Genetic and epigenetic alterations in carcinogenesis

Pattern of organ remodeling in chronic non-communicable diseases is due to endogenous regulations and falls under the category of Kauffman's self-organization: A case of arterial neointimal pathology

Clinical diagnosis is based on analysis of pathologic findings that may result in perceived patterns. The same is true for diagnostic pathology: Pattern analysis is a foundation of the histopathology-based diagnostic system and, in conjunction with clinical and laboratory findings, forms a basis for the classification of diseases. Any histopathology diagnosis is based on the explicit assumption that the same diseased condition should result in formation of the same (or highly similar) morphologic patterns in different individuals; it is a standard approach in microscopic pathology, including that of non-communicable chronic diseases with organ remodeling. During fifty years of examining diseased tissues under microscopy, I keep asking the same question: Why is a similarity of patterns expected for chronic organ remodeling? For infection diseases, xenobiotic toxicity and deficiencies forming an identical pathologic pattern in different individuals is understandable and logical: The same infection, xenobiotic, or deficiency strikes the same target, which results in identical pathology. The same is true for Mendelian diseases: The same mutations lead to the same altered gene expressions and the same pathologic pattern. But why does this regularity hold true for chronic diseases with organ remodeling? Presumable causes (or risk factors) for a particular chronic disease differ in magnitude and duration between individuals, which should result in various series of transformations. Yet, mysteriously enough, pathological remodeling in a particular chronic disease always falls into a main dominating pattern, perpetuating and progressing in a similar fashion in different patients. Furthermore, some chronic diseases of different etiologies and dissimilar causes/risk factors manifest as identical or highly similar patterns of pathologic remodeling. HYPOTHESIS: I hypothesize that regulations governing a particular organ's chronic remodeling were selected in evolution as the safest response to various insults and physiologic stress conditions. This hypothesis implies that regulations directing diseased chronic remodeling always preexist but normally are controlled; this control can be disrupted by a diverse range of non-specific signals, liberating the pathway for identical pathologic remodeling. This hypothesis was tested in an analysis of arterial neointimal formation, the identical pathology occurring in different diseases and pathological conditions: graft vascular disease in organ transplantation, in-stent restenosis, peripheral arterial diseases, idiopathic intimal hyperplasia, Kawasaki disease, coronary atherosclerosis and as reaction to drugs. The hypothesis suggests that arterial intimal cells are poised between only two alternative pathways: the pathway with controlled intimal cell proliferation or the pathway where such control is disrupted, ultimately leading to the progressive neointimal pathology. By this property the arterial neointimal formation constitutes a special case of Kauffman's self-organization. This new hypothesis gives a parsimonious explanation for identical pathological patterns of arterial remodeling (neointimal formation), which occurs in diseases of different etiologies and due to dissimilar causes/risk factors, or without any etiology and causes/risk factors at all. This new hypothesis also suggests that regulation facilitating intimal cell proliferation cannot be overwritten or annulled because this feature is vital for arterial differentiation, cell renewal, and integrity. This hypothesis suggests that studying numerous, and likely interchangeable, non-specific signals that disrupt regulation controlling intimal cell proliferation is unproductive; instead, a study of the controlling regulation(s) itself should be a priority of our research.

Role of Porphyromonas gingivalis in oral squamous cell carcinoma development: A systematic review

OBJECTIVE

The target of the current systematic review is to gather and synthesize the most recent scientific information about the role of Porphyromonas gingivalis in the molecular pathways of oral squamous cell carcinoma (OSCC).

BACKGROUND

Oral squamous cell carcinoma is the most common malignancy of the oral cavity, with a poor prognosis and a low survival rate. Etiology is multifactorial but consumption of tobacco and alcohol is the most important risk factors. P gingivalis is a Gram-negative anaerobic bacterium commonly found in oral microbiota that has been linked to periodontal disease (PD), and recently to OSCC. However, its association with OSCC development is not well defined.

MATERIAL AND METHODS

A bibliographic research was carried out selecting articles published until 2019, on PubMed, Web of Science, and Scopus databases, with the keywords "Porphyromonas gingivalis," "oral cancer," "oral squamous cell carcinoma," and "periodontal pathogen."

RESULTS

Seventeen articles, 14 in vitro and three in animal models, were selected. Models mimicking OSCC were OSCC pre-established cell lines (11 studies), OSCC/ healthy human biopsies (three studies), and animals with OSCC (three studies). P gingivalis strains used to cause infection in these studies were ATCC 33277, 381, and W83.

CONCLUSIONS

Porphyromonas gingivalis could play an important role in OSCC development and could be involved in three different stages: epithelial-mesenchymal transition of malignant cells, neoplastic proliferation, and tumor invasion. Current findings emphasize the convenience of treatment and control approaches of PD as part of the primary prevention of OSCC.

Long non-coding SNHG1 in cancer

OBJECTIVES

Long non-coding RNAs (lncRNAs) consist of a cluster of RNAs having >200 nucleotides lacking protein-coding function. Recent studies indicate that lncRNAs are involved in various cellular processes and their aberrant expression may lead to tumour development and progression. They may also serve as oncogenes or tumour suppressor genes in other diseases. In this review, we emphasize current investigations involving clinical management, tumour progression and the molecular mechanism of SNHG1 in human cancer.

MATERIALS AND METHODS

We investigate and summarize recent studies regarding the biologic functions and mechanisms of lncRNA SNHG1 in tumorigenesis. Related studies were obtained through a systematic search of google scholar, PubMed, Embase and Cochrane Library.

RESULTS

SNHG1 is a novel oncogenic lncRNA aberrantly expressed in different diseases including colorectal, liver, lung, prostate, gastric and esophageal cancers as well as ischemic stroke, nasopharyngeal carcinoma, laryngeal squamous cell carcinoma, neuroblastoma, renal cell carcinoma and osteosarcoma. Upregulation of SNHG1 was significantly associated with advanced tumour stage, tumour size, TNM stage and decreased overall survival. Furthermore, aberrant expression of SNHG1 contributes to cell proliferation, metastasis, migration and invasion of cancer cells.

CONCLUSION

SNHG1 likely acts as a useful tumour biomarker for cancer diagnosis, prognosis and treatment.

Molecular biology of gynecological cancer

Cancer is a pathological condition in which the balance between cell growth and death is disordered. Various molecules have been reported to be involved in the oncogenic process of invasion, metastasis and resistance to treatment. An exponential growth in the collection of genomic and proteomic data in the past 20 years has provided major advances in understanding the molecular mechanisms of human cancer, which has been applied to diagnostic and treatment strategies. Targeted therapies have been developed and adopted, particularly for advanced, refractory or recurrent cancers, depending on individual molecular profiles. The aim of the present review is to provide a report of the current literature regarding the molecular biology of gynecological cancers.

