MBD1, MBD2 and CGBP genes at chromosome 18q21 are infrequently mutated in human colon and lung cancers

In silico prediction and interaction of resveratrol on methyl-CpG binding proteins by molecular docking and MD simulations study

Resveratrol enhances the BRCA1 gene expression and the MBD family of proteins bind to the promoter region of the BRCA1 gene. However, the molecular interaction is not yet reported. Here we have analyzed the binding affinity of resveratrol with MBD proteins. Our results suggest that resveratrol binds to the MBD proteins with higher binding affinity toward MeCP2 protein (ΔG = −6.5) by sharing four hydrogen bonds as predicted by molecular docking studies. Further, the molecular dynamics simulations outcomes showed that the backbones of all three protein–ligand complexes are stabilized after the period of 75 ns, constantly fluctuating around the deviations of 0.4 Å, 0.5 Å and 0.7 Å for MBD1, MBD2 and MeCP2, respectively. The inter-molecular hydrogen bonding trajectory analysis for protein–ligand complexes also support the strong binding between MeCP2–resveratrol complex. Further, binding free energy calculations showed binding energy of −94.764 kJ mol⁻¹, −53.826 kJ mol⁻¹ and −36.735 kJ mol⁻¹ for MeCP2–resveratrol, MBD2–resveratrol and MBD1–resveratrol complexes, respectively, which also supported our docking results. Our study also highlighted that the MBD family of proteins forms a binding interaction with other signaling proteins that are involved in various cancer initiation pathways.

Resveratrol enhances the BRCA1 gene expression and the MBD family of proteins bind to the promoter region of the BRCA1 gene.

The Cxxc1 subunit of the Trithorax complex directs epigenetic licensing of CD4+ T cell differentiation

Different dynamics of gene expression are observed during cell differentiation. In T cells, genes that are turned on early or turned off and stay off have been thoroughly studied. However, genes that are initially turned off but then turned on again after stimulation has ceased have not been defined; they are obviously important, especially in the context of acute versus chronic inflammation. Using the Th1/Th2 differentiation paradigm, we found that the Cxxc1 subunit of the Trithorax complex directs transcription of genes initially down-regulated by TCR stimulation but up-regulated again in a later phase. The late up-regulation of these genes was impaired either by prolonged TCR stimulation or Cxxc1 deficiency, which led to decreased expression of Trib3 and Klf2 in Th1 and Th2 cells, respectively. Loss of Cxxc1 resulted in enhanced pathogenicity in allergic airway inflammation in vivo. Thus, Cxxc1 plays essential roles in the establishment of a proper CD4⁺ T cell immune system via epigenetic control of a specific set of genes.

Targeting epigenetic regulators for cancer therapy: mechanisms and advances in clinical trials

Epigenetic alternations concern heritable yet reversible changes in histone or DNA modifications that regulate gene activity beyond the underlying sequence. Epigenetic dysregulation is often linked to human disease, notably cancer. With the development of various drugs targeting epigenetic regulators, epigenetic-targeted therapy has been applied in the treatment of hematological malignancies and has exhibited viable therapeutic potential for solid tumors in preclinical and clinical trials. In this review, we summarize the aberrant functions of enzymes in DNA methylation, histone acetylation and histone methylation during tumor progression and highlight the development of inhibitors of or drugs targeted at epigenetic enzymes.

MBD1 promotes the malignant behavior of gallbladder cancer cells and induces chemotherapeutic resistance to gemcitabine

Background

Methyl-CpG binding domain protein 1 (MBD1), which couples DNA methylation to transcriptional repression, has been implicated in transcriptional regulation, heterochromatin formation, genomic stability, cell cycle progression and development. It has also been proven that MBD1 is involved in tumor development and progression. However, whether MBD1 is involved in tumorigenesis, especially in gallbladder cancer, is totally unknown.

Methods

Human GBC-SD and SGC996 cells were used to perform experiments. Invasion, wound healing and colony formation assays were performed to evaluate cell viability. A CCK-8 assay was performed to assess gallbladder cancer cell viability after gemcitabine treatment. Western blot analysis was used to evaluate changes in protein expression. Human gallbladder cancer tissues and adjacent nontumor tissues were subjected to immunohistochemical staining to detect protein expression.

