Dual targeting of DDX3 and eIF4A by the translation inhibitor rocaglamide A

The translation inhibitor rocaglamide A (RocA) has shown promising antitumor activity because it uniquely clamps eukaryotic initiation factor (eIF) 4A onto polypurine RNA for selective translational repression. As eIF4A has been speculated to be a unique target of RocA, alternative targets have not been investigated. Here, we reveal that DDX3 is another molecular target of RocA. Proximity-specific fluorescence labeling of an O-nitrobenzoxadiazole-conjugated derivative revealed that RocA binds to DDX3. RocA clamps the DDX3 protein onto polypurine RNA in an ATP-independent manner. Analysis of a de novo-assembled transcriptome from the plant Aglaia, a natural source of RocA, uncovered the amino acid critical for RocA binding. Moreover, ribosome profiling showed that because of the dominant-negative effect of RocA, high expression of eIF4A and DDX3 strengthens translational repression in cancer cells. This study indicates that sequence-selective clamping of DDX3 and eIF4A, and subsequent dominant-negative translational repression by RocA determine its tumor toxicity. [Display omitted] •RocA clamps DDX3 on polypurine sequences in an ATP-independent manner•Gln360 in DDX3 is a critical residue for RocA binding•RocA⋅DDX3 complex inhibits protein synthesis in a dominant-negative manner•eIF4A and DDX3 abundance correlates with RocA sensitivity in cancer cells Chen et al. demonstrated the translation inhibitor rocaglamide A (RocA) alternatively targets DDX3, in addition to eIF4A. As RocA converts DDX3 and eIF4A into dominant-negative translational repressors, the abundance of those proteins in cells is an indicator of RocA sensitivity.