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Human B lymphoblastoid cells contain distinct patterns of cathepsin activity in endocytic compartments and regulate MHC class II transport in a cathepsin S‐independent manner
Author(s) -
Lautwein Alfred,
Kraus Marianne,
Reich Michael,
Burster Timo,
Brandenburg J.,
Overkleeft Herman S.,
Schwarz Gerold,
Kammer Winfried,
Weber Ekkehard,
Kalbacher Hubert,
Nordheim Alfred,
Driessen Christoph
Publication year - 2004
Publication title -
journal of leukocyte biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.819
H-Index - 191
eISSN - 1938-3673
pISSN - 0741-5400
DOI - 10.1189/jlb.0803367
Subject(s) - endocytic cycle , endosome , biology , proteases , microbiology and biotechnology , cathepsin , cell fractionation , cathepsin d , antigen processing , biochemistry , mhc class i , endocytosis , major histocompatibility complex , intracellular , cell , enzyme , gene
Endocytic proteolysis represents a major functional component of the major histocompatibility complex class II antigen‐presentation machinery. Although transport and assembly of class II molecules in the endocytic compartment are well characterized, we lack information about the pattern of endocytic protease activity along this pathway. Here, we used chemical tools that visualize endocytic proteases in an activity‐dependent manner in combination with subcellular fractionation to dissect the subcellular distribution of the major cathepsins (Cat) CatS, CatB, CatH, CatD, CatC, and CatZ as well as the asparagine‐specific endoprotease (AEP) in human B‐lymphoblastoid cells (BLC). Endocytic proteases were distributed in two distinct patterns: CatB and CatZ were most prominent in early and late endosomes but absent from lysosomes, and CatH, CatS, CatD, CatC, and AEP distributed between late endosomes and lysosomes, suggesting that CatB and CatZ might be involved in the initial proteolytic attack on a given antigen. The entire spectrum of protease activity colocalized with human leukocyte antigen‐DM and the C‐terminal and N‐terminal processing of invariant chain (Ii) in late endosomes. CatS was active in all endocytic compartments. Surprisingly and in contrast with results from dendritic cells, inhibition of CatS activity by leucine–homophenylalanine–vinylsulfone‐phenol prevented N‐terminal processing of Ii but did not alter the subcellular trafficking or surface delivery of class II complexes, as deferred from pulse‐chase analysis in combination with subcellular fractionation and biotinylation of cell‐surface protein. Thus, BLC contain distinct activity patterns of proteases in endocytic compartments and regulate the intracellular transport and surface‐delivery of class II in a CatS‐independent manner.