IARC Database of p53 gene mutations in human tumors and cell lines: updated compilation, revised formats and new visualisation tools

Characterization of a new mouse p53 variant: loss-of-function and gain-of-function

Background

p53 is a major tumor suppressor that is inactivated in over 50% of human cancer types through either mutation or inactivating interactions with viral or cellular proteins. The uncertainties around the link between p53 status, therapeutic response, and outcome in cancer suggest that additional factors may be involved. p53 isoforms that are generated via the alternative splicing pathway may be promising candidates for further investigation.

Result

In this study, we report one new p53 protein with two internally deleted regions, resulting in one deleted amino acid fragment (from amino acid residues 42 to 89) and one reading frame-shift region (from amino acid residues 90-120) compared to wild-type p53. The functional status of the new p53 protein, which has a defect in its proline-rich and N-terminal DNA-binding domains, was characterized as possessing an intact conformation, exhibiting no transactivation activity, exerting a dominant-negative effect and an interacting with a coactivator with an arginine methyltransferase activity.

Conclusion

Taken together, our findings provide valuable information about the structure and function of p53 for the regulation of transactivation activity and cellular protein-protein interactions. Furthermore, natural p53 isoforms will help us understand the functional roles of the p53 family and potential therapeutics for p53-dependent cancers.

Interactions between polycyclic aromatic hydrocarbons in complex mixtures and implications for cancer risk assessment

In this review we discuss the effects of exposure to complex PAH mixtures in vitro and in vivo on mechanisms related to carcinogenesis. Of particular concern regarding exposure to complex PAH mixtures is how interactions between different constituents can affect the carcinogenic response and how these might be included in risk assessment. Overall the findings suggest that the responses resulting from exposure to complex PAH mixtures is varied and complicated. More- and less-than additive effects on bioactivation and DNA damage formation have been observed depending on the various mixtures studied, and equally dependent on the different test systems that are used. Furthermore, the findings show that the commonly used biological end-point of DNA damage formation is insufficient for studying mixture effects. At present the assessment of the risk of exposure to complex PAH mixtures involves comparison to individual compounds using either a surrogate or a component-based potency approach. We discuss how future risk assessment strategies for complex PAH mixtures should be based around whole mixture assessment in order to account for interaction effects. Inherent to this is the need to incorporate different experimental approaches using robust and sensitive biological endpoints. Furthermore, the emphasis on future research should be placed on studying real life mixtures that better represent the complex PAH mixtures that humans are exposed to.

Identification of p53 and its isoforms in human breast carcinoma cells

In breast carcinoma, disruption of the p53 pathway is one of the most common genetic alterations. The observation that the p53 can express multiple protein isoforms adds a novel level of complexity to the outcome of p53 mutations. p53 expression was analysed by Western immunoblotting and immunohistochemistry using monoclonal antibodies DO-7, Pab240, and polyclonal antiserum CM-1. The more frequently p53-positive nuclear staining has been found in the invasive breast tumors. One of the most intriguing findings is that mutant p53 appears as discrete dot-shaped regions within the nucleus of breast cancer cells. In many malignant cells, the nucleolar sequestration of p53 is evident. These observations support the view that the nucleolus is involved directly in the mediation of p53 function or indirectly by the control of the localization of p53 interplayers. p53 expressed in the nuclear fraction of breast cancer cells revealed a wide spectrum of isoforms. p53 isoforms ΔNp53 (47 kDa) and Δ133p53 β (35 kDa), known as dominant-negative repressors of p53 function, were detected as the most predominant variants in nuclei of invasive breast carcinoma cells. The isoforms expressed also varied between individual tumors, indicating potential roles of these p53 variants in human breast cancer.

Prodigiosin rescues deficient p53 signaling and antitumor effects via upregulating p73 and disrupting its interaction with mutant p53

p53 reactivation offers a broad-based strategy for cancer therapy. In this study, we report the identification of prodigiosin that can reactivate p53 family-dependent transcriptional activity in p53-deficient human colon cancer cells. Prodigiosin and its structural analogue (compound R) induced the expression of p53 target genes accompanied by cell-cycle arrest and apoptosis in p53-deficient cancer cells. Prodigiosin restored p53 signaling in cancer cells harboring hotspot TP53 mutations, with little to no detectable cytotoxicity in normal human fibroblasts and with no genotoxicity. Prodigiosin induced the expression of p73 and disrupted its interaction with mutant p53, thereby rescuing p53 pathway deficiency and promoting antitumor effects. The disruption of mutant p53/p73 interaction was specific to prodigiosin and not related to mTOR inhibition. Our findings suggest that mutant p53 needs to be targeted in the context of p73 stimulation to allow efficient restoration of the p53 pathway. In exhibiting this capability, prodigiosin and its analogue provide lead compounds to rescue deficiencies in the p53 pathway in cancer cells by upregulating p73 and targeting mutant p53/p73 interaction there.

Genotype misclassification in genetic association studies of the rs1042522 TP53 (Arg72Pro) polymorphism: a systematic review of studies of breast, lung, colorectal, ovarian, and endometrial cancer

Preferential loss of heterozygosity at the rs1042522 locus of the tumor protein 53 gene (TP53) (Arg72Pro) is observed in several tumors. Genetic association studies in oncology often use tumor tissue rather than unaffected tissue for genotyping; in such cases, loss of heterozygosity at the TP53 locus could lead to differential misclassification and could bias estimates of association. We searched multiple databases (through March 8, 2011) for studies investigating the association of Arg72Pro with breast, lung, colorectal, ovarian, or endometrial cancer. Meta-analysis was performed with multilevel Bayesian models. Informative priors for the bias effect were derived from a meta-analysis of the same polymorphism in cervical cancer. Of 160 studies (68 breast, 42 lung, 26 colorectal, 16 ovarian, and 8 endometrial cancer), 22 used tumor tissue as the source of genotyping material for cases. Use of tumor tissue versus other sources of genotyping material was associated with an apparent protective effect of the proline allele (relative odds ratio = 0.78, 95% credible interval: 0.70, 0.88). The probability that use of tumor tissue induced bias was estimated to be higher than 99%. Use of tumor tissue as the source of genotyping material for cases is associated with significant bias in the estimate of the genetic effect in cancer genetic association studies.

Cancer of mice and men: old twists and new tails

In this review we set out to celebrate the contribution that mouse models of human cancer have made to our understanding of the fundamental mechanisms driving tumourigenesis. We take the opportunity to look forward to how the mouse will be used to model cancer and the tools and technologies that will be applied, and indulge in looking back at the key advances the mouse has made possible.

