Analysis of a RhoGEF, KIAA380, in neurite retraction

信号素是体内调节细胞迁移的排斥性引导信号，在体外培养的神经元中导致生长锥塌陷。生长锥体塌陷的特征是生长锥体中卵形和板形肌动蛋白结构的消失。Rho家族的小gtpase在响应细胞外刺激时调节肌动蛋白细胞骨架。之前，我们已经发现了rho特异性GEF KIAA0380对神经元培养细胞Neuro2A的神经突缩回有影响的证据。然后对KIAA0380的结合伙伴进行酵母双杂交筛选。因此，我们分离了丛蛋白b1作为kiaa380结合蛋白。通过进一步分析，我们确定kiaa380的PDZ结构域与丛蛋白B1的C端结合。我们接下来描述了丛蛋白b1的聚合导致Rho的激活，正如应力纤维形成所观察到的那样。有趣的是，缺乏DH结构域的突变体KIAA0380有效地抑制了Swiss 3T3细胞中依赖于多聚的Rho激活。我们决定进一步研究丛蛋白引起崩溃的机制。我们提供的证据表明，丛蛋白通过与Rho特异性鸟嘌呤核苷酸交换因子（GEF） KIAA0380的直接关联激活Rho。该RhoGEF在信号蛋白诱导的生长锥塌陷中的作用目前正在研究中。

Semaphorins are repulsive guidance cues that regulate cell migration in vivo and in cultured neurons lead to growth cone collapse in vitro. Growth cone collapse is characterised by a disappearance offilopodial and lamellipodial actin structures in the growth cone. Small GTPases of the Rho family regulate the actin cytoskeleton in response to extracellular stimuli. Previously, we had found evidence for an effect ofa Rho-specific GEF, KIAA0380, on neurite retraction of neuronal culture cells, Neuro2A. Then we carried out yeast two hybrid screeing for binding partners of KIAA0380.Consequently, we isolated plexin-B1 as a KIAA380-binding protein. By further analyses, we determined thatthe PDZ domain ofKIAA380 bind with the C terminus ofplexin B1. We next described that multimerisation of plexin-B1 led to activation of Rho, as observed by stress fiber formation. Interestingly a mutant KIAA0380 which lacks DH domain effectively inhibited the multimerization dependent Rho activation in Swiss 3T3 cells.We decided to study furtherthe mechanism bywhich plexins cause collapse.We present evidence foractivation of Rho by plexins via direct association with a Rho specific guanine nucleotide exchange factor (GEF), KIAA0380. The role of this RhoGEF in the growth cone collapse induced by semaphorins is currently being studied.