Cardiac glycoside induces cell death via FasL by activating calcineurin and NF-AT, but apoptosis initially proceeds through activation of caspases

Decrease in caspase activity is a common phenomenon in drug resistance. For effective therapeutic intervention, detection of such agents, which affects other pathway independent of caspases to promote cell death, might be important. Oleandrin, a polyphenolic glycoside induced cell death through activation of caspases in a variety of human tumour cells. In this report we provide evidence that besides caspases activation, oleandrin interacts with plasma membrane, changes fluidity of the membrane, disrupts Na(+)/K(+)-ATPase pump, enhances intracellular free Ca(2+) and thereby activates calcineurin. Calcineurin, in turns, activates nuclear transcription factor NF-AT and its dependent genes such as FasL, which induces cell death as a late response of oleandrin. Cell death at early stages is mediated by caspases where inhibitors partially protected oleandrin-mediated cell death in vector-transfected cells, but almost completely in Bcl-xL-overexpressed cells. Overall, our data suggest that oleandrin might be important therapeutic molecule in case of tumors where cell death pathway occurs due to deregulation of caspase-mediated pathway.