Cadmium inhibits human DNA mismatch repair in vivo

A single high-zinc activation enhancer can control two genes oriented head-to-head in Caenorhabditis elegans

Enhancers play critical roles in gene expression, but a full understanding of their complex functions has yet to be defined. The cellular response to excess zinc levels in Caenorhabditis elegans requires the HIZR-1 transcription factor, which binds the high-zinc activation (HZA) enhancer in the promoters of multiple target genes. Cadmium hijacks the excess zinc response by binding and activating HIZR-1. By analyzing the genome-wide transcriptional response to excess zinc and cadmium, we identified two positions in the genome where head-to-head oriented genes are both induced by metals. In both examples, a single predicted HZA enhancer is positioned between the two translational start sites. We hypothesized that a single enhancer can control both head-to-head genes, an arrangement that has not been extensively characterized. To test this hypothesis, we used CRISPR genome editing to precisely delete the HZAmT enhancer positioned between mtl-2 and T08G5.1; in this mutant, both head-to-head genes display severely reduced zinc-activated transcription, whereas zinc-activated transcription of more distant genes was not strongly affected. Deleting the HZAcF enhancer positioned between cdr-1 and F35E8.10 caused both head-to-head genes to display reduced cadmium-activated transcription, whereas cadmium-activated transcription of more distant genes was not strongly affected. These studies rigorously document that a single HZA enhancer can control two head-to-head genes, advancing our understanding of the diverse functions of enhancers.

Environmental Exposures to Metal Toxins as a Risk Factor for Colorectal Cancer: A Case-Control Study

INTRODUCTION

Colorectal cancer (CRC) is the third most common and third most deadly cancer in the United States The role environmental toxins may contribute to CRC incidence is unknown. Cadmium and arsenic are known human carcinogens, although previous data have primarily focused on occupational exposures only. There are no studies on the relationship between environment metal exposures and the incidence of CRC using individual-level measurements from biospecimens.

METHODS

A pilot case-control study was conducted. Urine and blood specimens were collected. Arsenic and cadmium were measured via inductively coupled plasma mass spectrometry. Logistic regression was used to estimate Odds Ratios of CRC incidence and 95% Confidence Intervals (CI) adjusted for age, gender, family history and smoking or urinary cotinine. Each metal was modeled as a binary variable (high versus low) based on the controls' median value or the limit of detection values.

RESULTS

Seventy-nine urine and 84 blood specimens were analyzed. Compared to those with low metal levels, the adjusted odds of incident CRC were 1.77 times higher (95% CI: 0.62-5.00), 1.90 times higher (95% CI: 0.68-5.31), and 1.29 times higher (95% CI:0.45-3.72), for those with higher urinary arsenic, urinary cadmium, and blood arsenic, respectively.

CONCLUSIONS

This is the first study evaluating individual-level measurements of environmental exposures to metal carcinogens and their association with CRC incidence. These pilot results are not statistically significant, although the mildly positive associations may become more profound as recruitment continues. Continued evaluation of environmental toxins and CRC incidence remains warranted.

A single high-zinc activation enhancer can control two genes orientated head-to-head in C. elegans

Enhancers play critical roles in gene expression, but a full understanding of their complex functions has yet to be defined. The cellular response to excess zinc levels in C. elegans requires the HIZR-1 transcription factor, which binds the high-zinc activation (HZA) enhancer in the promoters of multiple target genes. Cadmium hijacks the excess zinc response by binding and activating HIZR-1. By analyzing the genome-wide transcriptional response to excess zinc and cadmium, we identified two positions in the genome where head-to-head oriented genes are both induced by metals. In both examples, a single predicted HZA enhancer is positioned between the two translational start sites. We hypothesized that a single enhancer can control both head-to-head genes, an arrangement that has not been extensively characterized. To test this hypothesis, we used CRISPR genome editing to precisely delete the HZAmT enhancer positioned between mtl-2 and T08G5.1; in this mutant, both head-to-head genes display severely reduced zinc-activated transcription, whereas zinc-activated transcription of more distant genes was not strongly affected. Deleting the HZAcF enhancer positioned between cdr-1 and F35E8.10 caused both head-to-head genes to display reduced cadmium-activated transcription, whereas cadmium-activated transcription of more distant genes was not strongly affected. These studies rigorously document that a single HZA enhancer can control two head-to-head genes, advancing our understanding of the diverse functions of enhancers.

The role of cadmium in the pathogenesis of myeloid leukemia in individuals with anemia, deficiencies in vitamin D, zinc, and low calcium dietary intake

Iron deficiency, vitamin D deficiency and low calcium diet are frequent health problems with severe long- term consequences. Upon absorption from the duodenum, cadmium binds to transferrin, and cells with the highest density of transferrin receptor 1 (TfR1) take up the majority of the circulating cadmium. Nowadays, it is clear that individuals with iron deficiency anemia have increased blood levels of cadmium because of higher absorption rate, mediated by divalent metal transporter 1 (DMT1). However, the transient receptor potential vanilloid receptor 6 (TRPV6), known as a calcium carrier, is able to bind and transport cadmium as well. In the case of low calcium diet or vitamin D deficiency, TRPV6 may be overexpressed in the intestine and kidney tubules and absorbs (re-uptake in the case of renal tubules) cadmium in larger quantities, resulting in an increased cadmium blood levels. We speculate that the final event in the case of low calcium dietary diet and/or vitamin D deficiency is similar to what is observed in the case of iron deficiency, that cells with the highest levels of TfR1 (for example, megakaryocyte/erythrocyte progenitors and pro-erythroblasts) take up most of the circulating cadmium, which is powerful malignancy inductor, leading to appearance of acute myeloid leukemia (AML).

Biological Effects of Human Exposure to Environmental Cadmium

Cadmium (Cd) is a toxic metal for the human organism and for all ecosystems. Cd is naturally found at low levels; however, higher amounts of Cd in the environment result from human activities as it spreads into the air and water in the form of micropollutants as a consequence of industrial processes, pollution, waste incineration, and electronic waste recycling. The human body has a limited ability to respond to Cd exposure since the metal does not undergo metabolic degradation into less toxic species and is only poorly excreted. The extremely long biological half-life of Cd essentially makes it a cumulative toxin; chronic exposure causes harmful effects from the metal stored in the organs. The present paper considers exposure and potential health concerns due to environmental cadmium. Exposure to Cd compounds is primarily associated with an elevated risk of lung, kidney, prostate, and pancreatic cancer. Cd has also been linked to cancers of the breast, urinary system, and bladder. The multiple mechanisms of Cd-induced carcinogenesis include oxidative stress with the inhibition of antioxidant enzymes, the promotion of lipid peroxidation, and interference with DNA repair systems. Cd²⁺ can also replace essential metal ions, including redox-active ones. A total of 12 cancer types associated with specific genes coding for the Cd-metalloproteome were identified in this work. In addition, we summarize the proper treatments of Cd poisoning, based on the use of selected Cd detoxifying agents and chelators, and the potential for preventive approaches to counteract its chronic exposure.

