SIRT1 inhibition restores apoptotic sensitivity in p53-mutated human keratinocytes.

Mutations to the p53 gene are common in UV-exposed keratinocytes and contribute to apoptotic resistance in skin cancer. P53-dependent activity is modulated, in part, by a complex, self-limiting feedback loop imposed by miR-34a-mediated regulation of the lysine deacetylase, SIRT1. Expression of numerous microRNAs is dysregulated in squamous and basal cell carcinomas; however the contribution of specific microRNAs to the pathogenesis of skin cancer remains untested. Through use of RNAi, miRNA target site blocking oligonucleotides and small molecule inhibitors, this study explored the influence of p53 mutational status, SIRT1 activity and miR-34a levels on apoptotic sensitivity in primary (NHEK) and p53-mutated (HaCaT) keratinocyte cell lines. SIRT1 and p53 are overexpressed in p53-mutated keratinocytes, whilst miR-34a levels are 90% less in HaCaT cells. HaCaTs have impaired responses to p53/SIRT1/miR-34a axis manipulation which enhanced survival during exposure to the chemotherapeutic agent, camptothecin. Inhibition of SIRT1 activity in this cell line increased p53 acetylation and doubled camptothecin-induced cell death. Our results demonstrate that p53 mutations increase apoptotic resistance in keratinocytes by interfering with miR-34a-mediated regulation of SIRT1 expression. Thus, SIRT1 inhibitors may have a therapeutic potential for overcoming apoptotic resistance during skin cancer treatment.

Arsenic exposure disrupts epigenetic regulation of SIRT1 in human keratinocytes.

Arsenic is an environmental toxin which increases skin cancer risk for exposed populations worldwide; however the underlying biomolecular mechanism for arsenic-induced carcinogenesis is complex and poorly defined. Recent investigations show that histone deacetylase and DNA methyltransferase activity is impaired, and epigenetic patterns of gene regulation are consistently altered in cancers associated with arsenic exposure. Expression of the histone deacetylase SIRT1 is altered in solid tumours and haematological malignancies; however its role in arsenic-induced pathology is unknown. In this study we investigated the effect of arsenic on epigenetic regulation of SIRT1 and its targeting microRNA, miR-34a in primary human keratinocytes. Acetylation of histone H4 at lysine 16 (H4K16) increased in keratinocytes exposed to 0.5µM arsenite [As(III)]; and this was associated with chromatin remodelling at the miR-34a promoter. Moreover, although SIRT1 protein initially increased in these As(III)-exposed cells, after 24days expression was not significantly different from untreated controls. Extended exposure to low-dose As(III) (0.5µM; >5weeks) compromised the pattern of CpG methylation at SIRT1 and miR-34a gene promoters, and this was associated with altered expression for both genes. We have found that arsenic alters epigenetic regulation of SIRT1 expression via structural reorganisation of chromatin at the miR-34a gene promoter in the initial 24h of exposure; and over time, through shifts in miR-34a and SIRT1 gene methylation. Taken together, this investigation demonstrates that arsenic produces cumulative disruptions to epigenetic regulation of miR-34a expression, and this is associated with impaired coordination of SIRT1 functional activity.

Chronic high-dose testosterone impairs economic decision making, but has no effect on memory in male rats.

The goal is to understand consequences of anabolic-androgenic steroid (AAS) abuse on cognitive function, using rats as a model. Economic decision making was evaluated in an operant test of effort value discounting, where subjects choose between 2 levers that deliver large and small rewards differing in maximum value and reward contrast. The hypothesis is that chronic high-dose testosterone increases preference for large rewards. Male rats were treated chronically with testosterone (7.5 mg/kg) or vehicle. Initially, all rats preferred the large reward lever when large and small rewards remained fixed at 3 and 1 sugar pellets, respectively. When different reward values were introduced, and with increasing response requirements, testosterone-treated rats made fewer responses for the large reward, and increased omissions. They earned fewer rewards overall. To determine if testosterone impairs memory, rats were tested for recognition memory with the novel object recognition and social transmission of food preference tasks, and for spatial memory with the radial arm maze and Morris water maze. There was not effect of chronic high-dose testosterone on any memory task. These results suggest that testosterone shifts economic decision making towards larger rewards even when they are disadvantageous, but does not alter memory in rats.

