Alcohol, tobacco and breast cancer--collaborative reanalysis of individual data from 53 epidemiological studies, including 58,515 women with breast cancer and 95,067 women without the disease

Alcohol and tobacco consumption are closely correlated and published results on their association with breast cancer have not always allowed adequately for confounding between these exposures. Over 80% of the relevant information worldwide on alcohol and tobacco consumption and breast cancer were collated, checked and analysed centrally. Analyses included 58,515 women with invasive breast cancer and 95,067 controls from 53 studies. Relative risks of breast cancer were estimated, after stratifying by study, age, parity and, where appropriate, women's age when their first child was born and consumption of alcohol and tobacco. The average consumption of alcohol reported by controls from developed countries was 6.0 g per day, i.e. about half a unit/drink of alcohol per day, and was greater in ever-smokers than never-smokers, (8.4 g per day and 5.0 g per day, respectively). Compared with women who reported drinking no alcohol, the relative risk of breast cancer was 1.32 (1.19-1.45, P<0.00001) for an intake of 35-44 g per day alcohol, and 1.46 (1.33-1.61, P<0.00001) for >/=45 g per day alcohol. The relative risk of breast cancer increased by 7.1% (95% CI 5.5-8.7%; P<0.00001) for each additional 10 g per day intake of alcohol, i.e. for each extra unit or drink of alcohol consumed on a daily basis. This increase was the same in ever-smokers and never-smokers (7.1% per 10 g per day, P<0.00001, in each group). By contrast, the relationship between smoking and breast cancer was substantially confounded by the effect of alcohol. When analyses were restricted to 22 255 women with breast cancer and 40 832 controls who reported drinking no alcohol, smoking was not associated with breast cancer (compared to never-smokers, relative risk for ever-smokers=1.03, 95% CI 0.98-1.07, and for current smokers=0.99, 0.92-1.05). The results for alcohol and for tobacco did not vary substantially across studies, study designs, or according to 15 personal characteristics of the women; nor were the findings materially confounded by any of these factors. If the observed relationship for alcohol is causal, these results suggest that about 4% of the breast cancers in developed countries are attributable to alcohol. In developing countries, where alcohol consumption among controls averaged only 0.4 g per day, alcohol would have a negligible effect on the incidence of breast cancer. In conclusion, smoking has little or no independent effect on the risk of developing breast cancer; the effect of alcohol on breast cancer needs to be interpreted in the context of its beneficial effects, in moderation, on cardiovascular disease and its harmful effects on cirrhosis and cancers of the mouth, larynx, oesophagus and liver.

Locally resonant sonic materials

We have fabricated sonic crystals, based on the idea of localized resonant structures, that exhibit spectral gaps with a lattice constant two orders of magnitude smaller than the relevant wavelength. Disordered composites made from such localized resonant structures behave as a material with effective negative elastic constants and a total wave reflector within certain tunable sonic frequency ranges. A 2-centimeter slab of this composite material is shown to break the conventional mass-density law of sound transmission by one or more orders of magnitude at 400 hertz.

Hemodialysis versus peritoneal dialysis: a comparison of adjusted mortality rates

Although kidney transplantation is the preferred treatment method for patients with ESRD, most patients are placed on dialysis either while awaiting transplantation or as their only therapy. The question of which dialytic method provides the best patient survival remains unresolved. Survival analyses comparing hemodialysis and continuous ambulatory peritoneal dialysis/continuous cyclic peritoneal dialysis (CAPD/CCPD), a newer and less costly dialytic modality, have yielded conflicting results. Using data obtained from the Canadian Organ Replacement Register, we compared mortality rates between hemodialysis and CAPD/CCPD among 11,970 ESRD patients who initiated treatment between 1990 and 1994 and were followed-up for a maximum of 5 years. Factors controlled for include age, primary renal diagnosis, center size, and predialysis comorbid conditions. The mortality rate ratio (RR) for CAPD/CCPD relative to hemodialysis, as estimated by Poisson regression, was 0.73 (95% confidence interval: 0.68 to 0.78). No such relationship was found when an intent-to-treat Cox regression model was fit. Decreased covariable-adjusted mortality for CAPD/CCPD held within all subgroups defined by age and diabetes status, although the RRs increased with age and diabetes prevalence. The increased mortality on hemodialysis compared with CAPD/CCPD was concentrated in the first 2 years of follow-up. Although continuous peritoneal dialysis was associated with significantly lower mortality rates relative to hemodialysis after adjusting for known prognostic factors, the potential impact of unmeasured patient characteristics must be considered. Notwithstanding, we present evidence that CAPD/CCPD, a newer and less costly method of renal replacement therapy, is not associated with increased mortality rates relative to hemodialysis.

