The Italian journal of biochemistry最新文献

The genetic variability of H. sapiens mitochondrial DNA (mtDNA) can be either germ-line inherited or somatically acquired, and its effect on aging and longevity as well as on the pathogenesis of complex age-related diseases is a hot topic. Here we illustrate the complexity of such studies, related to the large genetic variability of mtDNA in different populations and the fact that the rate of the aging process is different in different cells, tissues and organs. As far as concern Alzheimer's disease, the accumulation of somatic mutations in several tissues have been investigated, as well as the inherited mtDNA variability. However, the issue is still controversial and further studies are needed to clarify the role of mtDNA variants in Alzheimer's disease. This review is aimed to summarize the most recent advances in this field. By high throughput mtDNA sequencing and the study of large cohorts of ethnically homogeneous subjects/patients, it is now possible to perform high dimensionality studies in order to clarify the genetic associations among several inherited mtDNA variants and longevity or age-associated diseases in humans.

Cytochrome bd is a quinol respiratory oxidase widely distributed among bacteria, where its expression favours survival under low O2 tensions, and in the presence of nitric oxide (NO) produced by the host immune system. NO reacts with and reversibly inhibits the haem-copper terminal oxidases (HCO) where it binds at the active site, containing a haem-iron and a copper (CuB). NO reacts also similarly with the copper-lacking active site of cytochrome bd, a structural peculiarity that allows one to address the question of whether CuB plays a role in the reaction with NO (and other ligands). In this minireview we discuss the properties of the reactions between bd-type oxidases and NO, and highlight consequences to cell/bacteria physiology.

In this research we aimed to investigate the interactions between growth factors (GFs) and dexamethasone (DEX) on cytoskeletal proteins GFAP and vimentin (VIM) expression under the following experimental condition: 24h pretreatment with bFGF, subsequent 72h switching in serum-free medium (SFM) and final addition of GFs, only one or more in the last 24h, after a prolonged (60h) DEX treatment. Western blot analysis data showed a marked GFAP expression in cultures submitted to our experimental condition comparing results to untreated or treated controls. In particular, the maximum level of GFAP expression is observed when EGF or INS or both together are added in a prolonged 60h DEX treatment. This finding well correlates with differentiative role played by glucocorticoids interacting with the "competence" factor bFGF and demonstrates as increased GFAP expression mostly depends on maturation, rather than proliferating status of astroglial cells in culture. VIM expression was instead significantly reduced after GFs addition in the last 24h of 60h DEX treatment, respect to control DEX-pretreated ones. Comparing the data to untreated controls, VIM expression was significantly enhanced after GFs addition. Collectively, our findings evidence an interactive effect between GFs and DEX in astroglial cultures, co-pretreated with DEX and bFGF, regulating cytoskeletal network under stressfull conditions.

The effect of peroxidized cardiolipin on the mitochondrial pore transition (MPT) induction and cytochrome c release in rat heart mitochondria was studied. Treatment of mitochondria with cardiolipin hydroperoxide (CLOOH) promoted matrix swelling and release of cytochrome c. Both these processes were inhibited by cyclosporine A and bongkrekic acid, indicating that peroxidized cardiolipin behaves as an inducer of MPT. Ca2+ accumulation was required for this effect. ANT (ADP/ATP carrier) is involved in the CLOOH-dependent MPT induction as suggested by the modulation by ligands and inhibitors of ANT. These results indicate that CLOOH lowers the threshold of Ca2+ for MPT induction. This synergistic effect of Ca2+ and CLOOH on MPT induction and cytochrome c release in mitochondria might have important implications in the apoptotic process as well as in several pathophysiological situations.

We described here the construction of two novel Saccharomyces cerevisiae strains in which the regulatory region of the SDH1 gene, coding for the succinate dehydrogenase flavoprotein subunit, was fused in frame to the reporter gene lacZ of E. coli, coding for beta-galactosidase. By this approach, SDH1 expression was studied in the yeast strain, flx1 delta-lacZ, lacking of a functional mitochondrial FAD translocator, Flx1p. The experiments described here are in line with the hypotesys that a correlation exists between defects in flavin cofactor homeostasis and mitochondrial apo-flavoprotein expression.