Transcriptionally active human papillomavirus is strongly associated with Barrett's dysplasia and esophageal adenocarcinoma.

OBJECTIVES: The role of human papillomavirus (HPV) in Barrett's esophagus (BE) remains unclear. The few studies that have previously investigated HPV and esophageal adenocarcinoma (EAC) or BE have produced either negative data or positive results of doubtful clinical/etiological significance or have detected only low-risk HPV types. We therefore prospectively determined the prevalence of biologically active HPV in esophageal epithelium of patients representing the Barrett's metaplasia-dysplasia-adenocarcinoma sequence. METHODS: HPV DNA was estimated by nested PCR and viral transcriptional activity detected by E6/7 oncogene mRNA expression and p16INK4A immunohistochemistry in fresh frozen and paraffin-embedded esophageal biopsies of patients with BE, Barrett's dysplasia (BD), and EAC, as well as controls. Biopsies were obtained from the transformation zone (squamocolumnar junction (SCJ)) and the lesion, or corresponding site in controls, i.e., 2 cm above the gastroesophageal junction (GEJ). RESULTS: Of the 261 patients, 81 were positive for HPV DNA. In controls and BE, the virus was mostly detected at the transformation zone. Compared with controls (18.0%), HPV positivity was significantly more common in BD (68.6%, incidence rate ratio (IRR) 2.94, 95% confidence interval (CI) 1.78-4.85, P<0.001) and EAC (66.7%, IRR 2.87, 95% CI 1.69-4.86, P<0.001), but not in BE (22.1%, IRR 1.06, 95% CI 0.60-1.85, P=0.85). Of the patients, 92.6% were high-risk (HR) HPV, i.e., types 16 and 18. Again, p16INK4A positivity was greatest in BD and EAC and much less in BE patients (44.1%, IRR 17.0 (95% CI 4.86-59.6, P<0.001), 44.4%, 17.0 (95% CI 4.87-59.4, P<0.001), and 10.6%, 3.93 (95% CI 1.01-15.3, P=0.048) respectively). In 66 HPV DNA-positive patients tested for E6/E7 mRNA, none of the control (n=16) or BE (n=13) individuals were positive, whereas 9/22 BD and 9/15 EAC patients demonstrated oncogene expression (P<0.001). When HPV DNA, p16INK4A, and E6/E7 mRNA were all positive, there was a very strong association with disease severity (SCJ: odds ratio (OR) 104, 95% CI 20.3-529, P<0.001; lesion: OR 62.2, 95% CI 12.4-311, P<0.001) than when all were negative. CONCLUSIONS: Transcriptionally active HR-HPV was strongly associated with BD and EAC, but was largely biologically irrelevant in BE and controls, suggesting a potential role in esophageal carcinogenesis. These data provide robust justification for further detailed longitudinal, interventional, and molecular studies.

A Retrospective Study of Acute Postoperative Pain After Cesarean Delivery in Patients With Opioid Use Disorder Treated With Opioid Agonist Pharmacotherapy.

OBJECTIVE: We aimed to quantify the effect of opioid agonist pharmacotherapy on pain management after cesarean delivery, compared with patients not on these medications. METHODS: Patients undergoing cesarean delivery at our institution between January 2016 and December 2018 were stratified by peripartum use of opioid agonist pharmacotherapy versus no agonist therapy. We compared 24-hour postoperative opioid consumption not including buprenorphine and methadone, in milligram morphine equivalents (MME) (primary outcome), highest pain score on a 0 to 10 numerical rating scale in the first 24 postoperative hours, and postoperative length of stay in hours (secondary outcomes) between groups. These outcomes were also compared after covariate adjustment using logistic regression. RESULTS: We identified 123 patients on opioid agonist pharmacotherapy - in the form of buprenorphine or methadone and 2856 patients not on these medications. The groups differed in demographic characteristics, including age, smoking, and marital status. Opioid consumption during the first 24 postoperative hours (median [interquartile range]) was 99 [75,120] MME for patients on agonist therapy and 30 [0, 64] MME among parturients not taking these medications ( P < 0.001). Highest pain scores during this time were also higher for patients on opioid agonist pharmacotherapy (mean [standard deviation]: 8.2 [1.6] vs 5.5 [2.2], P < 0.001 for the no agonist group). Postoperative length of stay was 73 [68, 77] hours for patients on agonist pharmacotherapy, and 71 [62, 76] hours for parturients taking no agonist ( P < 0.001). All differences remained significant after covariate adjustment. CONCLUSIONS: Parturients on opioid agonist pharmacotherapy have markedly increased opioid utilization and pain severity after cesarean delivery.

