Cathepsin S Regulates the Expression of Cathepsin L and the Turnover of γ-Interferon-inducible Lysosomal Thiol Reductase in B Lymphocytes

Abstract

Loading of antigenic peptide fragments on major histocompatibility complex class II molecules is essential for generation of CD4؉ T cell responses and occurs after cathepsin-mediated degradation of the invariant chain chaperone molecule. Cathepsins are expressed differentially in antigen presenting cells, and mice deficient in cathepsin S or cathepsin L exhibit severely impaired antigen presentation in peripheral lymphoid organs and the thymus, respectively. To determine whether these defects are due solely to the block in invariant chain cleavage, we used cathepsin-deficient B cells to examine the role of cathepsins S and B in the degradation of other molecules important in the class II presentation pathway. Our data indicate that neither cathepsin S nor B is critical for H-2M degradation or processing of precursor ␥-interferon-inducible lysosomal thiol reductase (GILT) to a mature thiol reductase, but suggest a role for cathepsin S in the turnover of mature GILT and in regulating levels of mature cathepsin L protein in B cells. Despite the presence of mature cathepsin L protein, no enzyme activity could be detected in B cells or dendritic cells. These experiments suggest a novel mechanism by which these functionally important enzymes may be regulated. Recognition of antigen (Ag) by CD4ϩ T cells requires presentation of short peptide fragments in the context of major histocompatibility complex (MHC) 1 class II molecules (1, 2). MHC class II molecules consist of an ␣/␤ heterodimer that is assembled in the endoplasmic reticulum in association with a third glycoprotein, invariant chain (Ii), which promotes the correct folding of the MHC class II molecules (3, 4). A region of Ii known as class II-associated Ii peptide (CLIP) occupies the MHC class II peptide-binding groove to prevent inappropriate peptide loading (5-7), and signals in the cytoplasmic domain of Ii target the MHC class II/Ii chain complex to MHC class II rich endosomal compartments (8 -11). Upon entering the endocytic pathway, Ii chain is cleaved in a defined stepwise manner by proteases known as cathepsins (12)(13)(14), leaving only CLIP associated with the MHC class II heterodimer. Removal of CLIP and subsequent loading of diverse peptides is mediated by the MHC class II-like molecule HLA-DM (H-2M in mice) prior to MHC class II transport to the cell surface (15, 16).The cathepsins are a large family of aspartyl (D and E) and cysteinal (B, S, and L) endosomal proteases that have been implicated as critical to MHC class II presentation (12-14, 17). However, recent studies using cathepsin-deficient mice have shown that cathepsin D (catD) and cathepsin B (catB) are unnecessary for MHC class II presentation (18, 19), whereas cathepsin S (catS) and cathepsin L (catL) are important for Ag presentation by discrete populations of cells (20 -23). Active catS was detected in B cells, dendritic cells (DCs), and peritoneal macrophages (pMs), where it was shown to be involved in the late stages of Ii degradation (21-23). CatL, however, was detected only in Ms an...

Cathepsin B Is Inhibited in Mutant Cells Selected during Persistent Reovirus Infection

“…In the absence of this chaperone, mature cathepsin L is degraded with faster kinetics (73). Moreover, the double-chain form of cathepsin L in some antigen-presenting cells is inactive (74), similar to that observed for cathepsin B in the studies reported here. Thus, the inhibition of cathepsin B and the cathepsin B-sequestration complex in LX cells may function in a manner analogous to the cathepsin L inhibitor p41 in antigen-presenting cells.…”

NADPH Oxidase Modifies Patterns of MHC Class II–Restricted Epitopic Repertoires through Redox Control of Antigen Processing

“…Alternatively, this disparity may be the result of the differential expression of cysteine cathepsins between these APCs. Although cathepsin L mRNA and protein is detectable in DCs, cathepsin L activity is notably absent (43,57,58). Macrophages, alternatively, express high levels of the active form of cathepsin L (4,41).…”

“…To achieve this, T cell hybridomas were first stably transfected with an NFA-T-enhanced IL-2 promoter-driven eGFP construct, followed by multiple rounds of selection by FACS to enrich those hybridoma clones that expressed eGFP only following presentation of their cognate peptide epitope by APCs (25). When added to BMMfs that were previously pulsed with HEL protein, we found that WT and Cybb 2/2 BMMfs were equally able to induce eGFP expression in two of the hybridomas (Hb1.9 and H46.13), indicating that the processing/presentation efficiency of HEL [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and HEL [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] peptides were unaffected by NOX2 (Fig. 2D).…”

“…To further interrogate the ability of NOX2 to alter processing patterns of a single Ag, we measured the efficiency of WT and Cybb 2/2 BMMfs to process four distinct HEL epitopes (HEL [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] , HEL [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] , HEL [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] , and HEL 74-90 ) from whole HEL protein and present them to epitope-specific CD4 + T cell hybridomas (Hb1.9, H30.44, H46.13, and B04, respectively) (26). To achieve this, T cell hybridomas...…”

Lysosomal Cysteine and Aspartic Proteases Are Heterogeneously Expressed and Act Redundantly to Initiate Human Invariant Chain Degradation

“…Notably, Priess lysates contained only background levels of CatB activity toward the substrate Z-Arg-Arg-AMC, but reacted considerably with the substrate Z-Phe-Arg-AMC, which is cleaved by both CatB and CatL. Primary human B cells and EBV-transformed B cell lines are known to contain active CatS and CatB, but apparently they lack CatL activity (7,32,34,35). Priess cells contained 41 kDa pro-CatL and the 29/34 kDa form of mature CatL, which were not detectable in MGAR cells (Fig.…”