Human APOBEC3G exhibits anti-human immunodeficiency virus-1 (HIV-1) activity by deaminating cytidines of the minus strand of HIV-1. Here, we report a solution structure of the C-terminal deaminase domain of wild-type APOBEC3G. The interaction with DNA was examined. Many differences in the interaction were found between the wild type and recently studied mutant APOBEC3Gs. The position of the substrate cytidine, together with that of a DNA chain, in the complex, was deduced. Interestingly, the deamination reaction of APOBEC3G was successfully monitored using NMR signals in real time. Real-time monitoring has revealed that the third cytidine of the d(CCCA) segment is deaminated at an early stage and that then the second one is deaminated at a late stage, the first one not being deaminated at all. This indicates that the deamination is carried out in a strict 3 0 -5 0 order. Virus infectivity factor (Vif) of HIV-1 counteracts the anti-HIV-1 activity of APOBEC3G. The structure of the N-terminal domain of APOBEC3G, with which Vif interacts, was constructed with homology modelling. The structure implies the mechanism of species-specific sensitivity of APOBEC3G to Vif action.

It has been reported that p53 acetylation, which promotes cellular senescence, can be regulated by the NAD⁺-dependent deacetylase SIRT1, the human homolog of yeast Sir2, a protein that modulates lifespan. To clarify the role of SIRT1 in cellular senescence induced by oxidative stress, we treated normal human diploid fibroblast TIG-3 cells with H₂O₂ and examined DNA cleavage, depletion of intracellular NAD⁺, expression of p21, SIRT1, and acetylated p53, cell cycle arrest, and senescence-associated β-galactosidase (SA-β-gal) activity. DNA cleavage was observed immediately in TIG-3 cells treated with H₂O₂, though no cell death was observed. NAD⁺ levels in TIG-3 cells treated with H₂O₂ were also decreased significantly. Pre-incubation with the poly (ADP-ribose) polymerase (PARP) inhibitor resulted in preservation of intracellular NAD⁺ levels. The amount of acetylated p53 was increased in TIG-3 cells at 4h after H₂O₂ treatment, while there was little to no decrease in SIRT1 protein expression. The expression level of p21 was increased at 12h and continued to increase for up to 24h. Additionally, exposure of TIG-3 cells to H₂O₂ induced cell cycle arrest at 24h and increased SA-β-gal activity at 48h. This pathway likely plays an important role in the acceleration of cellular senescence by oxidative stress.

Clinical evidence has implicated diabetes mellitus as one of the risk factors for the development and progression of Alzheimer’s disease (AD). However, the neurotoxic pathway activated due to abnormalities in glucose metabolism has not yet been identified in AD. In order to investigate the relationship between impaired cerebral glucose metabolism and the pathophysiology of AD, SH-SY5Y human neuroblastoma cells were exposed to glyceraldehyde (GA), an inhibitor of glycolysis. GA induced the production of GA-derived advanced glycation end-products (GA-AGEs) and cell apoptosis, glycolytic inhibition, decreases in the medium concentrations of diagnostic markers of AD, such as amyloid β 1-42 (Aβ42), and increases in tau phosphorylation. These results suggest that the production of GA-AGEs and/or inhibition of glycolysis induce AD-like alterations, and this model may be useful for examining the pathophysiology of AD.

Dynamic changes in CCAN organization during progression of the cell cycle are examined in chicken DT40 cells. CENP-C166-324 is sufficient for interphase centromere localization through association with CENP-L-N, and CENP-C643-864 is essential for mitotic centromere localization through binding to CENP-A nucleosomes.