Promoter methylation in circadian genes of endometrial cancers detected by methylation-specific PCR

"Time" for obesity-related cancer: The role of the circadian rhythm in cancer pathogenesis and treatment

The circadian rhythm is regulated by an intrinsic time-tracking system, composed both of a central and a peripheral clock, which influences the cycles of activities and sleep of an individual over 24 h. At the molecular level, the circadian rhythm begins when two basic helix-loop-helix/Per-ARNT-SIM (bHLH-PAS) proteins, BMAL-1 and CLOCK, interact with each other to produce BMAL-1/CLOCK heterodimers in the cytoplasm. The BMAL-1/CLOCK target genes encode for the repressor components of the clock, cryptochrome (Cry1 and Cry2) and the Period proteins (Per1, Per2 and Per3). It has been recently demonstrated that the disruption of circadian rhythm is associated with an increased risk of developing obesity and obesity-related diseases. In addition, it has been demonstrated that the disruption of the circadian rhythm plays a key role in tumorigenesis. Further, an association between the circadian rhythm disruptions and an increased incidence and progression of several types of cancer (e.g., breast, prostate, colorectal and thyroid cancer) has been found. As the perturbation of circadian rhythm has adverse metabolic consequences (e.g., obesity) and at the same time tumor promoter functions, this manuscript has the aim to report how the aberrant circadian rhythms affect the development and prognosis of different types of obesity-related cancers (breast, prostate, colon rectal and thyroid cancer) focusing on both human studies and on molecular aspects.

Understanding the significance of biological clock and its impact on cancer incidence

The circadian clock is an essential timekeeper that controls, for humans, the daily rhythm of biochemical, physiological, and behavioral functions. Irregular performance or disruption in circadian rhythms results in various diseases, including cancer. As a factor in cancer development, perturbations in circadian rhythms can affect circadian homeostasis in energy balance, lead to alterations in the cell cycle, and cause dysregulation of chromatin remodeling. However, knowledge gaps remain in our understanding of the relationship between the circadian clock and cancer. Therefore, a mechanistic understanding by which circadian disruption enhances cancer risk is needed. This review article outlines the importance of the circadian clock in tumorigenesis and summarizes underlying mechanisms in the clock and its carcinogenic mechanisms, highlighting advances in chronotherapy for cancer treatment.

Melatonin Inhibits 17β-Estradiol-Induced Epithelial-Mesenchymal Transition in Endometrial Adenocarcinoma Cells via Upregulating Numb Expression

OBJECTIVES

Melatonin (MLT) shows antitumor effects in various tumor types, including endometrial carcinoma. However, the molecular mechanism involved is unclear. In the current study, we investigated the effect of MLT on the estrogen-induced epithelial-mesenchymal transition (EMT) in endometrial adenocarcinoma cells and explored the pathway that might be involved.

DESIGN

Laboratory study was via cultured endometrial cancer cells. Design refers only to in vitro experiments.

METHODS

In cell culture experiments, cell growth was examined using CCK-8 assays. The expression of Numb and EMT markers in Ishikawa cells was examined using Western blot analysis and real-time PCR. Cell invasion was examined using transwell assays. Cell migration was examined using wound-healing assays and transwell assays. Using immunohistochemistry analysis, the expression of Numb in human endometrial cancers was examined.

RESULTS

In immunohistochemistry experiments, we found that 15.2% of atypical endometrial hyperplasia and 15.6% of endometrial carcinoma did not express Numb. In cell culture experiments, MLT inhibited cell proliferation, invasion, and migration induced by 17β-estradiol (E2) in endometrial cancer cells. MLT decreased the expression of vimentin and Slug and increased the expression of Numb and E-cadherin in Ishikawa cells. Numb knockdown in cancer cells significantly increased cell proliferation, invasion, and migration.

LIMITATIONS

No animal experiments were performed.

CONCLUSIONS

MLT blocked E2-induced cell growth and EMT in endometrial cancer cells via upregulating Numb expression.

Development and performance evaluation of TaqMan real-time fluorescence quantitative methylation specific PCR for detecting methylation level of PER2

BACKGROUND

PER2 gene methylation is closely related to the occurrence and progress of some cancers, but there is no method to quantitatively detect PER2 methylation in conventional laboratories. So, we established a TaqMan real-time fluorescence quantitative methylation specific PCR (TaqMan real-time FQ-MSP) assay and use it for quantitative detection of PER2 methylation in leukemia patients.

METHODS

According to the PER2 sequence searched by GenBank, a CpG sequence enrichment region of the PER2 gene promoter was selected, and the methylated and unmethylated target sequences were designed according to the law of bisulfite conversion of DNA to construct PER2 methylation positive and negative reference materials. Specific primers and probe were designed. The reference materials were continuously diluted into gradient samples by tenfold ratio to evaluate the analytical sensitivity, specificity, accuracy and reproducibility of the method, and the analytical sensitivity of TaqMan real-time FQ-MSP assay was compared with that of the conventional MSP assay. At the same time, the new-established TaqMan real-time FQ-MSP assay and the conventional MSP assay were used to detect the PER2 methylation level of 81 patients with leukemia, and the samples with inconsistent detection results of the two assays were sent to pyromethylation sequencing to evaluate the clinical detection performance.

RESULTS

The minimum detection limit of TaqMan real-time FQ-MSP assay for detecting PER2 methylation level established in this study was 6 copies/uL, and the coefficient of variation(CV) of intra-assay and inter-assay was less than 3%. Compared with the conventional MSP assay, it has higher analytical sensitivity. For the samples with inconsistent detection results, the results of pyrosequencing and TaqMan real-time FQ-MSP assay are consistent.

CONCLUSION

TaqMan real-time FQ-MSP assay of PER2 methylation established in this study has high detection performance and can be used for the detection of clinical samples.

The Expression and Function of Circadian Rhythm Genes in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is among the most common and lethal form of cancer worldwide. However, its diagnosis and treatment are still dissatisfactory, due to limitations in the understanding of its pathogenic mechanism. Therefore, it is important to elucidate the molecular mechanisms and identify novel therapeutic targets for HCC. Circadian rhythm-related genes control a variety of biological processes. These genes play pivotal roles in the initiation and progression of HCC and are potential diagnostic markers and therapeutic targets. This review gives an update on the research progress of circadian rhythms, their effects on the initiation, progression, and prognosis of HCC, in a bid to provide new insights for the research and treatment of HCC.