Mechanism of action of camptothecin

Camptothecin (CPT) class of compounds has been demonstrated to be effective against a broad spectrum of tumors. Their molecular target has been firmly established to be human DNA topoisomerase I (topo I). CPT inhibits topo I by blocking the rejoining step of the cleavage/religation reaction of topo-I, resulting in accumulation of a covalent reaction intermediate, the cleavable complex. The primary mechanism of cell killing by CPT is S-phase-specific killing through potentially lethal collisions between advancing replication forks and topo-I cleavable complexes. Collisions with the transcription machinery have also been shown to trigger the formation of long-lived covalent topo-I DNA complexes, which contribute to CPT cytotoxicity. Two novel repair responses to topo-I-mediated DNA damage involving covalent modifications of topo-I have been discovered. The first involves activation of the ubiquitin/26S proteasome pathway, leading to degradation of topo-I (CPT-induced topo-I downregulation). The second involves SUMO conjugation to topo-I. The potentials roles of these new mechanisms for repair of topo-I-mediated DNA damage in determining CPT sensitivity/resistance in tumor cells are discussed.

Specific probiotic therapy attenuates antibiotic induced visceral hypersensitivity in mice

BACKGROUND AND AIMS

Abdominal pain and discomfort are common symptoms in functional disorders and are attributed to visceral hypersensitivity. These symptoms fluctuate over time but the basis for this is unknown. Here we examine the impact of changes in gut flora and gut inflammatory cell activity on visceral sensitivity.

METHODS

Visceral sensitivity to colorectal distension (CRD) was assessed at intervals in healthy mice for up to 12 weeks, and in mice before and after administration of dexamethasone or non-absorbable antibiotics with or without supplementation with Lactobacillus paracasei (NCC2461). Tissue was obtained for measurement of myeloperoxidase activity (MPO), histology, microbiota analysis, and substance P (SP) immunolabelling.

RESULTS

Visceral hypersensitivity developed over time in healthy mice maintained without sterile precautions. This was accompanied by a small increase in MPO activity. Dexamethasone treatment normalised MPO and CRD responses. Antibiotic treatment perturbed gut flora, increased MPO and SP immunoreactivity in the colon, and produced visceral hypersensitivity. Administration of Lactobacillus paracasei in spent culture medium normalised visceral sensitivity and SP immunolabelling, but not intestinal microbiota counts.

CONCLUSION

Perturbations in gut flora and in inflammatory cell activity alter sensory neurotransmitter content in the colon, and result in altered visceral perception. Changes in gut flora may be a basis for the variability of abdominal symptoms observed in functional gastrointestinal disorders and may be prevented by specific probiotic administration.

Cancer incidence among Canadian kidney transplant recipients

A number of studies have observed increased cancer incidence rates among individuals who have received renal transplants. Generally, however, these studies have been limited by relatively small sample sizes, short follow-up intervals or focused on only one cancer site. We conducted a nationwide population-based study of 11,155 patients who underwent kidney transplantation between 1981 and 1998. Incident cancers were identified up to December 31, 1999, through record linkage to the Canadian Cancer Registry. Patterns of cancer incidence in the cohort were compared to the Canadian general population using standardized incidence ratios (SIRs). We examined variations in risk according time since transplantation, year of transplantation and age at transplantation. In our patient population, we observed a total of 778 incident cancers versus 313.2 expected (SIR = 2.5, 95% CI = 2.3-2.7). Site-specific SIRs were highest for cancer of the lip (SIR = 31.3, 95% CI = 23.5-40.8), non-Hodgkin's lymphoma (NHL) (SIR = 8.8, 95% CI = 7.4-10.5), and kidney cancer (SIR = 7.3, 95% CI = 5.7-9.2). SIRs for NHL and cancer of the lip and kidney were highest and among transplant patients. This study confirms previous findings of increased risks of posttransplant cancer. Our findings underscore the need for increased vigilance among kidney transplant recipients for cancers at sites where there are no population-based screening programs in place.

