Role of nPIST in activity-dependent synaptic trafficking of AMPARs

Activity-dependent synaptic trafficking of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) is a key molecular mechanism underlying N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) in the hippocampus, a cellular model of learning and memory. Transmembrane AMPAR regulatory proteins (TARPs) form protein complexes with AMPARs from the endoplasmic reticulum (ER), and perform an essential function in their synaptic trafficking. However, the molecular machinery that links synaptic activity and TARP-mediated AMPAR synaptic trafficking remains to be identified. In this thesis study, we investigated the functional role of nPIST (neuronal PDZ domain protein interacting specifically with TC10), a PDZ domain containing protein interacting with stargazin, the prototypic member of TARPs family in stargazin-mediated AMPAR synaptic trafficking. First, we found that nPIST is a physiological substrate for casein kinase 2 (CK2) phosphorylation, and NMDAR-dependent synaptic activity facilitates the exit of nPIST from the Golgi apparatus through CK2-mediated phosphorylation of its acidic cluster (AC) domain, Next, we found that thorough its PDZ domain nPIST interacts with guanylate kinase-associated protein (GKAP), a synaptic scaffolding protein known to form a complex with shank and PSD-95 family proteins, and disruption of this interaction blocks enhancement of AMPAR synaptic trafficking induced by NMDAR-dependent synaptic activity. Given the recent findings that CK2-mediated phosphorylation is associated with NMDAR-dependent LTP, and that the synaptic abundance of GKAP is dynamically regulated in a synaptic activity-dependent manner, these results suggest that nPIST might be an important element in the molecular machinery that translates synaptic activity into increased AMPAR synaptic trafficking in NMDAR-dependent LTP. In the pathogenesis of Alzheimer's disease (AD) and epileptic disorders, dysregulation of activity-dependent AMPAR synaptic trafficking, a potentially reversible functional change, is believed to precede an irreversible morphological change. Therefore, modification of CK2-mediated phosphorylation or protein interaction of nPIST would provide a novel therapeutic strategy for these intractable human diseases.