Measurement of translesion synthesis by fluorescent capillary electrophoresis: 7,8-dihydro-8-oxodeoxyguanosine bypass modulation by natural products

Translesion synthesis (TLS) relies on a series of specialized DNA polymerases able to insert a base either correctly or incorrectly opposite a lesion on a DNA template strand during replication or post-repair synthesis. To measure the correct or mutagenic outcome of 7,8-dihydro-8-oxodeoxyguanosine (8-oxodG) bypass by TLS DNA polymerases, a capillary electrophoresis (CE) method with fluorescent label has been developed. Two oligonucleotides were designed and hybridized: (i) a 72-mer oligonucleotide framing one 8-oxodG at position 40 and (ii) the 39-mer oligonucleotide complementary to the first strand from the 3' end to the lesion and labeled at the 5' end with a fluorochrome. After incubation with FHs 74 Int human intestinal epithelial cell nuclear proteins, in the presence of either deoxyadenosine triphosphate (dATP) or deoxycytidine triphosphate (dCTP), and denaturation, the resulting elongated oligomers were analyzed by fluorescent capillary electrophoresis. This primer extension assay was then validated in terms of linearity (linear range=0.5-2.5 nM), detectability (limits of detection and quantification=0.023 and 0.091 nM, respectively), and precision (total precisions=8.1% and 3.7% for dATP and dCTP, respectively, n=9). The addition of some natural phytochemicals to the reaction mix significantly influences the outcome of TLS either in an error-free way or in a mutagenic way.

Synergistic interaction between cisplatin and PARP inhibitors in non-small cell lung cancer

The antineoplastic agent cis-diammineplatinum(II) dichloride (cisplatin, CDDP) is part of the poorly effective standard treatment of non-small cell lung carcinoma (NSCLC). Here, we report a novel strategy to improve the efficacy of CDDP. In conditions in which CDDP alone or either of two PARP inhibitors, PJ34 hydrochloride hydrate or CEP 8983, used as standalone treatments were inefficient in killing NSCLC cells, the combination of CDDP plus PJ34 or that of CDDP plus CEP 8983 were found to kill a substantial fraction of the cells. This cytotoxic synergy could be recapitulated by combining CDDP and the siRNA-mediated depletion of the principal PARP isoform, PARP1, indicating that it is mediated by on-target effects of PJ34 or CEP 8983. CDDP and PARP inhibitors synergized in inducing DNA damage foci, mitochondrial membrane permeabilization leading to cytochrome c release, and dissipation of the inner transmembrane potential, caspase activation, plasma membrane rupture and loss of clonogenic potential in NSCLC cells. Collectively, our results indicate that CDDP can be advantageously combined with PARP inhibitors to kill several NSCLC cell lines, independently from their p53 status. Combined treatment with CDDP and PARP inhibitors elicits the intrinsic pathway of apoptosis.

Prediction of P53 mutants (multiple sites) transcriptional activity based on structural (2D&3D) properties

Prediction of secondary site mutations that reinstate mutated p53 to normalcy has been the focus of intense research in the recent past owing to the fact that p53 mutants have been implicated in more than half of all human cancers and restoration of p53 causes tumor regression. However laboratory investigations are more often laborious and resource intensive but computational techniques could well surmount these drawbacks. In view of this, we formulated a novel approach utilizing computational techniques to predict the transcriptional activity of multiple site (one-site to five-site) p53 mutants. The optimal MCC obtained by the proposed approach on prediction of one-site, two-site, three-site, four-site and five-site mutants were 0.775,0.341,0.784,0.916 and 0.655 respectively, the highest reported thus far in literature. We have also demonstrated that 2D and 3D features generate higher prediction accuracy of p53 activity and our findings revealed the optimal results for prediction of p53 status, reported till date. We believe detection of the secondary site mutations that suppress tumor growth may facilitate better understanding of the relationship between p53 structure and function and further knowledge on the molecular mechanisms and biological activity of p53, a targeted source for cancer therapy. We expect that our prediction methods and reported results may provide useful insights on p53 functional mechanisms and generate more avenues for utilizing computational techniques in biological data analysis.

Small-cell lung cancer: an update on targeted therapies

Lung cancer is the leading cause of cancer-related deaths world-wide and small-cell lung cancer (SCLC) accounts for up to 25% of lung cancer deaths. There has been a considerable amount of research in the understanding of the depth of biology of SCLC and utilizing this knowledge to develop targeted approaches. The treatment of SCLC remains a challenge, despite remarkable initial efficacy to combination chemotherapy and radiation therapy. The response is usually short-lived and the prognosis of SCLC has not changed over the past few decades, necessitating the critical need for evaluating novel agents/therapies. Several signaling pathways have been found to be activated in SCLC tumor cells, forming a rationale for blocking some of the drugable targets. Molecular changes and biological markers have been identified but remain to be validated. Novel and targeted agents have been evaluated but without much success. Increasing understanding of the biology and potential clinical evaluation of biomarkers will pave the way for more effective treatments.

p53 expression controls prostate cancer sensitivity to chemotherapy and the MDM2 inhibitor Nutlin-3

Prostate cancer is the second most commonly diagnosed cancer in men, and approximately one-third of those diagnosed succumb to the disease. The development of prostate cancer from small regions of hyperplasia to invasive tumors requires genetic and epigenetic alterations of critical cellular components to aid in the development of cells more adapted for aberrant growth. The p53 transcription factor is a critical element in the cell's ability to regulate the cell cycle and its response to DNA damage. Mutations within the DNA-binding domain of p53 are common and allow the formation of tetramers; however, these alterations prevent this protein complex from associating with target gene promoters. In the present study, we examined the effects of p53 functionality in prostate cancer cells that harbored wild-type (WT) or mutant forms of the protein in response to commonly used chemotherapeutic drugs. The androgen receptor positive 22Rv-1 and LNCaP prostate cancer cell lines carry WT p53 and were demonstrated to have a decrease in chemotherapeutic drug sensitivity when transfected with a dominant-negative (DN) p53. Conversely, expression of the WT p53 in the p53-mutated and more advanced DU145 prostate cancer cell line significantly increased its overall sensitivity to anti-neoplastic drugs. Furthermore, analysis of colony formation in soft agar revealed that the functional status of p53 in each cell line altered the cell's ability to proliferate in an anchorage-independent fashion. Prostate cancer colony growth was more prevalent when p53 transcriptional activity was decreased, whereas growth was more limited in the presence of functional p53. These results demonstrate that the functional status of the tumor suppressor p53 is important in the progression of prostate cancer and dictates the overall effectiveness a given drug would have on disease treatment.