Curative Potential of Substances with Bioactive Properties to Alleviate Cd Toxicity: A Review

Rapid urbanization and industrialization have led to alarming cadmium (Cd) pollution. Cd is a toxic heavy metal without any known physiological function in the organism, leading to severe health threat to the population. Cd has a long half-life (10-30 years) and thus it represents serious concern as it to a great extent accumulates in organs or organelles where it often causes irreversible damage. Moreover, Cd contamination might further lead to certain carcinogenic and non-carcinogenic health risks. Therefore, its negative effect on population health has to be minimalized. As Cd is able to enter the body through the air, water, soil, and food chain one possible way to defend and eliminate Cd toxicities is via dietary supplements that aim to eliminate the adverse effects of Cd to the organism. Naturally occurring bioactive compounds in food or medicinal plants with beneficial, mostly antioxidant, anti-inflammatory, anti-aging, or anti-tumorigenesis impact on the organism, have been described to mitigate the negative effect of various contaminants and pollutants, including Cd. This study summarizes the curative effect of recently studied bioactive substances and mineral elements capable to alleviate the negative impact of Cd on various model systems, supposing that not only the Cd-derived health threat can be reduced, but also prevention and control of Cd toxicity and elimination of Cd contamination can be achieved in the future.

Interaction Between Essential (Zn) and Toxic (Cd) Elements in Different Stages of Female Breast Cancer Patients, Resident in Different Cities of Sindh, Pakistan

Breast cancer is the most familiar solid tumor analyzed in women. Trace elements have critical roles in cancer biology. In this research, the relationship between carcinogenic element, cadmium (Cd), and anti-carcinogenic elements, zinc (Zn), in the scalp hair and blood samples of four stages of female breast cancer patients was studied. We have determined the essential trace (Zn) and toxic (Cd) elements, in biological samples (scalp hair and blood) of female breast cancer (n = 96 age ranging 22-35 years), residents of various cities of Pakistan. For comparative study, the biological samples of age-matched healthy (referent) subjects (n = 115) were also analyzed for selected metals. The validity and accuracy of the methodology were checked by using certified reference materials of biological referent materials (human hair (BCR 397) and ClinCheck lyophilized blood). The mean concentrations of Cd were found to be 3- to fourfold significantly higher in the scalp hair and blood samples of female breast patients as compared to referents, while reverse results were obtained in the case of Zn (p > 0.001). The observed data shows the significant effect of carcinogenic (Cd) and their balance towards the anti-carcinogenic (Zn) in humans.

Cadmium hijacks the high zinc response by binding and activating the HIZR-1 nuclear receptor

Cadmium is an environmental pollutant and significant health hazard that is similar to the physiological metal zinc. In Caenorhabditis elegans, high zinc homeostasis is regulated by the high zinc activated nuclear receptor (HIZR-1) transcription factor. To define relationships between the responses to high zinc and cadmium, we analyzed transcription. Many genes were activated by both high zinc and cadmium, and hizr-1 was necessary for activation of a subset of these genes; in addition, many genes activated by cadmium did not require hizr-1, indicating there are at least two mechanisms of cadmium-regulated transcription. Cadmium directly bound HIZR-1, promoted nuclear accumulation of HIZR-1 in intestinal cells, and activated HIZR-1-mediated transcription via the high zinc activation (HZA) enhancer. Thus, cadmium binding promotes HIZR-1 activity, indicating that cadmium acts as a zinc mimetic to hijack the high zinc response. To elucidate the relationships between high zinc and cadmium detoxification, we analyzed genes that function in three pathways: the pcs-1/phytochelatin pathway strongly promoted cadmium resistance but not high zinc resistance, the hizr-1/HZA pathway strongly promoted high zinc resistance but not cadmium resistance, and the mek-1/sek-1/kinase signaling pathway promoted resistance to high zinc and cadmium. These studies identify resistance pathways that are specific for high zinc and cadmium, as well as a shared pathway.

The role of autophagy in metal-induced urogenital carcinogenesis

Environmental and/or occupational exposure to metals such as Arsenic (As), Cadmium (Cd), and Chromium (Cr) have been shown to induce carcinogenesis in various organs, including the urogenital system. However, the mechanisms responsible for metal-induced carcinogenesis remain elusive. We and others have shown that metals are potent inducers of autophagy, which has been suggested to be an adaptive stress response to allow metal-exposed cells to survive in hostile environments. Albeit few, recent experimental studies have shown that As and Cd promote tumorigenesis via autophagy and that inhibition of autophagic signaling suppressed metal-induced carcinogenesis. In light of the newly emerging role of autophagic involvement in metal-induced carcinogenesis, the present review focuses explicitly on the mechanistic role of autophagy and potential signaling pathways involved in As-, Cd-, and Cr-induced urogenital carcinogenesis.

Chronic Exposure to Cadmium and Antioxidants Does Not Affect the Dynamics of Expanded CAG•CTG Trinucleotide Repeats in a Mouse Cell Culture System of Unstable DNA

More than 30 human disorders are caused by the expansion of simple sequence DNA repeats, among which triplet repeats remain the most frequent. Most trinucleotide repeat expansion disorders affect primarily the nervous system, through mechanisms of neurodysfunction and/or neurodegeneration. While trinucleotide repeat tracts are short and stably transmitted in unaffected individuals, disease-associated expansions are highly dynamic in the germline and in somatic cells, with a tendency toward further expansion. Since longer repeats are associated with increasing disease severity and earlier onset of symptoms, intergenerational repeat size gains account for the phenomenon of anticipation. In turn, higher levels of age-dependent somatic expansion have been linked with increased disease severity and earlier age of onset, implicating somatic instability in the onset and progression of disease symptoms. Hence, tackling the root cause of symptoms through the control of repeat dynamics may provide therapeutic modulation of clinical manifestations. DNA repair pathways have been firmly implicated in the molecular mechanism of repeat length mutation. The demonstration that repeat expansion depends on functional DNA mismatch repair (MMR) proteins, points to MMR as a potential therapeutic target. Similarly, a role of DNA base excision repair (BER) in repeat expansion has also been suggested, particularly during the removal of oxidative lesions. Using a well-characterized mouse cell model system of an unstable CAG•CTG trinucleotide repeat, we tested if expanded repeat tracts can be stabilized by small molecules with reported roles in both pathways: cadmium (an inhibitor of MMR activity) and a variety of antioxidants (capable of neutralizing oxidative species). We found that chronic exposure to sublethal doses of cadmium and antioxidants did not result in significant reduction of the rate of trinucleotide repeat expansion. Surprisingly, manganese yielded a significant stabilization of the triplet repeat tract. We conclude that treatment with cadmium and antioxidants, at doses that do not interfere with cell survival and cell culture dynamics, is not sufficient to modify trinucleotide repeat dynamics in cell culture.

Activation of the Erk/MAPK signaling pathway is a driver for cadmium induced prostate cancer

PURPOSE

Cadmium (Cd) is reported to be associated with carcinogenesis. The molecular mechanisms associated with Cd-induced prostate cancer (PCa) remain elusive.

