DNA damage-triggered apoptosis: critical role of DNA repair, double-strand breaks, cell proliferation and signaling

A central role of TRAX in the ATM-mediated DNA repair

DNA repair is critical for the maintenance of genome stability. Upon genotoxic stress, dysregulated DNA repair may induce apoptosis. Translin-associated factor X (TRAX), which was initially identified as a binding partner of Translin, has been implicated in genome stability. However, the exact role of TRAX in DNA repair remains largely unknown. Here, we showed that TRAX participates in the ATM/H2AX-mediated DNA repair machinery by interacting with ATM and stabilizing the MRN complex at double-strand breaks. The exogenous expression of wild-type (WT) TRAX, but not a TRAX variant lacking the nuclear localization signal (NLS), rescued the vulnerability of TRAX-null mouse embryo fibroblasts (MEFs). This finding confirms the importance of the nuclear localization of TRAX in the repair of DNA damage. Compared with WT MEFs, TRAX-null MEFs exhibited impaired DNA repair (for example, reduced phosphorylation of ATM and H2AX) after treatment with ultra violet-C or γ-ray irradiation and a higher incidence of p53-mediated apoptosis. Our findings demonstrate that TRAX is required for MRN complex-ATM-H2AX signaling, which optimizes DNA repair by interacting with the activated ATM and protects cells from genotoxic stress-induced apoptosis.

Streptococcus pneumoniae secretes hydrogen peroxide leading to DNA damage and apoptosis in lung cells

Streptococcus pneumoniae is a leading cause of pneumonia and one of the most common causes of death globally. The impact of S. pneumoniae on host molecular processes that lead to detrimental pulmonary consequences is not fully understood. Here, we show that S. pneumoniae induces toxic DNA double-strand breaks (DSBs) in human alveolar epithelial cells, as indicated by ataxia telangiectasia mutated kinase (ATM)-dependent phosphorylation of histone H2AX and colocalization with p53-binding protein (53BP1). Furthermore, results show that DNA damage occurs in a bacterial contact-independent fashion and that Streptococcus pyruvate oxidase (SpxB), which enables synthesis of H2O2, plays a critical role in inducing DSBs. The extent of DNA damage correlates with the extent of apoptosis, and DNA damage precedes apoptosis, which is consistent with the time required for execution of apoptosis. Furthermore, addition of catalase, which neutralizes H2O2, greatly suppresses S. pneumoniae-induced DNA damage and apoptosis. Importantly, S. pneumoniae induces DSBs in the lungs of animals with acute pneumonia, and H2O2 production by S. pneumoniae in vivo contributes to its genotoxicity and virulence. One of the major DSBs repair pathways is nonhomologous end joining for which Ku70/80 is essential for repair. We find that deficiency of Ku80 causes an increase in the levels of DSBs and apoptosis, underscoring the importance of DNA repair in preventing S. pneumoniae-induced genotoxicity. Taken together, this study shows that S. pneumoniae-induced damage to the host cell genome exacerbates its toxicity and pathogenesis, making DNA repair a potentially important susceptibility factor in people who suffer from pneumonia.

Alkylation and Carbamylation Effects of Lomustine and Its Major Metabolites and MGMT Expression in Canine Cells

DNA Alkylation is thought to be the reason for the efficacy of lomustine while carbamylation has been implicated as the cause for the side effects seen with lomustine treatment such as hepatotoxicity. In the alkylation study we show that lomustine and its metabolites form similar levels of the DNA adducts N⁷ hydroxyethylguanine and O⁶ hydroxyethyldeoxyguanosine. In terms of carbamylation, lomustine showed greater extent of carbamylation in the canine hepatocytes and lymphoma cell lines. The DNA repair enzyme O⁶ methylguanine DNA methyltransferase (MGMT) causes resistance of tumor cells to bifunctional nitrosourea, like lomustine. There is no data available regarding MGMT expression/activity in canine cells or tissues. Our study shows that there is low MGMT activity in the canine lymphoid cell line 17-71 while the GL-1 cells did not show any detectable enzyme activity or mRNA expression. The MGMT enzyme activity measured in canine hepatocytes is about 250-350 fmol/mg protein as compared to about 90 fmol/mg protein in 17-71 cells. We also show that MGMT mRNA expression in 17-71 cells and canine hepatocytes positively correlates with its enzyme activity in these cells.

Age-related change in γH2AX of Drosophila muscle: its significance as a marker for muscle damage and longevity

Muscle aging is closely related to unhealthy late-life and organismal aging. Recently, the state of differentiated cells was shown to be critical to tissue homeostasis. Thus, understanding how fully differentiated muscle cells age is required for ensuring healthy aging. Adult Drosophila muscle is a useful model for exploring the aging process of fully differentiated cells. In this study, we investigated age-related changes of γH2AX, an indicator of DNA strand breaks, in adult Drosophila muscle to document whether its changes are correlated with muscle degeneration and lifespan. The results demonstrate that γH2AX accumulation increases in adult Drosophila thoracic and leg muscles with age. Analyses of short-, normal-, and long-lived strains indicate that the age-related increase of γH2AX is closely associated with the extent of muscle degeneration, cleaved caspase-3 and poly-ubiquitin aggregates, and longevity. Further analysis of muscle-specific knockdown of heterochromatin protein 1a revealed that the excessive γH2AX accumulation in thoracic and leg muscles induces accelerated degeneration and decreases longevity. These data suggest a strong correlation between age-related muscle damage and lifespan in Drosophila. Our findings indicate that γH2AX may be a reliable biomarker for assessing muscle aging in Drosophila.

Biochemical biomarkers of sublethal effects in Rhinella arenarum late gastrula exposed to the organophosphate chlorpyrifos

We determined the biochemical and molecular effects of the organophosphate insecticide chlorpyrifos (CPF) in the late gastrula embryonic stage of the South American toad Rhinella arenarum continuously exposed from fertilization (24 h). Our objective was to evaluate these responses as potential biomarkers at low, sublethal levels of the toxicant. We first established the EC50 for embryo arrest in 21.3 mg/L, with a LOEC of 16 mg/L. At 4 mg/L CPF, some embryos were unable to complete the dorsal lip of the blastopore and the yolk plug became blur, probably because of abnormal cell migration. Acetylcholinesterase activity, the specific biomarker for organophosphates, was unaffected by any of the tested concentrations of CPF (2-14 mg/L). In turn, 2 mg/L CPF increased the reduced glutathione levels and inhibited glutathione-S-transferase activity, suggesting an oxidative stress and antioxidant response. Catalase was induced by CPF exposure at higher concentrations (8 and 14 mg/L). We also studied transcription factor c-Fos as a signaling event related to development in early embryogenesis. Analysis of nuclear c-Fos protein showed two bands, both enhanced in embryos exposed to 2 and 8 mg/L CPF. While nuclear Erk protein was practically unaffected, Mek protein levels were induced by the OP. Transcription factor c-Fos may be then linking oxidative stress with developmental alterations observed due to CPF exposure. These molecular and biochemical responses observed in R. arenarum gastrula at sublethal CPF exposures may replace non-responsive AChE as very early biomarkers in toad gastrula.

Role of p53 in the progression from ochratoxin A-induced DNA damage to gene mutations in the kidneys of mice

Carcinogenic doses of ochratoxin A (OTA) cause increases of mutant frequencies (MFs) of the red/gam gene (Spi(-)) in the kidneys of p53-deficient gpt delta mice, but not in p53-proficient mice. Here, we investigated the role of p53 in the progression from OTA-induced DNA damage to gene mutations. To this end, p53-proficient and -deficient mice were administered 5 mg/kg OTA for 3 days or 4 weeks by gavage. After 3 days of administration, comet assays were performed and there were no differences in the degrees of OTA-induced DNA damage between p53-proficient and -deficient mice. However, the frequencies of γ-H2AX-positive tubular epithelial cells in p53-deficient mice were significantly higher than those in p53-proficient mice, implying that p53 inhibited the progression from DNA damage to DNA double-strand breaks (DSBs). Evaluation of global gene expression and relevant mRNA/protein expression levels demonstrated that OTA increased the expression of Cdkn1a, which encodes the p21 protein, in p53-proficient mice, but not in p53-deficient mice. Moreover, in p53-deficient mice, mRNA levels of cell cycle progression and DSB repair (homologous recombination repair [HR])-related genes were significantly increased. Thus, G1/S arrest due to activation of the p53/p21 pathway may contribute to the prevention of DSBs in p53-proficient mice. In addition, single base deletions/insertions/substitutions were predominant, possibly due to HR. Overall, these results suggested that OTA induced DSBs at the carcinogenic target site in mice and that p53/p21-mediated cell cycle control prevented an increase in the formation of DSBs, leading to gene mutations.

Comparative proteomics analysis of global cellular stress responses to hydroxyurea-induced DNA damage in HeLa cells

Both environmental agents and spontaneous cellular events cause serious DNA damage, threatening the integrity of the genome. In response to replication stress or genotoxic agents triggered DNA damage, degradation of p12 subunit of DNA polymerase delta (Pol δ) results in an inter-conversion between heterotetramer (Pol δ4) and heterotrimer (Pol δ3) forms and plays a significant role in DNA damage response in eukaryotic cells. In this work, we used mass spectrometry-based proteomic approach to identify those cellular stress response protein changes corresponding to the degradation of p12 in DNA-damaged HeLa cells by the treatment with hydroxyurea (HU). A total of 736 ± 13 proteins in non-treated control group and 741 ± 19 protein spots in HU-treated cells were detected, of which 34 proteins (17 up-regulated and 17 down-regulated) exhibited significantly altered protein expression levels. Their physiological roles are mainly associated with cellular components, molecular functions, and biological processes by gene ontology analysis, among which 21 proteins were mapped to KEGG pathways. They are involved in 5 primary pathways with the subsets involving 16 secondary pathways by further KEGG analysis. More interestingly, the up-regulation of translationally controlled tumor protein was further identified to be associated with p12 degradation by Western blot analysis. Our works may enlarge and broaden our view for deeply understanding how global cellular stress responds to DNA damage, which could contribute to the etiology of human cancer or other diseases that can result from loss of genomic stability.

TALEN-mediated targeting of HPV oncogenes ameliorates HPV-related cervical malignancy

Persistent HPV infection is recognized as the main etiologic factor for cervical cancer. HPV expresses the oncoproteins E6 and E7, both of which play key roles in maintaining viral infection and promoting carcinogenesis. While siRNA-mediated targeting of E6 and E7 transcripts temporarily induces apoptosis in HPV-positive cells, it does not eliminate viral DNA within the host genome, which can harbor escape mutants. Here, we demonstrated that specifically targeting E6 and E7 within host DNA with transcription activator-like effector nucleases (TALENs) induces apoptosis, inhibits growth, and reduces tumorigenicity in HPV-positive cell lines. TALEN treatment efficiently disrupted E6 and E7 oncogenes, leading to the restoration of host tumor suppressors p53 and retinoblastoma 1 (RB1), which are targeted by E6 and E7, respectively. In the K14-HPV16 transgenic mouse model of HPV-driven neoplasms, direct cervical application of HPV16-E7-targeted TALENs effectively mutated the E7 oncogene, reduced viral DNA load, and restored RB1 function and downstream targets transcription factor E2F1 and cycling-dependent kinase 2 (CDK2), thereby reversing the malignant phenotype. Together, the results from our study suggest that TALENs have potential as a therapeutic strategy for HPV infection and related cervical malignancy.

Topical nitrogen mustard exposure causes systemic toxic effects in mice

Vesicating agents sulfur mustard (SM) and nitrogen mustard (NM) are reported to be easily absorbed by skin upon exposure causing severe cutaneous injury and blistering. Our studies show that topical exposure of NM (3.2mg) onto SKH-1 hairless mouse skin, not only caused skin injury, but also led to significant body weight loss and 40-80% mortality (120 h post-exposure), suggesting its systemic effects. Accordingly, further studies herein show that NM exposure initiated an increase in circulating white blood cells by 24h (neutrophils, eosinophils and basophils) and thereafter a decrease (neutrophils, lymphocytes and monocytes). NM exposure also reduced both white and red pulp areas of the spleen. In the small intestine, NM exposure caused loss of membrane integrity of the surface epithelium, abnormal structure of glands and degeneration of villi. NM exposure also resulted in the dilation of glomerular capillaries of kidneys, and an increase in blood urea nitrogen/creatinine ratio. Our results here with NM are consistent with earlier reports that exposure to higher SM levels can cause damage to the hematopoietic system, and kidney, spleen and gastrointestinal tract toxicity. These outcomes will add to our understanding of the toxic effects of topical vesicant exposure, which might be helpful towards developing effective countermeasures against injuries from acute topical exposures.

Pathway and time-resolved benzo[a]pyrene toxicity on Hepa1c1c7 cells at toxic and subtoxic exposure

Benzo[a]pyrene (B[a]P) is an environmental contaminant mainly studied for its toxic/carcinogenic effects. For a comprehensive and pathway orientated mechanistic understanding of the effects directly triggered by a toxic (5 μM) or a subtoxic (50 nM) concentration of B[a]P or indirectly by its metabolites, we conducted time series experiments for up to 24 h to study the effects in murine hepatocytes. These cells rapidly take up and actively metabolize B[a]P, which was followed by quantitative analysis of the concentration of intracellular B[a]P and seven representative degradation products. Exposure with 5 μM B[a]P led to a maximal intracellular concentration of 1604 pmol/5 × 10(4) cells, leveling at 55 pmol/5 × 10(4) cells by the end of the time course. Changes in the global proteome (>1000 protein profiles) and metabolome (163 metabolites) were assessed in combination with B[a]P degradation. Abundance profiles of 236 (both concentrations), 190 (only 5 μM), and 150 (only 50 nM) proteins were found to be regulated in response to B[a]P in a time-dependent manner. At the endogenous metabolite level amino acids, acylcarnitines and glycerophospholipids were particularly affected by B[a]P. The comprehensive chemical, proteome and metabolomic data enabled the identification of effects on the pathway level in a time-resolved manner. So in addition to known alterations, also protein synthesis, lipid metabolism, and membrane dysfunction were identified as B[a]P specific effects.

Carnosol induces ROS-mediated beclin1-independent autophagy and apoptosis in triple negative breast cancer

Background

In this study we investigated the in vitro and in vivo anticancer effect of carnosol, a naturally occurring polyphenol, in triple negative breast cancer.

Results

We found that carnosol significantly inhibited the viability and colony growth induced G2 arrest in the triple negative MDA-MB-231. Blockade of the cell cycle was associated with increased p21/WAF1 expression and downregulation of p27. Interestingly, carnosol was found to induce beclin1-independent autophagy and apoptosis in MDA-MB-231 cells. The coexistence of both events, autophagy and apoptosis, was confirmed by electron micrography. Induction of autophagy was found to be an early event, detected within 3 h post-treatment, which subsequently led to apoptosis. Carnosol treatment also caused a dose-dependent increase in the levels of phosphorylated extracellular signal-regulated kinase 1 and 2 (pERK1/2). Moreover, we show that carnosol induced DNA damage, reduced the mitochondrial potential and triggered the activation of the intrinsic and extrinsic apoptotic pathway. Furthermore, we found that carnosol induced a dose-dependent generation of reactive oxygen species (ROS) and inhibition of ROS by tiron, a ROS scavenger, blocked the induction of autophagy and apoptosis and attenuated DNA damage. To our knowledge, this is the first report to identify the induction of autophagy by carnosol.

Conclusion

In conclusion our findings provide strong evidence that carnosol may be an alternative therapeutic candidate against the aggressive form of breast cancer and hence deserves more exploration.

