Postmitochondrial regulation of apoptosis by bicarbonate.
Ion homeostasis may play a role in the regulation of apoptosis. The current study has shown such a role for bicarbonate (HCO(3)(-)). In apoptosis triggered by ATP depletion, the proapoptotic molecule Bax translocated from the cytosol to mitochondria, followed by cytochrome c release from the organelle, caspase activation, and development of apoptotic morphology. Apoptosis was significantly ameliorated, when HCO(3)(-) was omitted from the incubation medium. The HCO(3)(-) dependence was also demonstrated for apoptosis induced by staurosporine in HeLa cells. Of significance, when HCO(3)(-) was reintroduced, apoptosis was restored. The Cl(-)/HCO(3)(-) exchanger inhibitor DIDS suppressed apoptosis in HCO(3)(-)-containing medium, further supporting a role for intracellular HCO(3)(-) in apoptosis regulation. We subsequently examined HCO(3)(-)-dependent steps in the apoptotic cascade. Translocation of Bax and cytochrome c was not suppressed by the omission of HCO(3)(-), suggesting HCO(3)(-) regulation at postmitochondrial levels. In vitro reconstitution of caspase activation using exogenous cytochrome c and cytosolic extracts was not HCO(3)(-) dependent. HCO(3)(-) was not required for the enzymatic activity of recombinant caspases either. In conclusion, the results have provided compelling evidence for HCO(3)(-) regulation of apoptosis. Such regulation takes place at postmitochondrial levels, downstream of Bax/cytochrome c translocation.
Dong
Zheng
Z
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta, GA 30912, USA. zdong@mail.mcg.edu
Wang
Jinzhao
J
Zhong
Qiu
Q
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001639:Bicarbonates / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D004847:Epithelial Cells; D006367:HeLa Cells; D006706:Homeostasis; D006801:Humans; D007684:Kidney Tubules / Q000166:cytology; D034921:Lamin Type B / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C494828:Bax protein, rat; D001639:Bicarbonates; D003574:Cytochrome c Group; D034921:Lamin Type B; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D000255:Adenosine Triphosphate; D020169:Caspases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid