Notch-1 induction, a novel activity of SV40 required for growth of SV40-transformed human mesothelial cells

Metformin Induces Apoptosis and Inhibits Notch1 in Malignant Pleural Mesothelioma Cells

Malignant pleural mesothelioma (MPM) is an aggressive asbestos-related cancer arising from the mesothelial cells lining the pleural cavity. MPM is characterized by a silent clinical progression and a highly resistance to conventional chemo/radio-therapies. MPM patients die in a few months/years from diagnosis. Notch signaling is a well-conserved cell communication system, which regulates many biological processes. In humans, the dysregulation of Notch pathway potentially contributes to cancer onset/progression, including MPM. Metformin is the first-line drug used to treat type 2 diabetes mellitus. Metformin is proven to be an effective antitumor drug in preclinical models of different types of cancer. To date, clinical efficacy is being studied in many clinical trials. In this study, the anti-proliferative effect of metformin on MPM cells and the putative involvement of Notch1 as a mediator of metformin activities, were investigated. MPM cells showed high levels of Notch1 activation compared to normal pleural mesothelial cells. Furthermore, metformin treatment hampered MPM cell proliferation and enhanced the apoptotic process, accompanied by decreased Notch1 activation.

New Insights of Human Parvovirus B19 in Modulating Erythroid Progenitor Cell Differentiation

Human parvovirus B19 (B19), a human pathogen of the erythroparvovirus genus, is responsible for a variety of diseases. B19 cause less symptoms in healthy individuals, also cause acute and chronic anemia in immunodeficiency patients. Transient aplastic crisis and pure red cell aplasia are two kinds of anemic hemogram, respectively, in acute and chronic B19 infection phase, especially occurring in patients with a shortened red cell survival or with immunodeficiency. In addition, B19-infected pregnant women may cause hydrops fetalis or fetal loss. B19 possesses high affinity to bone marrow and fetal liver due to its extremely restricted cytotoxicity to erythroid progenitor cells (EPCs) mediated by viral proteins. The nonstructural protein NS1 is considered to be the major pathogenic factor, which has been shown to inhibit the differentiation and maturation of EPCs through inducing viral DNA damage responses and cell cycle arrest. The time phase property of NS1 activity during DNA replication and conformity to transient change of hemogram are suggestive of its role in regulating differentiation of hematopoietic cells, which is not completely understood. In this review, we summarized the bridge between B19 NS1 and Notch signaling pathway or transcriptional factors GATA, which play an important role in erythroid cell proliferation and differentiation, to provide a new insight of the potential mechanism of B19-induced differential inhibition of EPCs.

SV40 and human mesothelioma

Simian virus 40 (SV40) is a DNA tumor virus capable of infecting and transforming human mesothelial (HM) cells in vitro. Hamsters injected intracardially to expose most tissue types to SV40 preferentially develop mesotheliomas. In humans, asbestos is the main cause of mesothelioma, and asbestos and SV40 are co-carcinogens in transforming HM cells in tissue culture and in causing mesothelioma in hamsters. Laser microdissection experiments conducted in the laboratory of Adi Gazdar demonstrated that SV40 was present specifically in the malignant mesothelioma cells and not in nearby stromal cells. Further experiments demonstrated that SV40 remains episomal in HM cells and astrocytes because of the production of a long antisense RNA that represses viral capsid protein production. Thus, the potent SV40 oncoprotein, T-antigen (Tag), is expressed, but because the capsid proteins are not produced, the cells are not lysed and, instead, become transformed. Together this evidence suggests that SV40 may contribute to the development of mesotheliomas in humans. However, epidemiological evidence to support this hypothesis is lacking. This chapter also summarizes the introduction of SV40, a monkey virus, into the human population as an unrecognized contaminant of early poliovaccines. In addition to mesotheliomas, SV40 now is linked with brain cancers, osteosarcomas, and lymphomas in humans. Explanations are provided for the apparent geographic variations in SV40 prevalence and for controversies about the role of SV40 in human cancer.

Association Between Simian Virus 40 and Human Tumors

Simian virus 40 (SV40) is a small DNA tumor virus of monkey origin. This polyomavirus was administered to human populations mainly through contaminated polio vaccines, which were produced in naturally infected SV40 monkey cells. Previous molecular biology and recent immunological assays have indicated that SV40 is spreading in human populations, independently from earlier SV40-contaminated vaccines. SV40 DNA sequences have been detected at a higher prevalence in specific human cancer specimens, such as the brain and bone tumors, malignant pleural mesotheliomas, and lymphoproliferative disorders, compared to the corresponding normal tissues/specimens. However, other investigations, which reported negative data, did not confirm an association between SV40 and human tumors. To circumvent the controversies, which have arisen because of these molecular biology studies, immunological researches with newly developed indirect ELISA tests were carried out in serum samples from patients affected by the same kind of tumors as mentioned above. These innovative indirect ELISAs employ synthetic peptides as mimotopes/specific SV40 antigens. SV40 mimotopes do not cross-react with the homologous human polyomaviruses, BKPyV, and JCPyV. Immunological data obtained from indirect ELISAs, using SV40 mimotopes, employed to analyze serum samples from oncological patients, have indicated that these sera had a higher prevalence of antibodies against SV40 compared to healthy subjects. The main data on (i) the biology and genetics of SV40; (ii) the epidemiology of SV40 in the general population, (iii) the mechanisms of SV40 transformation; (iv) the putative role of SV40 in the onset/progression of specific human tumors, and (v) its association with other human diseases are reported in this review.

Expression of Numb and Gli1 in malignant pleural mesothelioma and their clinical significance

AIM OF STUDY

Malignant pleural mesothelioma (MPM) is a highly lethal and refractory to multimodal treatment tumor. Numb is considered as a tumor suppressor playing critical roles in determining cell fate and has been shown to target the oncogenic transcription factor Gli1 for Itch-dependent ubiquitination, resulting in suppression of the oncogenic sonic hedgehog signaling in medulloblastoma. This study was designed to analysis the role of Numb and Gli1 in MPM.

MATERIALS AND METHODS

Tissues of 61 MPM patients and 22 normal pleura as control were investigated. Numb and Gli1 expression were evaluated by immunohistochemistry. The associations with clinical and pathological parameters of the two markers were statistically analyzed, and the correlation between them was also demonstrated.

RESULTS

The expression levels of Numb with nuclear Gli1 exhibited a significant inverse correlation (r = -0.361 P < 0.05). In addition, Numb has an inverse correlation with ki-67 labeling index (P < 0.05), and nuclear Gli1 was found in associated with the tumor International Mesothelioma Interest Group-stage (P < 0.05). The overall survival was influenced by the expression of Numb (P < 0.05) and histological subtype (P < 0.05), further regression analysis showed that only histological subtype has a prognostic influence on survival (P < 0.05).