Age and exposure to arsenic alter base excision repair transcript levels in mice.

Arsenic (As) induces DNA-damaging reactive oxygen species. Most oxidative DNA damage is countered by base excision repair (BER), the capacity for which may be reduced in older animals. We examined whether age and consumption of As in lactational milk or drinking water influences BER gene transcript levels in mice. Lactating mothers and 24-week-old mice were exposed (24 h or 2 weeks) to As (2 or 50 p.p.m.) in drinking water. Lung tissue was harvested from adults, neonates (initially 1 week old) feeding from lactating mothers and untreated animals 1-26 weeks old. Transcripts encoding BER proteins were quantified. BER transcript levels decreased precipitously with age in untreated mice but increased in neonates whose mothers were exposed to 50 p.p.m. As for 24 h or 2 weeks. Treatment of 24-week-old mice with 2 or 50 p.p.m. As for 2 weeks decreased all transcript levels measured. Exposure to As attenuated the age-related transcript level decline for only one BER gene. We conclude that aging is associated with a rapid reduction of BER transcript levels in mice, which may contribute to decreased BER activity in older animals. Levels of As that can alter gene expression are transmitted to neonatal mice in lactational milk produced by mothers drinking water containing As, raising concerns about breastfeeding in countries having As-contaminated groundwater. Reduction of BER transcript levels in 24-week-old mice exposed to As for 2 weeks suggests As may potentiate sensitivity to itself in older animals.

Arsenic speciation in the freshwater crayfish, Cherax destructor Clark.

Arsenic is a proven carcinogen that is found in the soil in gold mining regions at concentrations that can be thousands of times greater than gold. During mining arsenic is released into the environment, easily entering surrounding water bodies. The yabby (Cherax destructor) is a common freshwater crustacean native to Australia's central and eastern regions. Increasing aquaculture and export of these animals has led us to question the effects of mine contamination on the yabbies themselves and to assess any potential risks to consumers. This study determined the species of arsenic present in a number of organs from the yabby. Several arsenic contaminated dam sites in the goldfields of western Victoria were sampled for yabby populations. Yabbies from these sites were collected and analysed for arsenic speciation using high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). Results showed that type of exposure influenced which arsenic species was present in each organ, and that as arsenic exposure increased the prevalence of inorganic arsenic species, mostly As(V), within the tissues increased. The bioaccessibility of the arsenic present in the abdominal muscle (the edible portion for humans) of the yabbies was assessed. It was found that the majority of the bioaccessible arsenic was present as inorganic As(III) and As(V).

Total arsenic accumulation in yabbies (Cherax destructor Clark) exposed to elevated arsenic levels in Victorian gold mining areas, Australia.