Pyramidalization of the glycosidic nitrogen provides the way for efficient cleavage of the N-glycosidic bond of 8-OxoG with the hOGG1 DNA repair protein

A mechanistic pathway for cleavage of the N-glycosidic bond of 8-oxo-2'-deoxyguanosine (oxoG) catalyzed with the human 8-oxoguanine glycosylase 1 DNA repair protein (hOGG1) is proposed in this theoretical study. The reaction scheme suggests direct proton addition to the glycosidic nitrogen N9 of oxoG from the Nε-ammonium of Lys249 residue of hOGG1 that is enabled owing to the N9 pyramidal geometry. The N9-pyramidalization of oxoG is induced within hOGG1 active site. The coordination of N9 nitrogen to the Nε-ammonium of Lys249 unveiled by available crystal structures enables concerted, synchronous substitution of the N9-C1' bond by the N9-H bond. The reaction is compared with other pathways already proposed by means of calculated activation energies. The ΔG(#) energy for the newly proposed reaction mechanism calculated with the B3LYP/6-31G(d,p) method 17.0 kcal mol(-1) is significantly lower than ΔG(#) energies for other reactions employing attack of the Nε-amino group to the anomeric carbon C1' of oxoG and attack of the Nε-ammonium to the N3 nitrogen of oxoG base. Moreover, activation energy for the oxoG cleavage proceeding via N9-pyramidalization is lower than energy calculated for normal G because the electronic state of the five-membered aromatic ring of oxoG is better suited for the reaction. The modification of aromatic character introduced by oxidation to the nucleobase thus seems to be the factor that is checked by hOGG1 to achieve base-specific cleavage.

The p53 pathway in hematopoiesis: lessons from mouse models, implications for humans

Aberrations in the p53 tumor suppressor pathway are associated with hematologic malignancies. p53-dependent cell cycle control, senescence, and apoptosis functions are actively involved in maintaining hematopoietic homeostasis under normal and stress conditions. Whereas loss of p53 function promotes leukemia and lymphoma development in humans and mice, increased p53 activity inhibits hematopoietic stem cell function and results in myelodysplasia. Thus, exquisite regulation of p53 activity is critical for homeostasis. Most of our understanding of p53 function in hematopoiesis is derived from genetically engineered mice. Here we summarize some of these models, the various mechanisms that disrupt the regulation of p53 activity, and their relevance to human disease.

Haploinsufficiency of Tumor Suppressor Genes is Driven by the Cumulative Effect of microRNAs, microRNA Binding Site Polymorphisms and microRNA Polymorphisms: An In silico Approach

Haploinsufficiency of tumor suppressor genes, wherein the reduced production and activity of proteins results in the inability of the cell to maintain normal cellular function, is one among the various causes of cancer. However the precise molecular mechanisms underlying this condition remain unclear. Here we hypothesize that single nucleotide polymorphisms (SNPs) in the 3′untranslated region (UTR) of mRNAs and microRNA seed sequence (miR-SNPs) may cause haploinsufficiency at the level of proteins through altered binding specificity of microRNAs (miRNAs). Bioinformatics analysis of haploinsufficient genes for variations in their 3′UTR showed that the occurrence of SNPs result in the creation of new binding sites for miRNAs, thereby bringing the respective mRNA variant under the control of more miRNAs. In addition, 19 miR-SNPs were found to result in non-specific binding of microRNAs to tumor suppressors. Networking analysis suggests that the haploinsufficient tumor suppressor genes strongly interact with one another, and any subtle alterations in this network will contribute to tumorigenesis.

Cigarette smoke and adverse health effects: An overview of research trends and future needs

A large volume of data has accumulated on the issues of tobacco and health worldwide. The relationship between tobacco use and health stems initially from clinical observations about lung cancer, the first disease definitively linked to tobacco use. Almost 35 years ago, the Office of the Surgeon General of the United States Health Service reviewed over 7000 research papers on the topic of smoking and health, and publicly recognized the role of smoking in various diseases, including lung cancer. Since then, numerous studies have been published that substantiate the strong association of tobacco use with a variety of adverse human health effects, most prominently with cancer and cardiovascular diseases. Cigarette smoking is regarded as a major risk factor in the development of lung cancer, which is the main cause of cancer deaths in men and women in the United States and the world. Major advances have been made by applying modern genetic technologies to examine the relationship between exposure to tobacco smoke and the development of diseases in human populations. The present review summarizes the major research areas of the past decade, important advances, future research needs and federal funding trends.

Analysis of p53 binding to DNA by fluorescence imaging microscopy

Transcription factors play a central role in cell biology through binding to target DNA elements and regulating gene expression. In this study, we used the p53 tumour suppressor as a model transcription factor to develop an imaging based assay to measure DNA binding. The assay utilizes fluorescence imaging microscopy to detect labelled p53 bound to DNA coated on microbeads. We demonstrate the ability to multiplex the assay by interrogating simultaneous binding to variant DNA sequences present on tractable beads. Additionally, the assay measures activation of p53 for increased DNA binding by a known peptide in addition to reactivation of mutant p53 by a small molecule. It may therefore be adaptable to a high-content imaging screen for compounds capable of restoring the function of mutant p53 associated with cancer.

Analysis of Tp53 codon 72 polymorphisms, Tp53 mutations, and HPV infection in cutaneous squamous cell carcinomas

Background

Non-melanoma skin cancers are one of the most common human malignancies accounting for 2–3% of tumors in the US and represent a significant health burden. Epidemiology studies have implicated Tp53 mutations triggered by UV exposure, and human papilloma virus (HPV) infection to be significant causes of non-melanoma skin cancer. However, the relationship between Tp53 and cutaneous HPV infection is not well understood in skin cancers. In this study we assessed the association of HPV infection and Tp53 polymorphisms and mutations in lesional specimens with squamous cell carcinomas.

Methods

We studied 55 cases of histologically confirmed cutaneous squamous cell carcinoma and 41 controls for the presence of HPV infection and Tp53 genotype (mutations and polymorphism).

Results

We found an increased number of Tp53 mutations in the squamous cell carcinoma samples compared with perilesional or control samples. There was increased frequency of homozygous Tp53-72R polymorphism in cases with squamous cell carcinomas, while the Tp53-72P allele (Tp53-72R/P and Tp53-72P/P) was more frequent in normal control samples. Carcinoma samples positive for HPV showed a decreased frequency of Tp53 mutations compared to those without HPV infection. In addition, carcinoma samples with a Tp53-72P allele showed an increased incidence of Tp53 mutations in comparison carcinomas samples homozygous for Tp53-72R.

