RNase-induced apoptosis: Fate of calcium-activated potassium channels

Abstract

The connection between the action of microbial RNases and Ca 2+-activated K + (K Ca) channels was investigated in human embryo kidney cells HEKhSK4 artificially expressing the channels. These channels protected HEKhSK4 cells from apoptosis induced by binase and 5K charge reversal mutant of RNase Sa. After the first 24 h, potassium current increased without increase in intracellular Ca 2+, and mitochondrial potential remained high. After 72 h, the concentration of calcium increased and mitochondria lost their potential. Whole-cell recordings of membrane currents through K Ca channels in RNase-treated cells demonstrated a biphasic pattern: initially their activity in cell population increased, peaked at 24 h, and then gradually decreased. In each individual cell we observed either an increase of the amplitude of K Ca current, or a complete shutdown of the channels. The activity of K Ca channels could be restored by removing RNases from the media. Based on this pattern and especially its timing, we hypothesize that toxic RNases downregulate K Ca channels at the level of transcription or translation. Our results indicate that new anticancer agents could be created on the basis of microbial RNases targeting K Ca channels.