MATERIALS AND METHODS

RWPE1, PWR1E and DU 145 cells were used. RT2 Profiler Array, real-time-quantitative-PCR, immunofluorescence, cell cycle, apoptosis, proliferation and colony formation assays along with Gene Set Enrichment Analysis (GSEA) were performed.

RESULT

Chronic Cd exposure of non-malignant RWPE1 and PWR1E cells promoted cell survival, proliferation and colony formation with inhibition of apoptosis. Even a two-week Cd exposure of PCa cell line (DU 145) significantly increased the proliferation and decreased apoptosis. RT2 profiler array of 84 genes involved in the Erk/MAPK pathway revealed induction of gene expression in Cd-RWPE1 cells compared to RWPE1. This was confirmed by individual TaqMan gene expression analysis in both Cd-RWPE1 and Cd-PWR1E cell lines. GSEA showed an enrichment of the Erk/MAPK pathway along with other pathways such as KEGG-ERBB, KEGG-Cell Cycle, KEGG-VEGF, KEGG-Pathways in cancer and KEGG-prostate cancer pathway. We randomly selected upregulated genes from Erk/MAPK pathway and performed profile analysis in a PCa data set from the TCGA/GDC data base. We observed upregulation of these genes in PCa compared to normal samples. An increase in phosphorylation of the Erk1/2 and Mek1/2 was observed in Cd-RWPE1 and Cd-PWR1E cells compared to parental cells, confirming that Cd-exposure induces activation of the Erk/MAPK pathway.

CONCLUSION

This study demonstrates that Erk/MAPK signaling is a major pathway involved in Cd-induced malignant transformation of normal prostate cells. Understanding these dominant oncogenic pathways may help develop optimal therapeutic strategies for PCa.

Levels of a mixture of heavy metals in blood and urine and all-cause, cardiovascular disease and cancer mortality: A population-based cohort study

People are exposed to heavy metals in many ways during the course of their daily life. However, the effect of mixtures of heavy metals on mortality in the U.S. general population is unclear. We aimed to investigate the association between heavy metal concentrations (blood [lead, cadmium and mercury] and urine [barium, cadmium, cobalt, cesium, molybdenum, lead, antimony, titanium, tungsten and uranium]) and all-cause, cardiovascular disease (CVD) and cancer mortality. Data were obtained from the National Health and Nutrition Examination Survey (NHANES) 1999-2014. Poisson regression was performed to analyze the associations between single-metal and multimetal exposure and mortality. The following variables were adjusted as covariates: demographic variables (age, education, sex and ethnicity), anthropometric variables (body mass index), lifestyle variables (family income, serum cotinine category and physical activity) and medical comorbidities (CVD and diabetes). A total of 26,056 subjects from the NHANES were included in the present study (mean follow-up, 7.4 years). The age of the participants ranged from 20 to 85 years. The blood metal mixture was associated with all-cause mortality (RR = 1.38, 95% CI 1.25, 1.51), CVD mortality (RR = 1.43, 95% CI 1.06, 1.94) and cancer mortality (RR = 1.41, 95% CI 1.12, 1.76) and cadmium had the highest weight in the weighted quantile sum (WQS) regression for all associations. The urinary metal mixture was associated with an increased risk of all-cause (RR = 1.48, 95% CI 1.30, 1.68) and cancer mortality (RR = 1.60, 95% CI 1.02, 2.52). Sex differences were found in the associations of both blood and urine metal mixtures with cancer mortality. Our study suggests a potential positive association for the concentrations of heavy metal mixtures with overall, CVD and cancer mortality based on a large sample of the U.S. general population. Nevertheless, further studies are needed to confirm these important findings.

Relationship between urinary β2 -microglobulin concentration and mortality in a cadmium-polluted area in Japan: A 35-year follow-up study

The relationship between urinary β₂ -microglobulin (β₂ -MG) and the risk of all-cause mortality and cause-specific mortality in a cadmium (Cd)-polluted area was investigated in 3139 inhabitants (1404 men and 1735 women) of the Kakehashi River basin in Japan at 35-year follow-up. The subjects had been participants in the 1981-1982 health impact survey that assessed Cd-induced renal dysfunction, as measured by the urinary β₂ -MG concentration. Hazard ratios were calculated to assess the risk of all-cause and cause-specific mortality according to the urinary β₂ -MG concentrations. Risk ratios (RRs) were assessed using the Fine and Gray regression model to account for competing risks of cause-specific mortality. The mortality rate was significantly higher in participants with urinary β₂ -MG concentrations >1000 μg/g creatinine (Cr) for men and >300 μg/g Cr for women. In the proportional hazard model, higher urinary β₂ -MG concentrations were associated with higher risks of circulatory disease, digestive system diseases, and kidney and urinary tract diseases in men and women, and with senility for women. However, when competing risk was accounted for, the RRs were significantly higher only for kidney and urinary tract diseases in men and women (RR for each increment of 1000 μg/g Cr [95% confidence interval]: 1.02 [1.00-1.04] for men, and 1.01 [1.00-1.02] for women). The long-term prognosis of participants with renal tubular dysfunction was poor, most likely due to kidney and renal tract diseases.

The Metallome of Lung Cancer and its Potential Use as Biomarker

Carcinogenesis is a very complex process in which metals have been found to be critically involved. In this sense, a disturbed redox status and metal dyshomeostasis take place during the onset and progression of cancer, and it is well-known that trace elements participate in the activation or inhibition of enzymatic reactions and metalloproteins, in which they usually participate as cofactors. Until now, the role of metals in cancer have been studied as an effect, establishing that cancer onset and progression affects the disturbance of the natural chemical form of the essential elements in the metabolism. However, it has also been studied as a cause, giving insights related to the high exposure of metals giving a place to the carcinogenic process. On the other hand, the chemical species of the metal or metallobiomolecule is very important, since it finally affects the biological activity or the toxicological potential of the element and their mobility across different biological compartments. Moreover, the importance of metal homeostasis and metals interactions in biology has also been demonstrated, and the ratios between some elements were found to be different in cancer patients; however, the interplay of elements is rarely reported. This review focuses on the critical role of metals in lung cancer, which is one of the most insidious forms of cancer, with special attention to the analytical approaches and pitfalls to extract metals and their species from tissues and biofluids, determining the ratios of metals, obtaining classification profiles, and finally defining the metallome of lung cancer.

The crosstalk between trace elements with DNA damage response, repair, and oxidative stress in cancer

DNA damage response (DDR) is a regulatory system responsible for maintaining genome integrity and stability, which can sense and transduce DNA damage signals. The severity of damage appears to determine DDRs, which can include damage repair, cell-cycle arrest, and apoptosis. Furthermore, defective components in DNA damage and repair machinery are an underlying cause for the development and progression of various types of cancers. Increasing evidence indicates that there is an association between trace elements and DDR/repair mechanisms. In fact, trace elements seem to affect mediators of DDR. Besides, it has been revealed that oxidative stress (OS) and trace elements are associated with cancer development. In this review, we discuss the role of some critical trace elements in the risk of cancer. In addition, we provide a brief introduction on DDR and OS in cancer. Finally, we will further review the interactions between some important trace elements including selenium, zinc, chromium, cadmium, and arsenic, and DDR, and OS in cancer.

