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The Wnt/β-catenin signaling pathway is abnormally activated in most colorectal cancers and in a proportion of other neoplasias. This activation initiates or contributes to carcinogenesis by regulating the expression of a large number of genes in tumor cells. The active vitamin D metabolite 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) inhibits Wnt/β-catenin signaling by several mechanisms at different points along the pathway. Additionally, paracrine actions of 1,25(OH)2D3 on stromal cells may also repress this pathway in neighbouring tumor cells. Here we review the molecular basis for the various mechanisms by which 1,25(OH)2D3 antagonizes Wnt/β-catenin signaling, preferentially in human colon carcinoma cells, and the consequences of this inhibition for the phenotype and proliferation rate. The effect of the vitamin D system on Wnt/β-catenin signaling and tumor growth in animal models will also be commented in detail. Finally, we revise existing data on the relation between vitamin D receptor expression and vitamin D status and the expression of Wnt/β-catenin pathway genes and targets in cancer patients. [ABSTRACT FROM AUTHOR]

Abstract: 1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) and other vitamin D compounds are promising molecules in the prevention and therapy of colon cancer and other neoplasias. To study the mechanism of action of 1,25(OH)2D3 in colon cancer cells, we carried out a comparative proteomic analysis of the nuclear fractions of SW480-ADH cells treated with 1,25(OH)2D3 or vehicle during 8 or 48h. 2D-DIGE analysis combined with MALDI-TOF-TOF mass spectrometry interrogation led to the identification of 59 differentially expressed unique proteins. Most identified proteins were nuclear, but several cytoskeleton-associated proteins were also detected. A good concordance between changes in expression at protein and RNA levels was observed for the validated proteins. A large group of identified proteins, such as SFPQ, SMARCE, KHSRP, TARDBP and PARP1, were involved in RNA processing or modification and have been ascribed to the spliceosome compartment of human cells. In addition, a smaller group of proteins (ERM (Ezrin, Radixin, Moesin) family, VCL, CORO1C, ACTB) were cytoskeleton-associated and played a role in cell adhesion and morphology. These results confirm the induction of epithelial phenotype by 1,25(OH)2D3 and suggest a role for vitamin D compounds in the regulation of the spliceosome and thus, in alternative splicing and possibly microRNA synthesis in colon cancer cells. [Copyright &y& Elsevier]

Abstract: Many studies support a protective action of vitamin D against colon cancer. 1α,25-Dihydroxyvitamin D3 (1,25(OH)2D3) exerts wide gene regulatory effects in human colon cancer cells. We previously reported that 1,25(OH)2D3 increases cytosolic Ca2+ concentration and transiently activates RhoA and its effector the Rho-associated coiled-kinase (ROCK), and later p38MAPK-MSK. We found that the inhibition of ROCK signaling by Y27632 or that of MSK by Ro318220 prevent the formation of epithelioid islands of SW480-ADH cells by 1,25(OH)2D3 and disrupts the adhesive phenotype of HT29 cells. ROCK and MSK inhibition also abrogates the induction of 1,25(OH)2D3 24-hydroxylase (CYP24), E-cadherin, and vinculin and the repression of cyclin D1 by 1,25(OH)2D3. Moreover, 1,25(OH)2D3 does not promote the localization of the tight junction protein occludin at the plasma membrane in cells expressing a dominant negative RhoA (N19-RhoA). In addition, 1,25(OH)2D3 specifically increases the level of the cysteine protease-inhibitor cystatin D, whereas that of cystatin SN is unaffected. The increase of cystatin D protein caused by 1,25(OH)2D3 is abrogated in N19-RhoA cells. Thus, activation of the RhoA-ROCK-p38MAPK-MSK signaling pathway is essential for the regulation of the phenotype and of the CST5/cystatin D candidate tumor suppressor and other target genes by 1,25(OH)2D3 in colon cancer cells. [ABSTRACT FROM AUTHOR]

Cancer initiation and progression result from genetic and epigenetic alterations caused by interactions between environmental and endogenous factors leading to aberrant cell signalling. Colorectal cancers (CRC) are linked to abnormal activation of the Wnt/β-catenin pathway, whose key feature is the nuclear accumulation of acetylated β-catenin in colon epithelial cells. Nuclear β-catenin acts as a transcriptional co-activator, targeting genes involved in cell proliferation and invasion. 1α,25-Dihydroxyvitamin D 3 (1,25(OH) 2 D 3 or calcitriol), the active form of vitamin D, antagonizes Wnt/β-catenin over-activation by engaging its high affinity receptor, VDR. Here we unveil that 1,25(OH) 2 D 3 -bound VDR activates Silent Information Regulator of Transcription, sirtuin 1 (SIRT1), leading to β-catenin deacetylation and nuclear exclusion, downregulation of its pro-tumourigenic target genes and inhibition of human colon carcinoma cell proliferation. Notably, orthogonal SIRT1 activation mimics nuclear exclusion of β-catenin while SIRT1 inhibition blocks the effects of 1,25(OH) 2 D 3 . Thus, SIRT1 emerges as a crucial mediator in the protective action of vitamin D against CRC. The mutual negative feedback loop unveiled here between Wnt and SIRT1 represents an important surrogate target in CRC. Since nuclear localisation of β-catenin is a critical driver of CRC that requires its acetylation, we provide a mechanistic foundation for the epidemiological evidence linking vitamin D deficiency and increased CRC risk and mortality., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

