Vitamin D receptor ligands, adenomatous polyposis coli, and the vitamin D receptor FokI polymorphism collectively modulate β‐catenin activity in colon cancer cells

Abstract

The activity of β-catenin, commonly dysregulated in human colon cancers, is inhibited by the vitamin D receptor (VDR), and this mechanism is postulated to explain the putative anti-cancer activity of vitamin D metabolites in the colon. We investigated the effect of a common FokI restriction site polymorphism (F/f) in the human VDR gene as well as the effect of antitumorigenic 1,25-dihydroxyvitamin D 3 (1,25D) and pro-tumorigenic lithocholic acid (LCA) VDR ligands on β-catenin transcriptional activity. Furthermore, the influence of a major regulatory protein of β-catenin, the APC tumor suppressor gene, on VDR-dependent inhibition of β-catenin activity was examined. We report herein that β-catenin-mediated transcription is most effectively suppressed by the VDR FokI variant F/M4 when 1,25D is limiting. Using Caco-2 colorectal cancer cells, it was observed that VDR ligands, 1,25D and LCA, both suppress β-catenin transcriptional activity, though 1,25D exhibited significantly greater inhibition. Moreover, 1,25D, but not LCA, suppressed endogenous expression of the β-catenin target gene DKK-4 independent of VDR DNA-binding activity. These results support β-catenin sequestration away from endogenous gene targets by 1,25D-VDR. This activity is most efficiently mediated by the FokI gene variant F/M4, a VDR allele previously associated with protection against colorectal cancer. Interestingly, we found the inhibition of β-catenin activity by 1,25D-VDR was significantly enhanced by wildtype APC. These results reveal a previously unrecognized role for 1,25D-VDR in APC/β-catenin cross-talk. Collectively, these findings strengthen evidence favoring a direct effect on the Wnt-signaling molecule β-catenin as one anti-cancer target of 1,25D-VDR action in the colorectum.

Vitamin D and colon cancer

“…First, it rapidly increases the amount of VDR bound to b-catenin, thus reducing the interaction between b-catenin and the transcription factors of the TCF/LEF family and leading to the repression of its target genes (Pálmer et al 2001). Shah et al (2006) confirmed the VDR/b-catenin interaction and characterised the protein domains involved, while Egan et al (2010) reported that wildtype APC enhances the inhibition of b-catenin/TCF transcriptional activity by 1,25(OH) 2 D 3 . Second, 1,25(OH) 2 D 3 induces b-catenin nuclear export linked to E-cadherin accumulation at the plasma membrane adherens junctions (Pálmer et al 2001).…”

Vitamin D and Wnt/β-Catenin Signaling

“…Notably, 1,25(OH) 2 D 3 inhibits DKK-4 expression in human colorectal (SW480-ADH, Caco-2) and breast (MCF-7, MDA-MB-468, MDA-MB-453) cancer cell lines [81,99]. The mechanism of DKK-4 repression is unclear.…”

“…In these cells different b-catenin transcriptional complexes distinctly modulate the activation of the OPN/Osteopontin gene promoter by ligand-activated VDR: b-catenin/LEF1 enhances the activation while b-catenin/TCF4 diminishes it. Recently, Egan et al [81] have reported that the inhibition of the transcriptional activity of b-catenin/TCF complexes by 1,25(OH) 2 D 3 in colon cancer cells is enhanced by wildtype APC. In addition, these authors have shown that the VDR ligand lithocolic acid also inhibits b-catenin transcriptional activity but to a lesser extent than 1,25 (OH) 2 D 3 and concordantly it is also less effective than 1,25(OH) 2 D 3 in promoting VDR binding to b-catenin.…”

“…The mechanism of DKK-4 repression is unclear. While in SW480-ADH cells a direct transcriptional repression mediated by VDR binding to the promoter is found [99], in Caco-2 cells a mutant VDR deficient in DNA binding mediates similar repression of DKK-4 to wild-type VDR [81]. In SW480-ADH cells, 1,25(OH) 2 D 3 promotes the binding of VDR and also of the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor to a consensus sequence adjacent to the transcription initiation site and the abrogation of histone H4 acetylation.…”

Lack of Associations between Vitamin D Metabolism-Related Gene Variants and Risk of Colorectal Cancer

“…Furthermore, vitamin D reduces expression of multiple antiapoptotic proteins and promotes induction of apoptosis (Guzey et al, 2002). Vitamin D/vitamin D receptor (VDR) complex inhibits the activity of β-catenin (Palmer et al, 2001;Egan et al, 2010) and 1, 25-dihydroxyvitamin D [1, 25(OH)2 D] has a possible role in β-catenin/APC cross talk (Egan et al, 2010). Vitamin D 25-hydroxylase (CYP2R1) is Recently, significant associations between CYP2R1 gene polymorphisms and circulating levels of 25(OH) D have been found (Bu at al., 2010).…”