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Infect. Immun., 01 1995, 82-87, Vol 63, No. 1
VM Gordon, KR Klimpel, N Arora, MA Henderson and SH Leppla
Before intoxication can occur, anthrax toxin protective antigen (PA),
Pseudomonas exotoxin A (PE), and diphtheria toxin (DT) must be activated by
proteolytic cleavage at specific amino acid sequences. Previously, it was
shown that PA and DT can be activated by furin. In Chinese hamster ovary
(CHO) cells, wild-type (RKKR) and cleavage site mutants of PA, each
administered with a modified form of anthrax toxin lethal factor (the N
terminus of lethal factor fused to PE domain III), had the following
potencies: RKKR (wild type) (concentration causing 50% cell death [EC50] =
12 ng/ml) > or = RAAR (EC50 = 18 ng/ml) > FTKR (EC50 = 24 ng/ml) >
STRR (EC50 = 49 ng/ml). In vitro cleavage of PA and cleavage site mutants
of PA by furin demonstrated that native PA (RKKR) and PA with the cleavage
sequence RAAR are substrates for furin. To characterize eukaryotic
proteases that play a role in activating bacterial toxins, furin-deficient
CHO cells were selected after chemical mutagenesis. Furin-deficient cells
were resistant to PE, whose cleavage site, RQPR, constitutes a furin
recognition site and to all PA cleavage site mutants, but were sensitive to
DT (EC50 = 2.9 ng/ml) and PA (EC50 = 23 ng/ml), whose respective cleavage
sites, RKKR and RVRR, contain additional basic residues. Furin-deficient
cells that were transfected with the furin gene regained sensitivity to PE
and PA cleavage site mutants. These studies provide evidence that furin can
activate the three toxins and that one or more additional proteases
contribute to the activation of DT and PA.
Copyright © 1995, American Society for Microbiology
Proteolytic activation of bacterial toxins by eukaryotic cells is performed by furin and by additional cellular proteases
Laboratory of Microbial Ecology, National Institute of Dental Research, Bethesda, Maryland 20892.
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