Circadian Rhythm Is Disrupted by ZNF704 in Breast Carcinogenesis

Copy number gain in chromosome 8q21 is frequently detected in breast cancer, yet the oncogenic potential underlying this amplicon in breast carcinogenesis remains to be delineated. We report here that ZNF704, a gene mapped to 8q21, is recurrently amplified in various malignancies including breast cancer. ZNF704 acted as a transcriptional repressor and interacted with the transcriptional corepressor SIN3A complex. Genome-wide interrogation of transcriptional targets revealed that the ZNF704/SIN3A complex represses a panel of genes including PER2 that are critically involved in the function of the circadian clock. Overexpression of ZNF704 prolonged the period and dampened the amplitude of the circadian clock. ZNF704 promoted the proliferation and invasion of breast cancer cells in vitro and accelerated the growth and metastasis of breast cancer in vivo. Consistently, the level of ZNF704 expression inversely correlated with that of PER2 in breast carcinomas, and high level of ZNF704 correlated with advanced histologic grades, lymph node positivity, and poor prognosis of patients with breast cancer, especially those with HER2⁺ and basal-like subtypes. These results indicate that ZNF704 is an important regulator of the circadian clock and a potential driver for breast carcinogenesis. SIGNIFICANCE: This study indicates that ZNF704 could be a potential oncogenic factor, disrupting circadian rhythm of breast cancer cells and contributing to breast carcinogenesis.

The molecular clock in the skin, its functionality, and how it is disrupted in cutaneous melanoma: a new pharmacological target?

The skin is the interface between the organism and the external environment, acting as its first barrier. Thus, this organ is constantly challenged by physical stimuli such as UV and infrared radiation, visible light, and temperature as well as chemicals and pathogens. To counteract the deleterious effects of the above-mentioned stimuli, the skin has complex defense mechanisms such as: immune and neuroendocrine systems; shedding of epidermal squamous layers and apoptosis of damaged cells; DNA repair; and pigmentary system. Here we have reviewed the current knowledge regarding which stimuli affect the molecular clock of the skin, the consequences to skin-related biological processes and, based on such knowledge, we suggest some therapeutic targets. We also explored the recent advances regarding the molecular clock disruption in melanoma, its impact on the carcinogenic process, and its therapeutic value in melanoma treatment.

Persistent Changes in Stress-Regulatory Genes in Pregnant Women or Children Exposed Prenatally to Alcohol

BACKGROUND

We have recently shown that binge or heavy levels of alcohol drinking increase deoxyribonucleic acid (DNA) methylation and reduce gene expression of proopiomelanocortin (POMC) and period 2 (PER2) in adult human subjects (Gangisetty et al., Alcohol Clin Exp Res, 43, 2019, 212). One hypothesis would be that methylation of these 2 genes is consistently associated with alcohol exposure and could be used as biomarkers to predict risk of prenatal alcohol exposure (PAE). Results of the present study provided some support for this hypothesis.

METHODS

We conducted a series of studies to determine DNA methylation changes in stress regulatory genes proopiomelanocortin (POMC) and period 2 (PER2) using biological samples from 3 separate cohorts of patients: (i) pregnant women who consumed moderate-to-high levels of alcohol or low/unexposed controls, (ii) children with PAE and non-alcohol-exposed controls, and (iii) children with PAE treated with or without choline.

RESULTS

We found pregnant women who consumed moderate-to-high levels of alcohol and gave birth to PAE children had higher DNA methylation of POMC and PER2. PAE children also had increased methylation of POMC and PER2. The differences in the gene methylation of PER2 and POMC between PAE and controls did not differ by maternal smoking status. PAE children had increased levels of stress hormone cortisol and adrenocorticotropic hormone. Choline supplementation reduced DNA hypermethylation and increased expression of POMC and PER2 in children with PAE.

CONCLUSIONS

These data suggest that PAE significantly elevates DNA methylation of POMC and PER2 and increases levels of stress hormones. Furthermore, these results suggest the possibility that measuring DNA methylation levels of PER2 and POMC in biological samples from pregnant women or from children may be useful for identification of a woman or a child with PAE.

A different methylation profile of circadian genes promoter in breast cancer patients according to clinicopathological features

One of the supposed mechanisms that may lead to breast cancer (BC) is an alteration of circadian gene expression and DNA methylation. We undertook an integrated approach to identify methylation pattern of core circadian promoter regions in BC patients with regard to clinical features. We performed a quantitative methylation-specific real-time PCR analysis of a promoter methylation profile in 107 breast tumor and matched non-tumor tissues. A panel of circadian genes CLOCK, BMAL1, PERIOD (PER1, 2, 3), CRYPTOCHROME (CRY1, 2) and TIMELESS as well as their association with clinicopathological characteristics were included in the analysis. Three out of the eight analyzed genes exhibited marked hypermethylation (PER1, 2, 3), whereas CLOCK, BMAL1, CRY2 showed significantly lower promoter CpG methylation in the BC tissues when compared to the non-tumor tissues. Among variously methylated genes we found an association between the elevated methylation level of PERs promoter region and molecular subtypes, histological subtypes and tumor grading of BC. Methylation status may be associated with a gene expression level of circadian genes in BC patients. An aberrant methylation pattern in circadian genes in BC may provide information that could be used as novel biomarkers in clinics and molecular epidemiology as well as play an important role in BC etiology.

Maternal stress and early-onset colorectal cancer

Early-onset colorectal cancer (EOCRC) is defined as colorectal cancer (CRC) diagnosed before the age of 50. Alarmingly, there has been a significant increase in EOCRC diagnoses' worldwide over the past several decades. Emerging data suggest EOCRCs have distinguishing clinical, pathological, biological and molecular features; and thus, are a fundamentally different subtype of CRCs. Unfortunately, there is no simple explanation for the causes of EOCRC. Scientifically rigorous studies are needed to determine what may be driving the challenging epidemiology of EOCRC. We contend here that a reasonable hypothesis is that prenatal risk factors such as maternal stress and associated sleeping disorders influence offspring epigenetic make-up, and shape immune system and gut health contributing to an increased risk for EOCRC.