Raltitrexed's effect on the development of neural tube defects in mice is associated with DNA damage, apoptosis, and proliferation

The causal metabolic pathway and the underlying mechanism between folate deficiency and neural tube defects (NTDs) remain obscure. Thymidylate (dTMP) is catalyzed by thymidylate synthase (TS) using the folate-derived one-carbon unit as the sole methyl donor. This study aims to examine the role of dTMP biosynthesis in the development of neural tube in mice by inhibition of TS via a specific inhibitor, raltitrexed (RTX). Pregnant mice were intraperitoneally injected with various doses of RTX on gestational day 7.5, and embryos were examined for the presence of NTDs on gestational day 11.5. TS activity and changes of dUMP and dTMP levels were measured following RTX treatment at the optimal dose. DNA damage was determined by detection of phosphorylated replication protein A2 (RPA2) and γ-H2AX in embryos with NTDs induced by RTX. Besides, apoptosis and proliferation were also analyzed in RTX-treated embryos with NTDs. We found that NTDs were highly occurred by the treatment of RTX at the optimal dose of 11.5 mg/kg b/w. RTX treatment significantly inhibited TS activity. Meanwhile, dTMP was decreased associated with the accumulation of dUMP in RTX-treated embryos. Phosphorylated RPA2 and γ-H2AX were significantly increased in RTX-treated embryos with NTDs compared to control. More apoptosis and decreased proliferation were also found in embryos with NTDs induced by RTX. These results indicate that impairment of dTMP biosynthesis caused by RTX led to the development of NTDs in mice. DNA damage and imbalance between apoptosis and proliferation may be potential mechanisms.

Genetic targeting of microglia

Genetic targeting of microglia and other myeloid cells in the central nervous system (CNS) is highly desirable as they are critical effectors and regulators of changes in CNS homeostasis during development as well as in health and disease. Therefore, genetic reprogramming of microglia could constitute a central approach for potentially reducing disease burden. Previous attempts to target only microglia in vivo failed because of the similarities to their hematopoietic relatives in the circulation. However, this concept has been challenged by recent results of developmental and gene expression profiling studies which used novel molecular biological tools to unravel the origin of microglia and to define their role as specialized tissue macrophages clearly distinct from monocytes or monocyte-derived macrophages. The aim of this review is to recapitulate the history of microglia targeting approaches and finally highlight recent achievements in the field. We will discuss the pros and cons of the newly available genetic tools, their potential for future microglia research and genetic strategies.

Human papillomavirus type 16 E6* induces oxidative stress and DNA damage

High-risk types of human papillomavirus (HPV) are the causative agents of virtually all cases of cervical cancer and a significant proportion of other anogenital cancers, as well as both oral and pharyngeal cancers. The high-risk types encode two viral oncogenes, E6 and E7, which work together to initiate cell transformation. Multiple steps involving the activities and interactions of both viral and cellular proteins are involved in the progression from HPV infection to cell transformation to cancer. The E6 oncoprotein is expressed as several isoforms: a full-length variant referred to as E6 and a few shorter isoforms collectively referred to as E6*. In this study, we found that expression of E6* increased the level of reactive oxygen species (ROS) in both HPV-positive and HPV-negative cells. This increased oxidative stress led to higher levels of DNA damage, as assessed by the comet assay, quantification of 8-oxoguanine, and poly(ADP-ribose) polymerase 1. The observed increase in ROS may be due to a decrease in cellular antioxidant activity, as we found that E6* expression also led to decreased expression of superoxide dismutase isoform 2 and glutathione peroxidase. These studies indicate that E6* may play an important role in virus-induced mutagenesis by increasing oxidative stress and DNA damage.

IMPORTANCE

Our findings demonstrate for the first time that an HPV gene product, E6*, can increase ROS levels in host cells. This ability may play a significant role both in the viral life cycle and in cancer development, because an increase in oxidative DNA damage may both facilitate HPV genome amplification and increase the probability of HPV16 DNA integration. Integration, in turn, is thought to be an important step in HPV-mediated carcinogenesis.

Proteolysis of the human DNA polymerase delta smallest subunit p12 by μ-calpain in calcium-triggered apoptotic HeLa cells

Degradation of p12 subunit of human DNA polymerase delta (Pol δ) that results in an interconversion between Pol δ4 and Pol δ3 forms plays a significant role in response to replication stress or genotoxic agents triggered DNA damage. Also, the p12 is readily degraded by human calpain in vitro. However, little has been done for the investigation of its degree of participation in any of the more common apoptosis. Here, we first report that the p12 subunit is a substrate of μ-calpain. In calcium-triggered apoptotic HeLa cells, the p12 is degraded at 12 hours post-induction (hpi), restored thereafter by 24 hpi, and then depleted again after 36 hpi in a time-dependent manner while the other three subunits are not affected. It suggests a dual function of Pol δ by its interconversion between Pol δ4 and Pol δ3 that is involved in a novel unknown apoptosis mechanism. The proteolysis of p12 could be efficiently blocked by both calpain inhibitor ALLN and proteasome inhibitor MG132. In vitro pull down and co-immunoprecipitation assays show that the μ-calpain binds to p12 through the interaction of μ-calpain with Pol δ other three subunits, not p12 itself, and PCNA, implying that the proteolysis of p12 by μ-calpain might be through a Pol δ4/PCNA complex. The p12 cleavage sites by μ-calpain are further determined as the location within a 16-amino acids peptide 28-43 by in vitro cleavage assays. Thus, the p12/Pol δ is a target as a nuclear substrate of μ-calpain in a calcium-triggered apoptosis and appears to be a potential marker in the study of the chemotherapy of cancer therapies.

Outflow tract ablation using a conditionally cytotoxic feline immunodeficiency viral vector

PURPOSE

To create an in vivo model of vector-mediated trabecular meshwork (TM) ablation and replacement.

METHODS

We generated a conditionally cytotoxic, trackable vector, HSVtkiG, that expressed herpes simplex virus 1 thymidine kinase (HSVtk) and enhanced green fluorescent protein (eGFP). We optimized HSVtkiG ablation in vitro with ganciclovir (GCV) in comparison to eGFP control vector GINSIN and investigated the mechanism. Right eyes of 24 rats were then injected intracamerally with either HSVtkiG or GINSIN, before intraperitoneal GCV was administered 1 week later. Intraocular pressure, central corneal thickness (CCT), and slit-lamp exams were assessed for 8 weeks. Transduction and ablation were followed by gonioscopic visualization of eGFP. Histology was obtained with TM cell counts and immunohistochemistry markers of inflammation.

RESULTS

Transduction and ablation parameters were established in vitro. Apoptosis was the cause of cell death. In vivo, transduction was seen gonioscopically to be targeted to the TM, followed by disappearance of eGFP marker fluorescence in HSVtkiG-transduced cells after injection of GCV. Ablation resulted in an IOP decrease of 25% in HSVtkiG-injected eyes 2 days after GCV but not in GINSIN or noninjected control eyes (P < 0.05). Trabecular meshwork cellularity was decreased at the time of lowest IOP and recovered thereafter, while CCT remained unchanged. Inflammation was absent.

CONCLUSIONS

A vector-based system for inducible ablation of cells of the outflow tract was developed. Trabecular meshwork ablation lowered IOP, and recovery of cellularity and IOP followed. This model may be useful to study pressure regulation by the TM, its stem cells, and migration patterns.

ATM kinase promotes both caspase-8 and caspase-9 activation during TNF-α-induced apoptosis of HeLa cells

In this study, we show that atraxia telangiectasia mutated kinase (ATM) activity is generally upregulated by different apoptotic stimuli, i.e. TNF-α, TRAIL, paclitaxel, or UV. Apoptotic progression is markedly attenuated by siATM-RNA through down regulation of caspase-8 and caspase-9 in parallel with decreases in FLIP-S (short form of cellular FLICE inhibitory protein) protein levels and Bid cleavage. In addition, ATM activity is upregulated through t-Cdc6 while caspase-8 and caspase-9 activities increase. Taken together, we suggest that ATM regulates caspase-8 activation by influencing levels of FLIP-S, ATM kinase activity is upregulated by t-Cdc6, and increased ATM activity plays an essential role in the amplification of apoptosis in TNF-α-stimulated HeLa cells.

