FXR silencing in human colon cancer by DNA methylation and KRAS signaling

Abstract

Farnesoid X receptor (FXR) is a bile acid nuclear receptor described through mouse knockout studies as a tumor suppressor for the development of colon adenocarcinomas. This study investigates the regulation of FXR in the development of human colon cancer. We used immunohistochemistry of FXR in normal tissue ( n = 238), polyps ( n = 32), and adenocarcinomas, staged I–IV ( n = 43, 39, 68, and 9), of the colon; RT-quantitative PCR, reverse-phase protein array, and Western blot analysis in 15 colon cancer cell lines; NR1H4 promoter methylation and mRNA expression in colon cancer samples from The Cancer Genome Atlas; DNA methyltransferase inhibition; methyl-DNA immunoprecipitation (MeDIP); bisulfite sequencing; and V-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) knockdown assessment to investigate FXR regulation in colon cancer development. Immunohistochemistry and quantitative RT-PCR revealed that expression and function of FXR was reduced in precancerous lesions and silenced in a majority of stage I-IV tumors. FXR expression negatively correlated with phosphatidylinositol-4, 5-bisphosphate 3 kinase signaling and the epithelial-to-mesenchymal transition. The NR1H4 promoter is methylated in ∼12% colon cancer The Cancer Genome Atlas samples, and methylation patterns segregate with tumor subtypes. Inhibition of DNA methylation and KRAS silencing both increased FXR expression. FXR expression is decreased early in human colon cancer progression, and both DNA methylation and KRAS signaling may be contributing factors to FXR silencing. FXR potentially suppresses epithelial-to-mesenchymal transition and other oncogenic signaling cascades, and restoration of FXR activity, by blocking silencing mechanisms or increasing residual FXR activity, represents promising therapeutic options for the treatment of colon cancer.

Bile acids regulate intestinal cell proliferation by modulating EGFR and FXR signaling

“…In fact, FXR is often silenced in colon tumors in humans (5). Interestingly, FXR activation also plays an anti-inflammatory role in experimental models of IBD (69).…”

The farnesoid X receptor and colon cancer

“…In approximately, 12% of human colon cancers and in several colon cancer cell lines, including SW620, FXR promoter methylation of a CpG island results in very low FXR expression. [26] Cabrerizo et al [27] found FXR promoter methylation at two additional CpG islands (-358 and -1890 bp). Furthermore, functional analysis of the 5'-promoter region of the human FXR gene in HepG2 cells suggests that hepatic nuclear factor 1a may be a transcription factor for FXR.…”

“…[24] FXR can also be regulated at the transcriptional level by the caudal-related homeobox 2. [25] Moreover, Bailey et al [26] showed that DNA methylation and KRAS signaling silence FXR in human CRC. In approximately, 12% of human colon cancers and in several colon cancer cell lines, including SW620, FXR promoter methylation of a CpG island results in very low FXR expression.…”

FXR and liver carcinogenesis

“…In human HCC, elevated SIRT1 is correlated with the absence of FXR [65] . Recently, Bailey et al [21] reported that diminished FXR expression in human colon cancer was partly due to both DNA methylation of the FXR promoter and increased KRAS signaling. Therefore, activation of oncogenic pathways may also be responsible for the reduced expression of FXR in liver cancer.…”

“…Interest in the potential function of FXR in cancer surged thereafter. Compared with matched normal tissues, FXR expression is significantly reduced in human tumor specimens [21][22][23][24][25] , and the downregulation of FXR is associated with malignant clinicopathological characteristics [23,26] . Loss of FXR leads to early mortality and/or promotes intestinal carcinogenesis in the mice with either a mutated APC gene (APC min/+ ) or chronic colitis [26][27][28] .…”