Epigenetic changes within the promoter regions of antigen processing machinery family genes in Kazakh primary esophageal squamous cell carcinoma

The esophageal squamous cell carcinoma (ESCC) is thought to develop through a multi-stage process. Epigenetic gene silencing constitutes an alternative or complementary mechanism to mutational events in tumorigenesis. Posttranscriptional regulation of human leukocyte antigen class I (HLA-I) and antigen processing machinery (APM) proteins expression may be associated with novel epigenetic modifications in cancer development. In the present study, we determined the expression levels of HLA-I antigen and APM components by immunohistochemistry. Then by a bisulfite-sequencing PCR (BSP) approach, we identified target CpG islands methylated at the gene promoter region of APM family genes in a ESCC cell line (ECa109), and further quantitative analysis of CpG site specific methylation of these genes in cases of Kazakh primary ESCCs with corresponding non-cancerous esophageal tissues using the Sequenom MassARRAY platform. Here we showed that the development of ESCCs was accompanied by partial or total loss of protein expression of HLA-B, TAP2, LMP7, tapasin and ERp57. The results demonstrated that although no statistical significance was found of global target CpG fragment methylation level sof HLA-B, TAP2, tapasin and ERp57 genes between ESCC and corresponding non-cancerous esophageal tissues, there was significant differences in the methylation level of several single sites between the two groups. Of thesse only the global methylation level of LMP7 gene target fragments was statistically higher (0.0517±0.0357) in Kazakh esophageal cancer than in neighboring normal tissues (0.0380±0.0214, p<0.05). Our results suggest that multiple CpG sites, but not methylation of every site leads to down regulation or deletion of gene expression. Only some of them result in genetic transcription, and silencing of HLA-B, ERp57, and LMP7 expression through hypermethylation of the promoters or other mechanisms may contribute to mechanisms of tumor escape from immune surveillance in Kazakh esophageal carcinogenesis.

Oxidative stress induces proliferation of colorectal cancer cells by inhibiting RUNX3 and activating the Akt signaling pathway

We recently reported that the tumor suppressor Runt-related transcription factor 3 (RUNX3) is silenced in colorectal cancer cells via oxidative stress-induced hypermethylation of its promoter. The resulting downregulation of RUNX3 expression influences cell proliferation. Activation of the Akt signaling pathway is also associated with cell survival and proliferation; however, the effects of oxidative stress on the relationship between RUNX3 and Akt signaling are largely unknown. Therefore, this study investigated the mechanisms involved in cell proliferation caused by oxidative stress-induced silencing of RUNX3. The levels of RUNX3 mRNA and protein were downregulated in response to treatment of the human colorectal cancer cell line SNU-407 with H2O2. Treatment of the cells with H2O2 also upregulated Akt mRNA and protein expression, and inhibited the binding of RUNX3 to the Akt promoter. The inverse correlation between the expression levels of RUNX3 and Akt in H2O2-treated cells was also associated with nuclear translocation of β-catenin and upregulation of cyclin D1 expression, which induced cell proliferation. H2O2 treatment also increased the binding of β-catenin to the cyclin D1 promoter. The results presented here demonstrate that reactive oxygen species silence the tumor suppressor RUNX3, enhance the Akt-mediated signaling pathway, and promote the proliferation of colorectal cancer cells.

Methylation kinetics and CpG-island methylator phenotype status in colorectal cancer cell lines

Background

Hypermethylation of CpG islands is thought to contribute to carcinogenesis through the inactivation of tumor suppressor genes. Tumor cells with relatively high levels of CpG island methylation are considered CpG island methylator phenotypes (CIMP). The mechanisms that are responsible for regulating the activity of de novo methylation are not well understood.

Results

We quantify and compare de novo methylation kinetics in CIMP and non-CIMP colon cancer cell lines in the context of different loci, following 5-aza-2’deoxycytidine (5-AZA)-mediated de-methylation of cells. In non-CIMP cells, a relatively fast rate of re-methylation is observed that starts with a certain time delay after cessation of 5-AZA treatment. CIMP cells, on the other hand, start re-methylation without a time delay but at a significantly slower rate. A mathematical model can account for these counter-intuitive results by assuming negative feedback regulation of de novo methylation activity and by further assuming that this regulation is corrupted in CIMP cells. This model further suggests that when methylation levels have grown back to physiological levels, de novo methylation activity ceases in non-CIMP cells, while it continues at a constant low level in CIMP cells.

Conclusions

We propose that the faster rate of re-methylation observed in non-CIMP compared to CIMP cells in our study could be a consequence of feedback-mediated regulation of DNA methyl transferase activity. Testing this hypothesis will involve the search for specific feedback regulatory mechanisms involved in the activation of de novo methylation.

Reviewers’ report

This article was reviewed by Georg Luebeck, Tomasz Lipniacki, and Anna Marciniak-Czochra

Detection and Clinical Significance of DLC1 Gene Methylation in Serum DNA from Colorectal Cancer Patients

OBJECTIVE

Deleted in liver cancer 1 (DLC1) is a new candidate tumor suppressor gene, whose down-regulation or even silence will result from promoter hypermethylation in various human cancers including colorectal cancer (CRC). The aim of this study is toevaluate the diagnostic role of DLC1gene methylationin the serum DNA from CRC patients.

METHODS

This study enrolled 85 CRC patients and 45 patients with benign colorectal diseases. Methylation-specific polymerase chain reaction (MSP) was used to determine the promoter methylation status of DLC1 gene in serum DNA. The combination of DLC1 methylation and conventional tumor markers was further analyzed.

RESULTS

Hypermethylation of DLC1 was detected in 42.4% (36/85) of CRC serums, while seldom in the benign controls(8.9%, 4/45) (P<0.001). The aberrant DLC1 methylation in serum DNA was not associated with patients' clinicopathological features and elevated CEA/CA19-9 levels. Furthermore, the combinational analysis of CEA, CA19-9 and DLC1 methylation showed a higher sensitivity and no reduced diagnostic specificity than CEA and CA19-9 combination for CRC diagnosis.

CONCLUSION

The serum DLC1 methylation may be a promising biomarker for the early detection of CRC, which will further increase the diagnostic efficiency in combination with CEA and CA19-9.

DNA methylation of human endogenous retrovirus in systemic lupus erythematosus

Previous studies have reported that T cells from active systemic lupus erythematosus (SLE) patients contained global hypomethylation and demethylation at the promoter of several genes, which may contribute to the pathogenesis of the disease. Currently there are scarce data on methylation of retroelements in patients with SLE. We estimated and compared the methylated levels of human endogenous retroviruses (HERV)-E and HERV-K in normal and SLE CD3+CD4+ T lymphocytes, CD8+ T and B lymphocytes by using combined bisulfite restriction analysis-interspersed repetitive sequences (COBRA-IRS). HERV-E LTR2C methylation level in CD3+CD4+ T lymphocytes of active SLE was significantly lower than inactive SLE and normal controls (P=0.023 and 0.035, respectively). Surprisingly, HERV-K LTR5_Hs hypomethylation was significantly detected in CD3+CD4+ T lymphocytes from patients with inactive SLE when compared with the active SLE and normal controls (P=0.027 and 0.002, respectively). Demethylation of HERV-K LTR5_Hs in B cells was also detected when compared with the normal controls (P=0.048). Furthermore, the hypomethylation of HERV-E LTR2C in CD3+CD4+ T lymphocytes was positively correlated with lymphopenia in active SLE, whereas the hypomethylation of HERV-K LTR5_Hs was significantly correlated with complement activity and Systemic Lupus Erythematosus Disease Activity Index score. In summary, for each lymphocyte subset in patients with SLE, IRS hypomethylation was found to be type specific. Further studies are needed to confirm and explain these observations.