BID preferentially activates BAK while BIM preferentially activates BAX, affecting chemotherapy response

Apoptosis is a highly regulated form of cell death that controls normal homeostasis as well as the antitumor activity of many chemotherapeutic agents. Commitment to death via the mitochondrial apoptotic pathway requires activation of the mitochondrial pore-forming proteins BAK or BAX. Activation can be effected by the activator BH3-only proteins BID or BIM, which have been considered to be functionally redundant in this role. Herein, we show that significant activation preferences exist between these proteins: BID preferentially activates BAK while BIM preferentially activates BAX. Furthermore, we find that cells lacking BAK are relatively resistant to agents that require BID activation for maximal induction of apoptosis, including topoisomerase inhibitors and TRAIL. Consequently, patients with tumors that harbor a loss of BAK1 exhibit an inferior response to topoisomerase inhibitor treatment in the clinic. Therefore, BID and BIM have nonoverlapping roles in the induction of apoptosis via BAK and BAX, affecting chemotherapy response.

Methanolic Extract Isolated from Root of Lycoris aurea Inhibits Cancer Cell Growth and Endothelial Cell Tube Formation In Vitro

In this study, we investigated the effect of methanolic extract isolated from the root of Lycoris aurea (LA) on the growth of cancer cells and the tube formation activity of endothelial cells. Various cancer cells were treated with LA at doses of 0.3, 1, 3, 10 or 30 μg/ml and LA significantly suppressed the growth of several cancer cell lines, including ACHN, HCT-15, K-562, MCF-7, PC-3 and SK-OV-3, in a dose-dependent manner. We also found that LA induced cell cycle arrest at G2/M phase in ACHN renal cell adenocarcinoma cells. Further study demonstrated that LA concentration-dependently inhibited the tube formation, which is a widely used in vitro model of reorganization stage of angiogenesis, in human umbilical vein endothelial cells. Collectively, these results show that LA inhibits the growth of cancer cells and tube formation of endothelial cells and the growth-inhibitory effect of LA might be mediated, at least in part, by blocking cell cycle progression.

Orthologous mammalian APOBEC3A cytidine deaminases hypermutate nuclear DNA

The human APOBEC3 gene cluster locus encodes polynucleotide cytidine deaminases. Although many act as viral restriction factors through mutation of single-stranded DNA, recent reports have shown that human APOBEC3A was capable of efficiently hypermutating nuclear DNA and inducing DNA breaks in genomic DNA. In addition, the enzyme was unique in efficiently deaminating 5-methylcytidine in single-stranded DNA. To appreciate the evolutionary relevance of these activities, we analyzed A3A-related enzymes from the rhesus and tamarin monkey, horse, sheep, dog, and panda. All proved to be orthologous to the human enzyme in all these activities revealing strong conservation more than 148 My. Hence, their singular role in DNA catabolism is a well-established mechanism probably outweighing any deleterious or pathological roles such as genomic instability and cancer formation.

Resveratrol protects mouse oocytes from methylglyoxal-induced oxidative damage

Methylglyoxal, a reactive dicarbonyl compound, is mainly formed from glycolysis. Methylglyoxal can lead to the dysfunction of mitochondria, the depletion of cellular anti-oxidation enzymes and the formation of advanced glycation ends. Previous studies showed that the accumulation of methylglyoxal and advanced glycation ends can impair the oocyte maturation and reduce the oocyte quality in aged and diabetic females. In this study, we showed that resveratrol, a kind of phytoalexin found in the skin of grapes, red wine and other botanical extracts, can alleviate the adverse effects caused by methylglyoxal, such as inhibition of oocyte maturation and disruption of spindle assembly. Besides, methylglyoxal-treated oocytes displayed more DNA double strands breaks and this can also be decreased by treatment of resveratrol. Further investigation of these processes revealed that methylglyoxal may affect the oocyte quality by resulting in excessive reactive oxygen species production, aberrant mitochondrial distribution and high level lipid peroxidation, and resveratrol can block these cytotoxic changes. Collectively, our results showed that resveratrol can protect the oocytes from methylglyoxal-induced cytotoxicity and this was mainly through the correction of the abnormity of cellular reactive oxygen species metabolism.

Post-translational regulation enables robust p53 regulation

Background

The tumor suppressor protein p53 plays important roles in DNA damage repair, cell cycle arrest and apoptosis. Due to its critical functions, the level of p53 is tightly regulated by a negative feedback mechanism to increase its tolerance towards fluctuations and disturbances. Interestingly, the p53 level is controlled by post-translational regulation rather than transcriptional regulation in this feedback mechanism.

Results

We analyzed the dynamics of this feedback to understand whether post-translational regulation provides any advantages over transcriptional regulation in regard to disturbance rejection. When a disturbance happens, even though negative feedback reduces the steady-state error, it can cause a system to become less stable and transiently overshoots, which may erroneously trigger downstream reactions. Therefore, the system needs to balance the trade-off between steady-state and transient errors. Feedback control and adaptive estimation theories revealed that post-translational regulation achieves a better trade-off than transcriptional regulation, contributing to a more steady level of p53 under the influence of noise and disturbances. Furthermore, post-translational regulation enables cells to respond more promptly to stress conditions with consistent amplitude. However, for better disturbance rejection, the p53- Mdm2 negative feedback has to pay a price of higher stochastic noise.

Conclusions

Our analyses suggest that the p53-Mdm2 feedback favors regulatory mechanisms that provide the optimal trade-offs for dynamic control.

Human APOBEC3A isoforms translocate to the nucleus and induce DNA double strand breaks leading to cell stress and death

Human APOBEC3 enzymes deaminate single stranded DNA. At least five can deaminate mitochondrial DNA in the cytoplasm, while three can deaminate viral DNA in the nucleus. However, only one, APOBEC3A, can hypermutate genomic DNA. We analysed the distribution and function of the two APOBEC3A isoforms p1 and p2 in transfected cell lines. Both can translocate to the nucleus and hypermutate CMYC DNA and induce DNA double strand breaks as visualized by the detection of ©H2AX or Chk2. APOBEC3A induced G1 phase cell cycle arrest and triggered several members of the intrinsic apoptosis pathway. Activation of purified human CD4+ T lymphocytes with PHA, IL2 and interferon α resulted in C->T hypermutation of genomic DNA and double stranded breaks suggesting a role for APOBEC3A in pro-inflammatory conditions. As chronic inflammation underlies many diseases including numerous cancers, it is possible that APOBEC3A induction may generate many of the lesions typical of a cancer genome.

Mitochondrial DNA damage induces apoptosis in senescent cells

Senescence is a cellular response to damage and stress. The senescence response prevents cancer by suppressing the proliferation of cells with a compromised genome and contributes to optimal wound healing in normal tissues. Persistent senescent cells are also thought to drive aging and age-associated pathologies through their secretion of inflammatory factors that modify the tissue microenvironment and alter the function of nearby normal or transformed cells. Understanding how senescent cells alter the microenvironment would be aided by the ability to induce or eliminate senescent cells at will in vivo. Here, we combine the use of the synthetic nucleoside analog ganciclovir (GCV) with herpes simplex virus thymidine kinase (HSVtk) activity to create or eliminate senescent human cells. We show that low concentrations of GCV induce senescence through the accumulation of nuclear DNA damage while higher concentrations of GCV, similar to those used in vivo, kill non-dividing senescent cells via mitochondrial DNA (mtDNA) damage and caspase-dependent apoptosis. Using this system, we effectively eliminated xenografted normal human senescent fibroblasts or induced senescence in human breast cancer cells in vivo. Thus, cellular senescence and mtDNA damage are outcomes of synthetic nucleoside analog treatment, indicating that the GCV-HSVtk combination can be used effectively to promote the targeted formation or eradication of senescent cells.

MGMT expression and pituitary tumours: relationship to tumour biology

Over the past half decade, temozolomide, an oral akylating chemotherapeutic agent, has been shown to have significant activity in the management of aggressive pituitary tumours. The expression of 06-methylguanine-DNA methyltransferase (MGMT), a DNA repair enzyme, is an important predictor of response to therapy. Low MGMT expression has been reported with a higher frequency amongst more aggressive pituitary tumours, suggesting MGMT may play a role in pituitary tumour progression. In this study, we performed a microarray analysis to determine whether there was a distinct gene expression profile between tumours with low MGMT and high MGMT expression. Overall, 1,403 differentially expressed genes were identified with raw p values less than 0.05. Gene set enrichment analysis (GSEA) revealed significant differences in the gene expression profile between high and low MGMT expressing pituitary tumours. High MGMT expressing pituitary tumours were found to have upregulation of components of the FGFR family and downstream signaling cascades such as PI3 K/Akt and MAPK pathways. Activation of genes involved in the DNA damage response and DNA repair pathways, as well as genes involved in transcription, were identified in pituitary tumours with low MGMT expression. These results form the basis of our proposed model to describe the role of MGMT in pituitary tumorigenesis.

