title: Exogenous Thyropin from p41 Invariant Chain Diminishes Cysteine Protease Activity and Affects IL-12 Secretion during Maturation of Human Dendritic Cells.
abstract: Dendritic cells (DC) play a pivotal role as antigen presenting cells (APC) and their maturation is crucial for effectively eliciting an antigen-specific immune response. The p41 splice variant of MHC class II-associated chaperone, called invariant chain p41 Ii, contains an amino acid sequence, the p41 fragment, which is a thyropin-type inhibitor of proteolytic enzymes. The effects of exogenous p41 fragment and related thyropin inhibitors acting on human immune cells have not been reported yet. In this study we demonstrate that exogenous p41 fragment can enter the endocytic pathway of targeted human immature DC. Internalized p41 fragment has contributed to the total amount of the immunogold labelled p41 Ii-specific epitope, as quantified by transmission electron microscopy, in particular in late endocytic compartments with multivesicular morphology where antigen processing and binding to MHC II take place. In cell lysates of treated immature DC, diminished enzymatic activity of cysteine proteases has been confirmed. Internalized exogenous p41 fragment did not affect the perinuclear clustering of acidic cathepsin S-positive vesicles typical of mature DC. p41 fragment is shown to interfere with the nuclear translocation of NF-κB p65 subunit in LPS-stimulated DC. p41 fragment is also shown to reduce the secretion of interleukin-12 (IL-12/p70) during the subsequent maturation of treated DC. The inhibition of proteolytic activity of lysosomal cysteine proteases in immature DC and the diminished capability of DC to produce IL-12 upon their subsequent maturation support the immunomodulatory potential of the examined thyropin from p41 Ii.
authors.affiliation: Department of Biochemistry, Molecular and Structural Biology, Jožef Stefan Institute, Ljubljana, Slovenia.
authors.forename: Tina
authors.initials: T
authors.lastname: Zavašnik-Bergant
authors.affiliation: Tissue Typing Centre, Blood Transfusion Centre of Slovenia, Ljubljana, Slovenia.
authors.forename: Martina
authors.initials: M
authors.lastname: Bergant Marušič
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000494:pharmacology*; D020134:Catalytic Domain; D002403:Cathepsins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003713:Dendritic Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D018664:Interleukin-12 / Q000378:metabolism*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D000944:Antigens, Differentiation, B-Lymphocyte; D005456:Fluorescent Dyes; D000949:Histocompatibility Antigens Class II; D021122:Protein Subunits; D014409:Tumor Necrosis Factor-alpha; C045084:invariant chain; D018664:Interleukin-12; D002403:Cathepsins