Li Daliang, Liu Lin, Li Wen-Hong
Departments of Cell Biology and Biochemistry, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, Texas 75390-9039, United States.
ACS Chem Biol. 2015 Apr 17;10(4):1054-63. doi: 10.1021/cb5007536. Epub 2015 Jan 27.
Numerous mammalian cells contain Zn2+ in their secretory granules. During secretion, Zn2+ is coreleased with granular cargos into extracellular medium so Zn2+ serves as a convenient surrogate marker for tracking the dynamics of secretion. Fluorescent Zn2+ sensors that can be selectively targeted to cells of interest would be invaluable tools for imaging Zn2+ release in multicellular systems including tissues and live animals. Exploiting the HaloTag labeling technology and using an optimized linker, we have engineered a fluorescent Zn2+ indicator that displayed a 15-fold fluorescence enhancement upon Zn2+ binding while reacting efficiently with a HaloTag enzyme in a cellular environment. Two-color imaging of ZIMIR-HaloTag and a red-emitting calcium indicator in pancreatic islet beta cells demonstrated that photoactivation of a channelrhodopsin was able to induce exocytosis of Zn2+/insulin granules and revealed heterogeneity in secretory activity along the cell membrane that was uncoupled from cellular Ca2+ activity. This integrated photonic approach for imaging and controlling the release of large dense core granules provides exquisite cellular selectivity and should facilitate future studies of stimulus-secretion coupling and paracrine signaling in secretory cells.
许多哺乳动物细胞的分泌颗粒中含有Zn2+。在分泌过程中,Zn2+与颗粒性物质一起释放到细胞外介质中,因此Zn2+可作为追踪分泌动态的便捷替代标志物。能够选择性靶向目标细胞的荧光Zn2+传感器,对于在包括组织和活体动物在内的多细胞系统中成像Zn2+释放而言,将是非常宝贵的工具。利用HaloTag标记技术并使用优化的连接子,我们设计了一种荧光Zn2+指示剂,它在结合Zn2+时荧光增强了15倍,同时在细胞环境中能与HaloTag酶高效反应。在胰岛β细胞中对ZIMIR-HaloTag和一种红色发射钙指示剂进行双色成像表明,光激活视紫红质通道能够诱导Zn2+/胰岛素颗粒的胞吐作用,并揭示了沿细胞膜的分泌活性异质性,这种异质性与细胞Ca2+活性无关。这种用于成像和控制大致密核心颗粒释放的集成光子方法具有出色的细胞选择性,应有助于未来对分泌细胞中刺激-分泌偶联和旁分泌信号传导的研究。