Identification of a p53 Response Element in the Promoter Region of the hMSH2 Gene Required for Expression in A2780 Ovarian Cancer Cells

Transcription networks rewire gene repertoire to coordinate cellular reprograming in prostate cancer

Transcription factors (TFs) represent the most commonly deregulated DNA-binding class of proteins associated with multiple human cancers. They can act as transcriptional activators or repressors that rewire the cistrome, resulting in cellular reprogramming during cancer progression. Deregulation of TFs is associated with the onset and maintenance of various cancer types including prostate cancer. An emerging subset of TFs has been implicated in the regulation of multiple cancer hallmarks during tumorigenesis. Here, we discuss the role of key TFs which modulate transcriptional cicuitries involved in the development and progression of prostate cancer. We further highlight the role of TFs associated with key cancer hallmarks, including, chromatin remodeling, genome instability, DNA repair, invasion, and metastasis. We also discuss the pluripotent function of TFs in conferring lineage plasticity, that aids in disease progression to neuroendocrine prostate cancer. At the end, we summarize the current understanding and approaches employed for the therapeutic targeting of TFs and their cofactors in the clinical setups to prevent disease progression.

Of the many cellular responses activated by TP53, which ones are critical for tumour suppression?

The tumour suppressor TP53 is a master regulator of several cellular processes that collectively suppress tumorigenesis. The TP53 gene is mutated in ~50% of human cancers and these defects usually confer poor responses to therapy. The TP53 protein functions as a homo-tetrameric transcription factor, directly regulating the expression of ~500 target genes, some of them involved in cell death, cell cycling, cell senescence, DNA repair and metabolism. Originally, it was thought that the induction of apoptotic cell death was the principal mechanism by which TP53 prevents the development of tumours. However, gene targeted mice lacking the critical effectors of TP53-induced apoptosis (PUMA and NOXA) do not spontaneously develop tumours. Indeed, even mice lacking the critical mediators for TP53-induced apoptosis, G1/S cell cycle arrest and cell senescence, namely PUMA, NOXA and p21, do not spontaneously develop tumours. This suggests that TP53 must activate additional cellular responses to mediate tumour suppression. In this review, we will discuss the processes by which TP53 regulates cell death, cell cycling/cell senescence, DNA damage repair and metabolic adaptation, and place this in context of current understanding of TP53-mediated tumour suppression.

A Truncated NRIP1 Mutant Amplifies Microsatellite Instability of Colorectal Cancer by Regulating MSH2/MSH6 Expression, and Is a Prognostic Marker of Stage III Tumors

Simple Summary

The alteration of mismatch repair (MMR) genes leads to microsatellite instability and plays a key role in colorectal cancer (CRC) pathogenesis and prognosis. The transcription factor NRIP1 is involved in intestinal tumorigenesis and is a good prognostic marker in CRC. In this study, we demonstrate that NRIP1 induces MSH2 and MSH6 MMR gene transcription and reduces microsatellite instability. A dominant-negative truncated NRIP1 mutant amplifies the MMR-deficient phenotype and appears as a key player in MSI-driven tumorigenesis since it significantly correlates with a short overall survival of patients with advanced CRC, especially MLH1-deficient ones.

Abstract

Microsatellite instability (MSI) is related to the alteration of mismatch repair (MMR) genes and plays a key role in colorectal cancer (CRC) pathogenesis. We previously reported that the transcription factor Nuclear Receptor Interacting Protein 1 (NRIP1) is involved in sporadic intestinal tumorigenesis. The aim of this study was to decipher its role in MSI CRC. By using different mouse models and engineered cell lines, we demonstrated that NRIP1 increased MSH2 and MSH6 MMR gene transcription and mRNA/protein levels. In human CRC cells, NRIP1 expression was associated with decreased MSI and the hypermutator phenotype, and with resistance to chemotherapy drugs. Using a cohort of 194 CRC patients, we detected in 22% of the cases a MSI-induced frameshift mutation in the NRIP1 coding sequence. This genetic alteration generates a truncated protein with a dominant negative activity that increased human CRC cell proliferation and impaired the regulation of MSH2 and MSH6 gene expression. Moreover, the NRIP1 mutant correlated with a decreased overall survival of patients with advanced CRC, especially when MLH1-deficient. By decreasing the expression of MSH2 and MSH6 gene expression, the NRIP1 variant may amplify MLH1-dependent CRC progression and behave as a new prognostic marker of advanced MSI CRC.

Mutant p53s and chromosome 19 microRNA cluster overexpression regulate cancer testis antigen expression and cellular transformation in hepatocellular carcinoma

A subset of hepatocellular carcinoma (HCC) overexpresses the chromosome 19 miRNA cluster (C19MC) and is associated with an undifferentiated phenotype marked by overexpression of cancer testis antigens (CTAs) including anti-apoptotic melanoma-A antigens (MAGEAs). However, the regulation of C19MC miRNA and MAGEA expression in HCCs are not understood. Here we show that, C19MC overexpression is tightly linked to a sub-set of HCCs with transcription-incompetent p53. Using next-generation and Sanger sequencing we found that, p53 in Hep3B cells is impaired by TP53-FXR2 fusion, and that overexpression of the C19MC miRNA-520G in Hep3B cells promotes the expression of MAGEA-3, 6 and 12 mRNAs. Furthermore, overexpression of p53-R175H and p53-R273H mutants promote miR-520G and MAGEA RNA expression and cellular transformation. Moreover, IFN-γ co-operates with miR-520G to promote MAGEA expression. On the other hand, metals such as nickel and zinc promote miR-526B but not miR-520G, to result in the suppression of MAGEA mRNA expression, and evoke cell death through mitochondrial membrane depolarization. Therefore our study demonstrates that a MAGEA-promoting network involving miR-520G, p53-defects and IFN-γ that govern cellular transformation and cell survival pathways, but MAGEA expression and survival are counteracted by nickel and zinc combination.