The mutagen and carcinogen cadmium is a high-affinity inhibitor of the zinc-dependent MutLα endonuclease

MutLα (MLH1-PMS2 heterodimer) is an endonuclease that acts during an early step of eukaryotic mismatch repair. We show that human MutLα endonuclease copurifies with two equivalents of bound zinc, at least one of which resides within the endonuclease active site. We also show that cadmium, a known inhibitor of zinc-dependent enzymes and a potent mutagen and carcinogen, is a high-affinity inhibitor of MutLα endonuclease and that exogenous MutLα significantly reverses the mismatch repair defect in cadmium-treated human cell nuclear extract or nuclear extract prepared from cadmium-treated cells. Because the mutagenic action of cadmium is largely due to the selective inhibition of mismatch repair, these findings suggest that MutLα is a primary cadmium target for mutagenesis and presumably, carcinogenesis as well.

MutLα (MLH1-PMS2 heterodimer), which acts as a strand-directed endonuclease during the initiation of eukaryotic mismatch repair, has been postulated to function as a zinc-dependent enzyme [Kosinski J, Plotz G, Guarné A, Bujnicki JM, Friedhoff P (2008) J Mol Biol 382:610–627]. We show that human MutLα copurifies with two bound zinc ions, at least one of which resides within the endonuclease active site, and that bound zinc is required for endonuclease function. Mutagenic action of the carcinogen cadmium, a known inhibitor of zinc-dependent enzymes, is largely due to selective inhibition of mismatch repair [Jin YH, et al. (2003) Nat Genet 34:326–329]. We show that cadmium is a potent inhibitor (apparent K_i ∼ 200 nM) of MutLα endonuclease and that cadmium inhibition is reversed by zinc. We also show that inhibition of mismatch repair in cadmium-treated nuclear extract is significantly reversed by exogenous MutLα but not by MutSα (MSH2-MSH6 heterodimer) and that MutLα reversal depends on integrity of the endonuclease active site. Exogenous MutLα also partially rescues the mismatch repair defect in nuclear extract prepared from cells exposed to cadmium. These findings indicate that targeted inhibition of MutLα endonuclease contributes to cadmium inhibition of mismatch repair. This effect may play a role in the mechanism of cadmium carcinogenesis.

A Node-Expressed Transporter OsCCX2 Is Involved in Grain Cadmium Accumulation of Rice

Excessive cadmium (Cd) accumulation in grains of rice (Oryza sativa L.) is a risk to food security. The transporters in the nodes of rice are involved in the distribution of mineral elements including toxic elements to different tissues such as grains. However, the mechanism of Cd accumulation in grains is largely unknown. Here, we report a node-expressed transporter gene, OsCCX2, a putative cation/calcium (Ca) exchanger, mediating Cd accumulation in the grains of rice. Knockout of OsCCX2 caused a remarkable reduction of Cd content in the grains. Further study showed that disruption of this gene led to a reduced root-to-shoot translocation ratio of Cd. Moreover, Cd distribution was also disturbed in different levels of internode and leaf. OsCCX2 is localized to plasma membrane, and OsCCX2 is mainly expressed in xylem region of vascular tissues at the nodes. OsCCX2 might function as an efflux transporter, responsible for Cd loading into xylem vessels. Therefore, our finding revealed a novel Cd transporter involved in grain Cd accumulation, possibly via a Ca transport pathway in the nodes of rice.

Metal dyshomeostasis based biomarkers of lung cancer using human biofluids

Metals, ratios, interactions and species in serum, urine and bronchoalveolar lavage fluid as biomarkers of lung cancer.

Acquired temozolomide resistance in human glioblastoma cell line U251 is caused by mismatch repair deficiency and can be overcome by lomustine

PURPOSE

Glioblastoma multiforme (GBM) is the most common malignant primary brain tumor in adults. While the alkylating agent temozolomide (TMZ) has prolonged overall survival, resistance evolution represents an important clinical problem. Therefore, we studied the effectiveness of radiotherapy and CCNU in an in vitro model of acquired TMZ resistance.

METHODS

We studied the MGMT-methylated GBM cell line U251 and its in vitro derived TMZ-resistant subline, U251/TMZ-R. Cytotoxicity of TMZ, CCNU, and radiation was tested. Both cell lines were analyzed for MGMT promotor status and expression of mismatch repair genes (MMR). The influence of MMR inhibition by cadmium chloride (CdCl₂) on the effects of both drugs was evaluated.

RESULTS

During the resistance evolution process in vitro, U251/TMZ-R developed MMR deficiency, but MGMT status did not change. U251/TMZ-R cells were more resistant to TMZ than parental U251 cells (cell viability: 92.0% in U251/TMZ-R/69.2% in U251; p = 0.032) yet more sensitive to CCNU (56.4%/80.8%; p = 0.023). The effectiveness of radiotherapy was not reduced in the TMZ-resistant cell line. Combination of CCNU and TMZ showed promising results for both cell lines and overcame resistance. CdCl₂-induced MMR deficiency increased cytotoxicity of CCNU.

CONCLUSION

Our results confirm MMR deficiency as a crucial process for resistance evolution to TMZ. MMR-deficient TMZ-resistant GBM cells were particularly sensitive to CCNU and to combined CCNU/TMZ. Effectiveness of radiotherapy was preserved in TMZ-resistant cells. Consequently, CCNU might be preferentially considered as a treatment option for recurrent MGMT-methylated GBM and may even be suitable for prevention of resistance evolution in primary treatment.

Subcellular distribution and cellular self-repair ability of fluorescent quantum dots emitting in the visible to near-infrared region

Semiconductor II-VI quantum dots (QDs), as high-performance fluorescent biological probes, have garnered significant attention due to their superior optical properties. To enable QDs for wide-ranging bioapplications, concerns about their in vitro behavior need to be fully addressed. Herein, for the first time, cellular behaviors of aqueous synthesized-QDs (aqQDs), whose maximum emission wavelength (λ _emission) covers the visible to near-infrared spectral window, are systematically investigated. Our results demonstrate that three different sized aqQDs feature distinct cellular distributions, i.e. aqQD530 (aqQDs whose λ _emission is 530 nm) and aqQD620 (aqQDs whose λ _emission is 620 nm) mainly distribute in the cytoplasm and nucleus, while aqQD730 (aqQDs whose λ _emission is 730 nm) mainly accumulates in the cytoplasm. Most significantly, the phenomenon that cellular self-repair ability is dependent on diameters of aqQDs is revealed for the first time. In particular, small-sized QDs (e.g. aqQD530 and aqQD620) severely deteriorate cellular self-repair ability, leading to an irreversible decrease in cell viability. In striking contrast, large-sized QDs (e.g. aqQD730) have little effect on cellular self-repair ability, and the cell viability is restored after removal of aqQD730 from the culture medium. Our results provide invaluable information for QD-relevant biosafety analysis, as well as suggest available guidance for the design of biocompatible QDs for wide utilization in biological and biomedical studies.

