Nuclear Chloride Ion-Selective Fluorescent Probe and Its Biological Applications

Owing to the biological significance of Cl^- in cells, several chemical fluorescent probes and biosensors have been constructed to monitor this anion in the cytosol and subcellular organelles. However, a fluorescent probe for the selective detection of nuclear Cl^- has not been described thus far. In the current study, we developed the first nuclear Cl^--selective biosensor, Cl-YFP-NLS, whose fluorescence was effectively quenched by this anion, and demonstrated that it is an efficient and powerful tool for determining the levels of nuclear Cl^-. The results of cell studies using Cl-YFP-NLS as the probe suggested that the level of Cl^- in the nucleus is lower than that in the cytosol. In addition, Cl-YFP-NLS along with lysosomal (Lyso-MQAE) and mitochondrial Cl^--selective fluorescent probes (Mito-MQAE) were utilized to determine the effects of various substances on the levels of Cl^- in subcellular organelles. The results showed that lysosomotropic agents decrease the lysosomal Cl^- concentration and increase the levels of mitochondrial and nuclear Cl^-. Also, observations suggested that substances capable of inducing mitochondrial outer membrane permeabilization without inducing lysosomal membrane permeabilization increase mitochondrial and nuclear Cl^- concentrations but they do not affect the level of lysosomal Cl^-. Moreover, a substance directly disrupting nuclear pore complexes increased the level of nuclear Cl^- and did not change the levels of lysosomal and mitochondrial Cl^-. Finally, nucleus-affecting substances that cause deoxyribonucleic acid damage and activate p53 and Bax increased the levels of mitochondrial and nuclear Cl^- without influencing the level of lysosomal Cl^-.