Retrograde neurotrophic signaling requires a protein interacting with receptor tyrosine kinases via C2H2 zinc fingers.

Neurotrophins at axonal terminals signal to cell bodies to regulate neuronal development via signaling endosomes containing activated Trk receptor tyrosine kinases and mitogen-activated protein kinases (MAPKs). Requirements for the formation of signaling endosomes remain, however, poorly characterized. Here we show that a novel Trk-interacting protein, NTRAP (neurotrophic factor receptor-associated protein), plays a crucial role in this signaling process. NTRAP interacts with the Trk intracellular domain through its C(2)H(2) zinc fingers in a kinase-dependent manner. It is associated with vesicles, some of which contain markers for signaling endosomes. Inhibition of NTRAP function suppresses neurotrophin-induced neurite outgrowth in PC12 cells by altering TrkA endocytic traffic, inhibiting the formation of endosomes containing persistently active MAPKs. In compartmentalized sensory neuron cultures, down-regulation of NTRAP abolishes the ability of neurotrophins applied to distal axons to activate the transcription factor adenosine 3',5'-monophosphate response element-binding protein (CREB) and to promote neuronal survival. We propose that NTRAP regulates retrograde neurotrophic signaling by controlling the formation of signaling endosomes.