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N E Abramova

Publications and source records attributed to N E Abramova.

10 recordsLinked to original sources
PubMed2001

Induction and repression of DAN1 and the family of anaerobic mannoprotein genes in Saccharomyces cerevisiae occurs through a complex array of regulatory sites.

The DAN/TIR mannoprotein genes of Saccharomyces cerevisiae (DAN1, DAN2, DAN3, DAN4, TIR1, TIR2, TIR3 and TIR4) are expressed in anaerobic cells while the predominant cell wall proteins Cwp1 and Cwp2 are down-regulated. Elements involved in activation and repression of the DAN/TIR genes were defined in this study, using the DAN1 promoter as a model. Nested deletions in a DAN1/lacZ reporter pinpointed regions carrying activation and repression elements. Inspection revealed two consensus sequences subsequently shown to be independent anaerobic response elements (AR1, consensus TCGTTYAG; AR2, consensus AAAAATTGTTGA). AR1 is found in all of the DAN/TIR promoters; AR2 is found in DAN1, DAN2 and DAN3. A 120 bp segment carrying two copies of AR1 preferentially activated transcription of lacZ under anaerobic conditions. A fusion of three synthetic copies of AR1 to MEL1 was also expressed anaerobically. Mutations in either AR1 site within the 120 bp segment caused a drastic loss of expression, indicating that both are necessary for activation and implying cooperativity between adjacent transcriptional activation complexes. A single AR2 site carried on a 46 bp fragment from the DAN1 promoter activated lacZ transcription under anaerobic conditions, as did a 26 bp synthetic AR2 fragment fused to MEL1. Nucleotide substitutions within the AR2 sequence eliminated the activity of the 46 bp segment. Ablation of the AR2 sequences in the full promoter caused a partial reduction of expression. The presence of the ATTGTT core (recognized by HMG proteins) in the AR2 sequence suggests that an HMG protein may activate through AR2. One region was implicated in aerobic repression of DAN1. It contains sites for the heme-induced Mot3 and Rox1 repressors.

Aerobiosis↗
PubMed2001

Regulatory mechanisms controlling expression of the DAN/TIR mannoprotein genes during anaerobic remodeling of the cell wall in Saccharomyces cerevisiae.

The DAN/TIR genes of Saccharomyces cerevisiae encode homologous mannoproteins, some of which are essential for anaerobic growth. Expression of these genes is induced during anaerobiosis and in some cases during cold shock. We show that several heme-responsive mechanisms combine to regulate DAN/TIR gene expression. The first mechanism employs two repression factors, Mox1 and Mox2, and an activation factor, Mox4 (for mannoprotein regulation by oxygen). The genes encoding these proteins were identified by selecting for recessive mutants with altered regulation of a dan1::ura3 fusion. MOX4 is identical to UPC2, encoding a binucleate zinc cluster protein controlling expression of an anaerobic sterol transport system. Mox4/Upc2 is required for expression of all the DAN/TIR genes. It appears to act through a consensus sequence termed the AR1 site, as does Mox2. The noninducible mox4Delta allele was epistatic to the constitutive mox1 and mox2 mutations, suggesting that Mox1 and Mox2 modulate activation by Mox4 in a heme-dependent fashion. Mutations in a putative repression domain in Mox4 caused constitutive expression of the DAN/TIR genes, indicating a role for this domain in heme repression. MOX4 expression is induced both in anaerobic and cold-shocked cells, so heme may also regulate DAN/TIR expression through inhibition of expression of MOX4. Indeed, ectopic expression of MOX4 in aerobic cells resulted in partially constitutive expression of DAN1. Heme also regulates expression of some of the DAN/TIR genes through the Rox7 repressor, which also controls expression of the hypoxic gene ANB1. In addition Rox1, another heme-responsive repressor, and the global repressors Tup1 and Ssn6 are also required for full aerobic repression of these genes.

Alleles↗
PubMed2000

Polynucleotide degradation during early stage response to oxidative stress is specific to mitochondria.

