Actinobacillus actinomycetemcomitans leukotoxin requires lipid microdomains for target cell cytotoxicity.
Actinobacillus actinomycetemcomitans produces a leukotoxin (Ltx) that kills leukocyte function-associated antigen-1 (LFA-1)-bearing cells from man, the Great Apes and Old World monkeys. The unique specificity of Ltx for the beta2 integrin, LFA-1, suggests it is capable of providing insight into the pathogenic mechanisms of Ltx and other RTX toxins. Using the Jurkat T cell line and an LFA-1-deficient Jurkat mutant (Jbeta2.7) as models, we found the initial effect of Ltx is to elevate cytosolic Ca2+ [Ca2+]c, an event that is independent of the Ltx/LFA-1 interaction. [Ca2+]c increases initiate a series of events that involve the activation of calpain, talin cleavage, mobilization to, and subsequent clustering of, LFA-1 in cholesterol and sphingolipid-rich regions of the plasma membrane known as lipid rafts. The association of Ltx and LFA-1 within lipid rafts is essential for cell lysis. Jbeta2.7 cells fail to accumulate Ltx in their raft fractions and are not killed, while cholesterol depletion experiments demonstrate the necessity of raft integrity for Ltx function. We propose that toxin-induced Ca2+ fluxes mobilize LFA-1 to lipid rafts where it associates with Ltx. These findings suggest that Ltx utilizes the raft to stimulate an integrin signalling pathway that leads to apoptosis of target cells.
Fong
Karen P
KP
The Leon Levy Research Center for Oral Biology, University of Pennsylvania, Philadelphia, PA 19104-6002, USA.
Pacheco
Cinthia M F
CM
Otis
Linda L
LL
Baranwal
Somesh
S
Kieba
Irene R
IR
Harrison
Gerald
G
Hersh
Elliot V
EV
Boesze-Battaglia
Kathleen
K
Lally
Edward T
ET
D001427:Bacterial Toxins / Q000378:metabolism / Q000494:pharmacology*; D018821:CD18 Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002784:Cholesterol / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D005098:Exotoxins / Q000378:metabolism / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D039041:Integrin alpha4beta1 / Q000378:metabolism; D019169:Jurkat Cells; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D021962:Membrane Microdomains / Q000187:drug effects* / Q000378:metabolism; D018613:Microscopy, Confocal; D016608:Talin / Q000378:metabolism
D001427:Bacterial Toxins; D018821:CD18 Antigens; D005098:Exotoxins; D039041:Integrin alpha4beta1; D016169:Lymphocyte Function-Associated Antigen-1; D016608:Talin; C018579:leukotoxin; D002784:Cholesterol; D002154:Calpain; D002118:Calcium