CONCLUSION

The results provide new evidence of Numb and Gli1 on the clinical characteristics of MPM, which may be helpful in clinical diagnosis and targeted therapy. Further research with larger sample size is needed.

New Perspectives on Diagnosis and Therapy of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare, but severe form of cancer, with an incidence that varies significantly within and among different countries around the world. It develops in about one to two persons per million of the general population, leading to thousands of deaths every year worldwide. To date, the MPM is mostly associated with occupational asbestos exposure. Asbestos represents the predominant etiological factor, with approximately 70% of cases of MPM with well-documented occupational exposure to asbestos, with the exposure time, on average greater than 40 years. Environmental exposure to asbestos is increasingly becoming recognized as a cause of mesothelioma, together with gene mutations. The possible roles of other cofactors, such as viral infection and radiation exposure, are still debated. MPM is a fatal tumor. This cancer arises during its early phase without clinical signs. Consequently, its diagnosis occurs at advanced stages. Standard clinical therapeutic approaches include surgery, chemo- and radiotherapies. Preclinical and clinical researches are making great strides in the field of this deadly disease, identifying new biomarkers and innovative therapeutic approaches. Among the newly identified markers and potential therapeutic targets, circulating microRNAs and the Notch pathway represent promising avenues that could result in the early detection of the tumor and novel therapeutic approaches.

Asbestos and SV40 in Malignant Pleural Mesothelioma from a Hyperendemic Area of North-Eastern Italy

Aims and background

Malignant mesothelioma is a fatal cancer of increasing incidence in north-eastern Italy. Together with asbestos, the polyomavirus SV40 was hypothesized to contribute to the onset of malignant mesothelioma. To investigate the putative role of SV40 in the individual susceptibility to asbestos-induced malignant mesothelioma, we conducted a molecular epidemiological study on a series of malignant mesothelioma patients from an area in north-eastern Italy hyperendemic for malignant pleural mesothelioma.

Methods and study design

We collected 63 mesothelioma samples from incidence cases of patients diagnosed with malignant pleural mesothelioma in the period 2009–2010. DNA was extracted from patients’ tissue biopsies using the BioRobot EZ1 Qiagen workstation. SV40 sequence detection and quantification was performed by specific real time PCR. The 74.6% of the 63 enrolled patients had a history of asbestos exposure. The epithelioid histotype was more prevalent in males (64.0%) and the mixed in females (61.5%) who showed significantly higher cancer co-morbidity (46.1% vs 12%, P = 0.005). SV40 was detected in 22% of MM tumors, with a low viral load. In SV40-positive patients, a threefold increased risk of asbestos exposure was observed, more evident in females (OR 4.32) than in males (OR 1.20).

Conclusions

Our findings indicate that a high prevalence of SV40 was present in malignant mesothelioma incident cases from an area hyperendemic for malignant mesothelioma in north-eastern Italy. Although asbestos is considered the main risk factor in malignant mesothelioma onset, a role for SV40 could be hypothesized.

Heterogeneous Contributing Factors in MPM Disease Development and Progression: Biological Advances and Clinical Implications

Malignant pleural mesothelioma (MPM) tumors are remarkably aggressive and most patients only survive for 5–12 months; irrespective of stage; after primary symptoms appear. Compounding matters is that MPM remains unresponsive to conventional standards of care; including radiation and chemotherapy. Currently; instead of relying on molecular signatures and histological typing; MPM treatment options are guided by clinical stage and patient characteristics because the mechanism of carcinogenesis has not been fully elucidated; although about 80% of cases can be linked to asbestos exposure. Several molecular pathways have been implicated in the MPM tumor microenvironment; such as angiogenesis; apoptosis; cell-cycle regulation and several growth factor-related pathways predicted to be amenable to therapeutic intervention. Furthermore, the availability of genomic data has improved our understanding of the pathobiology of MPM. The MPM genomic landscape is dominated by inactivating mutations in several tumor suppressor genes; such as CDKN2A; BAP1 and NF2. Given the complex heterogeneity of the tumor microenvironment in MPM; a better understanding of the interplay between stromal; endothelial and immune cells at the molecular level is required; to chaperone the development of improved personalized therapeutics. Many recent advances at the molecular level have been reported and several exciting new treatment options are under investigation. Here; we review the challenges and the most up-to-date biological advances in MPM pertaining to the molecular pathways implicated; progress at the genomic level; immunological progression of this fatal disease; and its link with developmental cell pathways; with an emphasis on prognostic and therapeutic treatment strategies.

Notch Signaling in Neuroendocrine Tumors

Carcinoids and neuroendocrine tumors (NETs) are a heterogeneous group of tumors that arise from the neuroendocrine cells of the GI tract, endocrine pancreas, and the respiratory system. NETs remain significantly understudied with respect to molecular mechanisms of pathogenesis, particularly the role of cell fate signaling systems such as Notch. The abundance of literature on the Notch pathway is a testament to its complexity in different cellular environments. Notch receptors can function as oncogenes in some contexts and tumor suppressors in others. The genetic heterogeneity of NETs suggests that to fully understand the roles and the potential therapeutic implications of Notch signaling in NETs, a comprehensive analysis of Notch expression patterns and potential roles across all NET subtypes is required.

MicroRNA and mRNA features of malignant pleural mesothelioma and benign asbestos-related pleural effusion

Introduction. We investigated the expression of microRNAs and mRNAs in pleural tissues from patients with either malignant pleural mesothelioma or benign asbestos-related pleural effusion. Methods. Fresh frozen tissues from a total of 18 malignant pleural mesothelioma and 6 benign asbestos-related pleural effusion patients were studied. Expression profiling of mRNA and microRNA was performed using standard protocols. Results. We discovered significant upregulation of multiple microRNAs in malignant pleural mesothelioma compared to benign asbestos-related pleural effusion. Hsa-miR-484, hsa-miR-320, hsa-let-7a, and hsa-miR-125a-5p were able to discriminate malignant from benign disease. Dynamically regulated mRNAs were also identified. MET was the most highly overexpressed gene in malignant pleural mesothelioma compared to benign asbestos-related pleural effusion. Integrated analyses examining microRNA-mRNA interactions suggested multiple altered targets within the Notch signaling pathway. Conclusions. Specific microRNAs and mRNAs may have diagnostic utility in differentiating patients with malignant pleural mesothelioma from benign asbestos-related pleural effusion. These studies may be particularly helpful in patients who reside in a region with a high incidence of mesothelioma.