The pioneering spirit of Takashi Sugimura: his studies of the biochemistry of poly(ADP-ribosylation) and of cancer

Takashi Sugimura has accomplished many scientific achievements in the field of biochemistry and in cancer research. Sugimura's group identified the novel polymer poly(ADP-ribose) in parallel to P. Mandel's and O. Hayaishi's groups and demonstrated the presence of the enzyme poly(ADP-ribose) polymerase (PARP). He also discovered the cognate catabolic enzyme, poly(ADP-ribose) glycohydrolase (PARG) and further elucidated the biology of poly(ADP-ribose). The astonishing discovery of pierisin, an apoptogenic peptide that ADP-ribosyaltes DNA, profoundly illuminates his scientific character and curiosity as well. Sugimura's work in cancer research shows an extraordinarily wide range, which includes the establishment of new methods in chemical carcinogenesis, the identification of various environmental mutagens/carcinogens and new tumour promoters. He also established the concept that cancer is a disease of DNA and contributed to the development of the concept of the multi-step model of carcinogenesis.

Genetic and epigenetic analysis of non-small cell lung cancer with NotI-microarrays

This study aimed to clarify genetic and epigenetic alterations that occur during lung carcinogenesis and to design perspective sets of newly identified biomarkers. The original method includes chromosome 3 specific NotI-microarrays containing 180 NotI clones associated with genes for hybridization with 40 paired normal/tumor DNA samples of primary lung tumors: 28 squamous cell carcinomas (SCC) and 12 adenocarcinomas (ADC). The NotI-microarray data were confirmed by qPCR and bisulfite sequencing analyses. Forty-four genes showed methylation and/or deletions in more than 15% of non-small cell lung cancer (NSCLC) samples. In general, SCC samples were more frequently methylated/deleted than ADC. Moreover, the SCC alterations were observed already at stage I of tumor development, whereas in ADC many genes showed tumor progression specific methylation/deletions. Among genes frequently methylated/deleted in NSCLC, only a few were already known tumor suppressor genes: RBSP3 (CTDSPL), VHL and THRB. The RPL32, LOC285205, FGD5 and other genes were previously not shown to be involved in lung carcinogenesis. Ten methylated genes, i.e., IQSEC1, RBSP3, ITGA 9, FOXP1, LRRN1, GNAI2, VHL, FGD5, ALDH1L1 and BCL6 were tested for expression by qPCR and were found downregulated in the majority of cases. Three genes (RBSP3, FBLN2 and ITGA9) demonstrated strong cell growth inhibition activity. A comprehensive statistical analysis suggested the set of 19 gene markers, ANKRD28, BHLHE40, CGGBP1, RBSP3, EPHB1, FGD5, FOXP1, GORASP1/TTC21, IQSEC1, ITGA9, LOC285375, LRRC3B, LRRN1, MITF, NKIRAS1/RPL15, TRH, UBE2E2, VHL, WNT7A, to allow early detection, tumor progression, metastases and to discriminate between SCC and ADC with sensitivity and specificity of 80-100%.

A systematic analysis on DNA methylation and the expression of both mRNA and microRNA in bladder cancer

BACKGROUND

DNA methylation aberration and microRNA (miRNA) deregulation have been observed in many types of cancers. A systematic study of methylome and transcriptome in bladder urothelial carcinoma has never been reported.

METHODOLOGY/PRINCIPAL FINDINGS

The DNA methylation was profiled by modified methylation-specific digital karyotyping (MMSDK) and the expression of mRNAs and miRNAs was analyzed by digital gene expression (DGE) sequencing in tumors and matched normal adjacent tissues obtained from 9 bladder urothelial carcinoma patients. We found that a set of significantly enriched pathways disrupted in bladder urothelial carcinoma primarily related to "neurogenesis" and "cell differentiation" by integrated analysis of -omics data. Furthermore, we identified an intriguing collection of cancer-related genes that were deregulated at the levels of DNA methylation and mRNA expression, and we validated several of these genes (HIC1, SLIT2, RASAL1, and KRT17) by Bisulfite Sequencing PCR and Reverse Transcription qPCR in a panel of 33 bladder cancer samples.

CONCLUSIONS/SIGNIFICANCE

We characterized the profiles between methylome and transcriptome in bladder urothelial carcinoma, identified a set of significantly enriched key pathways, and screened four aberrantly methylated and expressed genes. Conclusively, our findings shed light on a new avenue for basic bladder cancer research.

Hypomethylation of LINE-1 but not Alu in lymphocyte subsets of systemic lupus erythematosus patients

BACKGROUND

T lymphocytes from SLE patients have a global decrease in the 5-methylcytosine content. Previous studies have identified hypomethylation in the promoter of several genes but there is limited study in the interspersed repetitive sequences (IRSs).

METHODS

We examined and compared the methylation levels of long interspersed nuclear element 1s (LINE-1) and Alu elements in normal and SLE CD4+ T lymphocytes, CD8+ T lymphocytes and B lymphocytes by the combined bisulfite restriction analysis-interspersed repetitive sequences (COBRA-IRS).

RESULTS

Hypomethylation of LINE-1 but not Alu was found in CD4+ T lymphocytes, CD8+ T lymphocytes, and B lymphocytes of SLE patient (P=0.005, 0.002, and 0.007, respectively). Moreover, when the SLE patients were divided into active and inactive groups, LINE-1 hypomethylation was more significantly distinguished in both CD4+ and CD8+ T lymphocytes of patients from the active SLE group when compared to the controls. Surprisingly, Alu hypomethylation was also observed in CD8+ T lymphocytes from the inactive SLE group when compared to the normal controls (P=0.0056).

CONCLUSIONS

The hypomethylation in each lymphocyte subset of SLE was IRSs specific, mainly found in LINE-1 rather than Alu.

Reduced expression of lamin A/C correlates with poor histological differentiation and prognosis in primary gastric carcinoma

Background

Lamin A/C is very important in DNA replication, RNA dependent transcription and nuclear stabilization. Reduced or absent lamin A/C expression has been found to be a common feature of a variety of different cancers. To investigate the role of lamin A/C in gastric carcinoma (GC) pathogenesis, we analyzed the correlations between the lamin A/C expression level and clinicopathological factors and studied its prognostic role in primary GC.