Whole-genome sequencing of synchronous thyroid carcinomas identifies aberrant DNA repair in thyroid cancer dedifferentiation

The genetics underlying thyroid cancer dedifferentiation is only partly understood and has not yet been characterised using comprehensive pan-genomic analyses. We investigated a unique case with synchronous follicular thyroid carcinoma (FTC), poorly differentiated thyroid carcinoma (PDTC), and anaplastic thyroid carcinoma (ATC), as well as regional lymph node metastases from the PDTC and ATC from a single patient using whole-genome sequencing (WGS). The FTC displayed mutations in CALR, RB1, and MSH2, and the PDTC exhibited mutations in TP53, DROSHA, APC, TERT, and additional DNA repair genes - associated with an immense increase in sub-clonal somatic mutations. All components displayed an overrepresentation of C>T transitions with associated microsatellite instability (MSI) in the PDTC and ATC, with borderline MSI in the FTC. Clonality analyses pinpointed a shared ancestral clone enriched for mutations in TP53-associated regulation of DNA repair and identified important sub-clones for each tumour component already present in the corresponding preceding lesion. This genomic characterisation of the natural progression of thyroid cancer reveals several novel genes of interest for future studies. Moreover, the findings support the theory of a stepwise dedifferentiation process and suggest that defects in DNA repair could play an important role in the clonal evolution of thyroid cancer. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Census and evaluation of p53 target genes

The tumor suppressor p53 functions primarily as a transcription factor. Mutation of the TP53 gene alters its response pathway, and is central to the development of many cancers. The discovery of a large number of p53 target genes, which confer p53's tumor suppressor function, has led to increasingly complex models of p53 function. Recent meta-analysis approaches, however, are simplifying our understanding of how p53 functions as a transcription factor. In the survey presented here, a total set of 3661 direct p53 target genes is identified that comprise 3509 potential targets from 13 high-throughput studies, and 346 target genes from individual gene analyses. Comparison of the p53 target genes reported in individual studies with those identified in 13 high-throughput studies reveals limited consistency. Here, p53 target genes have been evaluated based on the meta-analysis data, and the results show that high-confidence p53 target genes are involved in multiple cellular responses, including cell cycle arrest, DNA repair, apoptosis, metabolism, autophagy, mRNA translation and feedback mechanisms. However, many p53 target genes are identified only in a small number of studies and have a higher likelihood of being false positives. While numerous mechanisms have been proposed for mediating gene regulation in response to p53, recent advances in our understanding of p53 function show that p53 itself is solely an activator of transcription, and gene downregulation by p53 is indirect and requires p21. Taking into account the function of p53 as an activator of transcription, recent results point to an unsophisticated means of regulation.

The transcription factor p53: not a repressor, solely an activator

The predominant function of the tumor suppressor p53 is transcriptional regulation. It is generally accepted that p53-dependent transcriptional activation occurs by binding to a specific recognition site in promoters of target genes. Additionally, several models for p53-dependent transcriptional repression have been postulated. Here, we evaluate these models based on a computational meta-analysis of genome-wide data. Surprisingly, several major models of p53-dependent gene regulation are implausible. Meta-analysis of large-scale data is unable to confirm reports on directly repressed p53 target genes and falsifies models of direct repression. This notion is supported by experimental re-analysis of representative genes reported as directly repressed by p53. Therefore, p53 is not a direct repressor of transcription, but solely activates its target genes. Moreover, models based on interference of p53 with activating transcription factors as well as models based on the function of ncRNAs are also not supported by the meta-analysis. As an alternative to models of direct repression, the meta-analysis leads to the conclusion that p53 represses transcription indirectly by activation of the p53-p21-DREAM/RB pathway.

Inhibition of p38 MAPK-dependent MutS homologue-2 (MSH2) expression by metformin enhances gefitinib-induced cytotoxicity in human squamous lung cancer cells

OBJECTIVES

Gefitinib, a quinazoline-derived tyrosine kinase inhibitor, has anti-tumor activity in vivo and in vitro. Human MutS homologue-2 (MSH2) plays a central role in promoting genetic stability by correcting DNA replication errors. The present study investigated the effects of p38 mitogen-activated protein kinase (MAPK) signal on gefitinib-induced MSH2 expression in two human non-small cell lung squamous cancer cell lines.

MATERIALS AND METHODS

After the gefitinib treatment, the expressions of MSH2 mRNA were determined by real-time PCR and RT-PCR analysis. Protein levels of MSH2, phospho-MKK3/6, phospho-p38 MAPK were determined by Western blot analysis. We used specific MSH2, and p38 MAPK small interfering RNA to examine the role of p38 MAPK-MSH2 signal in regulating the chemosensitivity of gefitinib. Cell viability was assessed by MTS assay, trypan blue exclusion, and colony-forming ability assay.

RESULTS

Exposure of gefitinib increased MSH2 protein and mRNA levels, which was accompanied by MKK3/6-p38 MAPK activation in H520 and H1703 cells. Moreover, blocking p38 MAPK activation by SB202190 significantly decreased gefitinib-induced MSH2 expression by increasing mRNA and protein instability. In contrast, enhancing p38 activation using constitutively active MKK6 (MKK6E) increased MSH2 protein and mRNA levels. Specific inhibition of MSH2 expression by siRNA enhanced gefitinib-induced cytotoxicity. Metformin, an anti-diabetic drug, might reduce cancer risk. In human lung squamous cancer cells, metformin decreased gefitinib-induced MSH2 expression and augmented the cytotoxic effect and growth inhibition by gefitinib. Transient expression of MKK6E or HA-p38 MAPK vector could abrogate metformin and gefitinib-induced synergistic cytotoxic effect in H520 and H1703 cells.

CONCLUSION

Together, down-regulation of MSH2 expression can be a possible strategy to enhance the sensitivity of gefitinib to human lung squamous cancer cells.

