Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.
Mol Biol Cell. 2011 Oct;22(20):3853-60. doi: 10.1091/mbc.E11-03-0277. Epub 2011 Aug 17.
Rab22 is a small GTPase that is localized on early endosomes and regulates early endosomal sorting. This study reports that Rab22 promotes nerve growth factor (NGF) signaling-dependent neurite outgrowth and gene expression in PC12 cells by sorting NGF and the activated/phosphorylated receptor (pTrkA) into signaling endosomes to sustain signal transduction in the cell. NGF binding induces the endocytosis of pTrkA into Rab22-containing endosomes. Knockdown of Rab22 via small hairpin RNA (shRNA) blocks NGF-induced pTrkA endocytosis into the endosomes and gene expression (VGF) and neurite outgrowth. Overexpression of human Rab22 can rescue the inhibitory effects of the Rab22 shRNA, suggesting a specific Rab22 function in NGF signal transduction, rather than off-target effects. Furthermore, the Rab22 effector, Rabex-5, is necessary for NGF-induced neurite outgrowth and gene expression, as evidenced by the inhibitory effect of shRNA-mediated knockdown of Rabex-5. Disruption of the Rab22-Rabex-5 interaction via overexpression of the Rab22-binding domain of Rabex-5 in the cell also blocks NGF-induced neurite outgrowth, suggesting a critical role of Rab22-Rabex-5 interaction in the biogenesis of NGF-signaling endosomes to sustain the signal for neurite outgrowth. These data provide the first evidence for an early endosomal Rab GTPase as a positive regulator of NGF signal transduction and cell differentiation.
Rab22 是一种小 GTPase，定位于早期内体，调节早期内体分拣。本研究报道 Rab22 通过将 NGF 和激活/磷酸化受体（pTrkA）分拣到信号内体中，促进 PC12 细胞中神经生长因子（NGF）信号依赖性轴突生长和基因表达，从而维持细胞内信号转导。NGF 结合诱导 pTrkA 内吞到含有 Rab22 的内体中。通过短发夹 RNA（shRNA）敲低 Rab22 会阻止 NGF 诱导的 pTrkA 内吞到内体中以及基因表达（VGF）和轴突生长。人 Rab22 的过表达可以挽救 Rab22 shRNA 的抑制作用，表明 Rab22 在 NGF 信号转导中具有特定功能，而不是脱靶效应。此外，Rab22 的效应物 Rabex-5 对于 NGF 诱导的轴突生长和基因表达是必要的，这可以通过 shRNA 介导的 Rabex-5 敲低的抑制作用来证明。通过在细胞中过表达 Rabex-5 的 Rab22 结合域破坏 Rab22-Rabex-5 相互作用也会阻止 NGF 诱导的轴突生长，表明 Rab22-Rabex-5 相互作用在 NGF 信号转导内体的生物发生中起关键作用，以维持信号促进轴突生长。这些数据首次提供了早期内体 Rab GTPase 作为 NGF 信号转导和细胞分化的正调节剂的证据。
