Supplemental Figure S2. EGF induces Snail in HT29 colon cancer cells. Cells were plated on collagen-coated 6 well plates in 10% serum. Twenty-four hrs later cells were deprived of serum and treated with vehicle (phosphate-buffered saline), 10 ng/ml EGF or 40 ng/ml TGFÎ². After 72 hrs cells were lysed and extracts probed for indicated proteins. Shown are blots representative of three independent platings.
ARTICLE ABSTRACTPurpose: We previously showed that EGF receptor (EGFR) promotes tumorigenesis in the azoxymethane/dextran sulfate sodium (AOM/DSS) model, whereas vitamin D suppresses tumorigenesis. EGFR–vitamin D receptor (VDR) interactions, however, are incompletely understood. Vitamin D inhibits the renin–angiotensin system (RAS), whereas RAS can activate EGFR. We aimed to elucidate EGFR–VDR cross-talk in colorectal carcinogenesis.Experimental Design: To examine VDR–RAS interactions, we treated Vdr+/+ and Vdr−/− mice with AOM/DSS. Effects of VDR on RAS and EGFR were examined by Western blotting, immunostaining, and real-time PCR. We also examined the effect of vitamin D3 on colonic RAS in Vdr+/+ mice. EGFR regulation of VDR was examined in hypomorphic EgfrWaved2 (Wa2) and Egfrwild-type mice. Angiotensin II (Ang II)–induced EGFR activation was studied in cell culture.Results:Vdr deletion significantly increased tumorigenesis, activated EGFR and β-catenin signaling, and increased colonic RAS components, including renin and angiotensin II. Dietary VD3 supplementation suppressed colonic renin. Renin was increased in human colon cancers. In studies in vitro, Ang II activated EGFR and stimulated colon cancer cell proliferation by an EGFR-mediated mechanism. Ang II also activated macrophages and colonic fibroblasts. Compared with tumors from EgfrWaved2 mice, tumors from Egfrwild-type mice showed upregulated Snail1, a suppressor of VDR, and downregulated VDR.Conclusions: VDR suppresses the colonic RAS cascade, limits EGFR signals, and inhibits colitis-associated tumorigenesis, whereas EGFR increases Snail1 and downregulates VDR in colonic tumors. Taken together, these results uncover a RAS-dependent mechanism mediating EGFR and VDR cross-talk in colon cancer. Clin Cancer Res; 20(22); 5848–59. ©2014 AACR.