Multiple effects of digoxin on subsets of cancer-associated genes through the alternative splicing pathway.

The signaling characteristics of Na(+)/K(+)-ATPase are distinct from its ion pumping activity. Cardiac glycosides modulate the Na(+)/K(+)-ATPase protein complex upon binding, activate downstream signaling pathways and increase [Ca(2+)]i. Recent studies demonstrate that the depletion of p53 and hypoxia-induced factor 1α proteins is caused by cardiac glycosides. However, the detailed mechanisms governing this process are not well known. In this study, we showed that the depletion of p53 proteins by digoxin involved not only inhibition of protein synthesis but also inhibition at the post-transcriptional level. Post-transcriptional regulation occurs via down-regulation of SRSF3, the primary splicing factor responsible for the switch from p53α to the p53β isoform. Digoxin also modulated G2/M arrest, DNA damage and apoptosis through the p53-dependent pathway in HeLa cells. In addition, digoxin was involved in epithelial-mesenchymal-transition progression via E-cadherin reduction and snail induction. Digoxin had similar effects to caffeine, another SRSF3-reduced agent, on the cell cycle profile and DNA damage of cells. Interestingly, combined digoxin and caffeine treatment blocked cell cycle progression and conferred resistance to cell death via snail induction. These findings demonstrate that down-regulation of splicing factor, such as SRSF3, to alter cell cycle progression, cell death and invasion is a potential target for the drug repositioning of cardiac glycosides.