A critical role of redox state in determining HL-60 cell granulocytic differentiation and apoptosis via involvement of PKC and NF-κB

The modifications of intracellular redox balance leads to important cellular changes in many cell types. Here, a causal relationship among redox state, granulocytic differentiation induced by all-trans retinoic acid (RA) or dibutyryl cAMP (dbcAMP) and apoptosis have been studied in the human acute promyelocytic leukaemia HL-60 cells. The modulation of intracellular reactive oxygen species levels by d, l-buthionine-(S, R) sulfoximide (BSO), and n-acetyl-l-cysteine (NAC) caused inducer- and time-dependent or stage-specific effects on HL-60 cell growth inhibition, differentiation and subsequent apoptosis. The presence of BSO during the commitment stage suppressed RA—but not dbcAMP-mediated differentiation, while NAC inhibited both. BSO alone and in combination with RA or dbcAMP-induced apoptosis, which was prevented by NAC in dbcAMP—but not in RA-treated cells. Using protein kinase C inhibitor, calphostin C, cross-talk effects between the intracellular redox state and PKC signalling was identified by demonstrating inducer-dependent changes in cell differentiation or apoptosis, which were associated with the changes in DNA-NF-κB binding activity. These observations suggest a critical role of redox state in determining HL-60 cell behaviour and provide new insights into the complex effects of redox perturbations on the intracellular signalling network via the involvement of PKC and NF-κB.     

Binding of prion proteins to lipid membranes

A key molecular event in prion diseases is the conversion of the normal cellular form of the prion protein (PrPC) to an aberrant form known as the scrapie isoform, PrPSc. Under normal physiological conditions PrPC is attached to the outer leaflet of the plasma membrane via a GPI-anchor. It has been proposed that a direct interaction between PrP and lipid membranes could be involved in the conversion of PrPC to its disease-associated corrupted conformation, PrPSc. Recombinant PrP can be refolded into an alpha-helical structure, designated alpha-PrP isoform, or into beta-sheet-rich states, designated beta-PrP isoform. The current study investigates the binding of recombinant PrP isoforms to model lipid membranes using surface plasmon resonance spectroscopy. The binding of alpha- and beta-PrP to negatively charged lipid membranes of POPG, zwitterionic membranes of DPPC, and model raft membranes composed of DPPC, cholesterol, and sphingomyelin is compared at pH 7 and 5, to simulate the environment at the plasma membrane and within endosomes, respectively. It is found that PrP binds strongly to lipid membranes. The strength of the association of PrP with lipid membranes depends on the protein conformation and pH, and involves both hydrophobic and electrostatic lipid-protein interactions. Competition binding measurements established that the binding of alpha-PrP to lipid membranes follows a decreasing order of affinity to POPG>DPPC>rafts.     

Associations between Apolipoprotein E Genotype, Diet, Body Mass Index, and Serum Lipids in Lithuanian Adult Population

Background

Apolipoprotein E (APOE) polymorphism is associated with lipid levels. Some studies have reported that blood lipid response to diet or obesity varies depending on APOE genotypes. The aim of this study was to assess the effect of APOE genotypes, the intake of saturated fatty acids (SFA), and obesity on serum lipid levels in Lithuanian adult population.

Methodology/Principal Findings

A cross-sectional health survey was carried out in five municipalities of Lithuania. The random sample was obtained from lists of 25–64 year-old inhabitants registered at primary health care centres. The data from 996 subjects (416 men and 580 women) were analysed in this study. Two single-nucleotide polymorphisms (rs429358 and rs7412) were assessed using a real-time polymerase chain reaction. 24-hour recall and food frequency questionnaire were used for evaluation of dietary habits. Serum lipids were determined using enzymatic methods.Men and women with the APOE2 genotype had the lowest level of total cholesterol (TC) (p = 0.002 for men, and p = 0.02 for women) and low-density lipoprotein cholesterol (LDL-C) (p<0.001). Multivariate linear regression analysis showed that age, genotype APOE2, SFA intake, and body mass index (BMI) were significant determinants of TC and LDL-C level (with p values ranging from 0.043 to 0.001). Our data did not reveal any statistically significant interactions between APOE genotype and SFA intake or between APOE genotype and BMI regarding TC and LDL-C level (all p>0.05). However, the predictive power of the regression model for LDL-C improved when gene-BMI interaction and gene-BMI interaction plus gene-nutrient interaction were added (p = 0.04 and p = 0.032 for R² change, respectively).

