SUMMARY Intestinal epithelial cells (IECs) play an important role as barrier and as cellular factories in charge of absorbing and processing dietary nutrients, as well as the secretion of defense molecules and the orchestration of immune responses. Alterations in the normal function of IECs contribute to pathologies like inflammatory bowel diseases (IBD). Importantly, patients with IBD are at an increased risk for colorectal cancer (CRC), which is one of the most prevalent neoplasias among the US population. Recent studies have shown the critical role of Paneth cell dysfunction in controlling IEC survival and the etiopathogeneis of intestinal inflammation. Therefore, understanding how different signaling cascades control intestinal homeostasis is a fundamental question in biology with potential therapeutic implications for IBD and CRC. We will address these questions in the context of PKCλ/ι. Our preliminary data demonstrate that the selective inactivation of PKCλ/ι in IECs results in the loss of Paneth cells, which provokes the break of the intestinal barrier, dysbiosis, intestinal inflammation and increased tumorigenesis. Importantly, PKCλ/ι expression decreases with progression in CD and it predicts poor survival in CRC. Of note, this Paneth cell defect is associated with increased crypt apoptosis, JNK activity and autophagy in PKCλ/ι-deficient IECs. Our hypothesis is that PKCλ/ι is an essential regulator of autophagy and cell death in intestinal cell homeostasis and inflammation-driven tumorigenesis. In this proposal we will address the following fundamental questions: (1) What is the role in vivo of JNK activation by PKCλ/ι deficiency in increased apoptosis of IECs and intestinal inflammation and tumorigenesis? (2) What are the mechanisms whereby PKCλ/ι inhibits JNK activity? (3) Is enhanced autophagy in PKCλ/ι-deficient IECs a survival mechanism in vivo to antagonize the increased JNK and apoptosis promoted by the loss of PKCλ/ι and to prevent intestinal inflammation and tumorigenesis? (4) What are the mechanisms whereby PKCλ/ι represses autophagy? Questions 1 and 2 will be answered by the experiments described in Aim 1; and questions 3 and 4 will be answered by the experiments described in Aim 2. This proposal will unveil a new paradigm whereby PKCλ/ι controls IEC apoptosis and autophagy and their role in intestinal homeostasis and inflammation-driven tumorigenesis, opening possibilities for new therapies.