NRAGE Inhibits Neurite Outgrowth Of NGF-induced PC12 Cells Through TrkA/MEK/ERK And AKT Signaling

The mechanisms of neuronal differentiation in PC12 cells are still not completely understood. NRAGE, also denominated as MAGE-D1 or Dlxin-1, was firstly identified as a molecule interacting with NGF low affinity receptor p75NTR to facilitate cell cycle arrest and NGF-dependent neuron apoptosis.Here we report that NRAGE is downregulated in NGF-induced differentiated PC12 cells. Knockdown of NRAGE by RNAi accelerates NGF-mediated differentiation of PC12 cells. In addition, overexpression of human NRAGE in PC12 cell inhibits NGF-induced neurite outgrowth. Consistent with these observations that NRAGE is found to significantly represses NGF-mediated ERK signaling, while knockdown of NRAGE increases NGF-induced ERK activation and this activation is MEK dependent.A further research reveal that overexpression of NRAGE down regulates TrkA expression and thereby block NGF-induced TrkA activation. To our surprise, NRAGE activates AKT/PKB pathway and induces AKT nuclear localization. Knockdown of NRAGE significantly represses AKT phosphorylation and kinase activity. More importantly, the accelerated neurite formation of PC12 cells by NRAGE knockdown can be totally blocked by reinforced expression of AKT.These data indicate for the first time that NRAGE is an endogenous inhibitor of NGF-induced PC12 differentiation by blocking the activation of MAPK signaling pathway and activating AKT pathway.