Conclusions/Significance

APOE genotypes, SFA intake, and obesity were found to be associated with blood lipid levels in Lithuanian adult population. Analysis of gene-diet and gene-obesity interactions did not confirm that the effects of diet and obesity on TC and LDL-C level significantly depended on APOE genotype.     

Aggregation and fibrillization of prions in lipid membranes

A key molecular event in prion diseases is the conversion of PrP (prion protein) from its normal cellular form (PrP(c)) into the disease-specific form (PrP(Sc)). The transition from PrP(c) to PrP(Sc) involves a major conformational change, resulting in amorphous aggregates and/or fibrillar amyloid deposits. Here, we review several lines of evidence implicating membranes in the conversion of PrP, and summarize recent results from our own work on the role of lipid membranes in conformational transitions of prion proteins. By establishing new correlations between in vivo biological findings with in vitro biophysical results, we propose a role for lipid rafts in prion conversion, which takes into account the structural heterogeneity of PrP in different lipid environments.     

Biochemical characterization of recombinant β-glucosyltransferase and analysis of global 5-hydroxymethylcytosine in unique genomes

5-Hydroxymethylcytosine (5-hmC) is an enzymatic oxidative product of 5-methylcytosine (5-mC). The Ten Eleven Translocation (TET) family of enzymes catalyze the conversion of 5-mC to 5-hmC. Phage-encoded glucosyltransferases are known to glucosylate 5-hmC, which can be utilized to detect and analyze the 5-hmC as an epigenetic mark in the mammalian epigenome. Here we have performed a detailed biochemical characterization and steady-state kinetic parameter analysis of T4 phage β-glucosyltransferase (β-GT). Recombinant β-GT glucosylates 5-hmC DNA in a nonprocessive manner, and binding to either 5-hmC DNA or uridine diphosphoglucose (UDP-glucose) substrates is random, with both binary complexes being catalytically competent. Product inhibition studies with β-GT demonstrated that UDP is a competitive inhibitor with respect to UDP-glucose and a mixed inhibitor with respect to 5-hmC DNA. Similarly, the glucosylated-5-hmC (5-ghmC) DNA is a competitive inhibitor with respect to 5-hmC DNA and mixed inhibitor with respect to UDP-glucose. 5-hmC DNA binds ~10 fold stronger to the β-GT enzyme when compared to its glucosylated product. The numbers of 5-hmC on target sequences influenced the turnover numbers for recombinant β-GT. Furthermore, we have utilized recombinant β-GT to estimate global 5-hmC content in a variety of genomic DNAs. Most of the genomic DNAs derived from vertebrate tissue and cell lines contained 5-hmC. DNA from mouse, human, and bovine brains displayed 0.5-0.9% of the total nucleotides as 5-hmC, which was higher compared to the levels found in other tissues. A comparison between cancer and healthy tissue genomes suggested a lower percentage of 5-hmC in cancer, which may reflect the global hypomethylation of 5-mC observed during oncogenesis.     

Autologous hematopoietic stem cell transplantation for systemic sclerosis

Systemic sclerosis is a rare disorder manifesting as skin and internal organ fibrosis, a diffuse vasculopathy, inflammation, and features of autoimmunity. Patients with diffuse cutaneous disease or internal organ involvement have a poor prognosis with high mortality. To date no therapy has been shown to reverse the natural course of the disease. Immune suppressive drugs are commonly utilized to treat patients, but randomized trials have generally failed to demonstrate any long-term benefit. In phase I/II trials, autologous hematopoietic stem cell transplantation (HSCT) has demonstrated impressive reversal of skin fibrosis, improved functionality and quality of life, and stabilization of internal organ function, but initial studies were complicated by significant treatment-related mortality. Treatment-related mortality was reduced by better pre-transplant evaluation to exclude patients with compromised cardiac function and by treating patients earlier in disease, allowing selected patients the option of autologous HSCT treatment. There are currently three ongoing randomized trials of autologous HSCT for systemic sclerosis: ASSIST (American Systemic Sclerosis Immune Suppression versus Transplant), SCOT (scleroderma cyclophosphamide versus Transplant), and ASTIS (Autologous Stem cell Transplantation International Scleroderma). The results from these trials should clarify the role of autologous HSCT in the currently limited therapeutic arsenal of severe systemic sclerosis.     