HGF/Met Signaling Is a Key Player in Malignant Mesothelioma Carcinogenesis

Malignant mesothelioma (MM) is a highly aggressive cancer related to asbestos or erionite exposure and resistant to current therapies. Hepatocyte Growth Factor (HGF) and its tyrosine kinase receptor Met regulate cell growth, survival, motility/migration, and invasion. HGF and Met are expressed in MM cells, suggesting that the HGF/Met signaling plays a role in development and progression of this tumor, by autocrine and/or paracrine mechanisms. Upregulation and ligand-independent activation of Met, which is under suppressive control of miR-34 family members, correlate with enhanced invasion, migration and metastatic potential in several cancers, including MM. Moreover, Simian Virus 40 (SV40) Tag expression also induces a HGF autocrine circuit in an Rb-dependent manner in human mesothelial cells (HM) and possibly other cell types, enhancing cell adhesion, invasion and angiogenesis. The resulting activation of Met causes HM transformation and cell cycle progression, and contributes to virus particle assembling and infection of adjacent cells. The constitutive activation of Met, frequently occurring in MM, has been successfully targeted in preclinical models of MM. In conclusion, Met expression, activation state, subcellular localization and also HGF co-receptors expression, such as CD44, have clinical relevance for novel targeted therapies in a cancer for which no effective treatment is currently available.

Viral carcinogenesis: factors inducing DNA damage and virus integration

Viruses are the causative agents of 10%-15% of human cancers worldwide. The most common outcome for virus-induced reprogramming is genomic instability, including accumulation of mutations, aberrations and DNA damage. Although each virus has its own specific mechanism for promoting carcinogenesis, the majority of DNA oncogenic viruses encode oncogenes that transform infected cells, frequently by targeting p53 and pRB. In addition, integration of viral DNA into the human genome can also play an important role in promoting tumor development for several viruses, including HBV and HPV. Because viral integration requires the breakage of both the viral and the host DNA, the integration rate is believed to be linked to the levels of DNA damage. DNA damage can be caused by both endogenous and exogenous factors, including inflammation induced by either the virus itself or by co-infections with other agents, environmental agents and other factors. Typically, cancer develops years to decades following the initial infection. A better understanding of virus-mediated carcinogenesis, the networking of pathways involved in transformation and the relevant risk factors, particularly in those cases where tumorigenesis proceeds by way of virus integration, will help to suggest prophylactic and therapeutic strategies to reduce the risk of virus-mediated cancer.

Increased levels of C-C chemokine RANTES in asbestos exposed workers and in malignant mesothelioma patients from an hyperendemic area

Background

Asbestos-induced mesothelial inflammatory processes are thought to be the basic mechanisms underlying Malignant Mesothelioma (MM) development. Detection of MM often occurs at late stage due to the long and unpredictable latent period and the low incidence in asbestos exposed individuals. The aim of this study was to investigate early immunological biomarkers to characterize the prognostic profile of a possible asbestos-induced disease, in subjects from a MM hyperendemic area.

Methods

The Luminex Multiplex Panel Technology was used for the simultaneous measurement of serum levels of a large panel of 47 analytes, including cytokines and growth factors, from workers previously exposed to asbestos (Asb-workers), asbestos-induced MM patients and healthy subjects. In addition, to explore the influence on serum cytokines profile exerted by SV40 infection, a cofactor in MM development, a quantitative real time PCR was performed for sequences detection in the N-terminal and intronic regions of the SV40 Tag gene. Statistical analysis was done by means of the Mann-Whitney test and the Kruskall-Wallis test for variance analysis.

Results

A variety of 25 cytokines linked to pulmonary inflammation and tumor development were found significantly associated with Asb-workers and MM patients compared with healthy controls. A specific pattern of cytokines were found highly expressed in Asb-workers: IFN-alpha (p<0.05), EOTAXIN (p<0.01), RANTES (p<0.001), and in MM patients: IL-12(p40), IL-3, IL-1 alpha, MCP-3, beta-NGF, TNF-beta, RANTES (p<0.001). Notably, the chemokine RANTES measured the highest serum level showing an increased gradient of concentration from healthy subjects to Asb-workers and MM patients (p<0.001), independently of SV40 infection.

Conclusion

This study shows that, in subjects from an hyperendemic area for MM, the C-C chemokine RANTES is associated with the exposure to asbestos fibres. If validated in larger samples, this factor could have the potential to be a critical biomarker for MM prognosis as recently reported for breast tumor.

Autocrine CSF-1R signaling drives mesothelioma chemoresistance via AKT activation

Clinical management of malignant pleural mesothelioma (MPM) is very challenging because of the uncommon resistance of this tumor to chemotherapy. We report here increased expression of macrophage colony-stimulating-factor-1-receptor (M-CSF/CSF-1R) mRNA in mesothelioma versus normal tissue specimens and demonstrate that CSF-1R expression identifies chemoresistant cells of mesothelial nature in both primary cultures and mesothelioma cell lines. By using RNAi or ligand trapping, we demonstrate that the chemoresistance properties of those cells depend on autocrine CSF-1R signaling. At the single-cell level, the isolated CSF-1R^pos cells exhibit a complex repertoire of pluripotency, epithelial–mesenchymal transition and detoxifying factors, which define a clonogenic, chemoresistant, precursor-like cell sub-population. The simple activation of CSF-1R in untransformed mesothelial cells is sufficient to confer clonogenicity and resistance to pemetrexed, hallmarks of mesothelioma. In addition, this induced a gene expression profile highly mimicking that observed in the MPM cells endogenously expressing the receptor and the ligands, suggesting that CSF-1R expression is mainly responsible for the phenotype of the identified cell sub-populations. The survival of CSF1R^pos cells requires active AKT (v-akt murine thymoma viral oncogene homolog 1) signaling, which contributed to increased levels of nuclear, transcriptionally competent β-catenin. Inhibition of AKT reduced the transcriptional activity of β-catenin-dependent reporters and sensitized the cells to senescence-induced clonogenic death after pemetrexed treatment. This work expands what is known on the non-macrophage functions of CSF-1R and its role in solid tumors, and suggests that CSF-1R signaling may have a critical pathogenic role in a prototypical, inflammation-related cancer such as MPM and therefore may represent a promising target for therapeutic intervention.

The role of key genes and pathways involved in the tumorigenesis of Malignant Mesothelioma

Malignant Mesothelioma (MM) is a very aggressive cancer with low survival rates and often diagnosed at an advanced stage. Several players have been implicated in the development of this cancer, such as asbestos, erionite and the simian virus 40 (SV40). Here, we have reviewed the involvement of erionite, SV40, as well as, the role of several genes (p16(INK4a), p14(ARF), NF2, LATS2, SAV, CTNNB1 and among others), the pathways (RAS, PI3K, Wnt, BCL and Hippo), and their respective roles in the development of MM.