Protein expression and methylation of DNA repair genes hMLH1, hMSH2, MGMT and BRCA1 and their correlation with clinicopathological parameters and prognosis in basal-like breast cancer

AIMS

Basal-like breast cancer (BLBC) is characterized by aggressive behaviour; its genesis is the perturbation of DNA repair as a consequence of BRCA1 methylation or mutation. We comparatively evaluated alterations of DNA repair proteins and p53 between BLBC and non-BLBC cases.

METHODS AND RESULTS

Tumour sections from 104 BLBC and 89 non-BLBC patients were immunostained for hMLH1, hMSH2, MGMT, BRCA1 and p53. Methylation status of DNA repair genes was analysed by methylation-specific PCR, and p53 mutation was examined by direct sequencing. Immunoreactive levels of hMLH1 and MGMT were lower in BLBC, whereas the levels of hMSH2 and p53 were higher, compared to non-BLBC (P ≤ 0.014). Reduced expression of hMLH1 [hazard ratio (HR) 5.26, P = 0.001] and preserved expression of MGMT (HR 2.58, P = 0.039) proved to be independent predictors of poor survival in BLBC patients. DNA repair genes were methylated in approximately 20-40% of BLBCs without a significant relationship between their methylation and p53 mutation. BRCA1 methylation was associated with the loss of its protein expression (P = 0.004). MGMT methylation was linked to larger tumour size (P < 0.001).

CONCLUSIONS

Perturbations of the DNA repair system might be different between BLBC and non-BLBC. Alterations of hMLH1 and MGMT appear important for tumour progression and survival in BLBC patients.

Type-specific cell line models for type-specific ovarian cancer research

BACKGROUND

OVARIAN CARCINOMAS CONSIST OF AT LEAST FIVE DISTINCT DISEASES: high-grade serous, low-grade serous, clear cell, endometrioid, and mucinous. Biomarker and molecular characterization may represent a more biologically relevant basis for grouping and treating this family of tumors, rather than site of origin. Molecular characteristics have become the new standard for clinical pathology, however development of tailored type-specific therapies is hampered by a failure of basic research to recognize that model systems used to study these diseases must also be stratified. Unrelated model systems do offer value for study of biochemical processes but specific cellular context needs to be applied to assess relevant therapeutic strategies.

METHODS

We have focused on the identification of clear cell carcinoma cell line models. A panel of 32 "ovarian cancer" cell lines has been classified into histotypes using a combination of mutation profiles, IHC mutation-surrogates, and a validated immunohistochemical model. All cell lines were identity verified using STR analysis.

RESULTS

Many described ovarian clear cell lines have characteristic mutations (including ARID1A and PIK3CA) and an overall molecular/immuno-profile typical of primary tumors. Mutations in TP53 were present in the majority of high-grade serous cell lines. Advanced genomic analysis of bona-fide clear cell carcinoma cell lines also support copy number changes in typical biomarkers such at MET and HNF1B and a lack of any recurrent expressed re-arrangements.

CONCLUSIONS

As with primary ovarian tumors, mutation status of cancer genes like ARID1A and TP53 and a general immuno-profile serve well for establishing histotype of ovarian cancer cell We describe specific biomarkers and molecular features to re-classify generic "ovarian carcinoma" cell lines into type specific categories. Our data supports the use of prototype clear cell lines, such as TOV21G and JHOC-5, and questions the use of SKOV3 and A2780 as models of high-grade serous carcinoma.

Transcriptional regulation of human DNA repair genes following genotoxic stress: trigger mechanisms, inducible responses and genotoxic adaptation

DNA repair is the first barrier in the defense against genotoxic stress. In recent years, mechanisms that recognize DNA damage and activate DNA repair functions through transcriptional upregulation and post-translational modification were the focus of intensive research. Most DNA repair pathways are complex, involving many proteins working in discrete consecutive steps. Therefore, their balanced expression is important for avoiding erroneous repair that might result from excessive base removal and DNA cleavage. Amelioration of DNA repair requires both a fine-tuned system of lesion recognition and transcription factors that regulate repair genes in a balanced way. Transcriptional upregulation of DNA repair genes by genotoxic stress is counteracted by DNA damage that blocks transcription. Therefore, induction of DNA repair resulting in an adaptive response is only visible through a narrow window of dose. Here, we review transcriptional regulation of DNA repair genes in normal and cancer cells and describe mechanisms of promoter activation following genotoxic exposures through environmental carcinogens and anticancer drugs. The data available to date indicate that 25 DNA repair genes are subject to regulation following genotoxic stress in rodent and human cells, but for only a few of them, the data are solid as to the mechanism, homeostatic regulation and involvement in an adaptive response to genotoxic stress.

Association of epidermal growth factor receptor mutations with human papillomavirus 16/18 E6 oncoprotein expression in non-small cell lung cancer

BACKGROUND

Lung cancers in women, in nonsmokers, and in patients with adenocarcinoma from Asia have more prevalent mutations in the epidermal growth factor receptor (EGFR) gene than their counterparts. However, the etiology of EGFR mutations in this population remains unclear. The authors hypothesized that the human papillomavirus (HPV) type 16/18 (HPV16/18) E6 oncoprotein may contribute to EGFR mutations in Taiwanese patients with lung cancer.

METHODS

One hundred fifty-one tumors from patients with lung cancer were enrolled to determine HPV16/18 E6 and EGFR mutations using immunohistochemistry and direct sequencing, respectively. Levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in lung tumors and cells were evaluated using immunohistochemistry and liquid chromatography-mass spectrometry/mass spectrometry. An supF mutagenesis assay was used to determine H2 O2 -induced mutation rates of lung cancer cells with or without E6 expression.