UVB suppresses PTEN expression by upregulating miR-141 in HaCaT cells

MicroRNAs (miRNAs) are 21 to 24 nucleotide, non-coding RNA molecules that post-transcriptionally regulate the expression of target genes. Ultraviolet B (UVB) radiation has been shown to inhibit phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression in HaCaT cells through an unknown mechanism. In this study, we investigated whether miR-141 can regulate UVB exposure-mediated inhibition of PTEN expression. Real-time RT-PCR, annexin V/fluorescein isothiocyanate staining, Western blotting and anti-miRNA oligonucleotide transfection were employed in this study. We found that upregulation of miR-141 expression after UVB irradiation was inversely correlated with PTEN expression levels in HaCaT cells. Furthermore, miR-141 expression increased apoptosis, while anti-miR-141 partly restored PTEN expression and reversed the pro-apoptosis effect of UVB. UVB suppresses the expression of PTEN by upregulating miR-141 in HaCaT cells. Therefore, miR-141 is a potential gene therapy target for UVB-induced photodamage.

UCN-01 induces S and G2/M cell cycle arrest through the p53/p21(waf1) or CHK2/CDC25C pathways and can suppress invasion in human hepatoma cell lines

BACKGROUND

UCN-01 (7-hydroxystaurosporine), a protein kinase inhibitor, has attracted a great deal of attention as a potent antitumour agent. Several clinical trials of UCN-01 alone or in combination with other agents for different tumour types are currently underway, and some of these trials have had positive results. Hepatocellular carcinoma has high incidence rates and is associated with poor prognosis and high mortality rates.

METHODS

Three different hepatoma cell lines (Huh7, HepG2, and Hep3B) were treated with different concentrations of UCN-01, and the anti-tumour effects of UCN-01 were evaluated. Following UCN-01 treatment, cell growth was measured using an MTT assay, cell cycle arrest was assayed using flow cytometry, and the mechanisms of cell cycle arrest and invasion inhibition were investigated through western blotting and a Matrigel invasion assay.

RESULTS

After a 72-h UCN-01 treatment, the growth of different hepatoma cell lines was significantly inhibited in a dose-dependent manner, with IC50 values ranging from 69.76 to 222.74 nM. Flow cytometry results suggested that UCN-01 inhibits proliferation in the hepatoma cells by inducing S and G2/M phase arrest, but not G1/S arrest, which differs from previous reports that used other tumour cell lines. Western blot results illustrated that UCN-01 induces a G2/M phase arrest, regardless of the status of the p53/P21(waf1) pathway, whereas the CHK2/CDC25C pathway and the p53/p21(waf1)pathway were involved in the UCN-01-induced S phase arrest. UCN-01 remarkably inhibited Huh7 cell invasion in a time-dependent manner. Suppression of Huh7 cell invasion may be due to the down-regulation of phosphorylated β-catenin by UCN-01.

CONCLUSIONS

These findings suggest that UCN-01 induces hepatoma cell growth inhibition by regulating the p53/p21(waf1) and CHK2/CDC25 pathways. Suppression of Huh7 cell invasion by UCN-01 may be due to the down-regulation of phosphorylated β-catenin. These data lend support for further studies on UCN-01 as a promising anti-HCC candidate.

Inhibition of histone deacetylase impacts cancer stem cells and induces epithelial-mesenchyme transition of head and neck cancer

The genome is organized and packed into the nucleus through interactions with core histone proteins. Emerging evidence suggests that tumors are highly responsive to epigenetic alterations that induce chromatin-based events and dynamically influence tumor behavior. We examined chromatin organization in head and neck squamous cell carcinoma (HNSCC) using acetylation levels of histone 3 as a marker of chromatin compaction. Compared to control oral keratinocytes, we found that HNSCC cells are hypoacetylated and that microenvironmental cues (e.g., microvasculature endothelial cells) induce tumor acetylation. Furthermore, we found that chemical inhibition of histone deacetylases (HDAC) reduces the number of cancer stem cells (CSC) and inhibits clonogenic sphere formation. Paradoxically, inhibition of HDAC also induced epithelial-mesenchymal transition (EMT) in HNSCC cells, accumulation of BMI-1, an oncogene associated with tumor aggressiveness, and expression of the vimentin mesenchymal marker. Importantly, we observed co-expression of vimentin and acetylated histone 3 at the invasion front of human HNSCC tumor tissues. Collectively, these findings suggest that environmental cues, such as endothelial cell-secreted factors, modulate tumor plasticity by limiting the population of CSC and inducing EMT. Therefore, inhibition of HDAC may constitute a novel strategy to disrupt the population of CSC in head and neck tumors to create a homogeneous population of cancer cells with biologically defined signatures and predictable behavior.

Effects of β-glucan extracted from Agaricus blazei on the expression of ERCC5, CASP9, and CYP1A1 genes and metabolic profile in HepG2 cells

The polysaccharide β-glucan has biological properties that stimulate the immune system and can prevent chronic pathologies, including cancer. It has been shown to prevent damage to DNA caused by the chemical and physical agents to which humans are exposed. However, the mechanism of β-glucan remains poorly understood. The objective of the present study was to verify the protective effect of β-glucan on the expression of the genes ERCC5 (involved in excision repair of DNA damage), CASP9 (involved in apoptosis), and CYP1A1 (involved in the metabolism of xenobiotics) using real-time polymerase chain reaction and perform metabolic profile measurements on the HepG2 cells. Cells were exposed to only benzo[a]pyrene (B[a]P), β-glucan, or a combination of B[a]P with β-glucan. The results demonstrated that 50 µg/mL β-glucan significantly repressed the expression of the ERCC5 gene when compared with the untreated control cells in these conditions. No change was found in the CASP9 transcript level. However, the CYP1A1 gene expression was also induced by HepG2 cells exposed to B[a]P only or in association with β-glucan, showing its effective protector against damage caused by B[a]P, while HepG2 cells exposed to only β-glucan did not show CYP1A1 modulation. The metabolic profiles showed moderate bioenergetic metabolism with an increase in the metabolites involved in bioenergetic metabolism (alanine, glutamate, creatine and phosphocholine) in cells treated with β-glucan and to a lesser extent treated with B[a]P. Thus, these results demonstrate that the chemopreventive activity of β-glucan may modulate bioenergetic metabolism and gene expression.

Protective effect of galantamine against oxidative damage using human lymphocytes: a novel in vitro model

BACKGROUND AND AIMS

Neurodegenerative disorders such as Alzheimer's disease are characterized in the initial stages by an increase in reactive oxygen species that trigger apoptosis or programmed cell death. It has been suggested that the synthetic alkaloid galantamine may offer protection against this cell loss. This investigation sought to assess the protective effect of galantamine against oxidative damage induced by hydrogen peroxide (H2O2) using human lymphocytes cultured in vitro as a model.

METHODS

Cell death can be measured indirectly using cell viability testing with trypan blue. Determination of the galantamine concentrations used was made possible by the negative correlation found between galantamine concentration and average mitotic index (MI).

RESULTS

Average viability of lymphocytes treated with low and medium concentrations of galantamine was significantly higher than the control.

CONCLUSION

Galantamine does indeed demonstrate a protective capacity against cell damage induced by hydrogen peroxide. This finding supports the possible use of the drug in treatment of neurodegenerative diseases related to oxidative stress.