Transcriptional adaptor and histone acetyltransferase proteins in Arabidopsis and their interactions with CBF1, a transcriptional activator involved in cold-regulated gene expression

The ARABIDOPSIS CBF transcriptional activators bind to the CRT/DRE regulatory element present in the promoters of many cold-regulated genes and stimulate their transcription. Expression of the CBF1 proteins in yeast activates reporter genes carrying a minimal promoter with the CRT/DRE as an upstream regulatory element. Here we report that this ability of CBF1 is dependent upon the activities of three key components of the yeast Ada and SAGA complexes, namely the histone acetyltransferase (HAT) Gcn5 and the transcriptional adaptor proteins Ada2 and Ada3. This result suggested that CBF1 might function through the action of similar complexes in ARABIDOPSIS In support of this hypothesis we found that ARABIDOPSIS has a homolog of the GCN5 gene and two homologs of ADA2, the first report of multiple ADA2 genes in an organism. The ARABIDOPSIS GCN5 protein has intrinsic HAT activity and can physically interact in vitro with both the ARABIDOPSIS ADA2a and ADA2b proteins. In addition, the CBF1 transcriptional activator can interact with the ARABIDOPSIS GCN5 and ADA2 proteins. We conclude that ARABIDOPSIS encodes HAT-containing adaptor complexes that are related to the Ada and SAGA complexes of yeast and propose that the CBF1 transcriptional activator functions through the action of one or more of these complexes.

Increasing thyroid cancer incidence in Canada, 1970-1996: time trends and age-period-cohort effects

We examined time trends in thyroid cancer incidence in Canada by age, time period and birth cohort between 1970 and 1996. Age-specific incidence rates by time period and birth cohort were calculated and age-period-cohort modelling used to estimate effects underlying the observed trends. Overall age-adjusted incidence rates of thyroid cancer doubled, from 3.3 and 1.1 per 100 000 in 1970-72 to 6.8 and 2.2 per 100 000 in 1994-96, among females and males respectively. Almost all the increase between 1970-72 and 1994-96 was due to papillary carcinoma of the thyroid. Age, birth cohort and period effects significantly improved the fit of the model for females, while age and birth cohort effects were significant determinants of the incidence among males. There were significant differences in the patterns/curvature for age, period and birth cohort effects between women and men. Our results suggest that the increases in thyroid cancer incidence in Canada may be associated with more intensive diagnostic activities and change in radiation exposure in childhood and adolescence. Temporal changes in reproductive factors among young women may explain some of the gender differences observed.

Genetic dissection of autoimmune type I diabetes in the BB rat

The BB rat is among the best models of insulin-dependent diabetes mellitus--with onset and pathogenesis closely resembling the human disease. One unusual feature is a severe T-cell lymphopenia, which appears to be inherited as a recessive trait controlled by a single gene, Lyp. Based on genetic analysis of several crosses, we show that development of diabetes involves at least three genes: Lyp, which is tightly linked to the neuropeptide Y (Npy) gene on chromosome 4, a gene linked to the major histocompatibility complex (MHC) on chromosome 20, and a third unmapped gene for which the Fischer rat strain carries an allele conferring resistance.

The effects of Lactobacillus strains and oat fiber on methotrexate-induced enterocolitis in rats

BACKGROUND & AIMS

Administration of methotrexate to rats on an elemental diet results in severe enterocolitis and death. Lactobacilli, an integral part of the healthy gastrointestinal microecology, may provide therapeutic benefits to help the recovery from enterocolitis. The purpose of this study was to evaluate the effects of lactobacilli and oatbase on methotrexate-induced enterocolitis in rats.