RESULTS

Patients with E6-positive tumors had a greater frequency of EGFR mutations than those with E6-negative tumors (41% vs 20%; P = .006). Levels of 8-oxo-dG were correlated with EGFR mutations (36% vs 16%; P = .012). Two stable clones of E6-overexpressing H157 and CL-3 cells were established for the supF mutagenesis assay. The data indicated that the cells with high E6 overexpression had higher H2 O2 -induced SupF gene mutation rates compared with the cells that expressed lower levels of E6 and compared with vector control cells.

CONCLUSIONS

HPV16/18 E6 may contribute in part to EGFR mutations in lung cancer, at least in the Taiwanese population.

The E2F1/Rb and p53/MDM2 pathways in DNA repair and apoptosis: understanding the crosstalk to develop novel strategies for prostate cancer radiotherapy

Both the p53- and E2F1-signaling pathways are defective in almost all types of tumors, suggesting very important roles for their signaling networks in regulating the process of tumorigenesis and therapy response. Studies on Radiation Therapy Oncology Group tissue samples have identified aberrant expression of p53, MDM2 (an E3 ubiquitin ligase that targets p53 for proteosomal degradation), and p16 (an upstream regulator of retinoblastoma and hence E2F1 in prostate cancer); abnormal expression of these biomarkers has been associated with clinical outcome after radiotherapy ± androgen deprivation therapy. Although the proapoptotic properties of p53 are well documented, a relatively new aspect of p53 function as an active mediator of prosurvival signaling pathways is now emerging. E2F1 is a transcription factor that possesses both proapoptotic and prosurvival properties. Thus, the role of E2F1 in the process of tumorigenesis versus apoptosis is a contested issue that needs to be resolved. Furthermore, the role of E2F1 in DNA repair is being increasingly recognized. Thus, novel approaches to curb the prosurvival and DNA repair capability of E2F1 while promoting apoptotic function are of interest. In this review, we discuss the challenges involved in targeting the p53/E2F1 pathways and the crosstalk networks, and further propose potential therapeutic strategies for prostate cancer management.

3,3',4,4',5,5'-hexahydroxystilbene impairs melanoma progression in a metastatic mouse model

Stilbenes comprise a group of polyphenolic compounds, which exert inhibitory effects on various malignancies. The aim of this study was to evaluate the antitumor effects of a previously unreported stilbene derivative-3,3',4,4',5,5'-hexahydroxystilbene, termed M8-on human melanoma cells. Cell-cycle analysis of the metastatic melanoma cell line M24met showed that M8 treatment induces G(2)/M arrest accompanied with a dose- and time-dependent upregulation of p21 and downregulation of CDK-2 and leads to apoptosis. M8 induces the expression of phosphorylated p53, proteins involved in the mismatch repair machinery (MSH6, MSH2, and MLH1) and a robust tail moment in a comet assay. In addition, M8 inhibited cell migration in Matrigel assays. Shotgun proteomics and western analysis showed the regulation among others of paxillin, integrin-linked protein kinase, p21-activated kinase, and ROCK-1 indicating that M8 inhibits mesenchymal and amoeboid cell migration. These in vitro data were confirmed in vivo in a metastatic human melanoma severe combined immunodeficient (SCID) mouse model. We showed that M8 significantly impairs tumor growth. M8 also interfered with the metastatic process, as M8 treatment prevented the metastatic spread of melanoma cells to distant lymph nodes in vivo. In summary, M8 exerts strong antitumor effects with the potential to become a new drug for the treatment of metastatic melanoma.

Age associated high level of major vault protein is p53 dependent

Major vault protein (MVP) represents the main component of vaults and has been linked to multi-drug resistance (MDR) in cancer cells. We previously reported that MVP plays an important role in the resistance of senescent human diploid fibroblasts (HDFs) to apoptosis and also that MVP expression is markedly reduced in young HDFs but not in senescent HDFs. In this study, designed to elucidate the regulation of MVP in young and senescent HDFs, we examined the levels of transcriptional factors for the MVP gene, which revealed that among the putative transcriptional factors, p53 decreased only in young HDFs, but not in senescent HDFs in response to H(2)O(2) treatment in the same mode as the expression of MVP. Moreover, the phosphorylation status of p53 increased only in senescent HDFs but not in young HDFs in response to H(2)O(2) treatment. Therefore, we tested the possibility of MVP regulation by p53 status. MVP is upregulated in p53 over-expressing young HDFs, while MVP is downregulated in p53-specific small interfering RNA (siRNA)-transfected senescent HDFs, which suggests that the expression of MVP would be p53 dependent. Furthermore, using chromatin immunoprecipitation (ChIP) assay, we observed that p53 binds directly to the MVP promoter. Taken together, these results suggest that p53 would be a major transcriptional factor for MVP gene expression.

Gene expression patterns in heterozygous Plk4 murine embryonic fibroblasts

Background

The polo-like kinases (Plks) are a group of serine/threonine kinases which have roles in many aspects of cellular function including the regulation of mitotic activity and cellular stress responses. This study focuses on Plk4, the most divergent member of the Plk family, which is necessary for proper cellular proliferation. More specifically, alterations in Plk4 levels cause significantly adverse mitotic defects including abnormal centrosome duplication and aberrant mitotic spindle formation. We sought to clarify the effect of reduced Plk4 levels on the cell by examining transcript profiles of Plk4 wild-type and heterozygous mouse embryonic fibroblasts (MEFs). Subsequently, the levels of several key proteins involved in the DNA damage response were examined.

Results

143 genes were found to be significantly up-regulated in the heterozygous MEFs compared to their wild-type counterparts, while conversely, 9 genes were down-regulated. Numerous genes with increased transcript levels in heterozygous MEFs were identified to be involved in p53-dependent pathways. Furthermore, examination of the promoter regions of all up- and down-regulated genes revealed that the majority contained putative p53 responsive elements.

