Furin activates Pseudomonas exotoxin A by specific cleavage in vivo and in vitro.

We have demonstrated that the native proenzymatic form of Pseudomonas exotoxin A can be cleaved at its specific activation site by furin in intact Chinese hamster ovary cells or in vitro by furin in isolated membrane fractions from these cells. We have compared the activity of furin in cell membrane fractions with that of purified, recombinant human furin. We have verified that RPE.40, a Pseudomonas toxin-resistant mutant cell strain, is mutant in the fur gene, and we have demonstrated that these cells are deficient in cleavage of the toxin. We have also determined that this cleavage of Pseudomonas toxin by furin takes place at the authentic activation site to release the 37-kDa active fragment.