Scavenging of extracellular H2O2 by catalase inhibits the proliferation of HER-2/Neu-transformed rat-1 fibroblasts through the induction of a stress response

High levels of reactive oxygen species (ROS) are associated with cytotoxicity. Alternatively, nontoxic levels of ROS like hydrogen peroxide (H(2)O(2)) can mediate the transmission of many intracellular signals, including those involved in growth and transformation. To identify pathways downstream of endogenous cellular H(2)O(2) production, the response of Rat-1 fibroblasts exhibiting differential HER-2/Neu receptor tyrosine kinase activity to removal of physiological H(2)O(2) concentrations was investigated. The proliferation of all cells was abolished by addition of the H(2)O(2) scavenger catalase to the culture medium. HER-2/Neu activity was not significantly affected by catalase treatment, suggesting that the target(s) of the H(2)O(2) signal lie downstream of the receptor in our model. ERK1/2 phosphorylation was blocked by catalase in fibroblasts expressing wild type Neu, however such a response did not occur in cells possessing activated mutant Neu. This indicates that the ERK1/2 response contributes little to the growth inhibition observed. By contrast, JNK1 activity increased following the addition of catalase or H(2)O(2), regardless of Neu activity or level of cell transformation. Phosphorylation of p38 MAPK was induced by H(2)O(2) but not by catalase. These observations suggest that scavenging of H(2)O(2) from the cellular environment blocks Rat-1 proliferation primarily through the activation of stress pathways.     

Molecular cloning and characterization of the human protein kinase D2. A novel member of the protein kinase D family of serine threonine kinases

We have isolated the full-length cDNA of a novel human serine threonine protein kinase gene. The deduced protein sequence contains two cysteine-rich motifs at the N terminus, a pleckstrin homology domain, and a catalytic domain containing all the characteristic sequence motifs of serine protein kinases. It exhibits the strongest homology to the serine threonine protein kinases PKD/PKCmicro and PKCnu, particularly in the duplex zinc finger-like cysteine-rich motif, in the pleckstrin homology domain and in the protein kinase domain. In contrast, it shows only a low degree of sequence similarity to other members of the PKC family. Therefore, the new protein has been termed protein kinase D2 (PKD2). The mRNA of PKD2 is widely expressed in human and murine tissues. It encodes a protein with a molecular mass of 105 kDa in SDS-polyacrylamide gel electrophoresis, which is expressed in various human cell lines, including HL60 cells, which do not express PKCmicro. In vivo phorbol ester binding studies demonstrated a concentration-dependent binding of [(3)H]phorbol 12,13-dibutyrate to PKD2. The addition of phorbol 12,13-dibutyrate in the presence of dioleoylphosphatidylserine stimulated the autophosphorylation of PKD2 in a synergistic fashion. Phorbol esters also stimulated autophosphorylation of PKD2 in intact cells. PKD2 activated by phorbol esters efficiently phosphorylated the exogenous substrate histone H1. In addition, we could identify the C-terminal Ser(876) residue as an in vivo phosphorylation site within PKD2. Phosphorylation of Ser(876) of PKD2 correlated with the activation status of the kinase. Finally, gastrin was found to be a physiological activator of PKD2 in human AGS-B cells stably transfected with the CCK(B)/gastrin receptor. Thus, PKD2 is a novel phorbol ester- and growth factor-stimulated protein kinase.     

A mouse model for mucopolysaccharidosis type III A (Sanfilippo syndrome)

Mucopolysaccharidosis type III A (MPS III A, Sanfilippo syndrome) is a rare, autosomal recessive, lysosomal storage disease characterized by accumulation of heparan sulfate secondary to defective function of the lysosomal enzyme heparan N- sulfatase (sulfamidase). Here we describe a spontaneous mouse mutant that replicates many of the features found in MPS III A in children. Brain sections revealed neurons with distended lysosomes filled with membranous and floccular materials with some having a classical zebra body morphology. Storage materials were also present in lysosomes of cells of many other tissues, and these often stained positively with periodic-acid Schiff reagent. Affected mice usually died at 7-10 months of age exhibiting a distended bladder and hepatosplenomegaly. Heparan sulfate isolated from urine and brain had nonreducing end glucosamine- N -sulfate residues that were digested with recombinant human sulfamidase. Enzyme assays of liver and brain extracts revealed a dramatic reduction in sulfamidase activity. Other lysosomal hydrolases that degrade heparan sulfate or other glycans and glycosaminoglycans were either normal, or were somewhat increased in specific activity. The MPS III A mouse provides an excellent model for evaluating pathogenic mechanisms of disease and for testing treatment strategies, including enzyme or cell replacement and gene therapy.     

Nickel and cobalt reagents promote selective oxidation of Z-DNA

The structural characteristics of Z-DNA were used to challenge the selectivity of guanine oxidation promoted by nickel and cobalt reagents. Base pairing and stacking within all helical structures studied previously had hindered access to guanine and limited its reaction. However, the Z-helix uniquely retains high exposure of guanine N7. This exposure was sufficient to direct oxidation specifically to a plasmid insert -(CG)(13)AATT(CG)(13)- that adopted a Z-conformation under native supercoiling. An alternative insert -(CG)(7)- retained its B-conformation and demonstrated the expected lack of reactivity. For a nickel salen complex made from a particularly bulky ligand, preferential reaction shifted to the junctions within the Z-DNA insert as is common for large reagents. Inactivation of the nickel reagents by high-salt concentrations prevented parallel investigations of Z-DNA, formed by oligonucleotides. However, the activity of Co(2+) was minimally affected by salt and consequently confirmed the high reactivity of 5'-p(CG)(4) in its Z-conformation. These reagents may now be applied to a broad array of targets, since their structural specificity remains predictable for both complex and helical assemblies of nucleic acids.     

