Risk of colon cancer increases in mice with no Vitamin D receptor in colon

Abstract 5215: Vitamin D receptor regulates intestinal barriers in colon cancer

Yong-guo Zhang, Rong Lu, Danika Bakke, Yinglin Xia and Jun Sun

Cancer Res 2018;78(13 Suppl):Abstract nr 5215.

Proceedings: AACR Annual Meeting 2018; April 14-18, 2018; Chicago, IL, DOI: 10.1158/1538-7445.AM2018-5215

Background Vitamin D and Vitamin D receptor (VDR) play important roles in the development of colon cancer. Tight junction structures are essential in intestinal barrier integrity, inflammation, and cancer. The disruption of tight junctions is a common manifestation of various diseases including cancers. Claudin-5 is a tight junction protein that is expressed in epithelia and endothelia and form paracellular barriers and pores that determine permeability. It is downregulated in colon cancer. Although VDR and Claudin-5 are all involved in colon cancer, it remains unclear whether they are closely related or function independently.

Methods In the current study, we investigate the novel role of VDR in regulating Claudin-5, using whole body VDR knockout mice (VDR-/-) and intestinal epithelial VDR knockout mice (VDRΔIEC). In vitro, VDR-/- embryonic fibroblasts (MEF) cells, cultured human intestinal epithelial cells, organoids, and human colon cancer samples were used to determine the molecular mechanism.

Results In intestinal samples of colon cancer patients, VDR expression is low, whereas the expression of Claudin-5 is also decreased. In the colon of VDR-/- mice and VDRΔIEC mice, deletion of VDR led to lower claudin-5 at the protein and mRNA levels. This observation was also confirmed by immunostaining of Claudin-5. In VDR-/- MEF cells, both Western blot and real time PCR revealed that VDR deletion led to lower protein and mRNA levels of claudin-5 in cells without any treatment. Vitamin D3 is known to increase VDR expression and activate VDR signaling. Protein and mRNA levels of Claudin-5 were significantly elevated in mice, mouse organoids, and human intestinal epithelial SKCO15 cells treated with 1, 25 vitamin D3. In contrast, knockdown of Claudin-5 using siRNA did not change the expression level of VDR protein in human colonic epithelial cells. Our data suggest that the Claudin-5 gene is a downstream target of the VDR signaling pathway.

Conclusion Taken together, we show that VDR is important for the maintenance of physiological level of Claudin-5. This study also reveals a complex role for vitamin D/VDR regulation of intestinal barrier functions in colon cancer.