Cadmium pollution and amphibians--Studies in tadpoles of Rana limnocharis

Cadmium is released into the environment in increasing amounts from different natural and anthropogenic activities contaminating the aquatic habitats. Amphibian tadpoles develop in water and hence are likely to be adversely affected by cadmium present in the aquatic environment. We have studied the toxic and genotoxic effects of CdCl2 on the tadpoles of Rana limnocharis. CdCl2 in the concentration range between 0.1 and 0.4 mg/L induced significant mortality in R. limnocharis tadpoles in a dose and time dependent manner. The 10-day LC50 which has more ecological relevance was far less than the 24-h LC50. Tadpoles exposed to CdCl2 metamorphosed at an early age possibly as a survival strategy to move out of the stressful environment. The body weight of the CdCl2 exposed animals at metamorphosis was lower compared to the control individuals which may affect survival and reproductive fitness in adult life. Besides, the average body length of the metamorphosed individuals in the CdCl2 exposed group was higher than the control group. CdCl2 was found to be genotoxic in micronucleus test and comet assay. The ambient concentration of Cd could reach up to 60 μg/L or more. Exposure to 18.5 μg/L of CdCl2 (1% of 24-h LC50) induced significant increase in DNA strand breaks as compared to the control. The present findings demonstrate that presence of cadmium in the aquatic environment can significantly alter the life history traits and cause DNA damage in amphibians and hence, could contribute towards their population decline.

Association Between Cd Exposure and Risk of Prostate Cancer: A PRISMA-Compliant Systematic Review and Meta-Analysis

Several observational studies on the association between Cd exposure and risk of prostate cancer have yielded inconsistent results. To address this issue, we conducted a meta-analysis to evaluate the correlation between Cd exposure and risk of prostate cancer.Relevant studies in PubMed and Embase databases were retrieved until October 2015. We compared the highest and lowest meta-analyses to quantitatively evaluate the relationship between Cd exposure and risk of prostate cancer. Summary estimates were obtained using a random-effects model.In the general population, high Cd exposure was not associated with increased prostate cancer (OR 1.21; 95% CI 0.91-1.64), whereas the combined standardized mortality ratio of the association between Cd exposure and risk of prostate cancer was 1.66 (95% CI 1.10-2.50) in populations exposed to occupational Cd. In addition, high D-Cd intake (OR 1.07; 95% CI 0.96-1.20) and U-Cd concentration (OR 0.86; 95% CI 0.48-1.55) among the general population was not related to the increased risk of prostate cancer. In the dose analysis, the summary relative risk was 1.07 (95% CI 0.73-1.57) for each 0.5 μg/g creatinine increase in U-Cd and 1.02 (95% CI 0.99-1.06) for each 10 μg/day increase of dietary Cd intake. However, compared with nonoccupational exposure, high occupational Cd exposure may be associated with the increased risk of prostate cancer.This meta-analysis suggests high Cd exposure as a risk factor for prostate cancer in occupational rather than nonoccupational populations. However, these results should be carefully interpreted because of the significant heterogeneity among studies. Additional large-scale and high-quality prospective studies are needed to confirm the association between Cd exposure and risk of prostate cancer.

In vivo DNA mismatch repair measurement in zebrafish embryos and its use in screening of environmental carcinogens

Impairment of DNA mismatch repair (MMR) function leads to the development and progression of certain cancers. Many environmental contaminants can target DNA MMR system. Currently, measurement of MMR activity is limited to in vitro or in vivo methods at the cell line level, and reports on measurement of MMR activity at the live organism level are lacking. Here, we report an efficient method to measure DNA MMR activity in zebrafish embryos. A G-T mismatch was introduced into enhanced green fluorescent protein (EGFP) gene. Repair of the G-T mismatch to G-C in the heteroduplex plasmid generates a functional EGFP expression. The heteroduplex plasmid and a similarly constructed homoduplex plasmid were injected in parallel into the same batch of embryos at 1-cell stage and EGFP expression in EGFP positive embryos was quantified at 24 h after injection. MMR efficiency was calculated as the total fluorescence intensity of embryos injected with the heteroduplex construct divided by that of embryos injected with the homoduplex construct. Our results showed 73% reduction of MMR activity in embryos derived from MMR-deficient mlh1 mutant fish (positive control) when compared with embryos from MMR-competent wild type AB line fish, indicating feasibility of in vivo MMR activity measurement in zebrafish embryos. We further applied this novel assay for measurement of MMR efficiency in embryos exposed to environmental chemicals such as cadmium chloride (CdCl2), benzo[a]pyrene (BaP), and perfluorooctanesulphonic acid (PFOS) from 6 hpf to 24 hpf. We observed significant reductions of MMR efficiency in embryos exposed to 0.1 μM CdCl2 (52%) and 0.5 μM BaP (34%), but no effect in embryos exposed to PFOS. Our study for the first time provides a model system for in vivo measurement of DNA MMR activity at the organism level, which has important implications in risk assessment of various environmental carcinogens.

Urinary cadmium concentration and risk of breast cancer: a systematic review and dose-response meta-analysis

Cadmium is a toxic and persistent heavy metal with estrogenic activities. We conducted a systematic review and meta-analysis of cohort, case-control, and cross-sectional studies of the association between urinary cadmium concentration, a biomarker of cadmium exposure, and breast cancer risk. Studies were identified by searching PubMed and Embase (to March 15, 2015) and by reviewing the reference lists of pertinent articles. Study-specific risk estimates were combined by using a random-effects model. We identified 2 cohort studies (with 67 breast cancer deaths) and 5 case-control studies and 1 cross-sectional study (with 1,416 cases and 5,083 controls) on urinary cadmium concentration in relation to breast cancer risk. The studies were published during the past 10 years (2006-2015). There was no consistent association between urinary cadmium and breast cancer mortality in the cohort studies. In case-control and cross-sectional studies, the pooled odds ratios were 2.24 (95% confidence interval: 1.50, 3.34; I(2) = 63.4%) for the highest versus lowest category of cadmium concentration and 1.66 (95% confidence interval: 1.23, 2.25) for each 0.5-µg/g creatinine increase of cadmium concentration. This meta-analysis suggests that a high cadmium exposure may be a risk factor for breast cancer, but large prospective studies are needed to confirm this finding.

Inhibition of cadmium- induced genotoxicity and histopathological changes in Nile tilapia fish by Egyptian and Tunisian montmorillonite clay

Cadmium (Cd) is an important inorganic toxicant widely distributed in the environment because of its various industrial uses. The aims of the current study were to investigate the efficacy of purified Egyptian and Tunisian montmorillonite clays (EMC and TMC) to inhibit genotoxicity and histological alterations induced by cadmium chloride (CdCl2) utilizing the Nile tilapia fish as an in vivo model. Chromosomal aberrations (CAs), micronucleus (MN) frequencies and DNA fingerprinting profile were genotoxic end points and histopathological changes that were used in this investigation. Six groups of fish were treated for 2 weeks and included control group, CdCl2-treated group and groups treated with EMC or TMC alone or in combination with CdCl2. The present results revealed that, treatment of fish with CdCl2 exhibited significant increased in the number of micronucleated erythrocytes (MnRBCs), frequency of CAs and instability of genomic DNA. Treatment of EMC and TMC in combination with CdCl2 significantly reduced the frequency of MnRBCs by the percentage of 53.28% and 60.77% and the frequency of CAs by 43.91% and 52.17% respectively. As well as, normalized DNA fingerprinting profile and significantly improved histopathological picture induced by Cadmium treatment. It is worth mention that both clays have the ability to tightly bind CdCl2 and decreased its cytotoxicity and genotoxicity; however, Tunisian clay was more efficient in binding with the CdCl2 than Egyptian clay.

