Colorectal cancer has a high mortality because it is typically detected at a late stage when treatment options are limited. Chemoprevention is therefore an important therapeutic strategy, and for high-risk patients the development of new drugs is a high priority. The epithelial layer suppresses inflammation in the colon by separating luminal contents from underlying tissues. Increasing epithelial barrier function is an important approach to prevention because inflammation is central to both tumor initiation and progression. Several lines of evidence from independent laboratories indicate that cGMP signaling is tumor suppressive in the intestine and might be harnessed as part of a novel treatment paradigm. Our long-term goal is to prevent and treat colon cancer and associated gastrointestinal disease by exploiting cGMP-signaling in the colon epithelium. Our central hypothesis is that signaling through PKG2 is barrier protective, and that this pathway can be harnessed for colon cancer prevention. Our objectives are: (1) to gain detailed information about cGMP/PKG2 signaling in the colon epithelium, (2) to test the importance of PKG2 in barrier-protection and tumor suppression, (3) to determine whether activation of PKG2 signaling by PDE-5 inhibitors is chemopreventative in preclinical models of colon cancer. We will test our central hypothesis and thereby accomplish the objective of this project by completion of the following aims: Aim 1: Test the hypothesis that DUSP10 and Claudin-4 are key effectors of cGMP/PKG2 signaling in colon epithelial cells. Aim 2: Test the hypothesis that PKG2 is barrier-protective in the colon epithelium. Aim 3: Test the hypothesis that PKG2 is tumor-suppressive in the colon and that activation with clinically relevant PDE-5 inhibitors is an effective chemoprevention strategy. The experiments proposed will measure the effect of PKG2 signaling and it's activation by PDE-5 inhibitors on barrier function, inflammation, and tumorigenesis using Prkg2-/- mice and both DSS/AOM and ApcMin/+ mouse cancer models. Our expected outcomes include detailed information about: (1) PKG2-dependent signaling in the colon epithelium and how it controls barrier integrity and susceptibility to colitis and colon cancer, and (2) the utility of PKG2 activation using clinically relevant PDE-5 inhibitors as a colon cancer chemoprevention strategy. Our projects impact will be the identification of a novel barrier-protective signaling pathway in the colon epithelium, and demonstration that this pathway can be targeted for colon cancer chemoprevention using drugs already proven safe in humans.