LAUSR

A20 is an anti-inflammatory protein with a dual ubiquitin-editing activity. Through its N-terminal ovarian tumor (OTU) domain, A20 negatively regulates NF-ĸB by removing the K63-linked ubiquitin chains on RIP1 that act as platforms for NF-ĸB activation downstream of tumor necrosis factor alpha (TNFα). On the other hand, A20 also catalyzes the addition of K48-linked ubiquitin chains on RIP1 via its C-terminal zinc finger domain 4 (ZnF4) to promote its proteasomal degradation. Through both mechanisms, A20 is a means of negative feedback on TNFα-induced NF-ĸB activity. Importantly, inactivation of A20 is frequently found in B-cell lymphomas, where loss-of-function A20 truncations promote cell proliferation and upregulation of NF-ĸB signaling. Among the post-translational modifications (PTMs) reported in A20, there are several phosphorylation events in its C-terminus, including within the ZnF4 domain. Besides its known E3 ubiquitin ligase activity, previous reports show that the C-terminal region of A20 is important for ubiquitin binding, having preference for K63-linked poly-ubiquitin. However, a little is known about the effects of phosphorylation at this region on A20 activity as well as its consequences in downstream signaling. Our current work suggests that phosphorylation in the C-terminus of A20 inhibits its E3 ubiquitin ligase activity and disrupts its interaction with ubiquitin, which may also affect its deubiquitinase activity by preventing its recruitment to ubiquitinated proteins in the TNFα receptor (TNFR) complex. We also propose that the C-terminal region is important for the formation of the A20 ubiquitin-editing complex, necessary to downregulate NF-ĸB-activated inflammatory signals. Based on these observations, we hypothesize that not only gene-inactivating mutations, but also post-translational mechanisms, such as phosphorylation, inhibit A20 to promote cancer development. Our research is now focused on understanding the upstream signaling that regulates A20 phosphorylation. Citation Format: Tania Lopez Palacios, Tsz-Yin Chan, Christina Egbert, Jacob Truman, Spencer Ashworth, Alec Vaughan, Joshua L. Andersen. The regulation of inflammatory signaling in cancer via A20 phosphorylation. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5028.