Urinary cadmium and mortality from all causes, cancer and cardiovascular disease in the general population: systematic review and meta-analysis of cohort studies

BACKGROUND

Cadmium is a toxic heavy metal distributed in the environment. We conducted a systematic review and meta-analysis to examine the association between urinary cadmium concentration and mortality from all causes, cancer and cardiovascular disease (CVD) in the general population.

METHODS

Studies were identified by searching PubMed and Embase (to 30 March 2015) and the reference lists of retrieved articles. We included prospective studies that reported hazard ratios (HR) with 95% confidence intervals (CI) for the association between urinary cadmium concentration and all-cause, cancer or CVD mortality. A random-effects model was used to combine study-specific results.

RESULTS

Nine cohort studies, including 5600 deaths from all causes, 1332 deaths from cancer and 1715 deaths from CVD, were eligible for inclusion in the meta-analysis. The overall HRs for the highest vs lowest category of urinary cadmium were1.44 (95% CI, 1.25-1.64; I(2 )= 40.5%) for all-cause mortality (six studies), 1.39 (95% CI, 0.96-1.99; I(2 )= 75.9%) for cancer mortality (four studies) and 1.57 (95% CI, 1.27-1.95; I(2 )= 34.0%) for CVD mortality (five studies). In an analysis restricted to six cohort studies conducted in populations with a mean urinary cadmium concentration of ≤1 µg/g creatinine, the HRs were 1.38 (95% CI, 1.17-1.63; I(2 )= 48.3%) for all-cause mortality, 1.56 (95% CI, 0.98-2.47; I(2 )= 81.0%) for cancer mortality and 1.50 (95% CI, 1.18-1.91; I(2 )= 38.2%) for CVD mortality.

CONCLUSIONS

Even at low-level exposure, cadmium appears to be associated with increased mortality. Further large prospective studies of cadmium exposure and mortality are warranted.

Reconfiguration of DNA methylation in aging

A complex interplay between multiple biological effects shapes the aging process. The advent of genome-wide quantitative approaches in the epigenetic field has highlighted the effective impact of epigenetic deregulation, particularly of DNA methylation, on aging. Age-associated alterations in DNA methylation are commonly grouped in the phenomenon known as "epigenetic drift" which is characterized by gradual extensive demethylation of genome and hypermethylation of a number of promoter-associated CpG islands. Surprisingly, specific DNA regions show directional epigenetic changes in aged individuals suggesting the importance of these events for the aging process. However, the epigenetic information obtained until now in aging needs a re-consideration due to the recent discovery of 5-hydroxymethylcytosine, a new DNA epigenetic mark present on genome. A recapitulation of the factors involved in the regulation of DNA methylation and the changes occurring in aging will be described in this review also considering the data available on 5 hmC.

Genoprotectivity of methanol and ethanol extracted leaf sap of Trigonella foenum-graecum in Allium cepa root assay

Fenugreek (Trigonella foenum-graecum) of Fabacecae family is widely distributed throughout the world and used as an old medicinal plant and traditional food. The present study deals with the investigation of the anti-genotoxic potential of methanol (MTG) and ethanol (ETG) extracted leaf sap of fenugreek on Allium cepa root tip cells, which were treated with cadmium sulfate (CdSO(4)). Three types of treatments were applied. First, roots were treated with different concentrations of methanolic and ethanolic extracts (0.1%, 0.5% and 1%) separately for 3 h each, followed by CdSO(4) treatment (at 250 ppm, for 3 h). Second, roots were first treated with CdSO(4) followed by extracts treatment. Third, root tips were treated with CdSO(4) with extracts treatments at the same time. For controls, roots with CdSO(4) (250 ppm) and distilled water served as positive and negative control, respectively. The results showed that the methanol and ethanol extracts of fenugreek modulated the genotoxic and clastogenic aberrations, which were induced by CdSO(4). The protection activity of MTG (1%) was 50% in the first treatment, 70% in the second treatment and 82% in the third treatment and 61%, 68% and 88% of ETG (1%), respectively. DNA rearrangements were also observed by revealing new RAPD bands in the total DNS samples isolated from Allium roots after treatmenst.

Physicochemical and in vitro biocompatibility evaluation of water-soluble CdSe/ZnS core/shell

Group II-VI semiconductor quantum dots (Q-dots) have found various applications in biomedical field during last decade. In this study, we have synthesized CdSe Q-dots and CdSe/ZnS core/shell (CS) by wet chemical route and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FT-IR) and Photoluminescence (PL) spectroscopy. CS formation was confirmed by red shift as well as enhancement in the luminescence peak compared to bare Q-dots. Processing parameters such as core and sulfur concentrations were optimized at maximum luminescence efficiency during the shell preparation. Effects of dialysis, aging and cell culture medium on the properties of the Q-dots and CS were also studied by luminescence and DLS techniques. DLS data showed Q-dots and CS to be stable, and there was no effect on the integrity of the Q-dots and CS after various modifications. CS was found to be hemocompatible and cytocompatible for human umbilical vein endothelial cells even at a high concentration of 0.1 mg/ml up to 48 h indicating high potential for CS in various biomedical applications.

Mechanisms of cadmium induced genomic instability

Cadmium is an ubiquitous environmental contaminant that represents hazard to humans and wildlife. It is found in the air, soil and water and, due to its extremely long half-life, accumulates in plants and animals. The main source of cadmium exposure for non-smoking human population is food. Cadmium is primarily toxic to the kidney, but has been also classified as carcinogenic to humans by several regulatory agencies. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Cadmium dose not induce direct DNA damage, however it induces increase in reactive oxygen species (ROS) formation, which in turn induce DNA damage and can also interfere with cell signalling. More important seems to be cadmium interaction with DNA repair mechanisms, cell cycle checkpoints and apoptosis as well as with epigenetic mechanisms of gene expression control. Cadmium mediated inhibition of DNA repair mechanisms and apoptosis leads to accumulation of cells with unrepaired DNA damage, which in turn increases the mutation rate and thus genomic instability. This increases the probability of developing not only cancer but also other diseases associated with genomic instability. In the in vitro experiments cadmium induced effects leading to genomic instability have been observed at low concentrations that were comparable to those observed in target organs and tissues of humans that were non-occupationally exposed to cadmium. Therefore, further studies aiming to clarify the relevance of these observations for human health risks due to cadmium exposure are needed.