Inhibition of tumor growth in vitro and in vivo by fucoxanthin against melanoma B16F10 cells

The present study was designed to evaluate the molecular mechanisms of fucoxanthin against melanoma cell lines (B16F10 cells). Fucoxanthin reduced the proliferation of B16F10 cells in a dose-dependent manner accompanied by the induction of cell cycle arrest during the G(0)/G(1) phase and apoptosis. Fucoxanthin-induced G(0)/G(1) arrest was associated with a marked decrease in the protein expressions of phosphorylated-Rb (retinoblastoma protein), cyclin D (1 and 2) and cyclin-dependent kinase (CDK) 4 and up-regulation of the protein levels of p15(INK4B) and p27(Kip1). Fucoxanthin-induced apoptosis was accompanied with the down-regulation of the protein levels of Bcl-xL, an inhibitor of apoptosis proteins (IAPs), resulting in a sequential activation of caspase-9, caspase-3, and PARP. Furthermore, the anti-tumor effect of fucoxanthin was assessed in vivo in Balb/c mice. Intraperitoneal administration of fucoxanthin significantly inhibited the growth of tumor mass in B16F10 cells implanted mice.

Association between XRCC1 and XRCC3 polymorphisms and colorectal cancer risk: a meta-analysis of 23 case-control studies

Several potential functional polymorphisms in the DNA repair gene X-ray repair cross-complementing group 1 (XRCC1) Arg399Gln (rs25487), Arg194Trp (rs1799782), Arg280His (rs25489) and X-ray repair cross-complementing group 3 (XRCC3) T241M (rs861539) have been implicated in colorectal cancer (CRC) risk, but the results are conflicting. Here, we performed a meta-analysis of 23 published case control datasets and assessed genetic heterogeneity between those datasets. All the case-control studies published from January 2000 to June 2012 on the association between those polymorphisms and CRC risk were identified by searching the electronic literature Medline. Statistical analysis was performed with the software programs Review Manager (version 4.2). For overall CRC, no significant association was observed, the pooled odds ratios for XRCC1 Arg399Gln, Arg194Trp, Arg280His, and XRCC3 T241M were 1.02 (95 % CI: 0.93, 1.12), 1.03 (95 % CI: 0.94, 1.14), 0.98 (95 % CI: 0.85, 1.13) and 1.03 (95 % CI: 0.85, 1.26), respectively. Furthermore, no significant association was observed in subgroup analyses based on ethnicity. The results suggested that these four SNPs evaluated are not associated with risk of CRC.

Variant 1 of KIAA0101, overexpressed in hepatocellular carcinoma, prevents doxorubicin-induced apoptosis by inhibiting p53 activation

KIAA0101 overexpression was detected in numerous malignant solid tumors and involved in tumor progression; however, the correlation between KIAA0101 expression level and human hepatocellular carcinoma (HCC) was controversial. Our data revealed abnormal expression of the KIAA0101 transcript variant 1 (KIAA0101 tv1) at both messenger RNA and protein levels in HCC tissues and cell lines assessed by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR), virtual northern blot, western blot, and immunohistochemical analysis, especially in stage 3-4 HCCs. NIH3T3 cells transfected with KIAA0101 tv1 induced colony formation in vitro and tumor xenorafts in vivo, implying the oncogenic potential of KIAA0101 tv1. Semiquantitative RT-PCR, real-time quantitative RT-PCR, and western blot analysis demonstrated that doxorubicin (Adriamycin, ADR) treatment down-regulated expression of the KIAA0101 tv1, whereas it increased the acetylation of the p53 protein. Additionally, KIAA0101 tv1 prevented cells from apoptosis caused by ADR through suppressing the acetylation of p53 at Lys382. Immunoprecipitation analysis and mammalian two-hybrid assay indicated that KIAA0101 tv1 bound to the transactivation region (1-42 amino acids) of p53 and strongly inhibits its transcriptional activity. Taken together, our data suggest that KIAA0101 tv1 played an important role in the late stage of metastatic HCC and prevented apoptosis after chemotherapeutic drug treatment through inhibiting the transcriptional activity of the p53 gene.

CONCLUSION

KIAA0101 tv1 may function as a regulator, promoting cell survival in HCC through regulating the function of p53. Suppression of the KIAA0101 tv1 function is likely to be a promising strategy to develop novel cancer therapeutic drugs.

Evaluation of cell proliferation, apoptosis, and DNA-repair genes as potential biomarkers for ethanol-induced CNS alterations

Background

Alcohol use disorders (AUDs) lead to alterations in central nervous system (CNS) architecture along with impaired learning and memory. Previous work from our group and that of others suggests that one mechanism underlying these changes is alteration of cell proliferation, apoptosis, and DNA-repair in neural stem cells (NSCs) produced as a consequence of ethanol-induced effects on the expression of genes related to p53-signaling. This study tests the hypothesis that changes in the expression of p53-signaling genes represent biomarkers of ethanol abuse which can be identified in the peripheral blood of rat drinking models and human AUD subjects and posits that specific changes may be correlated with differences in neuropsychological measures and CNS structure.

Results

Remarkably, microarray analysis of 350 genes related to p53-signaling in peripheral blood leukocytes (PBLs) of binge-drinking rats revealed 190 genes that were significantly altered after correcting for multiple testing. Moreover, 40 of these genes overlapped with those that we had previously observed to be changed in ethanol-exposed mouse NSCs. Expression changes in nine of these genes were tested for independent confirmation by a custom QuantiGene Plex (QGP) assay for a subset of p53-signaling genes, where a consistent trend for decreased expression of mitosis-related genes was observed. One mitosis-related gene (Pttg1) was also changed in human lymphoblasts cultured with ethanol. In PBLs of human AUD subjects seven p53-signaling genes were changed compared with non-drinking controls. Correlation and principal components analysis were then used to identify significant relationships between the expression of these seven genes and a set of medical, demographic, neuropsychological and neuroimaging measures that distinguished AUD and control subjects. Two genes (Ercc1 and Mcm5) showed a highly significant correlation with AUD-induced decreases in the volume of the left parietal supramarginal gyrus and neuropsychological measures.

Conclusions

These results demonstrate that alcohol-induced changes in genes related to proliferation, apoptosis, and DNA-repair are observable in the peripheral blood and may serve as a useful biomarker for CNS structural damage and functional performance deficits in human AUD subjects.

Betulinic Acid inhibits growth of cultured vascular smooth muscle cells in vitro by inducing g(1) arrest and apoptosis

Betulinic acid is a widely available plant-derived triterpene which is reported to possess selective cytotoxic activity against cancer cells of neuroectodermal origin and leukemia. However, the potential of betulinic acid as an antiproliferative and cytotoxic agent on vascular smooth muscle (VSMC) is still unclear. This study was carried out to demonstrate the antiproliferative and cytotoxic effect of betulinic acid on VSMCs using 3-[4,5-dimethylthizol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry cell cycle assay, BrdU proliferation assay, acridine orange/propidium iodide staining, and comet assay. Result from MTT and BrdU assays indicated that betulinic acid was able to inhibit the growth and proliferation of VSMCs in a dose-dependent manner with IC₅₀ of 3.8 μg/mL significantly (P < 0.05). Nevertheless, betulinic acid exhibited G₁ cell cycle arrest in flow cytometry cell cycle profiling and low level of DNA damage against VSMC in acridine orange/propidium iodide and comet assay after 24 h of treatment. In conclusion, betulinic acid induced G₁ cell cycle arrest and dose-dependent DNA damage on VSMC.

Involvement of intrinsic mitochondrial pathway in neosergeolide-induced apoptosis of human HL-60 leukemia cells: the role of mitochondrial permeability transition pore and DNA damage

CONTEXT

Quassinoids are biologically active secondary metabolites found exclusively in the Simaroubaceae family of plants. These compounds generally present important biological properties, including cytotoxic and antitumor properties.

OBJECTIVE

In the present study, the cytotoxic effects of neosergeolide, a quassinoid isolated from Picrolemma sprucei Hook. f., were evaluated in human promyelocytic leukemia cells (HL-60).

MATERIALS AND METHODS

Cytotoxicity and antiproliferative effects were evaluated by the MTT assay, May-Grünwald-Giemsa's staining, BrdU incorporation test, and flow cytometry procedures. The comet assay and micronuclei analysis were applied to determine the genotoxic and mutagenic potential of neosergeolide.