Antileukemic activity of combined epigenetic agents, DNMT inhibitors zebularine and RG108 with HDAC inhibitors, against promyelocytic leukemia HL-60 cells

DNMT inhibitors are promising new drugs for cancer therapies. In this study, we have observed the antileukemic action of two diverse DNMT inhibitors, the nucleoside agent zebularine and the non-nucleoside agent RG108, in human promyelocytic leukemia (PML) HL-60 cells. Zebularine but not RG108 caused dose- and time-dependent cell growth inhibition and induction of apoptosis. However, co-treatment with either drug at a non-toxic dose and all trans retinoic acid (RA) reinforced differentiation to granulocytes, while 24 or 48 h-pretreatment with zebularine or RG108 followed by RA alone or in the presence of HDAC inhibitors (sodium phenyl butyrate or BML-210) significantly accelerated and enhanced cell maturation to granulocytes. This occurs in parallel with the expression of a surface biomarker, CD11b, and early changes in histone H4 acetylation and histone H3K4me3 methylation. The application of both drugs to HL-60 cells in continuous or sequential fashion decreased DNMT1 expression, and induced E-cadherin promoter demethylation and reactivation at both the mRNA and the protein levels in association with the induction of granulocytic differentiation. The results confirmed the utility of zebularine and RG108 in combinations with RA and HDAC inhibitors to reinforce differentiation effects in promyelocytic leukemia.     

Evolutionary relationship of<Emphasis Type="Italic"> Alw</Emphasis>26I,<Emphasis Type="Italic"> Eco</Emphasis>31I and<Emphasis Type="Italic"> Esp</Emphasis>3I,restriction endonucleases that recognise overlapping sequences

Type II restriction endonucleases (ENases) have served as models for understanding the enzyme-based site-specific cleavage of DNA. Using the knowledge gained from the available crystal structures, a number of attempts have been made to alter the specificity of ENases by mutagenesis. The negative results of these experiments argue that the three-dimensional structure of DNA-ENase complexes does not provide enough information to enable us to understand the interactions between DNA and ENases in detail. This conclusion calls for alternative approaches to the study of structure-function relationships related to the specificity of ENases. Comparative analysis of ENases that manifest divergent substrate specificities, but at the same time are evolutionarily related to each other, may be helpful in this respect. The success of such studies depends to a great extent on the availability of related ENases that recognise partially overlapping nucleotide sequences (e.g. sets of enzymes that bind to recognition sites of increasing length). In this study we report the cloning and sequence analysis of genes for three Type IIS restriction-modification (RM) systems. The genes encoding the ENases Alw26I, Eco31I and Esp3I (whose recognition sequences are 5'-GTCTC-3', 5'-GGTCTC-3' and 5'-CGTCTC-3', respectively) and their accompanying methyltransferases (MTases) have been cloned and the deduced amino acid sequences of their products have been compared. In pairwise comparisons, the degree of sequence identity between Alw26I, Eco31I and Esp3I ENases is higher than that observed hitherto among ENases that recognise partially overlapping nucleotide sequences. The sequences of Alw26I, Eco31I and Esp3I also reveal identical mosaic patterns of sequence conservation, which supports the idea that they are evolutionarily related and suggests that they should show a high level of structural similarity. Thus these ENases represent very attractive models for the study of the molecular basis of variation in the specific recognition of DNA targets. The corresponding MTases are represented by proteins of unusual structural and functional organisation. Both M. Alw26I and M. Esp3I are represented by a single bifunctional protein, which is composed of an m(6)A-MTase domain fused to a m(5)C-MTase domain. In contrast, two separate genes encode the m(6)A-MTase and m(5)C-MTase in the Eco31I RM system. Among the known bacterial m(5)C-MTases, the m(5)C-MTases of M. Alw26I, M. Eco31I and M. Esp3I represent unique examples of the circular permutation of their putative target recognition domains together with the conserved motifs IX and X.     

A nomenclature for restriction enzymes,DNA methyltransferases,homing endonucleases and their genes

A nomenclature is described for restriction endonucleases, DNA methyltransferases, homing endonucleases and related genes and gene products. It provides explicit categories for the many different Type II enzymes now identified and provides a system for naming the putative genes found by sequence analysis of microbial genomes.