Arsenic is a proven carcinogen often found at high concentrations in association with gold and other heavy metals. The freshwater yabby, Cherax destructor Clark (Decapoda, Parastacidae), is a ubiquitous species native to Australia's central and eastern regions, with a growing international commercial market. However, in this region of Australia, yabby farmers often harvest organisms from old mine tailings dams with elevated environmental arsenic levels. Yabbies exposed to elevated environmental arsenic were found to accumulate and store as much as 100 microg/g arsenic in their tissues. The accumulation is proportional to the concentration of arsenic in the sediment and is high enough to be of concern for people who eat the yabbies. A comparison of arsenic levels in wild and lab-fed animals also was performed. Although there was no significant difference in the level of arsenic in the various organs of the wild animals, the animals purchased from a yabby farm showed a significantly higher arsenic concentration in their hepatopancreas (3.7 +/- 0.9 microg/g) compared to other organs (0.6-1.8 microg/g). Furthermore, after a 40-d exposure to food containing 200 to 300 microg/g inorganic arsenic, arsenate (As[V])-exposed animals showed a significant increase in tissue-specific arsenic accumulation, whereas arsenite (As[III])-exposed animals showed a lower, nonsignificant increase in As uptake, primarily in the hepatopancreas. These results have important implications for yabby growers and consumers alike.

ERBB3: A potential serum biomarker for early detection and therapeutic target for devil facial tumour 1 (DFT1).

Devil Facial Tumour 1 (DFT1) is one of two transmissible neoplasms of Tasmanian devils (Sarcophilus harrisii) predominantly affecting their facial regions. DFT1's cellular origin is that of Schwann cell lineage where lesions are evident macroscopically late in the disease. Conversely, the pre-clinical timeframe from cellular transmission to appearance of DFT1 remains uncertain demonstrating the importance of an effective pre-clinical biomarker. We show that ERBB3, a marker expressed normally by the developing neural crest and Schwann cells, is immunohistohemically expressed by DFT1, therefore the potential of ERBB3 as a biomarker was explored. Under the hypothesis that serum ERBB3 levels may increase as DFT1 invades local and distant tissues our pilot study determined serum ERBB3 levels in normal Tasmanian devils and Tasmanian devils with DFT1. Compared to the baseline serum ERBB3 levels in unaffected Tasmanian devils, Tasmanian devils with DFT1 showed significant elevation of serum ERBB3 levels. Interestingly Tasmanian devils with cutaneous lymphoma (CL) also showed elevation of serum ERBB3 levels when compared to the baseline serum levels of Tasmanian devils without DFT1. Thus, elevated serum ERBB3 levels in otherwise healthy looking devils could predict possible DFT1 or CL in captive or wild devil populations and would have implications on the management, welfare and survival of Tasmanian devils. ERBB3 is also a therapeutic target and therefore the potential exists to consider modes of administration that may eradicate DFT1 from the wild.

Metal ions and carcinogenesis.

Metals are essential for the normal functioning of living organisms. Their uses in biological systems are varied, but are frequently associated with sites of critical protein function, such as zinc finger motifs and electron or oxygen carriers. These functions only require essential metals in minute amounts, hence they are termed trace metals. Other metals are, however, less beneficial, owing to their ability to promote a wide variety of deleterious health effects, including cancer. Metals such as arsenic, for example, can produce a variety of diseases ranging from keratosis of the palms and feet to cancers in multiple target organs. The nature and type of metal-induced pathologies appear to be dependent on the concentration, speciation, and length of exposure. Unfortunately, human contact with metals is an inescapable consequence of human life, with exposures occurring from both occupational and environmental sources. A uniform mechanism of action for all harmful metals is unlikely, if not implausible, given the diverse chemical properties of each metal. In this chapter we will review the mechanisms of carcinogenesis of arsenic, cadmium, chromium, and nickel, the four known carcinogenic metals that are best understood. The key areas of speciation, bioavailability, and mechanisms of action are discussed with particular reference to the role of metals in alteration of gene expression and maintenance of genomic integrity.

Arsenic, mode of action at biologically plausible low doses: what are the implications for low dose cancer risk?

Arsenic is an established human carcinogen. However, there has been much controversy about the shape of the arsenic response curve, particularly at low doses. This controversy has been exacerbated by the fact that the mechanism(s) of arsenic carcinogenesis are still unclear and because there are few satisfactory animal models for arsenic-induced carcinogenesis. Recent epidemiological studies have shown that the relative risk for cancer among populations exposed to 10 microM), As induces down-regulation of DNA repair, oxidative DNA damage and apoptosis. This low dose adaptive (protective) response by a toxic agent is known as hormesis and is characteristic of many agents that induce oxidative stress. A mechanistic model for arsenic carcinogenesis based on these data would predict that the low dose risk for carcinogenesis should be sub-linear. The threshold dose where toxicity outweighs protection is hard to predict based on in vitro dose response data, but might be estimated if one could determine the form (metabolite) and concentration of arsenic responsible for changes in gene regulation in the target tissues.

