SIRT1 mediates the antagonism of Wnt/β-catenin pathway by vitamin D in colon carcinoma cells.
Cancer initiation and progression result from both genetic alterations and epigenetic reprograming caused by environmental or endogenous factors which can lead to aberrant cell signalling. Most colorectal cancers (CRC) are linked to the abnormal activation of the Wnt/ {beta}-catenin pathway, whose key feature is the accumulation of acetylated {beta}-catenin protein within the nucleus of colon epithelial cells. Nuclear {beta}- catenin acts as a transcriptional co-activator that alters the expression of many target genes involved in cell proliferation and invasion. The most active vitamin D metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3, calcitriol) can antagonize the over-activated Wnt/ {beta}-catenin pathway via binding to its high affinity receptor VDR. Here, we show that the activation of the SIRT1 deacetylase by 1,25(OH)2D3-bound VDR promotes deacetylation and nuclear exclusion of {beta}-catenin and, consequently, the downregulation of its pro-tumorigenic target genes and the inhibition of human colon carcinoma cell proliferation. Notably, orthogonal SIRT1 activation systematically drives nuclear exclusion of {beta}-catenin, highlighting the key role of SIRT1 in CRC. Since nuclear localization of {beta}-catenin is a critical driver of CRC initiation and progression that requires its acetylation, our results provide a mechanistic basis for the epidemiological evidence linking vitamin D deficiency and increased CRC risk and mortality.