Results

We found that MBD1 expression was significantly upregulated in gallbladder cancer tissues compared with that in surrounding normal tissues according to immunohistochemical analysis of 84 surgically resected gallbladder cancer specimens. These data also indicated that higher MBD1 expression was correlated with lymph node metastasis and poor survival in gallbladder cancer patients. Overexpression and deletion in vitro validated MBD1 as a potent oncogene promoting malignant behaviors in gallbladder cancer cells, including invasion, proliferation and migration, as well as epithelial–mesenchymal transition. Studies have demonstrated that epithelial–mesenchymal transition is common in gallbladder cancer, and it is well known that drug resistance and epithelial–mesenchymal transition are very closely correlated. Herein, our data show that targeting MBD1 restored gallbladder cancer cell sensitivity to gemcitabine chemotherapy.

Conclusions

Taken together, the results of our study revealed a novel function of MBD1 in gallbladder cancer tumor development and progression through participation in the gallbladder cancer epithelial–mesenchymal transition program, which is involved in resistance to gemcitabine chemotherapy. Thus, MBD1 may be a potential therapeutic target for gallbladder cancer.

The survival analysis and oncogenic effects of CFP1 and 14-3-3 expression on gastric cancer

Background & aim

Gastric cancer (GC) is the third-leading cause of cancer-related deaths. We established a prospective database of patients with GC who underwent surgical treatment. In this study, we explored the prognostic significance of the expression of CFP1 and 14-3-3 in gastric cancer, by studying the specimens collected from clinical subjects.

Materials & methods

Immunohistochemistry was used to detect the expression of CFP1 and 14-3-3 in 84 GC subjects, including 73 patients who have undergone radical gastrectomy and 11 patients who have not undergone radical surgery. Survival analysis was performed by km-plot data.

Results

According to the survival analysis, we can see that the survival time of patients with high expression of CFP1 is lower than the patients with low expression in gastric cancer, while the effect of 14-3-3 is just the opposite. The survival time of patients with higher expression of 14-3-3 is also longer.

Conclusion

The CFP1 and 14-3-3 genes can be used as prognostic markers in patients with GC, but the study is still needed to confirm.

Mbd2 enables tumourigenesis within the intestine while preventing tumour-promoting inflammation

Epigenetic regulation plays a key role in the link between inflammation and cancer. Here we examine Mbd2, which mediates epigenetic transcriptional silencing by binding to methylated DNA. In separate studies the Mbd2-/- mouse has been shown (1) to be resistant to intestinal tumourigenesis and (2) to have an enhanced inflammatory/immune response, observations that are inconsistent with the links between inflammation and cancer. To clarify its role in tumourigenesis and inflammation, we used constitutive and conditional models of Mbd2 deletion to explore its epithelial and non-epithelial roles in the intestine. Using a conditional model, we found that suppression of intestinal tumourigenesis is due primarily to the absence of Mbd2 within the epithelia. Next, we demonstrated, using the DSS colitis model, that non-epithelial roles of Mbd2 are key in preventing the transition from acute to tumour-promoting chronic inflammation. Combining models revealed that prior to inflammation the altered Mbd2-/- immune response plays a role in intestinal tumour suppression. However, following inflammation the intestine converts from tumour suppressive to tumour promoting. To summarise, in the intestine the normal function of Mbd2 is exploited by cancer cells to enable tumourigenesis, while in the immune system it plays a key role in preventing tumour-enabling inflammation. Which role is dominant depends on the inflammation status of the intestine. As environmental interactions within the intestine can alter DNA methylation patterns, we propose that Mbd2 plays a key role in determining whether these interactions are anti- or pro-tumourigenic and this makes it a useful new epigenetic model for inflammation-associated carcinogenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Alteration of methyl-CpG binding domain family in patients with chronic hepatitis B

BACKGROUND AND OBJECTIVE

Epigenetics contributes to the outcome of chronic hepatitis B virus (HBV) infection. However, the role of methyl-CpG binding domain (MBD) family in the natural history of chronic hepatitis B (CHB) has not been demonstrated. It is aimed to investigate the dynamic expression of MBD family and assess the potential association of MBD family in the progression of CHB.

