Cathepsin V is involved in the degradation of invariant chain in human thymus and is overexpressed in myasthenia gravis
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
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
View: Text | PDF
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

×

Figure 5

Options: View larger image (or click on image) Download as PowerPoint
Active form of Cat V is expressed in human thymus. (a) Identification of...
Active form of Cat V is expressed in human thymus. (a) Identification of human Cats V, L, and S in human thymus extracts. Equal amounts (7.5 μg) of lysosomal fractions from human thymus were subjected to SDS-PAGE (10% gel), followed by Western blot analysis using antihuman Cat V antibody, antihuman Cat S antibody (1:2000 dilution), and mAb33/1 and mAb33/2 recognizing human Cat L and human Cats L and V, respectively. (b) Inhibition of recombinant human Cat S using LHVS inhibitor. Cats V and S (10 ng) were incubated with 1 nM LHVS at 37°C for the indicated time before labeling with DCG-04 as described in Methods. Activity of Cat S was completely blocked by incubation with 1 nM LHVS at 37°C for 20 minutes, but that of Cat V was not. Recombinant human Cat V is present in two isoforms distinguished by differential glycosylation as described in 14. (c) Selective inhibition of Cat S but not of Cat V in thymus extracts. Lysosomal fractions (1.5 μg) from human thymus were incubated with or without LHVS (1 nM or 1 μM) at 37°C for 20 minutes before labeling with DCG-04. At 1 nM LHVS concentration, the remaining band represents Cat V, whereas at 1 μM LHVS all cathepsins are inhibited and thus not labeled by DCG-04.