Cathepsin V is involved in the degradation of invariant chain in human thymus and is overexpressed in myasthenia gravis
Eva Tolosa, … , Arthur Melms, Dieter Brömme
Eva Tolosa, … , Arthur Melms, Dieter Brömme
Published August 15, 2003
Citation Information: J Clin Invest. 2003;112(4):517-526. https://doi.org/10.1172/JCI18028.
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Article Autoimmunity

Cathepsin V is involved in the degradation of invariant chain in human thymus and is overexpressed in myasthenia gravis

Abstract

Stepwise degradation of the invariant chain (Ii) is required for the binding of antigenic peptides to MHC class II molecules. Cathepsin (Cat) L in the murine thymus and Cat S in peripheral APCs have both been implicated in the last step of Ii degradation that gives rise to the class II–associated invariant chain peptides (CLIP). Cat V has been recently described as highly homologous to Cat L and exclusively expressed in human thymus and testis, but with no mouse orthologue. We report that Cat V is the dominant cysteine protease in cortical human thymic epithelial cells, while Cat L and Cat S seem to be restricted to dendritic and macrophage-like cells. Active Cat V in thymic lysosomal preparations was demonstrated by active-site labeling. Recombinant Cat V was capable of converting Ii into CLIP efficiently, suggesting that Cat V is the protease that controls the generation of αβ-CLIP complexes in the human thymus, in analogy to Cat L in mouse. Comparison of Cat V expression between thymi from patients with myasthenia gravis and healthy controls revealed a significantly higher expression level in the pathological samples, suggesting a potential involvement of this protease in the immunopathogenesis of myasthenia gravis, an autoimmune disease almost invariably associated with thymic pathology.

Authors

Eva Tolosa, Weijie Li, Yoshiyuki Yasuda, Wolfgang Wienhold, Lisa K. Denzin, Alfred Lautwein, Christoph Driessen, Petra Schnorrer, Ekkehard Weber, Stefan Stevanovic, Raffael Kurek, Arthur Melms, Dieter Brömme

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Figure 6

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Degradation of Ii by human Cats V, L, and S and peptide loading on cathe...
Degradation of Ii by human Cats V, L, and S and peptide loading on cathepsin-processed αβIi complexes. (a) DA6.147 affinity column purified [35S] methionine-labeled HLA-DR3 αβIi complexes were digested with purified recombinant human Cats V, L, and S at the indicated concentrations in sodium acetate buffer, pH 5.0 as described in the Methods section. The digested products were separated by SDS-PAGE using 15% acrylamide gels. E-64 inactivated cathepsins at the 250 nM concentration were used as controls. All three cathepsins were capable to degrade Ii and to generate CLIP. Cats V and S were specific for the processing of Ii at enzyme concentrations expected to be present in the endosomal-lysosomal compartment, whereas Cat L activity was nonspecific at concentrations higher than 10 nM. The positions of the individual class II α and β chains, the Ii chain, CLIP, and the αβ peptide dimers are indicated on each gel. (b) Affinity purified radiolabeled HLA-DR αβIi complexes were digested with Cat V (50 nM), Cat L (10 nM), and Cat S (50 nM). The digestion mixtures were inactivated by E-64 and subsequently incubated with the DR3-specific MOMP peptide in the presence or absence of HLA-DM for 2 hours at 37°C. The formation of αβ peptides is shown after SDS-PAGE using 11.25% acrylamide gels.