Hibbert Andrew P, Morris Stephen J, Seidah Nabil G, Murphy Richard A
Centre for Neuronal Survival, Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
J Biol Chem. 2003 Nov 28;278(48):48129-36. doi: 10.1074/jbc.M300961200. Epub 2003 Sep 11.
Nerve growth factor and neurotrophin-3 (NT-3) are processed within the constitutive secretory pathway of neurons and neuroendocrine cells and are released continuously in an activity-independent fashion. In contrast, brain-derived neurotrophic factor (BDNF) is processed in the regulated secretory pathway, stored in vesicles, and released in response to neuronal activity, consistent with its role in modulating synaptic plasticity. In this study, we used vaccinia virus infection and transfection methods to monitor the processing and sorting of neurotrophin-4 (NT-4) in AtT-20 cells, which have been used as a model for the sorting of secretory proteins in neurons. Our data show that NT-4 is processed in the constitutive secretory pathway. The molecule is diffusely distributed within the cells and released, soon after being synthesized, in a manner that is not affected by cell depolarization. We further show that NT-4 and BDNF, when co-expressed, can form heterodimers that are constitutively released. In contrast, heterodimers of NT-3 and BDNF have been shown to be released through the regulated secretory pathway. Thus, NT-4, alone or when co-expressed with BDNF, is processed within and secreted by the constitutive secretory pathway.
神经生长因子和神经营养因子-3（NT-3）在神经元和神经内分泌细胞的组成型分泌途径中进行加工，并以与活性无关的方式持续释放。相比之下，脑源性神经营养因子（BDNF）在调节型分泌途径中进行加工，储存在囊泡中，并响应神经元活动而释放，这与其在调节突触可塑性中的作用一致。在本研究中，我们使用痘苗病毒感染和转染方法来监测神经营养因子-4（NT-4）在AtT-20细胞中的加工和分选，AtT-20细胞已被用作神经元中分泌蛋白分选的模型。我们的数据表明，NT-4在组成型分泌途径中进行加工。该分子在细胞内呈弥散分布，并在合成后不久以不受细胞去极化影响的方式释放。我们进一步表明，NT-4和BDNF共表达时可形成组成型释放的异二聚体。相比之下，NT-3和BDNF的异二聚体已被证明是通过调节型分泌途径释放的。因此，NT-4单独或与BDNF共表达时，在组成型分泌途径中进行加工并分泌。
