TY - JOUR T1 - Nerve Growth Factor Activates Persistent Rap1 Signaling in Endosomes JF - The Journal of Neuroscience JO - J. Neurosci. SP - 5406 LP - 5416 DO - 10.1523/JNEUROSCI.21-15-05406.2001 VL - 21 IS - 15 AU - Chengbiao Wu AU - Chun-Fai Lai AU - William C. Mobley Y1 - 2001/08/01 UR - http://www.jneurosci.org/content/21/15/5406.abstract N2 - We investigated a role for endogenous Rap1, a small monomeric GTP-binding protein of the Ras family, in nerve growth factor (NGF) signaling in PC12 cells. Although both epidermal growth factor (EGF) and NGF caused transient activation of Ras, only NGF induced the activation of Rap1. Moreover, Rap1 activation was sustained for hours, an effect that matched the sustained activation of the mitogen-activated protein kinase (MAPK) pathway. To investigate the molecular basis for Rap1 activation, we examined complexes containing C3G, a guanine nucleotide exchange factor for Rap1, and CrkL, an adapter protein known to influence Rap1 signaling. NGF induced the formation of a long-lived complex containing C3G/CrkL/Shp2/Gab2/TrkA. Linking the complex to Rap1 activation, we coprecipitated activated TrkA and activated MAPK with activated Rap1 in NGF-treated cells. Confocal microscopy and subcellular fractionation showed that activated Rap1 and the other proteins of the signaling complex were present in endosomes. Pretreatment of PC12 cells with brefeldin A (BFA), which disrupts the Golgi and endosomal compartments, had little effect on Ras activation but strongly inhibited NGF-induced Rap1 activation and continuing MAPK activation. We propose that endosomes are a site from which NGF induces the prolonged activation of Rap1 and MAPK. ER -