Conclusions

These studies suggest there are two separate pathways (HPV infection and Tp53 mutation) leading to cutaneous squamous cell carcinomas stratified by the Tp53 codon-72 polymorphism. The presence of a Tp53-72P allele is protective against cutaneous squamous cell carcinoma, and carcinoma specimens with Tp53-72P are more likely to have Tp53 mutations. In contrast Tp53-72R is a significant risk factor for cutaneous squamous cell carcinoma and is frequently associated with HPV infection instead of Tp53 mutations. Heterozygosity for Tp53-72R/P is protective against squamous cell carcinomas, possibly reflecting a requirement for both HPV infection and Tp53 mutations.

None-endoscopic Screening for Esophageal Squamous Cell Carcinoma- A Review

Esophageal cancer (EC) is the eighth most common cancer and sixth most frequent cause of cancer mortality worldwide. Esophageal squamous cell carcinoma (ESCC) is the most common type of EC. ESCC develops by progression from premalignant lesions, which are called esophageal squamous dysplasia (ESD). Prevention is the most effective strategy for controlling this disease. Generally, two methods may be defined for ESCC prevention. The aim of the first preventive method is to prevent the initiation of ESD by avoiding the known risk factors, or primary prevention. Secondary prevention focuses on detection of the disease in its early curable stage, thus preventing its progression into advanced stages. Endoscopy with iodine staining and biopsy is the diagnostic choice for ESD. However it is invasive and expensive, and not accepted by asymptomatic ESD cases. Therefore, it is necessary to find a non-endoscopic screening method. Despite the large number of studies conducted worldwide, no approved method has been developed for ESCC screening. Regarding the multi-factorial nature of ESCC, it is proposed that the use of a combination of various criteria, such as cytological examination, risk factors, genetic alteration, and molecular markers may result in the development of a comprehensive and effective ESCC screening program.

The NF-Y/p53 liaison: well beyond repression

NF-Y is a sequence-specific transcription factor - TF - targeting the common CCAAT promoter element. p53 is a master TF controlling the response to stress signals endangering genome integrity, often mutated in human cancers. The NF-Y/p53 - and p63, p73 - interaction results in transcriptional repression of a subset of genes within the vast NF-Y regulome under DNA-damage conditions. Recent data shows that NF-Y is also involved in pro-apoptotic activities, either directly, by mediating p53 transcriptional activation, or indirectly, by being targeted by a non coding RNA, PANDA. The picture is subverted in cells carrying Gain-of-function mutant p53, through interactions with TopBP1, a protein also involved in DNA repair and replication. In summary, the connection between p53 and NF-Y is crucial in determining cell survival or death.

Scutellaria litwinowii induces apoptosis through both extrinsic and intrinsic apoptotic pathways in human promyelocytic leukemia cells

Scutellaria is a genus of Lamiaceae with known antiproliferative potentials. Scutellaria litwinowii Bornm. & Sint. ex Bornm. is one of the Iranian species of Scutellaria. Although there are widespread reports about the cytotoxic and antitumor effects of some species of this genus, research on the molecular mechanism responsible for the anticancer effects of S. litwinowii has not yet been conducted. In the current study, the apoptotic effects of S. litwinowii on 2 myeloid cell lines, apoptosis-proficient HL60 cells and apoptosis-resistant K562 cells, were analyzed. An increase in the activity of caspases-3, -8, and -9, poly (ADP ribose) polymerase (PARP) cleavage, detection of phosphatidylserine on the outer layer of cell membrane and sub-G1 peak in the flow cytometry histogram of treated cells, suggested the induction of apoptosis. S. litwinowii also increased the Bax/Bcl-2 ratio. It could be concluded that S. litwinowii induced apoptosis in both apoptosis-proficient and apoptosis-resistant leukemic cells and it might be considered as a novel candidate in the treatment of hematological malignancies.

Effects of temperature on the p53-DNA binding interactions and their dynamical behavior: comparing the wild type to the R248Q mutant

Background

The protein p53 plays an active role in the regulation of cell cycle. In about half of human cancers, the protein is inactivated by mutations located primarily in its DNA-binding domain. Interestingly, a number of these mutations possess temperature-induced DNA-binding characteristics. A striking example is the mutation of Arg248 into glutamine or tryptophan. These mutants are defective for binding to DNA at 310 K although they have been shown to bind specifically to several p53 response elements at sub-physiological temperatures (298–306 K).

Methodology/Principal Findings

This important experimental finding motivated us to examine the effects of temperature on the structure and configuration of R248Q mutant and compare it to the wild type protein. Our aim is to determine how and where structural changes of mutant variants take place due to temperature changes. To answer these questions, we compared the mutant to the wild-type proteins from two different aspects. First, we investigated the systems at the atomistic level through their DNA-binding affinity, hydrogen bond networks and spatial distribution of water molecules. Next, we assessed changes in their long-lived conformational motions at the coarse-grained level through the collective dynamics of their side-chain and backbone atoms separately.

Conclusions

The experimentally observed effect of temperature on the DNA-binding properties of p53 is reproduced. Analysis of atomistic and coarse-grained data reveal that changes in binding are determined by a few key residues and provide a rationale for the mutant-loss of binding at physiological temperatures. The findings can potentially enable a rescue strategy for the mutant structure.

The synergistic therapeutic effect of cisplatin with Human papillomavirus E6/E7 short interfering RNA on cervical cancer cell lines in vitro and in vivo

Human papillomavirus (HPV) types 16 and 18 are the major etiologic factors in the development of cervical epithelial neoplasia. Our study was designed to validate antiviral short interfering RNA (siRNA) targeting the E6 and E7 oncogenes as a potential chemosensitizer of cisplatin (cis-diaminedichloroplatinum II; CDDP) in cervical carcinoma. Specifically, the therapeutic efficacy of combination of CDDP and E6/E7-specific siRNA was assessed in an in vivo cervical cancer xenograft models. The combination of CDDP and E6/E7-specific siRNA had greater efficacy than the combination of CDDP and E6-specific siRNA especially in terms of inducing cellular senescence. Through in vitro and in vivo experiments, the mechanism of synergy between these two treatments was revealed, demonstrating that the combination of E6/E7-specific siRNA and CDDP therapy was significantly superior to either modality alone. In vitro, long-term exposure of HeLa cells to the combination of CDDP and E6/E7-specific siRNA induced apoptosis and cellular senescence. In vivo, E6/E7-specific siRNA potentiated the antitumor efficacy of CDDP via induction of apoptosis, senescence and antiangiogenesis. Our results suggest that E6/E7-specific siRNA may be an effective sensitizer of CDDP chemotherapy in cervical cancer.