E-cadherin and its transcriptional repressor Snail1 (Snai1) are two factors that control epithelial phenotype. Expression of Snail1 promotes the conversion of epithelial cells to mesenchymal cells, and occurs concomitantly with the downregulation of E-cadherin and the upregulation of expression of mesenchymal genes such as those encoding fibronectin and LEF1. We studied the molecular mechanism controlling the expression of these genes in mesenchymal cells. Forced expression of E-cadherin strongly downregulated fibronectin and LEF1 RNA levels, indicating that E-cadherin-sensitive factors are involved in the transcription of these genes. E-cadherin overexpression decreased the transcriptional activity of the fibronectin promoter and reduced the interaction of beta-catenin and NF-kappaB with this promoter. Similar to beta-catenin, NF-kappaB was found, by co-immunoprecipitation and pull-down assays, to be associated with E-cadherin and other cell-adhesion components. Interaction of the NF-kappaB p65 subunit with E-cadherin or beta-catenin was reduced when adherens junctions were disrupted by K-ras overexpression or by E-cadherin depletion using siRNA. These conditions did not affect the association of p65 with the NF-kappaB inhibitor IkappaBalpha. The functional significance of these results was stressed by the stimulation of NF-kappaB transcriptional activity, both basal and TNF-alpha-stimulated, induced by an E-cadherin siRNA. Therefore, these results demonstrate that E-cadherin not only controls the transcriptional activity of beta-catenin but also that of NF-kappaB. They indicate too that binding of this latter factor to the adherens junctional complex prevents the transcription of mesenchymal genes.

Colorectal cancer is a major health problem worldwide. Epidemiological studies and work on experimental animals strongly suggest a protective effect of 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) against colon neoplasia. 1,25(OH)2D3 is a pleiotropic hormone that has multiple actions in the organism. By binding to the widely expressed high affinity vitamin D receptor (VDR) it regulates the transcription rate of many genes. Other non-genomic effects of 1,25(OH)2D3 also appear to modulate the physiology of numerous cell types. Human normal and cancer colon epithelial cells express VDR and the key enzymes involved in 1,25(OH)2D3 synthesis and degradation and are, thus, responsive to the hormone. 1,25(OH)2D3 inhibits proliferation, induces differentiation and sometimes the apoptosis of human colon cancer cells. A great variety of mechanisms and signaling pathways are involved. Since VDR mediates most, if not all, 1,25(OH)2D3 actions, the control of VDR expression is a crucial aspect of 1,25(OH)2D3 biology. Here, the molecular mechanisms underlying the actions of 1,25(OH)2D3 are reviewed and the repression of the VDR gene by the transcription factor SNAIL in human colon cancer cells is discussed. Understanding these mechanisms may provide the basis for the potential use of this hormone and its non-hypercalcemic derivatives in the prevention and treatment of colon cancer.

Epidemiological and preclinical data indicate that vitamin D and its most active metabolite 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] have anticancer activity. Accordingly, clinical trials are under way using several nonhypercalcemic 1alpha,25(OH)(2)D(3) analogues against various neoplasms including colon cancer. 1alpha,25(OH)(2)D(3) induces proliferation arrest and epithelial differentiation of human SW480-ADH colon cancer cells. We examined the gene expression profiles associated with 1alpha,25(OH)(2)D(3) exposure using oligonucleotide microarrays. 1alpha,25(OH)(2)D(3) changed the expression levels of numerous previously unreported genes, including many involved in transcription, cell adhesion, DNA synthesis, apoptosis, redox status, and intracellular signaling. Most genes were up-regulated, and only a small fraction were down-regulated. Fourteen of 17 candidate genes studied were validated as 1alpha,25(OH)(2)D(3) target genes by Northern and Western blotting or immunocytochemistry. They included c-JUN, JUNB, JUND, FREAC-1/FoxF1, ZNF-44/KOX7, plectin, filamin, keratin-13, G(0)S2, and the putative tumor suppressors NES-1 and protease M. There was little overlap between genes regulated after short (4 h) or long (48 h) exposure. Gene regulatory effects of 1alpha,25(OH)(2)D(3) in SW480-ADH cells differed from those in LS-174T cells, which lack E-cadherin and do not differentiate in response to 1alpha,25(OH)(2)D(3). Data from this study reveal that 1alpha,25(OH)(2)D(3) causes a profound change in gene expression profiles and provide a mechanistic basis to the ongoing clinical studies using nonhypercalcemic vitamin D(3) derivatives for colon cancer prevention and treatment.