Clinicopathologic Features and Treatment Outcomes in Patients with Stage I, High-Risk Histology or High-Grade Endometrial Cancer after Primary Staging Surgery: A Taiwanese Gynecologic Oncology Group Study

To investigate the clinicopathological features and treatment outcomes in patients with stage I, high-risk endometrial cancer. Patients with International Federation of Gynecology and Obstetrics stage I, papillary serous, clear cell, or grade 3 endometrioid carcinoma treated between 2000 and 2012 were analyzed for the clinical and pathological factors in relation to prognosis. A total of 267 patients (stage IA; n = 175, stage IB; n = 92) were included. Among the clinicopathological features, stage and age were significant prognostic factors. The recurrence rate and overall survival for stage IB versus IA were 22.8% versus 9.1% (p = 0.003) and 149.7 months versus 201.8 months (p < 0.001), respectively. The patients >60 years of age also had a higher recurrence rate (21.7% versus 9.7%, p = 0.008) and poorer survival (102.0 months versus 196.8 months, p = 0.001) than those ≤60 years of age. Distant recurrence (64.9%) occurred more frequently than local recurrence (24.3%) and local combined with distant recurrence (10.8%) (p < 0.001). The postoperative treatment modality had no impact on tumor recurrence rate, recurrence site, or overall survival. Distant recurrence is a major cause of treatment failure in patients with stage I, high-risk endometrial cancer. However, current adjuvant treatment appeared to have little effect in preventing its occurrence.

Identification of a microRNA signature associated with survivability in cervical squamous cell carcinoma

Background

The aim of this study is to find the potential miRNA expression signature capable of predicting survival time for cervical squamous cell carcinoma (CSCC) patients.

Methods

The expression of 332 miRNAs was measured in 131 (Training cohort) and 130 (Validation cohort) patients with CSCC in the Cancer Genome Atlas (TCGA) data portal. The miRNA expression signature was identified by Cox Proportion Hazard regression model to the Training data set, and subsequently validated in an independent Validation set. Kaplan-Meier curves and the receiver operating characteristic analyses of 5 years were used to access the overall survival of miRNA signature. MiRNA signature-gene target analysis was performed, followed by the construction of the regulatory network. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analysis were used to explore the function of target genes of miRNA signature.

Results

A 2-miRNA expression signature of hsa-mir-642a and hsa-mir-378c associated with survivability was identified in CSCC. Both of them had a significant diagnostic and prognostic value of patients with CSCC. A total of 345 miRNA signature-target pairs were obtained in the miRNA signature-gene target regulatory network, in which 316 genes were targets of has-mir-378c and has-mir-642a. Functional analysis of target genes showed that MAPK signaling pathway, VEGF signaling pathway and endocytosis were the significantly enriched signal pathways that covered most genes.

Conclusions

The 2-miRNA signature adds to the prognostic value of CSCC. In-depth interrogation of the 2-miRNAs will provide important biological insights that finding and developing novel molecularly prediction to improve prognosis for CSCC patients.

Epigenetic Basis of Circadian Rhythm Disruption in Cancer

Self-sustained and synchronized to environmental stimuli, circadian clocks are under genetic and epigenetic regulation. Recent findings have greatly increased our understanding of epigenetic plasticity governed by circadian clock. Thus, the link between circadian clock and epigenetic machinery is reciprocal. Circadian clock can affect epigenetic features including genomic DNA methylation, noncoding RNA, mainly miRNA expression, and histone modifications resulted in their 24-h rhythms. Concomitantly, these epigenetic events can directly modulate cyclic system of transcription and translation of core circadian genes and indirectly clock output genes. Significant findings interlocking circadian clock, epigenetics, and cancer have been revealed, particularly in breast, colorectal, and blood cancers. Aberrant methylation of circadian gene promoter regions and miRNA expression affected circadian gene expression, together with 24-h expression oscillation pace have been frequently observed.

Altered Circadian Rhythms and Breast Cancer: From the Human to the Molecular Level

Circadian clocks are fundamental, time-tracking systems that allow organisms to adapt to the appropriate time of day and drive many physiological and cellular processes. Altered circadian rhythms can result from night-shift work, chronic jet lag, exposure to bright lights at night, or other conditioning, and have been shown to lead to increased likelihood of cancer, metabolic and cardiovascular diseases, and immune dysregulation. In cases of cancer, worse patient prognoses and drug resistance during treatment have also been observed. Breast, colon, prostate, lung, and ovarian cancers and hepatocellular carcinoma have all been linked in one way or another with altered circadian rhythms. Critical elements at the molecular level of the circadian system have been associated with cancer, but there have been fairly few studies in this regard. In this mini-review, we specifically focus on the role of altered circadian rhythms in breast cancer, providing an overview of studies performed at the epidemiological level through assessments made in animal and cellular models of the disease. We also address the disparities present among studies that take into account the rhythmicity of core clock and other proteins, and those which do not, and offer insights to the use of small molecules for studying the connections between circadian rhythms and cancer. This article will provide the reader with a concise, but thorough account of the research landscape as it pertains to altered circadian rhythms and breast cancer.

The diagnostic role of DNA methylation in sporadic endometrial cancer: a systematic review and meta-analysis

Background

Although increasing numbers of methylated genes have been identified as biomarkers for endometrial cancer, the results have been inconsistent. We therefore carried out a systematic review and meta-analysis to evaluate the diagnostic accuracy of methylated genes as markers for sporadic endometrial cancer.

Results

A total of 22 studies including 1930 participants (sporadic endometrial cancer patients and normal individuals) met our eligibility criteria. The pooled sensitivity and specificity were 0.93 (95% confidence interval: 0.91−0.94) and 0.48 (95% confidence interval: 0.46–0.50), respectively. The area under the summary receiver operating characteristic curve was 0.8834. The presence of DNA methylation was significantly associated with lymph node metastasis of endometrial cancer (pooled odds ratio: 0.28, 95% confidence interval: 0.15–0.52, p < 0.001).

Materials and Methods

We searched the relevant literature systematically using the PubMed and Web of Science databases up to April 2017. Diagnostic accuracy variables were pooled and analyzed using Meta-DiSc software. Sensitivity analysis and publication bias were evaluated using Review Manager.

Conclusions

This meta-analysis suggests that the detection of DNA methylation is associated with lymph node metastasis, with high sensitivity but relatively low specificity for the diagnosis of sporadic endometrial cancer.

