Genome-wide DNA methylation patterns are frequently deregulated in cancer. There is considerable interest in targeting the methylation machinery in tumor cells using nucleoside analogs of cytosine, such as 5-aza-2-deoxycytidine (5-azadC). 5-azadC exerts its antitumor effects by reactivation of aberrantly hypermethylated growth regulatory genes and cytoxicity resulting from DNA damage. We sought to better characterize the DNA damage response of tumor cells to 5-azadC and the role of DNA methyltransferases 1 and 3B (DNMT1 and DNMT3B, respectively) in modulating this process. We demonstrate that 5-azadC treatment results in growth inhibition and G 2 arrest-hallmarks of a DNA damage response. 5-azadC treatment led to formation of DNA double-strand breaks, as monitored by formation of ␥-H2AX foci and comet assay, in an ATM (ataxiatelangiectasia mutated)-dependent manner, and this damage was repaired following drug removal. Further analysis revealed activation of key strand break repair proteins including ATM, ATR (ATM-Rad3-related), checkpoint kinase 1 (CHK1), BRCA1, NBS1, and RAD51 by Western blotting and immunofluorescence. Significantly, DNMT1-deficient cells demonstrated profound defects in these responses, including complete lack of ␥-H2AX induction and blunted p53 and CHK1 activation, while DNMT3B-deficient cells generally showed mild defects. We identified a novel interaction between DNMT1 and checkpoint kinase CHK1 and showed that the defective damage response in DNMT1-deficient cells is at least in part due to altered CHK1 subcellular localization. This study therefore greatly enhances our understanding of the mechanisms underlying 5-azadC cytotoxicity and reveals novel functions for DNMT1 as a component of the cellular response to DNA damage, which may help optimize patient responses to this agent in the future.DNA methylation is an essential epigenetic modification required for normal mammalian development, gene regulation, genomic imprinting, and chromatin structure (9). Methylation occurs at the C-5 position of cytosine within the CpG dinucleotide and is carried out by a family of DNA methyltransferases (DNMTs), DNMT1, DNMT3A, and DNMT3B (32). DNMT1 acts primarily as a maintenance methyltransferase by copying existing methylation patterns following DNA replication (53). DNMT3A and DNMT3B exhibit de novo methyltransferase activity and are required for establishing new methylation patterns during embryonic development (72). Deregulation of the DNA methylation machinery has been identified in several disease states, particularly cancer (78), and leads to global DNA hypomethylation of repetitive DNA, which has been linked to genomic instability (21) and, concomitantly, hypermethylation at the promoter regions of certain genes (tumor suppressors), leading to their aberrant silencing (43).The process of cytosine methylation is reversible and may be altered by biochemical and biological manipulation, making it an attractive target for therapeutic intervention. Demethylation and consequent reactivation of tumor ...

The de novo DNA methyltransferase Dnmt3a is one of three mammalian DNA methyltransferases that has been shown to play crucial roles in embryonic development, genomic imprinting and transcriptional silencing. Despite its importance, very little is known about how the enzymatic activity and transcriptional repression functions of Dnmt3a are regulated. Here we show that Dnmt3a interacts with multiple components of the sumoylation machinery, namely the E2 sumo conjugating enzyme Ubc9 and the E3 sumo ligases PIAS1 and PIASxalpha, all of which are involved in conjugating the small ubiquitin-like modifier polypeptide, SUMO-1, to its target proteins. Dnmt3a is modified by SUMO-1 in vivo and in vitro and the region of Dnmt3a responsible for interaction maps to the N-terminal regulatory domain. Functionally, sumoylation of Dnmt3a disrupts its ability to interact with histone deacetylases (HDAC1/2), but not with another interaction partner, Dnmt3b. Conditions that enhance the sumoylation of Dnmt3a in vivo abolish its capacity to repress transcription. These studies reveal a new level of regulation governing Dnmt3a whereby a post-translational modification can dramatically regulate its interaction with specific protein partners and alter its ability to repress transcription.

Transcription factors are proteins that regulate gene expression by binding to specific DNA sequences within gene promoter regions. Specificity protein (Sp) family transcription factors play a critical role in various cellular processes and have been shown to be associated with tumorigenesis. The Sp family consists of several members that contain a highly conserved DNA-binding domain composed of three zinc fingers at the C-terminus and serine/threonine- and glutamine-rich transactivation domains at the N-terminal. Sp1 is elevated in several cancers including prostate and is associated with the prognosis of patients. Sp1, Sp3, and Sp4 regulate a variety of cancer associated genes that are involved in cell cycle, proliferation, cell differentiation, and apoptosis. Studies have shown that in prostate cancer, Sp1 regulates important genes like androgen receptor, TGF-β, c-Met, fatty acid synthase, matrix metalloprotein (MT1-MMP), PSA, and α-integrin. These results highlight the importance of Sp1 in prostate cancer and emphasize the potential therapeutic value of targeting Sp1. Several strategies, including the use of natural and synthetic compounds, have been used to inhibit Sp1 in prostate cancer. These include polyphenol quercetin, betulinic acid, acetyl-11-keto-beta-boswellic acid, tea phenols, isothiocyanates, thiazolidinediones, arsenic trioxide, and selenium. This review will describe the association of Sp proteins in prostate cancer with a special emphasis on some of the agents tested to target Sp proteins for the treatment of this malignancy.