Discovery of Mdm2-MdmX E3 ligase inhibitors using a cell-based ubiquitination assay

E3 ubiquitin ligases are of interest as drug targets for their ability to regulate protein stability and function. The oncogene Mdm2 is an attractive E3 ligase to target, as it is the key negative regulator of the tumor suppressor p53, which controls the transcription of genes involved in cell fate. Overexpression of Mdm2 facilitates tumorigenesis by inactivating p53, and through p53-independent oncogenic effects. We developed a high-throughput cellular Mdm2 auto-ubiquitination assay, which we used to discover a class of small-molecule Mdm2 ligase activity inhibitors. These compounds inhibit Mdm2 and p53 ubiquitination in cells, reduce viability of cells with wild-type p53, and synergize with DNA-damaging agents to cause cell death. We determined that these compounds effectively inhibit the E3 ligase activity of the Mdm2-MdmX hetero-complex. This mechanism may be exploitable to create a new class of anti-tumor agents.

Specific replication factors are targeted by different genotoxic agents to inhibit replication

When mammalian cells experience DNA damaging stress, they block DNA replication to avoid erroneous replication of the damaged template. The cells that are unable to respond to DNA damage continue faulty DNA replication that results in incorporation of genomic lesions. To understand the regulation of replication machinery during stress, systemic studies have been carried out but they have been restricted to the evaluation of the mRNA levels and therefore have not been able to identify post-transcriptional changes, vital for immediate blocking of the progressing DNA replication. We have recently discovered that an essential replication factor is downregulated by radiation stress. In this study, we have carried out a systematic evaluation of protein levels of entire replication apparatus after different types of DNA damage. We report that, independent of the status of p53 and retinoblastoma protein, mammalian cells choose targets that are essential for prereplication, preinitiation, and elongation phases of replication. We imposed different kinds of stress to discern whether similar or unique responses are invoked, and we propose a model for inhibition of replication machinery in which mammalian cells target specific essential replication factors based on the experienced stress.

Recent advances in cytogenetics and molecular biology of adult hepatocellular tumors: implications for imaging and management

Focal nodular hyperplasia (FNH), hepatocellular adenoma (HCA), and hepatocellular carcinoma (HCC) compose hepatocellular neoplasms that occur in adults. These tumors demonstrate characteristic epidemiologic and histopathologic features and clinical and imaging manifestations. HCAs are monoclonal neoplasms characterized by increased predilection to hemorrhage or rupture and occasional transformation to HCC. On the other hand, FNH is a polyclonal tumorlike lesion that occurs in response to increased perfusion and has an indolent clinical course. Up to 90% of HCCs occur in the setting of cirrhosis. Chronic viral hepatitis (hepatitis B and hepatitis C) infection and metabolic syndrome are major risk factors that can induce HCCs in nonfibrotic liver. Recent advances in pathology and genetics have led to better understanding of the histogenesis, natural history, and molecular events that determine specific oncologic pathways used by these neoplasms. HCAs are now believed to result from specific genetic mutations involving TCF1 (transcription factor 1 gene), IL6ST (interleukin 6 signal transducer gene), and CTNNB1 (β catenin-1 gene); FNHs are characterized by an "imbalance" of angiopoietin. While the β catenin signaling pathway is associated with well- and moderately differentiated HCCs, mutations involving p53 (tumor protein 53 gene), MMP14 (matrix metalloproteinase 14 gene), and RhoC (Ras homolog gene family, member C) are associated with larger tumor size, higher tumor grade with resultant shortened tumor-free survival, and poor prognosis. Fibrolamellar carcinoma (FLC), a unique HCC subtype, exhibits genomic homogeneity that partly explains its better overall prognosis. On the basis of recent study results involving cytogenetics and oncologic pathways of HCCs, novel drugs that act against molecular targets are being developed. Indeed, sorafenib (a multikinase inhibitor) is currently being used in the successful treatment of patients with advanced HCC. Characterization of genetic abnormalities and genotype-phenotype correlations in adult hepatocellular tumors provides better understanding of tumor pathology and biology, imaging findings, prognosis, and response to molecular therapeutics.

Prognostic significance of p53 protein expression in early gastric cancer

Mutations of the p53 tumor suppressor gene have been associated with abnormalities in cell cycle regulation, DNA repair and synthesis, apoptosis, and it has been implicated in the prognosis of advanced gastric cancer. The aim of this study was to evaluate the occurrence of p53 gene mutation and its possible prognostic implications in early gastric cancer. In a retrospective study, we studied 80 patients with early gastric cancer treated surgically between 1982 and 2001. Mutation of p53 gene was investigated in surgical gastric specimens by immunohistochemistry, and results were analyzed in relation to gender, age, macroscopic appearance, size and location of tumor, presence of lymph nodes, Lauren's histological type, degree of differentiation, and the 5-year survival. The expression of p53 was more frequent among the intestinal type (p = 0.003), the differentiated (p = 0.007), and the macroscopically elevated tumors (p = 0.038). Nevertheless, the isolated expression of p53 was not associated with the 5-year survival, or with the frequency of lymph node involvement. The degree of differentiation was detected as an independent factor related to the outcome of patients (0.044). Significantly shorter survival time was found in p53-negative compared with p53-positive patients, when considering the degree of differentiation of tumors, as assessed by Cox regression analysis (0.049). The association of p53 with the intestinal type, the degree of differentiation and morphological characteristics, may reflect the involvement of chronic inflammatory process underlying early gastric cancer. In this population sample, the expression of p53 alone has no prognostic value for early gastric cancer. However, the significant difference in p53 expression between subgroups of degree of differentiation of tumors can influence post-operative outcome of patients and may be related to possible distinct etiopathogenic subtypes.

Loss of p53 in esophageal squamous cell carcinoma and the correlation with survival: analyses of gene mutations, protein expression, and loss of heterozygosity in Japanese patients

BACKGROUND

A high frequency of p53 protein expression or gene mutation has been reported in the early stages of esophageal squamous cell carcinoma (ESCC), and thus loss of p53 function is thought to be very important in esophageal carcinogenesis. However, there is controversy surrounding the correlation between p53 dysfunction and ESCC tumor progression. The complexity arises from the different modalities, such as mutation analysis, immunohistochemistry, and the detection of loss of heterozygosity (LOH) at the p53 genomic locus.

METHODS

In this study, we comprehensively analyzed p53 gene mutation, p53 protein expression, and LOH at 17p13 in 94 surgically resected Japanese cases of ESCC.

RESULTS

The frequency of p53 gene mutation was 60.6%. The rate of positive p53 protein expression was 56.4%. The frequency of LOH at 17p13 was 67.5%. There was a statistically significant correlation between the presence of a gene mutation and LOH, whereas, there was no significant correlation between gene mutation and protein expression.

