No abstract available

[en] Protein lysine methyltransferases (PKMTs) catalyze the methylation of lysine residues on many different cellular proteins. Despite extensive biochemical and structural studies, focusing on PKMT active site-peptide interactions, little is known regarding how PKMTs recognize globular substrates. To examine whether these enzymes recognize protein substrates through interactions that take place outside of the active site, we have measured SETD6 and SETD7 activity with both protein and peptide RelA substrate. We have utilized the MTase-Glo™ methyltransferase assay to measure the activity of SETD6 and SETD7 with the different RelA substrates and calculated the Michaelis-Menten (MM) parameters. We found an up to ∼12-fold increase in K_M of the PKMTs activity with RelA peptide relative to the respective full-length protein, emphasizing the significantly higher PKMT-protein interaction affinity. Examination of SETD6 and SETD7 activity toward the same RelA substrates highlight the similarity in substrate recognition for both PKMTs. Our results show that the interaction affinity of SETD6 and SETD7 with RelA is enhanced through interactions that occur outside of the active site leading to higher catalytic efficiency and specificity. These interactions can significantly vary depending on the PKMT and the specific methylation site on RelA. Overall, our results underline that PKMTs can recognize their substrates through docking interactions that occur out of the active site-peptide region for enhancing their activity and specificity in the cellular environment.

[en] 0pto-acoustic techniques have been used to measure vibrational energy relaxation in metyl halides and their mixtures with inert gases. Under certain conditions time-resolved measurements give direct evidence of a V-R-T relaxation channel parallel to he V-T relaxation channel. Comparison with infrared fluorescence data confirms this conclusion. (orig.)

[en] Background: The current proposed model of colorectal tumorigenesis is based primarily on CpG island methylator phenotype (CIMP), microsatellite instability (MSI), KRAS, BRAF, and methylation status of 0-6-Methylguanine DNA Methyltransferase (MGMT) and classifies tumors into five subgroups. The aim of this study is to validate this molecular classification and test its prognostic relevance. Methods: Three hundred two patients were included in this study. Molecular analysis was performed for five CIMP-related promoters (CRABP1, MLH1, p16INK4a, CACNA1G, NEUROG1), MGMT, MSI, KRAS, and BRAF. Methylation in at least 4 promoters or in one to three promoters was considered CIMP-high and CIMP-low (CIMP-H/L), respectively. Results: CIMP-H, CIMP-L, and CIMP-negative were found in 7.1, 43, and 49.9% cases, respectively. One hundred twenty-three tumors (41%) could not be classified into any one of the proposed molecular subgroups, including 107 CIMP-L, 14 CIMP-H, and two CIMP-negative cases. The 10 year survival rate for CIMP-high patients [22.6% (95%CI: 7–43)] was significantly lower than for CIMP-L or CIMP-negative (p = 0.0295). Only the combined analysis of BRAF and CIMP (negative versus L/H) led to distinct prognostic subgroups. Conclusion: Although CIMP status has an effect on outcome, our results underline the need for standardized definitions of low- and high-level CIMP, which clearly hinders an effective prognostic and molecular classification of colorectal cancer.

[en] Motivated by the previous observation [Kato et al., J. Chem. Phys. 132, 074309 (2010)] that the structure seen in the elastic electron scattering cross sections from CH₃X (X = F, Cl, Br, and I) molecules at intermediate energies (50 - 200 eV) is also found, at least in part, in the corresponding noble gas species, we measured differential cross sections for the elastic scattering of electrons from CH₃Cl at the low incident electron energies of 5, 10, and 20 eV for scattering angles from 20 .deg. up to 180 .deg. . We confirmed that, as we went to lower electron energies, the 'atomic-like' behavior faded out, and the 'molecular-like' behavior became increasingly prominent.