RESULTS

After 24 h exposure, neosergeolide strongly inhibited cancer cell proliferation (IC₅₀ 0.1 µM), and its activity seemed to be selective to tumor cells because it had no antiproliferative effect on human peripheral blood mononuclear cells (PBMC) at tested concentrations. Apoptosis was induced at submicromolar concentrations (0.05, 0.1, and 0.2 µM) as evidenced by morphological changes, mitochondrial depolarization, phosphatidylserine externalization, caspases activation, and internucleosomal DNA fragmentation. Additionally, neosergeolide effects were prevented by cyclosporine A (CsA), an inhibitor of the mitochondrial permeability transition (MPT) pore, which reinforced the participation of intrinsic pathways in the apoptotic process induced by this natural quassinoid. Direct DNA damage was further confirmed by comet assay and cytokinesis-block micronucleus test.

DISCUSSION AND CONCLUSION

The present study provided experimental evidence to support the underlying mechanism of action involved in the neosergeolide-mediated apoptosis. In addition, no antiproliferative effect or DNA damage effect of neosergeolide was evident in PBMC, highlighting its therapeutic potential.

A tumor growth inhibition model for low-grade glioma treated with chemotherapy or radiotherapy

PURPOSE

To develop a tumor growth inhibition model for adult diffuse low-grade gliomas (LGG) able to describe tumor size evolution in patients treated with chemotherapy or radiotherapy.

EXPERIMENTAL DESIGN

Using longitudinal mean tumor diameter (MTD) data from 21 patients treated with first-line procarbazine, 1-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea, and vincristine (PCV) chemotherapy, we formulated a model consisting of a system of differential equations, incorporating tumor-specific and treatment-related parameters that reflect the response of proliferative and quiescent tumor tissue to treatment. The model was then applied to the analysis of longitudinal tumor size data in 24 patients treated with first-line temozolomide (TMZ) chemotherapy and in 25 patients treated with first-line radiotherapy.

RESULTS

The model successfully described the MTD dynamics of LGG before, during, and after PCV chemotherapy. Using the same model structure, we were also able to successfully describe the MTD dynamics in LGG patients treated with TMZ chemotherapy or radiotherapy. Tumor-specific parameters were found to be consistent across the three treatment modalities. The model is robust to sensitivity analysis, and preliminary results suggest that it can predict treatment response on the basis of pretreatment tumor size data.

CONCLUSIONS

Using MTD data, we propose a tumor growth inhibition model able to describe LGG tumor size evolution in patients treated with chemotherapy or radiotherapy. In the future, this model might be used to predict treatment efficacy in LGG patients and could constitute a rational tool to conceive more effective chemotherapy schedules.

Effect of immunosuppressive drugs on spontaneous DNA repair in human peripheral blood mononuclear cells

INTRODUCTION

Immunosuppressive treatment increases the risk of post-transplant cancer. Cyclosporine reduced UV-induced DNA repair by peripheral blood mononuclear cells (PBMC) and increased cancer incidence in kidney transplant recipients. Calcineurin inhibitors (CNI), but not mammalian target of rapamycin (mTOR) inhibitors or mycophenolic acid, suppressed H₂O₂-induced DNA repair in human peripheral blood mononuclear cells (PBMC) in vitro at maintenance drug concentrations. DNA repair, when measured in quiescent cells, is named spontaneous DNA repair, and represents a basal ongoing DNA repair in response to endogenous DNA damage. The effect of immunosuppressive drugs on spontaneous DNA repair has not been investigated.

AIM

To investigate the effect of currently used immunosuppressive drugs on spontaneous DNA repair.

METHODS

Spontaneous DNA repair by human PBMC was tested in vitro in the presence of the CNI-cyclosporine and tacrolimus; mycophenolic acid (MPA); and the mTOR inhibitors-sirolimus and everolimus, at low to high nontoxic concentrations.

RESULTS

Cyclosporine and tacrolimus suppressed spontaneous DNA repair throughout the tested dose range. In contrast, MPA, sirolimus and everolimus did so only at the high doses.

CONCLUSION

A reduction in CNI dosage may lead to a decrease in the occurrence of post-transplant malignancy.

Ganoderma lucidum Extract Induces G1 Cell Cycle Arrest, and Apoptosis in Human Breast Cancer Cells

Ganoderma lucidum (Fr.) Karst is a traditional Chinese herb that has been widely used for centuries to treat various diseases including cancer. Herein, an ethanol-soluble and acidic component (ESAC), which mainly contains triterpenes, was prepared from G. lucidum and its anti-tumor effects in vitro were tested on human breast cancer cells. Our results showed that ESAC reduced the cell viability of MCF-7 and MDA-MB-231 cells in a concentration-dependent manner with IC50 of about 100 μg/mL and 60 μg/mL, respectively. DNA damage was detected by Comet assay and the increased expression of γ-H2AX after ESAC treatment was determined in MCF-7 cells. Moreover, ESAC effectively mediated G1 cell cycle arrest in both concentration- and time-dependent manners and induced apoptosis as determined by Hoechst staining, DNA fragment assay and Western blot analysis in MCF-7 cells. In conclusion, ESAC exerts anti-proliferation effects by inducing DNA damage, G1 cell cycle arrest and apoptosis in human breast cancer cells.

Effect of Epigallocatechingallate on Ultraviolet B-Induced Photo-Damage in Keratinocyte Cell Line

One type of traditional Chinese medicines, epigallocatechingallate (EGCG) has been commonly used as a clinical and skin health protective ingredient. It has been known to have photo-protective, anti-inflammatory, and anti-oxidant effects. However, little is known about the mechanisms of EGCG on UV-induced photo-aging and photo-carcinogenesis. In the present study, we investigated the photo-protective mechanisms of EGCG on UVB-induced skin damage, including the potency of EGCG to inhibit the UVB-induced cytotoxicity, secretion of cytokine (IL-6 and TNF-α), cellular apoptosis, expression of apoptosis-regulatory genes (p53–p21) and c-fos gene in cultured immortalized human keratinocyte HaCaT cells. EGCG treatment decreased UVB- induced cell cytotoxicity and apoptosis. It also inhibited the mRNA expressions of apoptosis-regulatory gene (p53 and p21) and c-fos gene. These results suggest that EGCG may have an inhibitory effect on UVB-induced photo-damage and apoptosis by blocking the cytokine secretion and the mRNA expressions of p53, p21 and c-fos genes.

DNA damage-induced cell death: from specific DNA lesions to the DNA damage response and apoptosis

DNA damaging agents are potent inducers of cell death triggered by apoptosis. Since these agents induce a plethora of different DNA lesions, it is firstly important to identify the specific lesions responsible for initiating apoptosis before the apoptotic executing pathways can be elucidated. Here, we describe specific DNA lesions that have been identified as apoptosis triggers, their repair and the signaling provoked by them. We discuss methylating agents such as temozolomide, ionizing radiation and cisplatin, all of them are important in cancer therapy. We show that the potentially lethal events for the cell are O(6)-methylguanine adducts that are converted by mismatch repair into DNA double-strand breaks (DSBs), non-repaired N-methylpurines and abasic sites as well as bulky adducts that block DNA replication leading to DSBs that are also directly induced following ionizing radiation. Transcriptional inhibition may also contribute to apoptosis. Cells are equipped with sensors that detect DNA damage and relay the signal via kinases to executors, who on their turn evoke a process that inhibits cell cycle progression and provokes DNA repair or, if this fails, activate the receptor and/or mitochondrial apoptotic cascade. The main DNA damage recognition factors MRN and the PI3 kinases ATM, ATR and DNA-PK, which phosphorylate a multitude of proteins and thus induce the DNA damage response (DDR), will be discussed as well as the downstream players p53, NF-κB, Akt and survivin. We review data and models describing the signaling from DNA damage to the apoptosis executing machinery and discuss the complex interplay between cell survival and death.