Notch signaling: targeting cancer stem cells and epithelial-to-mesenchymal transition

Notch signaling is an evolutionarily conserved pathway involved in cell fate control during development, stem cell self-renewal, and postnatal tissue differentiation. Roles for Notch in carcinogenesis, the biology of cancer stem cells, tumor angiogenesis, and epithelial-to-mesenchymal transition (EMT) have been reported. This review describes the role of Notch in the "stemness" program in cancer cells and in metastases, together with a brief update on the Notch inhibitors currently under investigation in oncology. These agents may be useful in targeting cancer stem cells and to reverse the EMT process.

Notch inhibitors for cancer treatment

Notch signaling is an evolutionarily conserved cell signaling pathway involved in cell fate during development, stem cell renewal and differentiation in postnatal tissues. Roles for Notch in carcinogenesis, in the biology of cancer stem cells and tumor angiogenesis have been reported. These features identify Notch as a potential therapeutic target in oncology. Based on the molecular structure of Notch receptor, Notch ligands and Notch activators, a set of Notch pathway inhibitors have been developed. Most of these inhibitors had shown anti-tumor effects in preclinical studies. At the same time, the combinatorial effect of these inhibitors with current chemotherapeutical drugs is still under study in different clinical trials. In this review, we describe the basics of Notch signaling and the role of Notch in normal and cancer stem cells as a logic way to develop different Notch inhibitors and their current stage of progress for cancer patient's treatment.

Mutant p53-Notch1 Signaling Axis Is Involved in Curcumin-Induced Apoptosis of Breast Cancer Cells

Notch1 has been reported to be highly expressed in triple-negative and other subtypes of breast cancer. Mutant p53 (R280K) is overexpressed in MDA-MB-231 triple-negative human breast cancer cells. The present study aimed to determine whether the mutant p53 can be a potent transcriptional activator of the Notch1 in MDA-MB-231 cells, and explore the role of this mutant p53-Notch1 axis in curcumin-induced apoptosis. We found that curcumin treatment resulted in an induction of apoptosis in MDA-MB-231 cells, together with downregulation of Notch1 and its downstream target, Hes1. This reduction in Notch1 expression was determined to be due to the decreased activity of endogenous mutant p53. We confirmed the suppressive effect of curcumin on Notch1 transcription by performing a Notch1 promoter-driven reporter assay and identified a putative p53-binding site in the Notch1 promoter by EMSA and chromatin immunoprecipitation analysis. Overexpression of mutant p53 increased Notch1 promoter activity, whereas knockdown of mutant p53 by small interfering RNA suppressed Notch1 expression, leading to the induction of cellular apoptosis. Moreover, curcumin-induced apoptosis was further enhanced by the knockdown of Notch1 or mutant p53, but it was decreased by the overexpression of active Notch1. Taken together, our results demonstrate, for the first time, that Notch1 is a transcriptional target of mutant p53 in breast cancer cells and suggest that the targeting of mutant p53 and/or Notch1 may be combined with a chemotherapeutic strategy to improve the response of breast cancer cells to curcumin.

Molecular genetics of ependymoma

Brain tumors are the leading cause of cancer death in children, with ependymoma being the third most common and posing a significant clinical burden. Its mechanism of pathogenesis, reliable prognostic indicators, and effective treatments other than surgical resection have all remained elusive. Until recently, ependymoma research was hindered by the small number of tumors available for study, low resolution of cytogenetic techniques, and lack of cell lines and animal models. Ependymoma heterogeneity, which manifests as variations in tumor location, patient age, histological grade, and clinical behavior, together with the observation of a balanced genomic profile in up to 50% of cases, presents additional challenges in understanding the development and progression of this disease. Despite these difficulties, we have made significant headway in the past decade in identifying the genetic alterations and pathways involved in ependymoma tumorigenesis through collaborative efforts and the application of microarray-based genetic (copy number) and transcriptome profiling platforms. Genetic characterization of ependymoma unraveled distinct mRNA-defined subclasses and led to the identification of radial glial cells as its cell type of origin. This review summarizes our current knowledge in the molecular genetics of ependymoma and proposes future research directions necessary to further advance this field.

The ticking time-bomb of asbestos: its insidious role in the development of malignant mesothelioma

The relationship between asbestos exposure and malignant mesothelioma (MM) has been well established. Despite bans on asbestos use in an increasing number of nations, the prolonged latency from exposure to diagnosis, and the ongoing presence and use of these dangerous fibres, have led to the increasing prevalence of this deadly disease worldwide. Whilst occupational contact has been implicated in the bulk of diagnosed cases over the past 50 years, a significant proportion of disease has been linked to para-occupational, domestic and environmental exposure. In this review, we will provide an update on the impact of historical and ongoing asbestos contact in both occupational and non-occupational settings. Furthermore, we will address the unresolved controversies surrounding the use of chrysotile asbestos, the effect of gender and genetics on development of this disease, childhood mesothelioma and co-aetiological factors including SV40 exposure.

Simian virus 40 transformation, malignant mesothelioma and brain tumors

Simian virus 40 (SV40) is a DNA virus isolated in 1960 from contaminated polio vaccines, that induces mesotheliomas, lymphomas, brain and bone tumors, and sarcomas, including osteosarcomas, in hamsters. These same tumor types have been found to contain SV40 DNA and proteins in humans. Mesotheliomas and brain tumors are the two tumor types that have been most consistently associated with SV40, and the range of positivity has varied about from 6 to 60%, although a few reported 100% of positivity and a few reported 0%. It appears unlikely that SV40 infection alone is sufficient to cause human malignancy, as we did not observe an epidemic of cancers following the administration of SV40-contaminated vaccines. However, it seems possible that SV40 may act as a cofactor in the pathogenesis of some tumors. In vitro and animal experiments showing cocarcinogenicity between SV40 and asbestos support this hypothesis.

