The endocytosis of AMPA receptors (AMPARs) underlies several forms of synaptic plasticity including NMDA receptor (NMDAR)-dependent long-term depression (LTD) but the molecular mechanisms responsible for this trafficking remain unknown. Here we demonstrate that PSD-95, a major postsynaptic density protein, plays a key role in NMDAR-triggered endocytosis of synaptic AMPARs because of its binding to AKAP150, a scaffold for specific protein kinases and phosphatases. Knockdown of PSD-95 with shRNA blocks NMDAR-triggered, but not constitutive nor mGluR-triggered endocytosis of AMPARs. Deletion of PSD-95’s SH3 and GK domains as well as a point mutation (L460P), both of which inhibit binding of PSD-95 to AKAP150, also block NMDAR-triggered AMPAR endocytosis. Furthermore, expression of a mutant AKAP150 that does not bind calcineurin inhibits this NMDAR-triggered trafficking event. These results suggest that PSD-95’s interaction with AKAP150 is critical for NMDAR-triggered AMPAR endocytosis and LTD, possibly because these scaffolds position calcineurin in the appropriate subsynaptic domain.
NMDA receptor (NMDAR)-dependent long-term depression (LTD) in the hippocampus
Serotonin (5-HT), a major neurotransmitter, has a large number of G protein-coupled receptors in mammals. On activation by exposure to their ligand, 5-HT 2 receptor subtypes increase IP3 levels and undergo desensitization and internalization. To visualize the receptor in cells during these processes, we have constructed a 5-HT 2A-enhanced GFP (SR2-GFP) fusion receptor. We show that this fusion receptor undergoes internalization on exposure to its natural ligand, 5-HT. Because 5-HT2A receptors activate the phospholipase C pathway, we studied the effect of protein kinase C (PKC) on the internalization process and found that activation of PKC by its specific activator phorbol 12-myristate 13-acetate, in the absence of 5-HT, leads to internalization of the receptor. Moreover, inhibition of PKC by its inhibitor sphingosine in the presence of 5-HT prevents the internalization process, suggesting that activation of PKC is sufficient and necessary for the internalization of 5-HT 2A receptors. We also show that SR2-GFP recycles back to the plasma membrane after 5-HT-dependent internalization, suggesting a mechanism for resensitization. In addition, receptors that have been internalized on addition of phorbol 12-myristate 13-acetate in the absence of 5-HT also recycle to the surface, with a time course similar to that seen after activation of the receptors by 5-HT. Our study suggests that 5-HT2A receptors internalize and return to the surface after both serotonin-and PKC-mediated processes. This study reveals a role for PKC in receptor internalization and also shows that 5-HT2A receptors are recycled.general feature of G protein-coupled receptors (GPCRs) is the existence of complex regulatory mechanisms that modulate receptor responsiveness. These mechanisms underlie important physiological phenomena such as signal transduction and plasticity. Many GPCRs also demonstrate rapid desensitization in the continued presence of agonists, due to uncoupling of the receptor from the G protein involved (1). In some systems, such as opiate and  2 adrenergic receptors, sequestration or internalization of receptors appears to occur as a part of the overall process of agonist-induced desensitization (2-9).The phenomena of receptor desensitization and downregulation are well described in 5-HT receptors (10-15). For example, phosphatidylinositol hydrolysis in bovine aorta mediated by 5-HT 2 receptors is markedly attenuated after brief treatments with agonists (16). 5-HT 2 receptor-induced Ca 2ϩ mobilization is rapidly diminished after agonist treatment of rat C6BU-1 glioma cells, and rapid decreases in 5-HT-induced currents are also seen in Xenopus oocytes expressing 5-HT 2A receptors (17,18).Sequestration or internalization of 5-HT 2A receptors is also thought to occur as part of the overall process of agonist-induced desensitization of 5-HT 2A receptors (19,20). The process of resensitization would require the recovery of the ability of the receptor to couple to G proteins. Although it is not clear that internalization of desensitized ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.