Akt Activation Emulates Chk1 Inhibition and Bcl2 Overexpression and Abrogates G2 Cell Cycle Checkpoint by Inhibiting BRCA1 Foci

Akt is perhaps the most frequently activated oncoprotein in human cancers. Overriding cell cycle checkpoint in combination with the inhibition of apoptosis are two principal requirements for predisposition to cancer. Here we show that the activation of Akt is sufficient to promote these two principal processes, by inhibiting Chk1 activation with concomitant inhibition of apoptosis. These activities of Akt cannot be recapitulated by the knockdown of Chk1 alone or by overexpression of Bcl2. Rather the combination of Chk1 knockdown and Bcl2 overexpression is required to recapitulate Akt activities. Akt was shown to directly phosphorylate Chk1. However, we found that Chk1 mutants in the Akt phosphorylation sites behave like wild-type Chk1 in mediating G2 arrest, suggesting that the phosphorylation of Chk1 by Akt is either dispensable for Chk1 activity or insufficient by itself to exert an effect on Chk1 activity. Here we report a new mechanism by which Akt affects G2 cell cycle arrest. We show that Akt inhibits BRCA1 function that induces G2 cell cycle arrest. Akt prevents the translocation of BRCA1 to DNA damage foci and, thereby, inhibiting the activation of Chk1 following DNA damage.     

Somatostatin-detergent interaction

The effect of cationic, anionic and nonionic detergents on the EPR spectrum of spin-labeled somatostatin has been studied. At detergent concentrations well above the critical micelle concentration, nonionic detergents do not alter the EPR spectrum. Sodium dodecyl sulfate markedly alters both the line height ratio and the hyperfine splitting constant, whilst dodecyltrimethylammonium bromide alters only slightly the hyperfine splitting constant and line height ratio. The somatostatin-sodium dodecyl sulfate complex appeared monodisperse by sedimentation equilibrium with about 17 g bound detergent per g peptide. Circular dichroic and difference spectra of the dodecyl sulfate-somatostatin complex show that the tryptophanyl residue is buried in a nonpolar environment and that the secondary and tertiary structure of the peptide is markedly altered. Sedimentation equilibrium studies suggest that two types of dodecyltrimethylammonium-somatostatin complex exist. One type resembles the dodecyl sulfate-peptide complex, whilst the other appears to include several peptide units with only about one gram bound detergent per gram peptide.     

Lower Neighborhood Socioeconomic Status Associated with Reduced Diversity of the Colonic Microbiota in Healthy Adults

In the United States, there are persistent and widening socioeconomic gaps in morbidity and mortality from chronic diseases. Although most disparities research focuses on person-level socioeconomic-status, mounting evidence suggest that chronic diseases also pattern by the demographic characteristics of neighborhoods. Yet the biological mechanisms underlying these associations are poorly understood. There is increasing recognition that chronic diseases share common pathogenic features, some of which involve alterations in the composition, diversity, and functioning of the gut microbiota. This study examined whether socioeconomic-status was associated with alpha-diversity of the colonic microbiota. Forty-four healthy adults underwent un-prepped sigmoidoscopy, during which mucosal biopsies and fecal samples were collected. Subjects’ zip codes were geocoded, and census data was used to form a composite indicator of neighborhood socioeconomic-status, reflecting household income, educational attainment, employment status, and home value. In unadjusted analyses, neighborhood socioeconomic-status explained 12–18 percent of the variability in alpha-diversity of colonic microbiota. The direction of these associations was positive, meaning that as neighborhood socioeconomic-status increased, so did alpha-diversity of both the colonic sigmoid mucosa and fecal microbiota. The strength of these associations persisted when models were expanded to include covariates reflecting potential demographic (age, gender, race/ethnicity) and lifestyle (adiposity, alcohol use, smoking) confounds. In these models neighborhood socioeconomic-status continued to explain 11–22 percent of the variability in diversity indicators. Further analyses suggested these patterns reflected socioeconomic variations in evenness, but not richness, of microbial communities residing in the sigmoid. We also found indications that residence in neighborhoods of higher socioeconomic-status was associated with a greater abundance of Bacteroides and a lower abundance of Prevotella, suggesting that diet potentially underlies differences in microbiota composition. These findings suggest the presence of socioeconomic variations in colonic microbiota diversity. Future research should explore whether these variations contribute to disparities in chronic disease outcomes.     

Understanding Performance Degradation in Cation‐Disordered Rock‐Salt Oxide Cathodes

The collective redox activities of transition‐metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li‐rich layered and cation‐disordered rock‐salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li‐ and Mn‐rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li‐rich rock‐salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li_1.3Nb_0.3Mn_0.4O₂ cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation‐disordered rock‐salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed.     

Simple and selective high-performance liquid chromatographic method for estimating plasma quinidine levels

A reversed-phase, high-performance liquid chromatographic method employing fluorescence detection is described for the rapid quantification of plasma levels of quinidine, dihydroquinidine and 3-hydroxyquinidine. It involves protein precipitation with acetonitrile followed by direct injection of the supernatant into the chromatograph. For the preparation of plasma standards, pure 3-hydroxyquinidine was isolated from human urine by a simplified thin-layer chromatographic procedure. The mobile phase for the chromatography was a mixture of 1.5 mM aqueous phosphoric acid and acetonitrile (90:10) at a flow-rate of 2 ml/min. The intra-assay coefficient of variation for the assay of quinidine and 3-hydroxyquinidine over the concentration range 2.5–20 μmole/l was < 1% for both. Interassay coefficients of variation for quinidine (10 μmole/l) and 3-hydroxyquinidine (5 μmole/l) were 3.5% and 4.0% with detection limits of 50 and 25 μmole/l respectively. The method correlated well (r² = 0.96) with an independently developed gas—liquid chromatographic—nitrogen detection assay for quinidine which also possessed a high degree of precision. (Intra-assay coefficient of variation 3.6% at 20 μmole/l). As expected, comparison of the high-performance liquid chromatographic assay with a published protein precipitation—fluorescence assay showed poor correlation (r² = 0.78).