Circadian gene methylation in rotating-shift nurses: a cross-sectional study

Investigating the methylation status of the circadian genes may contribute to a better understanding of the shift work-related circadian disruption in individuals exposed to artificial light at night. In the present study, we determined the methylation status of the circadian genes associated with a shift work pattern among nurses and midwives participating in a cross-sectional study in Lodz, Poland. Quantitative methylation polymerase chain reaction assays were used to assess promoter CpG methylation in PER1, PER2, PER3, CRY1, CRY2, BMAL1, CLOCK, and NPAS2 in genomic DNA from whole blood of 347 women having a rotating-shift work schedule and 363 women working days only. The percentage of methylated reference (PMR) was assessed using fluorescent probes for PER1, PER2, PER3, CRY1, and NPAS2, and the percentage of gene methylation, as the methylation index (MI), using two sets of primers for BMAL1, CLOCK, and CRY2. We tested the possible association between current and lifetime rotating night-shift work characteristics and circadian gene methylation by using proportional odds regression model with blood DNA methylation, categorized into tertiles, and adjusted for age, current smoking status, folate intake and blood collection time. The findings indicated that CpG methylation in PER2 promoter was significantly decreased (P < 0.004) among nurses and midwives currently working rotating shifts, as compared with day-working nurses and midwives. The lower percentage of PER2 methylation was associated with a higher monthly frequency of current night duties (2-7 night shifts, and eight or more night shifts per month) (P = 0.012) and was associated at borderline significance (P = 0.092) with the lifetime duration of shift work (>10 ≤ 20 years and >20 ≤ 43 years of rotating-shift work) among nurses and midwives (N = 710). Moreover, women with a longer lifetime duration of shift work presented a lower status of PER1 methylation (P = 0.040) than did the women with up to 10 years of rotating-shift work. Long lifetime duration of shift work (> 10 years) among current rotating night-shift workers (N =  347) was associated with BMAL1 hypomethylation (P = 0.013). Among eight of the investigated circadian genes, only PER1, PER2, and BMAL1 showed differential methylation attributable to the rotating-shift work of nurses and midwives. The findings on blood-based DNA methylation in the circadian genes may provide a better insight into the mechanistic principles underlying the possible health effects of night-shift work but these should be verified in further studies recruiting larger populations of shift workers.

Sleep quality and methylation status of core circadian rhythm genes among nurses and midwives

ABSTARCT Poor sleep quality or sleep restriction is associated with sleepiness and concentration problems. Moreover, chronic sleep restriction may affect metabolism, hormone secretion patterns and inflammatory responses. Limited recent reports suggest a potential link between sleep deprivation and epigenetic effects such as changes in DNA methylation profiles. The aim of the present study was to assess the potential association between poor sleep quality or sleep duration and the levels of 5-methylcytosine in the promoter regions of PER1, PER2, PER3, BMAL1, CLOCK, CRY1 CRY2 and NPAS2 genes, taking into account rotating night work and chronotype as potential confounders or modifiers. A cross-sectional study was conducted on 710 nurses and midwives (347 working on rotating nights and 363 working only during the day) aged 40-60 years. Data from in-person interviews about sleep quality, chronotype and potential confounders were used. Sleep quality and chronotype were assessed using Pittsburgh Sleep Quality Questionnaire (PSQI) and Morningness-Eveningness Questionnaire (MEQ), respectively. Morning blood samples were collected. The methylation status of the circadian rhythm genes was determined via quantitative methylation-specific real-time PCR assays (qMSP) reactions using DNA samples derived from leucocytes. The proportional odds regression model was fitted to quantify the relationship between methylation index (MI) as the dependent variable and sleep quality or sleep duration as the explanatory variable. Analyses were carried out for the total population as well as for subgroups of women stratified by the current system of work (rotating night shift/day work) and chronotype (morning type/intermediate type/evening type). A potential modifying effect of the system of work or the chronotype was examined using the likelihood ratio test. No significant findings were observed in the total study population. Subgroup analyses revealed two statistically significant associations between a shorter sleep duration and 1) methylation level in PER2 among day workers, especially those with the morning chronotype (OR = 2.31, 95%CI:1.24-4.33), and 2) methylation level in CRY2 among subjects with the intermediate chronotype, particularly among day workers (OR = 0.52, 95%CI:0.28-0.96). The study results demonstrated a positive association between average sleep duration of less than 6 hours and the methylation level of PER2 among morning chronotype subjects, and an inverse association for CRY2 among intermediate chronotype subjects, but only among day workers. Both the system of work and the chronotype turned out to be important confounders and modifiers in a number of analyses, making it necessary to consider them as potential covariates in future research on sleep deficiency outcomes. Further studies are warranted to explore this under-investigated topic.

Artificial light-at-night - a novel lifestyle risk factor for metabolic disorder and cancer morbidity

Both obesity and breast cancer are already recognized worldwide as the most common syndromes in our modern society. Currently, there is accumulating evidence from epidemiological and experimental studies suggesting that these syndromes are closely associated with circadian disruption. It has been suggested that melatonin (MLT) and the circadian clock genes both play an important role in the development of these syndromes. However, we still poorly understand the molecular mechanism underlying the association between circadian disruption and the modern health syndromes. One promising candidate is epigenetic modifications of various genes, including clock genes, circadian-related genes, oncogenes, and metabolic genes. DNA methylation is the most prominent epigenetic signaling tool for gene expression regulation induced by environmental exposures, such as artificial light-at-night (ALAN). In this review, we first provide an overview on the molecular feedback loops that generate the circadian regulation and how circadian disruption by ALAN can impose adverse impacts on public health, particularly metabolic disorders and breast cancer development. We then focus on the relation between ALAN-induced circadian disruption and both global DNA methylation and specific loci methylation in relation to obesity and breast cancer morbidities. DNA hypo-methylation and DNA hyper-methylation, are suggested as the most studied epigenetic tools for the activation and silencing of genes that regulate metabolic and monostatic responses. Finally, we discuss the potential clinical and therapeutic roles of MLT suppression and DNA methylation patterns as novel biomarkers for the early detection of metabolic disorders and breast cancer development.

Epigenetics in endometrial carcinogenesis - part 1: DNA methylation

Carcinogenesis is a multistep multifactorial process that involves the accumulation of genetic and epigenetic alterations. In the past two decades, there has been an exponential growth of knowledge establishing the importance of epigenetic changes in cancer. Our work focused on reviewing the main role of epigenetics in the pathogenesis of endometrial carcinoma, highlighting the reported results concerning each epigenetic mechanistic layer. The present review is the first part of this work, in which we examined the contribution of DNA methylation alterations for endometrial carcinogenesis.