METHODS

Quantitative real-time polymerase chain reaction (RT-PCR) was used to determine the mRNA levels of MBD family in peripheral blood mononuclear cells (PBMCs) from 223 patients with CHB as training cohort, 146 patients with CHB as validation cohort [immune-tolerant (IT), immune clearance (IC), non/low-replicative (LR) and HBeAg negative hepatitis (ENH)], and 14 healthy controls (HCs).

RESULTS

The mRNA levels of MeCP2, MBD1, MBD2 and MBD4 were upregulated in patients with CHB compared with HCs. MBD1 mRNA was highest expressed in IT phase than other phases. The optimal cut-off value for MBD1 mRNA in discriminating IT phase from CHB was 0.0305 in both training and validation cohorts. Both MBD2 and MBD4 mRNA were highest expressed in IC phase than other phases. Moreover, the optimal cut-off values for MBD2 and MBD4 mRNA in discriminating IC phase from CHB were 0.0069 and 0.00099. Furthermore, MBD2 plus MBD4 performed better than MBD2 alone for discriminating IC phase from CHB in training (area under the curve of receiver operating characteristics [AUC] 0.736 vs. 0.671, P=0.0225) and validation cohorts (AUC 0.754 vs. 0.665, P=0.004). MeCP2 mRNA was highest expressed in patients with S3+S4. MeCP2 mRNA has higher AUC than APRI score for predicting S3+S4 and S4 in fibrosis.

CONCLUSIONS

MBD family is involved in the pathogenesis of CHB and is correlated with disease progression, suggesting the value in evaluating disease severity.

Screening of Tumor Suppressor Genes in Metastatic Colorectal Cancer

Most tumor suppressor genes are commonly inactivated in the development of colorectal cancer (CRC). The activation of tumor suppressor genes may be beneficial to suppress the development and metastasis of CRC. This study analyzed genes expression and methylation levels in different stages of CRC. Genes with downregulated mRNA expression and upregulated methylation level in advanced CRC were screened as the potential tumor suppressor genes. After comparing the methylation level of screened genes, we found that MBD1 gene had downregulated mRNA expression and upregulated methylation levels in advanced CRC and continuously upregulated methylation level in the progression of CRC. Enrichment analysis revealed that genes expression in accordance with the elevated expression of MBD1 mainly located on chromosomes 17p13 and 17p12 and 8 tumor suppressor genes located on chromosome 17p13. Further enrichment analysis of transcription factor binding site identified that SP1 binding site had higher enrichment and could bind with MBD1. In conclusion, MBD1 may be a tumor suppressor gene in advanced CRC and affect the development and metastasis of CRC by regulating 8 tumor suppressor genes through binding with SP1.

LOC100287225, novel long intergenic non-coding RNA, misregulates in colorectal cancer

Colorectal cancer (CRC) is one of the most common cancers in the world; therefore, extensive research is needed to find new molecular therapeutic targets and biomarkers. LncRNA (long non-coding RNA), a new class of non-coding RNAs, has a crucial role in the onset and progression of various cancers including colorectal cancer. Research on lncRNA is still at initial stages and underlying molecular mechanisms of the vast majority of lncRNA have remained unclear. LOC100287225 is one of these novel lncRNAs (long intergenic non-coding RNA) located in the long arm of the chromosome 18. The purpose of this study was to determine the expression of LOC100287225 in colorectal tissue, and its misregulation in CRC patients. Quantitative real-time-PCR (qRT-PCR) was used to investigate the LOC100287225 expression in pairs of tumorous and adjacent tumor-free tissues of 39 colorectal cancer patients. Also, the relationship between the clinicopathology and expression of LOC100287225 was determined. QRT-PCR results revealed that not only is LOC100287225 expressed in the intestinal tissue, but has also been misregulated during tumorigenesis. Moreover, LOC100287225 RNA relative expression levels were significantly lower in tumor tissues compared with adjacent tumor-free tissues (P< 0.001). RNA expression level of LOC100287225 did not show significant correlation with clinical characteristics. In conclusion, our study demonstrated that LOC100287225 misregulation could be a potential target for gene therapy in colorectal cancer.

