Abstract A03: Determining the role of Vitamin D Receptor (VDR) and Retinoid X Receptor Alpha (RXRα) in colitis
Authors: April B. Cabang, Jay L. Morris, Michael J. Wargovich
Journal: Cancer Research (2017)

Abstract Inflammatory bowel disease (IBD), encompassing both ulcerative colitis and Crohn's disease, is a high risk factor for colorectal cancer (CRC). It is a lifelong inflammation-driven disorder with a poorly defined etiology contributing to limitations in available treatment options. A north to south gradient is associated with IBD incidence rate and recurrence, implicating low vitamin D level as a risk factor. Colitis and CRC patients have reduced VDR expression indicating VDR impairment in the etiology of colitis and its progression to CRC. VDR and RXRα heterodimerization is required to regulate inflammation and proliferation. Our group has shown that RXRα is also diminished in tumors from CRC patients. These led us to ask how an inflammatory microenvironment induces VDR/RXRα silencing. We hypothesize that in an inflammatory microenvironment promoter methylation drives VDR/RXRα silencing in chronic colitis and colitis-associated cancer (CAC), resulting in dysregulated proliferation and chronic inflammatory setting. Using dextran sodium sulfate (DSS) mouse models of colitis, we induced intestinal inflammation in mice with (1) fully functional VDR and RXRα and in mice that are (2) genetically haploinsufficient either in VDR or RXRα. At termination, we measured intestinal permeability using fluorescein isothiocyanate-labeled dextran and profiled serum cytokine/chemokine concentration using the Bio-Plex Pro mouse cytokine 23-plex assay kit (Bio-Rad, CA). Colon swiss rolls were made for histopathological evaluation and immunohistochemistry. To determine the ability of a pro-inflammatory cytokine elevated in colitis in promoting aberrant proliferation, we treated colon cancer cell lines (SW480 and LOVO) with Interleukin-6 (IL6). We monitored cell proliferation with the Incucyte Zoom System (Essen BioScience, MI). In this study, we report that (1) loss of VDR and RXRα elicits a pro-inflammatory chemokine/cytokine signature that exacerbates disease in DSS mouse model of colitis in part by increasing intestinal permeability and (2) IL6 promotes proliferation of colon cancer cells, suggesting that sustained IL6 exposure of epithelial cells in an inflamed colon can potentially drive tumorigenesis. We are currently investigating the epigenetic mechanisms of VDR and RXRα suppression. By understanding mechanisms underlying silencing of key inflammatory regulators, this project in the long-term can (1) contribute to target(s) identification for IBD and CAC prevention/therapy and (2) provide more evidence for the use epigenetic modulators (alone or in combination with standard Rx) for IBD, colon cancer, and other inflammation-driven diseases to overcome non-responsiveness to current therapies. Inflammatory bowel disease (IBD), encompassing both ulcerative colitis and Crohn's disease, is a high risk factor for colorectal cancer (CRC). It is a lifelong inflammation-driven disorder with a poorly defined etiology contributing to limitations in available treatment options. A north to south gradient is associated with IBD incidence rate and recurrence, implicating low vitamin D level as a risk factor. Colitis and CRC patients have reduced VDR expression indicating VDR impairment in the etiology of colitis and its progression to CRC. VDR and RXRα heterodimerization is required to regulate inflammation and proliferation. Our group has shown that RXRα is also diminished in tumors from CRC patients. These led us to ask how an inflammatory microenvironment induces VDR/RXRα silencing. We hypothesize that in an inflammatory microenvironment promoter methylation drives VDR/RXRα silencing in chronic colitis and colitis-associated cancer (CAC), resulting in dysregulated proliferation and chronic inflammatory setting. Using dextran sodium sulfate (DSS) mouse models of colitis, we induced intestinal inflammation in mice with (1) fully functional VDR and RXRα and in mice that are (2) genetically haploinsufficient either in VDR or RXRα. At termination, we measured intestinal permeability using fluorescein isothiocyanate-labeled dextran and profiled serum cytokine/chemokine concentration using the Bio-Plex Pro mouse cytokine 23-plex assay kit (Bio-Rad, CA). Colon swiss rolls were made for histopathological evaluation and immunohistochemistry. To determine the ability of a pro-inflammatory cytokine elevated in colitis in promoting aberrant proliferation, we treated colon cancer cell lines (SW480 and LOVO) with Interleukin-6 (IL6). We monitored cell proliferation with the Incucyte Zoom System (Essen BioScience, MI). In this study, we report that (1) loss of VDR and RXRα elicits a pro-inflammatory chemokine/cytokine signature that exacerbates disease in DSS mouse model of colitis in part by increasing intestinal permeability and (2) IL6 promotes proliferation of colon cancer cells, suggesting that sustained IL6 exposure of epithelial cells in an inflamed colon can potentially drive tumorigenesis. We are currently investigating the epigenetic mechanisms of VDR and RXRα suppression. By understanding mechanisms underlying silencing of key inflammatory regulators, this project in the long-term can (1) contribute to target(s) identification for IBD and CAC prevention/therapy and (2) provide more evidence for the use epigenetic modulators (alone or in combination with standard Rx) for IBD, colon cancer, and other inflammation-driven diseases to overcome non-responsiveness to current therapies. Citation Format: April B. Cabang, Jay L. Morris, Michael J. Wargovich. Determining the role of Vitamin D Receptor (VDR) and Retinoid X Receptor Alpha (RXRα) in colitis. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr A03.