Case-control study of candidate gene methylation and adenomatous polyp formation

PURPOSE

Colorectal cancer (CRC) is one of the most common and preventable forms of cancer but remains the second leading cause of cancer-related death. Colorectal adenomas are precursor lesions that develop in 70-90 % of CRC cases. Identification of peripheral biomarkers for adenomas would help to enhance screening efforts. This exploratory study examined the methylation status of 20 candidate markers in peripheral blood leukocytes and their association with adenoma formation.

METHODS

Patients recruited from a local endoscopy clinic provided informed consent and completed an interview to ascertain demographic, lifestyle, and adenoma risk factors. Cases were individuals with a histopathologically confirmed adenoma, and controls included patients with a normal colonoscopy or those with histopathological findings not requiring heightened surveillance (normal biopsy, hyperplastic polyp). Methylation-specific polymerase chain reaction was used to characterize candidate gene promoter methylation. Odds ratios (ORs) and 95 % confidence intervals (95% CIs) were calculated using unconditional multivariable logistic regression to test the hypothesis that candidate gene methylation differed between cases and controls, after adjustment for confounders.

RESULTS

Complete data were available for 107 participants; 36 % had adenomas (men 40 %, women 31 %). Hypomethylation of the MINT1 locus (OR 5.3, 95% CI 1.0-28.2) and the PER1 (OR 2.9, 95% CI 1.1-7.7) and PER3 (OR 11.6, 95% CI 1.6-78.5) clock gene promoters was more common among adenoma cases. While specificity was moderate to high for the three markers (71-97 %), sensitivity was relatively low (18-45 %).

CONCLUSION

Follow-up of these epigenetic markers is suggested to further evaluate their utility for adenoma screening or surveillance.

The Pathophysiologic Role of Disrupted Circadian and Neuroendocrine Rhythms in Breast Carcinogenesis

Most physiological processes in the brain and body exhibit daily (circadian) rhythms coordinated by an endogenous master clock located in the suprachiasmatic nucleus of the hypothalamus that are essential for normal health and functioning. Exposure to sunlight during the day and darkness at night optimally entrains biological rhythms to promote homeostasis and human health. Unfortunately, a major consequence of the modern lifestyle is increased exposure to sun-free environments during the day and artificial lighting at night. Additionally, behavioral disruptions to circadian rhythms (ie, repeated transmeridian flights, night or rotating shift work, or sleep disturbances) have a profound influence on health and have been linked to a number of pathological conditions, including endocrine-dependent cancers. Specifically, night shift work has been identified as a significant risk factor for breast cancer in industrialized countries. Several mechanisms have been proposed by which shift work-induced circadian disruptions promote cancer. In this review, we examine the importance of the brain-body link through which circadian disruptions contribute to endocrine-dependent diseases, including breast carcinogenesis, by negatively impacting neuroendocrine and neuroimmune cells, and we consider preventive measures directed at maximizing circadian health.

Retinoic acid-related orphan receptor RORβ, circadian rhythm abnormalities and tumorigenesis (Review)

Nuclear receptors are a superfamily of transcription factors including the steroid hormone receptors, non-steroid hormone receptors and the orphan nuclear receptor family. Retinoic acid-related orphan receptor (ROR)β, as a member of the orphan nuclear receptor family, plays an important regulatory role in the maintenance of a variety of physiological and pathological processes. RORβ has been determined to act as an osteogenic repressor in regulating bone formation, and is involved in regulating circadian rhythm. The findings of recent studies concerning the association between tumorigenesis and circadian rhythm have shown that an aberrant circadian rhythm may promote tumorigenesis and tumor progression. The mechanisms discussed in this review demonstrate how aberrant RORβ-induced circadian rhythm may become a new direction for future studies on tumorigenesis and strategy design for cancer prevention.

Circadian systems biology in Metazoa

Systems biology, which can be defined as integrative biology, comprises multistage processes that can be used to understand components of complex biological systems of living organisms and provides hierarchical information to decoding life. Using systems biology approaches such as genomics, transcriptomics and proteomics, it is now possible to delineate more complicated interactions between circadian control systems and diseases. The circadian rhythm is a multiscale phenomenon existing within the body that influences numerous physiological activities such as changes in gene expression, protein turnover, metabolism and human behavior. In this review, we describe the relationships between the circadian control system and its related genes or proteins, and circadian rhythm disorders in systems biology studies. To maintain and modulate circadian oscillation, cells possess elaborative feedback loops composed of circadian core proteins that regulate the expression of other genes through their transcriptional activities. The disruption of these rhythms has been reported to be associated with diseases such as arrhythmia, obesity, insulin resistance, carcinogenesis and disruptions in natural oscillations in the control of cell growth. This review demonstrates that lifestyle is considered as a fundamental factor that modifies circadian rhythm, and the development of dysfunctions and diseases could be regulated by an underlying expression network with multiple circadian-associated signals.

Epigenetic silencing of ARNTL, a circadian gene and potential tumor suppressor in ovarian cancer

Ovarian cancer is the fifth leading cause of cancer death and the most deadly gynecological malignancy in women. Epigenetic modifications play an important role in regulating gene transcription. Specifically, aberrant promoter hypermethylation has been implicated as a hallmark of cancer. In order to identify genes that are differentially methylated in ovarian cancer, we performed meDIP-chip in various ovarian cancer cell lines using Agilent 244K CpG island microarray. One of the targets, ARNTL which is a core component of the circadian clock is methylated in a sub-set of ovarian cancer cell lines. Combined bisulfite restriction analysis (COBRA) confirmed the results of the microarray. Additional analysis using ChIP-PCR revealed that promoter of ARNTL is enriched with the repressive histone mark H3K27me3 in CP70 and MCP2 ovarian cancer cells. Treatment with the EZH2 inhibitor (GSK126) significantly restored ARNTL expression in these cells (CP70 and MCP2). Further functional analysis demonstrated that overexpression of ARNTL inhibited cell growth and enhanced chemosensitivity of cisplatin in ovarian cancer cells. Finally, overexpression of ARNTL restored the rhythmic activity of c-MYC in ovarian cancer cells. These results suggested that ARNTL may be a tumor suppressor and is epigenetically silenced in ovarian cancer.