Methods

The expression of lamin A/C at mRNA level was detected by the reverse transcription-polymerase chain reaction (RT-PCR) and real time RT-PCR, and western blot was used to examine the protein expression. Lamin A/C expression and its prognostic significance were investigated by performing immunohistochemical analysis on a total of 126 GC clinical tissue samples.

Results

Both lamin A/C mRNA and protein expression were downregulated in the majority of tumours compared with corresponding normal gastric tissues (p = 0.011 and p = 0.036, respectively). Real time RT-PCR further validated that downregulation of lamin A/C is associated with poor histological differentiation (r = 0.438, p = 0.025). The immunohistochemical staining showed an evident decrease of lamin A/C expression in 55.6% (70/126) GC cases. Importantly, the negative lamin A/C expression correlated strongly with histological classification (r = 0.361, p = 0.034). Survival analysis revealed that patients with lamin A/C downregulation have a poorer prognosis (p = 0.034). In addition, lamin A/C expression was found to be an independent prognostic factor by multivariate analysis.

Conclusion

Data of this study suggest that lamin A/C is involved in the pathogenesis of GC, and it may serve as a valuable biomarker for assessing the prognosis for primary GC.

Spontaneous regression of pulmonary metastases from breast angiosarcoma

Spontaneous regression of cancer is a rare phenomenon. We present a rare case of pulmonary metastases in a 72-year-old woman with metastatic breast angiosarcoma. She was diagnosed with a breast angiosarcoma in 2005 and underwent a total mastectomy and postoperative radiotherapy. Unfortunately, a year later she was found to have multiple lung and scalp metastases but in a view of her poor general fitness, she was not a candidate for chemotherapy and was kept on regular followup. Despite the absence of any treatment, the followup chest X-ray showed a significant reduction in the number and size of lung nodules and her scalp lesions regressed completely. Seven months after the diagnosis of metastatic disease, the nodules in her scalp remain controlled.

Distinct TPEF/HPP1 gene methylation patterns in gastric cancer indicate a field effect in gastric carcinogenesis

BACKGROUND

Aberrant methylation of the transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 gene was recently reported in hyperplastic colon polyps, colorectal adenomas and carcinomas. However, there are only limited data on significance of transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 gene methylation in gastric adenocarcinomas.

AIM

The aim of this study was to determine the prevalence of transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 promoter methylation in gastric adenocarcinomas.

PATIENTS

Study population consists of 48 patients with gastric cancer and 11 dyspeptic patients.

METHODS

Using the Methylight assay, transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 gene methylation was assessed in fresh frozen cancer tissue and matched tumoural-free area of patients with gastric cancer and in the gastric mucosa of dyspeptic patients.

RESULTS

Transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 promoter gene methylation was observed in 35 of 48 (73%) gastric adenocarcinomas, and in 27 of 48 (56%) matched tumoural-free area cases (p=0.087). In contrast, the occurrence of transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 methylation was much lower in gastric mucosa of dyspeptics (1 of 11; 9%) and the difference was significant in comparison with both tumoural tissue (p=0.0001) and tumoural-free area (p=0.0047) of cancer patients. Transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 gene expression was significantly reduced in adenocarcinomas in comparison with matched tumoural-free area (p=0.022).

CONCLUSION

Our data suggest that methylation of transmembrane protein containing epidermal growth factor and folistatin domains/hyperplastic polyposis 1 is present in the majority of gastric adenocarcinomas and in the surrounding tumoural-free area, indicating that this epigenetic change may point to a field effect in the gastric mucosa.

Aromatic Amines in Experimental Cancer Research: Tissue-Specific Effects, an Old Problem and New Solutions

Carcinogenic aromatic amines usually produce tumors in specific target tissue, such as 2-acetylaminofluorene (AAF) producing liver tumors in rats, in contrast to some other structurally related arylamines. A hypothesis is presented that explains the mode of action in this rat liver model. Genotoxic and nongenotoxic effects work together and make AAF a complete rat liver carcinogen. The cytotoxic, promoting effects are particularly important. N-Hydroxy-2-aminofluorene and 2-nitrosofluorene, two metabolites of AAF, are able to uncouple the mitochondrial respiratory chain. They entertain a redox cycle that removes electrons from the respiratory chain and impairs ATP production. The dose-dependent opening of the mitochondrial permeability transition pore signals the viability of the cell. If the pore is opened to a certain extent, the cell is eliminated by apoptosis. As a consequence, oval cells proliferate, and as this process is overloaded, the liver transforms into a cirrhosis-like situation and thus provides the conditions under which initiated liver cells develop tumors. Such an interpretation is based on assumptions that have been debated for a long time. Some of these often forgotten developments are reviewed in support of the hypothesis, which allows a more comprehensive view of the complex in vivo situation at a time when in vitro models prevail.

High-throughput methylation profiling by MCA coupled to CpG island microarray

An abnormal pattern of DNA methylation occurs at specific genes in almost all neoplasms. The lack of high-throughput methods with high specificity and sensitivity to detect changes in DNA methylation has limited its application for clinical profiling. Here we overcome this limitation and present an improved method to identify methylated genes genome-wide by hybridizing a CpG island microarray with amplicons obtained by the methylated CpG island amplification technique (MCAM). We validated this method in three cancer cell lines and 15 primary colorectal tumors, resulting in the discovery of hundreds of new methylated genes in cancer. The sensitivity and specificity of the method to detect hypermethylated loci were 88% and 96%, respectively, according to validation by bisulfite-PCR. Unsupervised hierarchical clustering segregated the tumors into the expected subgroups based on CpG island methylator phenotype classification. In summary, MCAM is a suitable technique to discover methylated genes and to profile methylation changes in clinical samples in a high-throughput fashion.

Targeting Helicobacter pylori in gastric carcinogenesis

Gastric infection by Helicobacter pylori is an important risk factor for the development of gastric cancer. Recent research has identified both bacterial and host factors related to increased gastric cancer risk, including virulence-associated genes located in the cytotoxin-associated gene pathogenicity island and the vacuolating toxin A exotoxin, as well as polymorphisms in key cytokines and cytokine receptors that mediate the host's gastric inflammatory response. Early randomized trials indicate that eradicating H. pylori with antibiotics may prevent gastric cancer, although the effects so far have been modest, and are probably confined to individuals who had not developed preneoplastic lesions at the time of eradication. Targeting H. pylori to prevent gastric cancer may be best achieved through vaccination, better understanding of the molecular pathogenesis of H. pylori-associated carcinogenesis and additional chemopreventive strategies.

LINE-1 hypomethylation in cancer is highly variable and inversely correlated with microsatellite instability

Background

Alterations in DNA methylation in cancer include global hypomethylation and gene-specific hypermethylation. It is not clear whether these two epigenetic errors are mechanistically linked or occur independently. This study was performed to determine the relationship between DNA hypomethylation, hypermethylation and microsatellite instability in cancer.