A PLAC8-containing protein from an endomycorrhizal fungus confers cadmium resistance to yeast cells by interacting with Mlh3p

Cadmium is a genotoxic pollutant known to target proteins that are involved in DNA repair and in antioxidant defence, altering their functions and ultimately causing mutagenic and carcinogenic effects. We have identified a PLAC8 domain-containing protein, named OmFCR, by a yeast functional screen aimed at identifying genes involved in cadmium resistance in the endomycorrhizal fungus Oidiodendron maius. OmFCR shows a remarkable specificity in mediating cadmium resistance. Both its function and its nuclear localization in yeast strictly depend on the interaction with Mlh3p, a subunit of the mismatch repair (MMR) system. Although proteins belonging to the PLAC8 family are widespread in eukaryotes, they are poorly characterized and their biological role still remains elusive. Our work represents the first report about the potential role of a PLAC8 protein in physically coupling DNA lesion recognition by the MMR system to appropriate effectors that affect cell cycle checkpoint pathways. On the basis of cell survival assays and yeast growth curves, we hypothesize that, upon cadmium exposure, OmFCR might promote a higher rate of cell division as compared to control cells.

Mechanisms in cadmium-induced carcinogenicity: recent insights

Cadmium is an environmental pollutant,with relevant exposures at workplaces and in the general population. The carcinogenicity has been long established, most evident for tumors in the lung and kidney, but with increasing evidence also for other tumor locations. While direct interactions with DNA appear to be of minor importance, the interference with the cellular response to DNA damage, the deregulation of cell growth as well as resistance to apoptosis have been demonstrated in diverse experimental systems. With respect to DNA repair processes,cadmium has been shown to disturb nucleotide excision repair, base excision repair and mismatch repair; consequences are increased susceptibility towards other DNA damaging agents and endogenous mutagens. Furthermore, cadmium induces cell proliferation, inactivates negative growth stimuli, such as the tumor suppressor protein p53, and provokes resistance towards apoptosis. Particularly the combination of these multiple mechanisms may give rise to a high degree of genomic instability in cadmium-adapted cells, relevant not only for tumor initiation, but also for later steps in tumor development. Future research needs to clarify the relevance of these interactions for low exposure conditions in humans.

Environmental cadmium and breast cancer risk

Breast cancer is the most prevalent women's cancer, with an age-adjusted incidence of 122.9 per 100,000 US women. Cadmium, a ubiquitous carcinogenic pollutant with multiple biological effects, has been reported to be associated with breast cancer in one US regional case-control study. We examined the association of breast cancer with urinary cadmium (UCd), in a case-control sample of women living on Long Island (LI), NY (100 with breast cancer and 98 without), a region with an especially high rate of breast cancer (142.7 per 100,000 in Suffolk County) and in a representative sample of US women (NHANES 1999-2008, 92 with breast cancer and 2,884 without). In a multivariable logistic model, both samples showed a significant trend for increased odds of breast cancer across increasing UCd quartiles (NHANES, p=0.039 and LI, p=0.023). Compared to those in the lowest quartile, LI women in the highest quartile had increased risk for breast cancer (OR=2.69; 95% CI=1.07, 6.78) and US women in the two highest quartiles had increased risk (OR=2.50; 95% CI=1.11, 5.63 and OR=2.22; 95% CI=.89, 5.52, respectively). Further research is warranted on the impact of environmental cadmium on breast cancer risk in specific populations and on identifying the underlying molecular mechanisms.

Bi-directional routing of DNA mismatch repair protein human exonuclease 1 to replication foci and DNA double strand breaks

Human exonuclease 1 (hEXO1) is implicated in DNA metabolism, including replication, recombination and repair, substantiated by its interactions with PCNA, DNA helicases BLM and WRN, and several DNA mismatch repair (MMR) proteins. We investigated the sub-nuclear localization of hEXO1 during S-phase progression and in response to laser-induced DNA double strand breaks (DSBs). We show that hEXO1 and PCNA co-localize in replication foci. This apparent interaction is sustained throughout S-phase. We also demonstrate that hEXO1 is rapidly recruited to DNA DSBs. We have identified a PCNA interacting protein (PIP-box) region on hEXO1 located in its COOH-terminal ((788)QIKLNELW(795)). This motif is essential for PCNA binding and co-localization during S-phase. Recruitment of hEXO1 to DNA DSB sites is dependent on the MMR protein hMLH1. We show that two distinct hMLH1 interaction regions of hEXO1 (residues 390-490 and 787-846) are required to direct the protein to the DNA damage site. Our results reveal that protein domains in hEXO1 in conjunction with specific protein interactions control bi-directional routing of hEXO1 between on-going DNA replication and repair processes in living cells.

Characterization of a highly conserved binding site of Mlh1 required for exonuclease I-dependent mismatch repair

Mlh1 is an essential factor of mismatch repair (MMR) and meiotic recombination. It interacts through its C-terminal region with MutL homologs and proteins involved in DNA repair and replication. In this study, we identified the site of yeast Mlh1 critical for the interaction with Exo1, Ntg2, and Sgs1 proteins, designated as site S2 by reference to the Mlh1/Pms1 heterodimerization site S1. We show that site S2 is also involved in the interaction between human MLH1 and EXO1 or BLM. Binding at this site involves a common motif on Mlh1 partners that we called the MIP-box for the Mlh1 interacting protein box. Direct and specific interactions between yeast Mlh1 and peptides derived from Exo1, Ntg2, and Sgs1 and between human MLH1 and peptide derived from EXO1 and BLM were measured with K(d) values ranging from 8.1 to 17.4 microM. In Saccharomyces cerevisiae, a mutant of Mlh1 targeted at site S2 (Mlh1-E682A) behaves as a hypomorphic form of Exo1. The site S2 in Mlh1 mediates Exo1 recruitment in order to optimize MMR-dependent mutation avoidance. Given the conservation of Mlh1 and Exo1 interaction, it may readily impact Mlh1-dependent functions such as cancer prevention in higher eukaryotes.

Biomonitoring of human exposure to prestige oil: effects on DNA and endocrine parameters

Since 1960, about 400 tankers spilled more than 377765 tons of oil, with the Prestige accident (Galician coast, NW Spain, November 2002) the most recent. Taking into account the consistent large number of individuals exposed to oil that exists all over the world, it seems surprising the absence in the literature of studies focused on the chronic effects of this exposure on human health. In this work we evaluated the level of DNA damage by means of comet assay, and the potential endocrine alterations (prolactin and cortisol) caused by Prestige oil exposure in a population of 180 individuals, classified in 3 groups according to the tasks performed, and 60 controls. Heavy metals in blood were determined as exposure biomarkers, obtaining significant increases of aluminum, nickel and lead in the exposed groups as compared to controls. Higher levels of genetic damage and endocrine alterations were also observed in the exposed population. DNA damage levels were influenced by age, sex, and the use of protective clothes, and prolactin concentrations by the last two factors. Surprisingly, the use of mask did not seem to protect individuals from genetic or endocrine alterations. Moreover, polymorphisms in genes encoding for the main enzymes involved in the metabolism of oil components were analyzed as susceptibility biomarkers. CYP1A1-3'UTR and EPHX1 codons 113 and 139 variant alleles were related to higher damage levels, while lower DNA damage was observed in GSTM1 and GSTT1 null individuals.

