DNA repair mechanisms in dividing and non-dividing cells

DNA damage created by endogenous or exogenous genotoxic agents can exist in multiple forms, and if allowed to persist, can promote genome instability and directly lead to various human diseases, particularly cancer, neurological abnormalities, immunodeficiency and premature aging. To avoid such deleterious outcomes, cells have evolved an array of DNA repair pathways, which carry out what is typically a multiple-step process to resolve specific DNA lesions and maintain genome integrity. To fully appreciate the biological contributions of the different DNA repair systems, one must keep in mind the cellular context within which they operate. For example, the human body is composed of non-dividing and dividing cell types, including, in the brain, neurons and glial cells. We describe herein the molecular mechanisms of the different DNA repair pathways, and review their roles in non-dividing and dividing cells, with an eye toward how these pathways may regulate the development of neurological disease.     

Land Use Changes and GHG Emissions from Tropical Forest Conversion by Oil Palm Plantations in Riau Province,Indonesia

Increasing prices and demand for biofuel and cooking oil from importer countries have caused a remarkable expansion of oil palm plantations in Indonesia. In this paper, we attempt to monitor the expansion of oil palm plantations on peat land and in tropical forests. We measure the GHG emissions from the land conversion activities at provincial scale. Using Landsat images from three different periods (1990s, 2000s and 2012), we classified LULC of the Riau Province, which is the largest oil palm producing region in Indonesia. A hybrid method of integration, generated by combining automatic processing and manual analysis, yields the best results. We found that the tropical rainforest cover decreased from ∼63% in the 1990s to ∼37% in the 2000s. By 2012, the remaining tropical rainforest cover was only ∼22%. From the 1990s to the 2000s, conversion of forests and peat lands was the primary source of emissions, total CO₂ emitted to the atmosphere was estimated at ∼26.6 million tCO₂.y^-1, with 40.62% and 59.38% of the emissions from conversion of peat lands and forests, respectively. Between 2000 and 2012, the total CO₂ emitted to the atmosphere was estimated at ∼5.2 million tCO₂. y^-1, with 69.94% and 27.62% of the emissions from converted peat lands and converted forests, respectively. The results show that in the Riau Province, the oil palm industry boomed in the period from 1990 to 2000, with transformation of tropical forest and peat land as the primary source of emissions. The decrease of CO₂ emissions in the period from 2000 to 2012 is possibly due to the enforcement of a moratorium on deforestation.     

The Structures of Diethylaminoethylated Glucose and Oligosaccharides Derived from Cationic Starch

Phosphatidylethanolamine N-methyltransferase, which catalyzes all the three-step methylation from phosphatidylethanolamine to phosphatidylcholine, was purified to homogeneity from the membrane fraction of Zymomonas mobilis. The purified enzyme exhibited a single band on SDS- polyacrylamide gel electrophoresis and its molecular weight was estimated to be 42,000 on comparison with those of marker proteins. The three activities dependent on phosphatidylethanolamine, phosphatidyl-N monomethylethanolamine and phosphatidyl-N Af-dimethylethanolamine of the purified enzyme showed similar pH profiles with an optimum of pH 8.5, and were enhanced in the same manner by Triton X-100 and l-cysteine. The maximal velocities of the three reactions for S-adenosyl-l-methionine were 0.04, 1.36 and 0.69 nmol/mg protein/min with apparent Michaelis constant values of 3.6, 1.9 and 3.9 fiM, respectively, indicating that the first-step methylation is rate-limiting for the pathway in the organism.     

The Influence of Measurement Parameters on the Specific Rotation of Amino Acids

The effects of solute and hydrochloric acid concentrations on optical rotation were studied using 20 naturally occuring amino acids.

There appeared to be no common factor among the amino acids as far as the inclination of optical rotation was concerned. Lutz-Jirgenson’s rule could be applied to few amino acids in the cationic form. Therefore, in the determination of the optical rotation, the concentration of the solute, nature of solvent and temperature must be rigorously controlled. The optical conditions of measurement and the specific rotation of 20 amino acids were recommended based on this work.     

Identification of human plasma C1 inhibitor as a target protein for staphylococcal superantigen-like protein 5 (SSL5)

The family of staphylococcal superantigen-like proteins (SSLs) have a structure similar to bacterial superantigens but exhibit no superantigenic activity. These exoproteins have recently been shown to disturb the host immune defense system. One family member, SSL5, was reported to bind to human leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) and matrix metalloproteinase-9 (MMP-9) and to interfere with leukocyte trafficking. In the present study, we explored human plasma proteins bound by glutathione S-transferase (GST)-tagged recombinant SSL5 (GST-SSL5) and identified plasma protease C1 inhibitor (C1Inh) as a major SSL5-binding protein based on the results of peptide mass fingerprinting analysis with MALDI-TOFMS. GST-SSL5 was found to attenuate the inhibitory activity of recombinant histidine-tagged C1Inh (C1Inh-His) toward complement C1s. We also observed that the treatment of C1Inh-His with neuraminidase markedly decreased its binding to GST-SSL5. Moreover, C1Inh-His produced by Lec2 mutant cells (deficient in sialic acid biosynthesis) showed much lower binding affinity for SSL5 than that produced by the wild-type CHO-K1 cells, as assessed by pull-down assay. These results suggest that SSL5 binds to C1Inh in a sialic acid-dependent fashion and modulates the host immune defense through perturbation of the complement system in association with S. aureus infection.     

