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Endosomal proteolysis of diphtheria toxin without toxin translocation into the cytosol of rat liver in vivo.

Abstract : A detailed proteolysis study of internalized diphtheria toxin (DT) within rat liver endosomes was undertaken to determine whether DT-resistant species exhibit defects in toxin endocytosis, toxin activation by cellular enzymes or toxin translocation to its cytosolic target. Following administration of a saturating dose of wild-type DT or nontoxic mutant DT (mDT) to rats, rapid endocytosis of the intact 62-kDa toxin was observed coincident with the endosomal association of DT-A (low association) and DT-B (high association) subunits. Assessment of the subsequent post-endosomal fate of internalized mDT revealed a sustained endo-lysosomal transfer of the mDT-B subunit accompanied by a net decrease in intact mDT and mDT-A subunit throughout the endo-lysosomal apparatus. In vitro proteolysis of DT, using an endosomal lysate, was observed at both neutral and acidic pH, with the subsequent generation of DT-A and DT-B subunits (pH 7) or DT fragments with low ADP-ribosyltransferase activity (pH 4). Biochemical characterization revealed that the neutral endosomal DT-degrading activity was due to a novel luminal 70-kDa furin enzyme, whereas the aspartic acid protease cathepsin D (EC 3.4.23.5) was identified as being responsible for toxin degradation at acidic pH. Moreover, an absence of in vivo association of the DT-A subunit with cytosolic fractions was identified, as well as an absence of in vitro translocation of the DT-A subunit from cell-free endosomes into the external milieu. Based on these findings, we propose that, in rat, resistance to DT may originate from two different mechanisms: the ability of free DT-A subunits to be rapidly proteolyzed by acidic cathepsin D within the endosomal lumen, and/or the absence of DT translocation across the endosomal membrane, which may arise from the absence of a functional cytosolic translocation factor previously reported to participate in the export of DT from human endosomes.
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https://www.hal.inserm.fr/inserm-00270299
Contributor : Patrice Codogno <>
Submitted on : Friday, April 4, 2008 - 12:17:04 PM
Last modification on : Wednesday, October 14, 2020 - 4:05:58 AM

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Tatiana El Hage, Paulette Decottignies, François Authier. Endosomal proteolysis of diphtheria toxin without toxin translocation into the cytosol of rat liver in vivo.. FEBS Journal, Wiley, 2008, 275 (8), pp.1708-22. ⟨10.1111/j.1742-4658.2008.06326.x⟩. ⟨inserm-00270299⟩

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