Regulated DNA methylation and the circadian clock: implications in cancer

Since the cloning and discovery of DNA methyltransferases (DNMT), there has been a growing interest in DNA methylation, its role as an epigenetic modification, how it is established and removed, along with the implications in development and disease. In recent years, it has become evident that dynamic DNA methylation accompanies the circadian clock and is found at clock genes in Neurospora, mice and cancer cells. The relationship among the circadian clock, cancer and DNA methylation at clock genes suggests a correlative indication that improper DNA methylation may influence clock gene expression, contributing to the etiology of cancer. The molecular mechanism underlying DNA methylation at clock loci is best studied in the filamentous fungi, Neurospora crassa, and recent data indicate a mechanism analogous to the RNA-dependent DNA methylation (RdDM) or RNAi-mediated facultative heterochromatin. Although it is still unclear, DNA methylation at clock genes may function as a terminal modification that serves to prevent the regulated removal of histone modifications. In this capacity, aberrant DNA methylation may serve as a readout of misregulated clock genes and not as the causative agent. This review explores the implications of DNA methylation at clock loci and describes what is currently known regarding the molecular mechanism underlying DNA methylation at circadian clock genes.

Circadian clocks and tumor biology: what is to learn from human skin biopsies?

Some of the components of the circadian molecular clock have been shown to link directly to tumor suppression. Most studies on human tumorous biopsies with consistently down-regulated clock gene expression suggested a protective role for these genes against cancer formation. To highlight some limitations of this hypothesis we review these data in light of recent evidences from animal research, epidemiologic studies, and clinical data on skin tumors. We emphasize the role of circadian rhythmic orchestration in cellular metabolism with a potential in cancer development.

The circadian clock in cancer development and therapy

Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The central and peripheral clocks coordinately generate rhythmic gene expression in a tissue-specific manner in vivo to couple diverse physiological and behavioral processes to periodic changes in the environment. However, with the industrialization of the world, activities that disrupt endogenous homeostasis with external circadian cues have increased. This change in lifestyle has been linked to an increased risk of diseases in all aspects of human health, including cancer. Studies in humans and animal models have revealed that cancer development in vivo is closely associated with the loss of circadian homeostasis in energy balance, immune function, and aging, which are supported by cellular functions important for tumor suppression including cell proliferation, senescence, metabolism, and DNA damage response. The clock controls these cellular functions both locally in cells of peripheral tissues and at the organismal level via extracellular signaling. Thus, the hierarchical mammalian circadian clock provides a unique system to study carcinogenesis as a deregulated physiological process in vivo. The asynchrony between host and malignant tissues in cell proliferation and metabolism also provides new and exciting options for novel anticancer therapies.

Altered expression patterns of clock gene mRNAs and clock proteins in human skin tumors

The majority of our genes may be regulated in a daily rhythm, including the genes for cell cycle control. Epidemiological and genetic evidences suggest that disruption of circadian timing mechanisms makes our cells more vulnerable to cancer formation. The aim of this study was to investigate the relationship between expression patterns of circadian clock genes (period homolog (per)1, per2, clock, and cry1) and tumor development by analyzing human skin biopsies of malignant melanoma and nonmalignant naevus tumors. We found that mRNA levels and nuclear immunopositivity for the investigated clock genes were reduced by 30-60 % in both melanoma and in naevus biopsies if compared with adjacent nontumorous samples. The alterations in melanoma presented significant associations with clinicopathological characteristics (e.g., Breslow thickness). Contrary to previous reports, the moderate decrease of per1 expression seen in malignant tissues could not be linked to malignant transformation itself; rather, it reflects only the alterations in tissue composition. In turn, clock expression was upregulated in nontumorous cells of melanoma biopsies but not in melanoma cells or naevus cells. As this gene (clock) is closely related to cellular metabolism, our data suggest its role in the impaired regulation of metabolism in malignant tumors. Our results present the first clinical evidence for a possible link between circadian clock genes and human skin tumorigenesis.

Circadian rhythm disruption in cancer biology

Circadian rhythms show universally a 24-h oscillation pattern in metabolic, physiological and behavioral functions of almost all species. This pattern is due to a fundamental adaptation to the rotation of Earth around its own axis. Molecular mechanisms of generation of circadian rhythms organize a biochemical network in suprachiasmatic nucleus and peripheral tissues, building cell autonomous clock pacemakers. Rhythmicity is observed in transcriptional expression of a wide range of clock-controlled genes that regulate a variety of normal cell functions, such as cell division and proliferation. Desynchrony of this rhythmicity seems to be implicated in several pathologic conditions, including tumorigenesis and progression of cancer. In 2007, the International Agency for Research on Cancer (IARC) categorized "shiftwork that involves circadian disruption [as] probably carcinogenic to humans" (Group 2A in the IARC classification system of carcinogenic potency of an agentagent) (Painting, Firefighting, and Shiftwork; IARC; 2007). This review discusses the potential relation between disruptions of normal circadian rhythms with genetic driving machinery of cancer. Elucidation of the role of clockwork disruption, such as exposure to light at night and sleep disruption, in cancer biology could be important in developing new targeted anticancer therapies, optimizing individualized chronotherapy and modifying lighting environment in workplaces or homes.

CLOCK, PER2 and BMAL1 DNA methylation: association with obesity and metabolic syndrome characteristics and monounsaturated fat intake

The circadian clock system instructs 24-h rhythmicity on gene expression in essentially all cells, including adipocytes, and epigenetic mechanisms may participate in this regulation. The aim of this research was to investigate the influence of obesity and metabolic syndrome (MetS) features in clock gene methylation and the involvement of these epigenetic modifications in the outcomes. Sixty normal-weight, overweight and obese women followed a 16-weeks weight reduction program. DNA methylation levels at different CpG sites of CLOCK, BMAL1 and PER2 genes were analyzed by Sequenom's MassARRAY in white blood cells obtained before the treatment. Statistical differences between normal-weight and overweight + obese subjects were found in the methylation status of different CpG sites of CLOCK (CpGs 1, 5-6, 8 and 11-14) and, with lower statistical significance, in BMAL1 (CpGs 6-7, 8, 15 and 16-17). The methylation pattern of different CpG sites of the three genes showed significant associations with anthropometric parameters such as body mass index and adiposity, and with a MetS score. Moreover, the baseline methylation levels of CLOCK CpG 1 and PER2 CpGs 2-3 and 25 correlated with the magnitude of weight loss. Interestingly, the percentage of methylation of CLOCK CpGs 1 and 8 showed associations with the intake of monounsaturated and polyunsaturated fatty acids. This study demonstrates for the first time an association between methylation status of CpG sites located in clock genes (CLOCK, BMAL1 and PER2) with obesity, MetS and weight loss. Moreover, the methylation status of different CpG sites in CLOCK and PER2 could be used as biomarkers of weight-loss success, particularly CLOCK CPGs 5-6.

