Intracellular K+ inhibits apoptosis by suppressing the Apaf-1 apoptosome formation and subsequent downstream pathways but not cytochrome c release

Abstract

Cellular ionic homeostasis, fundamentally K þ homeostasis, has been implicated as a critical regulator of apoptosis. The intracellular K þ efflux on apoptotic insult and suppression of apoptosis by high concentration of extracellular K þ or after inhibition of this efflux by K þ channel blockers have established the crucial role of K þ in turning on the apoptotic machinery. Several contrasting observations have reported the antiapoptotic effect of intracellular K þ concentration to be the result of inhibition of cytochrome c release from mitochondria, but the exact inhibitory mechanism remains obscure. However, here we show the blockage of K þ efflux during apoptosis did not affect cytochrome c release from the mitochondria, still completely inhibited the formation of the apoptosome comprising Apaf-1, cytochrome c, caspase-9 and other accessories. As a consequence of this event, procaspase-9, -3, -8 and other death-related proteins were not processed. Furthermore, physiological concentrations of K þ also inhibited the processing of procaspase-3 by purified caspase-8 or -9, the nucleosomal DNA fragmentation by purified DFF40/CAD and the nuclear fragmentation to varying extents. Altogether, these findings suggest that the efflux of K þ is prerequisite not only for the formation of the apoptosome but also for the downstream apoptotic signaltransduction pathways.

The Therapeutic Potential of Modifying Inflammasomes and NOD-Like Receptors

“…In vitro experiments show that the K + threshold for inflammasome inhibition is in the 70 mM range (Petrilli et al, 2007). This seems to be a common feature of inflammatory and apoptotic caspases (Karki et al, 2007;Arlehamn et al, 2010). The trigger role of K + depletion in caspase-1 activation was known long before the inflammasome was discovered thanks to the pioneering experiments of Gabel and co-workers who showed that the K + selective ionophore nigericin, but not the Na + selective ionophore monensin, Fig.…”

Cellular Mechanisms Controlling Caspase Activation and Function

“…These proteins facilitate nucleotide exchange on Apaf-1, which is necessary for full apoptosome formation and subsequent caspase-9 activation. Interestingly, levels of other (nonprotein) cellular components, such nucleotides and ions, also appear to play critical roles in regulating certain steps in the activation of caspases and the apoptotic pathway (Cain et al 2001;Chandra et al 2006;Bao et al 2007;Karki et al 2007;Mei et al 2010). Because there have been a variety of recent reviews on the proteins that regulate caspases indirectly, these circumstances are not covered here (Schafer and Kornbluth 2006;Fadeel et al 2008;Krumschnabel et al 2009).…”

Glutathione Depletion and Disruption of Intracellular Ionic Homeostasis Regulate Lymphoid Cell Apoptosis

“…However, the exact mechanism by which the reduction in GSH i modulates the activation of the execution phase of apoptosis is still imprecise. A necessary role of K ϩ loss for the activation of execution caspases and apoptosome formation has also been demonstrated (5,60,61), whereas Cl Ϫ loss does not seem to play an important role in this phenomenon (62). Thus, we analyzed if the modulation of the execution phase of apoptosis by GSH transport was linked to the regulation of K ϩ loss.…”