Abstract TGFβ and BMP signaling through receptor-mediated activation of SMAD proteins is crucial for normal homeostasis in intestinal epithelium. Alterations in this pathway contribute to the development of colorectal cancers. To understand the role of these pathways in homeostasis of the colon we conditionally deleted loxP-flanked alleles of Smad4 in adult mouse colon. We used Lrig1CreERT allele to achieve greater than 80% SMAD4 gene deletion and a CK19CreERT allele for mosaic deletion in colonic epithelium. Our data indicates that SMAD4 activity regulates multiple interactions between intestinal epithelium cells and surrounding stroma and that deletion of SMAD4 in adult mouse colonic epithelial cells alters expression of cytokines, increases immune cell infiltration and predisposes mice to tumorigenesis. Increases in the chemokine CCL20 have been reported in CRC tumors beginning at the adenoma stage and it may regulate both Tregs and Th-17 cells in an active immune response. Luminex cytokine/chemokine array analysis revealed increased levels of CCL20 protein in colonic mucosa and RNAseq data revealed that when SMAD4 is knocked out in the epithelium there is an upregulation of CCL20 and CCR6 (receptor) mRNA in the epithelium and stroma, respectively. To further explore the regulation of CCL20, we used immortalized mouse colonocytes (IMC cells) to further determine how the TGFβ and BMP signaling pathways may be involved in CCL20 expression. We found that CCL20 mRNA expression was suppressed by TGFβ1 and BMP2 and increased by inhibitors of these pathways. The inhibition of CCL20 by the TGFβ and BMP2 pathways occurs even in the presence of a known strong inducer of CCL20, such as TNFα. We have further observed in mice induced to undergo deletion of SMAD4 in the intestinal epithelium that treatment with DSS results in 100% of mice developing mucinous adenocarcinomas in the distal colon. We conclude that ligand-dependent Smad4-mediated signaling provides important negative homeostatic regulation of CCL20 expression in colonic epithelium. Loss of Smad4 results in increased CCL20 expression and we are currently testing the hypothesis that CCL20 overexpression contributes to the inflammation induced carcinogenesis in this mouse model. Citation Format: Tasia D. Brown, Anna Means, Tanner Freeman, Connie Weaver, Keith Wilson, R. Daniel Beauchamp. CCL20 regulation via TGFB /BMP signaling pathway in murine immortalized colonocytes and colonic epithelium. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4429.