Abstract P33: Novel Reporter Cell Models for Efficient Interrogation of Helicase Activity in Cancer-associated DDX3X Mutations

Abstract DDX3X is an ATP-dependent RNA helicase involved in diverse cellular processes. Somatic mutations in the DDX3X gene exhibit oncogenic or tumor suppressive activities depending on cancer types. However, helicase modulating roles of specific DDX3X mutations remain elusive mainly due to lack of an appropriate cell culture model system. Here, we report our development of novel transgenic cell lines capable of interrogating DDX3X helicase activity. To evaluate the helicase activity of the DDX3X mutations in question, we designed a reporter plasmid that measures the luciferase signal corresponding to the helicase activity. Using 8 different point mutations in the DDX3X that we identified earlier in relapsed/refractory patients with diffuse large B cell lymphoma (DLBCL), we show that these DDX3X mutants displayed defective helicase activity. DDX3X mutant knock-in DLBCL cells also displayed abolished helicase unwinding capabilities, validating our reporter cell models. We were able to extend the application of our reporter cells to interrogate Y chromosome-linked male paralog DDX3Y. In male lymphoma patients, ectopic DDX3Y expression can compensate for DDX3X loss to restore global protein synthesis. We narrowed down DDX3Y helicase and ATPase domains to be critical for cellular translation, ruling out DDX3Y involvement in ribosomal elongation. Unexpectedly, DDX3Y helicase is less efficient in RNA unwinding as compared to DDX3X revealing subtle differences despite having a high level of homology. The developed DDX3X reporter cells can be applied widely to evaluate the effects of DDX3X mutations in diseases as well as study the biology of DDX3X and DDX3Y. Citation Format: Zhi Sheng Poh, James Tan Chia Wei, Brandon Han Siang Wong, Kottaiswamy Amuthavalli, Suat Hoon Tan, Nicholas Francis Grigoropoulos, Navin Kumar Verma. Novel Reporter Cell Models for Efficient Interrogation of Helicase Activity in Cancer-associated DDX3X Mutations abstract. In: Proceedings of Frontiers in Cancer Science; 2023 Nov 6-8; Singapore. Philadelphia (PA): AACR; Cancer Res 2024;84 (8Suppl): Abstract nr P33.