Methyl-CpG-Binding Protein (MBD) Family: Epigenomic Read-Outs Functions and Roles in Tumorigenesis and Psychiatric Diseases

Epigenetics is the study of the heritable changes on gene expression that are responsible for the regulation of development and that have an impact on several diseases. However, it is of equal importance to understand how epigenetic machinery works. DNA methylation is the most studied epigenetic mark and is generally associated with the regulation of gene expression through the repression of promoter activity and by affecting genome stability. Therefore, the ability of the cell to interpret correct methylation marks and/or the correct interpretation of methylation plays a role in many diseases. The major family of proteins that bind methylated DNA is the methyl-CpG binding domain proteins, or the MBDs. Here, we discuss the structure that makes these proteins a family, the main functions and interactions of all protein family members and their role in human disease such as psychiatric disorders and cancer.

Emerging Molecular and Biological Functions of MBD2, a Reader of DNA Methylation

DNA methylation is an epigenetic mark that is essential for many biological processes and is linked to diseases such as cancer. Methylation is usually associated with transcriptional silencing, but new research has challenged this model. Both transcriptional activation and repression have recently been found to be associated with DNA methylation in a context-specific manner. How DNA methylation patterns are interpreted into different functional output remains poorly understood. One mechanism involves the protein ‘readers’ of methylation, which includes the methyl-CpG binding domain (MBD) family of proteins. This review examines the molecular and biological functions of MBD2, which binds to CpG methylation and is an integral part of the nucleosome remodeling and histone deacetylation (NuRD) complex. MBD2 has been linked to immune system function and tumorigenesis, yet little is known about its functions in vivo. Recent studies have found the MBD2 protein is ubiquitously expressed, with relatively high levels in the lung, liver, and colon. Mbd2 null mice surprisingly show relatively mild phenotypes compared to mice with loss of function of other MBD proteins. This evidence has previously been interpreted as functional redundancy between the MBD proteins. Here, we examine and contextualize research that suggests MBD2 has unique properties and functions among the MBD proteins. These functions translate to recently described roles in the development and differentiation of multiple cell lineages, including pluripotent stem cells and various cell types of the immune system, as well as in tumorigenesis. We also consider possible models for the dynamic interactions between MBD2 and NuRD in different tissues in vivo. The functions of MBD2 may have direct therapeutic implications for several areas of human disease, including autoimmune conditions and cancer, in addition to providing insights into the actions of NuRD and chromatin regulation.

Methyl-CpG-binding domain proteins: readers of the epigenome

How DNA methylation is interpreted and influences genome regulation remains largely unknown. Proteins of the methyl-CpG-binding domain (MBD) family are primary candidates for the readout of DNA methylation as they recruit chromatin remodelers, histone deacetylases and methylases to methylated DNA associated with gene repression. MBD protein binding requires both functional MBD domains and methyl-CpGs; however, some MBD proteins also bind unmethylated DNA and active regulatory regions via alternative regulatory domains or interaction with the nucleosome remodeling deacetylase (NuRD/Mi-2) complex members. Mutations within MBD domains occur in many diseases, including neurological disorders and cancers, leading to loss of MBD binding specificity to methylated sites and gene deregulation. Here, we summarize the current state of knowledge about MBD proteins and their role as readers of the epigenome.

An epigenetic regulator: methyl-CpG-binding domain protein 1 (MBD1)

DNA methylation is an important form of epigenetic regulation in both normal development and cancer. Methyl-CpG-binding domain protein 1 (MBD1) is highly related to DNA methylation. Its MBD domain recognizes and binds to methylated CpGs. This binding allows it to trigger methylation of H3K9 and results in transcriptional repression. The CXXC3 domain of MBD1 makes it a unique member of the MBD family due to its affinity to unmethylated DNA. MBD1 acts as an epigenetic regulator via different mechanisms, such as the formation of the MCAF1/MBD1/SETDB1 complex or the MBD1-HDAC3 complex. As methylation status always changes along with carcinogenesis or neurogenesis, MBD1 with its interacting partners, including proteins and non-coding RNAs, participates in normal or pathological processes and functions in different regulatory systems. Because of the important role of MBD1 in epigenetic regulation, it is a good candidate as a therapeutic target for diseases.