An analysis of transcript levels in MEFs after exposure to either ionizing or ultraviolet radiation revealed a significant change between wild type and heterozygous MEFS for Plk4 transcript levels upon only UV exposure. Furthermore, changes in protein levels of several important cell check-point and apoptosis regulators were examined, including p53, Chk1, Chk2, Cdc25C and p21. In heterozygous MEFs, p53, p21 and Chk2 protein levels were at significantly higher levels. Furthermore, p53 activity was increased 5 fold in the Plk4 heterozygous MEFs.

Conclusion

Global transcript profiles and levels of key proteins involved in cellular proliferation and DNA damage pathways were examined in wild-type and Plk4 heterozygous MEFs. It was determined that Plk4 haploinsufficiency leads to changes in the levels of RNA accumulation for a number of key cellular genes as well as changes in protein levels for several important cell cycle/DNA damage proteins. We propose a model in which reduced Plk4 levels invoke an increase in p53 levels that leads to the aforementioned changes in global transcription profiles.

The ubiquitin-proteasome system in cancer, a major player in DNA repair. Part 2: transcriptional regulation

DNA repair is an indispensable part of a cell’s defence system against the devastating effects of DNA-damaging conditions. The regulation of this function is a really demanding situation, particularly when the stressing factors persist for a long time. In such cases, the depletion of existing DNA repair proteins has to be compensated by the induction of the analogous gene products. In addition, the arrest of transcription, which is another result of many DNA-damaging agents, needs to be overcome through regulation of transcription-specific DNA repair pathways. The involvement of the ubiquitin-proteasome system (UPS) in cancer- and chemotherapy-related DNA-damage repair relevant to the above transcriptional modification mechanisms are illustrated in this review. Furthermore, the contribution of UPS to the regulation of localization and accessibility of DNA repair proteins to chromatin, in response to cellular stress is discussed.

Cdc7 kinase is a predictor of survival and a novel therapeutic target in epithelial ovarian carcinoma

PURPOSE

There is a lack of prognostic and predictive biomarkers in epithelial ovarian carcinoma, and the targeting of oncogenic signaling pathways has had limited impact on patient survival in this highly heterogeneous disease. The origin licensing machinery, which renders chromosomes competent for DNA replication, acts as a convergence point for upstream signaling pathways. We tested the hypothesis that Cdc7 kinase, a core component of the licensing machinery, is predictive of clinical outcome and may constitute a novel therapeutic target in epithelial ovarian carcinoma.

EXPERIMENTAL DESIGN

A total of 143 cases of ovarian cancer and 5 cases of normal ovary were analyzed for Cdc7 protein expression dynamics and clinicopathologic features. To assess the therapeutic potential of Cdc7, expression was down-regulated by RNA interference in SKOV-3 and Caov-3 ovarian cancer cells.

RESULTS

Increased Cdc7 protein levels were significantly associated with arrested tumor differentiation (P = 0.004), advanced clinical stage (P = 0.01), genomic instability (P < 0.001), and accelerated cell cycle progression. Multivariate analysis shows that Cdc7 predicts disease-free survival independent of patient age, tumor grade and stage (hazard ratio, 2.03; confidence interval, 1.53-2.68; P < 0.001), with the hazard ratio for relapse increasing to 10.90 (confidence interval, 4.07-29.17) for the stages 3 to 4/upper Cdc7 tertile group relative to stages 1 to 2/lower Cdc7 tertile tumors. In SKOV-3 and Caov-3 cells, Cdc7 siRNA knockdown triggered high levels of apoptosis, whereas untransformed cells arrest in G(1) phase and remain viable.

CONCLUSIONS

Our findings show that Cdc7 kinase predicts survival and is a potent anticancer target in epithelial ovarian carcinoma, highlighting its potential as a predictor of susceptibility to small molecule kinase inhibitors currently in development.

Altered expression of mismatch repair proteins associated with acquisition of microsatellite instability in a clonal model of human T lymphocyte aging

The DNA mismatch repair system, the main postreplicative correction pathway in eukaryotic cells, has been shown to be involved in the acquisition of genetic damage during the aging of normal somatic cells, including those of the immune system. Previously, we showed that some but not all human T cell clones (TCC) in an in vitro culture aging model develop microsatellite instability (MSI), which is associated with altered expression of mismatch repair genes. Here, we analyzed levels of mismatch repair proteins as well as the corresponding mRNAs and related this to the development of microsatellite instability in TCC. Msh2, Msh3, Msh6, Pms1, and Pms2 protein expression was quantified by Western blotting. We found that clones not manifesting microsatellite instability in this in vitro model of T cell replicative aging, induced by persistent antigenic stimulation, maintain normal transcriptional control and coordination among the mismatch repair system genes, while clones which do manifest MSI display a general deregulation of gene expression, which is likely to contribute to its occurrence.

Taxanes, microtubules and chemoresistant breast cancer

The taxanes, paclitaxel and docetaxel are microtubule-stabilizing agents that function primarily by interfering with spindle microtubule dynamics causing cell cycle arrest and apoptosis. However, the mechanisms underlying their action have yet to be fully elucidated. These agents have become widely recognized as active chemotherapeutic agents in the treatment of metastatic breast cancer and early-stage breast cancer with benefits gained in terms of overall survival (OS) and disease-free survival (DFS). However, even with response to taxane treatment the time to progression (TTP) is relatively short, prolonging life for a matter of months, with studies showing that patients treated with taxanes eventually relapse. This review focuses on chemoresistance to taxane treatment particularly in relation to the spindle assembly checkpoint (SAC) and dysfunctional regulation of apoptotic signaling. Since spindle microtubules are the primary drug targets for taxanes, important SAC proteins such as MAD2, BUBR1, Synuclein-gamma and Aurora A have emerged as potentially important predictive markers of taxane resistance, as have specific checkpoint proteins such as BRCA1. Moreover, overexpression of the drug efflux pump MDR-1/P-gp, altered expression of microtubule-associated proteins (MAPs) including tau, stathmin and MAP4 may help to identify those patients who are most at risk of recurrence and those patients most likely to benefit from taxane treatment.

