HERG K+ channel conductance promotes H2O2-induced apoptosis in HEK293 cells: Cellular mechanisms

The human ether-a-go-go-related gene (JERG) encodes a delayed rectifier K+ channel, which is expressed in a variety of tissues and cells. Besides its well-recognized function in cellular eletrophysiology, HERG channels have also been implicated in neuronal differentiation and cell cycle regulation. We have recently found that HERG regulated apoptosis. To elucidate the signaling pathways, we performed studies in HEK293 cells stably expressing HERG channels. ELISA was used to quantify DNA fragmentation, a biochemical hallmark of apoptosis. In HERG-transfected HEK cells, the degree of DNA fragmentation was found consistently higher (similar to4-times) than in non-transfected cells. Correspondingly, remarkable activation of caspase 3, caspase 9 and cleavage of PARP were seen in HERG-expressing cells, which were otherwise minimal in non-transfected cells. Exposure of cells to H2O2 (10 hrs) at concentrations up to 1 mM, which is known to induce apoptosis in a variety of cells, caused minimal DNA fragmentation in non-transfected cells. HERG expression facilitates DNA fragmentation induced by H2O2 at a concentration-dependent fashion, starting at 200 muM and reaching maximum at 1 mM. Selective HERG channel inhibitors, dofetilide or E-4031 (5 muM) prevented DNA fragmentation. Inhibition of p38 by SB-2083580 alleviated DNA-F and PD-98059, which inhibited activation of ERKs, nearly abolished DNA-F. Immunoblotting analysis demonstrated that p38, SAPKs and ERKs MAP kinases were all substantially activated (>10-fold higher) in HERG-expressing cells vs. non-transfected cells. Akt activity was similar to4-fold lower in HERG cells vs. non-transfected cells in the absence of H2O2 and was slightly increased (similar to2-fold) after H2O2 exposure. We conclude that HERG channels facilitate cellular DNA fragmentation in HEK cells via concomitant activation of MAP kinases and inactiviation of Akt. Copyright (C) 2004 S. Karger Ag, Base l.