Methodology/Principal Findings

We examined 61 cancer cell lines and 60 colorectal carcinomas and their adjacent tissues using LINE-1 bisulfite-PCR as a surrogate for global demethylation. Colorectal carcinomas with sporadic microsatellite instability (MSI), most of which are due to a CpG island methylation phenotype (CIMP) and associated MLH1 promoter methylation, showed in average no difference in LINE-1 methylation between normal adjacent and cancer tissues. Interestingly, some tumor samples in this group showed increase in LINE-1 methylation. In contrast, MSI-showed a significant decrease in LINE-1 methylation between normal adjacent and cancer tissues (P<0.001). Microarray analysis of repetitive element methylation confirmed this observation and showed a high degree of variability in hypomethylation between samples. Additionally, unsupervised hierarchical clustering identified a group of highly hypomethylated tumors, composed mostly of tumors without microsatellite instability. We extended LINE-1 analysis to cancer cell lines from different tissues and found that 50/61 were hypomethylated compared to peripheral blood lymphocytes and normal colon mucosa. Interestingly, these cancer cell lines also exhibited a large variation in demethylation, which was tissue-specific and thus unlikely to be resultant from a stochastic process.

Conclusion/Significance

Global hypomethylation is partially reversed in cancers with microsatellite instability and also shows high variability in cancer, which may reflect alternative progression pathways in cancer.

The end adjusts the means: heterochromatin remodelling during terminal cell differentiation

All cells that constitute mature tissues in an eukaryotic organism undergo a multistep process of cell differentiation. At the terminal stage of this process, cells either cease to proliferate forever or rest for a very long period of time. During terminal differentiation, most of the genes that are required for cell 'housekeeping' functions, such as proto-oncogenes and other cell-cycle and cell proliferation genes, become stably repressed. At the same time, nuclear chromatin undergoes dramatic morphological and structural changes at the higher-order levels of chromatin organization. These changes involve both constitutively inactive chromosomal regions (constitutive heterochromatin) and the formerly active genes that become silenced and structurally modified to form facultative heterochromatin. Here we approach terminal cell differentiation as a unique system that allows us to combine biochemical, ultrastructural and molecular genetic techniques to study the relationship between the hierarchy of chromatin higher-order structures in the nucleus and its function(s) in dynamic packing of genetic material in a form that remains amenable to regulation of gene activity and other DNA-dependent cellular processes.

Measurements of metaphase and interphase chromosome aberrations transmitted through early cell replication rounds in human lymphocytes exposed to low-LET protons and high-LET 12C ions

Inheritable chromosome aberrations (CA) are of concern because cytogenetic damage may trigger the carcinogenic process. Moreover, stability of radiation-induced CA is a prerequisite for meaningful biological dosimetry. CA inheritability arguably depends on the aberration structure, with symmetrical exchanges being favoured over asymmetrical rearrangements, but it is also affected by radiation quality. CA induced by low-LET protons and high-LET 12C ions in G0 peripheral blood lymphocytes were measured in first- , second- and third-generation by combined FISH/harlequin staining of metaphase as well as prematurely condensed interphase chromosomes 1 and 2. As expected, the frequency of non-transmissible (NT) aberrations declined through replication rounds. A radiation-induced arrest occurred prior to first post-irradiation mitosis that prevalently affected aberrant cells. Aberrant cells incurred cycle delays also at subsequent cycles following proton-irradiation but not 12C ion-irradiation. As expected, the frequency of reciprocal translocations remained fairly stable while that of dicentrics was halved at each mitotic round. A significant fraction of complex-type exchanges was found in third-generation cells following both irradiations and appeared to be transmitted relatively more efficiently after protons than 12C ions. A low but stably transmitted frequency of transmissible (T)-type insertions were detected after 12C ions but not after low LET-irradiation. Our data support a differential ability by aberrant cells to progress through post-irradiation mitoses that is influenced by the aberration burden and radiation quality.

Genetic and epigenetic alterations of RB2/p130 tumor suppressor gene in human sporadic retinoblastoma: implications for pathogenesis and therapeutic approach

Human retinoblastoma occurs in two forms (familial and sporadic) both due to biallelic mutation of the RB1/p105 gene even if its loss is insufficient for malignancy. We have recently reported that loss of expression of the retinoblastoma-related protein pRb2/p130 correlates with low apoptotic index, suggesting that RB2/p130 gene could be involved in retinoblastoma. Mutational analysis of RB2/p130 in primary tumors showed a tight correlation between Exon 1 mutations and pRb2/p130 expression level in sporadic retinoblastoma. These mutations are located within a CpG-enriched region prone to de novo methylation. Analysis of RB2/p130 methylation status revealed that epigenetic events, most probably consequent to the Exon 1 mutations, determined the observed phenotype. Treatment of Weri-Rb1 cell line by 5-Aza-dC induced an increase in expression level of pRb2/p130, E2F1, p73 and p53. Overall, our results highlight a crucial role of epigenetic events in sporadic retinoblastoma, which opens a perspective for new therapeutic approaches.

Deregulated expression of Polycomb-group oncogenes in human malignant lymphomas and epithelial tumors

Genes belonging to the Polycomb-group (PcG) are epigenetic gene silencers with a vital role in the maintenance of cell identity. They contribute to regulation of various processes in both embryos and adults, including the cell cycle and lymphopoiesis. A growing body of work has linked human PcG genes to various hematological and epithelial cancers, identifying novel mechanisms of malignant transformation and paving the way to development of new cancer treatments and identification of novel diagnostic markers. This review addresses the current insights in the role of PcG genes in development of human malignancies.

Distinctive pattern of LINE-1 methylation level in normal tissues and the association with carcinogenesis

Genome-wide losses of DNA methylation have been regarded as a common epigenetic event in malignancies and may play crucial roles in carcinogenesis. Limited information is available on the global methylation status in normal tissues and other cancer types beyond colonic carcinoma. Here we applied the combined bisulfite restriction analysis PCR to evaluate the methylation status of LINE-1 repetitive sequences in genomic DNA derived from microdissected samples from several human normal and neoplastic tissues. We found that methylation of LINE-1 in leukocytes was independent of age and gender. In contrast, normal tissues from different organs showed tissue-specific levels of methylated LINE-1. Globally, most carcinomas including breast, colon, lung, head and neck, bladder, esophagus, liver, prostate, and stomach, revealed a greater percentage of hypomethylation than their normal tissue counterparts. Furthermore, DNA derived from sera of patients with carcinoma displayed more LINE-1 hypomethylation than those of noncarcinoma individuals. Finally, in a colonic carcinogenesis model, we detected significantly greater hypomethylation in carcinoma than those of dysplastic polyp and histological normal colonic epithelium. Thus, the methylation status is a unique feature of a specific tissue type and the global hypomethylation is a common epigenetic process in cancer, which may progressively evolve during multistage carcinogenesis.

