Abstract 3269: Ezrin binds to DEAD-box RNA helicase DDX3 and regulates its function and protein level

Abstract

Abstract Ezrin is a member of the ezrin-radixin-moesin (ERM) family of actin-membrane linker proteins that play key roles in regulating cell shape, movement, adhesion and signal transduction pathways. The expression of ezrin is linked to the metastatic progression in several cancers including osteosarcoma (OS). We discovered a small molecule, NSC305787, that inhibits ezrin activity and metastatic phenotype both in vitro and in vivo. We hypothesized that the anti-metastatic effects of NSC308787 could be mediated through preventing specific protein-protein interactions involving ezrin. In this study, we used affinity pull-down coupled with mass spectrometry-based proteomic approach to unravel putative ezrin interactors that are competed away by NSC305787. We identified a number of candidate ezrin binding proteins that are associated with metastatic behavior and implicated in the regulation of stress granule dynamics and protein translation initiation. We selected DDX3, a DEAD-box RNA helicase, as a candidate for further analysis. We confirmed that ezrin directly binds to DDX3. Depletion of ezrin protein expression by RNA interference in several cancer cell lines resulted in substantial reduction in DDX3 protein levels without affecting its transcription, which suggested that ezrin is required for post-transcriptional maintenance of DDX3 in the cell. Paradoxically, recombinant ezrin specifically inhibited the RNA duplex unwinding activity and stimulated the ATPase activity of DDX3. Our data suggest that ezrin regulates the translation of mRNAs with 5′ secondary structure through DDX3, at least in part, through maintaining its intracellular protein level and/or modulating its unwinding and ATPase activities. Therefore, our findings suggest that a novel function of ezrin regarding the regulation of mRNA translation exists that is independent from its classical role as a cytoskeletal cross-linker protein at the plasma membrane. Citation Format: Haydar Celik, Kamal P. Sajwan, Amrita V. Pai, Ben J. Marsh, Yasemin Saygideger Kont, Said Rahim, Jenny Han, Tsion Minas, Jeffrey A. Toretsky, Aykut Uren. Ezrin binds to DEAD-box RNA helicase DDX3 and regulates its function and protein level. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3269. doi:10.1158/1538-7445.AM2015-3269