Disease-associated mutations in GluK2 disrupt compartment-specific regulatory mechanisms controlling kainate receptor membrane trafficking

Missense mutations in the Grik2 gene that encodes the kainate receptor subunit GluK2 are associated with neurodevelopmental disorders, but how individual mutations perturb receptor regulation remains unclear. To investigate how disease-associated GluK2 mutations affect receptor trafficking and signalling we used lentiviral approaches to knockdown and replace endogenous GluK2 with tagged wild-type or mutant GluK2 constructs in primary rat neuronal cultures. We show that two disease-associated GluK2 mutations disrupt receptor trafficking through distinct molecular mechanisms. The neurodevelopmental disorder-associated A657T mutation impairs receptor folding and assembly, resulting in endoplasmic reticulum retention, proteasome-dependent degradation, and severely reduced surface expression. In contrast, the C-terminal mutation M867I, identified in patients with autism, markedly reduces PKC-dependent phosphorylation at S868. This does not impede maturation but uncouples GluK2 surface redistribution from activity-dependent signalling. Thus, pathogenic GluK2 variants selectively disrupt either receptor biogenesis or post-translational regulatory integration. Functionally, these mutations differentially alter downstream Ca²⁺ signalling responses, linking molecular defects to altered receptor output. These findings establish the GluK2 C-terminus as a critical control node for synaptic receptor homeostasis and illustrate how discrete mutations can uncouple distinct layers of membrane protein regulation.