Novel protein-protein interactions and signaling mechanisms in regulation of the AMPA receptor GluR2 subunit trafficking in cultured hippocampal neurons

AMPA receptor trafficking into and out of synapses underlies activity-dependent regulation of synaptic strength. Both PICK1 (P&barbelow;rotein I&barbelow;nteracting with C&barbelow;-K&barbelow;inase) and ABP (A&barbelow;MPA receptor B&barbelow;inding P&barbelow;rotein)/GRIP (G&barbelow;lutamate R&barbelow;eceptor I&barbelow;nteracting P&barbelow;rotein) bind to the AMPA receptor GluR2 subunit C-terminus, and are involved in receptor trafficking. Transfer of the receptor from ABP/GRIP to PICK1, facilitated by GluR2 S880 phosphorylation, may initiate receptor trafficking. Here I find novel protein interactions that regulate these steps. The PICK1 BAR (B&barbelow;in/A&barbelow;mphiphysin/R&barbelow;vs) domain interacts intermolecularly with the ABP/GRIP linker II region and intramolecularly with the PICK1 PDZ (P&barbelow;SD95/D&barbelow;lgA/Z&barbelow;O-1) domain. Binding of PKCalpha (P&barbelow;rotein K&barbelow;inase C&barbelow; alpha) or GluR2 to the PICK1 PDZ domain disrupts the intramolecular interaction, and facilitates the PICK1 BAR domain association with ABP/GRIP. Interference with the PICK1-ABP/GRIP interaction impairs 5880 phosphorylation of GluR2 by PKC, and decreases the constitutive surface expression of GluR2, the NMDA-induced endocytosis of G1uR2 and recycling of internalized GluR2. These findings suggest that the PICK1 interaction with ABP/GRIP is a critical step in controlling GluR2 trafficking.; Protein kinases play key roles in receptor trafficking through phosphorylating receptors or factors involved in receptor trafficking. However, a systematic investigation into the role of protein kinases in GluR2 trafficking is scarce. In this study, I demonstrate that activation of CaMKII (Calcium/calmodulin activated kinase II), but not PKC and PKA (P&barbelow;rotein K&barbelow;inase A&barbelow;) is required for GluR2 trafficking to the surface. Calcium release from internal stores mediated by IP-3 receptors and ryanodine receptors is also required for GluR2 trafficking to the surface. These data suggest a key role of CaMKII in GluR2 trafficking.; I also find an interaction between PICK1 and CaMKII that is meditated by the PICK1 BAR domain and the catalytic domain of CaMKII. Interestingly, only active CaMKII interacts with PICK1. As CaMKII plays an important role in GluR2 exocytosis, the PICK1-CaMKII interaction suggests that PICK1 may be involved in targeting active CaMKII to AMPA receptors to regulate receptor trafficking.