Epigenetic silencing of the circadian clock gene CRY1 is associated with an indolent clinical course in chronic lymphocytic leukemia

Disruption of circadian rhythm is believed to play a critical role in cancer development. Cryptochrome 1 (CRY1) is a core component of the mammalian circadian clock and we have previously shown its deregulated expression in a subgroup of patients with chronic lymphocytic leukemia (CLL). Using real-time RT-PCR in a cohort of 76 CLL patients and 35 normal blood donors we now demonstrate that differential CRY1 mRNA expression in high-risk (HR) CD38+/immunoglobulin variable heavy chain gene (IgVH) unmutated patients as compared to low-risk (LR) CD38−/IgVH mutated patients can be attributed to down-modulation of CRY1 in LR CLL cases. Analysis of the DNA methylation profile of the CRY1 promoter in a subgroup of 57 patients revealed that CRY1 expression in LR CLL cells is silenced by aberrant promoter CpG island hypermethylation. The methylation pattern of the CRY1 promoter proved to have high prognostic impact in CLL where aberrant promoter methylation predicted a favourable outcome. CRY1 mRNA transcript levels did not change over time in the majority of patients where sequential samples were available for analysis. We also compared the CRY1 expression in CLL with other lymphoid malignancies and observed epigenetic silencing of CRY1 in a patient with B cell acute lymphoblastic leukemia (B-ALL).

CHD1 remodels chromatin and influences transient DNA methylation at the clock gene frequency

Circadian-regulated gene expression is predominantly controlled by a transcriptional negative feedback loop, and it is evident that chromatin modifications and chromatin remodeling are integral to this process in eukaryotes. We previously determined that multiple ATP-dependent chromatin-remodeling enzymes function at frequency (frq). In this report, we demonstrate that the Neurospora homologue of chd1 is required for normal remodeling of chromatin at frq and is required for normal frq expression and sustained rhythmicity. Surprisingly, our studies of CHD1 also revealed that DNA sequences within the frq promoter are methylated, and deletion of chd1 results in expansion of this methylated domain. DNA methylation of the frq locus is altered in strains bearing mutations in a variety of circadian clock genes, including frq, frh, wc-1, and the gene encoding the frq antisense transcript (qrf). Furthermore, frq methylation depends on the DNA methyltransferase, DIM-2. Phenotypic characterization of Δdim-2 strains revealed an approximate WT period length and a phase advance of approximately 2 hours, indicating that methylation plays only an ancillary role in clock-regulated gene expression. This suggests that DNA methylation, like the antisense transcript, is necessary to establish proper clock phasing but does not control overt rhythmicity. These data demonstrate that the epigenetic state of clock genes is dependent on normal regulation of clock components.

Methylation analysis of circadian clock gene promoters in forensic autopsy specimens

DNA methylation in gene promoter regions influences gene expression. Circadian clock genes play an important role in the formation of a biological clock and aberrant methylation of these genes contributes to several disorders. In this study, we examined forensic autopsy specimens to determine whether DNA methylation status in the promoter regions of nine circadian clock genes (Per1, Per2, Per3, Cry1, Cry2, Bmal1, Clock, Tim, and Ck1e) is related to a change in acquired diathesis and/or causes of death. Methylation-specific PCR and direct sequencing methods revealed that the promoters of Per1, Cry2, Bmal1, Clock, and Ck1e were unmethylated in all the forensic autopsy specimens, while the promoters of Per2, Per3, Cry1, and Tim were partially methylated. Methylation status varied between individuals and between tissues in the same patient. A detailed analysis of methylation patterns in the Cry1 promoter region revealed that the patterns also varied between individuals and the Cry1 promoter had highly methylated patterns in two cases that had been exposed to methamphetamine. These results suggest that the methylation status of clock gene promoters varies between individuals. Methamphetamine use may influence methylation in the Cry1 gene promoter region and disturb circadian rhythmicity.

Perfect timing: epigenetic regulation of the circadian clock

In mammals, higher order chromatin structures are critical for downsizing the genome (packaging) so that the nucleus can be small. The adjustable density of chromatin also regulates gene expression, thus this post-genetic molecular mechanism is one of the routes by which phenotype is shaped. Phenotypes that arise without a concomitant mutation of the underlying genome are termed epigenetic phenomena. Here we discuss epigenetic phenomena from histone and DNA modification as it pertains to the dynamic regulatory processes of the circadian clock. Epigenetic phenomena certainly explain some regulatory aspects of the mammalian circadian oscillator.

Age-related changes in mesenchymal stem cells derived from rhesus macaque bone marrow

The regeneration potential of mesenchymal stem cells (MSCs) diminishes with advanced age and this diminished potential is associated with changes in cellular functions. This study compared MSCs isolated from the bone marrow of rhesus monkeys (rBMSCs) in three age groups: young (< 5 years), middle (8-10 years), and old (> 12 years). The effects of aging on stem cell properties and indicators of stem cell fitness such as proliferation, differentiation, circadian rhythms, stress response proteins, miRNA expression, and global histone modifications in rBMSCs were analyzed. rBMSCs demonstrated decreased capacities for proliferation and differentiation as a function of age. The production of heat shock protein 70 (HSP70) and heat shock factor 1 (HSF1) were also reduced with increasing age. The level of a core circadian protein, Rev-erb α, was significantly increased in rBMSCs from old animals. Furthermore, analysis of miRNA expression profiles revealed an up-regulation of mir-766 and mir-558 and a down-regulation of mir-let-7f, mir-125b, mir-222, mir-199-3p, mir-23a, and mir-221 in old rBMSCs compare to young rBMSCs. However, there were no significant age-related changes in the global histone modification profiles of the four histone core proteins: H2A, H2B, H3, and H4 on rBMSCs. These changes represent novel insights into the aging process and could have implications regarding the potential for autologous stem cells therapy in older patients.

Disrupting circadian homeostasis of sympathetic signaling promotes tumor development in mice

Background

Cell proliferation in all rapidly renewing mammalian tissues follows a circadian rhythm that is often disrupted in advanced-stage tumors. Epidemiologic studies have revealed a clear link between disruption of circadian rhythms and cancer development in humans. Mice lacking the circadian genes Period1 and 2 (Per) or Cryptochrome1 and 2 (Cry) are deficient in cell cycle regulation and Per2 mutant mice are cancer-prone. However, it remains unclear how circadian rhythm in cell proliferation is generated in vivo and why disruption of circadian rhythm may lead to tumorigenesis.

