Abstract A16: Smad4 pathways modulate induction of the chemokine Ccl20 and repress inflammation-induced carcinogenesis in mouse colon

Abstract

Abstract Inflammation regulates many aspects of gut homeostasis but is also a key component of colon cancer progression. While TGFβ signaling is known to regulate inflammatory responses within immune cells, we have uncovered a novel regulatory pathway in which TGFβ and BMP signaling suppress responses to inflammatory stimuli within the colonic epithelium. Using mice with conditional deletion of Smad4 in intestinal epithelium, we found that CCL20 expression was increased with Smad4 loss. Similarly, in murine immortalized colonocytes and human colon cancer cell lines, blocking TGFβ and/or BMP receptors increased CCL20 expression. CCL20 is upregulated in response to inflammatory signals such as TNF and IL-1β. CCL20 is also upregulated in colon cancer but the mechanism is not understood. We found that pre-treatment of colonocytes or colon cancer cells with TGFβ1 and BMP2 completely suppressed TNF- or IL-1β-induced CCL20 expression at the level of gene transcription. By chromatin immunoprecipitation, we found that TGFβ1/BMP2 treatment impaired binding of NFκB and phospho-STAT3 to the CCL20 promoter. To understand the significance of this regulation in chronic inflammation, we subjected Smad4 deleted and control mice to three rounds of dextran sodium sulfate (DSS)-mediated damage to the distal colon. We found that loss of Smad4 in mouse colonic epithelium was sufficient to induce tumorigenesis following damage-induced inflammation. Following DSS-mediated damage, Smad4-null epithelium developed invasive colorectal adenocarcinoma within two months of DSS treatment while Smad4+ control mice never develop tumors following DSS exposure. The Smad4 null tumors were histologically similar to those of human colitis-associated colon cancers. Prior to tumor formation, we saw an increase in CD8+ cells in Smad4-deleted colons, suggesting that tumor progression involves bidirectional crosstalk between the epithelium and immune cells and that this crosstalk is regulated in part by Smad4-mediated signaling within the epithelium. SMAD4, TGFβ receptors, or BMP receptors are often mutated in colon cancer. This loss of TGFβ and/or BMP signaling likely facilitates epithelial-immune cell crosstalk in colitis-associated colon cancers. Citation Format: Anna L. Means, Tanner J. Freeman, Connie J. Weaver, Chanjuan Shi, Mary K. Washington, Bronson C. Wessinger, Tasia Brown, David K. Flaherty, Kevin P. Weller, Robert J. Coffey, Keith T. Wilson, Robert D. Beauchamp. Smad4 pathways modulate induction of the chemokine Ccl20 and repress inflammation-induced carcinogenesis in mouse colon. [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 A16.