Elevated extracellular [K+] inhibits death-receptor- and chemical-mediated apoptosis prior to caspase activation and cytochrome c release.
Efflux of intracellular K(+) and cell shrinkage are features of apoptosis in many experimental systems, and a regulatory role has been proposed for cytoplasmic [K(+)] in initiating apoptosis. We have investigated this in both death-receptor-mediated and chemical-induced apoptosis. Using Jurkat T cells pre-loaded with the K(+) ion surrogate (86)Rb(+), we have demonstrated an efflux of intracellular K(+) during apoptosis that was concomitant with, but did not precede, other apoptotic changes, including phosphatidylserine externalization, mitochondrial depolarization and cell shrinkage. To further clarify the role of K(+) ions in apoptosis, cytoprotection by elevated extracellular [K(+)] was studied. Induction of apoptosis by diverse death-receptor and chemical stimuli in two cell lines was inhibited prior to phosphatidylserine externalization, mitochondrial depolarization, cytochrome c release and caspase activation. Using a cell-free system, we have demonstrated a novel mechanism by which increasing [K(+)] inhibited caspase activation. In control dATP-activated lysates, Apaf-1 oligomerized to a biologically active caspase processing approximately 700 kDa complex and an inactive approximately 1.4 MDa complex. Increasing [K(+)] inhibited caspase activation by preventing formation of the approximately 700 kDa complex, but not of the inactive complex. Thus intracellular and extracellular [K(+)] markedly affect caspase activation and the initiation of apoptosis induced by both death-receptor ligation and chemical stress.
Thompson
G J
GJ
MRC Toxicology Unit, Hodgkin Building, University of Leicester, P.O. Box 138, Lancaster Road, Leicester LE1 9HN, UK.
Langlais
C
C
Cain
K
K
Conley
E C
EC
Cohen
G M
GM
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000906:Antibodies / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism*; D003600:Cytosol / Q000502:physiology; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology; D005110:Extracellular Space / Q000502:physiology; D005434:Flow Cytometry; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D019169:Jurkat Cells; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology; D010718:Phosphatidylserines / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D018124:Receptors, Tumor Necrosis Factor / Q000187:drug effects / Q000502:physiology*; D012413:Rubidium / Q000493:pharmacokinetics; D013601:T-Lymphocytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000187:drug effects / Q000502:physiology
D000590:Amino Acid Chloromethyl Ketones; D000906:Antibodies; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D003574:Cytochrome c Group; D010718:Phosphatidylserines; D018124:Receptors, Tumor Necrosis Factor; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D011189:Potassium Chloride; D005047:Etoposide; D020169:Caspases; D012413:Rubidium; D011188:Potassium