Phosphoproteomic analysis of neurotrophin receptor TrkB signaling pathways in mouse brain.

1. The signaling pathways activated by trkB neurotrophin receptor have been studied in detail in cultured neurons, but little is known about the pathways activated by trkB in intact brain. TrkB is a tyrosine kinase and protein phosphorylation is a key regulatory process in the neuronal signal transduction pathways. 2. We have investigated trkB signaling in the transgenic mice overexpressing trkB in postnatal neurons (trkB.TK) using phosphoproteomics. 3. We found that several proteins are overphosphorylated on tyrosine residues in the brain of trkB.TK mice and identified some of these proteins. 4. We demonstrate that the well characterized signaling molecules mitogen-activated protein kinase (MAPK) and cyclic AMP responsive element binding protein (CREB) were phosphorylated at a higher level in the brain of trkB.TK mice when compared to the wild type littermates. Furthermore, we found that beta-actin was tyrosine phosphorylated in the brain of the transgenic mice. 5. Our results demonstrate that phosphoproteomics is a sensitive approach to investigate signaling pathways activated in mouse brain.