It is now widely accepted that F0F1ATPsynthase is present in membrane, beside as monomers, in homo-dimeric and higher homo-oligomeric forms, which probably play critical roles in determining mitochondrial morphology. One-step mild detergent extraction followed by blue native electrophoresis (BN-PAGE) is a very interesting tool for studying the native membrane protein assemblies which can be associated with second/third-dimensional SDS-PAGE, immunoblotting, in-gel enzyme activity staining and mass spectrometry analyses. By combining these techniques, we resolved monomers and higher oligomeric forms of ATPsynthase from bovine heart mitochondria. However, a critical point is the choice of the detergents, which strongly influence the protein pattern of BN-PAGE. By using Triton X-100 we obtained that, in spite of the same subunit composition, monomers have a much lower specific activity than dimers and the two forms have a different pattern of tyrosine phosphorylation, suggesting that monomers and dimers are functionally distinct in membrane. In addition, enzyme self-association appeared to occur independently from the binding to ATPsynthase of the inhibitor protein IF1. Dodecylmaltoside was optimal to extract the enzyme from single biopsy samples, allowing us to demonstrate that IF1 plays a central role in regulating the enzyme activity in heart in vivo. Only low concentration of digitonin maintained significant amounts of ATPsynthase oligomers, which seemed to retain intact their native catalytic properties.

In order to gain some insight into metabolism of mitochondria isolated from materials subjected to storage treatments, we compared mitochondria isolated from potato tubers grown and stored in the post-harvest without any chemicals (N-PTM), and tubers, from local market, treated for commercial purpose (T-PTM) with respect to the L-lactate metabolism. Although no oxygen consumption due to L-lactate was found in T-PTM, L-lactate dehydrogenase existence was shown as immunologically investigated. Consistently, no L-lactate dehydrogenase activity was detected. Contrarily, N-PTM proved to metabolize externally added L-lactate, with oxygen consumption and intramitochondrial pyridine nucleotide reduction. All together these findings show that commercial treatments of foodstuffs could result in changes in their metabolism.

DNA topoisomerase I constitutes a significant relaxing activity in nuclei of eukaryotic cells. The enzyme acts during several DNA transactions involving the generation of torsional stress in the DNA template. Moreover, antitumor agents targeting DNA topoisomerase I are used in the treatment of human cancers with significant clinical outcome. Major progress has been attained in recent years in the understanding of the basic cellular functions of DNA topoisomerase I. In particular, the consequences of topoisomerase I activity during transcription have been extensively investigated and constitute still a very active research area. Understanding of topoisomerase I inhibitors emphasizes drug activity against the enzyme, however the high drug potency cannot be explained by the DNA damage outcome only. Even though the understanding of enzyme structure has progressed in last years, however more insights into the activity of topoisomerase I poisons have not been achieved yet. Here, we will review landmark investigations on topoisomerase I involvement in different stages of the transcription process, addressing both enzyme functions as well as drug effects on molecular processes. Moreover, we will discuss recent findings on the targeting of topoisomerase I to pre-selected sites in transcribed chromatin by fusion to a sequence-specific DNA-binding protein domain.

The rDNA cluster is the genetic locus encoding the ribosomal RNAs and physically defines where ribosomes begin to be assembled. In the yeast Saccharomyces cerevisiae, the highly repetitive structure of this locus makes it a very interesting target for studies about genome stability, chromatin-mediated transcriptional silencing and progression of aging. In fact, recombination among the repeated units is suppressed in a WT cell. Moreover, when genes transcribed by RNA polymerase II are inserted in the rDNA cluster, their transcription is silenced. Finally, the formation of rDNA minicircles (ERCs) has been shown to be one of the causes of aging in yeast. DNA topoisomerase I have been shown to suppress recombination specifically at the rDNA of S.cerevisiae. Moreover, also the chromatin structure of this locus is affected in a top1 strain, because rDNA specific transcriptional silencing is abolished. Nonetheless, the molecular basis of how this enzyme interferes with these functions is yet unknown. Here are reported results obtained by in vivo studies of DNA protein interactions occurring on the rDNA locus. The analyses include a fine mapping of nucleosome positioning; RNA polymerase I transcription factors and DNA topoisomerase I cleavage sites. Important conclusions can be drawn: i) nucleosome positioning in the Non Transcribed Spacer is not affected by RNA polymerase I transcription; ii) the RNA polymerase I transcription factors bind DNA in vivo with a defined hierarchy; iii) the DNA topoisomerase I cleaves the NTS in very specific sites, but cleavage is not induced by RNA polymerase I transcription. These in vivo studies help to characterize the molecular basis of important phenomena as the transcriptional silencing and genome stability in yeast.