Abstract
Trafficking and biophysical properties of AMPA receptors (AMPARs) in the brain depend on interactions with associated proteins. We identify Shisa6, a single transmembrane protein, as a stable and directly interacting bona fide AMPAR auxiliary subunit. Shisa6 is enriched at hippocampal postsynaptic membranes and co-localizes with AMPARs. The Shisa6 C-terminus harbours a PDZ domain ligand that binds to PSD-95, constraining mobility of AMPARs in the plasma membrane and confining them to postsynaptic densities. Shisa6 expressed in HEK293 cells alters GluA1- and GluA2-mediated currents by prolonging decay times and decreasing the extent of AMPAR desensitization, while slowing the rate of recovery from desensitization. Using gene deletion, we show that Shisa6 increases rise and decay times of hippocampal CA1 miniature excitatory postsynaptic currents (mEPSCs). Shisa6-containing AMPARs show prominent sustained currents, indicating protection from full desensitization. Accordingly, Shisa6 prevents synaptically trapped AMPARs from depression at high-frequency synaptic transmission.
Highlights
Trafficking and biophysical properties of AMPA receptors (AMPARs) in the brain depend on interactions with associated proteins
Identification of additional components of native brain-derived AMPAR complexes has revealed a wide variety of mostly transmembrane proteins that directly interact with AMPARs14
Since AMPAR decay time is prolonged by Shisa[6], and deactivation and desensitization are closely related processes, we investigated whether Shisa[6] modulates AMPAR currents in response to prolonged desensitizing glutamate application (1 s, 1-ms glutamate (1 mM)) in HEK293 cells (Fig. 5c,d)
Summary
Trafficking and biophysical properties of AMPA receptors (AMPARs) in the brain depend on interactions with associated proteins. Identification of additional components of native brain-derived AMPAR complexes has revealed a wide variety of mostly transmembrane proteins that directly interact with AMPARs14. These proteins can potentially act as auxiliary subunits of AMPARs and affect channel kinetics, trafficking, surface mobility and activity-dependent regulation of these processes. Both TARPs and Cornichons decrease deactivation and desensitization rates of the activated AMPAR, and promote synaptic targeting. Overexpression in CA1 of CKAMP44/Shisa[9] increases the AMPAR deactivation time constant, slows down recovery from desensitization and decreases AMPAR short-term plasticity[21]. By altering biophysical properties of AMPARs, Shisa[6] keeps AMPARs in an activated state in the presence of glutamate, preventing full desensitization and synaptic depression
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