Epigenetics and colorectal cancer pathogenesis

Colorectal cancer (CRC) develops through a multistage process that results from the progressive accumulation of genetic mutations, and frequently as a result of mutations in the Wnt signaling pathway. However, it has become evident over the past two decades that epigenetic alterations of the chromatin, particularly the chromatin components in the promoter regions of tumor suppressors and oncogenes, play key roles in CRC pathogenesis. Epigenetic regulation is organized at multiple levels, involving primarily DNA methylation and selective histone modifications in cancer cells. Assessment of the CRC epigenome has revealed that virtually all CRCs have aberrantly methylated genes and that the average CRC methylome has thousands of abnormally methylated genes. Although relatively less is known about the patterns of specific histone modifications in CRC, selective histone modifications and resultant chromatin conformation have been shown to act, in concert with DNA methylation, to regulate gene expression to mediate CRC pathogenesis. Moreover, it is now clear that not only DNA methylation but also histone modifications are reversible processes. The increased understanding of epigenetic regulation of gene expression in the context of CRC pathogenesis has led to development of epigenetic biomarkers for CRC diagnosis and epigenetic drugs for CRC therapy.

Light-regulated and cell-specific methylation of the maize PEPC promoter

The molecular mechanisms governing PEPC expression in maize remain to be fully defined. Differential methylation of a region in the PEPC promoter has been shown to correlate with transcript accumulation, however, to date, investigations into the role of DNA methylation in maize PEPC expression have relied on the use of methylation-sensitive restriction enzymes. Bisulphite sequencing was used here to provide a single-base resolution methylation map of the maize PEPC promoter. It is shown that four cytosine residues in the PEPC promoter are heavily methylated in maize root tissue. In leaves, de-methylation of these cytosines is dependent on illumination and is coincident with elevated PEPC expression. Furthermore, light-regulated de-methylation of these cytosines occurs only in mesophyll cells. No methylation was discovered in the 0.6 kb promoter required for mesophyll-specific expression indicating that cytosine methylation is not required to direct the cell-specificity of PEPC expression. This raises interesting questions regarding the function of the cell-specific cytosine de-methylation observed in the upstream region of the PEPC promoter.

Cancer biology and NuRD: a multifaceted chromatin remodelling complex

The nucleosome remodelling and histone deacetylase (NuRD; also known as Mi-2) complex regulates gene expression at the level of chromatin. The NuRD complex has been identified - using both genetic and molecular analyses - as a key determinant of differentiation in mouse embryonic stem cells and during development in various model systems. Similar to other chromatin remodellers, such as SWI/SNF and Polycomb complexes, NuRD has also been implicated in the regulation of transcriptional events that are integral to oncogenesis and cancer progression. Emerging molecular details regarding the recruitment of NuRD to specific loci during development, and the modulation of these events in cancer, are used to illustrate how the inappropriate localization of the complex could contribute to tumour biology.

Promoter CpG island hypermethylation- and H3K9me3 and H3K27me3-mediated epigenetic silencing targets the deleted in colon cancer (DCC) gene in colorectal carcinogenesis without affecting neighboring genes on chromosomal region 18q21

Chromosomal loss of 18q21 is a frequent event in colorectal cancer (CRC) development, suggesting that this region harbors tumor suppressor genes (TSGs). Several candidate TSGs, among which methyl-CpG-binding domain protein 1 (MBD1), CpG-binding protein CXXC1, Sma- and Mad-related protein 4 (SMAD4), deleted in colon cancer (DCC) and methyl-CpG-binding domain protein 2 (MBD2) are closely linked on a 4-Mb DNA region on chromosome18q21. As TSGs can be epigenetically silenced, this study investigates whether MBD1, CXXC1, SMAD4, DCC and MBD2 are subject to epigenetic silencing in CRC. Methylation-specific polymerase chain reaction and sodium bisulfite sequencing of these genes show that DCC, but not MBD1, CXXC1, SMAD4 and MBD2, has promoter CpG island methylation in CRC cell lines and tissues {normal mucosa [29.5% (18/61)], adenomas [81.0% (47/58)] and carcinomas [82.7% (62/75)] (P = 8.6 x 10(-9))} that is associated with reduced DCC expression, independent of 18q21 loss analyzed by multiplex ligation-dependent probe amplification. Reduced gene expression of CXXC1, SMAD4 and MBD2 correlates with 18q21 loss in CRC cell lines (P = 0.04, 0.02 and 0.02, respectively). Treatment with the demethylating agent 5-aza-2'-deoxycytidine, but not with the histone deacetylase inhibitor trichostatin A exclusively restored DCC expression in CRC cell lines. Chromatin immunoprecipitation studies reveal that the DCC promoter is marked with repressive histone-tail marks H3K9me3 and H3K27me3, whereas activity related H3K4me3 was absent. Only active epigenetic marks were detected for MBD1, CXXC1, SMAD4 and MBD2. This study demonstrates specific epigenetic silencing of DCC in CRC as a focal process not affecting neighboring genes on chromosomal region 18q21.

