E. Lemichez et al., MEMBRANE TRANSLOCATION OF DIPHTHERIA-TOXIN FRAGMENT - A EXPLOITS EARLY TO LATE ENDOSOME TRAFFICKING MACHINERY, Molecular microbiology, 23(3), 1997, pp. 445-457
After reaching early endosomes by receptor-mediated endocytosis, dipht
heria toxin (DT) molecules have two possible fates. A large pool enter
s the degradative pathway whereas a few molecules become cytotoxic by
translocating their catalytic fragment A (DTA) into the cytosol. Impai
rment of DT degradation by microtubule depolymerization does not block
DT cytotoxicity. Therefore, DTA membrane translocation into the cytos
ol occurs from an endocytic compartment located upstream of late endos
omes. Comparisons between early endosomes and endocytic carrier vesicl
es in a cell-free translocation assay have demonstrated that early end
osomes are the earliest endocytic compartment from which DTA transloca
tes. DTA translocation is ATP-dependent, requires early endosomal acid
ification, and is increased by the addition of cytosol. Cytosol-depend
ent DTA translocation is GTP gamma S-insensitive but is blocked by ant
i-beta COP antibodies.