Carmustine-resistant cancer cells are sensitized to temozolomide as a result of enhanced mismatch repair during the development of carmustine resistance

The cytotoxicity of the monofunctional alkylator temozolomide (TMZ) is mediated by mismatch repair (MMR) triggered by O(6)-alkylguanine, whereas MMR protects cells against bifunctional alkylators, including carmustine (BCNU). Therefore, TMZ may be cytotoxic to BCNU-resistant cancer cells because MMR affects sensitivity to TMZ and BCNU in a converse way. We evaluated TMZ cytotoxicity on BCNU-resistant variant (CEM-R) compared with the parental CCRF-CEM cell line (CEM-S). The mechanisms of its BCNU-resistance involved DNA repairs including nucleotide excision repair, base excision repair, alkylguanine alkyltransferase, MMR, and apoptotic and survival pathways. In particular, transcript levels of MMR-related hMLH1 and hMSH2 were enhanced in CEM-R cells. CEM-R cells were 8-fold more BCNU-resistant but surprisingly 9-fold more TMZ-sensitive than were CEM-S cells. Although TMZ-induced adducts include N-alkylated purines and O(6)-alkylguaine, DNA excision repair was enhanced in CEM-R cells, suggesting the efficient repair of N-alkylation adducts. Cotreatment with methoxyamine, a base excision repair inhibitor, did not sensitize CEM-R cells to TMZ, suggesting little or no contribution of N-alkylation to TMZ-induced cytotoxicity. Cotreatment with O(6)-benzylguanine, an alkylguanine alkyltransferase inhibitor, further sensitized CEM-R cells to TMZ, confirming the cytotoxic impact of O(6)-alkylguanine. Cotreatment with cadmium chloride, an MMR inhibitor, disrupted the sensitivity of CEM-R cells to TMZ. The sensitivity to TMZ was reversed in the CEM-R variant clone that had been established by transfecting CEM-R cells with short hairpin hRNA against hMLH1, suggesting the critical role of MMR on sensitization to TMZ. In conclusion, BCNU-resistant CEM-R cells were sensitized to TMZ as a result of enhanced MMR during the development of BCNU resistance.

DNA mismatch repair: molecular mechanism, cancer, and ageing

DNA mismatch repair (MMR) proteins are ubiquitous players in a diverse array of important cellular functions. In its role in post-replication repair, MMR safeguards the genome correcting base mispairs arising as a result of replication errors. Loss of MMR results in greatly increased rates of spontaneous mutation in organisms ranging from bacteria to humans. Mutations in MMR genes cause hereditary nonpolyposis colorectal cancer, and loss of MMR is associated with a significant fraction of sporadic cancers. Given its prominence in mutation avoidance and its ability to target a range of DNA lesions, MMR has been under investigation in studies of ageing mechanisms. This review summarizes what is known about the molecular details of the MMR pathway and the role of MMR proteins in cancer susceptibility and ageing.

The PMS2 subunit of human MutLalpha contains a metal ion binding domain of the iron-dependent repressor protein family

DNA mismatch repair (MMR) is responsible for correcting replication errors. MutLalpha, one of the main players in MMR, has been recently shown to harbor an endonuclease/metal-binding activity, which is important for its function in vivo. This endonuclease activity has been confined to the C-terminal domain of the hPMS2 subunit of the MutLalpha heterodimer. In this work, we identify a striking sequence-structure similarity of hPMS2 to the metal-binding/dimerization domain of the iron-dependent repressor protein family and present a structural model of the metal-binding domain of MutLalpha. According to our model, this domain of MutLalpha comprises at least three highly conserved sequence motifs, which are also present in most MutL homologs from bacteria that do not rely on the endonuclease activity of MutH for strand discrimination. Furthermore, based on our structural model, we predict that MutLalpha is a zinc ion binding protein and confirm this prediction by way of biochemical analysis of zinc ion binding using the full-length and C-terminal domain of MutLalpha. Finally, we demonstrate that the conserved residues of the metal ion binding domain are crucial for MMR activity of MutLalpha in vitro.

Effects of cadmium on differentiation and cell cycle progression in cultured Xenopus kidney distal epithelial (A6) cells

Cadmium (Cd) is an important industrial and environmental pollutant, and the kidney is the primary organ to be affected. To elucidate the effects of Cd on cell proliferation, an epithelial cell line (A6) originally derived from the distal part of the Xenopus laevis kidney was cultured in media containing 10% fetal bovine serum. The effects of Cd (added as CdCl(2)) on cellular growth and differentiation from single cells to confluent epithelia were investigated by visual inspection and by measurement of the degree to which living cells covered a unit area. Over a concentration range from 5 to 50 microM, Cd did not affect the settling and adherence of single cells to the bottom of the culture well. The addition of 5 microM Cd for 4 days did not affect the ability of the A6 cells to develop confluent epithelia, measured as the area covered by adherent living epithelial cells (99 +/- 4% of the control value). However, 10 microM Cd did effectively inhibit development of confluent epithelia to 13 +/- 5% compared to control. Visual inspection of adherent cells exposed to 50 microM Cd for 7 days revealed no increase in cell number or in cell death, which indicated the induction of cell cycle arrest. Flow cytometric analysis showed that treatment of cells with Cd (0.4mM) for 24 hours induced a significant increase in the proportion of G1 phase cells from 58.6 +/- 3.9 to 80.6 +/- 3.7%, and a corresponding reduction in the proportion of cells in both the S and G2 phases from 24.0 +/- 3.6 to 13.4 +/- 3.3% and 17.2 +/- 1.7 to 5.8 +/- 2.1%, respectively. This study showed that Cd stopped cell proliferation in a very narrow concentration range, between 5 and 10 microM, and cell cycle analysis indicated that Cd arrested the cells in the G1 phase of the cell cycle.

Comparative evaluation of the toxicity and genotoxicity of cadmium in amphibian larvae (Xenopus laevis and Pleurodeles waltl) using the comet assay and the micronucleus test

The toxic and genotoxic potential of Cadmium (CdCl(2)) were evaluated by the micronucleus test (MNT) and comet assay (CA) using amphibian larvae (Xenopus laevis and Pleurodeles waltl). Acute toxicity results showed that Cd is toxic to Xenopus larvae exposed from 2 to 50 mg/L and to Pleurodeles from 5 to 50 mg/L, depending on the nature of the water (reconstituted water containing mineral salts or mineral water MW (Volvic)). The MNT results obtained in MW showed that Cd (2 mg/L) is genotoxic to Xenopus, whereas it was not genotoxic to Pleurodeles at all concentrations tested. The CA established that the genotoxicity of Cd to Xenopus and Pleurodeles larvae depends on the concentration, the exposure times, and the comet parameters (Tail DNA, ETM, OTM, and TL). The CA and MNT results were compared for their ability to detect genotoxic effects, considering the concentrations of Cd applied and the exposure time. The CA showed Cd to be genotoxic from the first day of exposure. In amphibians, the CA appears to be a sensitive and suitable method for detecting genotoxicity such as that caused by Cd.