METHODS

Rats received continuous intragastric infusion of elemental diet or with supplementation of oatbase, Lactobacillus reuteri R2LC, and Lactobacillus plantarum DSM 9843, with and without fermentation, from the beginning of the study. Methotrexate (20 mg/kg) was injected intraperitoneally on day 3, and the sampling was performed on day 6.

RESULTS

Lactobacilli and oatbase decreased body weight loss and intestinal permeability and increased bowel mucosal mass in enterocolitic rats. Administration of lactobacilli, but not oatbase, decreased the intestinal myeloperoxidase level, reestablished intestinal microecology, and reduced bacterial translocation to extraintestinal sites. Both lactobacilli and oatbase reduced plasma endotoxin levels. The effects of lactobacilli were greater with fermentation than without fermentation or oatbase alone, and L. plantarum was more effective in reducing intestinal pathogens than L. reuteri.

CONCLUSIONS

Exogenous administration of lactobacilli, especially L. plantarum with fermentation, is helpful in reducing the severity of enterocolitis in rats.

Inhibitory effects of Lactobacillus reuteri on visceral pain induced by colorectal distension in Sprague-Dawley rats

BACKGROUND AND AIMS

Probiotic bacteria are being investigated as possible treatments for many intestinal disorders. The present study aimed to explore the effects of live, heat killed, or gamma irradiated Lactobacillus reuteri on cardio-autonomic response and single fibre unit discharge in dorsal root ganglia to colorectal distension in healthy Sprague-Dawley rats housed under conventional conditions. The effects of this treatment on somatic pain were also examined.

METHODS

1x10(9) bacteria were given by gavage for nine days. Colorectal distension occurred under anaesthesia. Heart rate was measured through continuous electrocardiography. Single fibre unit discharge was recorded from the 6th left lumbar dorsal root ganglion. Somatic pain was evaluated by the tail flick and paw pressure tests.

RESULTS

Colorectal distension caused a pressure dependent bradycardia in the control (native medium) group. Treatment with live, heat killed, or gamma irradiated bacteria as well as their products (conditioned medium) prevented the pain response even during the maximum distension pressure (80 mm Hg). Both viable and non-viable bacteria significantly decreased dorsal root ganglion single unit activity to distension. No effects on somatic pain were seen with any treatment.

CONCLUSIONS

Oral administration of either live or killed probiotic bacteria or conditioned medium inhibited the constitutive cardio-autonomic response to colorectal distension in rats through effects on enteric nerves. These data may provide a novel explanation for beneficial probiotic effects on visceral pain.

26 S proteasome-mediated degradation of topoisomerase II cleavable complexes

DNA topoisomerase II (TOP2) cleavable complexes represent an unusual type of DNA damage characterized by reversible TOP2-DNA cross-links and DNA double strand breaks. Many antitumor drugs and physiological stresses are known to induce TOP2 cleavable complexes leading to apoptotic cell death and genomic instability. However, the molecular mechanism(s) for repair of TOP2 cleavable complexes remains unclear. In the current studies, we show that TOP2 cleavable complexes induced by the prototypic TOP2 poison VM-26 are proteolytically degraded by the ubiquitin/26 S proteasome pathway. Surprisingly the TOP2beta isozyme is preferentially degraded over TOP2alpha isozyme. In addition, transcription inhibitors such as 5,6-dichlorobenzimidazole riboside and camptothecin can substantially block VM-26-induced TOP2beta degradation. These results are consistent with a model in which the repair of TOP2beta cleavable complexes may involve transcription-dependent proteolysis of TOP2beta to reveal the protein-concealed double strand breaks.

