Fig 2: p85S6K interacts with GluA1 specifically. a Co-immunoprecipitation of AMPA receptors in hippocampal tissue lysates with Flag-p85S6K or empty vector (Mock) from HEK293 cell lysates. b Co-immunoprecipitation of myc-GluA1 or myc-GluA2 with Flag-p85S6K, with AKAP79 co-transfected in HEK293 cells. c Co-immunoprecipitation results for Flag-p85S6K or Flag-p70S6K with myc-GluA1, with AKAP79 co-transfected in HEK293 cells. d, e Co-immunoprecipitation of endogenous GluA1 with p85S6K in the PSD-1 fraction. f Confirmation of such interaction in vivo by in situ PLA. Scale bar, 10 μm. Representative blots or images of at least 3 independent experiments are shown. IP immunoprecipitation, IB immunoblot

Fig 3: p85S6K is fractionated into PSDs and is involved in spatial and recognition memory. a, b Fractionation of PSDs from mouse hippocampus showed enrichment of p85S6K but not p70S6K in PSDs. The indicated subcellular fractions (8 µg protein for Syn and non-Syn fractions and 10 µg protein for other fractions) were analyzed by immunoblotting with anti-phosphorylated p70S6K, anti-p70S6K, anti-PSD95, anti-synaptophysin, and anti-GAPDH antibodies. n = 3 independent experiments. p-p85S6K: phosphorylated p85S6K. c Synaptosome trypsin digestion showed postsynaptic localization of p85S6K. Representative blots or images of 3 independent experiments are shown. d, e The expression of p85S6K and p70S6K after knockdown of p85S6K (p85S6K KD) in hippocampus of WT mice. Control mice were injected with AAVs expressing control shRNA. n = 4 mice per group. t = 8.835, df = 6, P = 0.0001. f–k Morris water maze was performed to examine effects of downregulation of p85S6K on spatial learning and memory. n = 12 mice for control and n = 11 mice for p85S6K KD. f The latency of mice to locate the hidden platform in the training period. F(1, 21) = 9.742, P = 0.0052 for p85S6K expression manipulation. g The average speed of mice in the training period. h The time in the target quadrant in the probe test. t = 2.257, df = 21, P = 0.0348. i The average speed of mice in the probe test. j The number of platform crossings in the probe test. t = 2.383, df = 21, P = 0.0267. k Representative swimming trajectories in the probe test from different groups of mice. The green circle represents the hidden platform. l Discrimination index in the NOR test. n = 8 mice per group. t = 2.550, df = 14, P = 0.0231. Data are presented as mean ± SEM. Unpaired t test, two-tailed (e, h–j, l) and repeated measures two-way ANOVA followed by Tukey's test (f, g). Ctl, control. *P < 0.05, ***P < 0.001