Methods for promoting, inhibiting and detecting toxin entry into cells
In vitro delivery of the diphtheria toxin (DT) catalytic (C) domain from the lumen of purified early endosomes to the external milieu requires the addition of both ATP and a cytosolic translocation factor (CTF) complex. The results presented here demonstrate that β-COP plays an essential role in the cytosolic release of the C-domain and is mediated by a consensus peptide sequence found on several bacterial toxins and in HIV-1 reverse transcriptase. The invention features methods for inhibiting cell death that include the administration of compounds based on this consensus sequence that inhibit the translocation of the catalytic domain of toxins or transcription factors. Also featured are methods for identifying compounds that inhibit cell death, and methods for identifying compounds that promote cell death by blocking or accelerating, respectively, the rate of toxin/factor endosomal translocation.
1. A method of identifying a compound that is capable of inhibiting cell death in a mammal comprising the following steps:
a) isolating, from a mammalian cell, an early endosome comprising a toxin selected from the group consisting of Diptheria toxin, Botulinum toxin, Anthrax toxin Lethal Factor (LF), and Anthrax toxin Edema Factor (EF);
b) placing said endosomes in a cytosolic buffer;
c) contacting said endosomes with a cytosolic translocation factor complex, comprising beta-COP;
d) contacting said endosomes with said compound;
e) acidifying said endosome; and
f) measuring translocation of said toxin, wherein a decreased level of said translocation relative to that observed in the absence of said compound indicates that said compound is capable of inhibiting said cell death.
2. The method of claim 1 , wherein said toxin is a fusion protein comprising IL-2.
3. The method of claim 2 , wherein said toxin is DAB 389 IL-2.
4. The method of claim 1 , wherein said cytosolic translocation factor comprises Hsp 90.
5. The method of claim 1 wherein said cytosolic translocation factor comprises TrR-1.
6. The method of claim 1 , wherein measuring said translocation comprises measuring the ADP-ribosylation of elongation factor-2.
7. The method of claim 1 , wherein said toxin Diphtheria toxin.
8. A method of identifying a compound that is capable of promoting cell death in a mammal comprising the following steps:
a) isolating, from a mammalian cell, an early endosome comprising a toxin selected from the group consisting of Diptheria toxin, Botulinum toxin, Anthrax toxin Lethal Factor (LF), and Anthrax toxin Edema Factor (EF);
b) placing said endosomes in a cytosolic buffer;
c) contacting said endosomes with a cytosolic translocation factor complex, comprising beta-COP;
d) contacting said endosomes with said compound;
e) acidifying said endosome; and
f) measuring translocation of said toxin, wherein a decreased level of said translocation relative to that observed in the absence of said compound indicates that said compound is capable of promoting said cell death.
9. The method of claim 8 , wherein said toxin is a fusion protein comprising IL-2.
10. The method of claim 9 , wherein said fusion protein is DAB 389 IL-2.
11. The method of claim 8 , wherein said cytosolic translocation factor comprises Hsp 90.
12. The method of claim 8 , wherein said cytosolic translocation factor comprises TrR-1.
13. The method of claim 8 , wherein measuring said translocation comprises measuring the ADP-ribosylation of elongation factor-2.
14. The method of claim 8 , wherein said toxin is Diphtheria toxin.
15. The method of claim 8 , wherein said toxin is Botulinum toxin.
16. The method of claim 8 , wherein said toxin is Anthrax toxin Lethal Factor (LF).
17. The method of claim 8 , wherein said toxin is Anthrax toxin Edema Factor (EF).
18. The method of claim 8 , wherein said mammalian cell is a human cell.
19. The method of claim 1 , wherein said toxin is Botulinum toxin.
20. The method of claim 1 , wherein said toxin is Anthrax toxin Lethal Factor (LF).
21. The method of claim 1 , wherein said toxin is Anthrax toxin Edema Factor (EF).
22. The method of claim 1 , wherein said mammalian cell is a human cell.