SUMO-1 conjugation to topoisomerase I: A possible repair response to topoisomerase-mediated DNA damage

Ubiquitin/26S proteasome-dependent degradation of topoisomerase I (TOP1) has been suggested to be a unique repair response to TOP1-mediated DNA damage. In the current study, we show that treatment of mammalian cells or yeast cells expressing human DNA TOP1 with camptothecin (CPT) induces covalent modification of the TOP1 by SUMO-1/Smt3p, a ubiquitin-like protein. This conclusion is based on the following observations: (i) Mammalian DNA TOP1 conjugates induced by CPT were cross-reactive with SUMO-1/Smt3p-specific antibodies both in yeast expressing human DNA TOP1 as well as mammalian cells. (ii) The formation of TOP1 conjugates was shown to be dependent on UBC9, the E2 enzyme for SUMO-1/Smt3p. (iii) TOP1 physically interacts with UBC9. (iv) Ubc9 mutant yeast cells expressing human DNA TOP1 was hypersensitive to CPT, suggesting that UBC9/SUMO-1 may be involved in the repair of TOP1-mediated DNA damage.

Crystal structure of the VHS and FYVE tandem domains of Hrs, a protein involved in membrane trafficking and signal transduction

We have determined the 2 A X-ray structure of the 219-residue N-terminal VHS and FYVE tandem domain unit of Drosophila Hrs. The unit assumes a pyramidal structure in which the much larger VHS domain (residues 1-153) forms a rectangular base and the FYVE domain occupies the apical end. The VHS domain is comprised of an unusual "superhelix" of eight alpha helices, and the FYVE domain is mainly built of loops, two double-stranded antiparallel sheets, and a helix stabilized by two tetrahedrally coordinated zinc atoms. The two-domain structure forms an exact 2-fold-related homodimer through antiparallel association of mainly FYVE domains. Dimerization creates two identical pockets designed for binding ligands with multiple negative charges such as citrate or phosphatidylinositol 3-phosphate.

Risk factors for prostate cancer: results from the Canadian National Enhanced Cancer Surveillance System. The Canadian Cancer Registries Epidemiology Research Group

OBJECTIVES

To evaluate the relationship between prostate cancer and several potential lifestyle risk factors.

METHODS

We analyzed data obtained from a population-based case-control study conducted in eight Canadian provinces. Risk estimates were generated by applying multivariate logistic regression methods to 1623 histologically confirmed prostate cancer cases and 1623 male controls aged 50-74.

RESULTS

Cases were more likely to have a first-degree relative with a history of cancer, particularly prostate cancer (OR = 3.1, 95% CI = 1.8-5.4). Reduced risks of prostate cancer were observed among those of Indian descent (OR = 0.2, 95% CI = 0.1-0.5) or any Asian descent (OR = 0.3, 95% CI = 0.2-0.6) relative to those of western European descent. Total fat consumption, tomato and energy intake, were not associated with prostate cancer. The risk of prostate cancer was inversely related to the number of cigarettes smoked daily (p = 0.06) and cigarette pack-years (p < 0.01), while no association was observed between the total number of smoking years or the number of years since smoking cessation. Anthropometric measures and moderate and strenuous levels of leisure time physical activity were not strongly related to prostate cancer. In contrast, strenuous occupational activities at younger ages appeared protective.

CONCLUSIONS

Our analyses are limited by the absence of data related to tumor severity and screening history. Further studies are needed to investigate the relationship between behavioral risk factors and prostate cancer screening practices.

Inhibition of TNFalpha attenuates infarct volume and ICAM-1 expression in ischemic mouse brain

The purpose of our study was to determine whether inhibiting the action of tumor necrosis factor-alpha (TNFalpha) attenuates brain injury and reduces inflammatory responses in the mouse during ischemia and reperfusion. Mice underwent middle cerebral artery occlusion (MCAO) for 1 h followed by 23 h reperfusion. Monoclonal neutralizing anti-murine TNFalpha antibody (mAb) was administrated intraventricularly in the mouse with temporary MCAO. Infarct volume in the anti-TNFalpha mAb treated mice was significantly smaller than that in the control group (p < 0.05). The number of intercellular adhesion molecule-1 (ICAM-1)-positive vessels in the ischemic area of the anti-TNFalpha mAb-treated group was significantly less than that in the control group. Our study demonstrated that blocking TNFalpha reduced brain injury and attenuated ICAM-1 expression during transient cerebral ischemia.

