in generating HTL responses that were restricted by more than one MHC class II allele (i.e., promiscuous responses). The CD4 HTL clones were able to directly recognize Aurora-A-expressing tumor cells in an antigen-specific and MHC class II-restricted manner and some of the clones displayed cytolytic activity toward Aurora-A + tumor cells. Both of these peptides were capable of stimulating in vitro T cell responses in patients with bladder cancer.     

Metabolic engineering of Saccharomyces cerevisiae producing nicotianamine: potential for industrial biosynthesis of a novel antihypertensive substrate

Nicotianamine (NA), a metal chelator, is ubiquitous in higher plants. In humans, NA inhibits angiotensin I-converting enzyme (ACE), and consequently reduces high blood pressure. Nicotianamine is synthesized from the trimerization of S-adenosylmethionine (SAM) by NA synthase (NAS). Here, we aimed to produce large amounts of NA fermentatively by introducing the Arabidopsis AtNAS2 gene into Saccharomyces cerevisiae strain SCY4. This strain can accumulate up to 100 times the usual amount of SAM, and this is considered desirable for overproduction of NA. Nicotianamine was produced in the engineered yeast, and the NA level increased with incubation time until the stationary phase. The maximum concentration of intracellular NA obtained was 766+/-33 microg/g wet weight. Successful production of NA in S. cerevisiae should pave the way for industrial production of this novel antihypertensive substrate.     

Ligand-induced effects on pyruvate dehydrogenase kinase isoform 2

Tryptophan fluorescence was used to analyze binding of ligands to human pyruvate dehydrogenase isoform 2 (PDHK2) and to demonstrate effects of ligand binding on distal structure of PDHK2 that is required for binding to the inner lipoyl domain (L2) of the dihydrolipoyl acetyltransferase. Ligand-altered binding of PDHK2 to L2 and effects of specific ligands on PDHK2 oligomeric state were characterized by analytical ultracentrifugation. ATP, ADP, and pyruvate markedly quenched the tryptophan fluorescence of PDHK2 and gave maximum quenching/L0.5 estimates: approximately 53%/3 microM for ATP; approximately 49%/15 microM for ADP; and approximately 71%/approximately 590 microM for pyruvate. The conversion of Trp-383 to phenylalanine completely removed ATP- and ADP-induced quenching and > or = 80% of the absolute decrease in fluorescence due to pyruvate. The W383F-PDHK2 mutant retained high catalytic activity. Pyruvate, added after ADP, quenched Trp fluorescence with an L0.5 of 3.4 microM pyruvate, > or = 150-fold lower concentration than needed with pyruvate alone. ADP-enhanced binding of pyruvate was maintained with W383F-PDHK2. Binding of PDHK2 dimer to L2 is enhanced when L2 are housed in oligomeric structures, including the glutathione S-transferase (GST)-L2 dimer, and further strengthened by reduction of the lipoyl groups (GST-L2(red)) (Hiromasa and Roche (2003) J. Biol. Chem. 278, 33681-33693). Binding of PDHK2 to GST-L2(red) was modestly hindered by 200 microM level of ATP or ADP or 5.0 mM pyruvate; a marked change to nearly complete prevention of binding was observed with ATP or ADP plus pyruvate at only 100 microM levels, and these conditions caused PDHK2 dimer to associate to a tetramer. These changes should make major contributions to synergistic inhibition of PDHK2 activity by ADP and pyruvate. Ligand-induced changes that interfere with PDHK2 binding to GST-L2(red) may involve release of an interdomain cross arm between PDHK2 subunits in which Trp-383 plays a critical anchoring role.