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J. postsynaptic density (PSD) to limit CP-AMPAR basal synaptic incorporation. In addition, we found that AKAP150 palmitoylation is required for LTP induced by weaker stimulation that recruits CP-AMPARs to synapses but not stronger stimulation that recruits GluA2-containing RICTOR AMPARs. Thus, AKAP150 palmitoylation controls its subcellular localization to maintain proper basal and activity-dependent regulation of synaptic AMPAR subunit composition. In Brief Purkey et al. uncover a requirement for palmitoylation of the postsynaptic scaffold protein AKAP150 in regulating Ca2+-permeable AMPA receptors to control synaptic plasticity. Graphical CC-90003 Abstract INTRODUCTION AMPARs are the primary mediators of fast excitatory neurotransmission in the CNS, and regulation of the number and activity of postsynaptic AMPARs is crucial for forms of synaptic plasticity that support learning and memory, including NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) and longterm depression (LTD) (Huganir and Nicoll, 2013). AMPARs are tetramers assembled from GluA1C4 subunits, with incorporation of GluA2 subunits decreasing channel conductance and inhibiting Ca2+ influx. After the early postnatal period, the majority of AMPARs at hippocampal CA1 synapses under basal conditions are Ca2+-impermeable GluA1/2 or GluA2/3 heterotetramers (Lu et al., 2009; Rozov et al., 2012; Stubblefield and Benke, 2010). However, Ca2+-permeable GluA1 homomeric receptors (CP-AMPARs) can be recruited to hippocampal synapses from extrasynaptic and/or intracellular stores to regulate synaptic strength during LTP, LTD, and homeostatic plasticity (Aoto et al., 2008; Soares et al., 2013; Lu et al., 2007; Plant et al., 2006; Sanderson et al., 2016, 2012, 2018; Sutton et al., 2006; Thiagarajan et al., 2005; Yang et al., 2008; but see Adesnik and Nicoll, 2007; Gray et al., 2007). These recruited CP-AMPARs, because of both greater single-channel conductance and Ca2+ permeability, can in turn not only influence the level of plasticity expression but also alter the capacity of synapses to undergo subsequent plasticity, so-called metaplasticity. Importantly, CP-AMPAR-mediated metaplasticity in the nucleus accumbens and amygdala is, respectively, linked to reward learning relevant for drug addiction and fear memory extinction relevant for post-traumatic stress disorder (Clem and Huganir, 2010; Wolf, 2016). However, the roles of CP-AMPARs in regulating LTP and LTD and metaplasticity at hippocampal synapses relevant for spatial and contextual learning and memory are less clear and remain controversial. We know that phosphorylation and dephosphorylation of S845 in the GluA1 C-terminal domain by the cAMP-dependent protein kinase PKA and the Ca2+-calmodulin-dependent protein phosphatase 2B/calcineurin (CaN) regulate CP-AMPAR synaptic insertion and removal, respectively (Esteban et al., 2003; He et al., 2009; Hu et al., 2007; Man et al., 2007; Oh et al., 2006; Qian et al., 2012; Sun et al., 2005; Yang et al., 2008). However, we still do not understand how postsynaptic PKA and CaN signaling are coordinated to control CP-AMPAR trafficking between intracellular compartments, such as recycling endosomes (REs), the extrasynaptic membrane, and the postsynaptic density (PSD). An increasing body of evidence indicates that the scaffold protein AKAP79/150 (human79/rodent150; gene) CC-90003 targets both PKA and CaN to AMPARs to regulate GluA1 phosphorylation and trafficking to control LTP and LTD balance and homeostatic potentiation (Diering et al., 2014; Jurado et al., 2010; Lu et al., 2007; Sanderson et al., 2012, 2016, 2018; Tunquist et al., 2008; Zhang et al., 2013). Thus, a key question is how is the post-synaptic localization of CC-90003 AKAP79/150 itself regulated. AKAP79/150 is targeted to the postsynaptic plasma membrane primarily by an N-terminal poly-basic domain that binds to PIP2, cortical F-actin, and cadherin adhesion molecules and secondarily by an internal domain that binds PSD-95, a major structural scaffold of the PSD (Colledge et al., 2000; DellAcqua et al., 1998; Gomez et al., 2002; Gorski et al., 2005; Robertson et al., 2009). More recently we discovered that AKAP79/150 is S-palmitoylated on two conserved Cys residues (C36 and C129 human/123 mouse) within the N-terminal targeting domain by the RE-localized palmitoyl acyltransferase DHHC2 (Keith CC-90003 et al., 2012; Woolfrey et al., 2015). AKAP palmitoylation is not required for its general targeting to the plasma membrane or its binding to F-actin (Gomez et al., 2002) but is required for its specific localization to dendritic REs and association with cholesterol-rich, detergent-resistant membrane lipid rafts (Delint-Ramirez et al., 2011; Keith et al., 2012). Of note, the PSD is biochemically defined by its detergent insolubility, and accordingly, many PSD proteins are palmitoylated and lipid-raft associated, including PSD-95 (El-Husseini et al., 2002; Fukata and Fukata, 2010; Fukata et al., 2013; Globa and Bamji, 2017; Keith et al., 2012; Noritake et CC-90003 al., 2009; Sezgin et al., 2017). However, it is not known if AKAP79/150 palmitoylation also controls its association with the PSD. In contrast to other protein lipidations like myristoylation and prenylation, palmitoylation is reversible, with.