Comparison of tissue dosimetry in the mouse following chronic exposure to arsenic compounds.

Several chronic bioassays have been conducted in multiple strains of mice in which various concentrations of arsenate or arsenite were administered in the drinking water without a tumorigenic effect. However, one study (Ng et al., 1999) reported a significant increase in tumor incidence in C57Bl/6J mice exposed to arsenic in their drinking water throughout their lifetime, with no tumors reported in controls. A physiologically based pharmacokinetic model for arsenic in the mouse has previously been developed (Gentry et al., 2004) to investigate potential differences in tissue dosimetry of arsenic species across various strains of mice. Initial results indicated no significant differences in blood, liver, or urine dosimetry in B6C3F1 and C57Bl/6 mice for acute or subchronic exposure. The current work was conducted to compare model-predicted estimates of tissue dosimetry to additional kinetic information from the (C57Bl/6 xCBA)F1 and TgAc mouse. The results from the current modeling indicate that the pharmacokinetic parameters derived based on information in the B6C3F1 mouse adequately describe the measured concentrations in the blood/plasma, liver, and urine of both the (C57Bl/6 x CBA)F1 and TgAc mouse, providing further support that the differences in response observed in the chronic bioassays are not related to strain-specific differences in pharmacokinetics. One significant finding was that no increases in skin or lung concentrations of arsenic species in the (C57Bl/6 x CBA)F1 strain were observed following administration of low concentrations (0.2 or 2 mg/U of arsenate in the drinking water, even though differences in response in the skin were reported. These data suggest that pharmacodynamic changes may be observed following exposure to arsenic compounds without an observable change in tissue dosimetry. These results provided further indirect support for the existence of inducible arsenic efflux in these tissues.

Self-reported student confidence in troubleshooting ability increases after completion of an inquiry-based PCR practical.

Inquiry-based learning (IBL) activities are complementary to the processes of laboratory discovery, as both are focused on producing new findings through research and inquiry. Here, we describe the results of student surveys taken pre- and postpractical to an IBL undergraduate practical on PCR. Our analysis focuses primarily student perceptions of knowledge acquisition and their ability to troubleshoot problems. The survey results demonstrate significant self-reported gains in knowledge related to DNA structure and PCR, and an increase in confidence with "troubleshooting problems during scientific experiments." We conclude that the IBL-based approach that combines PCR primer design with wet laboratory experimentation using student-designed primers, provides students a sense of confidence by imparting workplace and research skills that are integral to diverse forms and applications of laboratory practices.

Upregulation of glutathione-related genes and enzyme activities in cultured human cells by sublethal concentrations of inorganic arsenic.

Inorganic arsenic (iAs), a known human carcinogen, acts as a tumor promoter in part by inducing a rapid burst of reactive oxygen species (ROS) in mammalian cells. This causes oxidative stress and a subsequent increase in the level of cellular glutathione (GSH). Glutathione, a ubiquitous reducing sulfhydryl tripeptide, is involved in ROS detoxification and its increase may be part of an adaptive response to the oxidative stress. Glutathione related enzymes including glutathione reductase (GR) and glutathioneS-transferase (GST) also play key roles in these processes. In this study the regulatory effects of inorganic arsenite (As(III)) on the activities of GSH-related enzymes were investigated in cultured human keratinocytes. Substantial increases in GR enzyme activity and mRNA levels were shown in keratinocytes and other human cell lines after exposure to low, subtoxic, micromolar concentrations of As(III) for 24 h. Upregulation of GSH synthesis paralleled the upregulation of GR as shown by increases in glutamate-cysteine lyase (GCL) enzyme activity and mRNA levels, cystine uptake, and intracellular GSH levels. Glutathione S-transferase activity was also shown to increase slightly in keratinocytes, but not in fibroblasts or breast tumor cells. Overall the results show that sublethal arsenic induces a multicomponent response in human keratinocytes that involves upregulation of parts, but not all of the GSH system and counteracts the acute toxic effects of iAs. The upregulation of GR has not previously been shown to be an integral part of this response, although GR is critical for maintaining levels of reduced GSH.

