Amino-terminal domains of kainate receptors determine the differential dependence on Neto auxiliary subunits for trafficking

Abstract

The kainate receptor (KAR), a subtype of glutamate receptor, mediates excitatory synaptic responses at a subset of glutamatergic synapses. However, the molecular mechanisms underlying the trafficking of its different subunits are poorly understood. Here we use the CA1 hippocampal pyramidal cell, which lacks KARmediated synaptic currents, as a null background to determine the minimal requirements for the extrasynaptic and synaptic expression of the GluK2 subunit. We find that the GluK2 receptor itself, in contrast to GluK1, traffics to the neuronal surface and synapse efficiently and the auxiliary subunits Neto1 and Neto2 caused no further enhancement of these two trafficking processes. However, the regulation of GluK2 biophysical properties by Neto proteins is the same as that of GluK1. We further determine that it is the amino-terminal domains (ATDs) of GluK1 and GluK2 that control the strikingly different trafficking properties between these two receptors. Moreover, the ATDs are critical for synaptic expression of heteromeric receptors at mossy fiber-CA3 synapses and also mediate the differential dependence on Neto proteins for surface and synaptic trafficking of GluK1 and GluK2. These results highlight the fundamental differences between the two major KAR subunits and their interplay with Neto auxiliary proteins.

Signal peptide represses GluK1 surface and synaptic trafficking through binding to amino-terminal domain

“…All KAR subunits share a common topology and previous studies focused on the role of their cytoplasmic C-terminal domains (CTDs) for receptor trafficking 2 , 17 . Recently, several studies uncovered an unexpected role of the extracellular amino-terminal domain (ATD) for GluK2 synaptic targeting 15 , 18 , 19 , and we further discover that it is the amino-terminal regions (ATRs, including signal sequence and ATD) that control the different trafficking properties between GluK1 and GluK2 15 . However, the ATR sequences between GluK1 and GluK2 are quite conserved except for regions around N-terminal signal sequences.…”

Subunit-specific role for the amino-terminal domain of AMPA receptors in synaptic targeting

“…This tripartite bridging complex plays a critical role in synapse formation and maintenance (31,32). Recent evidence has shown that the ATD of kainate receptors is critical for their synaptic localization (33)(34)(35). Furthermore, the neuronal pentraxins interact with the ATD of GluA4 (15) as well as other GluA subunits (16).…”

Neto Auxiliary Subunits Regulate Interneuron Somatodendritic and Presynaptic Kainate Receptors to Control Network Inhibition

“…Despite overwhelming evidence supporting the ability of Neto2 to regulate recombinant GluK1-, GluK2-, and GluK5-containing KARs (Copits et al, 2011; Fisher, 2015; Fisher and Mott, 2012, 2013; Griffith and Swanson, 2015; Palacios-Filardo et al, 2016; Sheng et al, 2015; Sheng et al, 2017; Straub et al, 2011b; Zhang et al, 2009) and native GluK1 containing KARs in developing peripheral neurons (Vernon and Swanson, 2017), physiological relevance for endogenous Neto2 functional regulation of native KARs in central neurons has remained elusive. Indeed prior work failed to detect any defect in CA3 pyramidal cell KAR function in Neto2KO mice and Neto2 was not able to compensate for the dramatic defects observed in Neto1KOs (Tang et al, 2011, Wyeth et al, 2014, Straub et al, 2011a).…”