| We have identified an E 3 ubiquitin ligase , Nedd 4 2 , that associates with the TrkA receptor and is phosphorylated upon NGF binding . ^^^ The binding of Nedd 4 2 to TrkA through a PPXY motif leads to the ubiquitination and downregulation of TrkA . ^^^ Activated TrkA receptor levels and the survival of NGF dependent sensory neurons , but not BDNF dependent sensory neurons , are directly influenced by Nedd 4 2 expression . ^^^ |