Molecular characterization and analysis of the biosynthetic gene cluster for the antitumor antibiotic mitomycin C from Streptomyces lavendulae NRRL 2564

BACKGROUND

The mitomycins are natural products that contain a variety of functional groups, including aminobenzoquinone- and aziridine-ring systems. Mitomycin C (MC) was the first recognized bioreductive alkylating agent, and has been widely used clinically for antitumor therapy. Precursor-feeding studies showed that MC is derived from 3-amino-5-hydroxybenzoic acid (AHBA), D-glucosamine, L-methionine and carbamoyl phosphate. A genetically linked AHBA biosynthetic gene and MC resistance genes were identified previously in the MC producer Streptomyces lavendulae NRRL 2564. We set out to identify other genes involved in MC biosynthesis.

RESULTS

A cluster of 47 genes spanning 55 kilobases of S. lavendulae DNA governs MC biosynthesis. Fourteen of 22 disruption mutants did not express or overexpressed MC. Seven gene products probably assemble the AHBA intermediate through a variant of the shikimate pathway. The gene encoding the first presumed enzyme in AHBA biosynthesis is not, however, linked within the MC cluster. Candidate genes for mitosane nucleus formation and functionalization were identified. A putative MC translocase was identified that comprises a novel drug-binding and export system, which confers cellular self-protection on S. lavendulae. Two regulatory genes were also identified.

CONCLUSIONS

The overall architecture of the MC biosynthetic gene cluster in S. lavendulae has been determined. Targeted manipulation of a putative MC pathway regulator led to a substantial increase in drug production. The cloned genes should help elucidate the molecular basis for creation of the mitosane ring system, as well efforts to engineer the biosynthesis of novel natural products.

Activation of topoisomerase II-mediated excision of chromosomal DNA loops during oxidative stress

Hydrogen peroxide (H2O2), a reactive oxygen species (ROS), is known to induce oxidative stress and apoptosis. U937 cells treated with H2O2 were shown to produce high molecular weight (HMW) DNA fragments approximately 50 to 100 kb in size in <1 min. The formation of these HMW DNA fragments is reversible and shown to be mediated by DNA topoisomerase II (TOP2). Following this initial event, formation of irreversible HMW DNA fragments and nucleosomal ladders occurs. Our results thus demonstrate a potential role of TOP2 in oxidative damage of DNA and apoptotic cell death.

Angiotensin II induced cerebral microvascular inflammation and increased blood-brain barrier permeability via oxidative stress

Although hypertension has been implicated in the pathogenesis of vascular disease, its role in inflammatory responses, especially in brain, remains unclear. In this study we found key mechanisms by which angiotensin II (AngII) mediates cerebral microvascular inflammation. C57BL/6 male mice were subjected to slow-pressor dose of AngII infusion using osmotic mini-pumps at a rate of 400 ng/kg/min for 14 days. Vascular inflammation in the brain was evaluated by analysis of leukocyte-endothelial interaction and blood-brain barrier (BBB) permeability. Results from intravital microscopy of pial vessels in vivo, revealed a 4.2 fold (P<0.05, compared to vehicle) increase in leukocyte adhesion on day 4 of AngII infusion. This effect persisted through day 14 of AngII infusion, which resulted in a 2.6 fold (P<0.01, compared to vehicle) increase in leukocyte adhesion. Furthermore, evaluation of BBB permeability by Evans Blue extravasation showed that Ang II significantly affected the BBB, inducing 3.8 times (P<0.05, compared to vehicle) higher permeability. Previously we reported that AngII mediated hypertension promotes oxidative stress in the vasculature. Thus, we used the superoxide scavenger; 4-hydroxy-TEMPO (Tempol) to determine whether AngII via oxidative stress could contribute to higher leukocyte adhesion and increased BBB permeability. Tempol was given via drinking water (2 mmol) on day 4th following Ang II infusion, since oxidative stress increases in this model on day 4. Treatment with Tempol significantly attenuated the increased leukocyte/endothelial interactions and protected the BBB integrity on day 14 of AngII infusion. In conclusion, AngII via oxidative stress increases cerebral microvasculature inflammation and leads to greater immune-endothelial interaction and higher BBB permeability. This finding may open new avenues for the management of nervous system pathology involving cerebrovascular inflammation.

