Visual Overview
Abstract
This is the first work to use a newly designed Li+-selective photoswitchable probe Sabrina Heng Lithium (SHL) in living colon cancer cells to noninvasively monitor cation channel activity in real time by the appearance of lithium hot spots detected by confocal microscopy. Punctate Li+ hot spots are clustered in the lamellipodial leading edges of HT29 human colon cancer cells and are colocalized with aquaporin-1 (AQP1) channels. AQP1 is a dual water and cyclic-nucleotide-gated cation channel located in lamellipodia and is essential for rapid cell migration in a subset of aggressive cancers. Both the Li+ hot spots and cell migration are blocked in HT29 cells by the AQP1 ion channel antagonist AqB011. In contrast, Li+ hot spots are not evident in a poorly migrating colon cancer cell line, SW620, which lacks comparable membrane expression of AQP1. Knockdown of AQP1 by RNA interference in HT29 cells significantly impairs Li+ hot spot activity. The SHL probe loaded in living cells shows signature chemical properties of ionic selectivity and reversibility. Dynamic properties of the Li+ hot spots, turning on and off, are confirmed by time-lapse imaging. SHL is a powerful tool for evaluating cation channel function in living cells in real time, with particular promise for studies of motile cells or interlinked networks not easily analyzed by electrophysiological methods. The ability to reset SHL by photoswitching allows monitoring of dynamic signals over time. Future applications of the Li+ probe could include high-throughput optical screening for discovering new classes of channels, or finding new pharmacological modulators for nonselective cation channels.
Footnotes
- Received December 3, 2018.
- Accepted March 5, 2019.
This work was supported by the Australian Research Council [Grants DP160104641 and DP190101745]. Sensor development was supported by the Centre for Nanoscale BioPhotonics, with funding from the Australian Research Council [Grant CE140100003].
Part of this work was presented at the 2018 Biophysics Conference, and the abstract was published in the following Biophysical Journal conference proceedings: Pei JV, Heng S, De Ieso M, Sylvia G, Kourghi M, Abell AD, and Yool AJ (2018) Real-Time Imaging of Lithium ‘Hot-Spots’: An Analysis of Ion Conductance in Aquaporin-1 using Novel Photo-Switchable Sensor. Biophys J 114:360a DOI: 10.1016/j.bpj.2017.11.1999.
↵This article has supplemental material available at molpharm.aspetjournals.org.
- Copyright © 2019 by The Author(s)
This is an open access article distributed under the CC BY-NC Attribution 4.0 International license.