Plays a role in hippocampal-dependent synaptic plasticity, learning and memory. Involved in the formation of spines and functional synaptic contacts by modulating the translational activity of the cytoplasmic polyadenylation element-binding protein CPEB3. Promotes ubiquitination of CPEB3, and hence induces CPEB3-dependent mRNA translation activation of glutamate receptor GRIA1 and GRIA2. Can function as an E3 ubiquitin-protein ligase to activate monoubiquitination of JAG1 (in vitro), thereby regulating the Notch pathway. Acts as a tumor suppressor; inhibits malignant cell transformation of medulloblastoma (MB) cells by inhibiting the Notch signaling pathway.