Maintenance of oxidative phosphorylation protects cells from Actinobacillus actinomycetemcomitans leukotoxin-induced apoptosis.
Subnanomolar concentrations (3 x 10(-10) M) of Actinobacillus actinomycetemcomitans leukotoxin (Ltx) trigger apoptosis of JY cells, as shown by a decrease in mitochondrial transmembrane potential (DeltaPsim), hyperproduction of reactive oxygen species (ROS) and release of cytochrome c from the intermembrane space. When compared with heat-inactivated leukotoxin (DeltaI Ltx) controls, ATP levels in Ltx-treated JY cells continued to decrease during a 24 h experiment while cytoplasmic ADP concentrations were increasing. These results suggest that a blockage occurred in ATP/ADP exchange. To maintain ATP/ADP exchange, JY cells were transfected with bcl-2 and bcl-xL and incubated with Ltx. ATP levels of the transfected cells decreased to 67% (JY/bcl-2) and 73% (JY/bcl-xL) after the experiment. Furthermore, cytochrome c remained localized to the mitochondrial fraction of Ltx-treated JY/bcl-2 and JY/bcl-xL cells, whereas its presence in the cytoplasmic fraction of JY/gen cells suggests an uncoupling of electron transport. Expression of bcl-2 and bcl-xL in cells inhibited downstream apoptotic events such as cleavage of poly(ADP-ribose) polymerase, DNA fragmentation and activation of a family of caspases. The results indicate that Ltx induces apoptosis through a mitochondrial pathway that involves decreased levels of the ADP in the mitochondrial matrix, a lack of substrate for ATP synthetase and arrest of oxidative phosphorylation.
Yamaguchi
N
N
Leon Levy Research Center for Oral Biology, University of Pennsylvania School of Dental Medicine, 4010 Locust Street, Philadelphia, PA 19104-6002, USA.
Kieba
I R
IR
Korostoff
J
J
Howard
P S
PS
Shenker
B J
BJ
Lally
E T
ET
D000255:Adenosine Triphosphate / Q000378:metabolism; D016976:Aggregatibacter actinomycetemcomitans; D017209:Apoptosis; D001427:Bacterial Toxins / Q000494:pharmacology*; D053148:Caspase 3; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D003603:Cytotoxins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005098:Exotoxins / Q000494:pharmacology*; D015870:Gene Expression; D010085:Oxidative Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein
D001427:Bacterial Toxins; D003574:Cytochrome c Group; D003603:Cytotoxins; D005098:Exotoxins; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; C018579:leukotoxin; D000255:Adenosine Triphosphate; D053148:Caspase 3; D053179:Caspase 7; D053453:Caspase 9; D020169:Caspases