Tissue Tropism of SV40 Transformation of Human Cells: Role of the Viral Regulatory Region and of Cellular Oncogenes

SV40 has been detected prevalently in a limited panel of human tumors: mesothelioma, bone and brain tumors, and lymphoma. These are the same tumor types that are specifically induced by SV40 when injected into hamsters, a finding that has raised concerns about the possible pathogenic role of SV40 in humans. Two different SV40 isolates differing in the number of 72-bp elements in the virus regulatory region, archetypal SV40 (1ESV40), which contains one 72 bp, and nonarchetypal SV40 (wtSV40), which contains two 72 bp, have been detected in human tumors. 1ESV40 has been prevalently detected in brain tumors, with wtSV40 prevalently in mesothelioma. The apparent different cell tropism could be related to the virus (i.e., possibly to the number of 72-bp elements) and to different expression of cellular genes, known to play a critical role in SV40-mediated transformation of human cells, such as Notch-1 and c-Met. To test for possible differences in tissue tropism, we infected primary human mesothelial cells (HM) and primary human astrocytes (Ast) with 1ESV40 and with wtSV40 from 2 different SV40 strains, 776 and Baylor. All viruses transformed astrocytes; only wtSV40 transformed HM. Intracellular signaling of c-Met and Notch-1 was differently induced by these 2 viruses in HM and Ast. Differences in Notch-1 expression and signaling (i.e., downstream effectors, c-Myc, HEY-1, HES-1, and HEY-L) appeared to influence SV40-mediated transformation of primary astrocytes and mesothelial cells. Our results provide a biological rationale to the observation that 1ESV40 is prevalently detected in brain tumors and wtSV40 in mesotheliomas.

Advances in the biology of malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive cancer with a very poor prognosis. Although the mechanism of carcinogenesis is not fully understood, approximately 80% of malignant pleural mesothelioma can be attributed to asbestos fiber exposure. This disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of their first symptoms. Currently, malignant pleural mesothelioma therapy is guided by clinical stage and patient characteristics rather than by the histological or molecular features of the tumor. Several molecular pathways involved in malignant pleural mesothelioma have been identified; these include cell cycle regulation, apoptosis, growth factor pathways, and angiogenesis. Unfortunately, several agents targeting these processes, including erlotinib, gefitinib, and imatinib, have proven ineffective in clinical trials. A greater understanding of the molecular pathways involved in malignant pleural mesothelioma is needed to develop better diagnostics, therapeutics, and preventative measures. Moreover, understanding the biological basis of mesothelioma progression may facilitate personalized treatment approaches, and early identification of poor prognostic indicators may help reduce the heterogeneity of the clinical response. This paper reviews advances in the molecular biology of malignant pleural mesothelioma in terms of pathogenesis, the major molecular pathways and the associated therapeutic strategies, and the roles of biomarkers.

ErbB2 induces Notch1 activity and function in breast cancer cells

The ErbB2 (Her2/neu epidermal growth receptor family) oncogene is overexpressed in 30% to 40% of human breast cancers. Cyclin D1 is the regulatory subunit of the holoenzyme that phosphorylates and inactivates the retinoblastoma (pRb) tumor suppressor and is an essential downstream target of ErbB2-induced tumor growth. Herein, we demonstrate that ErbB2 induces the activity of the Notch signaling pathway. ErbB2 induction of DNA synthesis, contact-independent growth, and mammosphere induction required Notch1. ErbB2-induced cyclin D1 and cyclin D1 expression was suficient to induce Notch1 activity, and conversely, genetic deletion of Notch1 in mammary epithelial cells using foxed Notch (Notch(fl/fl)) mice demonstrated that cyclin D1 is induced by Notch1. Genetic deletion of cyclin D1 or small interfering RNA (siRNA) to cyclin D1-reduced Notch1 activity and reintroduction of cyclin D1 into cyclin D1-deficient cells restored Notch1 activity through the inhibition of Numb, an endogenous inhibitor of Notch1 activity. Thus, cyclin D1 functions downstream as a genetic target of Notch1, amplifies Notch1 activity by repressing Numb, and identifies a novel pathway by which ErbB2 induces Notch1 activity via the induction of cyclin D1.

Notch3 cooperates with the EGFR pathway to modulate apoptosis through the induction of bim

Notch signaling is a highly conserved pathway important for normal embryonic development and cancer. We previously demonstrated a role for Notch3 in lung cancer pathogenesis. Notch3 inhibition resulted in tumor apoptosis and growth suppression. In vitro, these effects were enhanced when the epidermal growth factor receptor (EGFR) pathway was also inhibited, suggesting significant cross-talk between the two pathways. How Notch3 and epidermal growth factor receptor-mitogen-activated protein kinase (EGFR-MAPK) pathways cooperate in modulating apoptosis is not yet known. In this study, we provide evidence that Notch3 regulates Bim, a BH-3-only protein, via MAPK signaling. Furthermore, loss of Bim expression prevents tumor apoptosis induced by Notch3 inhibition. Using gamma-secretase inhibitor and erlotinib in a xenograft model, Bim induction and tumor inhibition were observed to be enhanced compared with either agent alone, consistent with our previous observation of significant synergism between Notch and EGFR-ras-MAPK signaling. Thus, our data support the hypothesis that Notch3 not only has a crucial role in lung cancer through regulating apoptosis, but also cooperates with the EGFR-MAPK pathway in modulating Bim.

Tumour-initiating cells: challenges and opportunities for anticancer drug discovery

The hypothesis that cancer is driven by tumour-initiating cells (popularly known as cancer stem cells) has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of haematopoietic and solid malignancies. Furthermore, it seems that tumour-initiating cells might be resistant to many conventional cancer therapies, which might explain the limitations of these agents in curing human malignancies. Although much work is still needed to identify and characterize tumour-initiating cells, efforts are now being directed towards identifying therapeutic strategies that could target these cells. This Review considers recent advances in the cancer stem cell field, focusing on the challenges and opportunities for anticancer drug discovery.

Opposite effects of Notch-1 and Notch-2 on mesothelioma cell survival under hypoxia are exerted through the Akt pathway

Malignant mesothelioma (MM) is a cancer of the lining of the lungs, heart, and intestine and is known to respond poorly to chemotherapy. Here we show that malignant mesothelial cells have an elevated Notch signaling pathway compared with normal human mesothelial cells. We studied the role of Notch in MM under normoxic and hypoxic conditions, the latter condition best recapitulating the MM microenvironment. Genetic and chemical modulation of the Notch pathway indicated that MM cells are dependent on Notch signaling. More specifically, this signaling was Notch-1 dependent as the result of its negative transcriptional regulation on phosphatase and tensin homologue (PTEN), which led to activation of the prosurvival phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway. Our study also provides evidence that whereas Notch-1 is elevated in the malignant setting, Notch-2 is diminished. This differential expression of the two Notch isoforms benefits cancer cell survival because reexpression of Notch-2 was toxic to MM cells. The mechanism of Notch-2 toxicity to MM cells countered that of Notch-1, as it was the result of positive transcriptional regulation of PTEN and inhibition of the PI3K/Akt/mTOR signaling pathway. These results provide new insight into the role of Notch in MM and suggest that Notch pathway inhibitors may be useful in the treatment of this deadly disease.