Resistance and gain-of-resistance phenotypes in cancers harboring wild-type p53

Chemotherapy is the bedrock for the clinical management of cancer, and the tumor suppressor p53 has a central role in this therapeutic modality. This protein facilitates favorable antitumor drug response through a variety of key cellular functions, including cell cycle arrest, senescence, and apoptosis. These functions essentially cease once p53 becomes mutated, as occurs in ∼50% of cancers, and some p53 mutants even exhibit gain-of-function effects, which lead to greater drug resistance. However, it is becoming increasingly evident that resistance is also seen in cancers harboring wild-type p53. In this review, we discuss how wild-type p53 is inactivated to render cells resistant to antitumor drugs. This may occur through various mechanisms, including an increase in proteasomal degradation, defects in post-translational modification, and downstream defects in p53 target genes. We also consider evidence that the resistance seen in wild-type p53 cancers can be substantially greater than that seen in mutant p53 cancers, and this poses a far greater challenge for efforts to design strategies that increase drug response in resistant cancers already primed with wild-type p53. Because the mechanisms contributing to this wild-type p53 "gain-of-resistance" phenotype are largely unknown, a concerted research effort is needed to identify the underlying basis for the occurrence of this phenotype and, in parallel, to explore the possibility that the phenotype may be a product of wild-type p53 gain-of-function effects. Such studies are essential to lay the foundation for a rational therapeutic approach in the treatment of resistant wild-type p53 cancers.

Chromatin structure following UV-induced DNA damage-repair or death?

In eukaryotes, DNA is compacted into a complex structure known as chromatin. The unravelling of DNA is a crucial step in DNA repair, replication, transcription and recombination as this allows access to DNA for these processes. Failure to package DNA into the nucleosome, the individual unit of chromatin, can lead to genomic instability, driving a cell into apoptosis, senescence, or cellular proliferation. Ultraviolet (UV) radiation damage causes destabilisation of chromatin integrity. UV irradiation induces DNA damage such as photolesions and subjects the chromatin to substantial rearrangements, causing the arrest of transcription forks and cell cycle arrest. Highly conserved processes known as nucleotide and base excision repair (NER and BER) then begin to repair these lesions. However, if DNA repair fails, the cell may be forced into apoptosis. The modification of various histones as well as nucleosome remodelling via ATP-dependent chromatin remodelling complexes are required not only to repair these UV-induced DNA lesions, but also for apoptosis signalling. Histone modifications and nucleosome remodelling in response to UV also lead to the recruitment of various repair and pro-apoptotic proteins. Thus, the way in which a cell responds to UV irradiation via these modifications is important in determining its fate. Failure of these DNA damage response steps can lead to cellular proliferation and oncogenic development, causing skin cancer, hence these chromatin changes are critical for a proper response to UV-induced injury.

A nucleoside anticancer drug, 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (TAS106), sensitizes cells to radiation by suppressing BRCA2 expression

Background

A novel anticancer drug 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (ECyd, TAS106) has been shown to radiosensitize tumor cells and to improve the therapeutic efficiency of X-irradiation. However, the effect of TAS106 on cellular DNA repair capacity has not been elucidated. Our aim in this study was to examine whether TAS106 modified the repair capacity of DNA double-strand breaks (DSBs) in tumor cells.

Methods

Various cultured cell lines treated with TAS106 were irradiated and then survival fraction was examined by the clonogenic survival assays. Repair of sublethal damage (SLD), which indicates DSBs repair capacity, was measured as an increase of surviving cells after split dose irradiation with an interval of incubation. To assess the effect of TAS106 on the DSBs repair activity, the time courses of γ-H2AX and 53BP1 foci formation were examined by using immunocytochemistry. The expression of DNA-repair-related proteins was also examined by Western blot analysis and semi-quantitative RT-PCR analysis.

Results

In clonogenic survival assays, pretreatment of TAS106 showed radiosensitizing effects in various cell lines. TAS106 inhibited SLD repair and delayed the disappearance of γ-H2AX and 53BP1 foci, suggesting that DSB repair occurred in A549 cells. Western blot analysis demonstrated that TAS106 down-regulated the expression of BRCA2 and Rad51, which are known as keys among DNA repair proteins in the homologous recombination (HR) pathway. Although a significant radiosensitizing effect of TAS106 was observed in the parental V79 cells, pretreatment with TAS106 did not induce any radiosensitizing effects in BRCA2-deficient V-C8 cells.

Conclusions

Our results indicate that TAS106 induces the down-regulation of BRCA2 and the subsequent abrogation of the HR pathway, leading to a radiosensitizing effect. Therefore, this study suggests that inhibition of the HR pathway may be useful to improve the therapeutic efficiency of radiotherapy for solid tumors.

Alpinia pricei Rhizome Extracts Induce Cell Cycle Arrest in Human Squamous Carcinoma KB Cells and Suppress Tumor Growth in Nude Mice

Alpinia pricei has been shown to induce apoptosis in human squamous carcinoma (KB) cells. In this study, we report the effectiveness of the ethanol (70%) extracts of A. pricei rhizome (AP extracts) in terms of tumor regression as determined using both in vitro cell culture and in vivo athymic nude mice models of KB cells. We found that the AP extract (25–200 μg/mL) treatment decreased the proliferation of KB cells by arresting progression through the G2/M phase of the cell cycle. This cell cycle blockade was associated with reductions in cyclin A and B1, Cdc2, and Cdc25C, and increased p21/WAF1, Wee1, p53 and phospho-p53 (p-p53) in a dose- and time-dependent manner. Moreover, we found that AP extract treatment decreased metalloproteinase-9 (MMP-9) and urokinase plasminogen activator (u-PA) expression, while expression of their endogenous inhibitors, tissue inhibitor of MMP-1 (TIMP-1) and plasminogen activator inhibitor-1 (PAI-1), were increased in KB cells. Furthermore, AP extract treatment effectively delayed tumor incidence in nude mice inoculated with KB cells and reduced the tumor burden. AP extract treatment also induced apoptotic DNA fragmentation, as detected by in situ TUNEL staining. Thus, A. pricei may possess antitumor activity in human squamous carcinoma (KB) cells.

Engineering a waste management enzyme to overcome cancer resistance to apoptosis: adding DNase1 to the anti-cancer toolbox

Cancer treatment is often complicated by resistance to conventional anti-cancer treatment and to more recently developed immunotherapy and gene therapy. These therapeutic modalities aim at activating death pathways within cancer cells. Attempts to activate the apoptotic death pathway, by overexpressing proapoptotic signals, are compromised by cancer defense mechanisms, which disrupt the apoptotic-signaling cascade downstream of the overexpressed component. Here, we describe a therapeutic option of triggering apoptosis without activating the apoptotic-signaling cascade or using the native apoptosis executioner nuclease. We have engineered Deoxyribonuclease-1 (DNase1), a waste-management enzyme, by deleting its signal peptide, adding a nuclear localization signal, and mutating its actin-binding site. Apoptosis studies and colony-forming assay for assessing cell viability were conducted in apoptosis-resistant Mel-Juso human melanoma cells. The modified DNase1 reduced cell viability by 77% relative to controls. It also induced typical microscopic features of cellular apoptosis, such as Terminal Transferase dUTP Nick-End Labeling-positive cells and DNA fragmentation. Quantification of apoptosis by Laser scanning cytometry demonstrated high-killing efficiency of 70-100%. The results suggest that this modified DNase1 can efficiently eliminate apoptosis-resistant cancer cells through apoptosis. Coupled to different tissue-specific gene expression elements, this recombinant DNase1 may serve as a platform for eliminating a variety of cancer types.

Silibinin-induced apoptosis in MCF7 and T47D human breast carcinoma cells involves caspase-8 activation and mitochondrial pathway

Silibinin, a natural flavonoid, under phase I/II clinical trial in prostate cancer patients was aimed to evaluate its chemotherapeutic potential in human breast cancer cell MCF7 and T47D. Results showed that T47D cells were found to be more sensitive to silibinin than MCF7 as observed by proliferation, clonogenic, and apoptotic assays, which was abrogated by pan-caspase inhibitor but remained unaffected by p53 inhibitor. Apoptotic events in both cell types differ temporally and also by magnitude that involved mitochondrial and caspase-8 activation pathway. These results have relevance in understanding silibinin treatment to breast tumor.