Methodology/Principal Findings

Mice lacking Per1 and 2, Cry1 and 2, or one copy of Bmal1, all show increased spontaneous and radiation-induced tumor development. The neoplastic growth of Per-mutant somatic cells is not controlled cell-autonomously but is dependent upon extracellular mitogenic signals. Among the circadian output pathways, the rhythmic sympathetic signaling plays a key role in the central-peripheral timing mechanism that simultaneously activates the cell cycle clock via AP1-controlled Myc induction and p53 via peripheral clock-controlled ATM activation. Jet-lag promptly desynchronizes the central clock-SNS-peripheral clock axis, abolishes the peripheral clock-dependent ATM activation, and activates myc oncogenic potential, leading to tumor development in the same organ systems in wild-type and circadian gene-mutant mice.

Conclusions/Significance

Tumor suppression in vivo is a clock-controlled physiological function. The central circadian clock paces extracellular mitogenic signals that drive peripheral clock-controlled expression of key cell cycle and tumor suppressor genes to generate a circadian rhythm in cell proliferation. Frequent disruption of circadian rhythm is an important tumor promoting factor.

Circadian rhythm and its role in malignancy

Circadian rhythms are daily oscillations of multiple biological processes directed by endogenous clocks. The circadian timing system comprises peripheral oscillators located in most tissues of the body and a central pacemaker located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Circadian genes and the proteins produced by these genes constitute the molecular components of the circadian oscillator which form positive/negative feedback loops and generate circadian rhythms. The circadian regulation extends beyond clock genes to involve various clock-controlled genes (CCGs) including various cell cycle genes. Aberrant expression of circadian clock genes could have important consequences on the transactivation of downstream targets that control the cell cycle and on the ability of cells to undergo apoptosis. This may lead to genomic instability and accelerated cellular proliferation potentially promoting carcinogenesis. Different lines of evidence in mice and humans suggest that cancer may be a circadian-related disorder. The genetic or functional disruption of the molecular circadian clock has been found in various cancers including breast, ovarian, endometrial, prostate and hematological cancers. The acquisition of current data in circadian clock mechanism may help chronotherapy, which takes into consideration the biological time to improve treatments by devising new therapeutic approaches for treating circadian-related disorders, especially cancer.

Circadian rhythms and cancer

The circadian clock is an endogenous time keeping system shared by most organisms. In mammals, a master pacemaker in the hypothalamus orchestrates temporal alignment of behavior and physiology by transmitting daily signals to multiple clocks in peripheral tissues. Disruption of this communication has a profound affect on human health and has been linked to diverse pathogenic conditions, including cancer. At the center of the molecular circadian machinery is a set of clock genes, generating rhythmic oscillations on a cellular level. In the past several years, research from different fields has revealed the complexity and ubiquitous nature of circadian regulation, uncovering intriguing associations between clock components and cellular pathways implicated in tumorigenesis. In this review, we discuss the emerging role of circadian genes in hematological and hormone-related malignancies. These new insights suggest that manipulating circadian biology as a way to fight cancer, as well as, other life threatening diseases is within the realm of possibility.

The crosstalk between physiology and circadian clock proteins

In mammals, many physiological processes present diurnal variations, and most of these rhythms persist even in absence of environmental timing cues. These endogenous circadian rhythms are generated by intracellular timing mechanisms termed circadian clocks. In mammals, the master clock is located in the suprachiasmatic nuclei (SCN), but other brain regions and most peripheral tissues contain circadian clocks. These clocks are responsive to environmental cues, in particular light/dark and feeding/fasting cycles. In the last few years, tissue-specific knock-out and transgenic mouse models have helped to define the physiological roles of specific clocks. Recent reports indicate that the clock-physiology connection is bi-directional, and physiological cues, in particular the energetic status of the cell, can feed into the clockwork. This effect was discovered unexpectedly in molecular analyses of clock protein modifications. Beyond the positive and negative transcription/translation feedback loops of the molecular oscillator lies another level of complexity. Post-translational modifications of clock proteins are both critical for the timing of the clock feedback mechanism and to provide regulatory fine-tuning. This review summarizes recent advances in our understanding of the roles of peripheral clocks and of post-translational modifications occurring on clock proteins. These two matters are at the intersection of physiology, metabolism, and the circadian system.

Circadian proteins and genotoxic stress response

The circadian clock is an evolutionarily conserved time-keeping system that coordinates the physiology of the organism with daily changes in the environment. A growing body of evidence gradually leads to the conception that virtually all aspects of the biochemical, physiological, and behavioral functions of the animal are linked to circadian regulation. Moreover, proper synchronization of various processes through the activity of circadian components is important for the well-being of many organisms, including humans. The focus of this review is the circadian control of an organism's response to genotoxic stress, which is a major contributor to life-threatening human pathologies such as cancer and cardiovascular disease.

Epigenetic inactivation of the circadian clock gene BMAL1 in hematologic malignancies

Disruption of circadian rhythms, daily oscillations in biological processes that are regulated by an endogenous clock, has been linked to tumorigenesis. Normal and malignant tissues often show asynchronies in cell proliferation and metabolic rhythms. Cancer chronotherapy takes biological time into account to improve the therapy. However, alterations of the circadian clock machinery genes have rarely been reported in human cancer. Herein, we show that the BMAL1 gene, a core component of the circadian clock, is transcriptionally silenced by promoter CpG island hypermethylation in hematologic malignancies, such as diffuse large B-cell lymphoma and acute lymphocytic and myeloid leukemias. We also describe how BMAL1 reintroduction in hypermethylated leukemia/lymphoma cells causes growth inhibition in colony assays and nude mice, whereas BMAL1 depletion by RNA interference in unmethylated cells enhances tumor growth. We also show that BMAL1 epigenetic inactivation impairs the characteristic circadian clock expression pattern of genes such as C-MYC, catalase, and p300 in association with a loss of BMAL1 occupancy in their respective promoters. Furthermore, the DNA hypermethylation-associated loss of BMAL1 also prevents the recruitment of its natural partner, the CLOCK protein, to their common targets, further enhancing the perturbed circadian rhythm of the malignant cells. These findings suggest that BMAL1 epigenetic inactivation contributes to the development of hematologic malignancies by disrupting the cellular circadian clock.