Selective Inhibition of Intracellular Kv1.3 Potassium Channels by Lentivirus-Mediated Expression of Agitoxin

Non-plasma membrane Kv1.3 voltage-gated potassium channels, particularly those localized to the inner mitochondrial membrane, is pro-survival in that inhibition of these channels enhances apoptosis of cancer cells. Paradoxically, cells that lack Kv1.3 show resistance to cytotoxic agents suggesting a pro-death role of the same channels. Currently reported genetic and pharmacological reagents block both plasma membrane and intracellular Kv1.3 and lack absolute selectivity for intracellular Kv1.3. We designed a lentivirus for intracellular expression of the Kv1.3-selective peptide toxin agitoxin and created a Jurkat lymphocyte cell line that constitutively expressed intracellular agitoxin to selectively inhibit intracellular Kv1.3. Agitoxin-expressing Jurkat cells demonstrated relative resistance to cytokine-induced apoptosis, whereas direct extracellular application of agitoxin, or control cells expressing EGFP alone, failed to demonstrate this cyto- protection. We concluded that the intracellular Kv1.3 served a pro-death role, and a selective inhibition of this target reduced lymphocyte apoptosis by cytokine stimulation as reported previously for Kv1.3-null cells.