Methylguanine methyltransferase activity deficiency in immature rat mammary epithelial cells parallels increased carcinogenic susceptibility

The prepubertal breast is more susceptible than the mature breast to the carcinogenic effects of ionizing radiation, and potentially to cigarette smoke and alkylating chemotherapeutics. Mammary epithelial cells (MECs) from sexually immature (3-week (wk)-old) Fischer 344 rats were more sensitive than mature (8-wk-old) rats to the carcinogenic, lethal, and mutagenic effects of N-nitroso-N-methylurea (NMU). The work reported here was undertaken to better define this age-specific susceptibility of the mammary gland to NMU. Using the alkaline comet assay, it was found that MECs from immature but not mature rats displayed an increase in single-strand DNA breaks or alkali-labile lesions 2 h following NMU treatment. Hoechst staining indicated apoptosis was not responsible for the increase. Inhibition of methylguanine methyltransferase (MGMT) did not affect immature MECs but caused mature MECs to recapitulate the immature response to NMU. Direct measurement of MGMT activity revealed that immature MECs are significantly deficient in MGMT activity relative to mature MECs. MECs had the lowest MGMT activity of all organs tested. Immature kidneys, which preferentially developed nephroblastomas after NMU treatment, also displayed significantly lower MGMT activity than mature kidneys. These results suggest that age-related differences in MGMT activity may play a significant role in age-differential susceptibility to rat mammary gland and kidney carcinogenesis, and argue the importance of extending these studies to humans. They also provide a mechanistic basis for studying, as potentially initiating events in breast cancer, exposures of prepubertal girls to alkylating agents, to which humans are exposed in cigarette smoke, the diet, and as chemotherapy.

Dynamic relocation of epigenetic chromatin markers reveals an active role of constitutive heterochromatin in the transition from proliferation to quiescence

Quiescent lymphocytes have small nuclei, filled with masses of facultative heterochromatin. Upon receiving mitogenic signals, these cells undergo nuclear enlargement, chromatin decondensation, the reactivation of cell proliferation, and changes in the intranuclear positioning of key genes. We examined the levels and intranuclear localization of major histone modifications and non-histone heterochromatin proteins in quiescent and reactivated mouse spleen lymphocytes. Dramatic and selective changes in localization of two heterochromatin-associated proteins, the histone variant macroH2A and HP1α occurred during lymphocyte reactivation. Reciprocal changes in the locations of these two proteins were observed in activated lymphocytes and cultured mouse fibroblasts induced into quiescence. We also describe a new apocentric nuclear compartment with a unique set of histone modifications that occurs as a zone of chromatin surrounding centromeric heterochromatin in differentiated lymphocytes. It is within this zone that the most significant changes occur in the transition from proliferation to quiescence. Our results suggest that constitutive centromeric heterochromatin plays an active role in cell differentiation and reactivation.

Review article: helicobacter pylori and molecular events in precancerous gastric lesions

Gastric cancer can be divided into intestinal type and diffuse type that differ substantially in epidemiology and pathogenesis. The most important aetiological factor associated both with intestinal and diffuse gastric cancer, is Helicobacter pylori. Exposure of gastric epithelial cells to H. pylori results in an inflammatory reaction with the production of reactive oxygen species and nitric oxide that, in turn, deaminates DNA causing mutations. The complex interplay between H. pylori strain, inflammation and host characteristics may directly promote diffuse type gastric cancer or induce a cascade of morphological events, i.e. atrophy, intestinal metaplasia and dysplasia, finally leading to intestinal type gastric cancer. Two mechanisms, genetic and epigenetic have been held to play a role in the molecular alterations underlying gastric carcinogenesis. The former, comprising changes in the DNA sequence, is irreversible; the latter, involving DNA methylation, is potentially reversible by eliminating the triggering agents. If H. pylori is eradicated before development of stable mutations, the risk of gastric cancer will likely be prevented. Thus, eradication of H. pylori might immediately reduce the risk of diffuse type gastric cancer, whereas prevention of intestinal type gastric cancer may be less effective if patients are treated later in the evolution of the carcinogenic process.

Spontaneous regression in small cell esophageal carcinoma

Spontaneous regression or remission of cancers has been defined as the disappearance of the malignancies without any treatment or with obviously inadequate treatment. Spontaneous regression is rare, while any case with a small cell carcinoma in the esophagus was not found in the literature. We experienced a 73-year-old man with small-cell carcinoma in the thoracic esophagus whom underwent esophagectomy with lymphadenectomy. A pathological examination of the resected specimens found metastasis from the small cell carcinoma in the mediastinal lymph nodes, but no malignant cells in the esophageal lesion--an ulcer scar from which the biopsy specimen was taken to be a small-cell carcinoma. This may be the first case report that spontaneous regression in a small-cell carcinoma in the esophagus was found by esophagectomy and pathological examination.

Genome-wide analysis of DNA methylation status of CpG islands in embryoid bodies, teratomas, and fetuses

Differentiation of embryonic stem (ES) cells into embryoid bodies (EBs) provides an in vitro system for the study of early lineage determination during mammalian development. We have previously reported that there are 247 CpG islands that potentially have tissue-dependent and differentially methylated regions (T-DMRs). This provided evidence that the formation of DNA methylation patterns at CpG islands is a crucial epigenetic event underlying mammalian development. Here we present an analysis by the restriction landmark genomic scanning (RLGS) using NotI as a landmark enzyme of the genome-wide methylation status of CpG islands of ES cells and EBs and of teratomas produced from ES cells. These results are considered in relation to the methylation status of CpG islands of genomic DNA from normal fetus (10.5dpc) and adult tissues. We have prepared a DNA methylation panel that consists of 259 T-DMRs and includes novel T-DMRs that are distinctly methylated or unmethylated in the teratomas. The DNA methylation pattern was complex and differed for the ES cells, EBs, and teratomas, providing evidence that differentiation of cells involves both de novo DNA methylation as well as demethylation. Comparison of the numbers of T-DMRs, that were differentially methylated or unmethylated among the cells and tissue types studied, revealed that the teratomas were the most epigenetically different from ES cells. Thus, analysis of the DNA methylation profiles prepared in this study provides new insights into the differentiation of ES cells and development of fetus, EB, teratoma, and somatic tissues.

Review article: what have we learnt from gastric biopsy?

Pathologists would claim that the most reliable information obtained on gastric diseases is pathology-based. This manuscript summarizes the four major biopsy-based contributions to the current knowledge of non-neoplastic gastric diseases: (i) the in vivo definition of gastritis; (ii) the recognition of the clinicopathological patterns of gastritis; (iii) the morphological links between gastritis and stomach cancer; and finally (iv) the recent information on the possible reversibility of early or advanced precancerous gastric lesions.