A novel mechanism of late gene silencing drives SV40 transformation of human mesothelial cells

Suppression of the late gene expression, usually by integration of the viral DNA into the host genome, is a critical step in DNA tumor virus carcinogenesis. SV40 induces high rates of transformation in infected primary human mesothelial cells in tissue culture, leading to the formation of immortal cell lines (SV40-transformed human mesothelial cell lines, S-HML). The studies described here were designed to elucidate the unusual susceptibility of primary human mesothelial cells to SV40 carcinogenesis. We found that S-HML contained wild-type, mostly episomal SV40 DNA. In these cells, the early genes that code for the viral oncogenes are expressed; at the same time, the synthesis of the late genes, capsid proteins, is suppressed and S-HML are not lysed. Late gene suppression is achieved through the production of antisense RNA molecules. These antisense RNA molecules originate in the early region of the SV40 circular chromosome and proceed in antisense orientation into the late gene region, leading to the formation of highly unstable double-strand RNA, which is rapidly degraded. Our results reveal a novel biological mechanism responsible for the suppression of late viral gene products, an important step in viral carcinogenesis in humans.

Pathogenesis of malignant pleural mesothelioma and the role of environmental and genetic factors

BACKGROUND

Malignant pleural mesothelioma (MPM) is a rare and aggressive tumor for which no effective therapy exists despite the discovery of many possible molecular and genetic targets. The late stage of MPM diagnosis and the long latency that exist between some exposures and diagnosis have made it difficult to comprehensively evaluate the role of risk factors and their downstream molecular effects.

METHODS

This manuscript is a review of current literature about the pathogenesis of malignant mesothelioma. In this overview, current published studies concerning pathogenesis of malignant mesothelioma are reviewed, with insights into its etiology and pathogenesis. We searched pubmed using the following subjects: mesothelioma, radiation, genetics, pediatric malignant mesothelioma, SV40 virus, and growth factors. We selected 350 valuable articles of which 152 sources were used to complete this review.

CONCLUSION

Many risk factors for MPM development have been recognized including environmental exposures, genetic susceptibility, viral contamination, and radiation. In this review, we discuss the current molecular and genetic contributors to MPM pathogenesis and the risk factors associated with these carcinogenic processes.

Mesothelioma epidemiology, carcinogenesis, and pathogenesis

OPINION STATEMENT

The incidence of mesothelioma has gone from almost none to the current 2500-3000 cases per year in the USA. This estimate is an extrapolation based on information available from the Surveillance, Epidemiology and End Results (SEER) Program that collects information on approximately 12% of the US population. Mesothelioma is a cancer that is linked to exposure to carcinogenic mineral fibers. Asbestos and erionite have a proven causative role; the possible role of other mineral fibers in causing mesothelioma is being investigated. Asbestos is considered the main cause of mesothelioma in the US and in the Western world. The capacity of asbestos to induce mesothelioma has been linked to its ability to cause the release of TNF-alpha (that promotes mesothelial cells survival), other cytokines and growth factors, and of mutagenic oxygen radicals from exposed mesothelial cells and nearby macrophages. Some investigators proposed that as a consequence of the regulations to prevent exposure and to forbid and/or limit the use of asbestos, the incidence of mesothelioma in the US (and in some European countries) should have started to decline before or around the year 2000, and sharply decline thereafter. Unfortunately, there are no data available yet to support this optimistic hypothesis. Simian virus 40 (SV40) infection and radiation exposure are additional causes, although their contribution to the overall incidence of mesothelioma is unknown. Recent data from several laboratories indicate that asbestos exposure and SV40 infection are co-carcinogens in causing mesothelioma in rodents and in causing malignant transformation of human mesothelial cells in tissue culture. An exciting new development comes from the discovery that genetic susceptibility to mineral fiber carcinogenesis plays a critical role in the incidence of this cancer in certain families. It is hoped that the identification of this putative mesothelioma gene will lead to novel mechanistically driven preventive and therapeutic approaches.

Pathogenesis of malignant pleural mesothelioma and the role of environmental and genetic factors

Malignant pleural mesothelioma (MPM) is a rare, aggressive tumor for which no effective therapy exists despite the discovery of many possible molecular and genetic targets. Many risk factors for MPM development have been recognized including environmental exposures, genetic susceptibility, viral contamination, and radiation. However, the late stage of MPM diagnosis and the long latency that exists between some exposures and diagnosis have made it difficult to comprehensively evaluate the role of risk factors and their downstream molecular effects. In this review, we discuss the current molecular and genetic contributors in MPM pathogenesis and the risk factors associated with these carcinogenic processes.

Cross-talk between notch and the estrogen receptor in breast cancer suggests novel therapeutic approaches

High expression of Notch-1 and Jagged-1 mRNA correlates with poor prognosis in breast cancer. Elucidating the cross-talk between Notch and other major breast cancer pathways is necessary to determine which patients may benefit from Notch inhibitors, which agents should be combined with them, and which biomarkers indicate Notch activity in vivo. We explored expression of Notch receptors and ligands in clinical specimens, as well as activity, regulation, and effectors of Notch signaling using cell lines and xenografts. Ductal and lobular carcinomas commonly expressed Notch-1, Notch-4, and Jagged-1 at variable levels. However, in breast cancer cell lines, Notch-induced transcriptional activity did not correlate with Notch receptor levels and was highest in estrogen receptor alpha-negative (ERalpha(-)), Her2/Neu nonoverexpressing cells. In ERalpha(+) cells, estradiol inhibited Notch activity and Notch-1(IC) nuclear levels and affected Notch-1 cellular distribution. Tamoxifen and raloxifene blocked this effect, reactivating Notch. Notch-1 induced Notch-4. Notch-4 expression in clinical specimens correlated with proliferation (Ki67). In MDA-MB231 (ERalpha(-)) cells, Notch-1 knockdown or gamma-secretase inhibition decreased cyclins A and B1, causing G(2) arrest, p53-independent induction of NOXA, and death. In T47D:A18 (ERalpha(+)) cells, the same targets were affected, and Notch inhibition potentiated the effects of tamoxifen. In vivo, gamma-secretase inhibitor treatment arrested the growth of MDA-MB231 tumors and, in combination with tamoxifen, caused regression of T47D:A18 tumors. Our data indicate that combinations of antiestrogens and Notch inhibitors may be effective in ERalpha(+) breast cancers and that Notch signaling is a potential therapeutic target in ERalpha(-) breast cancers.