[en] CH₃F, CH₃Cl, CH₃Br were seeded into Ar van der Waals clusters by means of a pulsed supersonic molecular beam. Ions formed by electron impact were observed by time-of-flight mass spectroscopy. Enhancement of the CH₂X⁺ signal relative to the CH₃X⁺ was noted. By changing the seed concentration it was shown that this was due to Ar rather than the (CH₃X)₂ dimer. These results are energetically compatible with a Penning energy transfer from Ar. Protonation of the CH₃X ions was observed related to the number of clusters containing more than one seed molecule. A difference in CH₄Cl⁺and CH₄Br⁺ production was noted. This is interesting considering the similarity of the gas-phase proton affinity of the CH₃Cl and CH₃Br

[en] Chronic low dose inorganic arsenic exposure causes cells to take on an epithelial-to-mesenchymal phenotype, which is a crucial process in carcinogenesis. Inorganic arsenic is not a mutagen and thus epigenetic alterations have been implicated in this process. Indeed, during the epithelial-to-mesenchymal transition, morphologic changes to cells correlate with changes in chromatin structure and gene expression, ultimately driving this process. However, studies on the effects of inorganic arsenic exposure/withdrawal on the epithelial-to-mesenchymal transition and the impact of epigenetic alterations in this process are limited. In this study we used high-resolution microarray analysis to measure the changes in DNA methylation in cells undergoing inorganic arsenic-induced epithelial-to-mesenchymal transition, and on the reversal of this process, after removal of the inorganic arsenic exposure. We found that cells exposed to chronic, low-dose inorganic arsenic exposure showed 30,530 sites were differentially methylated, and with inorganic arsenic withdrawal several differential methylated sites were reversed, albeit not completely. Furthermore, these changes in DNA methylation mainly correlated with changes in gene expression at most sites tested but not at all. This study suggests that DNA methylation changes on gene expression are not clear-cut and provide a platform to begin to uncover the relationship between DNA methylation and gene expression, specifically within the context of inorganic arsenic treatment. - Highlights: • Transient and permanent methylation patterns are modulated by iAs exposure. • Arsenite contributes to the epithelial-to-mesenchymal transition. • Arsenite mediated epigenetic changes play a role in EMT.

[en] The normalized orthopositronium quenching rate, ₁Z_eff, has been measured for CH₃F, CH₃Cl, CH₃Br, and CH₃I in the gas phase. Silica aerogel was used as the positronium formation medium and the microchambers. The ₁Z_eff values obtained are ₁Z_eff(CH₃F)=0.46±0.03, ₁Z_eff(CH₃Cl)=0.58±0.05, ₁Z_eff(CH₃Br)=0.70±0.04, and ₁Z_eff(CH₃I)=2.1±0.2. The ₁Z_eff value for CH₃I is significantly larger than expected for pick-off quenching. It is probably caused by spin-conversion quenching through spin-orbit interaction.

[en] Differential cross sections (DCSs) for excitation of the C-H stretch vibrations for CH₃F, CH₃Cl, CH₃Br and CH₃I were measured by electron impact. Resonance enhancement was observed for the C-H stretch at 6.6, 5.9, 5.5 and 4.7 eV respectively. For CH₃F this is attributed to a ²A₁ shape resonance formed through temporary occupation of the LUMO and for the heavier halogens to a ²E shape resonance formed through temporary occupation of the LUMO+1. DCSs for excitation of the C-X stretch were also measured for CH₃F and CH₃Cl. The shift in the resonance energy is discussed in context to the substitution effect of the halogens.

[en] The structure of brain-derived neurotrophic factor (BDNF) gene is complex, which is composed of eight non-coding exons and one coding exon, each of them has its own unique promoter. Multiple BDNF transcripts have distinct functional properties and epigenetic modulation of BDNF gene transcription is implicated in the neurological disorders. In the present study, rat models with amyloid-β (Aβ) intrahippocampal injection and PC12 cells were used to explore the role of DNA methylation in the promoters of BDNF exon Ⅳ and exon Ⅵ in BDNF suppression caused by Aβ. We found that Aβ inhibited BDNF expression accompanying with hypermethylation in BDNF exon Ⅳ promoter, meanwhile, S-adenosylmethionine (SAM), primary methyl donor, reversed the low BDNF expression through demethylation in BDNF exon Ⅳ promoter. No methylation change was observed in BDNF exon Ⅵ promoter. The alteration of DNA methylation caused by Aβ or SAM was mediated by DNA methyltransferase 3A (DNMT3A). These data suggest that methylation change in BDNF exon Ⅳ is involved in the regulation of BDNF expression by Aβ or SAM, and further support the view of specific epigenetic modifications of a certain BDNF gene transcript.