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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"Interestingly, upregulation of CDKIs by calcitriol is associated with calcitriol-induced increased expression of Retinoblastoma protein (pRb) and its later phosphorylation [Ji et al., 2002; Washington et al., 2011]. This leads to the binding of pRb to E2F transcription factor causing inactivation of E2F target proteins, such as cyclin E and c-Myc, and subsequent cell cycle block [Brelvi and Studzinski, 1986; Gartel et al., 2001; Wilson et al., 2002]. In colon cancer cells, calcitriol enhances the expression of E-cadherin and subsequent transport of b-catenin from the cell nuclei to plasma membrane. "
[Show abstract][Hide abstract]ABSTRACT: The role of vitamin D as a treatment option for neoplastic diseases, once considered to have a bright future, remains controversial. The preclinical studies discussed herein show compelling evidence that Vitamin D Derivatives (VDDs) can convert some cancer and leukemia cells to a benign phenotype, by differentiation/maturation, cell cycle arrest or induction of apoptosis. Further, there is considerable, though still evolving, knowledge of the molecular mechisms underlying these changes. However, the attempts to clearly document that the treatment outcomes of human neoplastic diseases can be positively influenced by VDDs have been, so far, disappointing. The clinical trials to date of VDDs, alone or combined with other agents, have not shown consistent results. It is our contention, shared by others, that there were limitations in the design or execution of these trials which have not yet been fully addressed. Based on the connection between upregulation of JNK by VDDs and DNA repair, we propose a new avenue of attack on cancer cells by increasing the toxicity of the current, only partially effective, cancer chemotherapeutic drugs by combining them with VDDs. This can impair DNA repair and thus kill the malignant cells, warranting a comprehensive study of this novel concept. This article is protected by copyright. All rights reserved
Full-text · Article · Mar 2016 · Journal of Cellular Biochemistry
"Chromatin compaction is associated with silencing of gene transcription and other functions of genome maintenance such as DNA replication and DNA damage response and repair (16–20). Deacetylation of histones represses the transcription of tumor suppressor genes such as the cyclin-dependent kinase inhibitor, p21 p21(WAF1/CIP1), and the DNA damage repair gene BRCA1, and directly or indirectly promotes the expression, activity, or downstream effects of known oncogenes such as c-MYC (21), RAS (22, 23), and AKT (24). Direct deacetylation of non-histone proteins p53, STAT3, c-MYC, α-tubulin, and Hsp90 is implicated in tumorigenesis (15, 25–27). "
[Show abstract][Hide abstract]ABSTRACT: Epithelial ovarian cancer remains the deadliest gynecologic malignancy. Despite advances in treatment, new approaches are needed. Histone deacetylases (HDACs) are a family of enzymes that regulate gene expression by removing acetyl groups from lysine residues on histones and non-histone proteins. Inhibition of HDACs with small molecules has led to the development of histone deacetylase inhibitors (HDACi) that are in clinical use, primarily for hematologic malignancies. Although clinical trials with HDACi as single agents in solid tumors have been disappointing, data from independent labs and recent work by our group show that class I selective HDACi have potent anti-tumor effects in pre-clinical models of ovarian cancer. This review summarizes the role of HDACs in ovarian cancer and the potential niche for selective class I HDACi, particularly HDAC3 in ovarian cancer therapy.
Full-text · Article · May 2014 · Frontiers in Oncology
"C-myc is a Wnt signaling-targeted gene, the product of which in part mediates the pro-proliferative action of constitutively activated Wnt signaling. Butyrate influences c-myc expression at several levels, resulting in a net downregulation of c-myc levels 36. Our array data indicated that c-myc is expressed at higher levels in SW620 cells than in LT97 cells, and is downregulated by butyrate in LT97 cells. "
[Show abstract][Hide abstract]ABSTRACT: Dietary fiber intake is linked to a reduced risk of colon cancer. This effect may in part be due to butyrate, the fermentation product of fiber in the colon. Butyrate is a short-chain fatty acid that acts as a histone deacetylase inhibitor (HDACi). Butyrate induces apoptosis and represses clonal growth of colorectal cancer (CRC) cells, in a manner dependent upon the hyperactivation of Wnt /beta-catenin signaling. While fiber has been linked to CRC prevention, in vitro studies on the action of butyrate have used CRC cell lines, instead of cells representative of earlier stages of colonic neoplasia, which are the likely target of butyrate-mediated preventive activity. The LT97 cell line is derived from a microadenoma, the earliest stage of colonic neoplasia from which cells can be isolated. We characterized LT97 cells with respect to effects of butyrate on Wnt signaling and apoptosis, and we determined whether modulation of CREB binding protein (CBP)/p300 activity influences the ability of butyrate to induce Wnt activity and apoptosis. We report that in LT97 cells, butyrate induces apoptosis, strongly upregulates Wnt signaling, and the upregulation of Wnt signaling is dependent upon CBP/p300 activity. In addition, findings from overexpression experiments suggest differences between CBP and p300 in their ability to influence Wnt signaling in LT97 cells; p300, but not CBP, stimulates basal Wnt activity. We also evaluated differences in gene expression between early stage LT97 cells and late stage metastatic SW620 CRC cells that exhibit markedly different cellular phenotypes. The comparative gene expression analyses revealed differences that may impact neoplastic progression and the sensitivity to the effects of butyrate. The findings have implications for the prevention of CRC by fiber/butyrate.
Full-text · Article · Feb 2014 · Journal of Cancer