Methyl-CpG binding domain 1 gene polymorphisms and lung cancer risk in a Chinese population

Polymorphisms of the methyl-CpG binding domain 1 (MBD1) gene may influence MBD1 activity on gene expression profiles, thereby modulating individual susceptibility to lung cancer. To test this hypothesis, we investigated the associations of four MBD1 polymorphisms and lung cancer risk in a Chinese population. Single locus analysis revealed significant associations between two polymorphisms (rs125555 and rs140689) and lung cancer risk (p=0.011 and p=0.005, respectively). Since the two polymorphisms were in linkage disequilibrium, further haplotype analyses were performed and revealed a significant association with lung cancer (global test p-value=0.0041). Our results suggested that MBD1 polymorphisms might be involved in the development of lung cancer. Validation of these findings in larger studies of other populations is needed.

The loss of methyl-CpG binding protein 1 leads to autism-like behavioral deficits

Methyl-CpG binding proteins (MBDs) are central components of DNA methylation-mediated epigenetic gene regulation. Alterations of epigenetic pathways are known to be associated with several neurodevelopmental disorders, particularly autism. Our previous studies showed that the loss of Mbd1 led to reduced hippocampal neurogenesis and impaired learning in mice. However, whether MBD1 regulates the autism-related cognitive functions remains unknown. Here we show that Mbd1 mutant (Mbd1(-/-)) mice exhibit several core deficits frequently associated with autism, including reduced social interaction, learning deficits, anxiety, defective sensory motor gating, depression and abnormal brain serotonin activity. Furthermore, we find that Mbd1 can directly regulate the expression of Htr2c, one of the serotonin receptors, by binding to its promoter, and the loss of Mbd1 led to elevated expression of Htr2c. Our results, therefore, demonstrate the importance of epigenetic regulation in mammalian brain development and cognitive functions. Understanding how the loss of Mbd1 could lead to autism-like behavioral phenotypes would reveal much-needed information about the molecular pathogenesis of autism.

Chromatin-modifying proteins in cancer

Chromatin-modifying proteins mold the genome into areas that are accessible for transcriptional activity and areas that are transcriptionally silent. This epigenetic gene regulation allows for different transcriptional programs to be conducted in different cell types at different timepoints-despite the fact that all cells in the organism contain the same genetic information. A large amount of data gathered over the last decades has demonstrated that deregulation of chromatin-modifying proteins is etiologically involved in the development and progression of cancer. Here we discuss how epigenetic alterations influence cancer development and review known cancer-associated alterations in chromatin-modifying proteins.

Mechanisms of disease: methyl-binding domain proteins as potential therapeutic targets in cancer

The methyl-CpG-binding domain (MBD) proteins 'read' and interpret the methylation moieties on DNA, and thus are critical mediators of many epigenetic processes. Currently, the MBD family comprises five members; MBD1, MBD2, MBD3, MBD4 and MeCP2. Although not a 'classical' MBD protein, Kaiso also mediates transcriptional repression by using zinc finger domains to bind its targets. Since DNA hypermethylation is a well-recognized mechanism underlying gene silencing events in both tumorigenesis and drug resistance, it is likely that the MBD proteins may be important modulators of tumorigenesis. We review the recent work addressing this possibility, and discuss several of the MBD proteins as potentially excellent novel therapeutic targets.

Implication of abnormal epigenetic patterns for human diseases

Significant evidences have brought new insights on the mechanisms by which epigenetic machinery proteins regulate gene expression, leading to a redefinition of chromatin regulation in terms of modification of core histones, DNA methylation, RNA-mediated silencing pathways, action of methylation-dependent sensitive insulators and Polycomb/Trithorax group proteins. Consistent with these fundamental aspects, an increasing number of human pathologies have been found to be associated with aberrant epigenetics regulation, including cancer, mental retardation, neurodegenerative symptoms, imprinting disorders, syndromes involving chromosomal instabilities and a great number of human life-threatening diseases. The possibility of reversing epigenetic marks, in contrast to genetic code, may provide new pharmacological targets for emerging therapeutic intervention.

