Performance in long-term memory tasks is augmented by a phosphorylated growth factor receptor fragment

To elucidate the role of enhanced phosphoinositide-3-kinase (PI3-kinase) activity in memory, a synthetic phosphopeptide (TAT-YPMDM) containing the p85 regulatory subunit receptor-binding motif (YXXM) coupled to the cell transduction domain of HIV-TAT protein was employed. This phosphopeptide bound the p85 subunit of PI3-kinase, and was internalized by both granule and pyramidal neurons when injected into the hippocampus. Increased lipid kinase activity and enhanced phosphorylation of the PI3-kinase substrates Akt (protein kinase B) and ribosomal S6 kinase were associated with TAT-YPMDM administration. Bilateral infusion of the phosphopeptide into the dorsal hippocampus after training improved performance in three hippocampus-dependent memory tasks: contextual fear conditioning, trace fear conditioning, and the Morris water maze. Both the biochemical and behavioral effects of the TAT-YPMDM phosphopeptide could be blocked by wortmannin. No effect was observed when a nonphosphorylated peptide (TAT-YMDM), or a second, unrelated phosphopeptide (TAT-YPLDL) was utilized. In addition, infusion of the TAT-YPMDM phosphopeptide did not interfere with memory acquisition or 4 hr memory. In addition, pretesting administration did not affect the ability to recall a previously established long-term memory. These findings suggest that stimulation of PI3-kinase activity by phosphorylated receptor fragments containing the YMDM motif augments long-term memory.