Abstract 3854: Antizyme inhibitor editing modulates nuclear localization but not antizyme binding: Implications for prostate cancer

Abstract

Abstract The endogenous antizyme inhibitor (AZIN) binds to, and is a key regulator of, the cell cycle suppressor antizyme. Antizyme itself is a key regulator of ornithine decarboxylase (ODC), the rate-limiting enzyme in the polyamine synthesis. We have measured the expression and localization of AZIN in 202 prostate cancer specimens, along with 26 adjacent benign samples, and found that nuclear localization of AZIN is dramatically associated with worse outcome. Upregulation and nuclear localization of AZIN have been observed in several cancers, as has editing of the AZIN1 mRNA. Other have hypothesized that the RNA- edited AZIN (edAZIN) may have an increased affinity to antizyme and that could explain the association of edAZIN to the various cancers. We have studied the mechanism behind the nuclear localization of AZIN and found the single base pair substitution caused by RNA editing is sufficient to result in nuclear localization of the protein in all cell types tested. To determine if the nuclear localization might result from increased antizyme-edAZIN affinity, we developed fluorescent protein FRET sensor for protein-protein interaction using Clover-AZIN and antizyme-mRuby2 fusion proteins. Unexpectedly, we found that the editing event decreases edAZIN affinity for antizyme, notwithstanding increased interaction in vivo. Thus, the data indicate that the change in protein localization to the nucleus may be more important to oncogenic function than the actual degree of binding to antizyme. Other functional differences between edAZIN and AZIN might be explained by altered kinetics of binding, by the contribution of an additional adapter protein that modulates the intracellular antizyme:AZIN complex, or by competition for AZIN binding by other partners whose interaction is affected by the editing event. Therefore, we plan to identify AZIN and edAZIN interacting proteins by using proteomic analysis and later study the interaction between AZIN or edAZIN with their binding partners in more detail. Furthermore, our validated FRET assays can be used to identify antagonists of AZIN-antizyme binding (no antagonists are currently known). Given the important role of AZIN in tumor growth, discovery of small-molecule inhibitors of AZIN should lead to antitumor therapies. Citation Format: James M. Rice, Aram Ghalali, Liangzhe Wang, Amanda Kusztos, Finith Jernigan, Chin Lee Wu, Bruce Zetter, Michael S. Rogers. Antizyme inhibitor editing modulates nuclear localization but not antizyme binding: Implications for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3854.