CONCLUSIONS

Despite the importance of loss of p53 function in esophageal carcinogenesis, none of the examined parameters, either singly or combined, correlated with overall survival. Taken together, p53 function is a primary target for esophageal carcinogenesis but there is no apparent correlation with the malignant phenotype in ESCC.

Cooperative role of the RNA-binding proteins Hzf and HuR in p53 activation

The RNA-binding protein Hzf (hematopoietic zinc finger) plays important roles in mRNA translation in cerebellar Purkinje cells and adipocytes. We along with others have reported that the expression of the Hzf gene is transcriptionally regulated by the p53 tumor suppressor protein. We show here that Hzf regulates p53 expression in cooperation with HuR. Hzf and HuR independently interact with the 3' untranslated region (UTR) of p53 mRNA, which facilitates the cytoplasmic localization of p53 mRNA in the presence of the ARF tumor suppressor protein. In the absence of Hzf and HuR, p53 induction by p19(ARF) is significantly attenuated, and the cells consequently acquire resistance to p19(ARF). Thus, these findings demonstrate that in addition to Mdm2 inhibition, p19(ARF) increases the concentration of p53 through posttranscriptional control of p53 mRNA and suggest critical roles for the RNA-binding proteins Hzf and HuR in p53 induction.

iASPP is over-expressed in human non-small cell lung cancer and regulates the proliferation of lung cancer cells through a p53 associated pathway

Background

iASPP is a key inhibitor of tumour suppressor p53 and is found to be up-regulated in certain malignant conditions. The present study investigated the expression of iASPP in clinical lung cancer, a leading cancer type in the world, and the biological impact of this molecule on lung cancer cells.

Methods

iASPP protein levels in lung cancer tissues were evaluated using an immunohistochemical method. In vitro, iASPP gene expression was suppressed with a lentvirus-mediated shRNA method and the biological impact after knocking down iASSP on lung cancer cell lines was investigated in connection with the p53 expression status.

Results

We showed here that the expression of iASPP was significantly higher in lung cancer tissues compared with the adjacent normal tissues. iASPP shRNA treatment resulted in a down-regulation of iASPP in lung cancer cells. There was a subsequent reduction of cell proliferation of the two lung tumour cell lines A459 and 95D both of which had wild-type p53 expression. In contrast, reduction of iASPP in H1229 cells, a cell with little p53 expression, had no impact on its growth rate.

Conclusions

iASPP regulates the proliferation and motility of lung cancer cells. This effect is intimately associated with the p53 pathway. Together with the pattern of the over-expression in clinical lung cancers, it is concluded that iASPP plays an pivotal role in the progression of lung cancer and is a potential target for lung cancer therapy.

p53 functional activation is independent of its genotype in five esophageal squamous cell carcinoma cell lines

p53 mutations have been found in many esophageal squamous cell carcinoma (ESCC) clinical specimens and cell lines. We reasoned that functional inactivation of wild-type p53 or the functional activation of mutant-type p53 might exist in these specimens and cell lines. In this study, we identified the correlation between p53 functional activation and its genotype in five different ESCC cell lines. To examine the potential p53 activation in a certain ESCC cell line, DNA damage methods including X-ray exposure and cisplatin treatment were employed to treat cells. Further, the expression of p53 protein and four transcripts of well-known p53 target genes were investigated using Western blot and reverse transcriptionpolymerase chain reaction (RT-PCR) after cell exposure to DNA damage. The results showed that in KYSE 30 cell line with mutant p53 and KYSE 150 with wild-type p53, p53 could be activated by DNA damages. However, p53 could not be activated following the DNA damages in YES 2 with wild-type p53, KYSE 70 with mutant p53, and EC9706 with unknown p53 genotype. All our data indicated that p53 function in certain cells is not closely correlated with its genotype. To judge p53 function in a particular cell line, it is important to examine the p53 functional activation, but not to simply rely on the p53 genotype.

The C terminus of p53 binds the N-terminal domain of MDM2

The p53 tumor suppressor interacts with its negative regulator Mdm2 via the former's N-terminal region and core domain, yet the extreme p53 C-terminal region contains lysine residues ubiquitinated by Mdm2 and can bear post-translational modifications that inhibit Mdm2-p53 association. We show that the Mdm2-p53 interaction is decreased upon deletion, mutation or acetylation of the p53 C terminus. Mdm2 decreases the association of full-length but not C-terminally deleted p53 with a DNA target sequence in vitro and in cells. Further, using multiple approaches, we show that a peptide from the p53 C terminus directly binds the Mdm2 N terminus in vitro. We also show that p300-acetylated p53 inefficiently binds Mdm2 in vitro, and Nutlin-3 treatment induces C-terminal modification(s) of p53 in cells, explaining the low efficiency of Nutlin-3 in dissociating p53-MDM2 in vitro.

DeltaN133p53 expression levels in relation to haplotypes of the TP53 internal promoter region

The transcription of the DeltaN133p53 isoform of the TP53 gene is controlled by an internal promoter region (IPR) containing eight polymorphisms in 11 common haplotypes, following a resequencing of 47 Caucasians. We assayed the functional effects of the commonest six haplotypes on the promoter activity with a luciferase reporter system, in HeLa and 293T cells. These studies showed that different IPR haplotypes are associated with differences in the promoter activity resulting in marked variation in the baseline expression of DeltaN133p53. In vivo quantitative-polymerase chain reaction (PCR) on human tissues confirmed that the baseline levels of DeltaN133p53 showed haplotype specific differences that paralleled those seen in vitro. When cell lines were treated with camptothecin, the fold-increase in DeltaN133p53 levels was dose-dependent but haplotype-independent (i.e., similar for all the haplotypes). Finally, we used an electrophoretic mobility shift assay to analyze the rs1794287 polymorphism and found changes in the pattern of protein binding. This partially confirmed our in silico analysis showing that the polymorphism rs1794287 can affect the function of the internal promoter by changing its affinity for several transcription factors. Thus, we showed that the expression of DeltaN133p53 is under genetic control, and suggested the presence of interindividual differences underlying this mechanism.