Stimulation of topoisomerase II-mediated DNA damage via a mechanism involving protein thiolation

The breakage/reunion reaction of DNA topoisomerase II (TOP2) can be interrupted by DNA intercalators (e.g., doxorubicin), enzyme binders (e.g., etoposide), or DNA lesions (e.g., abasic sites) to produce TOP2-mediated DNA damage. Here, we demonstrate that thiol alkylation of TOP2 can also produce TOP2-mediated DNA damage. This conclusion is supported by the following observations using purified TOP2: (1) Thiol-reactive quinones were shown to induce TOP2-mediated DNA cleavage. (2) Thiol-reactive compounds such as N-ethylmaleimide (NEM), disulfiram, and organic disulfides [e.g., 2,2'-dithiobis(5-nitropyridine)] were also shown to induce TOP2-mediated DNA cleavage with similar reaction characteristics as thiol-reactive quinones. (3) TOP2-mediated DNA cleavage induced by thiol-reactive quinones was completely abolished using mutant yeast TOP2 with all cysteine residues replaced with alanine (cysteineless TOP2). These results suggest the possibility that cellular DNA damage could occur indirectly through thiolation of a nuclear protein, TOP2. The implications of this reaction in carcinogenesis and apoptotic cell death are discussed.

SUMO-1 conjugation to human DNA topoisomerase II isozymes

Topoisomerase I-mediated DNA damage induced by camptothecin has been shown to induce rapid small ubiquitin-related modifier (SUMO)-1 conjugation to topoisomerase I. In the current study, we show that topoisomerase II-mediated DNA damage induced by teniposide (VM-26) results in the formation of high molecular weight conjugates of both topoisomerase IIalpha and IIbeta isozymes in HeLa cells. Immunological characterization of these conjugates suggests that both topoisomerase IIalpha and IIbeta isozymes are conjugated to SUMO-1. The involvement of SUMO-1/UBC9 in the modification of topoisomerase II isozymes is also supported by the demonstration of physical interaction between topoisomerase II and SUMO-1/UBC9. Surprisingly, ICRF-193, which does not induce topoisomerase II-mediated DNA damage but traps topoisomerase II into a circular clamp conformation, is also shown to induce similar SUMO-1 conjugation to topoisomerase II isozymes. In addition, we show that both oxidative and heat shock stresses, which can cause protein damage, rapidly increase nuclear SUMO-1 conjugates. These studies raise the question on whether SUMO-1 conjugation to topoisomerases is an indirect result of a DNA damage response or a direct result because of protein conformational changes.

Chromium(VI)-induced nuclear factor-kappa B activation in intact cells via free radical reactions

Incubation of chromium(VI) [Cr(VI)] with cultured Jurkat cells resulted in activation of DNA binding activity of the nuclear factor (NF)-kappa B. In a combination with glutathione reductase, a Cr(VI) reducing agent, Cr(VI) expressed an enhanced activity in induction of NF-kappa B. This activation of NF-kappa B was decreased by a metal chelator, diethylene-triaminepentaacetic acid or catalase, but increased by superoxide dismutase. Addition of Mn2+, which reacts with Cr(IV) and inhibits Cr(IV)-mediated hydroxyl radical (.OH) generation via Fenton-like reaction, attenuated the activation of NF-kappa B. Sodium formate, an .OH radical scavenger, also inhibited the activation. Electron spin resonance measurements showed that the incubation of Cr(VI) with intact Jurkat cells generated reactive Cr(V) intermediate. Glutathione reductase and NADPH enhanced Cr(V) generation. Electron spin resonance spin trapping measurements using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trapping agent provided evidence that the incubation of Cr(VI) with the Jurkat cells in the presence of glutathione reductase generated .OH radicals. H2O2 enhanced .OH radical generation and also enhanced Cr(V) formation, indicating the role of Cr(IV) in .OH radical generation. We conclude that Cr(VI) can activate NF-kappa B in vitro via Cr(IV)-mediated free radical reactions. We hypothesize that Cr(VI)-mediated NF-kappa B activation may be involved in the mechanism of Cr(VI)-induced carcinogenicity.

