Yan Yan, Eipper Betty A, Mains Richard E
Department of Neuroscience, UCONN Health Center, Farmington, CT 06030, USA.
Department of Neuroscience, UCONN Health Center, Farmington, CT 06030, USA; Molecular Biology and Biophysics, UCONN Health Science Center, Farmington, CT 06030, USA.
Neuropharmacology. 2016 Aug;107:227-238. doi: 10.1016/j.neuropharm.2016.03.050. Epub 2016 Mar 30.
Exogenous brain-derived neurotrophic factor (BDNF), acting through TrkB, is known to promote neurite formation and branching. This response to BDNF was eliminated by inhibition of TrkB kinase and by specific inhibition of the GEF1 domain of Kalirin, which activates Rac1. Neurons from Kalrn knockout mice were unable to activate Rac1 in response to BDNF. BDNF-triggered neurite outgrowth was abolished when Kalrn expression was reduced using shRNA that targets all of the major Kalrn isoforms, and reduced in neurons from Kalrn knockout mice. The Kalrn isoforms expressed early in development also include a GEF2 domain that activates RhoA. However, BDNF-stimulated neurite outgrowth in Kalrn knockout neurons was rescued by expression of Kalirin-7, which includes only the GEF1 domain but lacks the GEF2 domain. Dendritic morphogenesis, which requires spatially restricted, coordinated changes in the actin cytoskeleton and in the organization of microtubules, involves essential contributions from multiple Rho GEFs. Since Tiam1, another Rho GEF, is also required for BDNF-stimulated neurite outgrowth, an inhibitory fragment of Tiam1 (PHn-CC-EX) was tested and found to interfere with both Kalirin and Tiam1 GEF activity. The prolonged TrkB activation observed in response to BDNF in Kalrn knockout neurons and the altered time course and extent of ERK, CREB and Akt activation observed in the absence of Kalrn would be expected to alter the response of these neurons to other regulatory factors.
外源性脑源性神经营养因子（BDNF）通过TrkB发挥作用，已知可促进神经突的形成和分支。对BDNF的这种反应可通过抑制TrkB激酶以及特异性抑制激活Rac1的Kalirin的GEF1结构域来消除。来自Kalrn基因敲除小鼠的神经元无法对BDNF做出反应而激活Rac1。当使用靶向所有主要Kalrn异构体的短发夹RNA（shRNA）降低Kalrn表达时，BDNF触发的神经突生长被消除，并且在Kalrn基因敲除小鼠的神经元中减少。在发育早期表达的Kalrn异构体还包括一个激活RhoA的GEF2结构域。然而，通过表达仅包含GEF1结构域但缺乏GEF2结构域的Kalirin-7，可挽救Kalrn基因敲除神经元中BDNF刺激的神经突生长。树突形态发生需要肌动蛋白细胞骨架和微管组织在空间上受到限制的协调变化，涉及多个Rho鸟嘌呤核苷酸交换因子（Rho GEF）的重要作用。由于另一种Rho GEF Tiam1也是BDNF刺激的神经突生长所必需的，因此测试了Tiam1的一个抑制片段（PHn-CC-EX），发现它会干扰Kalirin和Tiam1的GEF活性。在Kalrn基因敲除神经元中观察到的对BDNF的TrkB激活延长，以及在没有Kalrn的情况下观察到的ERK、CREB和Akt激活的时间进程和程度改变，预计会改变这些神经元对其他调节因子的反应。
