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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.

Mutations in the WNT/beta-catenin pathway are responsible for initiating the majority of colorectal cancers (CRCs). We have previously shown that hyperactivation of this signaling by histone deacetylase inhibitors (HDACis) such as butyrate, a fermentation product of dietary fiber, promotes CRC cell apoptosis. The extent of association between beta-catenin and the transcriptional coactivator CREB-binding protein (CBP) influences WNT/catenin signaling and, therefore, colonic cell physiology. CBP functions as a histone acetylase (HAT); therefore, we hypothesized that the modulation of WNT/catenin activity by CBP modifies the ability of the HDACi butyrate to hyperinduce WNT signaling and apoptosis in CRC cells. Our findings indicate that CBP affects the hyperinduction of WNT activity by butyrate. ICG-001, which specifically blocks association between CBP and beta-catenin, abrogates the butyrate-triggered increase in the number of CRC cells with high levels of WNT/catenin signaling. Combination treatment of CRC cells with ICG-001 and butyrate results in cell type-specific effects on apoptosis. Further, both butyrate and ICG-001 repress CRC cell proliferation, with additive effects in suppressing cell growth. Our study strongly suggests that ICG-001-like agents would be effective against butyrate/HDACi-resistant CRC cells. Therefore, ICG-001-like agents may represent an important therapeutic option for CRCs that exhibit low-fold hyperactivation of WNT activity and apoptosis in the presence of HDACis. The findings generated from this study may lead to approaches that utilize modulation of CBP activity to facilitate CRC therapeutic or chemopreventive strategies.