Myeloid-derived suppressor cells impair the quality of dendritic cell vaccines

Myeloid-derived suppressor cells (MDSC) are important regulators of the immune system and key players in tumor-induced suppression of T-cell responses. CD14+HLA-DR-/low MDSC have been detected in a great number of malignancies, including melanoma. MDSC are known to be impaired in their ability to differentiate along the myeloid lineage, e.g., into dendritic cells (DC). This is a concern for utilization of monocyte-derived DC for vaccination of patients with melanoma or other cancers exhibiting accumulation of CD14+ MDSC. When producing DC according to standard operating procedures of two currently ongoing clinical trials, we found that MDSC co-purified with monocytes isolated by elutriation. MDSC frequencies did not affect yield or viability of the produced DC, but induced a dose-dependent decrease in DC maturation, ability to take up antigen, migrate and induce T-cell IFNγ production. Changes in DC characteristics were most notable when 'pathological' frequencies of >50% CD14+HLA-DR- cells were present in the starting culture. The impaired DC quality could not be explained by altered cytokine production or increased oxidative stress in the cultures. Tracking of HLA-DR- cells throughout the culture period revealed that the observed changes were partially due to the impaired maturation and functionality of the originally HLA-DR- population, but also to their negative effects on HLA-DR+ cells. In conclusion, MDSC could be induced to differentiate into DC but, due to the impairment of overall DC vaccine quality when >50% HLA-DR- cells were present in the starting culture, their removal could be advisable.

Cloning, expression, and characterization of a human inosine triphosphate pyrophosphatase encoded by the itpa gene

ITP and dITP exist in all cells. dITP is potentially mutagenic, and the levels of these nucleotides are controlled by inosine triphosphate pyrophosphatase (EC ). Here we report the cloning, expression, and characterization of a 21.5-kDa human inosine triphosphate pyrophosphatase (hITPase), an enzyme whose activity has been reported in many animal tissues and studied in populations but whose protein sequence has not been determined before. At the optimal pH of 10.0, recombinant hITPase hydrolyzed ITP, dITP, and xanthosine 5'-triphosphate to their respective monophosphates whereas activity with other nucleoside triphosphates was low. K(m) values for ITP, dITP, and xanthosine 5'-triphosphate were 0.51, 0.31, and 0.57 mm, respectively, and k(cat) values were 580, 360, and 640 s(-1), respectively. A divalent cation was absolutely required for activity. The gene encoding the hITPase cDNA sequence was localized by radiation hybrid mapping to chromosome 20p in the interval D20S113-D20S97, the same interval in which the ITPA inosine triphosphatase gene was previously localized. A BLAST search revealed the existence of many similar sequences in organisms ranging from bacteria to mammals. The function of this ubiquitous protein family is proposed to be the elimination of minor potentially mutagenic or clastogenic purine nucleoside triphosphates from the cell.

Reaction of Cr(VI) with ascorbate and hydrogen peroxide generates hydroxyl radicals and causes DNA damage: role of a Cr(IV)-mediated Fenton-like reaction

Incubation of Cr(VI) with ascorbate generated Cr(V), Cr(IV) and ascorbate-derived carbon-centered alkyl radicals, as well as formyl radicals. H2O2 caused generation of hydroxyl radicals (OH) and much higher levels of Cr(V), showing that .OH can be generated via a Cr(IV)-mediated Fenton-like reaction (Cr(IV) + H2O2-->Cr(V) + .OH + OH-). 1,10-Phenanthroline and deferoxamine inhibited the formation of both .OH and Cr(V) from the reaction of Cr(VI) with ascorbate in the presence of H2O2. Electrophoretic assays showed that ascorbate-derived free radicals caused DNA double-strand breaks. .OH radicals generated by Cr(V)- and Cr(IV)-mediated Fenton-like reactions also caused DNA double-strand breaks. HPLC measurements showed that .OH radicals generated by Cr(IV) and Cr(V) from H2O2 caused 2'-deoxyguanine hydroxylation to form 8-hydroxy-2'-deoxyguanine.