Primary Production and Effects of Enrichment with Nitrate and Phosphate on Phytoplankton in the Barra Bonita Reservoir (State of São Paulo,Brazil)

Primary productivity of the phytoplankton was evaluated by the ¹⁴C and dissolved oxygen methods in December 1981 at the Barra Bonita Reservoir (São Paulo State, Brazil). The primary production varied between 0.17 to 14.51 mg C m⁻³h⁻¹ at 4 and 0 m depth, respectively. About 57 to 94% of the photosynthetic activity was due to phytoplankton > 50 μm. The highest value of assimilation rate (3.36 mg C mg Chl⁻¹h⁻¹) was found in the surface water. Dissolved nutrient concentrations were very high and consisted mainly of nitrate. Light penetration was low, the aphotic zone accounting for about 90% of the water column. Enrichment with nitrate and phosphate showed that both N and P stimulated the production of biomass (chlorophyll a), mainly due to the addition of phosphate. The enrichment experiment also indicated that phosphate addition has a significant stimulatory effect on the growth of Melosira sp. The limiting effect of light penetration on photosynthetic activity is more severe than that of nutrients.     

Feedback inhibition of amidophosphoribosyltransferase regulates the rate of cell growth via purine nucleotide, DNA, and protein syntheses

To clarify the contributions of amidophosphoribosyltransferase (ATase) and its feedback regulation to the rates of purine de novo synthesis, DNA synthesis, protein synthesis, and cell growth, mutated human ATase (mhATase) resistant to feedback inhibition by purine ribonucleotides was engineered by site-directed mutagenesis and expressed in CHO ade (-)A cells (an ATase-deficient cell line of Chinese hamster ovary fibroblasts) and in transgenic mice (mhATase-Tg mice). In Chinese hamster ovary transfectants with mhATase, the following parameters were examined: ATase activity and its subunit structure, the metabolic rates of de novo and salvage pathways, DNA and protein synthesis rates, and the rate of cell growth. In mhATase-Tg mice, ATase activity in the liver and spleen, the metabolic rate of the de novo pathway in the liver, serum uric acid concentration, urinary excretion of purine derivatives, and T lymphocyte proliferation by phytohemagglutinin were examined. We concluded the following. 1) ATase and its feedback inhibition regulate not only the rate of purine de novo synthesis but also DNA and protein synthesis rates and the rate of cell growth in cultured fibroblasts. 2) Suppression of the de novo pathway by the salvage pathway is mainly due to the feedback inhibition of ATase by purine ribonucleotides produced via the salvage pathway, whereas the suppression of the salvage pathway by the de novo pathway is due to consumption of 5-phosphoribosyl 1-pyrophosphate by the de novo pathway. 3) The feedback inhibition of ATase is more important for the regulation of the de novo pathway than that of 5-phosphoribosyl 1-pyrophosphate synthetase. 4) ATase superactivity leads to hyperuricemia and an increased bromodeoxyuridine incorporation in T lymphocytes stimulated by phytohemagglutinin.     

Inhibition of insulin-induced activation of Akt by a kinase-deficient mutant of the epsilon isozyme of protein kinase C

Akt, also known as protein kinase B, is a protein-serine/threonine kinase that is activated by growth factors in a phosphoinositide (PI) 3-kinase-dependent manner. Although Akt mediates a variety of biological activities, the mechanisms by which its activity is regulated remain unclear. The potential role of the epsilon isozyme of protein kinase C (PKC) in the activation of Akt induced by insulin has now been examined. Expression of a kinase-deficient mutant of PKCepsilon (epsilonKD), but not that of wild-type PKCepsilon or of kinase-deficient mutants of PKCalpha or PKClambda, with the use of adenovirus-mediated gene transfer inhibited the phosphorylation and activation of Akt induced by insulin in Chinese hamster ovary cells or L6 myotubes. Whereas the epsilonKD mutant did not affect insulin stimulation of PI 3-kinase activity, the phosphorylation and activation of Akt induced by a constitutively active mutant of PI 3-kinase were inhibited by epsilonKD, suggesting that epsilonKD affects insulin signaling downstream of PI 3-kinase. PDK1 (3'-phosphoinositide-dependent kinase 1) is thought to participate in Akt activation. Overexpression of PDK1 with the use of an adenovirus vector induced the phosphorylation and activation of Akt; epsilonKD inhibited, whereas wild-type PKCepsilon had no effect on, these actions of PDK1. These results suggest that epsilonKD inhibits the insulin-induced phosphorylation and activation of Akt by interfering with the ability of PDK1 to phosphorylate Akt.