Rit contributes to nerve growth factor-induced neuronal differentiation via activation of B-Raf-extracellular signal-regulated kinase and p38 mitogen-activated protein kinase cascades
Rit contributes to nerve growth factor-induced neuronal differentiation via activation of B-Raf-extracellular signal-regulated kinase and p38 mitogen-activated protein kinase cascades
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DOI：
10.1128/mcb.25.2.830-846.2005
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发表时间：
2005-01-01
影响因子：
5.3
通讯作者：
Andres, DA
中科院分区：
文献类型：
--
作者：
Shi, GX;Andres, DA
Rit是一个新的Ras GT3亚家族的原始成员之一，该亚家族使用不同的效应子途径转化NIH 3 T3细胞并诱导嗜铬细胞瘤细胞（PC 6）分化。在这项研究中，我们发现生长因子（包括神经生长因子（NGF））对PC 6细胞的刺激会导致Rit快速且延长的激活。活性Rit的异位表达促进PC6神经突生长，其在形态上不同于致癌Ras所促进的神经突生长（通过增加神经突分支来证明），并刺激细胞外信号调节激酶（ERK）和p38促分裂原活化蛋白（MAP）激酶信号通路的活化。此外，Rit诱导的分化依赖于两个MAP激酶级联，因为MEK抑制阻断Rit诱导的神经突生长，而p38阻断抑制神经突伸长和分支，但不抑制神经突起始。令人惊讶的是，虽然Rit不能刺激NIH 3 T3细胞中的ERK活性，但它有效地激活了PC 6细胞中的ERK。这种细胞类型特异性可以通过Rit无法激活C-Raf而结合并刺激神经元Raf亚型B-Raf的发现来解释。重要的是，选择性下调Rit基因在PC6细胞中的表达显著改变了NGF依赖的MAP激酶级联反应，抑制了p38和ERK激酶的激活。此外，NGF促进神经元分化的能力被Rit敲低减弱。因此，Rit通过将特定的营养因子信号偶联到B-Raf/ERK和p38 MAP激酶级联的持续激活中而参与神经元发育和再生的新途径。
Rit is one of the original members of a novel Ras GTPase subfamily that uses distinct effector pathways to transform NIH 3T3 cells and induce pheochromocytoma cell (PC6) differentiation. In this study, we find that stimulation of PC6 cells by growth factors, including nerve growth factor (NGF), results in rapid and prolonged Rit activation. Ectopic expression of active Rit promotes PC6 neurite outgrowth that is morphologically distinct from that promoted by oncogenic Ras (evidenced by increased neurite branching) and stimulates activation of both the extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein (MAP) kinase signaling pathways. Furthermore, Rit-induced differentiation is dependent upon both MAP kinase cascades, since MEK inhibition blocked Rit-induced neurite outgrowth, while p38 blockade inhibited neurite elongation and branching but not neurite initiation. Surprisingly, while Rit was unable to stimulate ERK activity in NIH 3T3 cells, it potently activated ERK in PC6 cells. This cell type specificity is explained by the finding that Rit was unable to activate C-Raf, while it bound and stimulated the neuronal Raf isoform, B-Raf. Importantly, selective down-regulation of Rit gene expression in PC6 cells significantly altered NGF-dependent MAP kinase cascade responses, inhibiting both p38 and ERK kinase activation. Moreover, the ability of NGF to promote neuronal differentiation was attenuated by Rit knockdown. Thus, Rit is implicated in a novel pathway of neuronal development and regeneration by coupling specific trophic factor signals to sustained activation of the B-Raf/ERK and p38 MAP kinase cascades.