Bcl-X(L) and calyculin A prevent translocation of Bax to mitochondria during apoptosis.
During many forms of apoptosis, Bax, a pro-apoptotic protein of the Bcl-2 family, translocates from the cytosol to the mitochondria and induces cytochrome c release, followed by caspase activation and DNA degradation. Both Bcl-X(L) and the protein phosphatase inhibitor calyculin A have been shown to prevent apoptosis, and here we investigated their impact on Bax translocation. ML-1 cells incubated with either anisomycin or staurosporine exhibited Bax translocation, cytochrome c release, caspase 8 activation, and Bid cleavage; only the latter two events were caspase-dependent, confirming that they are consequences in this apoptotic pathway. Both Bcl-X(L) and calyculin A prevented Bax translocation and cytochrome c release. Bcl-X(L) is generally thought to heterodimerize with Bax to prevent cytochrome c release and yet they remain in different cellular compartments, suggesting that their heterodimerization at the mitochondria is not the primary mechanism of Bcl-X(L)-mediated protection. Using chemical cross-linking agents, Bax appeared to exist as a monomer in undamaged cells. Upon induction of apoptosis, Bax formed homo-oligomers in the mitochondrial fraction with no evidence for cross-linking to Bcl-2 or Bcl-X(L). Considering that both Bcl-X(L) and calyculin A inhibit Bax translocation, we propose that Bcl-X(L) may regulate Bax translocation through modulation of protein phosphatase or kinase signaling.
Ganju
Neema
N
Department of Pharmacology and Toxicology, Dartmouth Medical School, 7650 Remsen, Hanover, NH 03755, USA.
Eastman
Alan
A
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000841:Anisomycin / Q000494:pharmacology; D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol; D018922:HL-60 Cells; D006801:Humans; D008387:Marine Toxins; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010080:Oxazoles / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D000590:Amino Acid Chloromethyl Ketones; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D003574:Cytochrome c Group; D008387:Marine Toxins; D010080:Oxazoles; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D000841:Anisomycin; C059041:calyculin A; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases