SUMOylation Is an Inhibitory Constraint that Regulates the Prion-like Aggregation and Activity of CPEB3

Protein synthesis is crucial for the maintenance of long-term-memory-related synaptic plasticity. The prion-like cytoplasmic polyadenylation element-binding protein 3 (CPEB3) regulates the translation of several mRNAs important for long-term synaptic plasticity in the hippocampus. Here, we provide evidence that the prion-like aggregation and activity of CPEB3 is controlled by SUMOylation. In the basal state, CPEB3 is a repressor and is soluble. Under these circumstances, CPEB3 is SUMOylated in hippocampal neurons both in vitro and in vivo. Following neuronal stimulation, CPEB3 is converted into an active form that promotes the translation of target mRNAs, and this is associated with a decrease of SUMOylation and an increase of aggregation. A chimeric CPEB3 protein fused to SUMO cannot form aggregates and cannot activate the translation of target mRNAs. These findings suggest a model whereby SUMO regulates translation of mRNAs and structural synaptic plasticity by modulating the aggregation of the prion-like protein CPEB3.