Hypermethylation of the p16 gene and lack of p16 expression in hepatoblastoma

Hepatoblastoma is the most frequent pediatric liver tumor that develops mostly in young children. Abnormal regulation of cell cycle regulatory genes including p16 has been described, displaying no p16 mRNA and p16 protein in hepatoblastomas. The inactivation of p16, leading to the disruption of cell cycle control is involved in many types of human malignancies. However, the mechanism of the p16 inactivation in hepatoblastomas has not yet been elucidated. In this present study, we examined the methylation status of the p16 gene promoter by using methylation-specific PCR in 24 cases of hepatoblastomas and in 20 cases of corresponding non-neoplastic liver tissue. Aberrant methylation of 5' CpG islands of p16 was present in 12 of 24 (50.0%) cases of hepatoblastoma. Clinicopathologic parameters were not associated with the methylation status of p16. To correlate the methylation status of p16 with the expression of p16, immunohistochemical staining was done in tumors and non-neoplastic liver tissue. All non-neoplastic liver tissues displayed moderate, but heterogeneous immunoreactivity for p16. Eight of 12 (66.6%) methylation-positive hepatoblastomas showed a complete lack of immunoreactivity for p16. The other 4 methylation-positive hepatoblastomas had heterogeneous immunoreactivity. Nine of 12 (75.0%) unmethylated cases of hepatoblastoma displayed diffuse immunoreactivity, whereas 3 cases of unmethylated hepatoblastoma were not immunostained for p16. Our data indicate that the hypermethylation of p16 is a major mechanism of the transcriptional repression of p16 in hepatoblastomas, and we suggest that the inactivation of p16, leading to the lack of p16, may play an important role in the tumorigenesis of hepatoblastomas.

p16 Hypermethylation in the early stage of hepatitis B virus-associated hepatocarcinogenesis

Abnormality of the p16 expression is involved in the pathogenesis of hepatocellular carcinoma (HCC), and hypermethylation of p16 gene is known as a major p16 inactivation mechanism. Cirrhotic nodule (CN) is now regarded as a preneoplastic lesion that is frequently associated with microscopic foci of HCC through dysplastic nodules (DNs). This observation clearly supports a multistep hepatocarcinogenesis from CNs through DNs. We thus examined the methylation status of p16 gene in HCCs surrounded by DNs and CNs to define the significance of p16 hypermethylation in the early stage of hepatocarcinogenesis. We tested 24 hepatitis B virus (HBV)-associated CNs, 37 DNs, and 18 HCCs within DNs that were microdissected from paraffin-embedded tissue sections. Frequency of p16 hypermethylation was significantly high in HCCs within DNs (15/18. 83.3%) and it increased from CNs (15/24. 62.5%) through DNs (26/37, 70.3%). Interestingly, 11 out of 12 (91.7%) HCC associated with methylation-positive DNs revealed hypermethylation of p16, and 18 out of 23 (78.2%) DNs associated with methylation-positive CNs showed p16 hypermethylation. These data suggest that p16 hypermethylation in the early stages, CNs and DNs may predispose to HCC. In addition, p16 methylation status of five cell lines with or without HBV infection was examined to test whether the high frequency of hypermethylation is related to HBV infection. HBV-infected cell lines were exclusively methylation-positive. These data suggest that high frequency of hypermethylation may be associated with hepatitis B virus infection.

Assessment of safety/risk vs. Public health concerns: Aflatoxins and hepatocarcinoma

Hepatocellular carcinoma, (HCC) is a serious health problem. It is prevalent in certain parts of the world where food contamination with aflatoxin is common. Aflatoxin, especially AFB(1), has been shown to induce HCC in many species of laboratory and wild animals, including subhuman primates. Carcinogenesis studies have demonstrated that AFB(1) is a potent genotoxic carcinogen. After bioactivation it may covalently bind with protein and with DNA. The former reaction is positively correlated with AFB(1) exposure, and the latter signifies initiation of the carcinogenesis process.With these biomarkers, epidemiological studies have amply demonstrated the etiological role of aflatoxin in HCC. However, hepatitis B virus also contributes to the development of HCC. Risks and VSD (virtual safe dose) have been estimated from animal and epidemiological studies. These estimates further confirm that AFB(1) is a potent carcinogen. Furthermore, the effects of AFB(1) exposure and hepatitis B are synergistic. Some preventive measures, such as lowering the contamination level of AFB(1) in food and appropriate vaccination programs, have been implemented in many parts of the world. Chemopreventive agents. which may abolish or reduce the effects of AFB(1) are being tested for their effectiveness.

Epigenetic marks by DNA methylation specific to stem, germ and somatic cells in mice

BACKGROUND

DNA methylation is involved in many gene functions such as gene-silencing, X-inactivation, imprinting and stability of the gene. We recently found that some CpG islands had a tissue-dependent and differentially methylated region (T-DMR) in normal tissues, raising the possibility that there may be more CpG islands capable of differential methylation.

RESULTS

We investigated the genome-wide DNA methylation pattern of CpG islands by restriction landmark genomic scanning (RLGS) in mouse stem cells (ES, EG and trophoblast stem) before and after differentiation, and sperm as well as somatic tissues. A total of 247 spots out of 1500 (16%) showed differences in the appearance of their RLGS profiles, indicating that CpG islands having T-DMR were numerous and widespread. The methylation pattern was specific, and varied in a precise manner according to cell lineage, tissue type and during cell differentiation.

CONCLUSIONS

Genomic loci with altered methylation status seem to be more common than has hitherto been realized. The formation of DNA methylation patterns at CpG islands is one of the epigenetic events which underlies the production of various cell types in the body. These findings should have implications for the use of embryonic stem cells and cells derived from them therapeutically, and also for the cloning of animals by the transfer of somatic cell nuclei.

NotI subtraction and NotI-specific microarrays to detect copy number and methylation changes in whole genomes

Methylation, deletions, and amplifications of cancer genes constitute important mechanisms in carcinogenesis. For genome-wide analysis of these changes, we propose the use of NotI clone microarrays and genomic subtraction, because NotI recognition sites are closely associated with CpG islands and genes. We show here that the CODE (Cloning Of DEleted sequences) genomic subtraction procedure can be adapted to NotI flanking sequences and to CpG islands. Because the sequence complexity of this procedure is greatly reduced, only two cycles of subtraction are required. A NotI-CODE procedure can be used to prepare NotI representations (NRs) containing 0.1-0.5% of the total DNA. The NRs contain, on average, 10-fold less repetitive sequences than the whole human genome and can be used as probes for hybridization to NotI microarrays. These microarrays, when probed with NRs, can simultaneously detect copy number changes and methylation. NotI microarrays offer a powerful tool with which to study carcinogenesis.

