Lithium 'Hot-spots': Real-time Analysis of non-selective cation channel activity in migrating cancer cells
2019
Work here is the first to use a newly designed Li + -selective photoswitchable probe
(9SHL9) in living colon cancer cells to non-invasively 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, co-localized with aquaporin-1 (AQP1) channels. AQP1 is a dual
water and cyclic-nucleotide-gated cation channel, located in lamellipodia and 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 RNAi 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 non-selective
cation channels.
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