AUX1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues

Plants employ a specialized transport system composed of separate influx and efflux carriers to mobilize the plant hormone auxin between its site(s) of synthesis and action. Mutations within the permease-like AUX1 protein significantly reduce the rate of carrier-mediated auxin uptake within Arabidopsis roots, conferring an agravitropic phenotype. We are able to bypass the defect within auxin uptake and restore the gravitropic root phenotype of aux1 by growing mutant seedlings in the presence of the membrane-permeable synthetic auxin, 1-naphthaleneacetic acid. We illustrate that AUX1 expression overlaps that previously described for the auxin efflux carrier, AtPIN2, using transgenic lines expressing an AUX1 promoter::uidA (GUS) gene. Finally, we demonstrate that AUX1 regulates gravitropic curvature by acting in unison with the auxin efflux carrier to co-ordinate the localized redistribution of auxin within the Arabidopsis root apex. Our results provide the first example of a developmental role for the auxin influx carrier within higher plants and supply new insight into the molecular basis of gravitropic signalling.     

Regulation of the DNA-dependent protein kinase (DNA-PK) activity in eukaryotic cells

The DNA-dependent protein kinase (DNA-PK) is a trimeric nuclear serine/threonine protein kinase consisting of a large catalytic sub-unit and the Ku heterodimer that regulates kinase activity by its association with DNA. DNA-PK is a major component of the DNA double strand break repair apparatus, and cells deficient in one of its component are hypersensitive to ionizing radiation. DNA-PK is also required to lymphoid V(D)J recombination and its absence confers in mice a severe combined immunodeficiency phenotype. The purpose of this review is to summarize the current knowledge on the mechanisms that contribute to regulate DNA-PK activity in vivo or in vitro and relates them to the role of DNA-PK in cellular functions. Finally, the studies devoted to drug-inhibition of DNA-PK in order to enhance cancer therapy by DNA-damaging agents are presented.     

Variations in levels of clonality among Populus nigra L. stands of different ages

The evolution of genotypic diversity with population age remains poorly explored in clonal plant populations despite the potential for important shifts to occur through the course of time. Woody sprouting species are particularly under-represented in studies investigating intra-specific variations in levels of clonality from one locality to the next and through time. In this study we sought to determine the incidence and frequency of replicate genotypes in natural Populus nigra L. (Salicaceae) stands of different ages. Ten stands of this woody riparian sprouting species were selected in each of three distinct age groups (young, middle-aged and old) along a 30 km stretch of the River Garonne (south-west France). Leaf samples were collected from 15 neighbouring trees in each stand (450 samples in total) and replicate genotypes were identified using five SSR markers. Replicate genotypes were identified in two-thirds of all stands sampled (i.e. 50 of young stands, 100 of middle-aged stands and 50% of old stands). Young stands had significantly fewer replicated genotypes than middle-aged or old stands, while middle-aged stands had the greatest number of replicated genotypes. Replicate genotypes were most often found to occur as nearest neighbours and formed relatively small, discrete units (i.e. 2–4 trees growing in close proximity to one another). This suggests that asexual regeneration frequently occurs through flood-training in this species, although asexual regeneration from translocated fragments also evidently occurs as evidenced by 11 cases of replicate genotypes occurring in widely separated stands (up to 19 km apart). The results of this study highlight the need for a hierarchical sampling strategy in space and across age groups for an accureate understanding of the genotypic structure of woody sprouting species populations. Conservation and management of effective population sizes will benefit from better insight into not only spatial, but also temporal variations in levels of genotypic diversity.Co-ordinating editor: J. Tuomi     

Diaphorase can metabolize some vasorelaxants to NO and eliminate NO scavenging effect of 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO)

Diaphorase was studied as a possible oxidoreductase participating in NO production from some vasorelaxants. In the presence of NADH or NADPH, diaphorase can convert selected NO donors, glycerol trinitrate (GTN) and formaldoxime (FAL) to nitrites and nitrates with NO as an intermediate. This activity of diaphorase was inhibited by diphenyleneiodonium (DPI) (inhibitor of some NADPH-dependent flavoprotein oxidoreductases), while it remained uninhibited by NG-nitro-L-arginine methyl ester (inhibitor of NO synthase) 7-Ethoxyresorufin (inhibitor of cytochrome P-450 1A1 and cytochrome P-450 NADPH-dependent reductase) inhibited the conversion of GTN only. Existence of NO as an intermediate of the reaction was supported by results of electron paramagnetic resonance spectroscopy. In addition to its ability to affect the above mentioned NO donors, diaphorase was able to reduce 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) and thus to eliminate its NO scavenging effect. This activity of diaphorase could also be inhibited by DPI. The reaction of diaphorase with GTN and PTIO was not affected by superoxide dismutase (SOD) or catalase. Reaction of FAL with diaphorase was lowered with SOD by 38 % indicating the partial participation of superoxide anion probably generated by the reaction of diaphorase with NADH or NADPH. Catalase had no effect. Diaphorase could apparently be one of the enzymes participating in the metabolism of studied NO donors to NO. The easy reduction and consequent elimination of PTIO by diaphorase could affect its use as an NO scavenger in biological tissues.