RNA editing at Arg607 controls AMPA receptor exit from the endoplasmic reticulum

AMPA-receptor (AMPAR) transport to synapses plays a critical role in the modulation of synaptic strength. We show that the functionally critical GluR2 subunit stably resides in an intracellular pool in the endoplasmic reticulum (ER). GluR2 in this pool is extensively complexed with GluR3 but not with GluR1, which is mainly confined to the cell surface. Mutagenesis revealed that elements in the C terminus including the PDZ motif are required for GluR2 forward-transport from the ER. Surprisingly, ER retention of GluR2 is controlled by Arg607 at the Q/R-editing site. Reversion to Gln (R607Q) resulted in rapid release from the pool and elevated surface expression of GluR2 in neurons. Therefore, Arg607 is a central regulator. In addition to channel gating, it also controls ER exit and may thereby ensure the availability of GluR2 for assembly into AMPARs.