Oxidative stress is known to modulate RNA expression in both prokaryotic and eukaryotic cells. We have previously determined that a preferential and calcium-dependent downregulation of mitochondrial RNA occurs in HA-1 hamster fibroblasts in response to hydrogen peroxide, and that this is accompanied by the degradation of mitochondrial genomic DNA. Here we extended these studies to determine whether downregulation is specific to transcripts derived from mitochondrial-encoded genes; to determine whether genomic DNA degradation occurs in the nucleus; and to compare overall polynucleotide stress response with cellular growth arrest and apoptosis. We observed that nuclear genome-encoded mRNAs whose protein products are targeted for the electron transport chain of mitochondria were not degraded. Furthermore, early stage degradation of genomic DNA, assessed within the first 5 h of peroxide exposure, was specific to mitochondria, as nuclear genomic DNA was not degraded under the same treatment conditions. These differential degradations occurred under conditions where extensive growth-arrest and moderate apoptosis were observed, and were accompanied by significant induction of the growth arrest mRNAs gadd45, gadd153, and adapt15/gadd7. Combined, these results indicate that there is a general degradation of mitochondrial- but not nuclear-polynucleotides during early stage response of HA-1 fibroblasts to oxidative stress.

Animals↗
PubMed1998

Oxidative stress causes a general, calcium-dependent degradation of mitochondrial polynucleotides.

Oxidative stress has many effects on biological cells, including the modulation of gene expression. Reactive oxygen species are known to up-regulate and down-regulate RNA expression in prokaryotic and eukaryotic cells. We have previously reported that a preferential and calcium-dependent down-regulation of mitochondrial RNAs occurs when HA-1 hamster fibroblasts are exposed to hydrogen peroxide. Here we extend these studies to determine whether this down-regulation is specific to mitochondria RNA or involves general polynucleotide degradation. Degradation and associated decreases in the levels of 16S mitochondrial rRNA following exposure of cells to 400 microM hydrogen peroxide were found to be dependent on calcium at 2 and 5 h. Degradation of mitochondrial genomic DNA was also observed following peroxide exposure, and occurred at similar time points as for mitochondrial RNA degradation. As with mitochondrial RNA degradation, this mitochondrial genomic DNA degradation was dependent on calcium. These results indicate that there is a general, calcium-dependent degradation of mitochondrial polynucleotides following exposure of HA-1 fibroblasts to oxidative stress, and suggest that a dramatic shut-down in mitochondrial biosynthesis is an early-stage response to oxidative stress.

Animals↗
PubMed1995

Different antioxidant activities of bioflavonoid rutin in normal and iron-overloading rats.

The effects of rutin on liver microsomes, peritoneal macrophages, and blood neutrophils isolated from iron-overloading (IOL) and normal rats were studied. The formation of 2-thiobarbituric acid-reactive products and the level of lucigenin-amplified chemiluminescence (CL) were determined in liver microsomes. Oxygen radical production by phagocytes was measured by luminol- and lucigenin-amplified CL and superoxide dismutase-sensitive cytochrome c reduction. These ex vivo findings were compared with the in vitro effects of rutin on cellular free processes. It was found that rutin administration sharply suppressed free radical production in liver microsomes and by phagocytes of IOL animals and only slightly affected these processes in normal rats. The selective inhibitory effect of rutin under pathologic conditions induced by iron overload is thought to be due to the formation of inactive iron-rutin complexes which are unable to catalyse the conversion of superoxide ion into reactive hydroxyl radicals, a process responsible for the free radical-mediated toxic effects of iron overload. These findings may account for the favourable effects of the treatment of pathologies associated with iron overload with rutin.

Acridines↗
PubMed1995

Study of antioxidant properties of metal aspartates.

The effects of Zn, Mg, Cr, Cu, and Mn aspartates, their commercial formulation Inzolen, and the individual commercial medicine Unizinc, on oxygen radical production by enzymes [xanthine oxidase, horseradish peroxidase, and reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase] and phagocytic cells (human blood leukocytes) have been studied. The formation of oxygen radicals was measured by luminol- and lucigenin-amplified chemiluminescence and by the reduction of cytochrome c. All these compounds (excluding Cr aspartate) turn out to be inhibitors of oxygen radical formation in the systems studied (excluding horseradish peroxidase). Their inhibitory activities were a consequence of both the scavenging of free radicals and the inhibition of xanthine oxidase and NADPH oxidase activities. As expected, the most active free-radical scavengers were transition metal Cu and Mn aspartates, which mimicked the activities of copper-zinc and manganese dismutases. However, surprisingly non-transition metal Zn and Mg aspartates were also able to scavenge oxygen radicals. It was suggested that the scavenging activities of Zn and Mg aspartates may be explained by affecting the rate of spontaneous dismutation of the superoxide ion. In addition, it was found that Zn aspartate is an efficient inhibitor of the formation of the most reactive hydroxyl radicals. These antioxidant properties of Zn aspartate make it important in medicine for the prevention and treatment of free radical pathologies.

Antioxidants↗