title: Cathepsin L maturation and activity is impaired in macrophages harboring M. avium and M. tuberculosis.
abstract: Mycobacterium tuberculosis-infected macrophages demonstrate diminished capacity to present antigens via class II MHC molecules. Since successful class II MHC-restricted antigen presentation relies on the actions of endocytic proteases, we asked whether the activities of cathepsins (Cat) B, S and L-three major lysosomal cysteine proteases-are modulated in macrophages infected with pathogenic Mycobacterium spp. Infection of murine bone marrow-derived macrophages with either Mycobacterium avium or M. tuberculosis had no obvious effect on Cat B or Cat S activity. In contrast, the activity of Cat L was altered in infected cells. Specifically, whereas the 24-kDa two-chain mature form of active Cat L predominated in uninfected cells, we observed an increase in the steady-state activity of the precursor single-chain (30 kDa) and 25-kDa two-chain forms of the enzyme in cells infected with either M. avium or M. tuberculosis. Pulse-chase analyses revealed that maturation of nascent, single-chain Cat L into the 25-kDa two-chain form was impaired in infected macrophages, and that maturation into the 24-kDa two-chain form did not occur. Consistent with these data, M. avium infection inhibited the IFNgamma-induced secretion of active two-chain Cat L by macrophages. Viable bacilli were not required to disrupt Cat L maturation, suggesting that a constitutively expressed mycobacterial component was responsible. The absence of the major active form of lysosomal Cat L in M. avium- and M. tuberculosis-infected macrophages may influence the types of T cell epitopes generated in these antigen-presenting cells, and/or the rate of class II MHC peptide loading.
authors.affiliation: Department of Microbiology, Ohio State University, 484 West 12th Avenue, Columbus, OH 43210, USA.
authors.forename: Rajeev M
authors.initials: RM
authors.lastname: Nepal
authors.forename: Stephanie
authors.initials: S
authors.lastname: Mampe
authors.forename: Brian
authors.initials: B
authors.lastname: Shaffer
authors.forename: Ann H
authors.initials: AH
authors.lastname: Erickson
authors.forename: Paula
authors.initials: P
authors.lastname: Bryant
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000942:Antigens, Bacterial / Q000276:immunology; D001854:Bone Marrow Cells / Q000201:enzymology / Q000276:immunology / Q000382:microbiology; D002401:Cathepsin B / Q000172:deficiency; D056668:Cathepsin L; D002403:Cathepsins / Q000172:deficiency / Q000276:immunology*; D003546:Cysteine Endopeptidases / Q000276:immunology*; D004789:Enzyme Activation / Q000276:immunology; D018984:Epitopes, T-Lymphocyte / Q000276:immunology; D005802:Genes, MHC Class II; D007371:Interferon-gamma / Q000276:immunology; D008264:Macrophages / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D018345:Mice, Knockout; D009162:Mycobacterium avium / Q000276:immunology*; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D010455:Peptides / Q000276:immunology; D011499:Protein Processing, Post-Translational / Q000276:immunology; D014376:Tuberculosis / Q000276:immunology*
chemical_list: D000942:Antigens, Bacterial; D018984:Epitopes, T-Lymphocyte; D010455:Peptides; D007371:Interferon-gamma; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C028217:cathepsin S