The SV40 large T antigen-p53 complexes bind and activate the insulin-like growth factor-I promoter stimulating cell growth

Inactivation of cellular p53 is a crucial step in carcinogenesis. Accordingly, p53 is inactivated in most human cancers by different mechanisms. In cells infected with DNA tumor viruses, p53 is bound to the viral tumor antigens (Tag). The current "dogma" views the Tag-p53 complexes as a way of sequestering and inactivating p53. Using primary human cells and SV40-transformed human cells, we show that in addition to inactivating p53 tumor suppressor activities, the Tag-p53 complex has growth stimulatory activities that are required for malignant cell growth. We found that in human cells, Tag-p53 complexes regulate transcription of the insulin-like growth factor I (IGF-I) gene by binding to the IGF-I promoter together with pRb and p300. Depletion of p53 leads to structural rearrangements of this multiprotein complex, resulting in IGF-I promoter transcriptional repression and growth arrest. Our data provide a novel mechanistic and biological interpretation of the p53-Tag complexes and of DNA tumor virus transformation in general. In the model we propose, p53 is not a passive inactive partner of Tag. Instead the p53-Tag complex promotes malignant cell growth through its ability to activate the IGF-I signaling pathway.

The many faces of Notch signaling in skin-derived cells

Since the cloning of the Drosophila gene in the 1980s, decades of research have sought to dissect the intricacies of the mammalian Notch signaling cascade. The intrigue of this pathway undoubtedly lies in its ability to influence diverse cellular processes, including differentiation, cell fate, homeostasis, survival, proliferation and angiogenesis. Based on its evolutionary conservation and its fundamental role in development, it is not surprising that deregulation of the Notch signaling pathway can result in neoplastic growth. While originally of particular interest to immunologists based on its chief role in influencing T-cell fate decisions and tumor oncogenesis in T-cell acute lymphoblastic leukemia, pigment cell biologists have recently taken notice of the Notch cascade based on studies suggesting the importance of this pathway in regulating melanocyte stem cell survival and melanoma progression. We will review the Notch signaling literature as it relates to skin homeostasis, melanocytic stem cells and melanoma tumorigenesis.

Inhibition of Notch signaling induces apoptosis of myeloma cells and enhances sensitivity to chemotherapy

Drug resistance remains a critical problem in the treatment of patients with multiple myeloma. Recent studies have determined that Notch signaling plays a major role in bone marrow (BM) stroma-mediated protection of myeloma cells from de novo drug-induced apoptosis. Here, we investigated whether pharmacologic inhibition of Notch signaling could affect the viability of myeloma cells and their sensitivity to chemotherapy. Treatment with a gamma-secretase inhibitor (GSI) alone induced apoptosis of myeloma cells via specific inhibition of Notch signaling. At concentrations toxic for myeloma cell lines and primary myeloma cells, GSI did not affect normal BM or peripheral blood mononuclear cells. Treatment with GSI prevented BM stroma-mediated protection of myeloma cells from drug-induced apoptosis. The cytotoxic effect of GSI was mediated via Hes-1 and up-regulation of the proapoptotic protein Noxa. In vivo experiments using xenograft and SCID-hu models of multiple myeloma demonstrated substantial antitumor effect of GSI. In addition, GSI significantly improved the cytotoxicity of the chemotherapeutic drugs doxorubicin and melphalan. Thus, this study demonstrates that inhibition of Notch signaling prevents BM-mediated drug resistance and sensitizes myeloma cells to chemotherapy. This may represent a promising approach for therapeutic intervention in multiple myeloma.

Simian virus 40 in humans

Simian virus 40 (SV40) is a monkey virus that was administered to human populations by contaminated vaccines which were produced in SV40 naturally infected monkey cells. Recent molecular biology and epidemiological studies suggest that SV40 may be contagiously transmitted in humans by horizontal infection, independently from the earlier administration of SV40-contaminated vaccines.SV40 footprints in humans have been found associated at high prevalence with specific tumor types such as brain and bone tumors, mesotheliomas and lymphomas and with kidney diseases, and at lower prevalence in blood samples from healthy donors. Contrasting reports appeared in the literature on the circulation of SV40 in humans by contagious transmission and its association, as a possible etiologic cofactor, with specific human tumors. As a consequence of the conflicting results, a considerable debate has developed in the scientific community. In the present review we consider the main results obtained by different groups investigating SV40 sequences in human tumors and in blood specimens, the putative role of SV40 in the onset/progression of specific human tumors, and comment on the hypotheses arising from these data.

Restoration of p53 expression in human cancer cell lines upregulates the expression of Notch1: implications for cancer cell fate determination after genotoxic stress

Following genotoxic stress, transcriptional activation of target genes by p53 tumor suppressor is critical in cell fate determination. Here we report that the restoration of p53 function in human cancer cell lines that are deficient in p53 function upregulated the expression of Notch1. Interestingly, the expression of wild-type p53 in human prostate and breast cancer cell lines correlated well with increased expression of Notch1. Furthermore, knockdown of p53 expression in cancer cells that express wild-type p53 resulted in reduced expression of Notch1. Importantly, genotoxic stress to cancer cells that resulted in activation of p53 also upregulated the expression of Notch1. Moreover, p53-mediated induction of Notch1 expression was associated with stimulation of the activity of Notch-responsive reporters. Notably, p53 differentially regulated the expression of Notch family members: expression of Notch2 and Notch4 was not induced by p53. Significantly, treatment of cells with gamma secretase inhibitor, an inhibitor of Notch signaling, increased susceptibility to apoptosis in response to genotoxic stress. Together, our observations suggest that p53-mediated upregulation of Notch1 expression in human cancer cell lines contributes to cell fate determination after genotoxic stress.

Apoptosis in T cell acute lymphoblastic leukemia cells after cell cycle arrest induced by pharmacological inhibition of notch signaling

In this report, inhibitors of the gamma-secretase enzyme have been exploited to characterize the antiproliferative relationship between target inhibition and cellular responses in Notch-dependent human T cell acute lymphoblastic leukemia (T-ALL) cell lines. Inhibition of gamma-secretase led to decreased Notch signaling, measured by endogenous NOTCH intracellular domain (NICD) formation, and was associated with decreased cell viability. Flow cytometry revealed that decreased cell viability resulted from a G(0)/G(1) cell cycle block, which correlated strongly to the induction of apoptosis. These effects associated with inhibitor treatment were rescued by exogenous expression of NICD and were not mirrored when a markedly less active enantiomer was used, demonstrating the gamma-secretase dependency and specificity of these responses. Together, these data strengthen the rationale for using gamma-secretase inhibitors therapeutically and suggest that programmed cell death may contribute to reduction of tumor burden in the clinic.