Substitution of Ala for Tyr567 in RB69 DNA polymerase allows dAMP to be inserted opposite 7,8-dihydro-8-oxoguanine

Accurate copying of the genome by DNA polymerases is challenging due in part to the continuous damage inflicted on DNA, which results from its contact with reactive oxygen species (ROS), producing lesions such as 7,8-dihydro-8-oxoguanine (8-oxoG). The deleterious effects of 8-oxoG can be attributed to its dual coding potential that leads to G --> T transversions. The wild-type (wt) pol alpha family DNA polymerase from bacteriophage RB69 (RB69pol) prefers to insert dCMP as opposed to dAMP when situated opposite 8-oxoG by >2 orders of magnitude as demonstrated using pre-steady-state kinetics (k(pol)/K(d,app)). In contrast, the Y567A mutant of RB69pol inserts both dCMP and dAMP opposite 8-oxoG rapidly and with equal efficiency. We have determined the structures of preinsertion complexes for the Y567A mutant with dATP and dCTP opposite a templating 8-oxoG in a 13/18mer primer-template (P/T) at resolutions of 2.3 and 2.1 A, respectively. Our structures show that the 8-oxoG residue is in the anti conformation when paired opposite dCTP, but it flips to a syn conformation forming a Hoogstein base pair with an incoming dATP. Although the Y567A substitution does not significantly change the volume of the pocket occupied by anti-8-oxoG, it does provide residue G568 the flexibility to move deeper into the minor groove of the P/T to accommodate, and stabilize, syn-8-oxoG. These results support the hypothesis that it is the flexibility of the nascent base pair binding pocket (NBP) in the Y567A mutant that allows efficient insertion of dAMP opposite 8-oxoG.

New biomarkers for lung cancer

IMPORTANCE OF THE FIELD

Despite many efforts to improve early detection, lung cancer remains the leading cause of cancer deaths. Stage is the main determinant of prognosis and the basis for deciding treatment options. Screening tests for lung cancer have not been successful so far.

AREAS COVERED IN THE REVIEW

The article reviews the available literature related to biomarkers in use at present and those that could be used for early diagnosis, staging, prognosis, response to therapy and prediction of recurrence. The single biomarkers are analysed, divided according to the technological methods used and the locations of sampling.

WHAT THE READER WILL GAIN

The reader will gain knowledge on biomarkers in use and those now under study. The reader will also gain insights into the difficulties pertaining to the development of biomarkers, results reproducibility and clinical application.

TAKE HOME MESSAGE

Although some markers seem to be promising, at present there is no consensus on the proven value of their clinical use in lung cancer. The future lies probably in a panel of biomarkers instead of individual assays, or in predictive models derived from the integration of clinical variables and gene expression profiles.

Oncoapoptosis: a novel molecular therapeutic for cancer treatment

Many cancer cells refractory to radiation treatment and chemotherapy proliferate due to loss of intrinsic programmed cell death (apoptosis) regulation. Consequently, the resolution of these cancers are many times outside the management capabilities of conventional therapeutics. We have developed a replication defective herpes simplex virus system which triggers apoptosis specifically in transformed human cells, termed oncoapoptosis. Susceptibility to virus induced cell death is dependent on the p53 protein status in the tumor cells, indicating specific targeting of the treatment. Primary cells which produce functional p53 are resistant to oncoapoptotic killing but not to apoptosis induced by nonviral environmental factors. Thus, induction of apoptosis by nonreplicating virus is a feasible molecular therapeutic approach for killing human cancer cells. Our findings have important implications in designing novel virus-based anticancer strategies.

A review of the molecular mechanisms of chemically induced neoplasia in rat and mouse models in National Toxicology Program bioassays and their relevance to human cancer

Tumor response in the B6C3F1 mouse, F344 rat, and other animal models following exposure to various compounds provides evidence that people exposed to these or similar compounds may be at risk for developing cancer. Although tumors in rodents and humans are often morphologically similar, underlying mechanisms of tumorigenesis are often unknown and may be different between the species. Therefore, the relevance of an animal tumor response to human health would be better determined if the molecular pathogenesis were understood. The underlying molecular mechanisms leading to carcinogenesis are complex and involve multiple genetic and epigenetic events and other factors. To address the molecular pathogenesis of environmental carcinogens, the authors examine rodent tumors (e.g., lung, colon, mammary gland, skin, brain, mesothelioma) for alterations in cancer genes and epigenetic events that are associated with human cancer. National Toxicology Program (NTP) studies have identified several genetic alterations in chemically induced rodent neoplasms that are important in human cancer. Identification of such alterations in rodent models of chemical carcinogenesis caused by exposure to environmental contaminants, occupational chemicals, and other compounds lends further support that they are of potential human health risk. These studies also emphasize the importance of molecular evaluation of chemically induced rodent tumors for providing greater public health significance for NTP evaluated compounds.

Expression of glutathione-S-transferases isoenzymes and p53 in exfoliated human bladder cancer cells

OBJECTIVES

This study investigates the usefulness of glutathione-S-transferases (GST) isoenzymes and p53 immunostaining as a marker of malignancy in urinary cytology, and evaluates their potential effect in increasing diagnostic accuracy in a series of urine cytologic samples. They are also correlated with cytopathology diagnosis and histopathologic diagnosis.

MATERIALS AND METHODS

In this study, the slides from 124 bladder carcinoma patients prepared by the cytocentrifugation method were observed. The cytomorphologic properties of these cancer cells were determined. Moreover, the immunocytochemical distributions of GST alpha (GSTA), pi (GSTP), mu (GSTM4), theta (GSTT1) isoenzymes and p53 protein were studied for the patients.

RESULTS

The urothelial cancer cells had small cytoplasm and rough nuclear membrane. The chromatin granules were heterogeneously distributed in each malignant cell's nucleus. There was a pleomorphism of the malignant cells' nuclei. According to immunocytopathologic observations, the urothelial cancer cells had stronger staining intensity than the benign cells had in 48% of cases for GSTA, 46% of cases for GSTP, 38% of cases for GSTM4, and 42% of cases for GSTT1. For all papillary cases, the malignant cells were stained negative, while the benign cells were positive. For 83% of patients, the malignant cells were stained positive for p53. There was a significant difference in GSTA (P = 0.006), GSTT1 (P = 0.004), GSTP (P = 0.000) and p53 (P = 0.000) expressions for benign cells whereas, a non-statistical difference in the malignant cells for GSTA, GSTT1, GSTP, GSTM4, and p53 expressions (P > 0.05).

CONCLUSIONS

GST isoenzymes and p53 immunostaining were not found to be markers of malignancy in urinary cytology.

