The deubiquitinating enzyme USP46 regulates AMPA receptor ubiquitination and trafficking

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPARs) are the primary mediators for inter-neuronal communication and play a crucial role in higher brain functions including learning and memory. Our previous work demonstrated that AMPARs are subject to ubiquitination by the E3 ligase Nedd4, resulting in EPS15-mediated receptor internalization and Ubiquitin (Ub)-proteasome pathway (UPP)-dependent degradation. Protein ubiquitination is a highly dynamic and reversible process, achieved via the balance between ubiquitination and deubiquitination. However, deubiquitination of mammalian AMPARs and the responsible deubiquitinating enzymes remain elusive. In this study, we identify USP46 as the deubiquitinating enzyme for AMPARs. We find that AMPARs are subject to K63 type ubiquitination, and USP46 is able to deubiquitinate AMPARs in vivo and in vitro. In heterologous cells and neurons, expression of USP46 results in a significant reduction in AMPAR ubiquitination, accompanied by a reduced rate in AMPAR degradation and an increase in surface AMPAR accumulation. By contrast, knockdown of USP46 by RNAi leads to elevated AMPAR ubiquitination and a reduction in surface AMPARs at synapses in neurons. Consistently, miniature excitatory postsynaptic currents recordings show reduced synaptic strength in neurons expressing USP46-selective RNAi. These results demonstrate USP46-mediated regulation of AMPAR ubiquitination and turnover, which may play an important role in synaptic plasticity and brain function.