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Novel detection and differential utilization of a c-myc transcriptional block in colon cancer chemoprevention

Department of Oncology, Albert Einstein Cancer Center, Montefiore Medical Center, Bronx, New York 10467, USA.
Cancer Research (Impact Factor: 9.28). 12/2002; 62(21):6006-10.
Source: PubMed

ABSTRACT Mutations in the adenomatous polyposis coli (APC) gene, which initiate almost all human colon cancers, directly target the proto-oncogene, c-myc, by elevating beta-catenin/T-cell factor (TCF) signaling. We have shown that agents ascribed chemopreventive activity for colon cancer in fact also stimulate beta-catenin/TCF activity in vitro. Their effects on c-myc transcription were assayed using a novel variant of fluorescence in situ hybridization that detects c-myc transcription sites in intact nuclei. Increased transcriptional initiation of c-myc induced by the short-chain fatty acid, butyrate, consistent with elevated beta-catenin/TCF activity, was efficiently abrogated by a block to transcriptional elongation, resulting in decreased c-myc expression. 1alpha,25-Dihydroxyvitamin D(3) also induced transcriptional blockage. In contrast, the nonsteroidal anti-inflammatory drug, sulindac, increased c-myc expression, an effect attributable at least in part to its failure to induce transcriptional blockage. We have described a novel approach for evaluating the effects of chemopreventive agents on the expression of a gene critical in colonic tumorigenesis.

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    • "In conclusion, we have now demonstrated that transcriptional attenuation triggered by butyrate or vitamin D 3 plays an important role in the down regulation of two key genes that regulate colonic cell maturation and transformation—c-myc and cyclin D1 (Wilson et al., 2002), and data above—therefore eliminating the increased steady state levels of c-myc and cyclin D1 which might be expected from the elevation in Wnt signaling. Recent data (Daroqui and Augenlicht, unpublished work) demonstrate that this mechanism of transcriptional attenuation appears to be involved in regulating the expression of a significant percent of genes for which expression is altered in the extensive reprogramming initiated by butyrate (Mariadason et al., 2000). "
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    • "Quantitative real-time RT-PCR (QPCR) was performed as described previously (Wilson et al., 2002). Relative values were determined from a standard curve of HCT116 cDNA and expressed relative to ␤-actin. "
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