Proper patterns of genome-wide DNA methylation, mediated by DNA methyltransferases DNMT1, -3A and -3B, are essential for embryonic development and genomic stability in mammalian cells. The de novo DNA methyltransferase DNMT3B is of particular interest because it is frequently overexpressed in tumor cells and is mutated in immunodeficiency, centromere instability and facial anomalies (ICF) syndrome. In order to gain a better understanding of DNMT3B, in terms of the targeting of its methylation activity and its role in genome stability, we biochemically purified endogenous DNMT3B from HeLa cells. DNMT3B co-purifies and interacts, both in vivo and in vitro, with several components of the condensin complex (hCAP-C, hCAP-E and hCAP-G) and KIF4A. Condensin mediates genome-wide chromosome condensation at the onset of mitosis and is critical for proper segregation of sister chromatids. KIF4A is proposed to be a motor protein carrying DNA as cargo. DNMT3B also interacts with histone deacetylase 1 (HDAC1), the co-repressor SIN3A and the ATP-dependent chromatin remodeling enzyme hSNF2H. Further more, DNMT3B co-localizes with condensin and KIF4A on condensed chromosomes throughout mitosis. These studies therefore reveal the first direct link between the machineries regulating DNA methylation and mitotic chromosome condensation in mammalian cells.

BackgroundThe prognosis for patients with breast tumor metastases to brain is extremely poor. Identification of prognostic molecular markers of the metastatic process is critical for designing therapeutic modalities for reducing the occurrence of metastasis. Although ubiquitously present in most human organs, large-conductance calcium- and voltage-activated potassium channel (BKCa) channels are significantly upregulated in breast cancer cells. In this study we investigated the role of KCNMA1 gene that encodes for the pore-forming α-subunit of BKCa channels in breast cancer metastasis and invasion.MethodsWe performed Global exon array to study the expression of KCNMA1 in metastatic breast cancer to brain, compared its expression in primary breast cancer and breast cancers metastatic to other organs, and validated the findings by RT-PCR. Immunohistochemistry was performed to study the expression and localization of BKCa channel protein in primary and metastatic breast cancer tissues and breast cancer cell lines. We performed matrigel invasion, transendothelial migration and membrane potential assays in established lines of normal breast cells (MCF-10A), non-metastatic breast cancer (MCF-7), non-brain metastatic breast cancer cells (MDA-MB-231), and brain-specific metastatic breast cancer cells (MDA-MB-361) to study whether BKCa channel inhibition attenuates breast tumor invasion and metastasis using KCNMA1 knockdown with siRNA and biochemical inhibition with Iberiotoxin (IBTX).ResultsThe Global exon array and RT-PCR showed higher KCNMA1 expression in metastatic breast cancer in brain compared to metastatic breast cancers in other organs. Our results clearly show that metastatic breast cancer cells exhibit increased BKCa channel activity, leading to greater invasiveness and transendothelial migration, both of which could be attenuated by blocking KCNMA1.ConclusionDetermining the relative abundance of BKCa channel expression in breast cancer metastatic to brain and the mechanism of its action in brain metastasis will provide a unique opportunity to identify and differentiate between low grade breast tumors that are at high risk for metastasis from those at low risk for metastasis. This distinction would in turn allow for the appropriate and efficient application of effective treatments while sparing patients with low risk for metastasis from the toxic side effects of chemotherapy.

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Curcumin (Cur) has been extensively studied in several types of malignancies including colorectal cancer (CRC); however its clinical application is greatly affected by low bioavailability. Several strategies to improve the therapeutic response of Cur are being pursued, including its combination with small molecules and drugs. We investigated the therapeutic efficacy of Cur in combination with the small molecule tolfenamic acid (TA) in CRC cell lines. TA has been shown to inhibit the growth of human cancer cells in vitro and in vivo, via targeting the transcription factor specificity protein1 (Sp1) and suppressing survivin expression. CRC cell lines HCT116 and HT29 were treated with TA and/or Cur and cell viability was measured 24–72 hours post-treatment. While both agents caused a steady reduction in cell viability, following a clear dose/time-dependent response, the combination of TA+Cur showed higher growth inhibition when compared to either single agent. Effects on apoptosis were determined using flow cytometry (JC-1 staining to measure mitochondrial membrane potential), Western blot analysis (c-PARP expression) and caspase 3/7 activity. Reactive oxygen species (ROS) levels were measured by flow cytometry and the translocation of NF-kB into the nucleus was determined using immunofluorescence. Results showed that apoptotic markers and ROS activity were significantly upregulated following combination treatment, when compared to the individual agents. This was accompanied by decreased expression of Sp1, survivin and NF-kB translocation. The combination of TA+Cur was more effective in HCT116 cells than HT29 cells. These results demonstrate that TA may enhance the anti-proliferative efficacy of Cur in CRC cells.

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