NOTCH1-induced T-cell leukemia in transgenic zebrafish

Activating mutations in the NOTCH1 gene have been found in about 60% of patients with T-cell acute lymphoblastic leukemia (T-ALL). In order to study the molecular mechanisms by which altered Notch signaling induces leukemia, a zebrafish model of human NOTCH1-induced T-cell leukemia was generated. Seven of sixteen mosaic fish developed a T-cell lymphoproliferative disease at about 5 months. These neoplastic cells extensively invaded tissues throughout the fish and caused an aggressive and lethal leukemia when transplanted into irradiated recipient fish. However, stable transgenic fish exhibited a longer latency for leukemia onset. When the stable transgenic line was crossed with another line overexpressing the zebrafish bcl2 gene, the leukemia onset was dramatically accelerated, indicating synergy between the Notch pathway and the bcl2-mediated antiapoptotic pathway. Reverse transcription-polymerase chain reaction analysis showed that Notch target genes such as her6 and her9 were highly expressed in NOTCH1-induced leukemias. The ability of this model to detect a strong interaction between NOTCH1 and bcl2 suggests that genetic modifier screens have a high likelihood of revealing other genes that can cooperate with NOTCH1 to induce T-ALL.

Stable expression of intracellular Notch suppresses v-Src-induced transformation in avian neural cells

Understanding how disruption of differentiation contributes to the cancer cell phenotype is required to identify alterations essential for malignant transformation and provide experimental basis for their correction. We investigated whether primary quail neuroretina cells, transformed by a conditional v-Src mutant (QNR/v-src(ts)), could revert to a normal phenotype, in response to the stable expression of constitutively active Notch1 intracellular domain (ICN). This model system was chosen because Notch signaling plays an instructive role in cell fate determination during NR development, and because the intrinsic capacity of QNR cultures to differentiate is blocked by v-Src. We report that stable ICN expression results in suppression of QNR/v-src(ts) cell transformation in the presence of an active oncoprotein. This phenotypic reversion coincides with a major switch in cell identity, as these undifferentiated cells acquire glial differentiation traits. Both changes appear to be mediated by CBF, a transcription factor that binds to ICN and activates target genes. Cells restored to a normal and differentiated phenotype have undergone changes in the functioning of signaling effectors, essentially regulating cell morphology and cytoskeleton organization. This dominant interference may be partially mediated by an autocrine/paracrine mechanism, as revertant cells secrete a factor(s), which inhibits transformation properties of QNR/v-src(ts) cells.

The role of SV40 in malignant mesothelioma and other human malignancies

SV40 is a DNA tumor virus thrust upon human populations primarily as a contaminant in various vaccine preparations. Some estimates suggest that millions of people are currently infected with the virus. The virus causes primary brain tumors, bone tumors, lymphomas, and mesotheliomas when injected into some rodent models. It has also been detected in a similar spectrum of human tumors. However, epidemiological studies have failed to conclusively demonstrate a higher incidence of disease in affected populations. To date, over 60 reports from 49 different laboratories have shown SV40 sequences in tissues from human cancer patients. Six studies, however, have failed to detect evidence of virus in similar tissues. Some have suggested that SV40 may act as a cocarcinogen with asbestos to cause mesothelioma formation, or that it may be responsible for the 10-20% of mesotheliomas with no reported history of asbestos exposure. This report briefly covers the historical evidence for SV40 carcinogenesis and then covers experiments now underway to better understand the role of SV40 in human mesotheliomas.

Tumor suppressor gene alterations in patients with malignant mesothelioma due to environmental asbestos exposure in Turkey

BACKGROUND

Environmental asbestos exposure can cause the grave lung and pleura malignancies with a high mortality rate, and it is also associated with increased rate of other organ malignancies. Asbestos exposure can develop genotoxic effects and damage in the pleura and lungs.

OBJECTIVE

In this study, we aimed to determine tumor suppressor gene (TSG) loss in genomic DNA which was isolated from pleural fluid and blood samples of patients with Malignant Pleural Mesothelioma (MPM) due to environmental asbestos exposure.

DESIGN AND PATIENTS

Prospective study of period from 2001 to 2003 in 17 patients with MPM.

METHODS

A total of 12 chromosomal regions were researched by comparing genomic DNA samples isolated from blood and pleural effusion (using PCR, and polyacrylamide gel electrophoresis denaturizing), on 2 different chromosomes which have 9 different polymorphic determinants at 6q and 3 different polymorphic determinants at 9p using molecular genetic methods on 13 patients clinico-pathologically diagnosed MPM.

RESULTS

Loss of Heterozygosity (LOH) was determined at D6S275 in one patient, at D6S301 in another, at D6S474 in 2, at ARG1 in 2, at D6S1038 in 2 and at D6S1008 in 3 patients. In 7 (54%) of the 13 patients, we found LOH in at least one site. No LOH was determined at any informative loci in 6 patients. Of the 13 patients, no investigated markers were determined at 9p.

CONCLUSION

In this study, genomic DNA samples obtained from MPM patients with asbestos exposure revealed that they contained important genotoxic damage. We found no other study on this subject at molecular level in pleural effusion either in Turkey or in the Med-line literature. We believe that this study will provide important support for other research into molecular-genetic variations, both on this subject and other malignancies, and may also constitute a base for early diagnosis and gene therapy research in the future.

Intracellular activated Notch1 is critical for proliferation of Kaposi's sarcoma-associated herpesvirus-associated B-lymphoma cell lines in vitro

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumor virus expressing latent antigens critical for pathogenesis. The mechanism by which KSHV mediates oncogenesis has not been fully elucidated. Notch signaling is an evolutionarily conserved pathway controlling diverse events related to development, proliferation, and tissue homeostasis. Deregulation of Notch signaling has also been shown to be highly correlated with oncogenesis. Here we show that the activated intracellular domain of Notch1 (ICN) is aberrantly accumulated in latently KSHV-infected pleural effusion lymphoma cells and results in increased proliferation. Specifically, growth of the infected cells was dramatically inhibited at the G(1) phase by treatment with a gamma-secretase inhibitor which specifically blocks the production of ICN. Increased ICN also up-regulated the cyclin D1 cell cycle regulator. Taken together, these studies define an important mechanism directly linking latent KSHV infection to induction of oncogenesis through dysregulation of the conserved Notch signaling pathway.

Cross reactivity between many anti-human antibodies for their hamster homologs provide the tools to study the signal transduction pathway activated by asbestos and SV40 in the malignant mesothelioma model

The aim of this study was to test the possibility of using human antibodies to study the pathogenic mechanism of SV40 and asbestos in a hamster mesothelioma model. The cellular lysates from human and hamster primary mesothelial cells were tested by Western blot analysis. All of the antibodies we tested (HGF, Notch, VEGF, Sp1, p53, PP2A, p-ERK1, p-c-jun, Fra1, Fra2, MMP1, MMP9, NFkappaB p65, IkappaB, GAPDH) cross-reacted with their hamster counterparts. These data indicate that hamster mesothelioma model and more in general hamster experimental model, can be used for functional studies because many mouse, rabbit, and goat monoclonal antibodies prepared against human antigens cross-react with their hamster counterparts.