There is compelling evidence that colorectal carcinogenesis is promoted by a combination of microbiota-dependent and host-dependent mechanisms that trigger epithelial cell inflammatory signaling. This is particularly true in colitis-associated cancer (CAC) with longstanding ulcerative colitis (UC) predisposing to CAC. Most prior studies have focused on the activation aspect of inflammatory regulation, but the mechanisms involved in extinguishing the inflammatory response are less well understood and this represents a major gap in scientific knowledge. The Beauchamp lab has discovered that TGFb signaling via SMAD4 has a central inhibitory role in colon epithelial cell inflammatory signaling beyond its well-known roles in regulation of lymphoid and myeloid cell immune response. Furthermore, after DSS-induced colitis, 70% of the mice with adult-onset deletion of the Smad4 gene in intestinal epithelium developed invasive carcinomas of the distal colon that are morphologically similar to those seen in human CACs, compared to no tumors in control mice. A key chemokine we found to be regulated by the SMAD4 pathway is CCL20. The role of CCL20 in immune response is complex with both pro-inflammatory and anti-inflammatory functions. In humans, CCL20 is upregulated in both UC and Crohn?s Disease. Furthermore, CCL20 is elevated in adenomas and colorectal cancers (CRC), suggesting that it may influence cancer susceptibility. Based on these preliminary observations, my central hypothesis is that SMAD4 functions as an immune-modulator in colonic epithelial cells through inhibition of pro-inflammatory chemokine and cytokine production; and loss of SMAD4 results in altered immune cell infiltration and tumorigenesis, and these alterations are partially dependent on the CCL20/CCR6 axis.
The first aim of this study is to determine the immune-modulating effects of SMAD4 in colonic epithelial cells using immunohistochemistry, flow cytometry, cell sorting, and single cell RNA-sequencing.
The second aim i s to determine the requirement for CCL20 signaling through the CCR6 receptor in the inflammatory response and tumorigenesis regulated by SMAD4 in colonic epithelium. This will be examined by combining bi- allelic loss of CCR6 and conditional intestinal loss of Smad4. This work will uncover novel mechanisms regulating inflammation in the colon and identify key cell-cell interactions that could be targeted to abrogate pathologic inflammation and its resulting diseases including inflammatory bowel disease and CAC. I have enrolled in Vanderbilt?s Cancer Biology Ph.D. program. The experiments described in this application will serve as the substance for my graduate dissertation and the mentoring committee outlined will serve as my thesis committee following completion of my qualifying exam in January 2019. All experiments will be conducted under the mentorship of distinguished surgeon-scientist, Dr. R. Daniel Beauchamp, with the additional assistance of Vanderbilt University collaborators who are leaders in their respective fields. !
Chronic inflammation is a major cause of cancer. This is particularly true of colitis-associated cancers, with longstanding ulcerative colitis predisposing to colon cancer. These experiments will focus on identifying novel mechanisms and cell-cell interactions that are responsible for the development of colitis-associated cancers that may be exploited as therapeutic targets to treat inflammatory bowel disease and prevent it?s associated malignant transformation.