The associated contributions of p53 and the DNA mismatch repair protein Msh6 to spontaneous tumorigenesis

DNA mismatch repair (MMR) is a highly conserved system that repairs DNA adducts acquired during replication, as well as some forms of exogenous/endogenous DNA damage. Additionally, MMR proteins bind to DNA adducts that are not removed by MMR and influence damage-response mechanisms other than repair. Hereditary non-polyposis colorectal cancer, as well as mouse models for MMR deficiency, illustrate that MMR proteins are required for maintenance of genetic stability and tumor suppression. In both humans and mice, the phenotype associated with Msh6-associated tumorigenesis is distinct from that of Msh2. In this study, we hypothesized that Msh6-/-;p53+/- mice would display earlier tumor onset than their Msh6-/- or p53+/- counterparts, indicating that concomitant loss of these two tumor suppressors contributes to tumorigenesis via mechanisms that are only partially interrelated. We generated a Msh6-/-;p53+/- mouse model which succumbed to malignant disease at an accelerated rate and with a tumor spectrum distinct from both Msh6-/- and p53+/- models. Alteration of tumor phenotype in the Msh6-/-;p53+/- mice included a marked increase in microsatellite instability that was associated with loss of heterozygosity of the remaining p53 allele. Also, genetic instability was inversely correlated with survival. This manuscript marks the first in vivo investigation into the association between Msh6 and p53, and their combined role in the suppression of spontaneous tumorigenesis, cell survival and genomic stability. Our results support the hypothesis that p53 and Msh6 are functionally interrelated and that, with concomitant mutation, these tumor suppressors act together to accelerate tumorigenesis.

p53 in recombination and repair

Convergent studies demonstrated that p53 regulates homologous recombination (HR) independently of its classic tumour-suppressor functions in transcriptionally transactivating cellular target genes that are implicated in growth control and apoptosis. In this review, we summarise the analyses of the involvement of p53 in spontaneous and double-strand break (DSB)-triggered HR and in alternative DSB repair routes. Molecular characterisation indicated that p53 controls the fidelity of Rad51-dependent HR and represses aberrant processing of replication forks after stalling at unrepaired DNA lesions. These findings established a genome stabilising role of p53 in counteracting error-prone DSB repair. However, recent work has also unveiled a stimulatory role for p53 in topoisomerase I-induced recombinative repair events that may have implications for a gain-of-function phenotype of cancer-related p53 mutants. Additional evidence will be discussed which suggests that p53 and/or p53-regulated gene products also contribute to nucleotide excision, base excision, and mismatch repair.

Prognosis in patients with hepatocellular carcinoma correlates to mutations of p53 and/or hMSH2 genes

Association of gene alterations and prognosis has not fully been elucidated in hepatocellular carcinoma (HCC). To clarify the relationship between p53 and hMSH2 mutations and prognosis, we analysed these mutations in 83 HCC cases and assessed their association with various clinicopathological factors. The 3-year disease-free survival (DFS) or overall survival (OS) rates in HCC patients with p53 mutation and p53 wild/hMSH2 mutation significantly decreased compared with those without these mutations (14.3% and 37.5% versus 67.5% for DFS; 35.7% and 50.0% versus 96.4% for OS, respectively). In the multivariate analysis, categories by p53 and hMSH2 mutation status, and liver cirrhosis demonstrated statistical significances for DFS and OS. Moreover, the frequency of patients with p53 and/or hMSH2 mutations in intrahepatic metastasis (75.0%) was significantly higher than that in multicentric occurrence (14.3%). Thus, p53 and hMSH2 mutations will be useful for identifying subsets of HCC patients with poor prognosis.

HIF-1alpha induces genetic instability by transcriptionally downregulating MutSalpha expression

Hypoxia promotes genetic instability by undefined mechanisms. The transcription factor HIF-1alpha is crucial for the cellular response to hypoxia and is frequently overexpressed in human cancers, resulting in the activation of genes essential for cell survival. Here, we demonstrate that HIF-1alpha is responsible for genetic instability at the nucleotide level by inhibiting MSH2 and MSH6, thereby decreasing levels of the MSH2-MSH6 complex, MutSalpha, which recognizes base mismatches. HIF-1alpha displaces the transcriptional activator Myc from Sp1 binding to repress MutSalpha expression in a p53-dependent manner; Sp1 serves as a molecular switch by recruiting HIF-1alpha to the gene promoter under hypoxia. Furthermore, in human sporadic colon cancers, HIF-1alpha overexpression is statistically associated with the loss of MSH2 expression, especially when p53 is immunochemically undetectable. These findings indicate that the regulation of DNA repair is an integral part of the hypoxic response, providing molecular insights into the mechanisms underlying hypoxia-induced genetic instability.

Alterations of p53, Bcl-2, and hMSH2 protein expression in the cirrhotic, macroregenerative, dysplastic nodules and hepatocellular carcinomas in Upper Egypt

BACKGROUND

Hepatocarcinogenesis involves alterations in p53, Bcl-2 and human Mut S homologue-2 (hMSH2) genes. In Upper Egypt, the clinicopathologic and genetic changes during hepatocarcinogensis (cirrhotic nodules (CN); macroregenerative nodules (MRN) and dysplastic nodules (DN) are unknown.

METHODS

To examine these issues, 48 hepatic resection specimens entailing 25 CN, 16 MRN, 23 DN and 48 hepatocellular carcinoma (HCC) were immunohistochemically evaluated for p53, Bcl-2 and hMSH2 protein expression.

