Shank/ProSAP promotes surface GluR6 in dendritic spines and is down-regulated by actinfilin (AF) and Cul3, both of which decrease GluR6. A) AF keeps Shank levels low, but RNAi to AF strongly promotes expression of Shank in hippocampal neurons. B) Reduction of Cul3 (Cul3+/− mice) results in increased GluR6 and Shank in postsynaptic densities (PSD). WCE, whole cell extract. Also shown is the % change in each synaptic protein in Cul3+/− mice. C) Elevating Shank levels by overexpressing Shank3 in cortical neurons increases not only the number of dendritic spines, but the likelihood of detecting surface GluR6 in a spine (C1). For comparison, control neurons with lower Shank levels are also shown (C2). The % values indicate the % of spines that have detectable surface GluR6.