Activity-Dependent Palmitoylation Controls SynDIG1 Stability, Localization, and Function.

UNLABELLED: Synapses are specialized contacts between neurons. Synapse differentiation-induced gene I (SynDIG1) plays a critical role during synapse development to regulate AMPA receptor (AMPAR) and PSD-95 content at excitatory synapses. Palmitoylation regulates the localization and function of many synaptic proteins, including AMPARs and PSD-95. Here we show that SynDIG1 is palmitoylated, and investigate the effects of palmitoylation on SynDIG1 stability and localization. Structural modeling of SynDIG1 suggests that the membrane-associated region forms a three-helical bundle with two cysteine residues located at positions 191 and 192 in the juxta-transmembrane region exposed to the cytoplasm. Site-directed mutagenesis reveals that C191 and C192 are palmitoylated in heterologous cells and positively regulates dendritic targeting in neurons. Like PSD-95, activity blockade in a rat hippocampal slice culture increases SynDIG1 palmitoylation, which is consistent with our prior demonstration that SynDIG1 localization at synapses increases upon activity blockade. These data demonstrate that palmitoylation of SynDIG1 is regulated by neuronal activity, and plays a critical role in regulating its stability and subcellular localization, and thereby its function. SIGNIFICANCE STATEMENT: Palmitoylation is a reversible post-translation modification that has recently been recognized as playing a critical role in the localization and function of many synaptic proteins. Here we show that activity-dependent palmitoylation of the atypical AMPA receptor auxiliary transmembrane protein SynDIG1 regulates its stability and localization at synapses to regulate function and synaptic strength.