Structural determinants of BRCA1 translational regulation

The BRCA1 gene is involved in sporadic breast and ovarian cancer mainly through reduced expression. BRCA1 mRNAs containing different leader sequences show different patterns of expression. In a normal mammary gland mRNA with a shorter leader sequence, 5'-UTRa is expressed only, whereas in breast cancer tissue mRNA with a longer leader, 5'-UTRb is expressed also. We show that the translation efficiency of transcripts containing 5'-UTRb is 10 times lower than those containing 5'-UTRa. The structures of 5'-UTRa and 5'-UTRb were determined by chemical and enzymatic probing aided by a new method developed for monitoring the number of co-existing stable conformers. Specific factors responsible for reduced translation of mRNA containing 5'-UTRb were determined using a variety of transcripts with mutations in the leader sequence. These factors include a stable secondary structure formed by truncated Alu element and upstream AUG codons. The novel mechanism by which BRCA1 may be involved in sporadic breast and ovarian cancer is proposed. It is based on the expression patterns of BRCA1 mRNAs and differences in their translatability. According to this mechanism the deregulation of the BRCA1 transcription in cancer, resulting in a higher proportion of translationally inhibited transcripts containing 5'-UTRb, contributes to the decrease in the BRCA1 protein observed in sporadic breast and ovarian cancers.

Expression and localization of the homeodomain-containing protein HEX in human thyroid tumors

Homeobox genes are involved in neoplastic transformation of both epithelial and hemopoietic tissues. The divergent homeobox gene HEX is expressed in the anterior visceral endoderm during early mouse development and in some adult tissues of endodermal origin, including liver and thyroid. Whereas a role in leukemyogenesis has been proposed already, few data are available on the involvement of HEX in human epithelial tumors. Herein, we analyzed HEX expression and subcellular localization in a series of 55 human thyroid tumors and in several tumoral cell lines. HEX mRNA was detected by RT-PCR either in normal tissues or in thyroid adenomas and differentiated (papillary and follicular) carcinomas. HEX mRNA was also expressed in most undifferentiated carcinomas. Subcellular localization of HEX protein was investigated by immunohistochemistry. In normal tissues and adenomas, HEX protein was present both in nucleus and cytoplasm. In contrast, both differentiated and undifferentiated carcinomas, as well as the tumoral cell lines investigated, showed HEX protein only in the cytoplasm. These findings suggest that regulation of HEX entry in the nucleus of thyrocytes may represent a critical step during human thyroid tumorigenesis.

Silencing of HTR1B and reduced expression of EDN1 in human lung cancers, revealed by methylation-sensitive representational difference analysis

Aberrantly hypermethylated genes in human lung cancers were searched for by a genome scanning technique, methylation-sensitive-representational difference analysis (MS-RDA). A total of 59 DNA fragments were isolated as those methylated more heavily in either/both of two lung squamous cell carcinoma cell lines, EBC-1 and LK-2, than in a primary culture of normal human bronchial epithelium, NHBE. Thirty-four DNA fragments, whose hypermethylation was confirmed in primary squamous cell carcinomas, were sequenced. By database searches, 17 of them were shown to be located within 2 kb of putative CpG islands, and five of the 17 DNA fragments had transcribed regions of known genes in their vicinities. By RT-PCR of the five genes in the carcinoma cell lines and NHBE, decreased expression of HTR1B (5-hydroxytryptamine receptor 1B) and EDN1 (endothelin-1) was observed. Sequencing after bisulfite modification showed that the CpG island in the promoter region of HTR1B was hypermethylated, while that of EDN1 was not. Demethylation and re-expression of HTR1B were observed after treatment of LK-2 cells with 5-aza-2'-deoxycytidine. In primary lung cancers, decreased mRNA expression of HTR1B was observed in 11 of 20 cases, and that of EDN1 was in 16 of 20 cases. Immunohistochemical analysis of endothelin-1 confirmed that its immunoreactivity was reduced in squamous cell carcinoma cells compared with that in normal bronchial epithelial cells. Considering that endothelin-1 induces apoptosis in melanoma cells and that silencing of endothelin receptor B is observed in prostate cancers, its reduced expression was speculated to confer a growth advantage to lung cancer cells. MS-RDA was shown to isolate DNA fragments that are hypermethylated and silenced, such as HTR1B, and those whose expressions are altered and the methylation statuses outside the promoter region are altered, such as EDN1.

Antimutagenesis and anticarcinogenesis, from the past to the future

Observations on cancer causation are some 150 years old, but actual detailed research on elements bearing on cancer started at the beginning of the twentieth century. Rapid progress, however, is only some 40 years old. Studies in humans documented certain lifestyle related factors to lead to cancer, and research in animal models strengthened this information. With the realization that there are carcinogens that in a metabolically activated attack DNA, in contrast to other agents that act by promoting, enhancing processes through totally distinct mechanisms, it became possible to develop and apply tests for DNA reactivity, in a prokaryotic organism, the widely used Salmonella typhimurium test by Ames and in a eukaryotic system, namely freshly explanted liver cells displaying evidence of DNA repair by Williams. A battery of these two tests are over 90% accurate in defining genotoxicity. Virtually all documented human carcinogens are genotoxic. With advances in molecular biology, mutational events are traced to changes in tumor suppressor genes or in oncogenes, that can serve as markers of risk. In addition, reactive oxygen systems (ROS) are involved in both the early steps in cancer and in the developmental aspects. Thus, foods containing antioxidants such as vegetables, fruits, soy products, cocoa and tea that counteract ROS are protective in cancer causation and development. Worldwide application of current knowledge and mechanisms to cancer prevention, the definitive means of cancer control, is likely to lower not only cancer but also heart disease risk in the current century.

Involvement of poly(ADP-ribose) polymerase in trophoblastic cell differentiation during tumorigenesis

Poly(ADP-ribose) polymerase (Parp) monitors DNA strand breaks and poly(ADP-ribosyl)ates nuclear proteins using NAD as a substrate. The participation of Parp in DNA damage responses has been demonstrated by recent studies using Parp knockout mice. On the other hand, accumulated evidence has shown that Parp is involved in the regulation of gene expression and cell differentiation. In this study, the role of Parp in tumorigenesis and differentiation was studied with Parp-/- embryonic stem (ES) cells. When Parp+/+, Parp+/-, and Parp-/- ES cells were injected subcutaneously into nude mice, teratocarcinoma-like tumors developed from ES cells. However, only tumors derived from Parp-/- ES cells showed trophoblast giant cells (TGCs) containing single or multiple megalo-nuclei. These TGCs are located in a large blood-lake like hemorrhage. This example suggests that Parp is not essential for tumor formation, however, it is involved in trophoblastic cell differentiation and could consequently affect tumor phenotype.

Loss of chromosomal integrity in human mammary epithelial cells subsequent to escape from senescence

The genomic changes that foster cancer can be either genetic or epigenetic in nature. Early studies focused on genetic changes and how mutational events contribute to changes in gene expression. These point mutations, deletions and amplifications are known to activate oncogenes and inactivate tumor suppressor genes. More recently, multiple epigenetic changes that can have a profound effect on carcinogenesis have been identified. These epigenetic events, such as the methylation of promoter sequences in genes, are under active investigation. In this review we will describe a methylation event that occurs during the propagation of human mammary epithelial cells (HMEC) in culture and detail the accompanying genetic alterations that have been observed.