Publication

Cathepsin G, and not the asparagine-specific endoprotease, controls the processing of myelin basic protein in lysosomes from human B lymphocytes

Journal Paper/Review - May 1, 2004

Units
PubMed

Citation
Burster T, Kalbacher H, Stevanovic S, Lehmann R, Melms A, Wiendl H, Schwarz G, Brandenburg J, Reich M, Lautwein A, Falk K, Rotzschke O, Marin-Esteban V, Tolosa E, Beck A, Driessen C. Cathepsin G, and not the asparagine-specific endoprotease, controls the processing of myelin basic protein in lysosomes from human B lymphocytes. Journal of immunology (Baltimore, Md. : 1950) 2004; 172:5495-503.
Type
Journal Paper/Review (English)
Journal
Journal of immunology (Baltimore, Md. : 1950) 2004; 172
Publication Date
May 1, 2004
Issn Print
0022-1767
Pages
5495-503
Brief description/objective

The asparagine-specific endoprotease (AEP) controls lysosomal processing of the potential autoantigen myelin basic protein (MBP) by human B lymphoblastoid cells, a feature implicated in the immunopathogenesis of multiple sclerosis. In this study, we demonstrate that freshly isolated human B lymphocytes lack significant AEP activity and that cleavage by AEP is dispensable for proteolytic processing of MBP in this type of cell. Instead, cathepsin (Cat) G, a serine protease that is not endogenously synthesized by B lymphocytes, is internalized from the plasma membrane and present in lysosomes from human B cells where it represents a major functional constituent of the proteolytic machinery. CatG initialized and dominated the destruction of intact MBP by B cell-derived lysosomal extracts, degrading the immunodominant MBP epitope and eliminating both its binding to MHC class II and a MBP-specific T cell response. Degradation of intact MBP by CatG was not restricted to a lysosomal environment, but was also performed by soluble CatG. Thus, the abundant protease CatG might participate in eliminating the immunodominant determinant of MBP. Internalization of exogenous CatG represents a novel mechanism of professional APC to acquire functionally dominant proteolytic activity that complements the panel of endogenous lysosomal enzymes.