Belliveau Daniel J, Bani-Yaghoub Mahmud, McGirr Becky, Naus Christian C G, Rushlow Walter J
Departments of Anatomy and Cell Biology, The University of Western Ontario, London, Ontario N6A 5A5.
Neurogenesis & Brain Repair Group, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.
J Biol Chem. 2006 Jul 28;281(30):20920-20931. doi: 10.1074/jbc.M600026200. Epub 2006 May 26.
Gap junctions have traditionally been described as transmembrane channels that facilitate intercellular communication via the passage of small molecules. Connexins, the basic building blocks of gap junctions, are expressed in most mammalian tissues including the developing and adult central nervous system. During brain development, connexins are temporally and spatially regulated suggesting they play an important role in the proper formation of the central nervous system. In the current study, connexins 32 and 43 were overexpressed in PC12 cells to determine whether connexins are involved in neuronal differentiation. Both connexin 32 and 43 were appropriately trafficked to the cell membrane following overexpression and resulted in the formation of functional gap junctions. Connexin overexpression was found to cause enhanced neurite outgrowth in PC12 cells treated with nerve growth factor to initiate neuritogenesis. Surprisingly, however, enhanced neurite outgrowth was found to be the consequence of functional hemichannel formation as opposed to traditional intercellular communication. Additional analysis revealed that ATP was released into the media likely through hemichannels and acted on purinergic receptors to cause enhanced neurite outgrowth. Collectively, the results of the current study suggest that connexins may play an important role in neuronal differentiation by non-traditional mechanisms.
传统上，间隙连接被描述为跨膜通道，可通过小分子的传递促进细胞间通讯。连接蛋白是间隙连接的基本组成部分，在包括发育中的和成年的中枢神经系统在内的大多数哺乳动物组织中都有表达。在大脑发育过程中，连接蛋白在时间和空间上受到调控，这表明它们在中枢神经系统的正常形成中发挥着重要作用。在本研究中，连接蛋白32和43在PC12细胞中过表达，以确定连接蛋白是否参与神经元分化。过表达后，连接蛋白32和43均被正确转运至细胞膜，并导致功能性间隙连接的形成。研究发现，连接蛋白过表达会使经神经生长因子处理以启动神经突发生的PC12细胞中的神经突生长增强。然而，令人惊讶的是，神经突生长增强是功能性半通道形成的结果，而非传统的细胞间通讯。进一步分析表明，ATP可能通过半通道释放到培养基中，并作用于嘌呤能受体，从而导致神经突生长增强。总体而言，本研究结果表明，连接蛋白可能通过非传统机制在神经元分化中发挥重要作用。