Effect of arsenic on transcription factor AP-1 and NF-kappaB DNA binding activity and related gene expression.

Both acute (24 h) and chronic (10-20 week) exposure of human fibroblast cells to low dose sodium arsenite (As(III)) significantly affects activating protein-1 (AP-1) and nuclear factor kappa B (NF-kappa B) DNA binding activity. Short-term treatment with 0.1-5 microM As(III) up-regulates expression of c-Fos and c-Jun and the redox regulators, thioredoxin (Trx) and Redox factor-1 (Ref-1) and activates both AP-1 and NF-kappa B binding. Chronic exposure to 0.1 or 0.5 microM As(III) decreased c-Jun, c-Fos and Ref-1 protein levels and AP-1 and NF-kappa B binding activity, but increased Trx expression. Short term exposure to phorbol 12-myristate 13-acetate (TPA), a phorbol ester tumour promoter, or hydrogen peroxide (H(2)O(2)) also activates AP-1 and NF-kappa B binding. However, pre-treatment with As(III) prevents this increase. These results suggest that As(III) may alter AP-1 and NF-kappa B activity, in part, by up-regulating Trx and Ref-1. The different effects of short- versus long-term As(III) treatment on acute-phase response to oxidative stress reflect changes in the expression of Ref-1, c-Fos and c-Jun, but not Trx.

Exposure to As(III) and As(V) changes the Ca²âº-activation properties of the two major fibre types from the chelae of the freshwater crustacean Cherax destructor.

Arsenic is a known carcinogen found in the soil in gold mining regions at concentrations thousands of times greater than gold. Mining releases arsenic into the environment and surrounding water bodies. The main chemical forms of arsenic found in the environment are inorganic arsenite (As(III)) and arsenate (As(V)). Yabbies (Cherax destructor) accumulate arsenic at levels comparable to those in the sediment of their environment but the effect on their physiological function is not known. The effects of arsenic exposure (10 ppm sodium arsenite, AsNaO2 - 5.7 ppm As(III)) and 10 ppm arsenic acid, Na2HAsO4·7H2O - 2.6 ppm As(V)) for 40 days on the contractile function of the two major fibre types from the chelae were determined. After exposure, individual fibres were isolated from the chela, "skinned" (membrane removed) and attached to the force recording apparatus. Contraction was induced in solutions containing increasing [Ca(2+)] until a maximum Ca(2+)-activation was obtained. Submaximal force responses were plotted as a percentage of the maximum Ca(2+)-activated force. As(V) exposure resulted in lower levels of calcium required for activation than As(III) indicating an increased sensitivity to Ca(2+) after long term exposure to arsenate compared to arsenite. Myosin heavy chain and tropomyosin content in individual fibres was also decreased as a result of arsenic exposure. Single fibres exposed to As(V) produced significantly more force than muscle fibres from control animals. Long-term exposure of yabbies to arsenic alters the contractile function of the two major fibre types in the chelae.

SIRT1 modulates miRNA processing defects in p53-mutated human keratinocytes.

