Colorectal cancer risk is increased in shift workers with presumed circadian disruption. Intestinal epithelial cell proliferation is gated throughout each day by the circadian clock. Period 2 (Per2) is a key circadian clock gene. Per2 mutant (Per2m/m) mice show an increase in lymphomas and deregulated expression of cyclin D and c-Myc genes that are key to proliferation control. We asked whether Per2 clock gene inactivation would accelerate intestinal and colonic tumorigenesis. The effects of PER2 on cell proliferation and β-catenin were studied in colon cancer cell lines by its down-regulation following RNA interference. The effects of Per2 inactivation in vivo on β-catenin and on intestinal and colonic polyp formation were studied in mice with Per2 mutation alone and in combination with an Apc mutation using polyp-prone ApcMin/+ mice. Down-regulation of PER2 in colon cell lines (HCT116 and SW480) increases β-catenin, cyclin D, and cell proliferation. Down-regulation of β-catenin along with Per2 blocks the increase in cyclin D and cell proliferation. Per2m/m mice develop colonic polyps and show an increase in small intestinal mucosa β-catenin and cyclin D protein levels compared with wild-type mice. ApcMin/+Per2m/m mice develop twice the number of small intestinal and colonic polyps, with more severe anemia and splenomegaly, compared with ApcMin/+ mice. These data suggest that Per2 gene product suppresses tumorigenesis in the small intestine and colon by down-regulation of β-catenin and β-catenin target genes, and this circadian core clock gene may represent a novel target for colorectal cancer prevention and control.

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The present work demonstrates the use of a dielectrophoretic lab-on-a-chip device in effectively separating different cancer cells of epithelial origin for application in circulating tumor cell (CTC) identification. This study uses dielectrophoresis (DEP) to distinguish and separate MCF-7 human breast cancer cells from HCT-116 colorectal cancer cells. The DEP responses for each cell type were measured against AC electrical frequency changes in solutions of varying conductivities. Increasing the conductivity of the suspension directly correlated with an increasing frequency value for the first cross-over (no DEP force) point in the DEP spectra. Differences in the cross-over frequency for each cell type were leveraged to determine a frequency at which the two types of cell could be separated through DEP forces. Under a particular medium conductivity, different types of cells could have different DEP behaviors in a very narrow AC frequency band, demonstrating a high specificity of DEP. Using a microfluidic DEP sorter with optically transparent electrodes, MCF-7 and HCT-116 cells were successfully separated from each other under a 3.2 MHz frequency in a 0.1X PBS solution. Further experiments were conducted to characterize the separation efficiency (enrichment factor) by changing experimental parameters (AC frequency, voltage, and flow rate). This work has shown the high specificity of the described DEP cell sorter for distinguishing cells with similar characteristics for potential diagnostic applications through CTC enrichment. V C 2013 American Institute of Physics. [http://dx

We examined the importance of histone methylation by the polycomb group proteins in the mouse circadian clock mechanism. Endogenous EZH2, a polycomb group enzyme that methylates lysine 27 on histone H3, co-immunoprecipitates with CLOCK and BMAL1 throughout the circadian cycle in liver nuclear extracts. Chromatin immunoprecipitation revealed EZH2 binding and di-and trimethylation of H3K27 on both the Period 1 and Period 2 promoters. A role of EZH2 in cryptochrome-mediated transcriptional repression of the clockwork was supported by overexpression and RNA interference studies. Serum-induced circadian rhythms in NIH 3T3 cells in culture were disrupted by transfection of an RNA interfering sequence targeting EZH2. These results indicate that EZH2 is important for the maintenance of circadian rhythms and extend the activity of the polycomb group proteins to the core clockwork mechanism of mammals.The circadian clock mechanism in the mouse is driven by interacting positive and negative transcriptional feedback loops (1, 2). The negative feedback loop is essential for clockwork function and involves CLOCK⅐BMAL1 enhanced expression of three Period genes (mPer 1-3) and two Cryptochrome genes (mCry1 and mCry2) (3-5). Negative feedback is provided by a CRY⅐PER complex that rhythmically enters the nucleus to inhibit CLOCK⅐BMAL1-mediated transcription via a mechanism that does not substantially alter CLOCK⅐BMAL1 binding to mPer1 and mPer2 promoters (3, 6). Other clockcontrolled genes may be regulated by other mechanisms, as CLOCK⅐BMAL1 binds rhythmically to the promoter of the Dbp gene (7).The positive transcriptional feedback loop involves the regulation of Bmal1 transcription by CLOCK⅐BMAL1-mediated transcription of the nuclear orphan receptor genes Rev-erb␣ and Rora (8 -11). The orphan receptor gene products act on the Bmal1 promoter to generate a circadian rhythm in Bmal1 RNA levels that is antiphase to the mPer and mCry RNA rhythms. The positive feedback loop appears to provide stability to the core clock mechanism (12).Changes in chromatin structure due to post-translational modifications of histones are required for transcriptional regulation of gene expression (13,14), and circadian genes are no exception (7,(15)(16)(17)(18). Previously, we showed in the liver clock that the promoter regions of mPer1 and mPer2 undergo rhythmic acetylation of histone H3 that correlates with their transcriptional activation (16). We proposed that at the time of transcriptional inhibition the mCRY proteins disrupt a CLOCK⅐BMAL1⅐coactivator complex thereby reducing histone acetyltransferase activity. As histone deacetylase activity is constantly associated with the CLOCK⅐BMAL1 nuclear complex, the balance between acetylation and deacetylation of H3 on circadian promoters appears to be regulated by the rhythmic regulation of histone acetyltransferase activity, with deacetylation predominating during transcriptional repression. Other groups have also reported H3 acetylation rhythms at circadian promoters (17,18).Our search for other chroma...