Escherichia coli K1 polysialic acid O-acetyltransferase gene, neuO, and the mechanism of capsule form variation involving a mobile contingency locus

Potential O-acetylation of the sialic acid residues of Escherichia coli K1, groups W-135, Y, and C meningococci, and group B Streptococcus capsular polysaccharides modifies their immunogenicity and susceptibility to glycosidases. Despite the biological importance of O-acetylation, no sialic or polysialic acid O-acetyltransferase has been identified in any system. Here we show that the E. coli K1 O-acetyltransferase encoded by neuO is genetically linked to the endo-neuraminidase tail protein gene of a chromosomal accretion element, designated CUS-3, with homology to lambdoid bacteriophage. Molecular epidemiological analysis established concordance between O-acetyltransferase and CUS-3 in a set of E. coli K1 strains. Deleting neuO eliminated enzymatic activity, which was restored by complementation in trans, and confirmed by (13)C-NMR analysis of the acetylated product. Analysis of mutants that accumulate intracellular polysialic acid because of export defects (kpsM and kpsS) or an inability to synthesize the sialic acid precursor, N-acetylmannosamine (neuC), indicated that NeuO does not require constant association with its substrate for activity. DNA sequencing and PCR analysis of neuO from strains that had undergone random capsule form variation showed that slip strand DNA mispairing or unequal recombination resulted in gain or loss of (5'-AAGACTC-3')(n) heptanucleotide repeats (where n approximately equals 14-39) located in the neuO 5' region. These repeats code for a previously undescribed structure designated the poly(Psi) motif. The unexpected discovery of the neuO contingency locus (hypervariable gene controlling expression of a surface epitope) in E. coli, and of a potential phage for redistributing variant neuO alleles, provides a robust system for investigating the functions of localized hypermutability in pathogen evolution.     

Acetylated H4K16 by MYST1 protects UROtsa cells from arsenic toxicity and is decreased following chronic arsenic exposure

Arsenic, a human carcinogen that is associated with an increased risk of bladder cancer, is commonly found in drinking water. An important mechanism by which arsenic is thought to be carcinogenic is through the induction of epigenetic changes that lead to aberrant gene expression. Previously, we reported that the SAS2 gene is required for optimal growth of yeast in the presence of arsenite (As^III). Yeast Sas2p is orthologous to human MYST1, a histone 4 lysine 16 (H4K16) acetyltransferase. Here, we show that H4K16 acetylation is necessary for the resistance of yeast to As^III through the modulation of chromatin state. We further explored the role of MYST1 and H4K16 acetylation in arsenic toxicity and carcinogenesis in human bladder epithelial cells. The expression of MYST1 was knocked down in UROtsa cells, a model of bladder epithelium that has been used to study arsenic-induced carcinogenesis. Silencing of MYST1 reduced acetylation of H4K16 and induced sensitivity to As^III and to its more toxic metabolite monomethylarsonous acid (MMA^III) at doses relevant to high environmental human exposures. In addition, both As^III and MMA^III treatments decreased global H4K16 acetylation levels in a dose- and time-dependent manner. This indicates that acetylated H4K16 is required for resistance to arsenic and that a reduction in its levels as a consequence of arsenic exposure may contribute to toxicity in UROtsa cells. Based on these findings, we propose a novel role for the MYST1 gene in human sensitivity to arsenic.     

Polymorphic acetylation and aminopyrine demethylation in Gilbert's syndrome.

Polymorphic acetylation was investigated in twenty-seven patients with Gilbert's syndrome using the sulphadimidine test. Whereas the finding of 51% slow acetylators in seventy-eight control persons agreed well with the expected frequency in a continental European population, the prevalence of slow acetylators in Gilbert's syndrome was increased to 78% (P less than 0.03, Woolf's G-test). After oral administration of 14C-aminopyrine there was no significant difference between seventeen patients with Gilbert's syndrome and twenty-seven normal controls in total plasma clearance of aminopyrine (280 +/- SD 100 and 270 +/- 60 ml/min) and in the disappearance curve of 14CO2 in breath (0.23 +/- 0.04 and 0.22 +/- 0.03 h-1, respectively). Thus, whereas aminopyrine metabolism appears unaffected in the examined patients, the data documents a new association between slow acetylator status and Gilbert's syndrome.     

BET蛋白与脑认知功能关系的研究进展

溴结构域和超末端结构域(BET)蛋白能识别乙酰化组蛋白并与之结合,同时与染色质调节因子相互作用或招募转录起始复合物,从而启动基因转录。近几年,BET蛋白抑制剂的合成推进了BET蛋白相关表观遗传学研究。本文综述BET蛋白的结构和功能、BET蛋白抑制剂、BET蛋白在学习和记忆中的作用、BET蛋白在老年痴呆症中的作用以及BET蛋白在药物成瘾中的作用。     

Arsenicals produce stable progressive changes in DNA methylation patterns that are linked to malignant transformation of immortalized urothelial cells

Aberrant DNA methylation participates in carcinogenesis and is a molecular hallmark of a tumor cell. Tumor cells generally exhibit a redistribution of DNA methylation resulting in global hypomethylation with regional hypermethylation; however, the speed in which these changes emerge has not been fully elucidated and may depend on the temporal location of the cell in the path from normal, finite lifespan to malignant transformation. We used a model of arsenical-induced malignant transformation of immortalized human urothelial cells and DNA methylation microarrays to examine the extent and temporal nature of changes in DNA methylation that occur during the transition from immortal to malignantly transformed. Our data presented herein suggest that during arsenical-induced malignant transformation, aberrant DNA methylation occurs non-randomly, progresses gradually at hundreds of gene promoters, and alters expression of the associated gene, and these changes are coincident with the acquisition of malignant properties, such as anchorage independent growth and tumor formation in immunocompromised mice. The DNA methylation changes appear stable, since malignantly transformed cells removed from the transforming arsenical exhibited no reversion in DNA methylation levels, associated gene expression, or malignant phenotype. These data suggest that arsenicals act as epimutagens and directly link their ability to induce malignant transformation to their actions on the epigenome.