Anti-proliferative protein Tob negatively regulates CPEB3 target by recruiting Caf1 deadenylase.

Tob is a member of the anti-proliferative protein family, which functions in transcription and mRNA decay. We have previously demonstrated that Tob is involved in the general mechanism of mRNA decay by mediating mRNA deadenylation through interaction with Caf1 and a general RNA-binding protein, PABPC1. Here, we focus on the role of Tob in the regulation of specific mRNA. We show that Tob binds directly to a sequence-specific RNA-binding protein, cytoplasmic polyadenylation element-binding protein 3 (CPEB3). CPEB3 negatively regulates the expression of a target by accelerating deadenylation and decay of its mRNA, which it achieves by tethering to the mRNA. The carboxyl-terminal RNA-binding domain of CPEB3 binds to the carboxyl-terminal unstructured region of Tob. Tob then binds Caf1 deadenylase and recruits it to CPEB3 to form a ternary complex. The CPEB3-accelerated deadenylation was abrogated by a dominant-negative mutant of either Caf1 or Tob. Together, these results indicate that Tob mediates the recruitment of Caf1 to the target of CPEB3 and elicits deadenylation and decay of the mRNA. Our results provide an explanation of how Tob regulates specific biological processes.