Regulation of Necroptosis and inflammation

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Abstract The term programmed necrosis or necroptosis has been used to distinguish several types of cell death such as apoptosis, autophagy, and pyroptosis. Necroptosis has been linked to inflammation response and diseases, which is a contributing factor for tumor initiation and progression. The protein kinase RIP1 and RIP3 are critical for the activation of necroptosis. Many studies have shown a complex functional interplay between RIP1 and RIP3 in regulating necrosome formation and necroptosis. Misregulation of this pathway would trigger abnormal tissue homeostasis, inflammation response, and caner initiation or progression. For example, abnormal RIP3-induced necroptosis in intestinal epithelium cause inflammatory bowel disease, which is linked to the development of colorectal cancer. Although RIP3 is a crucial kinase in necroptosis, how RIP3 is regulated in cells is not clear. We recently found that Parkin regulates RIP3 during necroptosis. Parkin is an E3 ubiquitin ligase that is encoded by the PARK2 gene. Mutation in the PARK2 gene is the most frequent cause of autosomal recessive early onset of Parkinson's Disease (PD). Emerging evidence suggests that Parkin also functions as a tumor suppressor, although how Parkin functions as a tumor suppressor remains unclear. Recently, we found that Parkin is a negative regulator of necroptosis and inflammation. Parkin promotes RIP3 ubiquitination, inhibits RIP3 phosphorylation, necrosome formation, and necroptosis in various cells. Conversely, deletion of the Parkin gene results in increased necroptosis. Importantly, deletion of the Park2 gene promotes inflammation and hyperplasia in vivo. Interestingly, we also found that Parkin itself is regulated by AMP-activated protein kinase (AMPK). Based on these preliminary results, we hypothesize that the AMPK-Parkin pathway is an important negative regulator of RIP3 by promoting RIP3 ubiquitination and inactivation. Further, the AMPK-Parkin-RIP3 pathway suppresses inflammation-induced tumorigenesis. To test this hypothesis, we propose the following Specific Aims: 1. To study the role of Parkin in RIP3 regulation and necroptosis; 2. To study the regulation of Parkin by AMPK; 3. To study the role of Parkin in inflammation and cancer. These studies will reveal a novel role of Parkin in the regulation of RIP3, necroptosis, and inflammation. In addition, a new mechanism by which Parkin functions as a tumor suppressor will be revealed. Accordingly, these studies will have a high impact for cancer pathogenesis and future cancer prevention. !