BACKGROUND: Together with p53, the NAD-dependent lysine deacetylase SIRT1 and the microRNA miR-34a form a feedback loop which self-regulates SIRT1 expression and modulates p53-dependent responses. In addition to its well-described role in mediating transcriptional responses to genotoxic stress, p53 may also regulate microRNA processing and maturation. OBJECTIVE: This study explored the functional relationship among p53, SIRT1 and miR-34a, and the influence of p53 and SIRT1 on microRNA biogenesis and maturation in primary (NHEK) and p53-mutated (HaCaT) keratinocyte cell lines. METHODS: RNAi, miRNA target site blocking oligonucleotides and small molecule inhibitors were used to modulate activity and expression of SIRT1 and p53. Changes in microRNA and mRNA were analysed by qRT-PCR and protein expression was determined by immunoblotting. RESULTS: Mature miR-34a decreased in p53-suppressed NHEK cells, whereas ablation of SIRT1 reduced the primary transcript (pri-miR-34a). When either SIRT1 expression or activity was inhibited in combination with p53 ablation, pri-miR-34a levels increased and mature miR-34a levels decreased. Under these same conditions, additional p53-regulated microRNAs (miRs 16-1/15, 145 and 107) also failed to mature. In HaCaT cells, primary microRNA transcripts for miR-16-1/15, miR-145 miR200c/141 and miRNA-107, but not miR-34a, were approximately 8-fold higher than in NHEK cells. However, the levels of mature microRNA sequences in HaCaT cells were only 1.5-2 fold higher (miR-16-1, miR-145), unchanged (miR-107) or decreased (miR-200c/141, miR-34a) compared to NHEK cells. CONCLUSIONS: Our results suggest that p53 mutations interfere with efficient microRNA biogenesis in keratinocytes, and that SIRT1 functions in combination with p53 in this process.

Modulation of arsenic-induced epidermal growth factor receptor pathway signalling by resveratrol.

Arsenic (As) is both a human carcinogen and an effective anticancer drug. These aspects of arsenic toxicity develop as a consequence of arsenic-induced oxidative stress and modifications to signal pathway activity which alter gene expression. Resveratrol (RVL) a food antioxidant found in grapes and other fruits, exhibits anti-carcinogenic properties by reducing oxidative stress and restoring signal pathway control. This study investigated the impact of RVL on arsenite [As(III)]-induced cell signalling in HaCaT keratinocytes by assaying phosphorylation status of epidermal growth factor receptor (EGFR) signalling intermediates and measuring changes in expression of Phase II and DNA repair biomarkers. As(III) exposure produced dose-dependent toxicity which was associated with increased activation of EGFR pathway intermediates, cSrc, Rac1 and extracellular signal-regulated kinases 1 and 2 (ERK1/2). Arsenic-mediated ERK1/2 activation negatively regulated DNA polymerase beta expression and up regulated heme-oxygenase-1 at toxic concentrations. RVL treatment modulated As(III)-mediated ERK1/2 activation by shifting the balance of cSrc regulatory domain phosphorylation. These effects significantly altered the response of the EGFR pathway to growth factor-induced stimulation. Our research provides evidence that treatment with pharmacologically relevant doses of RVL influences cellular responses to As(III), largely due to RVL-mediated changes to Src and ERK1/2 activation.

Modulation of DNA polymerase beta-dependent base excision repair in cultured human cells after low dose exposure to arsenite.

Base excision repair (BER) is crucial for development and for the repair of endogenous DNA damage. However, unlike nucleotide excision repair, the regulation of BER is not well understood. Arsenic, a well-established human carcinogen, is known to produce oxidative DNA damage, which is repaired primarily by BER, whilst high doses of arsenic can also inhibit DNA repair. However, the mechanism of repair inhibition by arsenic and the steps inhibited are not well defined. To address this question we have investigated the regulation of DNA polymerase beta (Pol beta) and AP endonuclease (APE1), in response to low, physiologically relevant doses of arsenic. GM847 lung fibroblasts and HaCaT keratinocytes were exposed to sodium arsenite, As(III), and mRNA, protein levels and BER activity were assessed. Both Pol beta and APE1 mRNA exhibited significant dose-dependant down regulation at doses of As(III) above 1 microM. However, at lower doses Pol beta mRNA and protein levels, and consequently, BER activity were significantly increased. In contrast, APE1 protein levels were only marginally increased by low doses of As(III) and there was no correlation between APE1 and overall BER activity. Enzyme supplementation of nuclear extracts confirmed that Pol beta was rate limiting. These changes in BER correlated with overall protection against sunlight UV-induced toxicity at low doses of As(III) and produced synergistic toxicity at high doses. The results provide evidence that changes in BER due to low doses of arsenic could contribute to a non-linear, threshold dose response for arsenic carcinogenesis.