RESULTS

HCC was common in males than in females (2.6:1, P<0.05) and with hepatitis C virus than hepatitis B virus infection (77.1% vs. 18.7%, P=0.001). p53 expression was found in DN (3/23) and HCC (12/48). Its average weighted scores were high in DN/HCC as compared with CN (1.60+/-0.40 and 7.20+/-1.20, P=0.0001). Bcl-2 expression was seen in CN, MRN, DN and HCC (7/48). Its average weighted scores were high in DN (7.60+/-1.60), HCC (6.86+/-0.85) as compared with CN (6.14+/-0.42) and MRN (6.50+/-0.50, P=0.22). hMSH2 average weighted scores were reduced in HCC (7.94+/-1.06) as compared with CN (8.47+/-0.52), MRN (8.00+/-1.00) and DN (8.20+/-0.80, P>0.05).

CONCLUSION

In Upper Egypt: (1) HCC had similar clinicopathologic features to those in the high-risk regions, and (2) alterations of the p53, Bcl-2 and hMSH2 proteins occur during hepatocarcinogensis.

The mismatch DNA repair heterodimer, hMSH2/6, regulates BLM helicase

The human MSH2/6 complex is essential for mismatch recognition during the repair of replication errors. Although mismatch repair components have been implicated in DNA homologous recombination repair, the exact function of hMSH2/6 in this pathway is unclear. Here, we show that the recombinant hMSH2/6 protein complex stimulated the ability of the Bloom's syndrome gene product, BLM, to process Holliday junctions in vitro, an activity that could also be regulated by p53. Consistent with these observations, hMSH6 colocalized with BLM and phospho-ser15-p53 in hydroxyurea-induced RAD51 nuclear foci that may correspond to the sites of presumed stalled DNA replication forks and more likely the resultant DNA double-stranded breaks. In addition, we show that hMSH2 and hMSH6 coimmunoprecipitated with BLM, p53, and RAD51. Both the number of RAD51 foci and the amount of the BLM-p53-RAD51 complex are increased in hMSH2- or hMSH6-deficient cells. These data suggest that hMSH2/6 formed a complex with BLM-p53-RAD51 in response to the damaged DNA forks during double-stranded break repair.

Do beta-tubulin mutations have a role in resistance to chemotherapy?

beta-tubulin is the target of various antitubulin agents used in the treatment of cancer. After beta tubulin was shown to confer resistance to antitubulin agents in established cell lines, several studies have investigated the DNA sequence of this compound in clinical samples. However, these findings are highly controversial, since sequencing experiments showed that the original clinical observation of mutations in the gene resulted from inclusion of non-functional beta-tubulin pseudogenes. At least nine such pseudogenes are known, and all share substantial sequence homology with the functional gene. Subsequent studies have concluded that beta-tubulin mutations in clinical samples are rare, and unlikely to contribute to drug resistance. Here, we overview the beta-tubulin gene family and summarise the results of studies done comparing beta-tubulin mutations with antitubulin drug resistance.

Mechanisms of human DNA repair: an update

The human genome, comprising three billion base pairs coding for 30000-40000 genes, is constantly attacked by endogenous reactive metabolites, therapeutic drugs and a plethora of environmental mutagens that impact its integrity. Thus it is obvious that the stability of the genome must be under continuous surveillance. This is accomplished by DNA repair mechanisms, which have evolved to remove or to tolerate pre-cytotoxic, pre-mutagenic and pre-clastogenic DNA lesions in an error-free, or in some cases, error-prone way. Defects in DNA repair give rise to hypersensitivity to DNA-damaging agents, accumulation of mutations in the genome and finally to the development of cancer and various metabolic disorders. The importance of DNA repair is illustrated by DNA repair deficiency and genomic instability syndromes, which are characterised by increased cancer incidence and multiple metabolic alterations. Up to 130 genes have been identified in humans that are associated with DNA repair. This review is aimed at updating our current knowledge of the various repair pathways by providing an overview of DNA-repair genes and the corresponding proteins, participating either directly in DNA repair, or in checkpoint control and signaling of DNA damage.

Morphological Changes and Apoptosis in Radial Growth Phase Melanoma Cell Lines Following Ultraviolet-B Irradiation

BACKGROUND

Knowledge about the morphologic changes following ultraviolet irradiation in the earliest stages of melanomas is still lacking.

METHODS

To investigate these changes, an in vitro system consisting of radial growth phase Wistar melanoma cell lines (WM35 and WM3211) was established. Cells were irradiated with a single erythemogenic dose of UVB (10 mJ/cm2) and evaluated for morphologic changes.

RESULTS

When compared with the non-irradiated cells, inverted light microscopy revealed increased cellular branching, cytoplasmic size, and multinucleation in the irradiated cells. Transmission electron microscopy revealed the features of increased metabolic activity (hyperplasia of the mitochondria and Golgi) and those of ultrastructural atypia (pleomorphism of the nuclei and nucleoli, increased euchromatin, and nucleolar margination) in the irradiated cells. Moreover, UVB irradiation caused an increase in the apoptotic activity. These alterations were associated with up-regulation of p53, Bcl-2, and the second mismatch repair protein (hMSH2), as revealed by Western blot analysis.

CONCLUSIONS

UVB irradiation can induce apoptosis, morphologic changes, and altered expression of p53, Bcl-2, and hMSH2 in radial growth phase melanoma cell lines. Up-regulation of p53, Bcl-2, and hMSH2 suggests that these factors are involved in the altered balance between survival and apoptosis induced by UVB. Further investigation will be needed to determine if apoptosis and ultrastructural atypia reflect underlying DNA damage and genomic instability induced by UVB.

hMSH2 expression is driven by AP1-dependent regulation through phorbol-ester exposure

Mammalian mismatch repair (MMR) plays a prominent role in genomic stability and toxicity induced by some DNA damaging agents. Advance in the appreciation of regulation mechanisms of the key MMR protein hMSH2 would certainly lead to valuable information on its role and to a better understanding of MMR system dysfunctions with respect to their consequences in cells. We have previously reported that, in myeloid leukemic U937 cell line, the expression of hMSH2 MMR protein is regulated by protein kinase C (PKC) activity. Here we show that the increase of protein level following PKC activation by phorbol ester (TPA) treatment parallels that of hMSH2 mRNA. Our results support the view that the hMSH2 gene is prone to transcriptional regulation upon TPA induction, and that AP-1 is a factor implicated in the transactivation. When losing the AP-1-dependent hMSH2 promoter activity, either by mutating the AP-1 binding sites of the hMSH2 promoter or by using a dominant negative c-Jun factor, the hMSH2 overexpression induced by TPA is abolished both in vitro and in vivo. Thus the control of hMSH2 expression by PKC appears to be dependent, at least partially, on an up-regulation mediated by AP-1 transactivation.

