TOB Proteins Repress Translation via the CCR4–NOT Deadenylase Complex Independent of Deadenylation

Transducer of ErbB2 (TOB) proteins have been shown to promote mRNA decay through interactions with the CCR4–NOT complex and poly(A)-binding protein (PABP). While their role in deadenylation-mediated mRNA degradation is well established, their potential function in translational control remains to be elucidated. Here, we employed an in vitro translation system combined with an RNA tethering strategy to examine the function of TOB1 and TOB2 in translation. Our results demonstrate that TOB1 and TOB2 act as repressors of translation initiation, independent of deadenylation. Notably, this translational repression selectively targets eIF4A-dependent translation, while translation driven by eIF4A-independent IRES elements remains unaffected. While the interaction between TOB proteins and PABP appears to be dispensable, as disruption of this interaction only partially reduces translational repression, the knockdown of CNOT1, the scaffold of the CCR4–NOT complex, substantially relieves this repression, highlighting its indispensable role in the mechanism. Collectively, our findings uncover a previously unrecognized function of TOB proteins as direct repressors of translation initiation, independent of mRNA decay, and highlight a specific reliance on eIF4A activity and CCR4–NOT complex integrity.