Analysis of CPEB Family Protein Member CPEB4 Function in Mammalian Neurons: A Dissertation

Abstract

Local protein synthesis is required for long-term memory formation in the brain. One protein family, Cytoplasmic Polyadenylation Element binding Protein (CPEB) that regulates protein synthesis is found to be important for long-term memory formation possibly through regulating local protein synthesis in neurons. The well-studied member of this family, CPEB1, mediates both translational repression and activation of its target mRNAs by regulating mRNA polyadenylation. Mouse with CPEB1 KO shows defect in memory extinction but not long-term memory formation. Three more CPEB1 homologs (CPEB2-4) are identified in mammalian system. To test if CPEB2-4 may have redundant role in replacing CPEB1 in mediating local protein synthesis, the RNA binding specificity of these homologs are studied by SELEX. The result shows CPEB2-4 bind to RNAs with consensus sequence that is distinct from CPE, the binding site of CPEB1. This distinction RNA binding specificity between CPEB1 and CPEB2-4 suggests CPEB2-4 cannot replace CPEB1 in mediating local protein synthesis. For CPEB2-4 have distinct RNA binding specificity compared to CPEB1, they are referred as CPEB-like proteins. One of CPEB-like protein, CPEB3, binds GluR2 mRNA and represses its translation. The subcellular localization of CPEB family proteins during glutamate over stimulation is also studied. The CPEB family proteins are identified as nucleus/cytoplasm shuttling proteins that depend on CRM1 for nuclear export. CPEB-like proteins share similar nuclear export ciselement that is not present in CPEB1. Over-stimulation of neuron by glutamate induces the nuclear accumulation of CPEB family proteins possibly through disrupted nuclear export. This nuclear accumulation of CPEB family protein is induced by imbalance of calcium metabolism in the neurons. Biochemical and cytological results suggest CPEB4 protein is associated with ER membrane peripherally in RNA independent manner. This research provides general description of biochemical, cytological properties of CPEB family proteins.