Dynamic expression profile of p21WAF1/CIP1 and Ki-67 predicts survival in rectal carcinoma treated with preoperative radiochemotherapy

PURPOSE

We investigated p53 and its downstream effectors p21WAF1/CIP1, BAX, and hMSH2 as well as the proliferation marker Ki-67 (mki-67/MIB-1) in patients undergoing preoperative radiochemotherapy for rectal carcinoma to identify prognostic and predictive factors. The focus of this study was on the dynamics of these genetic markers in a longitudinal study-that is, before and after radiochemotherapy.

PATIENTS AND METHODS

Expression of p53, BAX, p21WAF1/CIP1, Ki-67, and hMSH2 was investigated by immunohistochemistry in pre- and posttherapeutic tumor samples in 66 patients. Tumor DNA was screened for p53 mutations by single-strand conformation polymorphism-polymerase chain reaction (SSCP-PCR). Paired tumor samples (pretherapy and posttherapy) were collected prospectively.

RESULTS

Patients with a decrease in p21 expression following radiochemotherapy had better disease-free survival (P =.03). Similarly, patients with an increase in proliferative activity as measured by increased Ki-67 expression posttherapy had better disease-free survival (P <.005). In addition, we observed a significantly better prognosis for patients with high hMSH2 expression. In contrast, pretherapeutic levels of p53, BAX, or p21 expression and p53 mutation had no prognostic value, indicating that the combination of radiotherapy and chemotherapy might override defects in these genes.

CONCLUSION

These findings are novel and support the clinical relevance of p21 in the suppression of both proliferation and apoptosis. Thus, the dynamic induction of p21WAF1/CIP1 was associated with a lower proliferative activity but an ultimately worse treatment outcome following neoadjuvant radiochemotherapy and tumor resection. Induction of p21, therefore, represents a novel resistance mechanism in rectal cancer undergoing preoperative radiochemotherapy.

p53 mutated in the transactivation domain retains regulatory functions in homology-directed double-strand break repair

The tumor suppressor p53 transcriptionally transactivates cellular target genes that are implicated in growth control, apoptosis, and DNA repair. However, several studies involving p53 core domain mutants suggested that regulatory functions in recombinative repair do not require transcriptional transactivation and are separable from growth-regulation and apoptosis. Leu22 and Trp23 within the transactivation domain of human p53 play a critical role in binding basal components of the transcription machinery and, therefore, in the transactivation activity of p53. To further delineate whether p53 target genes are involved in recombination regulation, we ectopically expressed p53(22Q,23S) in p53-negative cell lines, which carry reporter systems for different homology-directed double-strand break (DSB) repair events. Like wild-type p53, p53(22Q,23S) efficiently downregulated homologous recombination on two chromosomally integrated substrates without affecting exchange on a substrate for the compound pathway of gene conversion and nonhomologous end joining. Only upon lowering the p53 protein to DNA substrate ratio by several orders of magnitude, we noticed a weak defect of a p53 transactivation domain mutant in DSB repair assays. In conclusion, molecular interactions of p53 within the N-terminal domain are not required to restrain DNA recombination, but might contribute to this genome stabilizing function.

Reduced expression of hMSH2 protein is correlated to poor survival for soft tissue sarcoma patients

BACKGROUND

Deregulation of DNA mismatch repair is a common mechanism for the development of hereditary nonpolyposis colon carcinoma and related familiar cancers, but it also plays a role in the tumorigenesis of sporadic cancers. Although the protein expression of the two main components of DNA mismatch repair, hMSH2 and hMLH1, has been described in soft tissue sarcoma (STS) patients, its prognostic impact is yet to be determined.

METHODS

The authors investigated the expression of the DNA repair proteins hMSH2 and hMLH1 by Western blot analysis in tumor samples of 57 STS patients. The correlation between the expression of hMSH2/hMLH1 and survival was studied in a Cox proportional hazards regression model, which was adjusted for the prognostic effects of staging, tumor entity, and radicality of tumor resection.

RESULTS

Nine of 57 STS (16%) showed reduced expression of hMSH2 and reduced expression of hMLH1 was detected in seven STS patients (12%). In a Kaplan-Meier analysis, the median survival for patients with reduced expression of the hMSH2 protein was 18 months, whereas the patients with a normal expression of hMSH2 survived for an average of 68 months. A multivariate Cox proportional hazards regression model revealed a significant correlation between the reduced expression of the hMSH2 protein and poor survival (relative risk = 4.7; 95% confidence interval [CI]: 1.3-17.2; P = 0.019).

CONCLUSIONS

Reduced expression of the hMSH2 protein is an independent negative prognostic factor for STS patients.

p53-related pathways and the molecular pathogenesis of melanoma

Cutaneous malignant melanoma (CMM) is a life-threatening cancer that can have a poor prognosis with high metastatic potential. Its incidence is rapidly increasing worldwide. Its molecular alterations involve multiple pathways, including those related to p53. Since 1981, more than 380 papers containing the terms 'p53 and melanoma' as key words in the Abstract have been published in the literature. However, in spite of these extensive investigations, a review of p53 and associated genes in CMM is still lacking. To remedy this issue, this review seeks to provide a brief overview of p53 and discuss the genes targeted along its related pathways.