Association of genetic polymorphisms, mRNA expression of p53 and p21 with chronic benzene poisoning in a chinese occupational population

DNA damage induced by benzene reactive metabolites is thought of as an important mechanism underlying benzene hematotoxicity and genotoxicity, and genetic variation in cell-cycle control genes may contribute to susceptibility to chronic benzene poisoning (CBP). Using a case-control study that included 307 benzene-poisoned patients and 299 workers occupationally exposed to benzene in south China, we aimed to investigate the association between genetic polymorphisms of p53 and p21 and the odds of CBP. To investigate whether benzene exposure may influence mRNA expression of p53 and p21 in benzene-exposed workers, we also chose 39 CBP workers, 38 occupationally benzene-exposure workers, and 37 nonexposure workers in the same region of China. PCR-restriction fragment length polymorphism technique was applied to detect polymorphisms of p53 (rs17878362, rs1042522, and rs1625895) and p21 (rs1801270 and rs1059234), and real-time PCR was applied to detect the quantity of gene mRNA expression. We found that p21 C98A variant genotypes (CA+AA) or C70T variant genotypes (CT+TT) were associated with decreased odds of CBP [odds ratio (OR), 0.51; 95% confidence interval (95% CI), 0.32-0.83, and OR, 0.53; 95% CI, 0.29-0.95, respectively. Further analysis showed the decreased odds of CBP in the subjects with p21 CC/AT diplotype (OR, 0.51; 95% CI, 0.30-0.85). In addition, p53 mRNA expression of CBP workers or benzene-exposure workers was significantly lower than that of nonexposure workers. Although these results require confirmation and extension, our results show that polymorphisms in p21 may be protective against the risk of CBP in the Chinese occupational population.

Primary urothelial carcinoma of the upper tract: important clinicopathological factors predicting bladder recurrence after surgical resection

The aim of the present study was to further characterize potential clinicopathological predictors for urinary bladder recurrence-free survival (UBRFS) in patients with primary urothelial carcinoma of the upper urinary tract (UUT-UC). The present series included 385 cases of surgically treated primary localized UUT-UC without previous or concurrent urothelial carcinoma of the urinary bladder. Among the 374 patients with follow-up information, clinicopathological features and therapeutic information including whether they received a laparoscopy-assisted nephroureterectomy (LNU) and adjuvant chemotherapy were correlated with UBRFS. After a median follow up of 69 months, 86 patients (23%) developed urinary bladder recurrence. The median time to develop urinary bladder recurrence was 12 months. At the univariate level, an increment in histological grade (P= 0.0321), a prominent papillary configuration (P= 0.0004), LNU (P= 0.0397) and male gender (P= 0.0401) significantly predicted an inferior UBRFS. At the multivariate level, increase of histological grade (P < 0.0001, relative risk (RR) = 3.776), prominent papillary configuration (P < 0.0001, RR = 3.244), and male gender (P= 0.0463, RR = 1.444) independently predicted UBRFS. In conclusion, male patients and those with high-grade and papillary UUT-UC, and who received LNU had higher risks of urinary bladder recurrence. Accordingly, for these patients, more intensive follow up coupled with postoperative intravesical adjuvant therapy to prevent urinary bladder recurrence should also be considered.

HIF2alpha inhibition promotes p53 pathway activity, tumor cell death, and radiation responses

Approximately 50% of cancer patients receive radiation treatment, either alone or in combination with other therapies. Tumor hypoxia has long been associated with resistance to radiation therapy. Moreover, the expression of hypoxia inducible factors HIF1alpha and/or HIF2alpha correlates with poor prognosis in many tumors. Recent evidence indicates that HIF1alpha expression can enhance radiation-induced apoptosis in cancer cells. We demonstrate here that HIF2alpha inhibition promotes tumor cell death and, in contrast to HIF1alpha, enhances the response to radiation treatment. Specifically, inhibiting HIF2alpha expression augments p53 activity, increases apoptosis, and reduces clonogenic survival of irradiated and non-irradiated cells. Moreover, HIF2alpha inhibition promotes p53-mediated responses by disrupting cellular redox homeostasis, thereby permitting reactive oxygen species (ROS) accumulation and DNA damage. These results correlate with altered p53 phosphorylation and target gene expression in untreated human tumor samples and show that HIF2alpha likely contributes to tumor cell survival including during radiation therapy.

Control of p53 multimerization by Ubc13 is JNK-regulated

The p53 tumor suppressor protein is a key regulator of cellular proliferation and survival whose function is tightly regulated at the levels of transcription and protein stability. Here, we unveil the fine control of p53 on translationally active polysomes. We have previously reported that Ubc13, an E2 ubiquitin-conjugating enzyme, directly regulates p53 localization and transcriptional activity. We now demonstrate that the association of p53 and Ubc13 on polysomes requires ongoing translation and results in p53 ubiquitination that interferes with its tetramerization. JNK phosphorylation of p53 at Threonine 81 occurring on polysomes is required for the dissociation of Ubc13 from p53, leading to p53 multimerization and transcriptional activation. Inhibition of JNK activity or expression of a nonphosphorylatable mutant of p53 maintains an Ubc13-p53 complex that inhibits p53 multimerization. Our findings reveal a layer in the regulation of p53 multimerization that requires the concerted action of JNK and Ubc13 on polysome-bound p53.

siRNA-mediated down-regulation of iASPP promotes apoptosis induced by etoposide and daunorubicin in leukemia cells expressing wild-type p53

Oncoprotein inhibitory member of the ASPP family (iASPP) is a key inhibitor of tumor suppressor p53. Our previous study revealed that the expression of iASPP in acute leukemia (AL) patients was higher than that of normal control which implied that iASPP might play an important role in the pathogenesis and/or disease progression of AL. In this study, the iASPP expression was blocked by RNA interference (RNAi) in two leukemic cell lines, Nalm6 and K562, to explore the effects of iASPP on leukemia cells. The results indicated that down-regulation of endogenous iASPP increased p53-dependent apoptosis of leukemia cells. Thus, iASPP could be a molecular target in leukemia therapy.

The efficiency and fidelity of 8-oxo-guanine bypass by DNA polymerases delta and eta

A DNA lesion created by oxidative stress is 7,8-dihydro-8-oxo-guanine (8-oxoG). Because 8-oxoG can mispair with adenine during DNA synthesis, it is of interest to understand the efficiency and fidelity of 8-oxoG bypass by DNA polymerases. We quantify bypass parameters for two DNA polymerases implicated in 8-oxoG bypass, Pols δ and η. Yeast Pol δ and yeast Pol η both bypass 8-oxoG and misincorporate adenine during bypass. However, yeast Pol η is 10-fold more efficient than Pol δ, and following bypass Pol η switches to less processive synthesis, similar to that observed during bypass of a cis-syn thymine-thymine dimer. Moreover, yeast Pol η is at least 10-fold more accurate than yeast Pol δ during 8-oxoG bypass. These differences are maintained in the presence of the accessory proteins RFC, PCNA and RPA and are consistent with the established role of Pol η in suppressing ogg1-dependent mutagenesis in yeast. Surprisingly different results are obtained with human and mouse Pol η. Both mammalian enzymes bypass 8-oxoG efficiently, but they do so less processively, without a switch point and with much lower fidelity than yeast Pol η. The fact that yeast and mammalian Pol η have intrinsically different catalytic properties has potential biological implications.