Jin Ming, Guan Chen-bing, Jiang Yun-ai, Chen Gang, Zhao Chun-tao, Cui Kai, Song Yuan-quan, Wu Chien-ping, Poo Mu-ming, Yuan Xiao-bing
Institute of Neuroscience, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, and Graduate School of the Chinese Academy of Sciences, Shanghai 200031, China.
J Neurosci. 2005 Mar 2;25(9):2338-47. doi: 10.1523/JNEUROSCI.4889-04.2005.
Cytoplasmic Ca2+ elevation and changes in Rho GTPase activity are both known to mediate axon guidance by extracellular factors, but the causal relationship between these two events has been unclear. Here we show that direct elevation of cytoplasmic Ca2+ by extracellular application of a low concentration of ryanodine, which activated Ca2+ release from intracellular stores, upregulated Cdc42/Rac, but downregulated RhoA, in cultured cerebellar granule cells and human embryonic kidney 293T cells. Chemoattractive turning of the growth cone triggered by a gradient of ryanodine was blocked by overexpression of mutant forms of Cdc42 but not of RhoA in Xenopus spinal cord neurons. Furthermore, Ca2+-induced GTPase activity correlated with activation of protein kinase C and required a basal activity of Ca2+/calmodulin-dependent protein kinase II. Thus, Rho GTPases may mediate axon guidance by linking upstream Ca2+ signals triggered by guidance factors to downstream cytoskeletal rearrangements.
已知细胞质Ca2+升高和Rho GTPase活性变化均介导细胞外因子对轴突的导向作用，但这两个事件之间的因果关系尚不清楚。在这里，我们表明，通过细胞外应用低浓度的ryanodine直接升高细胞质Ca2+，ryanodine可激活细胞内钙库释放Ca2+，在培养的小脑颗粒细胞和人胚肾293T细胞中，可上调Cdc42/Rac，但下调RhoA。在非洲爪蟾脊髓神经元中，由ryanodine梯度触发的生长锥化学吸引性转向被Cdc42突变体形式的过表达所阻断，但未被RhoA突变体形式的过表达所阻断。此外，Ca2+诱导的GTPase活性与蛋白激酶C的激活相关，并且需要Ca2+/钙调蛋白依赖性蛋白激酶II的基础活性。因此，Rho GTPases可能通过将导向因子触发的上游Ca2+信号与下游细胞骨架重排联系起来，从而介导轴突导向。