Epigenetics provides a new generation of oncogenes and tumour-suppressor genes

Cancer is nowadays recognised as a genetic and epigenetic disease. Much effort has been devoted in the last 30 years to the elucidation of the 'classical' oncogenes and tumour-suppressor genes involved in malignant cell transformation. However, since the acceptance that major disruption of DNA methylation, histone modification and chromatin compartments are a common hallmark of human cancer, epigenetics has come to the fore in cancer research. One piece is still missing from the story: are the epigenetic genes themselves driving forces on the road to tumorigenesis? We are in the early stages of finding the answer, and the data are beginning to appear: knockout mice defective in DNA methyltransferases, methyl-CpG-binding proteins and histone methyltransferases strongly affect the risk of cancer onset; somatic mutations, homozygous deletions and methylation-associated silencing of histone acetyltransferases, histone methyltransferases and chromatin remodelling factors are being found in human tumours; and the first cancer-prone families arising from germline mutations in epigenetic genes, such as hSNF5/INI1, have been described. Even more importantly, all these 'new' oncogenes and tumour-suppressor genes provide novel molecular targets for designed therapies, and the first DNA-demethylating agents and inhibitors of histone deacetylases are reaching the bedside of patients with haematological malignancies.

Methyl-CpG-binding proteins in cancer: blaming the DNA methylation messenger

In recent years, epigenetic alterations have come to prominence in cancer research. In particular, hypermethylation of CpG islands located in the promoter regions of tumor-suppressor genes is now firmly established as an important mechanism for gene inactivation in cancer. One of the most remarkable achievements in the field has been the identification of the methyl-CpG-binding domain family of proteins, which provide mechanistic links between specific patterns of DNA methylation and histone modifications. Although many of the current data indicate that methyl-CpG-binding proteins play a key role in maintaining a transcriptionally inactive state of methylated genes, MBD4 is also known to be involved in excision repair of T:G mismatches. The latter is a member of this family of proteins and appears to play a role in reducing mutations at 5-methylcytosine. This review examines the contribution of methyl-CpG-binding proteins in the epigenetic pathway of cancer.Key words: methyl-CpG-binding, MeCP2, DNA methylation, Rett syndrome, cancer epigenetics.

Epigenetics and cancer

Epigenetic mechanisms act to change the accessibility of chromatin to transcriptional regulation locally and globally via modifications of the DNA and by modification or rearrangement of nucleosomes. Epigenetic gene regulation collaborates with genetic alterations in cancer development. This is evident from every aspect of tumor biology including cell growth and differentiation, cell cycle control, DNA repair, angiogenesis, migration, and evasion of host immunosurveillance. In contrast to genetic cancer causes, the possibility of reversing epigenetic codes may provide new targets for therapeutic intervention.

Pol ι Is a Candidate for the Mouse Pulmonary Adenoma Resistance 2 Locus, a Major Modifier of Chemically Induced Lung Neoplasia

In this study, we performed systematic candidate gene analyses of the Pulmonary adenoma resistance 2 locus. Differential gene expression in lung tissues and nucleotide polymorphisms in coding regions between A/J and BALB/cJ mice were examined using reverse transcription-PCR and direct sequencing. Although not all genes in the interval were analyzed at this moment due to the recent database updating, we have found that the Pol iota gene, encoding the DNA polymerase iota, contains 25 nucleotide polymorphisms in its coding region between A/J and BALB/cJ mice, resulting in a total of ten amino acid changes. Primer extension assays with purified BALB/cJ and A/J proteins in vitro demonstrate that both forms of Pol iota are active but that they may differ in substrate discrimination, which may affect the formation of Kras2 mutations in mouse lung tumors. Altered expression of POL iota protein and an amino acid-changing nucleotide polymorphism were observed in human lung cancer cells, suggesting a possible role in the development of lung cancer. Thus, our data support the Pol iota gene as a modifier of lung tumorigenesis by altering DNA polymerase activity.